U.S. patent application number 17/395598 was filed with the patent office on 2021-11-25 for communication system, base station device and communication terminal device.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Yoshitaka HARA, Mitsuru MOCHIZUKI, Hideki MORISHIGE, Masayuki NAKAZAWA, Kuniyuki SUZUKI.
Application Number | 20210367685 17/395598 |
Document ID | / |
Family ID | 1000005764612 |
Filed Date | 2021-11-25 |
United States Patent
Application |
20210367685 |
Kind Code |
A1 |
MORISHIGE; Hideki ; et
al. |
November 25, 2021 |
COMMUNICATION SYSTEM, BASE STATION DEVICE AND COMMUNICATION
TERMINAL DEVICE
Abstract
A signal is transmitted and received between a base station
device and a communication terminal device that are included in a
communication system, through a multi-element antenna including a
plurality of antenna elements. At least one of the base station
device and the communication terminal device includes a PHY
processing unit that is a calibration unit that performs
calibration of phases and amplitudes of beams formed by the antenna
elements when the signal is transmitted and received. The PHY
processing unit obtains a correction value for the phases and the
amplitudes of the beams in the respective antenna elements so that
the phases and the amplitudes of the beams are identical among the
antenna elements, and performs the calibration based on the
obtained correction value.
Inventors: |
MORISHIGE; Hideki; (Tokyo,
JP) ; NAKAZAWA; Masayuki; (Tokyo, JP) ;
MOCHIZUKI; Mitsuru; (Tokyo, JP) ; HARA;
Yoshitaka; (Tokyo, JP) ; SUZUKI; Kuniyuki;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Chiyoda-ku
JP
|
Family ID: |
1000005764612 |
Appl. No.: |
17/395598 |
Filed: |
August 6, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16751467 |
Jan 24, 2020 |
11128389 |
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17395598 |
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16417752 |
May 21, 2019 |
10601526 |
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16751467 |
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15565359 |
Oct 9, 2017 |
10348422 |
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PCT/JP2016/061190 |
Apr 6, 2016 |
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16417752 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 7/0842 20130101;
H04B 7/10 20130101; H04W 72/042 20130101; H04B 17/12 20150115; H01Q
3/2605 20130101; H04B 7/0413 20130101; H04B 7/0617 20130101; H04B
7/0634 20130101; H04W 16/28 20130101; H04W 72/04 20130101 |
International
Class: |
H04B 17/12 20060101
H04B017/12; H04B 7/10 20060101 H04B007/10; H04W 16/28 20060101
H04W016/28; H04W 72/04 20060101 H04W072/04; H04B 7/0413 20060101
H04B007/0413; H04B 7/06 20060101 H04B007/06; H01Q 3/26 20060101
H01Q003/26 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2015 |
JP |
2015-081060 |
Claims
1. A communication system comprising a base station device and a
communication terminal device between which a signal is transmitted
and received through a multi-element antenna including a plurality
of antenna elements, wherein at least one of said base station
device and said communication terminal device includes a
calibration unit that performs calibration of phases and amplitudes
of beams formed by said antenna elements when said signal is
transmitted and received, and the calibration unit is configured to
arrange a plurality of calibration reference signals to be
transmitted from the plurality of antenna elements, in positions of
a subframe in which neither reference signals nor physical channels
are arranged, and transmit the plurality of calibration reference
signals.
2. The communication system according to claim 1, wherein the
reference signals or the physical channels are arranged in OFDM
symbols that are not adjacent to each other, and the plurality of
calibration reference signals are arranged in OFDM symbols between
the reference signals or between the physical channels.
3. The communication system according to claim 1, wherein the
reference signals or the physical channels are arranged in OFDM
symbols that are not adjacent to each other, and when OFDM symbols
in which the plurality of calibration reference signals should be
arranged overlap OFDM symbols in which the reference signals or the
physical channels should be arranged, the plurality of calibration
reference signals are preferentially arranged in the OFDM
symbols.
4. The communication system according to claim 1, wherein the
reference signals or the physical channels are arranged in OFDM
symbols that are not adjacent to each other, and when OFDM symbols
in which the plurality of calibration reference signals should be
arranged overlap OFDM symbols in which the reference signals or the
physical channels should be arranged, the reference signals or the
physical channels are preferentially arranged in the OFDM
symbols.
5. A base station device that transmits and receives a signal
through a multi-element antenna including a plurality of antenna
elements, the base station device comprising a calibrating unit
configured to perform calibration of phases and amplitudes of beams
formed by the antenna elements when the signal is transmitted and
received, wherein the calibration unit is configured to arrange a
plurality of calibration reference signals to be transmitted from
the plurality of antenna elements, in positions of a subframe in
which neither reference signals nor physical channels are arranged,
and transmit the plurality of calibration reference signals.
6. A communication terminal device that transmits and receives a
signal through a multi-element antenna including a plurality of
antenna elements, the communication terminal device comprising a
calibrating unit configured to perform calibration of phases and
amplitudes of beams formed by the antenna elements when the signal
is transmitted and received, wherein the calibration unit is
configured to arrange a plurality of calibration reference signals
to be transmitted from the plurality of antenna elements, in
positions of a subframe in which neither reference signals nor
physical channels are arranged, and transmit the plurality of
calibration reference signals.
Description
CROSS REFERENCE RO RELATED APPLICATIONS
[0001] This application is a continuation of and claims the benefit
of priority under 35 U.S.C. .sctn. 120 from U.S. application Ser.
No. 16/751,467 filed Jan. 24, 2020, which is a continuation of U.S.
application Ser. No. 16/417,752 filed May 21, 2019 (now U.S. Pat.
No. 10,601,526 issued Mar. 24, 2020), which is a continuation of
U.S. application Ser. No. 15/565,359 filed Oct. 9, 2017 (now U.S.
Pat. No. 10,348,422 issued Jul. 9, 2019), the entire contents of
which is incorporated herein by reference. U.S. application Ser.
No. 15/565,359 is a National Stage of PCT/JP2016/061190 filed Apr.
6, 2016, which claims the benefit of priority under 35 U.S.C.
.sctn. 119 from Japanese Application No. 2015-081060 filed Apr. 10,
2015.
TECHNICAL FIELD
[0002] The present invention relates to a communication system in
which radio communication is performed between a communication
terminal device such as a user equipment device and a base station
device.
BACKGROUND ART
[0003] The 3rd generation partnership project (3GPP), the standard
organization regarding the mobile communication system, is studying
communication systems referred to as long term evolution (LTE)
regarding radio sections and system architecture evolution (SAE)
regarding the overall system configuration including a core network
and a radio access network, which will be hereinafter collectively
referred to as a network as well (for example, see Non-Patent
Documents 1 to 13). This communication system is also referred to
as 3.9 generation (3.9 G) system.
[0004] As the access scheme of the LTE, orthogonal frequency
division multiplexing (OFDM) is used in a downlink direction and
single carrier frequency division multiple access (SC-FDMA) is used
in an uplink direction. Further, differently from the wideband code
division multiple access (W-CDMA), circuit switching is not
provided but a packet communication system is only provided in the
LTE.
[0005] The decisions by 3GPP regarding the frame configuration in
the LTE system described in Non-Patent Document 1 (Chapter 5) will
be described with reference to FIG. 1. FIG. 1 is a diagram
illustrating the configuration of a radio frame used in the LTE
communication system. With reference to FIG. 1, one radio frame is
10 ms. The radio frame is divided into ten equally sized subframes.
The subframe is divided into two equally sized slots. The first and
sixth subframes contain a downlink synchronization signal per radio
frame. The synchronization signals are classified into a primary
synchronization signal (P-SS) and a secondary synchronization
signal (S-SS).
[0006] Non-Patent Document 1 (Chapter 5) describes the decisions by
3GPP regarding the channel configuration in the LTE system. It is
assumed that the same channel configuration is used in a closed
subscriber group (CSG) cell as that of a non-CSG cell.
[0007] A physical broadcast channel (PBCH) is a channel for
downlink transmission from a base station device (hereinafter may
be simply referred to as a "base station") to a communication
terminal device (hereinafter may be simply referred to as a
"communication terminal") such as a user equipment device
(hereinafter may be simply referred to as a "user equipment"). A
BCH transport block is mapped to four subframes within a 40 ms
interval. There is no explicit signaling indicating 40 ms
timing.
[0008] A physical control format indicator channel (PCFICH) is a
channel for downlink transmission from a base station to a
communication terminal. The PCFICH notifies the number of
orthogonal frequency division multiplexing (OFDM) symbols used for
PDCCHs from the base station to the communication terminal. The
PCFICH is transmitted per subframe.
[0009] A physical downlink control channel (PDCCH) is a channel for
downlink transmission from a base station to a communication
terminal. The PDCCH notifies of the resource allocation information
for downlink shared channel (DL-SCH) being one of the transport
channels described below, resource allocation information for a
paging channel (PCH) being one of the transport channels described
below, and hybrid automatic repeat request (HARQ) information
related to DL-SCH. The PDCCH carries an uplink scheduling grant.
The PDCCH carries acknowledgement (Ack)/negative acknowledgement
(Nack) that is a response signal to uplink transmission. The PDCCH
is referred to as an L1/L2 control signal as well.
[0010] A physical downlink shared channel (PDSCH) is a channel for
downlink transmission from a base station to a communication
terminal. A downlink shared channel (DL-SCH) that is a transport
channel and a PCH that is a transport channel are mapped to the
PDSCH.
[0011] A physical multicast channel (PMCH) is a channel for
downlink transmission from a base station to a communication
terminal. A multicast channel (MCH) that is a transport channel is
mapped to the PMCH.
[0012] A physical uplink control channel (PUCCH) is a channel for
uplink transmission from a communication terminal to a base
station. The PUCCH carries Ack/Nack that is a response signal to
downlink transmission. The PUCCH carries a channel quality
indicator (CQI) report. The CQI is quality information indicating
the quality of received data or channel quality. In addition, the
PUCCH carries a scheduling request (SR).
[0013] A physical uplink shared channel (PUSCH) is a channel for
uplink transmission from a communication terminal to a base
station. An uplink shared channel (UL-SCH) that is one of the
transport channels is mapped to the PUSCH.
[0014] A physical hybrid ARQ indicator channel (PHICH) is a channel
for downlink transmission from a base station to a communication
terminal. The PHICH carries Ack/Nack that is a response signal to
uplink transmission. A physical random access channel (PRACH) is a
channel for uplink transmission from the communication terminal to
the base station. The PRACH carries a random access preamble.
[0015] A downlink reference signal (RS) is a known symbol in the
LTE communication system. The following five types of downlink
reference signals are defined: a cell-specific reference signal
(CRS), an MB SFN reference signal, a data demodulation reference
signal (DM-RS) being a UE-specific reference signal, a positioning
reference signal (PRS), and a channel state information reference
signal (CSI-RS). The physical layer measurement objects of a
communication terminal include reference signal received power
(RSRP).
[0016] The transport channels described in Non-Patent Document 1
(Chapter 5) will be described. A broadcast channel (BCH) among the
downlink transport channels is broadcast to the entire coverage of
a base station (cell). The BCH is mapped to the physical broadcast
channel (PBCH).
[0017] Retransmission control according to a hybrid ARQ (HARQ) is
applied to a downlink shared channel (DL-SCH). The DL-SCH can be
broadcast to the entire coverage of the base station (cell). The
DL-SCH supports dynamic or semi-static resource allocation. The
semi-static resource allocation is also referred to as persistent
scheduling. The DL-SCH supports discontinuous reception (DRX) of a
communication terminal for enabling the communication terminal to
save power. The DL-SCH is mapped to the physical downlink shared
channel (PDSCH).
[0018] The paging channel (PCH) supports DRX of the communication
terminal for enabling the communication terminal to save power. The
PCH is required to be broadcast to the entire coverage of the base
station (cell). The PCH is mapped to physical resources such as the
physical downlink shared channel (PDSCH) that can be used
dynamically for traffic.
[0019] The multicast channel (MCH) is used for broadcast to the
entire coverage of the base station (cell). The MCH supports SFN
combining of multimedia broadcast multicast service (MBMS) services
(MTCH and MCCH) in multi-cell transmission. The MCH supports
semi-static resource allocation. The MCH is mapped to the PMCH.
[0020] Retransmission control according to a hybrid ARQ (HARQ) is
applied to an uplink shared channel (UL-SCH) among the uplink
transport channels. The UL-SCH supports dynamic or semi-static
resource allocation. The UL-SCH is mapped to the physical uplink
shared channel (PUSCH).
[0021] A random access channel (RACH) is limited to control
information. The RACH involves a collision risk. The RACH is mapped
to the physical random access channel (PRACH).
[0022] The HARQ will be described. The HARQ is the technique for
improving the communication quality of a channel by combination of
automatic repeat request (ARQ) and error correction (forward error
correction). The HARQ is advantageous in that error correction
functions effectively by retransmission even for a channel whose
communication quality changes. In particular, it is also possible
to achieve further quality improvement in retransmission through
combination of the reception results of the first transmission and
the reception results of the retransmission.
[0023] An example of the retransmission method will be described.
If the receiver fails to successfully decode the received data, in
other words, if a cyclic redundancy check (CRC) error occurs
(CRC=NG), the receiver transmits "Nack" to the transmitter. The
transmitter that has received "Nack" retransmits the data. If the
receiver successfully decodes the received data, in other words, if
a CRC error does not occur (CRC=OK), the receiver transmits "AcK"
to the transmitter. The transmitter that has received "Ack"
transmits the next data.
[0024] The logical channels described in Non-Patent Document 1
(Chapter 6) will be described. A broadcast control channel (BCCH)
is a downlink channel for broadcast system control information. The
BCCH that is a logical channel is mapped to the broadcast channel
(BCH) or downlink shared channel (DL-SCH) that is a transport
channel.
[0025] A paging control channel (PCCH) is a downlink channel for
transmitting paging information and system information change
notifications. The PCCH is used when the network does not know the
cell location of a communication terminal. The PCCH that is a
logical channel is mapped to the paging channel (PCH) that is a
transport channel.
[0026] A common control channel (CCCH) is a channel for
transmission control information between communication terminals
and a base station. The CCCH is used in the case where the
communication terminals have no RRC connection with the network. In
the downlink direction, the CCCH is mapped to the downlink shared
channel. (DL-SCH) that is a transport channel. In the uplink
direction, the CCCH is mapped to the uplink shared channel (UL-SCH)
that is a transport channel.
[0027] A multicast control channel (MCCH) is a downlink channel for
point-to-multipoint transmission. The MCCH is used for transmission
of MBMS control information for one or several MTCHs from a network
to a communication terminal. The MCCH is used only by a
communication terminal during reception of the MBMS. The MCCH is
mapped to the multicast channel (MCH) that is a transport
channel.
[0028] A dedicated control channel (DCCH) is a channel that
transmits dedicated control information between a communication
terminal and a network on a point-to-point basis. The DCCH is used
when the communication terminal has an RRC connection. The DCCH is
mapped to the uplink shared channel (UL-SCH) in uplink and mapped
to the downlink shared channel (DL-SCH) in downlink.
[0029] A dedicated traffic channel (DTCH) is a point-to-point
communication channel for transmission of user information to a
dedicated communication terminal. The DTCH exists in uplink as well
as downlink. The DTCH is mapped to the uplink shared channel
(UL-SCH) in uplink and mapped to the downlink shared channel
(DL-SCH) in downlink.
[0030] A multicast traffic channel (MTCH) is a downlink channel for
traffic data transmission from a network to a communication
terminal. The MTCH is a channel used only by a communication
terminal during reception of the MBMS. The MTCH is mapped to the
multicast channel (MCH).
[0031] CGI represents a cell global identifier. ECGI represents an
E-UTRAN cell global identifier. A closed subscriber group (CSG)
cell is introduced in the LTE, and the long term evolution advanced
(LTE-A) and universal mobile telecommunication system (UMTS)
described below.
[0032] The closed subscriber group (CSG) cell is a cell in which
subscribers who are allowed use are specified by an operator
(hereinafter, also referred to as a "cell for specific
subscribers"). The specified subscribers are allowed to access one
or more cells of a public land mobile network (PLMN). One or more
cells to which the specified subscribers are allowed access are
referred to as "CSG cell(s)". Note that access is limited in the
PLMN.
[0033] The CSG cell is part of the PLMN that broadcasts a specific
CSG identity (CSG ID) and broadcasts "TRUE" in a CSG indication.
The authorized members of the subscriber group who have registered
in advance access the CSG cells using the CSG ID that is the access
permission information.
[0034] The CSG ID is broadcast by the CSG cell or cells. A
plurality of CSG IDs exist in the LTE communication system. The CSG
IDs are used by communication terminals (UEs) for making access
from CSG-related members easier.
[0035] The locations of communication terminals are tracked based
on an area composed of one or more cells. The locations are tracked
for enabling tracking the locations of communication terminals and
calling communication terminals, in other words, incoming calling
to communication terminals even in an idle state. An area for
tracking locations of communication terminals is referred to as a
tracking area.
[0036] 3GPP is studying base stations referred to as Home-NodeB
(Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base
station for, for example, household, corporation, or commercial
access service in UTRAN/E-UTRAN.
[0037] Non-Patent Document 2 discloses three different modes of the
access to the HeNB and HNB. Specifically, an open access mode, a
closed access mode, and a hybrid access mode are disclosed.
[0038] The individual modes have the following characteristics. In
the open access mode, the HeNB and HNB are operated as a normal
cell of a normal operator. In the closed access mode, the HeNB and
HNB are operated as a CSG cell. The CSG cell is a CSG cell where
only CSG members are allowed access. In the hybrid access mode, the
HeNB and HNB are operated as CSG cells where non-CSG members are
allowed access at the same time. In other words, a cell in the
hybrid access mode (also referred to as a hybrid cell) is the cell
that supports both of the open access mode and the closed access m
ode.
[0039] In 3GPP, among all physical cell identities (PCIs) is a
range of PCIs reserved by the network for use by CSG cells (see
Chapter 10.5.1.1 of Non-Patent Document 1). Division of the PCI
range is also referred to as PCI split. The information about PCI
split (also referred to as PCI split information) is broadcast in
the system information from a base station to communication
terminals being served thereby. Being served by a base station
means taking the base station as a serving cell.
[0040] Non-Patent Document 3 discloses the basic operation of a
communication terminal using PCI split. The communication terminal
that does not have the PCI split information needs to perform cell
search using all PCTs, for example, using all 504 codes. On the
other hand, the communication terminal that has the PCI split
information is capable of performing cell search using the PCI
split information.
[0041] Further, 3GPP is pursuing specifications standard of long
term evolution advanced (LTE-A) as Release 10 (see Non-Patent
Documents 4 and 5). The LTE-A is based on the LTE radio
communication system and is configured by adding several new
techniques to the system.
[0042] Carrier aggregation (CA) is studied for the LTE-A system, in
which two or more component carriers (CCs) are aggregated to
support wider transmission bandwidths up to 100 MHz.
[0043] In the case where CA is configured, a UE has a single RRC
connection with a network (NW). In RRC connection, one serving cell
provides NAS mobility information and security input. This cell is
referred to as a primary cell (PCell). In downlink, a carrier
corresponding to PCell is a downlink primary component carrier (DL
PCC). In uplink, a carrier corresponding to PCell is an uplink
primary component carrier (UL PCC).
[0044] A secondary cell (SCell) is configured to form a serving
cell group with PCell, in accordance with the UE capability. In
downlink, a carrier corresponding to SCell is a downlink secondary
component carrier (DL SCC). In uplink, a carrier corresponding to
SCell is an uplink secondary component carrier (UL SCC).
[0045] A serving cell group of one PCell and one or more SCells is
configured for one UE.
[0046] The new techniques in the LTE-A include the technique of
supporting wider bands (wider bandwidth extension) and the
coordinated multiple point transmission and reception (CoMP)
technique. The CoMP studied for LTE-A in 3GPP is described in
Non-Patent Document 6.
[0047] The traffic flow of a mobile network is on the rise, and the
communication rate is also increasing. It is expected that the
communication rate and the traffic flow will be further increased
when the operations of the LTE and the LTE-A are fully
initiated.
[0048] Widespread use of smartphones and tablet terminals
explosively increases traffic in cellular radio communications,
causing a fear of insufficient radio resources all over the
world.
[0049] To deal with the problem of increased traffic, 3GPP is
developing specifications of Release 12. In the specifications of
Release 12, the use of small eNBs is studied to satisfy a
tremendous volume of traffic in the future. In an example technique
under study, a large number of small eNBs are installed to
configure a large number of small cells, thus increasing spectral
efficiency for increased communication capacity.
[0050] In Release 12, dual connectivity is discussed as the
technique of connecting a communication terminal to both a macro
cell and a small cell when the macro cell and the small cell
overlap each other (see Non-Patent Document 8).
[0051] For increasingly sophisticated mobile communications, the
fifth generation (hereinafter also referred to as "5G") radio
access system is studied, whose service is aimed to be launched in
2020 and afterward. For example, in the Europe, an organization
named METIS summarizes the requirements for 5G (see Non-Patent
Document 9).
[0052] Among the requirements in the 5G radio access system are a
system capacity 1000 times as high as, a data transmission rate 100
times as high as, a data latency one tenth ( 1/10) as low as, and
simultaneously connected communication terminals 100 times as many
as those in the LTE system, to further reduce the power consumption
and device cost.
[0053] In order to satisfy such requirements, techniques for
enabling spatial multiplexing such as multiple-input
multiple-output (MIMO) and beamforming using multi-element antennas
are being studied to increase the data transmission capacity using
frequencies over a wide frequency range as well as to increase the
data transmission rate through increase in spectral efficiency.
[0054] In the MIMO and the beamforming using multi-element
antennas, phases and outputs of the respective antenna elements
included in a multi-element antenna are set and adjusted. Thus, the
set accuracy of the phases and the outputs of the respective
antenna elements influences the performance. Here, the
multi-element antenna is calibrated to increase the set accuracy of
the phases and the outputs of the respective antenna elements.
[0055] The rotating element electric field vector (REV) method (see
Non-Patent Document 10) and the relative calibration (see
Non-Patent Document 11) are being studied as methods for
calibrating the multi-element antenna. Furthermore, the
self-calibration method (see Non-Patent Document 12) and the
Over-The-Air (OTA) method (see Non-Patent Document 13) are being
studied as calibration execution methods.
PRIOR-ART DOCUMENTS
Non-Patent Documents
[0056] Non-Patent Document 1: 3GPP TS36.300 V12.4.0 [0057]
Non-Patent Document 2: 3GPP S1-083461 [0058] Non-Patent Document 3:
3GPP R2-082899 [0059] Non-Patent Document 4: 3GPP TR 36.814 V9.0.0
[0060] Non-Patent Document 5: 3GPP TR 36.912 V10.0.0 [0061]
Non-Patent Document 6: 3GPP TR 36.819 V11.2.0 [0062] Non-Patent
Document 7: 3GPP TS 36.141 V12.6.0 [0063] Non-Patent Document 8:
3GPP TR36.842 V12.0.0 [0064] Non-Patent Document 9: "Scenarios,
requirements and KPIs for 5G mobile and wireless system", [online],
Apr. 30, 2013, ICT-317669-METIS/D1.1, [Searched on Apr. 2, 2015],
Internet <https://www.metis2020.com/documents/deliverables/>
[0065] Non-Patent Document 10: Seiji MANO, Takashi KATAGI, "A
Method for Measuring Amplitude and Phase of Each Radiating Element
of a Phased Array Antenna, Rotating Element Electric Field Vector
Method", The Transactions of the Institute of Electronics and
Communication Engineers of Japan, B, Vol. J65-B, No. 5, pp.
555-560, May 1982 [0066] Non-Patent Document 11: Yoshitaka HARA,
Yasuhiro YANO, Hiroshi KUBO, "Antenna Calibration Using Frequency
Selection in OFDMA/TDD Systems", IEICE Technical Report
RCS2007-143, January 2008 [0067] Non-Patent Document 12: Yasunori
NOUDA, Yoshitaka HARA, Yasuhiro YANO, Hiroshi KUBO, "An Antenna
Array Auto-Calibration Method with Bidirectional Channel
Measurement for TDD Systems", IEICE Technical Report RCS2008-12,
May 2008 [0068] Non-Patent Document 13: X. Hou, et al,
"Experimental Study of Advanced MU-MIMO Scheme with Antenna
Calibration for the Evolving LTE TDD System", IEEE 23rd PIMRC,
2012
SUMMARY
Problems to be Solved by the Invention
[0069] In the MIMO and the beamforming using multi-element
antennas, the throughput of the multi-element antennas needs to be
improved. However, the following problems lie in improving the
throughput of the multi-element antennas.
[0070] The first point will be described below. Without matching
phase and amplitude differences among the antenna elements,
problems occur which include: (a) uncontrollable beam directivity
with which beams cannot be directed in a desired direction; (b)
decrease in gain expressed by, for example, equivalent isotropic
radiated power (abbreviated as EIRP); and (c) increase in side lobe
power which increases interference with other users. Particularly,
accuracy is required in MIMO transmission for controlling null
points.
[0071] The second point will be described below. It is necessary to
eliminate temperature and temporal variations in phase and
amplitude differences among the antenna elements. However, since
broadband communication increases the frequency bandwidth, an
amplifier and a filter, etc. cause a problem of significantly
influencing amounts of the temperature and temporal variations.
[0072] Unlike the conventional configurations in which an amplifier
and a filter are placed in an indoor room with temperature control
and connected to an antenna outdoor through cables for extension,
outdoor installation of an amplifier, for example, an active phased
array antenna (APAA) is being studied. Since the temperature
variations increase in such a case, the calibration in operation is
important.
[0073] The object of the present invention is to provide a
communication system capable of calibration with higher accuracy to
match phase and amplitude differences in beam among a plurality of
antenna elements included in a multi-element antenna and capable of
communication with a relatively high throughput.
Means to Solve the Problems
[0074] The communication system according to the present invention
is a communication system including a base station device and a
communication terminal device between which a signal is transmitted
and received through a multi-element antenna including a plurality
of antenna elements, wherein at least one of the base station
device and the communication terminal device includes a calibration
unit that performs calibration of phases and amplitudes of beams
formed by the antenna elements when the signal is transmitted and
received, and the calibration unit obtains a correction value for
the phases and the amplitudes of the beams in the respective
antenna elements so that the phases and the amplitudes of the beams
are identical among the antenna elements, and performs the
calibration based on the obtained correction value.
Effects of the Invention
[0075] The communication system according to the present invention
is a communication system including a base station device and a
communication terminal device. A signal is transmitted and received
between the base station device and the communication terminal
device through a multi-element antenna including a plurality of
antenna elements. At least one of the base station device and the
communication terminal device includes a calibration unit. The
calibration unit performs calibration of phases and amplitudes of
beams formed by the antenna elements when the signal is transmitted
and received. The calibration unit obtains a correction value for
the phases and the amplitudes of the beams in the respective
antenna elements so that the phases and the amplitudes of the beams
are identical among the antenna elements, and performs the
calibration based on the obtained correction value. Since the
calibration can be performed with higher accuracy, it is possible
to match phase and amplitude differences in beam among a plurality
of antenna elements included in a multi-element antenna. Thus, a
communication system capable of communication with a relatively
high throughput can be implemented.
[0076] These and other objects, features, aspects and advantages of
the present invention will become more apparent from the following
detailed description of the present invention when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0077] FIG. 1 is a diagram illustrating the configuration of a
radio frame for use in an LTE communication system.
[0078] FIG. 2 is a block diagram showing the overall configuration
of an LTE communication system 200 under discussion of 3GPP.
[0079] FIG. 3 is a block diagram showing the configuration of a
user equipment 202 shown in FIG. 2, which is a communication
terminal according to the present invention.
[0080] FIG. 4 is a block diagram showing the configuration of a
base station 203 shown in FIG. 2, which is a base station according
to the present invention.
[0081] FIG. 5 is a block diagram showing the configuration of an
MME according to the present invention.
[0082] FIG. 6 is a flowchart showing an outline from a cell search
to an idle state operation performed by a communication terminal
(UE) in the LTE communication system.
[0083] FIG. 7 shows the concept of a cell configuration when macro
eNBs and small eNBs coexist.
[0084] FIG. 8 is a block diagram illustrating a configuration of a
communication apparatus in a communication system according to a
first embodiment of the present invention.
[0085] FIG. 9 is a block diagram illustrating an example
configuration of a PHY processing unit 901, a control unit 9411,
and n antenna elements 909, 922, . . . , and 935.
[0086] FIG. 10 is a block diagram illustrating the example
configuration of the PHY processing unit 901, the control unit
9411, and the n antenna elements 909, 922, . . . , and 935.
[0087] FIG. 11 is a block diagram illustrating an example
configuration of the PHY processing unit 901, the control unit
9411, and the n antenna elements 909, 922, . . . , and 935.
[0088] FIG. 12 is a block diagram illustrating the example
configuration of the PHY processing unit 901, the control unit
9411, and the n antenna elements 909, 922, . . . , and 935.
[0089] FIG. 13 is a block diagram illustrating another example
configuration of a PHY processing unit 901A, a control unit 9412,
and the n antenna elements 909, 922, . . . , and 935.
[0090] FIG. 14 is a block diagram illustrating the other example
configuration of the PHY processing unit 901A, the control unit
9412, and the n antenna elements 909, 922, . . . , and 935.
[0091] FIG. 15 is a block diagram illustrating another example
configuration of the PHY processing unit 901A, the control unit
9412, and the n antenna elements 909, 922, . . . , and 935.
[0092] FIG. 16 is a block diagram illustrating the other example
configuration of the PHY processing unit 901A, the control unit
9412, and the n antenna elements 909, 922, . . . , and 935.
[0093] FIG. 17 illustrates example mapping in transmission data of
a first antenna element.
[0094] FIG. 18 illustrates example mapping in transmission data of
a second antenna element to an n-th antenna element.
[0095] FIG. 19 illustrates examples of mapping and the reception
power at each frequency, in transmission data of the first antenna
element.
[0096] FIG. 20 illustrates another example mapping in the
transmission data of the first antenna element.
[0097] FIG. 21 illustrates another example mapping in the
transmission data of the second antenna element to the n-th antenna
element.
[0098] FIG. 22 further illustrates another example mapping in the
transmission data of the first antenna element.
[0099] FIG. 23 further illustrates another example mapping in the
transmission data of the second antenna element.
[0100] FIG. 24 further illustrates another example mapping in the
transmission data of the third antenna element.
[0101] FIG. 25 further illustrates another example mapping in the
transmission data of the fourth antenna element.
[0102] FIG. 26 further illustrates another example mapping of
transmission data in the transmission data of the first antenna
element.
[0103] FIG. 27 further illustrates another example mapping in the
transmission data of the second antenna element to the n-th antenna
element.
[0104] FIG. 28 is a flowchart indicating an example procedure on
calibration processes in a communication system according to a
fourth embodiment.
[0105] FIG. 29 is a flowchart indicating an example procedure on
calibration processes in a communication system according to a
first modification of the fourth embodiment.
[0106] FIG. 30 is a flowchart indicating an example procedure on
calibration processes in a communication system according to a
second modification of the fourth embodiment.
[0107] FIG. 31 is a flowchart indicating an example procedure on
calibration processes in a communication system according to a
third modification of the fourth embodiment.
[0108] FIG. 32 illustrates an example sequence on calibration in a
communication system according to a fifth embodiment.
[0109] FIG. 33 illustrates another example sequence on calibration
in the communication system according to the fifth embodiment.
[0110] FIG. 34 illustrates an example configuration of a subframe
when cal-RSs are mapped to a physical downlink shared channel
region.
[0111] FIG. 35 illustrates another example configuration of a
subframe when cal-RSs are mapped to a physical downlink shared
channel region.
[0112] FIG. 36 illustrates an example configuration of a subframe
when cal-RSs are mapped to an MBSFN region.
[0113] FIG. 37 illustrates an example configuration of a subframe
when cal-RSs are mapped to an ABS region.
[0114] FIG. 38 illustrates an example configuration of a subframe
when cal-RSs of each antenna group are mapped to a physical
downlink shared channel region according to a seventh
embodiment.
[0115] FIG. 39 illustrates an example configuration of a subframe
when cal-RSs are mapped to a part of the frequency axis in a
physical downlink shared channel region according to an eighth
embodiment.
[0116] FIG. 40 illustrates another example configuration of a
subframe when cal-RSs are mapped to a part of the frequency axis in
a physical downlink shared channel region according to the eighth
embodiment.
[0117] FIG. 41 illustrates an example configuration of a subframe
when cal-RSs for each antenna group are mapped to a part of the
frequency axis in a physical downlink shared channel region
according to the eighth embodiment.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0118] FIG. 2 is a block diagram showing an overall configuration
of an LTE communication system 200, which is under discussion of
3GPP. FIG. 2 will be described. A radio access network is referred
to as an evolved universal terrestrial radio access network
(E-UTRAN) 201. A user equipment device (hereinafter, referred to as
a "user equipment (UE)") 202 that is a communication terminal
device is capable of radio communication with a base station device
(hereinafter, referred to as a "base station (E-UTRAN Node B:
eNB)") 203 and transmits and receives signals through radio
communication.
[0119] Here, the "communication terminal device" covers not only a
user equipment device such as a movable mobile phone terminal
device, but also an unmovable device such as a sensor. In the
following description, the "communication terminal device" may be
simply referred to as a "communication terminal".
[0120] The E-UTRAN is composed of one or a plurality of base
stations 203, provided that a control protocol for the user
equipment 202 such as a radio resource control (RRC), and user
planes such as a packet data convergence protocol (PDCP), radio
link control (RLC), medium access control (MAC), or physical layer
(PHY) are terminated in the base station 203.
[0121] The control protocol radio resource control (RRC) between
the user equipment 202 and the base station 203 performs broadcast,
paging, RRC connection management, and the like. The states of the
base station 203 and the user equipment 202 in RRC are classified
into RRC IDLE and RRC CONNECTED.
[0122] In RRC IDLE, public land mobile network (PLMN) selection,
system information (SI) broadcast, paging, cell re-selection,
mobility, and the like are performed. In RRC CONNECTED, the user
equipment has RRC connection and is capable of transmitting and
receiving data to and from a network. In RRC CONNECTED, for
example, handover (HO) and measurement of a neighbor cell are
performed.
[0123] The base stations 203 are classified into eNBs 207 and
Home-eNBs 206. The communication system 200 includes an eNB group
203-1 including a plurality of eNBs 207 and a Home-eNB group 203-2
including a plurality of Home-eNBs 206. A system, composed of an
evolved packet core (EPC) being a core network and an E-UTRAN 201
being a radio access network, is referred to as an evolved packet
system (EPS). The EPC being a core network and the E-UTRAN 201
being a radio access network may be collectively referred to as a
"network".
[0124] The eNB 207 is connected to an MME/S-GW unit (hereinafter,
also referred to as an "MME unit") 204 including a mobility
management entity (MME), a serving gateway (S-GW), or an MME and an
S-GW by means of an S1 interface, and control information is
communicated between the eNB 207 and the MME unit 204. A plurality
of MME units 204 may be connected to one eNB 207. The eNBs 207 are
connected to each other by means of an X2 interface, and control
information is communicated between the eNBs 207.
[0125] The Home-eNB 206 is connected to the MME unit 204 by means
of an S1 interface, and control information is communicated between
the Home-eNB 206 and the MME unit 204. A plurality of Home-eNBs 206
are connected to one MME unit 204. Or, the Home-eNBs 206 are
connected to the MME units 204 through a Home-eNB gateway (HeNBGW)
205. The Home-eNB 206 is connected to the HeNBGW 205 by means of an
S1 interface, and the HeNBGW 205 is connected to the MME unit 204
by means of an S1 interface.
[0126] One or a plurality of Home-eNBs 206 are connected to one
HeNBGW 205, and information is communicated therebetween through an
S1 interface. The HeNBGW 205 is connected to one or a plurality of
MME units 204, and information is communicated therebetween through
an S1 interface.
[0127] The MME units 204 and HeNBGW 205 are entities of higher
layer, specifically, higher nodes, and control the connections
between the user equipment (UE) 202 and the eNB 207 and the
Home-eNB 206 being base stations. The MME units 204 configure an
EPC being a core network. The base station 203 and the HeNBGW 205
configure the E-UTRAN 201.
[0128] Further, 3GPP is studying the configuration below. The X2
interface between the Home-eNBs 206 is supported. In other words,
the Home-eNBs 206 are connected to each other by means of an X2
interface, and control information is communicated between the
Horne-eNBs 206. The HeNBGW 205 appears to the MME unit 204 as the
Home-eNB 206. The HeNBGW 205 appears to the Home-eNB 206 as the MME
unit 204.
[0129] The interfaces between the Home-eNBs 206 and the MME units
204 are the same, which are the S1 interfaces, in both cases where
the Home-eNB 206 is connected to the MME unit 204 through the
HeNBGW 205 and it is directly connected to the MME unit 204.
[0130] The base station device 203 may configure a single cell or a
plurality of cells. Each cell has a range predetermined as a
coverage in which the cell can communicate with the user equipment
202 and performs radio communication with the user equipment 202
within the coverage. In the case where one base station device 203
configures a plurality of cells, every cell is configured so as to
communicate with the user equipment 202.
[0131] FIG. 3 is a block diagram showing the configuration of the
user equipment 202 of FIG. 2 that is a communication terminal
according to the present invention. The transmission process of the
user equipment 202 shown in FIG. 3 will be described. First, a
transmission data buffer unit 303 stores the control data from a
protocol processing unit 301 and the user data from an application
unit 302. The data stored in the transmission data buffer unit 303
is passed to an encoding unit 304 and is subjected to an encoding
process such as error correction. There may exist the data output
from the transmission data buffer unit 303 directly to a modulating
unit 305 without the encoding process. The data encoded by the
encoding unit 304 is modulated by the modulating unit 305. The
modulated data is converted into a baseband signal, and the
baseband signal is output to a frequency converting unit 306 and is
then converted into a radio transmission frequency. After that, a
transmission signal is transmitted from an antenna 307 to the base
station 203.
[0132] The user equipment 202 executes the reception process as
follows. The radio signal from the base station 203 is received
through the antenna 307. The received signal is converted from a
radio reception frequency into a baseband signal by the frequency
converting unit 306 and is then demodulated by a demodulating unit
308. The demodulated data is passed to a decoding unit 309 and is
subjected to a decoding process such as error correction. Among the
pieces of decoded data, the control data is passed to the protocol
processing unit 301, and the user data is passed to the application
unit 302. A series of processes by the user equipment 202 is
controlled by a control unit 310. This means that, though not shown
in FIG. 3, the control unit 310 is connected to the individual
units 301 to 309.
[0133] FIG. 4 is a block diagram showing the configuration of the
base station 203 of FIG. 2 that is a base station according to the
present invention. The transmission process of the base station 203
shown in FIG. 4 will be described. An EPC communication unit 401
performs data transmission and reception between the base station
203 and the EPC (such as the MME unit 204), HeNBGW 205, and the
like. A communication with another base station unit 402 performs
data transmission and reception to and from another base station.
The EPC communication unit 401 and the communication with another
base station unit 402 each transmit and receive information to and
from a protocol processing unit 403. The control data from the
protocol processing unit 403, and the user data and the control
data from the EPC communication unit 401 and the communication with
another base station unit 402 are stored in a transmission data
buffer unit 404.
[0134] The data stored in the transmission data buffer unit 404 is
passed to an encoding unit 405 and is then subjected to an encoding
process such as error correction. There may exist the data output
from the transmission data buffer unit 404 directly to a modulating
unit 406 without the encoding process. The encoded data is
modulated by the modulating unit 406. The modulated data is
converted into a baseband signal, and the baseband signal is output
to a frequency converting unit 407 and is then converted into a
radio transmission frequency. After that, a transmission signal is
transmitted from an antenna 408 to one or a plurality of user
equipments 202.
[0135] The reception process of the base station 203 is executed as
follows. A radio signal from one or a plurality of user equipments
202 is received through the antenna 408. The received signal is
converted from a radio reception frequency into a baseband signal
by the frequency converting unit 407, and is then demodulated by a
demodulating unit 409. The demodulated data is passed to a decoding
unit 410 and is then subjected to a decoding process such as error
correction. Among the pieces of decoded data, the control data is
passed to the protocol processing unit 403, the EPC communication
unit 401, or the communication with another base station unit 402,
and the user data is passed to the EPC communication unit 401 and
the communication with another base station unit 402. A series of
processes by the base station 203 is controlled by a control unit
411. This means that, though not shown in FIG. 4, the control unit
411 is connected to the individual units 401 to 410.
[0136] FIG. 5 is a block diagram showing the configuration of the
MME according to the present invention. FIG. 5 shows the
configuration of an MME 204a included in the MME unit 204 shown in
FIG. 2 described above. A PDN GW communication unit 501 performs
data transmission and reception between the MME 204a and the PDN
GW. A base station communication unit 502 performs data
transmission and reception between the MME 204a and the base
station 203 by means of the S1 interface. In the case where the
data received from the PDN GW is user data, the user data is passed
from the PDN GW communication unit 501 to the base station
communication unit 502 via a user plane communication unit 503 and
is then transmitted to one or a plurality of base stations 203. In
the case where the data received from the base station 203 is user
data, the user data is passed from the base station communication
unit 502 to the PDN GW communication unit 501 via the user plane
communication unit 503 and is then transmitted to the PDN GW.
[0137] In the case where the data received from the PDN GW is
control data, the control data is passed from the PDN GW
communication unit 501 to a control plane control unit 505. In the
case where the data received from the base station 203 is control
data, the control data is passed from the base station
communication unit 502 to the control plane control unit 505.
[0138] A HeNBGW communication unit 504 is provided in the case
where the HeNBGW 205 is provided, which performs data transmission
and reception between the MME 204a and the HeNBGW 205 by means of
the interface (IF) according to an information type. The control
data received from the HeNBGW communication unit 504 is passed from
the HeNBGW communication unit 504 to the control plane control unit
505. The processing results of the control plane control unit 505
are transmitted to the PDN GW via the PDN GW communication unit
501. The processing results of the control plane control unit 505
are transmitted to one or a plurality of base stations 203 by means
of the S1 interface via the base station communication unit 502,
and are transmitted to one or a plurality of HeNBGWs 205 via the
HeNBGW communication unit 504.
[0139] The control plane control unit 505 includes a NAS security
unit 505-1, an SAE bearer control unit 505-2, and an idle state
mobility managing unit 505-3, and performs an overall process for
the control plane. The NAS security unit 505-1 provides, for
example, security of a non-access stratum (NAS) message. The SAE
bearer control unit 505-2 manages, for example, a system
architecture evolution (SAE) bearer. The idle state mobility
managing unit 505-3 performs, for example, mobility management of
an idle state (LTE-IDLE state, which is merely referred to as idle
as well), generation and control of a paging signal in the idle
state, addition, deletion, update, and search of a tracking area of
one or a plurality of user equipments 202 being served thereby, and
tracking area list management.
[0140] The MME 204a distributes a paging signal to one or a
plurality of base stations 203. In addition, the MME 204a performs
mobility control of an idle state. When the user equipment is in
the idle state and an active state, the MME 204a manages a list of
tracking areas. The MME 204a begins a paging protocol by
transmitting a paging message to the cell belonging to a tracking
area in which the UE is registered. The idle state mobility
managing unit 505-3 may manage the CSG of the Home-eNBs 206 to be
connected to the MME 204a, CSG IDs, and a whitelist.
[0141] An example of a cell search method in a mobile communication
system will be described next. FIG. 6 is a flowchart showing an
outline from a cell search to an idle state operation performed by
a communication terminal (UE) in the LTE communication system. When
starting a cell search, in Step ST601, the communication terminal
synchronizes slot timing and frame timing by a primary
synchronization signal (P-SS) and a secondary synchronization
signal (S-SS) transmitted from a neighbor base station.
[0142] The P-SS and S-SS are collectively referred to as a
synchronization signal (SS). Synchronization codes, which
correspond one-to-one to PCIs assigned per cell, are assigned to
the synchronization signals (SSs). The number of PCIs is currently
studied in 504 ways. The 504 ways of PCIs are used for
synchronization, and the PCIs of the synchronized cells are
detected (specified).
[0143] In Step ST602, next, the user equipment detects a
cell-specific reference signal (CRS) being a reference signal (RS)
transmitted from the base station per cell and measures the
reference signal received power (RSRP). The codes corresponding
one-to-one to the PCIs are used for the reference signal RS.
Separation from another cell is enabled by correlation using the
code. The code for RS of the cell is derived from the PCI specified
in Step ST601, so that the RS can be detected and the RS received
power can be measured.
[0144] In Step ST603, next, the user equipment selects the cell
having the best RS received quality, for example, the cell having
the highest RS received power, that is, the best cell, from one or
more cells that have been detected up to Step ST602.
[0145] In Step ST604, next, the user equipment receives the PBCH of
the best cell and obtains the BCCH that is the broadcast
information. A master information block (MIB) containing the cell
configuration information is mapped to the BCCH over the PBCH.
Accordingly, the MIB is obtained by obtaining the BCCH through
reception of the PBCH. Examples of the MIB information include the
downlink (DL) system bandwidth (also referred to as a transmission
bandwidth configuration (dl-bandwidth)), the number of transmission
antennas, and a system frame number (SFN).
[0146] In Step ST605, next, the user equipment receives the DL-SCH
of the cell based on the cell configuration information of the MIB,
to thereby obtain a system information block (SIB) 1 of the
broadcast information BCCH. The SIB1 contains the information about
the access to the cell, information about cell selection, and
scheduling information on another SIB (SIBk; k is an integer equal
to or greater than two). In addition, the SIB1 contains a tracking
area code (TAC).
[0147] In Step ST606, next, the communication terminal compares the
TAC of the SIB1 received in Step ST605 with the TAC portion of a
tracking area identity (TAI) in the tracking area list that has
already been possessed by the communication terminal. The tracking
area list is also referred to as a TAI list. TAI is the
identification information for identifying tracking areas and is
composed of a mobile country code (MCC), a mobile network code
(MNC), and a tracking area code (TAC). MCC is a country code. MNC
is a network code. TAC is the code number of a tracking area.
[0148] If the result of the comparison of Step ST606 shows that the
TAC received in Step ST605 is identical to the TAC included in the
tracking area list, the user equipment enters an idle state
operation in the cell. If the comparison shows that the TAC
received in Step ST605 is not included in the tracking area list,
the communication terminal requires a core network (EPC) including
MME and the like to change a tracking area through the cell for
performing tracking area update (TAU).
[0149] The device configuring a core network (hereinafter, also
referred to as a "core-network-side device") updates the tracking
area list based on an identification number (such as UE-ID) of a
communication terminal transmitted from the communication terminal
together with a TAU request signal. The core-network-side device
transmits the updated tracking area list to the communication
terminal. The communication terminal rewrites (updates) the TAC
list of the communication terminal based on the received tracking
area list. After that, the communication terminal enters the idle
state operation in the cell.
[0150] Widespread use of smartphones and tablet terminal devices
explosively increases traffic in cellular radio communications,
causing a fear of insufficient radio resources all over the world.
To increase spectral efficiency, thus, it is studied to downsize
cells for further spatial separation.
[0151] In the conventional configuration of cells, the cell
configured by an eNB has a relatively-wide-range coverage.
Conventionally, cells are configured such that
relatively-wide-range coverages of a plurality of cells configured
by a plurality of macro eNBs cover a certain area.
[0152] When cells are downsized, the cell configured by an eNB has
a narrow-range coverage compared with the coverage of a cell
configured by a conventional eNB. Thus, in order to cover a certain
area as in the conventional case, a larger number of downsized eNBs
than the conventional eNBs are required.
[0153] In the description below, a "macro cell" refers to a cell
having a relatively wide coverage, such as a cell configured by a
conventional eNB, and a "macro eNB" refers to an eNB configuring a
macro cell. A "small cell" refers to a cell having a relatively
narrow coverage, such as a downsized cell, and a "small eNB" refers
to an eNB configuring a small cell.
[0154] The macro eNB may be, for example, a "wide area base
station" described in Non-Patent Document 7.
[0155] The small eNB may be, for example, a low power node, local
area node, or hotspot. Alternatively, the small eNB may be a pico
eNB configuring a pico cell, a femto eNB configuring a femto cell,
HeNB, remote radio head (RRH), remote radio unit (RRU), remote
radio equipment (RRE), or relay node (RN). Still alternatively, the
small eNB may be a "local area base station" or "home base station"
described in Non-Patent Document 7.
[0156] FIG. 7 shows the concept of the cell configuration in which
macro eNBs and small eNBs coexist. The macro cell configured by a
macro eNB has a relatively-wide-range coverage 701. A small cell
configured by a small eNB has a coverage 702 whose range is
narrower than that of the coverage 701 of a macro eNB (macro
cell).
[0157] When a plurality of eNBs coexist, the coverage of the cell
configured by an eNB may be included in the coverage of the cell
configured by another eNB. In the cell configuration shown in FIG.
7, as indicated by a reference "704" or "705", the coverage 702 of
the small cell configured by a small eNB may be included in the
coverage 701 of the macro cell configured by a macro eNB.
[0158] As indicated by the reference "705", the coverages 702 of a
plurality of, for example, two small cells may be included in the
coverage 701 of one macro cell. A user equipment (UE) 703 is
included in, for example, the coverage 702 of the small cell and
performs communication via the small cell.
[0159] In the cell configuration shown in FIG. 7, as indicated by a
reference "706", the coverage 701 of the macro cell configured by a
macro eNB may overlap the coverages 702 of the small cells
configured by small eNBs in a complicated manner.
[0160] As indicated by a reference "707", the coverage 701 of the
macro cell configured by a macro eNB may not overlap the coverages
702 of the small cells configured by small eNBs.
[0161] Further, as indicated by a reference "708", the coverages
702 of a large number of small cells configured by a large number
of small eNBs may be configured in the coverage 701 of one macro
cell configured by one macro eNB.
[0162] The following problems (1) and (2) lie in improving the
throughput of the multi-element antennas.
[0163] (1) Without matching phase and amplitude differences among
the antenna elements, problems occur which include: (a)
uncontrollable beam directivity with which beams cannot be directed
in a desired direction; (b) decrease in gain expressed by, for
example, equivalent isotropic radiated power (abbreviated as EIRP);
and (c) increase in side lobe power which increases interference
with other users.
[0164] (2) It is necessary to eliminate temperature and temporal
variations in phase and amplitude differences among the antenna
elements. However, since broadband communication increases the
frequency bandwidth, an amplifier and a filter, etc. cause a
problem of significantly influencing amounts of the temperature and
temporal variations.
[0165] The first embodiment will disclose a method for calibration
with higher accuracy to match phase and amplitude differences in
beam among a plurality of antenna elements included in a
multi-element antenna.
[0166] FIG. 8 is a block diagram illustrating a configuration of a
communication apparatus in a communication system according to the
first embodiment of the present invention. The communication
apparatus may be a base station or a user equipment. In other
words, the communication system according to the first embodiment
includes a base station and a user equipment, and at least one of
the base station and the user equipment is embodied by the
communication apparatus in FIG. 8.
[0167] The communication apparatus includes a physical layer (PHY)
processing unit 801, a plurality of antenna elements 802 to 805,
and a control unit 806. The plurality of antenna elements 802 to
805 are n antenna elements 802 to 805 (n is a natural number),
specifically, a first antenna element 802, a second antenna element
803, a third antenna element 804, . . . , and an n-th antenna
element 805. The first antenna element 802 to the n-th antenna
element 805 are connected to the PHY processing unit 801. The first
antenna element 802 to the n-th antenna element 805 form a
multi-element antenna.
[0168] The PHY processing unit 801 performs, according to an
instruction given from the control unit 806, respective processes
of generating a transmission signal, mapping, extracting a
reception signal, and demapping. The control unit 806 controls
timing on transmission and reception, allocation of time resources,
frequency resources, and code resources, transmission power, and a
phase value and an amplitude value for the antenna elements.
[0169] The PHY processing unit 801 corresponds to a calibration
unit that calibrates phases and amplitudes of beams formed by the
antenna elements 802 to 805, upon transmission and reception of a
signal. The PHY processing unit 801 obtains a correction value for
the phases and the amplitudes of the beams in the respective
antenna elements 802 to 805 so that the phases and the amplitudes
of the beams are identical among the antenna elements 802 to 805,
and calibrates the phases and the amplitudes based on the obtained
correction value.
[0170] Next, an example procedure of the control processes in the
communication apparatus will be described with the signal flow. The
control unit 806 determines whether calibration is necessary. When
determining that calibration is necessary, the control unit 806
determines timing, a frequency, and the transmission power for the
calibration, and notifies the PHY processing unit 801 of these.
[0171] Specifically, the PHY processing unit 801 performs the
calibration as follows. The PHY processing unit 801 maps
calibration RSs (may be hereinafter referred to as "cal-RSs"), sets
a transmission power value, and transmits a signal with
predetermined timing using a predetermined antenna element
according to an instruction given from the control unit 806.
[0172] Furthermore, the PHY processing unit 801 causes a
predetermined antenna element to receive the transmitted signal,
according to an instruction given from the control unit 806. The
PHY processing unit 801 demaps calibration RSs from the received
signal, calculates propagation properties from the value obtained
from the demapping, and notifies the control unit 806 of the
propagation properties.
[0173] The control unit 806 analyzes relative values of the antenna
elements 802 to 805 or differences with an ideal value of the
propagation properties measured in an anechoic chamber in advance,
for example, before shipment, calculates a correction value for the
phases and the amplitudes of the antenna elements 802 to 805 from
the analyzed values or the difference values, and notifies the PHY
processing unit 801 of the correction value.
[0174] The PHY processing unit 801 sets the correction value given
from the control unit 806 so that an offset is added to the
subsequent signals.
[0175] Whether the control unit 806 needs to perform calibration
may be determined through periodically (on a regular basis)
executing the processes by the control unit 806 and the PHY
processing unit 801 as described above, based on a difference
between a currently set value and a result of the correction value
that is calculated by the control unit 806 for the phases and the
amplitudes of the antenna elements 802 to 805.
[0176] When the communication apparatus is a base station, the
communication apparatus may start calibration according to an
instruction from a maintenance management apparatus in high layer.
Accordingly, the maintenance management apparatus in high layer,
for example, prevents a situation where a plurality of base
stations overlapping in cell coverage thereof simultaneously
perform calibration (may be hereinafter referred to as a
"calibration situation"), and can avoid occurrence of a non-service
area.
[0177] Similarly, when a base station that is a communication
apparatus receives notification indicating whether the surrounding
base stations are in a calibration situation from themselves and
the surrounding base stations are not yet in the calibration
situation, the own base station may start calibration. Conversely,
the base station may notify the surrounding base stations of
whether the own base station is in a calibration situation.
[0178] Alternatively, when the base station is provided with a
temperature sensor and the temperature variations become larger
than or equal to a predetermined value, the base station may start
calibration. Transmission power amplifiers, phasers, and filters
that separate and extract a required frequency have temperature
characteristics, and thus, the transmission power amplifiers, the
phasers, and the filters are known for having respective
variations. Inaccuracy of the beam control subject to the
variations in the transmission power amplifiers, the phasers, and
the filters can be corrected by causing the base station to start
calibration when the temperature variations become larger than or
equal to a predetermined value as described above.
[0179] Alternatively, the communication apparatus may start
calibration according to a request from a corresponding apparatus.
When the communication apparatus is a base station and the
corresponding apparatus is a base station or a repeater, the
corresponding apparatus knows or can learn a carrier to noise ratio
(abbreviated as CNR) or a signal to noise ratio (abbreviated as
SNR) for use in a normal operation with appropriate directivity.
Thus, the corresponding apparatus may instruct the communication
apparatus to start calibration, for example, when the CNR or the
SNR is smaller than or equal to a predetermined value due to the
temperature and temporal variations, etc.
[0180] When a user equipment for calibration is provided, more
specifically, when a user equipment is always placed at a specific
position or when a user equipment moved to a specific position is
determined as a user equipment for calibration, the user equipment
may instruct a communication apparatus to start calibration as
described above.
[0181] Alternatively, a user equipment transmits, to an evolved
packet core (EPC), quality information such as received power and
the SNR as well as Global Positioning System (GPS) position
information collected using, for example, a minimum drive test
(MDT) function. Then, if the EPC detects a difference with the
normal operation based on the received quality information and
there is the difference, the EPC may notify an instruction to start
calibration to the base station.
[0182] Particularly, in a transmission system, for example, the
control unit 806 may set a correction value for a phase and an
amplitude of the transmission system by handling the timing to
execute calibration as the timing with which the transmission
system does not transmit data for communication with the
corresponding apparatus. Furthermore, in a reception system, the
control unit 806 may set a correction value for a phase and an
amplitude of the reception system by handling the timing to execute
calibration as the timing with which the reception system has not
received data for communication with the corresponding apparatus.
In time division duplex (abbreviated as TDD), calibration may be
performed during a gap duration that is a switching time between
transmission and reception.
[0183] Furthermore, the control unit 806 may limit frequencies at
which calibration is to be executed to a part of the frequencies,
that is, to a sub-band. Accordingly, normal communication (service)
is possible with a resource that has not been calibrated.
Furthermore, when it is clear that, for example, the transmission
power amplifiers, the phasers, and the filters have little
variations in the temperature, etc., calibration is not required at
the sub-band at which they have been calibrated, and the
performance can be guaranteed by interpolation.
[0184] Similarly, calibration at the sub-band before increase in
the temperature variations can guarantee the performance.
[0185] Furthermore, when the antenna elements have various
distances, the control unit 806 divides the antenna elements into
several groups according to the distances, and increases the
transmission power for a group of relatively distant antenna
elements more than that of a group of relatively close antenna
elements, which improves the SNR and thus is effective. Here, some
of the antenna elements may belong to a plurality of groups.
[0186] Furthermore, no correction by the control unit 806 is also
effective when a value is significantly different from a
calibration value measured in, for example, an anechoic chamber,
before shipment or from correction values in the past record. For
example, when a large truck passes right in front, normal
calibration is possible by skipping the current calibration and
performing the next calibration.
[0187] Furthermore, when the correction value exceeds a change
acceptable value that is the largest value up to which change is
acceptable, multipath is detected and separated. When calibration
is performed only with principal waves and a value falls within the
acceptable values, calibration with the value is also effective.
Such a calibration is effective, for example, when a large sign is
placed closer and multipath normally occurs.
[0188] Example signal flows of the PHY processing unit 801 and the
control unit 806 will be described with reference to FIGS. 9 and
10. FIGS. 9 and 10 are block diagrams illustrating an example
configuration of a PHY processing unit 901, a control unit 9411,
and n antenna elements 909, 922, . . . , and 935. FIGS. 9 and 10
are connected across a border BL1.
[0189] The PHY processing unit 901 includes a plurality of encoder
units, a plurality of modulating units, a plurality of switching
units, a plurality of demodulating units, a plurality of decoder
units. The PHY processing unit 901 corresponds to a calibration
unit.
[0190] The plurality of encoder units are n encoder units (n is a
natural number) consisting of, specifically, a first encoder unit
902, a second encoder unit 915, . . . , and an n-th encoder unit
928. The plurality of modulating units are n modulating units (n is
a natural number) consisting of, specifically, a first modulating
unit 907, a second modulating unit 920, . . . , and an n-th
modulating unit 933. The plurality of switching units are n
switching units (n is a natural number) consisting of,
specifically, a first switching unit 908, a second switching unit
921, . . . , and an n-th switching unit 934.
[0191] The plurality of demodulating units are n demodulating units
(n is a natural number) consisting of, specifically, a first
demodulating unit 910, a second demodulating unit 923, . . . , and
an n-th demodulating unit 936. The plurality of decoder units are n
decoder units (n is a natural number) consisting of, specifically,
a first decoder unit 911, a second decoder unit 924, . . . , and an
n-th decoder unit 937.
[0192] Furthermore, a plurality of antenna elements, specifically,
the n antenna elements (n is a natural number) consisting of the
first antenna element 909, the second antenna element 922, . . . ,
and the n-th antenna element 935 are provided to correspond to the
plurality of encoder units 902, 915, . . . , and 928, and the
plurality of decoder units 911, 924, . . . , and 937,
respectively.
[0193] The first encoder unit 902 includes a first transmission
data generating unit 903, a first calibration RS mapping unit 904,
a first transmission power setting unit 905, and a first
transmission correction processing unit 9061. The first decoder
unit 911 includes a first reception correction processing unit
9121, a first calibration RS extracting unit 913, and a first
response characteristics calculating unit 914.
[0194] The second encoder unit 915 includes a second transmission
data generating unit 916, a second calibration RS mapping unit 917,
a second transmission power setting unit 918, and a second
transmission correction processing unit 9191. The second decoder
unit 924 includes a second reception correction processing unit
9251, a second calibration RS extracting unit 926, and a second
response characteristics calculating unit 927.
[0195] The n-th encoder unit 928 includes an n-th transmission data
generating unit 929, an n-th calibration RS mapping unit 930, an
n-th transmission power setting unit 931, and an n-th transmission
correction processing unit 9321. The n-th decoder unit 937 includes
an n-th reception correction processing unit 9381, an n-th
calibration RS extracting unit 939, and an n-th response
characteristics calculating unit 940.
[0196] In FIGS. 9 and 10, the first encoder unit 902, the first
modulating unit 907, the first switching unit 908, and the first
antenna element 909 form a first transmission system. The second
encoder unit 915, the second modulating unit 920, the second
switching unit 921, and the second antenna element 922 form a
second transmission system. The n-th encoder unit 928, the n-th
modulating unit 933, the n-th switching unit 934, and the n-th
antenna element 935 form an n-th transmission system.
[0197] In FIGS. 9 and 10, the first antenna element 909, the first
switching unit 908, the first demodulating unit 910, and the first
decoder unit 911 form a first reception system. The second antenna
element 922, the second switching unit 921, the second demodulating
unit 923, and the second decoder unit 924 form a second reception
system. The n-th antenna element 935, the n-th switching unit 934,
the n-th demodulating unit 936, and the n-th decoder unit 937 form
an n-th reception system.
[0198] FIGS. 9 and 10 illustrate an example relative calibration in
TDD systems. In the example of FIGS. 9 and 10, the first
transmission system makes a transmission, and the second to the
n-th reception systems receive the transmission to calculate
response characteristics in the second to the n-th reception
systems.
[0199] When the control unit 9411 determines to execute
calibration, the PHY processing unit 901 performs the following
processes according to an instruction from the control unit
9411.
[0200] The first transmission data generating unit 903 generates
transmission data, and gives it to the first calibration RS mapping
unit 904. The first calibration RS mapping unit 904 maps (inserts)
cal-RSs to be transmitted with the timing and at the frequency that
are instructed from the control unit 9411, to the transmission data
given from the first transmission data generating unit 903. The
first calibration RS mapping unit 904 gives the first transmission
power setting unit 905 the transmission data to which the cal-RSs
are mapped.
[0201] The first transmission power setting unit 905 sets a
transmission power value corresponding to a distance between a
transmission antenna element (may be hereinafter referred to as a
"transmission antenna") and a reception antenna element (may be
hereinafter referred to as a "reception antenna") as necessary to
achieve accuracy of a correction value through predetermined
calibration. The first transmission power setting unit 905 gives
the first transmission correction processing unit 9061 the set
transmission power value.
[0202] The first transmission correction processing unit 9061 gives
the first modulating unit 907 a signal to be transmitted, while
maintaining a correction value with the phase and the amplitude
that are currently set. The first modulating unit 907 performs
modulation such as OFDM on the signal given from the first
transmission correction processing unit 9061. The first modulating
unit 907 gives the first switching unit 908 the modulated
signal.
[0203] The first switching unit 908 switches between transmission
and reception of the TDD. The first switching unit 908 passes, to
the first antenna element 909, the modulated signal given from the
first modulating unit 907. The first antenna element 909 transmits
the modulated signal given from the first modulating unit 907.
[0204] The second antenna elements 922 to the n-th antenna element
935 receive the signal transmitted by the first antenna element
909. Here, in contrast to the first switching unit 908, the second
switching unit 921 to the n-th switching unit 934 make connections
to enable reception of signals by the second reception system to
the n-th reception system, respectively.
[0205] The second demodulating unit 923 to the n-th demodulating
unit 936 demodulate the signals received by the second antenna
elements 922 to the n-th antenna element 935, respectively, to, for
example, OFDM. The second reception correction processing unit 9251
to the n-th reception correction processing unit 9381 are given the
signals demodulated by the second demodulating unit 923 to the n-th
demodulating unit 936, respectively.
[0206] The second reception correction processing unit 9251 to the
n-th reception correction processing unit 9381 give a demodulated
signal given from the second demodulating unit 923 to the n-th
demodulating unit 936 to the second calibration RS extracting unit
926 to the n-th calibration RS extracting unit 939, respectively,
while maintaining phases and amplitudes that are currently set.
[0207] The second calibration RS extracting unit 926 to the n-th
calibration RS extracting unit 939 extract cal-RS portions from the
signal given from the second reception correction processing unit
9251 to the n-th reception correction processing unit 9381 and give
them to the second response characteristics calculating unit 927 to
the n-th response characteristics calculating unit 940,
respectively.
[0208] Based on a fact that the transmitted cal-RSs are known, the
second response characteristics calculating unit 927 to the n-th
response characteristics calculating unit 940 calculate propagation
properties from fluctuations in the known signals. The second
response characteristics calculating unit 927 to the n-th response
characteristics calculating unit 940 notify the control unit 9411
of the calculated propagation properties.
[0209] The control unit 9411 calculates a correction value, for
example, with respect to the second antenna element 922 so that the
phases and the amplitudes are identical to the phase and the
amplitude of the second antenna element 922. Here, the correction
value is calculated in consideration of the respective distances of
the second antenna element 922 to the n-th antenna element 935 from
the first antenna element 909.
[0210] Upon setting the calculated correction value to each of the
second reception correction processing unit 9251 to the n-th
reception correction processing unit 9381, the control unit 9411
can match the phases and the amplitudes of signals received by the
second antenna element 922 to the n-th antenna element 935.
[0211] If the first and third reception systems are calibrated with
the same processes with transmission from the second transmission
system, the correction value for the first reception correction
processing unit 9121 can also be calculated. Thus, the phase and
the amplitude of the first reception system can be matched with
those of the second reception system.
[0212] Although the above examples describe reception of the same
average reception power through all the antenna elements, they are
not limited to such. Side lobes may be reduced by, for example,
tapering the antenna elements to change the average reception power
for each of the antenna elements. Here, the amplitude value of a
received signal can be changed to a desired value by comparing the
amplitude value with a desired amplitude value in a normal
operation, for example, before shipment.
[0213] FIGS. 11 and 12 are block diagrams illustrating an example
configuration of the PHY processing unit 901, the control unit
9411, and the n antenna elements 909, 922, . . . , and 935. FIGS.
11 and 12 are connected across a border BL2. Since the
configuration of FIGS. 11 and 12 is the same as that of FIGS. 9 and
10, the same references will be assigned to the same portions and
the common description thereof will be omitted.
[0214] Following the calibration of the reception systems
illustrated in FIGS. 9 and 10, FIGS. 11 and 12 illustrate an
example calibration of transmission systems using the relative
calibration in the TDD systems, with the same configuration as that
in FIGS. 9 and 10.
[0215] When the control unit 9411 determines to execute
calibration, the PHY processing unit 901 performs the following
processes according to an instruction from the control unit
9411.
[0216] The first transmission data generating unit 903 generates
transmission data, and gives it to the first calibration RS mapping
unit 904. The first calibration RS mapping unit 904 maps (inserts)
cal-RSs to be transmitted with the timing and at the frequency that
are instructed by the control unit 9411, to the transmission data
given from the first transmission data generating unit 903. The
first calibration RS mapping unit 904 gives the first transmission
power setting unit 905 the transmission data to which the cal-RSs
are mapped.
[0217] The first transmission power setting unit 905 sets a
transmission power value corresponding to a distance between a
transmission antenna and a reception antenna as necessary to
achieve accuracy of a correction value through predetermined
calibration. The first transmission power setting unit 905 gives
the first transmission correction processing unit 9061 the set
transmission power value.
[0218] The first transmission correction processing unit 9061 gives
the first modulating unit 907 a signal to be transmitted, while
maintaining a correction value with the phase and the amplitude
that are currently set. The first modulating unit 907 performs
modulation such as OFDM on the signal given from the first
transmission correction processing unit 9061. The first modulating
unit 907 gives the first switching unit 908 the modulated
signal.
[0219] The first switching unit 908 switches between transmission
and reception of the TDD. The first switching unit 908 passes, to
the first antenna element 909, the modulated signal given from the
first modulating unit 907. The first antenna element 909 transmits
the modulated signal given from the first modulating unit 907.
[0220] The described processes may be performed in an order of the
second transmission system, the third transmission system, . . . ,
and the n-th transmission system, or a part of the processes may be
simultaneously performed by a plurality of the transmission
systems. Simultaneously performing the part of the processes can
shorten a time required for calibration.
[0221] Furthermore, transmission systems for performing the
processes may be added one by one as in REV method, for example,
the second transmission system, the second transmission system+the
third transmission system, . . . , and the second transmission
system+the third transmission system+ . . . +the n-th transmission
system.
[0222] The second antenna elements 922 to the n-th antenna element
935 receive the signal transmitted by the first antenna element
909. Here, in contrast to the first switching unit 908, the second
switching unit 921 to the n-th switching unit 934 make connections
to enable reception of signals by the second reception system to
the n-th reception system, respectively.
[0223] The second demodulating unit 923 to the n-th demodulating
unit 936 demodulate the signals received by the second antenna
elements 922 to the n-th antenna element 935, respectively, to, for
example, OFDM. The second reception correction processing unit 9251
to the n-th reception correction processing unit 9381 are given the
signals demodulated by the second demodulating unit 923 to the n-th
demodulating unit 936, respectively.
[0224] The second reception correction processing unit 9251 to the
n-th reception correction processing unit 9381 give a demodulated
signal given from the second demodulating unit 923 to the n-th
demodulating unit 936 to the second calibration RS extracting unit
926 to the n-th calibration RS extracting unit 939, respectively,
while maintaining phases and amplitudes that are currently set.
[0225] The second calibration RS extracting unit 926 to the n-th
calibration RS extracting unit 939 extract cal-RS portions from the
signal given from the second reception correction processing unit
9251 to the n-th reception correction processing unit 9381 and give
them to the second response characteristics calculating unit 927 to
the n-th response characteristics calculating unit 940,
respectively.
[0226] Based on a fact that the transmitted cal-RSs are known, the
second response characteristics calculating unit 927 to the n-th
response characteristics calculating unit 940 calculate propagation
properties from fluctuations in the known signals. The second
response characteristics calculating unit 927 to the n-th response
characteristics calculating unit 940 notify the control unit 9411
of the calculated propagation properties.
[0227] The control unit 9411 calculates a correction value so that,
for example, phases of the second to the n-th transmission signals
transmitted through the second antenna element 922 to the n-th
antenna element 935, respectively, are identical to one another
with respect to the reception system including the first antenna
element 909. Here, the correction value is calculated in
consideration of the respective distances (phase rotation by a
distance, amplitude attenuation) among the first antenna element
909 to the n-th antenna element 935.
[0228] Upon adding the calculated correction value to the current
correction value and setting the correction value to each of the
second transmission correction processing unit 9191 to the n-th
transmission correction processing unit 9321, the control unit 9411
can match the phases and the amplitudes of signals transmitted by
the second antenna element 922 to the n-th antenna element 935.
[0229] If the second reception system is calibrated with the same
processes with transmission from the first transmission system, the
phase and the amplitude of the first transmission system can be
also matched with the others.
[0230] Although the above examples describe transmission of the
same average transmission power through all the antenna elements,
they are not limited to such. Side lobes may be reduced by, for
example, tapering the antenna elements to change the average
transmission power for each of the antenna elements. Here, the
amplitude value of a transmission signal can be changed to a
desired value by comparing the amplitude value with a desired
amplitude value that is known.
[0231] FIGS. 13 and 14 are block diagrams illustrating another
example configuration of a PHY processing unit 901A, a control unit
9412, and the n antenna elements 909, 922, . . . , and 935. FIGS.
13 and 14 are connected across a border BL3.
[0232] The PHY processing unit 901A includes a plurality of encoder
units, a plurality of modulating units, a plurality of switching
units, a plurality of demodulating units, a plurality of decoder
units. The PHY processing unit 901A corresponds to a calibration
unit.
[0233] The plurality of encoder units are n encoder units (n is a
natural number) consisting of, specifically, a first encoder unit
902A, a second encoder unit 915A, . . . , and an n-th encoder unit
928A. The plurality of modulating units are n modulating units (n
is a natural number) consisting of, specifically, the first
modulating unit 907, the second modulating unit 920, . . . , and
the n-th modulating unit 933. The plurality of switching units are
n switching units (n is a natural number) consisting of,
specifically, the first switching unit 908, the second switching
unit 921, . . . , and the n-th switching unit 934.
[0234] The plurality of demodulating units are n demodulating units
(n is a natural number) consisting of, specifically, the first
demodulating unit 910, the second demodulating unit 923, . . . ,
and the n-th demodulating unit 936. The plurality of decoder units
are n decoder units (n is a natural number) consisting of,
specifically, a first decoder unit 911A, a second decoder unit
924A, . . . , and an n-th decoder unit 937A.
[0235] Furthermore, a plurality of antenna elements, specifically,
the n antenna elements (n is a natural number) consisting of the
first antenna element 909, the second antenna element 922, . . . ,
and the n-th antenna element 935 are provided to correspond to the
plurality of encoder units 902A, 915A, . . . , and 928A, and the
plurality of decoder units 911A, 924A, . . . , and 937A,
respectively.
[0236] The first encoder unit 902A includes the first transmission
data generating unit 903, the first calibration RS mapping unit
904, the first transmission power setting unit 905, and a first
transmission phase rotation unit 9062. The first decoder unit 911A
includes a first reception phase rotation unit 9122, the first
calibration RS extracting unit 913, and the first response
characteristics calculating unit 914.
[0237] The second encoder unit 915A includes the second
transmission data generating unit 916, the second calibration RS
mapping unit 917, the second transmission power setting unit 918,
and a second transmission phase rotation unit 9192. The second
decoder unit 924A includes a second reception phase rotation unit
9252, the second calibration RS extracting unit 926, and the second
response characteristics calculating unit 927.
[0238] The n-th encoder unit 928A includes the n-th transmission
data generating unit 929, the n-th calibration RS mapping unit 930,
the n-th transmission power setting unit 931, and an n-th
transmission phase rotation unit 9322. The n-th decoder unit 937A
includes an n-th reception phase rotation unit 9382, the n-th
calibration RS extracting unit 939, and the n-th response
characteristics calculating unit 940.
[0239] In FIGS. 13 and 14, the first encoder unit 902A, the first
modulating unit 907, the first switching unit 908, and the first
antenna element 909 form a first transmission system. The second
encoder unit 915A, the second modulating unit 920, the second
switching unit 921, and the second antenna element 922 form a
second transmission system. The n-th encoder unit 928A, the n-th
modulating unit 933, the n-th switching unit 934, and the n-th
antenna element 935 form an n-th transmission system.
[0240] In FIGS. 13 and 14, the first antenna element 909, the first
switching unit 908, the first demodulating unit 910, and the first
decoder unit 911A form a first reception system. The second antenna
element 922, the second switching unit 921, the second demodulating
unit 923, and the second decoder unit 924A form a second reception
system. The n-th antenna element 935, the n-th switching unit 934,
the n-th demodulating unit 936, and the n-th decoder unit 937A form
an n-th reception system.
[0241] Since the configuration of FIGS. 13 and 14 includes the same
configuration as that of FIGS. 9 and 10, the same references will
be assigned to the same portions and the common description thereof
will be omitted. FIGS. 13 and 14 illustrate an example of the REV
method in the TDD systems. FIGS. 13 and 14 illustrate an example in
which the second reception phase rotation unit 9252 to the n-th
reception phase rotation unit 9382 successively rotate the phases
and the control unit 9412 obtains a phase having the highest
reception power, while the first transmission system makes a
transmission and the second to the n-th reception systems receive
the transmission.
[0242] FIGS. 15 and 16 are block diagrams illustrating another
example configuration of the PHY processing unit 901A, the control
unit 9412, and the n antenna elements 909, 922, . . . , and 935.
FIGS. 15 and 16 are connected across a border BL4. Since the
configuration of FIGS. 15 and 16 is the same as that of FIGS. 13
and 14, the same references will be assigned to the same portions
and the common description thereof will be omitted.
[0243] Following the calibration of the reception systems
illustrated in FIGS. 13 and 14, FIGS. 15 and 16 illustrate an
example calibration of transmission systems in the REV method using
the TDD systems, with the same configuration as that in FIGS. 13
and 14. FIGS. 15 and 16 illustrate an example in which the second
transmission phase rotation unit 9192 to the n-th transmission
phase rotation unit 9322 successively rotate the phases, and the
control unit 9412 obtains a phase having the highest reception
power.
[0244] When each of the calibration RS mapping units 904 to 930
transmits the cal-RSs, it may radio-transmit an information bit
indicating that the subframe or the slot is used for calibration so
that a user equipment, the surrounding repeaters, and the
surrounding cells can recognize the calibration.
[0245] The user equipment can perform random access by avoiding the
timing of calibration (may be hereinafter referred to as
"calibration timing"). The surrounding repeaters and the
surrounding cells can avoid simultaneous calibration.
Alternatively, the surrounding repeaters and the surrounding cells
may be notified through a cable. Alternatively, the surrounding
user equipments may be notified via the surrounding repeaters and
the surrounding cells through a cable.
[0246] Notification of whether calibration is normally performed is
effective. If the calibration is not normally performed, it is
probable that, for example, some antenna elements are electrically
or physically damaged and lack their function. Thus, having a
function of detecting, no matter how many times a correction value
is measured, whether the correction value is significantly larger
than values set in the past (including a value set immediately
before) is also effective.
[0247] If a failure in calibration is detected, for example, the
reciprocity of transmission and reception cannot be guaranteed.
Thus, the precoding/postcoding under control of beams may not
operate normally, and the SNR becomes worse. Accordingly,
communication cannot be performed normally, and interference occurs
in a cell that is normally operating.
[0248] Thus, notifying an RRC IDLE user equipment existing in the
area that the calibration is not normally performed, through
broadcast information is effective. Furthermore, individually
notifying a user equipment during communication using the radio
resource control (RRC) is effective. Furthermore, notifying a user
equipment moving into a cell through handover as configuration
information for the cell is effective.
[0249] There are the following five calibration states (1) to
(5).
[0250] (1) State 1: Calibration has not yet been executed.
[0251] (2) State 2: During calibration
[0252] (3) State 3: Calibration has failed.
[0253] (4) State 4: Calibration is to be started after a
predetermined time.
[0254] (5) State 5: Calibration has been normally completed.
[0255] Notifying information indicating each of the above five
calibration states (1) to (5) separately from information
indicating whether calibration is successful is effective.
[0256] Alternatively, collectively notifying some of the states (1)
to (5) enables an amount of information to be reduced, which is
effective.
[0257] Notifying a calibration level, specifically, information
indicating, for example, whether the reciprocity can be supported
and whether a direction of arrival can be ascertained is also
effective. Notifying this information to an RRC IDLE user equipment
existing in the area through broadcast information is effective.
Furthermore, individually notifying a user equipment during
communication of such information using an RRC message such as an
RRC connection setup message and an RRC connection reconfiguration
message is effective. Furthermore, notifying also a user equipment
moving into a cell through handover of such information as
configuration information for the cell is effective.
[0258] Similarly, individually notifying, using the radio resource
control (RRC), a base station about whether a user equipment is
normally performing calibration or about a calibration state is
effective.
[0259] As described above according to the first embodiment, the
PHY processing unit that is a calibration unit obtains a correction
value for the phases and the amplitudes of the beams in the
respective antenna elements so that the phases and the amplitudes
of the beams are identical among the antenna elements, and
calibrates the phases and the amplitudes based on the obtained
correction value. Since the calibration can be performed with
higher accuracy, it is possible to match phase and amplitude
differences in beam among a plurality of antenna elements included
in a multi-element antenna. Thus, a communication system capable of
communication with a relatively high throughput can be
implemented.
Second Embodiment
[0260] The first embodiment describes a method for enabling
improvement of a throughput by matching phase and amplitude
differences among antenna elements included in a multi-element
antenna. The second embodiment will disclose a method for solving a
problem with requiring a long time to transmit the same number of
cal-RSs when mapping of the cal-RSs for each of the antenna
elements for calibration temporally varies.
[0261] This method is a method for arranging reference signals for
calibration (cal-RSs) in the same subframe in an antenna element
that transmits the cal-RSs.
[0262] FIG. 17 illustrates example mapping in transmission data of
a first antenna element. FIG. 18 illustrates example mapping in
transmission data of a second antenna element to an n-th antenna
element. The horizontal axis represents a time t, and the vertical
axis represents a frequency f in FIGS. 17 and 18. In FIGS. 17 and
18, a reference "1306" denotes a resource block.
[0263] In the example of FIG. 17, the first antenna element
transmits cal-RSs 1302 that are localized in a first slot 1303 and
a first subframe 1304, and transmits normal OFDM symbols 1301 in
the remaining portions.
[0264] As illustrated in FIG. 18, transmission data during the same
duration in the second antenna element to the n-th antenna element
is a null 1307. In other words, in the second antenna element to
the n-th antenna element, the transmission data in a slot 1308 and
a subframe 1309 during a duration in which the cal-RSs 1302 are to
be transmitted by the first antenna element is the null 1307,
whereas normal OFDM symbols 1305 are transmitted in the remaining
portions.
[0265] Although the slot indicates a time corresponding to 7 OFDM
symbols and the subframe indicates a time corresponding to 14 OFDM
symbols, they may be any minimum slot allocated on a per particular
user unit basis.
[0266] Since the cal-RSs 1302 are arranged during a particular
duration in the example of FIG. 17, calibration is possible during
this duration and the time required for calibration can be
shortened.
[0267] Although the first antenna element transmits the cal-RSs
1302 with the second and third OFDM symbols in the example of FIG.
17, transmitting cal-RSs of another antenna element using the
fourth and fifth OFDM symbols in the same slot or the same subframe
is also effective.
[0268] Furthermore, not only shifting the time but also using a
different orthogonal code is effective to enable the cal-RSs for
each of the antenna elements to be orthogonalized and separated. It
is more preferred to set a code to an orthogonal code even with the
phase rotated.
[0269] Similarly, transmitting the cal-RSs at a part of the
frequencies through the first antenna element and transmitting the
cal-RSs at a different frequency through another antenna element
are also effective.
[0270] The cal-RSs may be identical signals among all the antenna
elements if code-multiplexing is not used.
[0271] Since such processes enable use of the energy in the entire
frequency domain, the SNR can be increased and the accuracy of
calibration can be improved. Furthermore, since nothing is
transmitted through the other antenna elements, interference can be
reduced and the accuracy of calibration can be improved.
[0272] The method for transmitting the cal-RSs in a particular
frequency domain is effective when the SNR is sufficiently
favorable. Since a plurality of antenna elements can be
simultaneously calibrated using this method, the time required for
calibration can be shortened.
[0273] In the REV method, the same signals as those of the first
antenna element may be mapped for the second to the n-th antenna
elements, instead of the null.
[0274] FIG. 19 illustrates examples of mapping and the reception
power at each frequency, in transmission data of the first antenna
element. Part (a) of FIG. 19 illustrates an example of mapping in
the transmission data of the first antenna element, and part (b) of
FIG. 19 illustrates the reception power at each frequency in the
transmission data of the first antenna element.
[0275] In the example of FIG. 19, the first antenna element
transmits cal-RSs 1402 that are localized in a first slot 1403 and
a first subframe 1404, and transmits normal OFDM symbols 1401 in
the remaining portions, similarly as the example in FIG. 17.
[0276] Since the entire frequency domain is used herein, response
characteristics at each frequency can be calculated. Thus,
fluctuations in the amplitude and the phase at each frequency can
be detected. Fluctuations in the received power are calculated from
the detected amplitude and phase. As illustrated in FIG. 19, when
fluctuations in the received power P for each of the OFDM symbols
1401 are larger, it is possible to determine the presence of
frequency-selective multipath fading.
[0277] When transmission antenna elements and reception antenna
elements for calibration are not moved and the multipath is
detected, it is possible to determine occurrence of a state
different from a normal state such as the presence of scatterers in
close proximity. No calibration at the sub-band is effective. Here,
it is preferred to use the correction value in the previous
calibration and the phase rotation.
[0278] Since the scatterers occurring in close proximity normally
move far in a predetermined time, detecting fluctuations in the
amplitude and the phase at each frequency again after a lapse of a
certain time is effective.
[0279] Alternatively, the fluctuations may be calculated and set
from the correction value and the phase rotation at the close band.
Interpolation such as linear interpolation is also effective.
[0280] Furthermore, when the multipath is detected, separation
between principal waves and delay waves through, for example,
calculation of a delay profile and calibration only with the
principal waves are effective. Accordingly, influence of the
multipath can be removed, and appropriate calibration can be
performed.
[0281] According to the second embodiment, when transmitting
respective cal-RSs from a plurality of antenna elements, the PHY
processing unit that is a calibration unit arranges the cal-RSs in
the same subframe as described above. Accordingly, since all the
antenna elements can be calibrated during the same duration, the
time required for calibration can be shortened.
Third Embodiment
[0282] The second embodiment describes a method for temporally
localizing the mapping of cal-RSs for each antenna element that is
required for calibration to enable shortening of the time required
for calibration. However, the transmission sometimes overlaps with
those of the other CHs or the other RSs, and the current standards
do not cover such requirement. Thus, a non-avoidable problem with
the requirement occurs. The third embodiment will disclose a method
for solving the problem by providing a new mapping method.
[0283] FIG. 20 illustrates another example mapping in the
transmission data of the first antenna element. FIG. 21 illustrates
another example mapping in the transmission data of the second
antenna element to the n-th antenna element. FIGS. 20 and 21
illustrate example mapping of downlink transmission bits for which
a slot or a subframe for calibration or resource blocks 1504 and
1508 are provided.
[0284] As illustrated in FIG. 20, special mapping of not
transmitting a part of CRSs 1503 on a subframe for transmitting
cal-RSs 1502 is provided for the first antenna element. Normal OFDM
symbols 1501 are transmitted in the remaining portions.
[0285] As illustrated in FIG. 21, special mapping of not
transmitting a part of CRSs 1507 on a subframe for transmitting a
null 1506 is provided for the second antenna element to the n-th
antenna element. Normal OFDM symbols 1505 are transmitted in the
remaining portions.
[0286] FIG. 22 further illustrates another example mapping in the
transmission data of the first antenna element. FIG. 23 further
illustrates another example mapping in the transmission data of the
second antenna element. FIG. 24 further illustrates another example
mapping in the transmission data of the third antenna element. FIG.
25 further illustrates another example mapping in the transmission
data of the fourth antenna element.
[0287] In FIGS. 22, 23, 24, and 25, references "1604", "1608",
"1612", and "1616" denote resource blocks, and references "1601",
"1605", "1609", and "1613" denote normal OFDM symbols,
respectively.
[0288] As illustrated in FIGS. 22, 23, 24, and 25, possible
positions of cal-RSs 1602, 1606, 1610, and 1614 may be defined in
advance only with the timing that does not overlap CRSs 1603, 1607,
1611, and 1615, respectively. Here, the cal-RSs can be arranged,
for example, only between the first OFDM symbol and the third OFDM
symbol or between the fourth OFDM symbol and the fifth OFDM symbol
in each slot.
[0289] FIG. 26 further illustrates another example mapping of
transmission data in the transmission data of the first antenna
element. FIG. 27 further illustrates another example mapping in
transmission data of the second antenna element to the n-th antenna
element. In FIGS. 26 and 27, references "1704" and "1708" denote
resource blocks, and references "1701" and "1705" denote normal
OFDM symbols, respectively. Furthermore, in FIG. 27, a reference
"1706" denotes a null.
[0290] As illustrated in FIGS. 26 and 27, cal-RSs 1702 may be
mapped to positions that do not overlap mapping positions of CRSs
1703 and 1707, respectively. With this, a collision can be
avoided.
[0291] Alternatively, as illustrated in FIGS. 20 and 21, when
cal-RSs overlap the other CHs or the other RSs, the cal-RSs may be
preferentially arranged.
[0292] As described above, the PHY processing unit that is a
calibration unit arranges the cal-RSs in positions where the other
reference signals or the other physical channels of a subframe are
not arranged according to the third embodiment. Accordingly, since
the timing of transmitting the cal-RSs can be prevented from
overlapping the timing of transmitting the other reference signals
or the other physical channels, the cal-RSs can avoid a collision
with the other reference signals or the other physical
channels.
Fourth Embodiment
[0293] The third embodiment discloses providing a subframe for
calibration and transmitting RSs for calibration (cal-RSs) on the
subframe. A base station may not transmit the other channels
(abbreviated as CHs) or the other RSs on the subframe. The subframe
for calibration of not transmitting the other CHs or the other RSs
will be referred to as a calibration-specific subframe.
[0294] However, the base station normally transmits some physical
CHs or RSs that are not intended for calibration, every subframe.
Thus, without any ingenuity, a problem with incapability to
configure a calibration-specific subframe occurs. The fourth
embodiment will disclose a method for solving such a problem.
[0295] A base station sets a subframe having no data to be
transmitted to a calibration-specific subframe. The base station
may set a subframe having no data to be scheduled to a
calibration-specific subframe. The base station sets one or more
subframes included in subframes having no data to be transmitted or
scheduled to calibration-specific subframes. The one or more
subframes may be determined according to the necessity of the
calibration-specific subframes.
[0296] The base station determines a radio link at which the
calibration-specific subframe is set. For example, when there is no
data to be scheduled in a DL subframe, the DL subframe is set to a
calibration-specific subframe. Alternatively, when there is no data
to be scheduled in a UL subframe, the UL subframe may be set to a
calibration-specific subframe. Alternatively, when there is no data
to be scheduled in either a DL subframe or a UL subframe with the
same timing as the DL subframe, at least one of the DL subframe and
the UL subframe may be set to a calibration-specific subframe.
[0297] The base station may determine in advance a radio link to be
calibrated. The radio link is determined in advance as, for
example, the DL. Here, when there is no data to be scheduled in a
DL subframe, the DL subframe is set to a calibration-specific
subframe. Thus, even when there is no data to be scheduled in a UL
subframe, the UL subframe is not set to a calibration-specific
subframe. Here, the UL is not used for setting a
calibration-specific subframe.
[0298] When a radio link to be calibrated is set to the DL, it is
possible to eliminate influence of interference with the UL from a
UE. For example, when a base station that supports the TDD sets a
radio link to be calibrated to the DL, it can execute calibration
without influence of interference caused by uplink transmission
performed by a UE being served by a cell having an antenna to be
calibrated and by a UE being served by another cell or another base
station. Examples of the uplink transmission in the LTE include a
SR and a PRACH. As such, using the DL in calibration can further
improve the accuracy of calibration.
[0299] As an alternative example, a base station that supports the
FDD sets radio links to be calibrated to the DL and the UL. When
there is no data to be scheduled in either a DL subframe or a UL
subframe with the same timing as the DL subframe, both of the DL
subframe and the UL subframe are set to calibration-specific
subframes. Accordingly, calibration for a transmission system and a
reception system of an antenna element can be performed within
these subframes, and the time required for calibration can be
shortened.
[0300] The base station detects a subframe having no data to be
transmitted or scheduled, and sets the subframe to a
calibration-specific subframe.
[0301] The following four examples (1) to (4) will be disclosed as
example subjects that detect a subframe having no data to be
transmitted or scheduled.
[0302] (1) Scheduler
[0303] This option may be used when, for example, a scheduler
performs scheduling. It is easy to provide the scheduler with a
function of detecting the presence or absence of data to be
transmitted or scheduled.
[0304] (2) MAC
[0305] This option may be used when, for example, the MAC performs
scheduling. It is easy to provide the MAC with the function of
detecting the presence or absence of data to be transmitted or
scheduled.
[0306] (3) PHY Processing Unit
[0307] This option may be used when, for example, a subframe having
no data to be transmitted is detected. It is easy to provide the
PHY processing unit with a function of detecting the presence or
absence of data to be transmitted.
[0308] (4) RRC
[0309] This option may be used when, for example, the RRC sets the
DRX, etc. The RRC recognizes, through the DRX, a subframe on which
data is not transmitted or scheduled. Thus, it is easy to provide
the RRC with the function of detecting the presence or absence of
data to be transmitted or scheduled.
[0310] The following four examples (1) to (4) will be disclosed as
example subjects that set the detected subframe to a
calibration-specific subframe.
[0311] (1) Scheduler
[0312] This option may be used when, for example, a scheduler, the
MAC, or the RRC detects the presence or absence of data to be
transmitted or scheduled. When the scheduler, the MAC, or the RRC
detects the absence of the data, the scheduler is notified of the
absence of the data. The scheduler sets the subframe detected using
the information to a calibration-specific subframe.
[0313] (2) MAC
[0314] The scheduler described in (1) above may be replaced with
the MAC.
[0315] (3) PHY Processing Unit
[0316] This option may be used when, for example, the scheduler,
the MAC, the PHY processing unit, or the RRC detects the presence
or absence of data to be transmitted or scheduled. When the
scheduler, the MAC, the PHY processing unit, or the RRC detects the
absence of the data, the PHY processing unit is notified of the
absence of the data. The PHY processing unit sets the subframe
detected using the information to a calibration-specific
subframe.
[0317] (4) RRC
[0318] This option may be used when, for example, the RRC detects
the presence or absence of data to be transmitted or scheduled.
When the RRC detects the absence of the data, it sets the subframe
detected using the information to a calibration-specific
subframe.
[0319] Aside from these, the subjects that detect a subframe having
no data to be transmitted or scheduled and the subjects that set a
subframe to a calibration-specific subframe may be appropriately
combined. The subjects may be combined according to a configuration
of a base station and the required performance.
[0320] The base station determines which antenna element is to be
calibrated. The base station determines which antenna element is
categorized as a transmission antenna element for calibration or as
a reception antenna element for calibration.
[0321] The base station maps RSs for calibration (cal-RSs) of the
transmission antenna element for calibration to a
calibration-specific subframe. Cal-RSs of a plurality of antenna
elements may be mapped to one calibration-specific subframe. The
PHY processing unit may map the cal-RSs using information on a
calibration-specific subframe.
[0322] The subject that sets a calibration-specific subframe may
notify the PHY processing unit of the information on the
calibration-specific subframe. The base station transmits cal-RSs
of a transmission antenna for calibration on the
calibration-specific subframe.
[0323] The RSs for calibration may not be specific to calibration.
The RSs may be used for other applications. Alternatively, the
existing RSs may be used instead. Examples of the existing RSs
include CRSs, CSI-RSs, and sounding reference signals (SRS), etc.
Which RSs are to be used may be determined in advance, and the RSs
may be mapped to a calibration-specific subframe. A sequence or a
resource to be mapped has already been determined for the existing
RSs. Since no new RS is set, the complexity of a communication
system can be avoided.
[0324] Furthermore, the calibration-specific subframes may be used
for other applications. The RSs to be used for other applications
may be mapped to a calibration-specific subframe. The method
disclosed in the fourth embodiment is applicable.
[0325] A base station that transmits cal-RSs from a transmission
antenna element for calibration on a calibration-specific subframe
receives the cal-RSs on the calibration-specific subframe through a
reception antenna element for calibration. The base station derives
a calibration value for a transmission system of an antenna
element, using a reception result of the cal-RSs for each
transmission antenna element for calibration.
[0326] The base station may calibrate a reception system of an
antenna element in a similar method. The base station that
transmits cal-RSs from a transmission antenna element for
calibration on a calibration-specific subframe receives the cal-RSs
on the calibration-specific subframe through a reception antenna
element for calibration. The base station derives a calibration
value for the reception system of the antenna element, using a
reception result of the cal-RSs for each reception antenna element
for calibration.
[0327] FIG. 28 is a flowchart indicating an example procedure on
calibration processes in the communication system according to the
fourth embodiment. FIG. 28 illustrates an example self-calibration
in a base station.
[0328] In Step ST4101, the base station determines to execute
calibration. The judgment indicators disclosed in the first
embodiment may be used in this determination.
[0329] In Step ST4102, the base station determines the presence or
absence of a subframe having no data to be transmitted (may be
hereinafter referred to as "non-transmission-data subframe"). This
determination may be made, for example, per subframe. This
determination may be made per a plurality of subframes. When the
presence of a non-transmission-data subframe is determined, the
processes proceed to Step ST4103. When the absence of the
non-transmission-data subframe is determined, the processes will be
put on hold until the presence of the non-transmission-data
subframe is determined.
[0330] In Step ST4103, the base station sets the subframe detected
in Step ST4102 to a calibration-specific subframe.
[0331] In Step ST4104, the base station maps RSs for calibration
(cal-RSs) of a transmission antenna element for calibration to the
calibration-specific subframe. Here, the base station may determine
which antenna element is categorized as a transmission antenna
element for calibration or as a reception antenna element for
calibration. More specifically, in Step ST4104, the base station
transmits the cal-RSs of the transmission antenna for calibration
on the calibration-specific subframe.
[0332] In Step ST4105, the base station receives the cal-RSs on the
calibration-specific subframe through a reception antenna element
for calibration.
[0333] In Step ST4106, the base station derives a calibration value
for a transmission system of an antenna element, using a reception
result of the cal-RSs for each transmission antenna element for
calibration.
[0334] In Step ST4107, the base station determines whether
calibration on all the antenna elements is completed. When the
completion of the calibration on all the antenna elements is
determined, the processes proceed to Step ST4108. If it is
determined that the calibration on all the antenna elements has not
been completed, the processes return to Step ST4102 to perform the
aforementioned processes on an antenna element that has not been
calibrated. The processes may be performed until completion of the
calibration of transmission systems and reception systems of all
the antenna elements.
[0335] In Step ST4108, the processes return to a normal operation.
In the normal operation, the calibration ends, and a normal
communication service is provided to user equipments being served.
The entire procedure ends after the process in Step ST4108.
[0336] Using the method disclosed in the fourth embodiment, a base
station can be equipped with a subframe for calibrating a
multi-element antenna. Accordingly, the base station can calibrate
antenna elements. Thus, the performance of the MIMO and the
beamforming using the multi-element antenna can be improved.
[0337] The fourth embodiment discloses that a base station sets a
subframe having no data to be transmitted or scheduled to a
calibration-specific subframe. As an alternative method, the
subframe having no data to be transmitted or scheduled may be
replaced with a subframe whose data to be transmitted or scheduled
is smaller than or equal to a predetermined amount of data. With a
small amount of data, calibration can be preferentially
executed.
[0338] The predetermined amount of data may be determined in
advance or set according to an operational environment and an
operational state. The predetermined amount of data is set, for
example, according to an ambient temperature. Alternatively, the
predetermined amount of data is set, for example, according to a
load of a base station. When the subframe has data smaller than or
equal to the predetermined amount of data, it means that the
subframe has data to be transmitted or scheduled. A method, which
will be disclosed in the second modification of the fourth
embodiment, for storing data not to be transmitted and transmitting
the data stored with the timing capable of subsequent transmission
of data may be applied to handling of this transmission data.
[0339] Accordingly, calibration can be executed flexibly according
to the operational environment. Thus, the performance of the MIMO
and the beamforming using the multi-element antenna can be
improved.
[0340] According to the fourth embodiment, the PHY processing unit
that is a calibration unit sets a subframe having no data to be
transmitted or scheduled to a cal-specific subframe that is a
subframe in which cal-RSs are arranged. Accordingly, even in the
presence of data to be transmitted or scheduled, the cal-specific
subframe can be configured. Thus, the calibration with higher
accuracy can be performed as described above.
First Modification of the Fourth Embodiment
[0341] The fourth embodiment discloses setting a subframe having no
data to be transmitted or scheduled to a calibration-specific
subframe. However, some systems may have a subframe to which a
signal and a CH to be transmitted irrespective of transmission data
are mapped.
[0342] Examples of the signal and the CH to be transmitted
irrespective of transmission data include a synchronization signal
required for initial search by a UE, a broadcast-information
transmission CH, and a control CH, etc. Examples of the signal and
the CH in the LTE include an SS, a PBCH, and a PDCCH.
[0343] In the presence of the signal and the CH, a problem with
incapability to configure a calibration-specific subframe even
according to the method of the fourth embodiment occurs. The first
modification will disclose a method for solving this problem.
[0344] The base station sets a subframe to which the signal and the
CH to be transmitted irrespective of transmission data are not
mapped, to a calibration-specific subframe. The base station sets
one or more subframes included in subframes to which the signal and
the CH to be transmitted irrespective of transmission data are not
mapped, to calibration-specific subframes. The one or more
subframes may be determined according to the necessity of the
calibration-specific subframes.
[0345] Among the signals and the CHs to be transmitted irrespective
of transmission data, this method may be applied to, for example, a
signal and a CH for which the subframe where they are scheduled is
determined in advance, and a signal and a CH to be periodically or
intermittently scheduled. These signals and CHs in the LTE include
an SS and a PBCH. The subframe to which these signals and CHs are
not mapped may be set to a calibration-specific subframe.
[0346] Another method will be disclosed. In the presence of a
subframe having no data to be transmitted or scheduled, a base
station does not transmit, on the subframe, the signal and the CH
to be transmitted irrespective of transmission data. Among the
signals and the CHs to be transmitted irrespective of transmission
data, this method may be applied to a signal and a CH for which the
subframe where they are scheduled is not determined in advance, or
a signal and a CH to be transmitted every subframe.
[0347] These signals and CHs in the LTE include a PDCCH, a PCFICH,
and a CRS. The base station may not transmit, on one or more
subframes included in subframes having no data to be transmitted or
scheduled, the signal and the CH to be transmitted irrespective of
transmission data.
[0348] The base station sets a subframe on which the signal and the
CH to be transmitted irrespective of transmission data are not
transmitted, to a calibration-specific subframe. Furthermore, this
method may be applied to a signal and a CH for which the subframe
where they are scheduled is determined in advance, and a signal and
a CH to be periodically or intermittently scheduled. This method is
applied to, for example, a case where calibration is required with
timing having no transmission data, etc. Accordingly, the
calibration timing can be optimized, and the accuracy of
calibration can be improved.
[0349] In the presence of a subframe having no data to be
transmitted or scheduled, when the subframe is set to a
calibration-specific subframe, the base station may not transmit,
on the subframe, a signal and a CH to be transmitted irrespective
of transmission data. Accordingly, when the subframe is not set to
a calibration-specific subframe, the base station can transmit, on
the subframe, a signal and a CH to be transmitted irrespective of
transmission data, and maintain a normal operation.
[0350] The above two methods may be combined. Accordingly, the base
station can set a calibration-specific subframe even in the
presence of a signal and a CH for which the subframe where they are
scheduled is determined in advance, a signal and a CH to be
periodically or intermittently scheduled, a signal and a CH for
which the subframe where they are scheduled is not determined in
advance, or a signal and a CH to be transmitted every subframe.
[0351] The methods according to the fourth embodiment may be
applied to a method for determining a radio link at which a
calibration-specific subframe is set, a method for detecting a
subframe to which a signal and a CH to be transmitted irrespective
of transmission data are not mapped, and a method for setting a
calibration-specific subframe. The transmission data may be
replaced with the signal and the CH to be transmitted irrespective
of the transmission data.
[0352] FIG. 29 is a flowchart indicating an example procedure on
calibration processes in a communication system according to the
first modification of the fourth embodiment. FIG. 29 illustrates an
example self-calibration in a base station. Since the flowchart of
FIG. 29 includes the same steps as those in the flowchart of FIG.
28 as described above, the same step numbers will be assigned to
the same Steps and the common description thereof will be
omitted.
[0353] After determining to execute calibration in Step ST4101, if
the absence of a non-transmission-data subframe is determined in
Step ST4102, the base station waits until the presence of the
non-transmission-data subframe is determined. If the presence of
the non-transmission-data subframe is determined in Step ST4102,
the processes proceed to Step ST4201.
[0354] In Step ST4201, the base station determines whether the SS
and the PBCH are not transmitted on the subframe detected in Step
ST4102. If it is determined that the SS and the PBCH are not
transmitted on the detected subframe, the processes proceed to Step
ST4103. If it is determined that the SS and the PBCH are
transmitted on the detected subframe, the processes return to Step
ST4102, and will be put on hold until the presence of the
non-transmission-data subframe is determined.
[0355] In Step ST4103, the base station sets the subframe detected
in Step ST4102 to a calibration-specific subframe. After the
detected subframe is set to a calibration-specific subframe, the
processes proceed to Step ST4202.
[0356] In Step ST4202, the base station stops transmitting a PDCCH,
a PCFICH, and a CRS on the calibration-specific subframe set in
Step ST4103. After the completion of the process in Step ST4202,
the processes proceed to Step ST4104.
[0357] In Step ST4104, the base station maps RSs for calibration
(cal-RSs) of a transmission antenna element for calibration to the
calibration-specific subframe. Here, the base station may determine
which antenna element is categorized as a transmission antenna
element for calibration or as a reception antenna element for
calibration.
[0358] More specifically, in Step ST4104, the base station
transmits the cal-RSs of the transmission antenna for calibration
on the calibration-specific subframe. After the completion of the
process in Step ST4104, the processes in Step ST4105 to Step ST4108
will be performed.
[0359] Even in the presence of a subframe to which a signal and a
CH to be transmitted irrespective of transmission data are mapped,
a subframe for calibrating a multi-element antenna can be provided
using the method disclosed in the first modification.
[0360] Accordingly, a subframe for calibration can be set more
flexibly than by the first embodiment. A calibration-specific
subframe can be set with the necessary timing such as when
temperature variations suddenly become larger, etc.
[0361] Thus, since the base station can calibrate antenna elements
with the necessary timing, the performance of the MIMO and the
beamforming using the multi-element antenna can be further
improved.
[0362] According to the method above, in the presence of a subframe
having no data to be transmitted or scheduled, the base station
does not transmit, on the subframe, a signal and a CH to be
transmitted irrespective of transmission data. However, the signal
and the CH may be muted as an alternative method. Furthermore, the
transmission power may be zero.
[0363] In the presence of a subframe having no data to be
transmitted or scheduled, the base station mutes, on the subframe,
the signal and the CH to be transmitted irrespective of
transmission data.
[0364] When the signal and the CH are not transmitted, the cal-RSs
can be mapped to symbols to which the signal and the CH are to be
mapped, thus enabling increase in the resource for cal-RSs.
[0365] In muting the signal and the CH, though the transmission
power of the signal and the CH is zero, the signal and the CH are
mapped. Thus, the resource cannot be used for the cal-RSs. Although
the resource for cal-RSs cannot be increased, only the adjustment
to the transmission power is required. Thus, the configuration and
the control for providing a calibration function can be
facilitated.
[0366] According to the method above, in the presence of a subframe
having no data to be transmitted or scheduled, the base station
either does not transmit on the subframe or mutes a signal and a CH
to be transmitted irrespective of transmission data. However, the
following process may be performed instead. Specifically, the base
station may either not transmit or mute the signal and the CH that
overlap a resource for transmitting cal-RSs.
[0367] As disclosed in the third embodiment, when cal-RSs overlap a
signal and a CH to be transmitted irrespective of transmission
data, the cal-RSs may be preferentially mapped to the resource.
Accordingly, when an amount of the resource required for the
cal-RSs is smaller, the signal and the CH to be transmitted
irrespective of transmission data can be transmitted, and decrease
in communication performance when the signal and the CH are
necessary can be prevented.
Second Modification of the Fourth Embodiment
[0368] In the fourth embodiment, a subframe having no transmission
data is set to a calibration-specific subframe. However, there are
some cases including a case where a base station has many UEs being
served thereby, a case where a huge volume of data is communicated,
and a case where the timing of having no transmission data does not
occur with the necessary timing. Here, waiting for the timing of
having no transmission data causes problems with delay in the
calibration and degradation in the performance. The second
modification will disclose a method for solving such problems.
[0369] The base station controls the transmission timing of data to
enable a calibration-specific subframe to be set with the necessary
timing of calibration. The base station, for example, sets a
calibration-specific subframe with the necessary timing of
calibration without transmitting data. The base station stores data
not to be transmitted, and transmits the stored data with the
timing capable of subsequent transmission of data.
[0370] The base station detects the necessary timing of
calibration. The timing may be detected by, for example, the
control unit 806 disclosed according to the first embodiment.
[0371] The base station may determine whether it is necessary to
stop transmitting data with the necessary timing of calibration.
The determination may be made, as a judgment criterion, depending
on the presence or absence of data to be transmitted with the
timing. The base station may determine that it is unnecessary to
stop transmitting data, for example, in the absence of data to be
transmitted with the timing.
[0372] The judging subject may be a subject that detects a subframe
having no data to be transmitted or scheduled as disclosed in the
fourth embodiment. The subject is enabled to perform the judgment
by obtaining information on the necessary timing of calibration
from the control unit 806.
[0373] When it is unnecessary to stop transmitting data, a
calibration-specific subframe is set with the timing. The method
disclosed in the fourth embodiment may be applied thereto. When
there is data to be transmitted with the necessary timing of
calibration, the base station stops transmitting data, and sets a
calibration-specific subframe.
[0374] The base station may determine the presence or absence of a
signal and a CH to be transmitted irrespective of transmission
data, with the necessary timing of calibration. The method
disclosed in the first modification of the fourth embodiment may be
applied to the determination and the setting of a
calibration-specific subframe.
[0375] The first modification of the fourth embodiment describes
that, in the presence of a signal and a CH for which the subframe
where they are scheduled is determined in advance, and a signal and
a CH to be periodically or intermittently scheduled, a subframe to
which these signals and CHs are not mapped may be set to a
calibration-specific subframe.
[0376] The necessary timing of calibration may or may not come
within the subframe to which these signals and CHs are not mapped.
If not, transmission of these signals and CHs may be stopped and a
calibration-specific subframe may be set.
[0377] The base station sets a calibration-specific subframe with
the necessary timing of calibration. Until completion of the
calibration, the base station does not transmit data. Transmission
of the data may be held.
[0378] The base station sets a calibration-specific subframe during
no transmission of data. A duration during no transmission of data
may be set per subframe or at transmission time intervals
(TTIs).
[0379] As an alternative method, data may not be transmitted during
a predetermined duration including the set calibration-specific
subframe. Setting the predetermined duration as short as possible
can reduce a delay in transmitting data. Furthermore, it is
possible to resume earlier the transmission of a signal and a CH to
be transmitted irrespective of transmission data and to minimize
losses in the synchronization and the control process in the UEs
being served.
[0380] When the predetermined duration is set longer than the
calibration-specific subframe, detection of the necessary timing of
calibration is deviated from the timing of transmitting data, and
thus occurrence of events such as a malfunction can be reduced. The
predetermined duration may be statically predetermined, or
semi-statically or dynamically determined by a base station.
[0381] The base station stores data not to be transmitted, and
transmits the stored data with the timing capable of subsequent
transmission of data. The process of storing data not to be
transmitted may be performed by, for example, a scheduler or the
MAC. Furthermore, the process may be performed by the PHY
processing unit. The scheduler, the MAC, or the PHY processing unit
may perform processes of storing, in an internal or external
storage device, data not to be transmitted and of retrieving the
stored transmission data by the timing capable of subsequent
transmission of data.
[0382] The base station maps cal-RSs of a transmission antenna for
calibration to the set calibration-specific subframe, and transmits
the cal-RSs on the subframe. The base station performs calibration
using the calibration-specific subframe. The method disclosed in
the fourth embodiment may be applied to this method.
[0383] The base station starts transmitting data with the timing
capable of transmission of data, after the predetermined duration.
Furthermore, the base station starts transmitting a signal and a CH
to be transmitted irrespective of transmission data, after the
predetermined duration. Accordingly, the base station returns to a
normal operation.
[0384] FIG. 30 is a flowchart indicating an example procedure on
calibration processes in a communication system according to the
second modification of the fourth embodiment. FIG. 30 illustrates
an example self-calibration in a base station. Since the flowchart
of FIG. 30 includes the same steps as those in the flowchart of
FIG. 28 described above, the same step numbers will be assigned to
the same Steps and the common description thereof will be
omitted.
[0385] After determining to execute calibration in Step ST4101, the
base station determines whether the calibration timing has come in
Step ST4301. If the base station determines that the calibration
timing has come, the processes proceed to Step ST4302. If the base
station determines that the calibration timing has not come, the
processes will be put on hold until it is determined that the
calibration timing has come.
[0386] In Step ST4302, the base station determines the presence or
absence of transmission data. If the base station determines the
presence of transmission data, the processes proceed to Step
ST4303. If the base station determines the absence of transmission
data, the processes proceed to Step ST4103.
[0387] In Step ST4303, the base station stops transmitting data
with the calibration timing, and stores the transmission data.
After completion of the process in Step ST4303, the processes
proceed to Step ST4103.
[0388] The base station that stores the transmission data in Step
ST4303 detects a non-transmission-data subframe with the
calibration timing, and sets the detected subframe to a
calibration-specific subframe in Step ST4103. After completion of
the process in Step ST4103, the processes proceed to Step
ST4104.
[0389] In Step ST4104, the base station maps cal-RSs of a
transmission antenna for calibration to the set
calibration-specific subframe, transmits the cal-RSs on the
subframe, and performs calibration. Since this method is the same
as that in FIG. 28, the description thereof will be omitted.
[0390] After the processes in Steps ST4105 and ST4106, if it is
determined in Steps ST4107 that calibration on all the antenna
elements is completed, the processes proceed to Step ST4304. If it
is determined that the calibration on all the antenna elements has
not been completed, the processes return to Step ST4302 to perform
the aforementioned processes on an antenna element that has not
been calibrated.
[0391] In Step ST4304, the base station resumes transmission of
data including the stored data, with the timing capable of
transmission of data. Accordingly, the base station returns to a
normal operation. The entire procedure ends after the process in
Step ST4304.
[0392] Using the method disclosed in the second modification
enables setting of a calibration-specific subframe with the
necessary timing of calibration, and execution of calibration on
the subframe.
[0393] Accordingly, even when a base station has many UEs being
served thereby or even when a huge volume of data is being
communicated, it is possible to prevent degradation in the
performance caused by delay in the calibration. Thus, the
performance of the MIMO and the beamforming using the multi-element
antenna can be further improved.
[0394] The method disclosed in the first modification of the fourth
embodiment may be applied to a case where there are a signal and a
CH to be transmitted irrespective of transmission data with the
necessary timing of calibration. Even in the presence of the signal
and the CH to be transmitted irrespective of transmission data, a
calibration-specific subframe can be set with the necessary timing
of calibration, and calibration can be performed on the
subframe.
[0395] Although what is disclosed in the aforementioned method is
that the base station stores data not to be transmitted and
transmits the stored data with the timing capable of subsequent
transmission of data, the method may be the others. As an
alternative method, the data not to be transmitted may be prevented
from being stored and transmitted. Furthermore, the data not to be
transmitted may be discarded without being stored.
[0396] For example, less important data may be prevented from being
stored and transmitted. Alternatively, transmission data with a
smaller acceptable amount of delay may be prevented from being
stored and transmitted. Examples of the data with a smaller
acceptable amount of delay include audio data and real-time game
data, etc. Furthermore, retransmission data may be prevented from
being stored and transmitted. This is because the retransmission is
performed and a problem is unlikely to occur even if the
retransmission data is skipped once or so. Accordingly, the
required storage capacity can be reduced.
[0397] Furthermore, the method according to the second modification
of the fourth embodiment may be performed on the transmission data
that can be held. Furthermore, the method according to the fourth
embodiment may be performed on the transmission data that cannot be
held.
[0398] Examples of the transmission data that can be held include
data with a larger acceptable amount of delay. Alternatively, data
with a lower QoS value or a larger QoS class identifier (QCI) value
may be used. Examples of the data include buffered streaming video
data and File Transfer Protocol (abbreviated as FTP) data, etc.
[0399] Examples of the transmission data that cannot be held
include data with a smaller acceptable amount of delay.
Alternatively, data with a higher QoS value or a smaller QCI value
may be used. Such examples include audio data and real-time game
data, etc.
[0400] Thus, the timing to execute calibration can be changed
according to the transmission data. Accordingly, the calibration
during communication can be more flexibly executed.
[0401] Although it is described that the method according to the
second modification of the fourth embodiment is performed on the
transmission data that can be held and the method according to the
fourth embodiment is performed on the transmission data that cannot
be held, the methods are not limited to such. When the execution of
calibration takes priority over transmission of data, the method
according to the second modification of the fourth embodiment may
be performed. Furthermore, when transmission of data takes priority
over the execution of calibration, the method according to the
fourth embodiment may be performed. Similarly, the timing to
execute calibration can be changed according to the transmission
data. Accordingly, the calibration during communication can be more
flexibly executed.
[0402] According to the second modification, the PHY processing
unit that is a calibration unit controls the timing to transmit
data to enable a subframe in which the cal-RSs are arranged to be
set. Accordingly, the cal-specific subframe can be set with the
necessary timing of calibration. Consequently, it is possible to
prevent delay in the calibration and degradation in the performance
caused by the delay in the calibration.
Third Modification of the Fourth Embodiment
[0403] The third modification will disclose another method for
solving the problems described in the second modification of the
fourth embodiment. The base station provides a subframe on which
neither data nor a signal or a CH that are irrelevant to
transmission data are transmitted. The base station provides a
subframe on which nothing is transmitted. In the following
description, the subframe on which nothing is transmitted may be
referred to as a "complete blank subframe (CBS)". The base station
maps only RSs for calibration to a CBS.
[0404] The following (1) to (6) will be disclosed as example
parameters for configuring the CBS.
[0405] (1) Offset; the offset represents the start timing. For
example, at least one of a start radio frame and a start subframe
may be set.
[0406] (1) Duration; the duration is a duration during which the
CBS occurs. For example, the number of one or more subframes may be
set.
[0407] (3) Period; the period is a period with which the CBS
occurs. This is useful when the CBS is periodically caused to
occur. For example, at least one of the number of radio frames and
the number of subframes may be set.
[0408] (4) End timing; for example, at least one of an end radio
frame and an end subframe may be set. As an alternative method, a
duration from the start to the end may be set. At least one of the
number of radio frames and the number of subframes may be set.
Furthermore, when the CBS is set to a long duration, for example, a
year, a date, and a time may be set. Furthermore, the end timing
may not be set. Here, once the CBS is set, the CBS is configured
until a switch of a cell is turned OFF. This option is effective,
for example, when the calibration continues to be executed until
the switch of the cell is turned OFF.
[0409] (5) A radio link configuring the CBS; for example, at least
one of the DL and the UL may be set.
[0410] (6) A combination of (1) to (5) above
[0411] Setting these parameters can identify configurations of the
CBS. These configurations may be changed. In the following
description, the parameter for configuring the CBS may be referred
to as "CBS setting information".
[0412] The following (1) to (3) will be disclosed as example
subjects that configure the CBS.
[0413] (1) The RRC
[0414] (2) The MAC
[0415] (3) The PHY processing unit
[0416] The base station first configures the CBS. The CBS may be
configured by setting the aforementioned parameters. Accordingly,
the subframe on which the CBS is configured is identified. Upon
determining to execute calibration, the base station sets the CBS
to a calibration-specific subframe. The base station may set the
CBS with the necessary timing of calibration as an alternative
method. The start timing, the end timing, and the period and the
duration required for the calibration may be used to set the CBS.
Furthermore, a radio link that performs calibration may be used to
set the CBS. The base station sets the CBS to a
calibration-specific subframe.
[0417] The base station maps cal-RSs of a transmission antenna for
calibration to the set calibration-specific subframe, and transmits
the cal-RSs on the subframe. Since the other signals and CHs of the
cal-RSs are not mapped to the CBS, the calibration-specific
subframe can be configured. Many resources can be used for
calibration.
[0418] When the CBS has transmission data, the base station stops
transmitting data. The transmission data may be held. The method
disclosed in the second modification of the fourth embodiment may
be applied to this method. Furthermore, even with occurrence of a
signal and a CH to be transmitted irrespective of the transmission
data, transmission of these signal and CH may be stopped.
[0419] FIG. 31 is a flowchart indicating an example procedure on
calibration processes in a communication system according to the
third modification of the fourth embodiment. FIG. 31 illustrates an
example self-calibration in a base station. Furthermore, FIG. 31
illustrates setting of the CBS with the necessary timing of
calibration. Since the flowchart of FIG. 31 includes the same steps
as those in the flowcharts of FIGS. 28 and 30 as described above,
the same step numbers will be assigned to the same Steps and the
common description thereof will be omitted.
[0420] The base station that determines to execute calibration in
Step ST4101 sets a CBS in Step ST4401. Here, the base station sets
the CBS with the necessary timing of calibration and according to a
radio link that performs calibration. After completion of the
process in Step ST4401, the processes proceed to Step ST4402.
[0421] In Step ST4402, the base station determines whether the
timing of the CBS has come. If the base station determines that the
timing of the CBS has come, the processes proceed to Step ST4302.
If the base station determines that the timing of the CBS has not
come, the process in Step ST4402 will be repeated until the next
timing of the CBS.
[0422] In Step ST4302, the base station determines the presence or
absence of transmission data. If the base station determines the
presence of transmission data, the processes proceed to Step
ST4303. If the base station determines the absence of transmission
data, the processes proceed to Step ST4403.
[0423] In Step ST4303, the base station stops transmitting data
with the calibration timing, and stores the transmission data.
After completion of the process in Step ST4303, the processes
proceed to Step ST4403.
[0424] The base station that stores the transmission data in Step
ST4303 maps cal-RSs to the CBS with the necessary timing of
calibration, and transmits the cal-RSs on the CBS in Step ST4403.
The base station may set the CBS with the necessary timing of
calibration to a calibration-specific subframe. The base station
maps cal-RSs of a transmission antenna for calibration to the set
calibration-specific subframe, and transmits the cal-RSs on the
subframe. After completion of the process in Step ST4403, the
processes proceed to Step ST4105.
[0425] After the processes in Steps ST4105 and ST4106, if it is
determined in Step ST4107 that calibration on all the antenna
elements is completed, the processes proceed to Step ST4304. If it
is determined that the calibration on the entire antenna has not
been completed, the processes return to Step ST4302 to perform the
aforementioned processes on an antenna element that has not been
calibrated.
[0426] In Step ST4304, the base station resumes transmission of
data including the stored data, with the timing capable of
transmission of data on a subframe that is not a CBS. When the CBS
end timing is set, configuring the CBS ends according to the
setting. The entire procedure ends after the process in Step
ST4304.
[0427] Configuring the CBS in advance using the method disclosed in
the third modification can facilitate setting of a
calibration-specific subframe. Furthermore, setting the CBS with
the necessary timing of calibration enables execution of
calibration with the necessary timing.
[0428] Accordingly, even when the base station has many UEs being
served thereby or even when a huge volume of data is communicated,
it is possible to prevent degradation in the performance caused by
delay in the calibration. Thus, the performance of the MIMO and the
beamforming using the multi-element antenna can be further
improved.
[0429] The method according to the first modification of the fourth
embodiment may be applied to a case where there are a signal and a
CH to be transmitted irrespective of transmission data with the
necessary timing of calibration. Even in the presence of the signal
and the CH to be transmitted irrespective of transmission data, a
calibration-specific subframe can be set with the necessary timing
of calibration, and calibration can be performed on the
subframe.
[0430] Although the third modification discloses configuring the
CBS and using the CBS for calibration, the CBS may be used for
other applications without being limited to the calibration. For
example, a subframe that transmits nothing may be provided to
suppress interference between cells.
[0431] Although the fourth embodiment to the third modification
thereof describe the calibration to be performed by the base
station, the methods disclosed in the fourth embodiment to the
third modification thereof are applicable to the calibration to be
performed by UEs. With application of the methods disclosed in the
fourth embodiment to the third modification thereof to the
calibration to be performed by UEs, the UEs can perform the
calibration during their operations.
[0432] The methods disclosed in the fourth embodiment to the third
modification thereof are applicable not only to the OFDM as an
access scheme but also to the other access schemes. With
application of the methods disclosed in the fourth embodiment to
the third modification thereof to the other access schemes, a
system using the other access schemes can perform the calibration
during operation.
Fifth Embodiment
[0433] The third and fourth embodiments disclose providing a
subframe for calibration or a calibration-specific subframe.
Furthermore, the third and fourth embodiments disclose that the
base station does not transmit the other CHs or RSs on the
subframe.
[0434] Normally, the base station transmits an RS for demodulation
and a control CH on every DL subframe. The base station transmits,
for example, a CRS and a PDCCH in the LTE. The RS for demodulation
is a signal for synchronization and demodulation by a UE. The
control CH includes information required for the UE to receive
data.
[0435] In the presence of a subframe without an RS for demodulation
and a control CH, the UE cannot normally receive data on the
subframe. Thus, when the UE does not recognize the timing of a
subframe for calibration, the UE recognizes the presence of an RS
for demodulation and a control CH on the subframe, and receives the
subframe.
[0436] Here, the UE has a problem with a possible malfunction
because it wrongly receives the subframe based on the assumption of
the presence of transmission data, despite no actual transmission
of the data on the subframe. The fifth embodiment will disclose a
method for solving such a problem.
[0437] The base station notifies the UE of information on signals
for calibration. The base station may notify the UE of information
on a calibration-specific subframe. The UE does not need to receive
data with the transmission timing of the calibration-specific
subframe, using the obtained information on the
calibration-specific subframe.
[0438] Examples of the information on the calibration-specific
subframe include information on the timing to transmit the
calibration-specific subframe. The example information is an
indication indicating a subframe on which the calibration-specific
subframe is transmitted.
[0439] The indication may be, for example, an indication of a
subframe number or the next subframe. The indication of subframes
after the n-th subframe may be "n". The indication may indicate
whether the subframes are consecutive. Furthermore, the indication
may indicate the number of consecutive subframes. The indication
may be information obtained by combining these.
[0440] Such information is more effective when the immediacy of
notifying the UE is required. Such information is effective, for
example, when a subframe having no transmission data is detected
and the detected subframe is set to a calibration-specific
subframe, as a method for immediately notifying the UE.
[0441] Examples of the other information on the
calibration-specific subframe include the CBS setting information
disclosed in the third modification of the fourth embodiment. These
parameters are more effective when the immediacy of notifying the
UE is not required. These parameters are more effective, for
example, when the necessary timing of calibration can be recognized
in advance or when the CBS is configured.
[0442] Examples of the other information on the
calibration-specific subframe include time stamps. The system frame
number (SFN) has the upper limit value. The time stamps are
effective when calibration-specific subframes are set at intervals
that exceed the upper limit value. The time stamps may be managed
by operation administration and maintenance (OAM) or obtained using
the Global Positioning System (GPS).
[0443] A method for notifying information on a calibration-specific
subframe from a base station to a UE will be disclosed. The base
station notifies the UE of the information from a cell to be
calibrated. The following (1) to (3) will be disclosed as specific
examples of the notification method.
[0444] (1) The information is notified by the RRC signaling. The
information may be broadcast to the UEs being served, or notified
individually to the UEs being served. When the information is
broadcast using broadcast information, many UEs can be
simultaneously notified. When the information is notified
individually to the UEs, it can be reliably notified via a
retransmission function. This method is highly compatible with a
case where, for example, each of the subject that detects a
subframe having no data to be transmitted or scheduled and the
subject that sets a subframe to a calibration-specific subframe as
disclosed in the fourth embodiment, and the subject that configures
the CBS as disclosed in the third modification of the fourth
embodiment is the RRC. Furthermore, this option is more effective
when information on the calibration-specific subframe does not
require the immediacy of notifying the UEs.
[0445] (2) The information is notified by the MAC signaling. The
information is notified individually to the UEs being served. This
method is highly compatible with a case where, for example, each of
the subject that detects a subframe having no data to be
transmitted or scheduled and the subject that sets a subframe to a
calibration-specific subframe as disclosed in the fourth
embodiment, and the subject that configures the CBS as disclosed in
the third modification of the fourth embodiment is the MAC or the
scheduler. Furthermore, this option is more effective when
information on the timing to transmit a calibration-specific
subframe requires the immediacy of notifying the UEs.
[0446] (3) The information is notified by a physical control
channel. The information is notified individually to the UEs being
served. This method is highly compatible with a case where, for
example, each of the subject that detects a subframe having no data
to be transmitted or scheduled and the subject that sets a subframe
to a calibration-specific subframe as disclosed in the fourth
embodiment, and the subject that configures the CBS as disclosed in
the third modification of the fourth embodiment is the PHY
processing unit. Furthermore, this option is more effective when
information on the timing to transmit a calibration-specific
subframe requires the immediacy of notifying the UEs.
[0447] FIG. 32 illustrates an example sequence on calibration in a
communication system according to the fifth embodiment. FIG. 32
illustrates an example method for detecting a subframe having no
data to be transmitted or scheduled and setting the subframe to a
calibration-specific subframe as disclosed in the fourth embodiment
and the first modification of the fourth embodiment.
[0448] In Step ST5101, the base station and a UE perform normal
communication. The base station that executes calibration detects a
non-transmission-data subframe that is a subframe having no
transmission data in Step ST5102.
[0449] In Step ST5103, the base station sets the detected subframe
to a calibration-specific subframe.
[0450] In Step ST5104, the base station notifies the UE of
information on the set calibration-specific subframe (hereinafter
may be referred to as "calibration-specific subframe
information").
[0451] In Step ST5105, the base station maps cal-RSs of a
transmission antenna for calibration to the calibration-specific
subframe during the subframe, and transmits the cal-RSs on the
subframe.
[0452] In Step ST5106, the base station performs a normal operation
after transmitting the cal-RSs on the calibration-specific
subframe.
[0453] The UE obtains the calibration-specific subframe information
in Step ST5104. In Step ST5107, the UE stops reception using the
obtained calibration-specific subframe information, during the
calibration-specific subframe.
[0454] In Step ST5108, the UE resumes the reception after the
calibration-specific subframe.
[0455] In Step ST5109, the base station and the UE perform normal
communication after the calibration-specific subframe.
[0456] The sequence illustrated in FIG. 32 is more effective when
the immediacy of notifying the UE is required. For example, the
base station detects the non-transmission-data subframe with a
scheduler in Step ST5102 and sets the detected subframe to a
calibration-specific subframe in Step ST5103.
[0457] The scheduler notifies the PHY processing unit of
information on the set calibration-specific subframe. The PHY
processing unit includes the calibration-specific subframe
information in the physical control channel as control information,
and notifies the UE of the information in Step ST5104. Since the
scheduler recognizes the amount of data to be transmitted on the
next subframe, the PHY processing unit can include information on
the calibration-specific subframe detected and set by the scheduler
in the physical control channel of a subframe preceding the
recognized subframe as control information, and notify the UE of
the information.
[0458] Accordingly, the UE can prevent occurrence of a malfunction
caused by receiving a calibration-specific subframe despite no
transmission of an RS for demodulation and a control CH on the
subframe, and wrongly receiving the subframe based on the
assumption of the presence of transmission data despite no actual
transmission of the data. Thus, the base station can calibrate the
multi-element antenna with the necessary timing, without causing
the UE to malfunction.
[0459] FIG. 33 illustrates another example sequence on calibration
in the communication system according to the fifth embodiment. FIG.
33 illustrates an example method for configuring the CBS that is
disclosed in the third modification of the fourth embodiment.
[0460] In Step ST5201, the base station and the UE perform normal
communication. The base station that executes calibration sets the
CBS with the calibration timing in Step ST5202.
[0461] In Step ST5203, the base station notifies the UE of
information on the set CBS (hereinafter may be referred to as "CBS
information").
[0462] The UE that has received the CBS information in Step ST5203
notifies the base station of a CBS-information notice response in
Step ST5204. The CBS-information notice response in Step ST5204 may
be omitted.
[0463] The base station that has received the CBS-information
notice response in Step ST5204 transmits cal-RSs on the CBS in Step
ST5205. Specifically, the base station maps cal-RSs of a
transmission antenna for calibration to the CBS, and transmits the
cal-RSs on the CBS.
[0464] In Step ST5206, the base station obeys the CBS setting and
performs a normal operation after the CBS.
[0465] The UE that has notified the base station of the
CBS-information notice response in Step ST5204 stops reception on
the CBS in Step ST5207. Specifically, the UE stops reception during
the CBS, using the obtained CBS information.
[0466] In Step ST5208, the UE resumes the reception after the CBS.
In Step ST5209, the base station and the UE perform normal
communication after the CBS.
[0467] The sequence illustrated in FIG. 33 is more effective when
the immediacy of notifying the UE is not required. In Step ST5202,
for example, the base station causes the RRC to set the CBS. In
Step ST5203, the RRC notifies the UE of the CBS information
included in the RRC signaling.
[0468] The UE that has received the RRC signaling may perform
reception-stop control on the CBS through the RRC, using the
obtained CBS information. The RRC in the UE may notify the MAC or
the PHY processing unit of the timing of the CBS to stop receiving
data on the subframe. Accordingly, the control by the RRC becomes
possible.
[0469] For example, when information is sent individually to the
UEs being served, each of the UEs may notify the base station of
the CBS-information notice response, whereas when information is
broadcast to the UEs being served, each of the UEs may not notify
the base station of the CBS-information notice response.
Accordingly, the UEs can stop reception during the CBS.
[0470] Accordingly, the UE can prevent occurrence of a malfunction
caused by receiving the CBS despite no transmission of an RS for
demodulation and a control CH on the subframe, and wrongly
receiving the subframe based on the assumption of the presence of
transmission data despite no actual transmission of the data. Thus,
the base station can calibrate the multi-element antenna with the
necessary timing, without causing the UE to malfunction.
[0471] The UE may communicate with another base station (cell)
during a calibration-specific subframe. Alternatively, the UE may
measure the other base station (cell). The operations of the UE
during the calibration-specific subframe may be predetermined as a
system. Alternatively, the base station may determine the
operations of the UE during the calibration-specific subframe and
notify the UE of the operations. This notice may be notified
together with information on the calibration-specific subframe.
Accordingly, the UE can use the subframe for other
applications.
[0472] Furthermore, the base station may notify adjacent base
stations of information on a calibration-specific subframe. This
notice may be notified by the X2 signaling. Accordingly, the
adjacent base stations can recognize the existence of the
calibration-specific subframe, and resources on the time axis or
the frequency axis. Furthermore, the adjacent base stations can
recognize the absence of transmission data and the absence of a CH
and an RS to be transmitted irrespective of the transmission data,
on the calibration-specific subframe. Thus, for example, data for
the UEs being served can be scheduled using the subframe, without
any concern about interference with adjacent base stations.
[0473] Furthermore, the base station may notify a core network side
node of information on the calibration-specific subframe. During
the calibration in the base station, the core network side node may
notify the information on the calibration-specific subframe that is
obtained from the base station, to a base station that requires
some special operations. These notices may be notified by the S1
signaling. Accordingly, the same advantages as those when
information on the calibration-specific subframe is notified to the
adjacent base stations can be produced.
[0474] The fifth embodiment may be applied not only to the
self-calibration but also to the OTA calibration. In the OTA, for
example, the base station transmits signals for calibration
(cal-RSs), and the UE receives the signals and derives a
calibration value. Thus, transmitting information on the signals
for calibration from the base station enables the UE to receive the
signals and derive the calibration value from the received
signals.
[0475] For example, in Step ST5107 of FIG. 32, the UE may receive
the signals for calibration during the calibration-specific
subframe, without stopping reception. The UE derives the
calibration value using the received signals for calibration.
[0476] Furthermore, similarly in Step ST5207 of FIG. 33, the UE may
receive the signals for calibration on the CBS, without stopping
reception on the CBS. The UE derives the calibration value using
the received signals for calibration on the CBS. The UE may notify
the base station of the derived calibration value. Accordingly, the
base station can perform the OTA calibration of a transmission
system antenna.
[0477] When a reception system is calibrated, the base station may
instruct the UE to transmit signals for calibration. The base
station may include the instruction information in information on
the signals for calibration or information on a
calibration-specific subframe and then may notify the UE of the
information. Alternatively, the information may be notified by
another signaling.
[0478] The UE that has received the instruction information, for
example, transmits the signals for calibration on the subframe
derived from the obtained information on the calibration-specific
subframe. Upon receipt of the signals for calibration transmitted
from the UE on the calibration-specific subframe, the base station
derives the calibration value.
[0479] For example, in Step ST5104 of FIG. 32, the base station
notifies the UE of information on the calibration-specific subframe
which includes information instructing transmission of the signals
for calibration on the subframe. The UE that has received the
information transmits the signals for calibration on the
calibration-specific subframe in Step ST5107.
[0480] The base station may receive the signals for calibration on
the calibration-specific subframe in Step ST5105. The base station
derives the calibration value using the received signals for
calibration.
[0481] Similarly in Step ST5203 of FIG. 33, the base station
notifies the UE of information on the CBS which includes
information instructing transmission of the signals for calibration
on the subframe. The UE that has received the information transmits
the signals for calibration on the calibration-specific subframe in
Step ST5207.
[0482] The base station may receive the signals for calibration on
the calibration-specific subframe in Step ST5205. The base station
derives the calibration value using the received signals for
calibration. Accordingly, the base station can perform the OTA
calibration of a transmission system antenna.
[0483] As described above, application of the fifth embodiment to
the OTA calibration enables ease of coordination for calibration
between the base station and the UE, for example, ease of matching
the calibration timing and the recognition of resources, etc. Thus,
the OTA calibration can be easily performed during the
operations.
[0484] As described above, a communication terminal is configured
not to receive a subframe in which cal-RSs are arranged, according
to the fifth embodiment. Accordingly, a malfunction of the
communication terminal can be prevented.
First Modification of the Fifth Embodiment
[0485] The first modification will disclose another method for
solving the problems in the fifth embodiment. The base station
configures the UEs being served thereby not to receive a
calibration-specific subframe. The DRX is used in this setting. The
base station configures the DRX so that the UEs being served
thereby do not receive data on a calibration-specific subframe. The
base station configures the DRX so that the UEs being served
thereby are in inactivity on the calibration-specific subframe.
[0486] Alternatively, the base station configures the DRX so that
the UEs being served thereby are not active on the
calibration-specific subframe. Furthermore, the base station may
not transmit data to the UEs being served thereby on the
calibration-specific subframe to enable configuration of the
calibration-specific subframe during inactivity of the configured
DRX.
[0487] The base station notifies the UEs being served thereby of
the DRX configuration. The notification method defined in the
conventional standards can be applied to this notification of the
DRX configuration.
[0488] The UEs being served do not receive data from the own cells
during inactivity of the configured DRX. Thus, the UEs do not
receive data while the base station is executing calibration.
[0489] Accordingly, the UE can prevent occurrence of a malfunction
caused by receiving the calibration-specific subframe despite no
transmission of an RS for demodulation and a control CH on the
subframe, and wrongly receiving the subframe based on the
assumption of the presence of transmission data despite no actual
transmission of the data. Thus, the base station can calibrate the
multi-element antenna with the necessary timing, without causing
the UE to malfunction.
[0490] Furthermore, the UE does not need any special processes on
the calibration, with the use of the existing function.
Furthermore, using the existing notification method, there is no
need to notify the UE of particular signaling for calibration.
[0491] Another setting method will be disclosed. A measurement gap
is used as the setting method. The base station configures a
measurement gap so that the UEs being served thereby do not receive
data on a calibration-specific subframe. The base station
configures a measurement gap to include a calibration-specific
subframe, for the UEs being served thereby.
[0492] The base station notifies the UEs being served thereby of
the measurement gap configuration. The notification method defined
in the conventional standards can be applied to this notification
of the measurement gap configuration. When the DL is used for
calibration, a measurement gap for the DL may be configured. When
the UL is used for calibration, a measurement gap for the UL may be
configured.
[0493] The UEs being served do not receive data from the own cells
during the configured measurement gap. Thus, the UEs do not receive
data while the base station is executing calibration. The UEs can
produce the same advantages as described above.
[0494] Although the DRX is configured only in the DL, the
measurement gap can be set also in the UL. Thus, even when
calibration is performed in the UL, using the measurement gap is
effective.
[0495] The methods disclosed in the fifth embodiment and the first
modification thereof are applicable not only to the OFDM as an
access scheme but also to the other access schemes.
Sixth Embodiment
[0496] The third embodiment discloses arranging RSs for
calibration, and other CHs or other RSs in the same subframe. The
sixth embodiment will disclose the specific examples.
[0497] A base station uses a physical downlink shared channel
region for transmitting cal-RSs. The base station maps the cal-RSs
to the physical downlink shared channel region. A physical downlink
shared channel is not mapped to the symbols to which the cal-RSs
are mapped. The rate matching and coding may be performed so that
the physical downlink shared channel is not mapped to the symbols
to which the cal-RSs are mapped.
[0498] Alternatively, after mapping a physical downlink shared
channel to a physical downlink shared channel region, the base
station may replace the symbols to which cal-RSs are mapped with
the cal-RSs. The base station does not transmit the physical
downlink shared channel on the symbols to which the cal-RSs are
mapped.
[0499] Accordingly, the RSs for calibration can be orthogonal to
the other CHs and the other RSs in a frequency domain and a time
domain. Thus, the RSs for calibration, the other CHs, and the other
RSs can be arranged in the same subframe, and calibration can be
performed during communication.
[0500] FIG. 34 illustrates an example configuration of a subframe
when cal-RSs are mapped to a physical downlink shared channel
region. The horizontal axis represents a time t, and the vertical
axis represents a frequency f in FIG. 34. FIG. 34 illustrates an
example in the LTE. In FIG. 34, a reference "6001" denotes a
subframe, and a reference "6002" denote symbol timing. In one
subframe, the first 3 symbols form a PDCCH region 6003, and the
subsequent 11 symbols form a PDSCH region 6004.
[0501] CRSs 6005 are mapped over the PDCCH region 6003 and the
PDSCH region 6004. A PDCCH and a PCFICH, etc. are mapped to the
PDCCH region 6003. PDSCHs are mapped to the PDSCH region 6004.
[0502] FIG. 34 illustrates an example of mapping cal-RSs to the
PDSCH region 6004. Cal-RSs 6006 of a first antenna element #1,
cal-RSs 6007 of a second antenna element #2, cal-RSs 6008 of a
third antenna element #3, and cal-RSs 6009 of a fourth antenna
element #4 are mapped to the PDSCH region 6004. PDSCHs 6010 are
mapped to the other symbols.
[0503] Such mapping of the cal-RSs 6006 to 6009 to the PDSCH region
6004 enables mapping of the cal-RSs 6006 to 6009, the PDSCHs 6010,
the PDCCH, and the CRSs 6005 within the same subframe. The base
station can transmit the cal-RSs 6006 to 6009, the PDSCHs, the
PDCCH, and the CRSs 6005 on the same subframe. Thus, calibration is
possible during the data communication with the UE.
[0504] Another method will be disclosed. The base station may not
map a physical downlink shared channel to a slot or a subframe to
which cal-RSs are mapped. The methods disclosed in the fourth
embodiment and the second modification of the fourth embodiment may
be applied to handling of the transmission data on the
subframe.
[0505] The base station may map cal-RSs to a subframe except for
subframes to which physical downlink shared channels where a paging
channel, a broadcast channel, or a random access response is mapped
are mapped. The base station may not map a physical downlink shared
channel over the entire frequency domain with the symbol timing to
map the cal-RSs. The base station may map the cal-RSs with the
symbol timing different from that of a synchronization signal, a
physical broadcast channel, or the other RSs.
[0506] FIG. 35 illustrates another example configuration of a
subframe when cal-RSs are mapped to a physical downlink shared
channel region. The horizontal axis represents a time t, and the
vertical axis represents a frequency f in FIG. 35. FIG. 35
illustrates an example in the LTE. In FIG. 35, a reference "6101"
denotes a subframe, and a reference "6102" denotes symbol timing.
In one subframe, the first 3 symbols form a PDCCH region 6103, and
the subsequent 11 symbols form a PDSCH region 6104.
[0507] CRSs 6105 are mapped over the PDCCH region 6103 and the
PDSCH region 6104. A PDCCH and a PCFICH, etc. are mapped to the
PDCCH region 6103.
[0508] FIG. 35 illustrates an example of mapping cal-RSs to the
PDSCH region 6104 without mapping a PDSCH. A cal-RS 6106 of the
first antenna element #1, a cal-RS 6107 of the second antenna
element #2, a cal-RS 6108 of the third antenna element #3, and a
cal-RS 6109 of the fourth antenna element #4 are mapped to the
PDSCH region 6104 without mapping any PDSCH. FIG. 35 illustrates an
example in which the base station maps the cal-RSs over the entire
frequency domain with the symbol timing to map the cal-RSs 6106 to
6109.
[0509] Such mapping of the cal-RSs 6106 to 6109 to the PDSCH region
6104 enables mapping of the cal-RSs 6106 to 6109, the PDCCH, and
the CRSs 6105 within the same subframe. The base station can
transmit the cal-RSs 6106 to 6109, the PDCCH, and the CRSs 6105 on
the same subframe. Since the control channel and the signals used
in demodulation and measurement are transmitted, the base station
can execute calibration during communication with the UE.
[0510] Furthermore, the base station does not schedule the UE using
the PDCCH. Accordingly, the UE does not need to receive the PDSCH,
and occurrence of a malfunction in the UE can be reduced.
[0511] Another example will be disclosed. Instead of the physical
downlink shared channel, a multimedia broadcast multicast service
single frequency network (MBSFN) region is used. Furthermore,
although a PMCH and a PDSCH are mapped to the MBSFN region, both
the PMCH and the PDSCH may replace the PDSCHs described above.
[0512] Accordingly, the RSs for calibration can be orthogonal to
the other CHs and the other RSs in a frequency domain and a time
domain. Thus, the RSs for calibration, the other CHs, and the other
RSs can be arranged in the same subframe, and calibration can be
performed during communication.
[0513] FIG. 36 illustrates an example configuration of a subframe
when cal-RSs are mapped to an MBSFN region. The horizontal axis
represents a time t, and the vertical axis represents a frequency
fin FIG. 36. FIG. 36 illustrates an example in the LTE. In FIG. 36,
a reference "6201" denotes the MBSFN subframe, and a reference
"6202" denotes symbol timing. In one subframe, the first 2 symbols
form a non-MBSFN region 6203, and the subsequent 12 symbols form an
MBSFN region 6204.
[0514] The CRSs 6105 are mapped to the non-MBSFN region 6203. A
PDCCH and a PCFICH, etc. are mapped to the non-MBSFN region 6203. A
PMCH and a PDSCH can be mapped to the MBSFN region 6204.
[0515] FIG. 36 illustrates an example of mapping cal-RSs to the
MBSFN region 6204 without mapping any PMCH. The cal-RS 6106 of the
first antenna element #1, the cal-RS 6107 of the second antenna
element #2, the cal-RS 6108 of the third antenna element #3, and
the cal-RS 6109 of the fourth antenna element #4 are mapped to the
MBSFN region 6204 without mapping any PMCH and any PDSCH. FIG. 36
illustrates an example in which the base station maps the cal-RSs
over the entire frequency domain with the symbol timing to map the
cal-RSs 6106 to 6109.
[0516] Such mapping of the cal-RSs 6106 to 6109 to the MBSFN region
6204 enables mapping of the cal-RSs 6106 to 6109, the PDCCH, and
the CRSs 6105 within the same subframe. The base station can
transmit the cal-RSs 6106 to 6109, the PDCCH, and the CRSs 6105 on
the same subframe. Since the control channel and the signals used
in demodulation and measurement are transmitted, the base station
can execute calibration during communication with the UE.
[0517] Furthermore, the base station does not schedule the UE using
the PDCCH. Accordingly, the UE does not need to receive the PDSCH,
and occurrence of a malfunction in the UE can be reduced.
[0518] When the PMCH is not transmitted in the MBSFN region 6204,
the base station does not transmit an RS for MBSFN. Thus, when
neither the PMCH nor the PDSCH is mapped to the MBSFN region 6204,
nothing is mapped to the MBSFN region 6204. Accordingly, resources
can be allocated to calibration more than those when the PDSCH
region is used.
[0519] Furthermore, the MBSFN subframe is not configured in a
subframe to which a synchronization signal, a physical broadcast
channel, or a paging channel is mapped. Thus, configuring an MBSFN
subframe and mapping cal-RSs to the MBSFN subframe enables the base
station to eliminate a process of mapping cal-RSs to a symbol or a
subframe except for symbols to which the synchronization signal and
the physical broadcast channel are mapped and subframes to which a
paging channel is mapped, if such a process exists. Accordingly,
the processes performed by the base station can be simplified.
[0520] Another example will be disclosed. An almost blank subframe
(ABS) is used. The ABS is a subframe to which the other CHs and RSs
than the CRSs are not mapped. Mapping the RSs for calibration to a
resource to which the CRSs of the ABS are not mapped enables
orthogonalization of the RSs for calibration with the other RSs
(CRSs) in a frequency domain and a time domain. Thus, the RSs for
calibration and the other RSs can be arranged in the same subframe,
and calibration can be performed during communication.
[0521] FIG. 37 illustrates an example configuration of a subframe
when cal-RSs are mapped to an ABS region. The horizontal axis
represents a time t, and the vertical axis represents a frequency
fin FIG. 37. FIG. 37 illustrates an example in the LTE. In FIG. 37,
a reference "6301" denotes the ABS region, and a reference "6302"
denotes symbol timing.
[0522] The CRSs 6105 are mapped to the ABS region 6301. The cal-RS
6106 of the first antenna element #1, the cal-RS 6107 of the second
antenna element #2, the cal-RS 6108 of the third antenna element
#3, and the cal-RS 6109 of the fourth antenna element #4 are mapped
to a resource where the CRSs 6105 are not mapped in the ABS region
6301. FIG. 37 illustrates an example in which the base station maps
the cal-RSs over the entire frequency domain with the symbol timing
to map the cal-RSs 6106 to 6109.
[0523] Such mapping of the cal-RSs 6106 to 6109 to the ABS region
6301 enables mapping of the cal-RSs 6106 to 6109 and the CRSs 6105
within the same subframe. The base station can transmit the cal-RSs
6106 to 6109 and the CRSs 6105 on the same subframe. Since the
signals used in demodulation and measurement are transmitted, the
base station can execute calibration during communication with the
UE.
[0524] Furthermore, any PDCCH is not transmitted in the ABS region
6301. If the ABS has been configured, the UE that is notified of
the configuration of the ABS from the base station does not have to
receive the ABS. The UE does not need to receive the ABS, and
occurrence of a malfunction in the UE can be reduced.
[0525] Furthermore, neither a PDCCH nor a PCFICH is transmitted in
the ABS region 6301. Since the PDCCH region can also be used as a
resource for calibration, resources can be allocated to calibration
more than those when the PDSCH region is used.
[0526] Furthermore, the ABS is not configured in a subframe to
which a synchronization signal, a physical broadcast channel, or a
paging channel is mapped. Thus, configuring an ABS and mapping
cal-RSs to the ABS enables the base station to eliminate a process
of mapping cal-RSs to a symbol or a subframe except for symbols to
which the synchronization signal and the physical broadcast channel
are mapped and subframes to which a paging channel is mapped, if
such a process exists. Accordingly, the processes performed by the
base station can be simplified.
[0527] Furthermore, the UE that performs calibration may not be
notified of, particularly, information on cal-RSs from the base
station, with the method disclosed in the fifth embodiment. The UE
may follow the scheduling by the PDCCH, the setting of the MBSFN
subframe, and the setting of the ABS as conventionally performed.
Thus, the UE neither needs to recognize the calibration nor needs
any special processes on the calibration. Accordingly, the
processes performed by the UE can be simplified.
[0528] The base station may specify information on the cal-RSs to
the UE. The base station may notify the UE of the information on
the cal-RSs. Examples of the information on the cal-RSs include a
radio frame, a subframe, a resource, and a sequence to which the
cal-RSs are mapped. Examples of the resource include a resource
block, a resource element, and a resource unit, etc.
[0529] Examples of the notification method includes notification by
the RRC signaling, the MAC signaling, and the PDCCH. For example,
when cal-RSs are mapped to a PDSCH region, the base station
notifies the UE of information on the cal-RSs.
[0530] Accordingly, the UE can recognize a subframe, a resource,
and a sequence to be calibrated. For example, the UE can determine
the absence of a PDSCH in a resource to which the cal-RSs are
mapped, among the received subframes.
[0531] Thus, the UE can perform a process of, for example, not
receiving the resource or discarding a result of demodulation on
the resource. Accordingly, the UE can accurately receive the
resource of the PDSCH.
[0532] The same holds true when the MBSFN subframe is used. The
base station may notify the UE of information on the MBSFN subframe
to which the cal-RSs are mapped. The configuration of the MBSFN
subframe may be notified including the information on the MBSFN
subframe to which the cal-RSs are mapped. For example, the UE can
determine the absence of a PMCH or a PDSCH in a resource to which
the cal-RSs are mapped, among the MBSFN subframes.
[0533] Thus, the UE can perform a process of, for example, not
receiving the resource or discarding a result of demodulation on
the resource. Accordingly, the UE can accurately receive the
resource of the PMCH or the PDSCH.
[0534] The same holds true when the ABS is used. The base station
may notify the UE of information on the ABS to which the cal-RSs
are mapped. The configuration of the ABS may be notified including
the information on the ABS to which the cal-RSs are mapped.
Accordingly, the UE can recognize a subframe to be calibrated.
[0535] Thus, even if the UE can receive RSs for calibration, it can
recognize that the signals are for calibration. Thus, the UE can
perform a process of, for example, not receiving the resource or
discarding a result of demodulation on the resource. Accordingly,
it is possible to prevent the UE from wrongly receiving the
ABS.
[0536] Furthermore, the base station may notify the adjacent base
stations of information on the cal-RSs, information on the MBSFN
subframe to which the cal-RSs are mapped, and information on the
ABS to which the cal-RSs are mapped. This notice may be notified by
the X2 signaling.
[0537] Normally, the adjacent base stations do not recognize
transmission of the cal-RSs on a normal subframe, the MBSFN
subframe, and the ABS. In the case where the cal-RSs have to be
transmitted with high power for calibration, the signals may
interfere the adjacent base stations.
[0538] Thus, notifying, from the base station, the adjacent base
stations of the information on the cal-RSs, the information on the
MBSFN subframe to which the cal-RSs are mapped, and the information
on the ABS to which the cal-RSs are mapped enables the adjacent
base stations to recognize the existence of the cal-RSs and the
resources on the time axis or the frequency axis. Consequently, for
example, the adjacent base stations can avoid data scheduling of
the UEs being served thereby, based on the assumption of the
interference from the base station.
[0539] Furthermore, the base station may notify the core network
side node of information on the cal-RSs, information on the MBSFN
subframe to which the cal-RSs are mapped, and information on the
ABS to which the cal-RSs are mapped.
[0540] During the calibration in the base station, the core network
side node may notify the information on the cal-RSs, the
information on the MBSFN subframe to which the cal-RSs are mapped,
and the information on the ABS to which the cal-RSs are mapped all
of which are obtained from the base station, to a base station that
requires some special operations.
[0541] These notices may be notified by the S1 signaling.
Accordingly, the same advantages as those in the previous
embodiments can be produced even when the base station notifies the
core network side node of the information on the cal-RSs, the
information on the MBSFN subframe to which the cal-RSs are mapped,
and the information on the ABS to which the cal-RSs are mapped.
Seventh Embodiment
[0542] The second, third, and sixth embodiments disclose
calibrating every antenna element using RSs for calibration.
According to these embodiments, as the number of the antenna
elements increases, the cal-RSs also increases. Thus, when all the
antenna elements are calibrated, the time to adjust the phase and
the amplitude of each of the antenna elements increases.
Furthermore, as the cal-RSs increases, the overhead increases.
Accordingly, a physical region for downlink available for actual
communication decreases, and thus a problem with incapability to
guarantee the communication performance that is originally expected
occurs. The seventh embodiment will disclose a method for solving
such problems.
[0543] The antenna elements included in a multi-element antenna of
the base station are grouped. Examples of the method for grouping
the antenna elements include a grouping method relying on
adjustment results obtained through calibration executed to form
beams by the multi-element antenna before shipment, before setting,
and during operations, and a grouping method based on a structure
of the multi-element antenna.
[0544] When the antenna elements are grouped according to the
adjustment results obtained through calibration, data of amplitude
adjustment values and phase adjustment values obtained as the
adjustment results are stored as calibration values obtained from
the calibration in the past, and the antenna elements having the
adjustment values within a predetermined range are grouped.
Examples of the predetermined range include a range of .+-.1 bit of
adjustment results obtained from a digital phase shifter used in
adjusting the phase. Thus, the antenna elements whose adjustment
results from the digital phase shifter fall within the range of
.+-.1 bit are handled as the same group.
[0545] In addition to this, in a multi-element antenna for
transmission, transmission signals output from the respective
antenna elements can be grouped according to signal levels received
by a reference reception system. Furthermore, in a multi-element
antenna for reception, grouping according to signal levels obtained
by receiving, through the respective antenna elements, a
transmission signal output from a reference transmission system is
possible.
[0546] Here, the reference reception system and the reference
transmission system are included in an arbitrary antenna element in
the multi-element antenna. The arbitrary antenna element is, for
example, an antenna element located in the center of all the
antenna elements, an antenna element each located at the four
corners of a set of all the antenna elements, one antenna element
in horizontal and vertical arrays of antenna elements, or an
antenna element located in the center of antenna elements formed
per sub-array antenna.
[0547] Examples of the method for grouping the antenna elements
based on a structure of the multi-element antenna include grouping
every antenna elements at an equal distance from a reference
antenna element, grouping every antenna elements collocated in the
horizontal or vertical direction, grouping antenna elements
according to the power distribution in a tapered sub-array antenna,
and grouping antenna elements every vertically polarized waves and
every horizontally polarized waves when a polarized wave antenna is
configured.
[0548] With application of the grouping method according to a
distance from a reference antenna element, a permissible accuracy
can be relaxed in adjustment performed every antenna group. The
tapered sub-array antenna is configured with weighting of the power
distribution within the multi-element antenna, in order to reduce
the side lobe level in an antenna radiation pattern. Thus, main
antenna elements that determine the beam shape, are positioned in
the center, and have larger output in transmission are grouped, and
only these main antenna elements are calibrated. Accordingly, the
time to adjust the phase and the amplitude of each of the antenna
elements can be shortened.
[0549] Since in the configuration of the polarized wave antenna,
the radio waves in the vertically polarized waves and in the
horizontally polarized waves are orthogonal to one another in their
relationship, signals simultaneously transmitted and received are
less subject to mutual interference. Thus, grouping antenna
elements for every polarized waves enables simultaneous calibration
of a vertical antenna and a horizontal antenna.
[0550] A method for calibrating an antenna element group obtained
by such grouping will be hereinafter described.
[0551] When a multi-element antenna for transmission is calibrated,
any one of the antenna elements in each antenna group transmits
cal-RSs, and a result of the calibration obtained by receiving the
signals through a reference reception system is reflected on all
the antenna elements in the same group.
[0552] When a multi-element antenna for reception is calibrated,
any one of the antenna elements in the group receives cal-RSs
output from a reference transmission system. Then, a result of the
calibration obtained through the reception is reflected on all the
antenna elements in the same group.
[0553] FIG. 38 illustrates an example configuration of a subframe
when cal-RSs of each antenna group are mapped to a physical
downlink shared channel region according to the seventh embodiment.
The horizontal axis represents a time t, and the vertical axis
represents a frequency fin FIG. 38.
[0554] In FIG. 38, a reference "7101" denotes a subframe, a
reference "7102" denotes symbol timing, and a reference "7105"
denotes a CRS. In one subframe, the first 3 symbols form a PDCCH
region 7103, and the subsequent 11 symbols form a PDSCH region
7104.
[0555] In contrast to the example disclosed in the sixth embodiment
of mapping the cal-RSs to a physical downlink shared channel region
in the LTE, FIG. 38 illustrates an example of arranging cal-RSs for
each antenna group. Since the configuration of the physical
downlink channel except for the cal-RSs is the same as that in FIG.
35, the description thereof will be omitted.
[0556] FIG. 38 illustrates an example of mapping the cal-RSs for
each antenna group, without mapping a PDSCH. A cal-RS 7106 of a
first antenna group #1, a cal-RS 7107 of a second antenna group #2,
a cal-RS 7108 of a third antenna group #3, and a cal-RS 7109 of a
fourth antenna group #4 are mapped to the PDSCH region 7104 without
mapping a PDSCH.
[0557] FIG. 38 illustrates an example in which the base station
maps the cal-RSs over the entire frequency domain with the symbol
timing to map the cal-RSs 7106 to 7109 for each antenna group.
[0558] Since the antenna elements are grouped and the cal-RSs are
set for each antenna group as described above, the number of the
cal-RSs can be reduced more than that when the cal-RSs are used for
each of the antenna elements. Accordingly, the time to adjust the
phase and the amplitude of each of the antenna elements can be
shortened. Furthermore, reduction in the number of the cal-RSs can
prevent degradation in the communication performance caused by
overhead.
[0559] Furthermore, using both the grouping method relying on
adjustment results obtained through calibration and the grouping
method based on the structure of the multi-element antenna can, for
example, relax the accuracy in adjusting the phase and the
amplitude of each of the antenna elements and simplify such
adjustment. Accordingly, the time required for calibration can be
shortened.
[0560] According to the seventh embodiment, the PHY processing unit
that is a calibration unit divides a plurality of antenna elements
into groups, and sets the cal-RSs for each of the groups.
Accordingly, increase in the cal-RSs can be suppressed. Thus,
increase in the time required for calibration can be suppressed.
Furthermore, it is possible to prevent decrease in the physical
region for downlink available for actual communication and
guarantee the communication performance.
Eighth Embodiment
[0561] The eighth embodiment will disclose an example of partially
thinning out the cal-RSs mapped over the entire frequency domain
with the symbol timing and arranging the cal-RSs, in each of the
antenna elements included in the multi-element antenna according to
the second, third, and sixth embodiments.
[0562] FIG. 39 illustrates an example configuration of a subframe
when cal-RSs are mapped to a part of the frequency axis in a
physical downlink shared channel region according to the eighth
embodiment. The horizontal axis represents a time t, and the
vertical axis represents a frequency fin FIG. 39.
[0563] In FIG. 39, a reference "8101" denotes a subframe, a
reference "8102" denotes symbol timing, and a reference "8105"
denotes a CRS. In one subframe, the first 3 symbols form a PDCCH
region 8103, and the subsequent 11 symbols form a PDSCH region
8104.
[0564] FIG. 39 illustrates an example of thinning out and arranging
the cal-RSs on the frequency axis, in contrast to the example
disclosed in the sixth embodiment of mapping the cal-RSs to a
physical downlink shared channel region in the LTE over the entire
frequency domain. Since the configuration of the physical downlink
channel except for the cal-RSs is the same as that in FIG. 35, the
description thereof will be omitted.
[0565] FIG. 39 illustrates an example of periodically thinning out
the cal-RSs of the antenna elements on the frequency axis and
mapping the cal-RSs to the PDSCH region 8104 without mapping a
PDSCH. Cal-RSs 8106 of the first antenna element #1, cal-RSs 8107
of the second antenna element #2, cal-RSs 8108 of the third antenna
element #3, and cal-RSs 8109 of the fourth antenna element #4 are
periodically thinned out and mapped to the PDSCH region 8104 with
the symbol timing on the frequency axis, without mapping a
PDSCH.
[0566] The cal-RSs for each antenna element may be arranged at
fixed frequencies according to the frequency characteristics of
each of the antenna elements, instead of the method for
periodically thinning out and arranging the cal-RSs on the
frequency axis.
[0567] Accordingly, thinning out the cal-RSs of each of the antenna
elements on the frequency axis reduces the number of the cal-RSs
arranged in a physical downlink shared channel region. Thus,
another channel can be arranged, and degradation in the
communication performance caused by overhead can be prevented.
[0568] FIG. 40 illustrates another example configuration of a
subframe when cal-RSs are mapped to a part of the frequency axis in
a physical downlink shared channel region according to the eighth
embodiment. FIG. 40 illustrates arranging cal-RSs of a plurality of
antenna elements within the same symbol timing when the cal-RSs of
each of the antenna elements are periodically thinned out and
arranged on the frequency axis.
[0569] The horizontal axis represents a time t, and the vertical
axis represents a frequency fin FIG. 40. In FIG. 40, a reference
"8201" denotes a subframe, a reference "8202" denotes symbol
timing, and a reference "8205" denotes a CRS. In one subframe, the
first 3 symbols form a PDCCH region 8203, and the subsequent 11
symbols form a PDSCH region 8204.
[0570] In FIG. 40, cal-RSs 8206 of the first antenna element #1,
cal-RSs 8207 of the second antenna element #2, and cal-RSs 8208 of
the third antenna element #3 are periodically arranged within the
same symbol timing in the PDSCH region 8204 on the frequency axis,
without mapping a PDSCH to the PDSCH region 8204.
[0571] Accordingly, arranging the cal-RSs of a plurality of antenna
elements within the same symbol timing can process the cal-RSs per
symbol timing, and reserve a substantial channel region.
Accordingly, the processing load can be reduced, and the
communication performance can be improved.
[0572] Furthermore, with the combination of the seventh and eighth
embodiments, it is possible to group antenna elements having the
same frequency characteristics, and execute calibration using
cal-RSs for each of the antenna element groups each of which is
obtained by thinning out the cal-RSs of any one of the antenna
elements and arranging the the cal-RSs on the frequency axis.
[0573] FIG. 41 illustrates an example configuration of a subframe
when cal-RSs for each antenna group are mapped to a part of the
frequency axis in a physical downlink shared channel region
according to the eighth embodiment. The horizontal axis represents
a time t, and the vertical axis represents a frequency fin FIG. 41.
In FIG. 41, a reference "8301" denotes a subframe, a reference
"8302" denotes symbol timing, and a reference "8305" denotes a CRS.
In one subframe, the first 3 symbols form a PDCCH region 8303, and
the subsequent 11 symbols form a PDSCH region 8304.
[0574] FIG. 41 illustrates an example of arranging the cal-RSs
thinned out on the frequency axis for each antenna group, in a
physical downlink shared channel region in the LTE.
[0575] In FIG. 41, cal-RSs 8306 of the first antenna group #1,
cal-RSs 8307 of the second antenna group #2, cal-RSs 8308 of the
third antenna group #3, and cal-RSs 8309 of the fourth antenna
group #4 are thinned out and arranged in the PDSCH region 8304 on
the frequency axis, without mapping a PDSCH.
[0576] With such a configuration, the number of the cal-RSs
arranged in a physical downlink shared channel region is reduced.
Accordingly, the time required for calibration can be shortened,
and degradation in the communication performance caused by overhead
can be prevented.
[0577] Furthermore, making null the regions other than the cal-RSs
thinned out and arranged on the frequency axis can increase the
transmission power and improve the SNR. Accordingly, the
communication performance can be improved.
[0578] As described above, the PHY processing unit that is a
calibration unit arranges the cal-RSs in a part of the entire
frequency domain of a subframe, according to the eighth embodiment.
In other words, the PHY processing unit partially thins out and
arranges cal-RSs mapped over the entire frequency domain.
Accordingly, the time required for calibration can be reduced.
Furthermore, degradation in the communication performance caused by
overhead can be prevented.
[0579] Although the previous embodiments describe a case where the
unit of resource to be set for calibration is a subframe, not
limited to the subframe but the unit of transmission time in a
system may be the unit of resource. The unit of resource may be,
for example, a TTI, a slot, or a symbol. Furthermore, the unit of
resource may be an integer multiple of the unit of transmission
time.
[0580] Although the previous embodiments describe a case where the
unit of resource for cal-RSs is a symbol, not limited to the symbol
but the basic time unit in a system may be the unit of resource.
Furthermore, the unit of resource may be an integer multiple of the
basic time unit. For example, the unit of resource may be the
timing of fast Fourier transform (FFT) in the OFDM. For example,
the unit of resource may be the basic time unit (Ts) in the
LTE.
[0581] Accordingly, flexible calibration can be performed on the
time axis. Thus, execution of the calibration during operation is
facilitated, and accuracy in the calibration can be improved. Thus,
the performance of the MIMO and the beamforming using the
multi-element antenna can be further improved.
[0582] The embodiments and the modifications thereof are merely
illustrations of the present invention and can be freely combined
within the scope of the invention. Also, any constituent elements
of the embodiments and the modifications thereof can be
appropriately modified or omitted. Such free combination of the
embodiments and the modifications thereof and appropriate
modification or omission of any constituent elements of the
embodiments and the modifications thereof enable appropriate
calibration according to an operational environment, and further
improvement in the performance of the MIMO and the beamforming
using the multi-element antenna.
[0583] While the invention has been described in detail, the
foregoing description is in all aspects illustrative and not
restrictive. It is therefore understood that numerous modifications
and variations can be devised without departing from the scope of
the invention.
DESCRIPTION OF REFERENCES
[0584] 801, 901, 901A PHY, 802, 909 first antenna element, 803, 922
second antenna element, 804 third antenna element, 805, 935 n-th
antenna element, 806, 9411, 9412 control unit, 902, 902A first
encoder unit, 903 first transmission data generating unit, 904
first calibration RS mapping unit, 905 first transmission power
setting unit, 9061 first transmission correction processing unit,
9062 first transmission phase rotation unit, 907 first modulating
unit, 908 first switching unit, 910 first demodulating unit, 911,
911A first decoder unit, 9121 first reception correction processing
unit, 9122 first reception phase rotation unit, 913 first
calibration RS extracting unit, 914 first response characteristics
calculating unit, 915, 915A second encoder unit, 916 second
transmission data generating unit, 917 second calibration RS
mapping unit, 918 second transmission power setting unit, 9191
second transmission correction processing unit, 9192 second
transmission phase rotation unit, 920 second modulating unit, 921
second switching unit, 923 second demodulating unit, 924, 924A
second decoder unit, 9251 second reception correction processing
unit, 9252 second reception phase rotation unit, 926 second
calibration RS extracting unit, 927 second response characteristics
calculating unit, 928, 928A n-th encoder unit, 929 n-th
transmission data generating unit, 930 n-th calibration RS mapping
unit, 931 n-th transmission power setting unit, 9321 n-th
transmission correction processing unit, 9322 n-th transmission
phase rotation unit, 933 n-th modulating unit, 934 n-th switching
unit, 936 n-th demodulating unit, 937, 937A n-th decoder unit, 9381
n-th reception correction processing unit, 9382 n-th reception
phase rotation unit, 939 n-th calibration RS extracting unit, 940
n-th response characteristics calculating unit.
* * * * *
References