U.S. patent application number 13/258428 was filed with the patent office on 2012-01-19 for channel-sounding method using a plurality of antennas, and apparatus for same.
Invention is credited to Jae Hoon Chung, Seung Hee Han, Yeong Hyeon Kwon, Min Seok Noh.
Application Number | 20120014349 13/258428 |
Document ID | / |
Family ID | 42781649 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120014349 |
Kind Code |
A1 |
Chung; Jae Hoon ; et
al. |
January 19, 2012 |
CHANNEL-SOUNDING METHOD USING A PLURALITY OF ANTENNAS, AND
APPARATUS FOR SAME
Abstract
The present invention relates to a wireless communication
system. More particularly, the present invention relates to a
method and to an apparatus for transmitting an SRS in a
multi-antenna system. The method comprises the steps of: acquiring
specific information for discriminating a first antenna group and a
second antenna group from among a plurality of antennas, wherein
said first antenna group includes one or more antennas which are
set to a turned-on state to perform communication with a base
station, and said second antenna group includes one or more other
antennas which are set to a turned-off state; transmitting an SRS
to the base station if a predetermined condition is satisfied,
under the condition that the second antenna group is set to the
turned-off state; and setting the second antenna group to a
turned-off state after the transmission of the SRS.
Inventors: |
Chung; Jae Hoon; (Anyang-si,
KR) ; Kwon; Yeong Hyeon; (Anyang-si, KR) ;
Han; Seung Hee; (Anyang-si, KR) ; Noh; Min Seok;
(Anyang-si, KR) |
Family ID: |
42781649 |
Appl. No.: |
13/258428 |
Filed: |
March 22, 2010 |
PCT Filed: |
March 22, 2010 |
PCT NO: |
PCT/KR2010/001753 |
371 Date: |
September 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61162323 |
Mar 22, 2009 |
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61178818 |
May 15, 2009 |
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61187285 |
Jun 16, 2009 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 72/0453 20130101;
H04B 7/0684 20130101; H04W 76/27 20180201; H04L 1/0026 20130101;
H04W 72/0446 20130101; H04L 5/0048 20130101; H04W 72/0406 20130101;
H04B 7/0693 20130101; H04L 1/1671 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/04 20090101
H04W072/04 |
Claims
1-14. (canceled)
15. A method of transmitting a sounding reference signal through
multiple antennas in a wireless communication system, the method
comprising: generating sounding reference sequences for multiple
antenna ports, wherein each sounding reference sequence is defined
using a base sequence number and a cyclic shift value; and mapping
each sounding reference sequence to resource elements of a
corresponding antenna port on a single carrier frequency division
multiple access (SC-FDMA) symbol, wherein the cyclic shift value is
given per each antenna port.
16. The method of claim 15, wherein sounding reference sequences of
all of the multiple antenna ports are mapped to the same set of
every two resource elements.
17. The method of claim 15, wherein sounding reference sequences
for a first group of antenna ports are mapped to a set of every two
resource elements, and sounding reference sequences for a second
group of antenna ports are mapped to another set of every two
resource elements.
18. The method of claim 15, wherein the SC-FDMA symbol is a last
SC-FDMA symbol of a subframe.
19. The method of claim 15, further comprising: transmitting the
mapped sounding sequence in uplink.
20. A method of processing a sounding reference signal transmitted
from multiple antennas in a wireless communication system, the
method comprising: receiving sounding reference sequences for
multiple antenna ports on resource elements of a single carrier
frequency division multiple access (SC-FDMA) symbol, wherein each
sounding reference sequence is defined using a base sequence number
and a cyclic shift value; and de-mapping each sounding reference
sequence from the resource elements of a corresponding antenna port
on the SC-FDMA symbol, wherein the cyclic shift value is given per
each antenna port.
21. The method of claim 20, wherein sounding reference sequences of
all of the multiple antenna ports are mapped to the same set of
every two resource elements.
22. The method of claim 20, wherein sounding reference sequences
for a first group of antenna ports are mapped to a set of every two
resource elements, and sounding reference sequences for a second
group of antenna ports are mapped to another set of every two
resource elements.
23. The method of claim 20, wherein the SC-FDMA symbol is a last
SC-FDMA symbol of a subframe.
24. The method of claim 20, further comprising: estimating an
uplink channel state using the de-mapped sounding sequence.
25. A communication apparatus used for a wireless communication
system, the communication apparatus comprising: a radio frequency
(RF) unit; and a processor, wherein the processor is configured to
generate sounding reference sequences for multiple antenna ports,
wherein each sounding reference sequence is defined using a base
sequence number and a cyclic shift value, and to map each sounding
reference sequence to resource elements of a corresponding antenna
port on a single carrier frequency division multiple access
(SC-FDMA) symbol, wherein the cyclic shift value is given per each
antenna port.
26. The communication apparatus of claim 25, wherein sounding
reference sequences of all of the multiple antenna ports are mapped
to the same set of every two resource elements.
27. The communication apparatus of claim 25, wherein sounding
reference sequences for a first group of antenna ports are mapped
to a set of every two resource elements, and sounding reference
sequences for a second group of antenna ports are mapped to another
set of every two resource elements.
28. The communication apparatus of claim 25, wherein the SC-FDMA
symbol is a last SC-FDMA symbol of a subframe.
29. The communication apparatus of claim 25, wherein the processor
is further configured to transmit the mapped sounding sequence in
uplink.
30. A communication apparatus used for a wireless communication
system, the communication apparatus comprising: a radio frequency
(RF) unit; and a processor, wherein the processor is configured to
receive sounding reference sequences for multiple antenna ports on
resource elements of a single carrier frequency division multiple
access (SC-FDMA) symbol, wherein each sounding reference sequence
is defined using a base sequence number and a cyclic shift value,
and to de-map each sounding reference sequence from the resource
elements of a corresponding antenna port on the SC-FDMA symbol,
wherein the cyclic shift value is given per each antenna port.
31. The communication apparatus of claim 30, wherein sounding
reference sequences of all of the multiple antenna ports are mapped
to the same set of every two resource elements.
32. The communication apparatus of claim 30, wherein sounding
reference sequences for a first group of antenna ports are mapped
to a set of every two resource elements, and sounding reference
sequences for a second group of antenna ports are mapped to another
set of every two resource elements.
33. The communication apparatus of claim 30, wherein the SC-FDMA
symbol is a last SC-FDMA symbol of a subframe.
34. The communication apparatus of claim 30, the processor is
further configured to estimate an uplink channel state using the
de-mapped sounding sequence.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system. Particularly, the present invention relates to a channel
sounding method using a plurality of antennas and an apparatus for
the same.
BACKGROUND ART
[0002] A 3rd Generation Partnership Project Long Term Evolution
(3GPP LTE) communication system, which is an example of a mobile
communication system to which the present invention may be applied,
will now be described in brief.
[0003] FIG. 1 is a diagram schematically showing a network
structure of an Evolved Universal Mobile Telecommunications System
(E-UMTS) as an exemplary mobile communication system. The E-UMTS
system has evolved from the conventional UMTS system and basic
standardization thereof is currently underway in the 3GPP. The
E-UMTS may be generally referred to as a Long Term Evolution (LTE)
system. For details of the technical specifications of the UMTS and
E-UMTS, refer to Release 7 and Release 8 of "3rd Generation
Partnership Project; Technical Specification Group Radio Access
Network".
[0004] Referring to FIG. 1, the E-UMTS includes a User Equipment
(UE) 120, eNBs (or eNode Bs or base stations) 110a and 110b, and an
Access Gateway (AG) which is located at an end of a network
(E-UTRAN) and connected to an external network. The eNBs may
simultaneously transmit multiple data streams for a broadcast
service, a multicast service, and/or a unicast service.
[0005] One or more cells may exist per eNB. A cell is set to use
one of bandwidths of 1.25, 2.5, 5, 10, and 20 MHz to provide a
downlink or uplink transport service to several UEs. Different
cells may be set to provide different bandwidths. The eNB controls
data transmission and reception for a plurality of UEs. The eNB
transmits downlink scheduling information with respect to downlink
data to notify a corresponding UE of a time/frequency domain in
which data is to be transmitted, coding, data size, and Hybrid
Automatic Repeat and reQuest (HARQ)-related information. In
addition, the eNB transmits uplink scheduling information with
respect to UL data to a corresponding UE to inform the UE of an
available time/frequency domain, coding, data size, and
HARQ-related information. An interface for transmitting user
traffic or control traffic may be used between eNBs. A Core Network
(CN) may include the AG, a network node for user registration of
the UE, and the like. The AG manages mobility of a UE on a Tracking
Area (TA) basis, wherein one TA includes a plurality of cells.
[0006] Although wireless communication technology has been
developed up to LTE based on Wideband Code Division Multiple Access
(WCDMA), the demands and expectations of users and providers
continue to increase. In addition, since other wireless access
technologies continue to be developed, new technology is required
to secure competitiveness in the future. For example, decrease of
cost per bit, increase of service availability, flexible use of a
frequency band, simple structure, open interface, and suitable
power consumption by a UE are required. Recently, standardization
of a new technology subsequent to LTE (Release 8/9) is in progress
in the 3GPP. In this specification, the technology is referred to
as "LTE-Advanced" or "LTE-A" (Release 10 or beyond).
DISCLOSURE
Technical Problem
[0007] An object of the present invention devised to solve the
problem lies in providing a channel sounding method using a
plurality of antennas in a wireless communication system and an
apparatus for the same.
[0008] Objects of the present invention are not limited to those
described above and other objects will be clearly understood by
those skilled in the art from the following description.
Technical Solution
[0009] In one aspect of the present invention, the object of the
present invention can be achieved by providing a method for a User
Equipment (UE) to transmit a Sounding Reference Signal (SRS) using
a plurality of antennas in a wireless communication system, the
method including acquiring specific information for discriminating
between a first antenna group and a second antenna group among the
plurality of antennas, the first antenna group including one or
more antennas which are set in a turn-on state for communication
with an eNode B and the second antenna group including one or more
other antennas which are set in a turn-off state, transmitting an
SRS to the eNode B through the second antenna group when a preset
condition is satisfied with the second antenna group being set in a
turn-off state, and setting the second antenna group in a turn-off
state after transmitting the SRS.
[0010] In another aspect of the present invention, provided herein
is a User Equipment (UE) including a plurality of antennas, a Radio
Frequency (RF) unit configured to transmit and receive a wireless
signal to and from an eNode B through the plurality of antennas, a
memory for storing information transmitted and received to and from
the eNode B and a parameter required for operation of the UE, and a
processor connected to the RF unit and the memory, the processor
being configured to control the RF unit and the memory, the
processor being configured to perform a Sounding Reference Signal
(SRS) transmission method including acquiring specific information
for discriminating between a first antenna group and a second
antenna group among the plurality of antennas, the first antenna
group including one or more antennas which are set in a turn-on
state for communication with the eNode B and the second antenna
group including one or more other antennas which are set in a
turn-off state, transmitting an SRS to the eNode B through the
second antenna group when a preset condition is satisfied with the
second antenna group being set in a turn-off state, and setting the
second antenna group in a turn-off state after transmitting the
SRS.
[0011] Here, the second antenna group may include antennas in which
an Antenna Gain Imbalance (AGI) has occurred.
[0012] Here, whether or not the specific condition may be satisfied
is determined based on whether or not a first duration for
transmitting the SRS has elapsed and the first duration may be set
to be longer than a second duration for SRS transmission through
the first antenna group. In this case, the first duration may be
set as a multiple of the second duration.
[0013] Here, an SRS may be transmitted to the eNode B through all
antennas provided for the UE when the preset condition is
satisfied.
[0014] Here, whether or not the specific condition is satisfied may
be determined based on whether or not an SRS request for the second
antenna group has been received from the eNode B. In this case, the
SRS request for the second antenna group may be performed through
L1/L2 control signaling.
Advantageous Effects
[0015] According to the embodiments of the present invention, it is
possible to efficiently perform channel sounding using a plurality
of antennas in a wireless communication system.
[0016] Advantages of the present invention are not limited to those
described above and other advantages will be clearly understood by
those skilled in the art from the following description.
DESCRIPTION OF DRAWINGS
[0017] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this application, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention.
[0018] In the drawings:
[0019] FIG. 1 illustrates a network structure of an E-UMTS as an
exemplary mobile communication system;
[0020] FIG. 2 illustrates structures of a control plane and a user
plane of a radio interface protocol between a UE and E-UTRAN based
on the 3GPP radio access network standard;
[0021] FIG. 3 illustrates physical channels used in a 3GPP system
and a general signal transmission method using the same;
[0022] FIG. 4 illustrates the structure of a radio frame used in an
LTE system;
[0023] FIG. 5 illustrates the structure of an uplink subframe used
in an LTE system;
[0024] FIG. 6 illustrates a procedure for performing channel
sounding in the case where closed-loop antenna selection is applied
in an LTE system;
[0025] FIG. 7 illustrates a method for multiplexing Sounding
Reference Signals (SRSs) in a Code Division Multiplexing (CDM)
manner according to an embodiment of the present invention;
[0026] FIG. 8 illustrates a method for multiplexing SRSs in a
Frequency Division Multiplexing (FDM) manner according to an
embodiment of the present invention;
[0027] FIG. 9 illustrates SRSs in a CDM/FDM manner according to an
embodiment of the present invention;
[0028] FIGS. 10 to 13 illustrate an example in which SRS resources
are allocated in a disjoint manner for each antenna according to an
embodiment of the present invention;
[0029] FIGS. 14 and 15 illustrate an example in which a plurality
of SRS transmission symbols is configured in a subframe according
to an embodiment of the present invention;
[0030] FIG. 16 illustrates a procedure for performing channel
sounding according to an embodiment of the present invention;
and
[0031] FIG. 17 is a block diagram illustrating a Base Station (BS)
and a User Equipment (UE) according to an embodiment of the present
invention.
BEST MODE
[0032] The above and other configurations, operations, and features
of the present invention will be easily understood from embodiments
of the present invention, which are described below with reference
to the accompanying drawings. The embodiments described below are
examples in which the features of the present invention are applied
to a 3GPP system.
[0033] FIG. 2 is a diagram showing structures of a control plane
and a user plane of a radio interface protocol between a UE and
E-UTRAN based on the 3GPP radio access network standard. The
control plane refers to a path used for transmitting control
messages which are used in the UE and the network to manage a call.
The user plane refers to a path used for transmitting data
generated in an application layer, e.g., voice data or Internet
packet data.
[0034] A physical (PHY) layer of a first layer provides an
information transfer service to an upper layer using a physical
channel. The PHY layer is connected to a Medium Access Control
(MAC) layer of an upper layer via a transport channel. Data is
transported between the MAC layer and the PHY layer via the
transport channel. Data is also transported between a physical
layer of a transmitting side and a physical layer of a receiving
side via a physical channel. The physical channel uses time and
frequency as radio resources. Specifically, the physical channel is
modulated using an Orthogonal Frequency Division Multiple Access
(OFDMA) scheme in downlink and is modulated using a Single-Carrier
Frequency Division Multiple Access (SC-FDMA) scheme in uplink.
[0035] A Medium Access Control (MAC) layer of a second layer
provides a service to a Radio Link Control (RLC) layer of an upper
layer via a logical channel. The RLC layer of the second layer
supports reliable data transmission. The function of the RLC layer
may be implemented by a functional block within the MAC. A Packet
Data Convergence Protocol (PDCP) layer of the second layer performs
a header compression function to reduce unnecessary control
information for efficient transmission of an Internet Protocol (IP)
packet such as IPv4 or IPv6 in a radio interface having a
relatively narrow bandwidth.
[0036] A Radio Resource Control (RRC) layer located at the
bottommost portion of a third layer is defined only in the control
plane. The RRC layer controls logical channels, transport channels,
and physical channels in relation to configuration,
re-configuration, and release of radio bearers. The radio bearer
refers to a service provided by the second layer to transmit data
between the UE and the network. To this end, the RRC layer of the
UE and the RRC layer of the network exchange RRC messages. The UE
is in an RRC connected mode if an RRC connection has been
established between the RRC layer of the radio network and the RRC
layer of the UE. Otherwise, the UE is in an RRC idle mode. A
Non-Access Stratum (NAS) layer located at an upper level of the RRC
layer performs functions such as session management and mobility
management.
[0037] One cell of the eNB is set to use one of bandwidths such as
1.25, 2.5, 5, 10, 15, and 20 MHz to provide a downlink or uplink
transmission service to UEs. Different cells may be set to provide
different bandwidths.
[0038] Downlink transport channels for data transmission from the
network to the UE include a Broadcast Channel (BCH) for
transmitting system information, a Paging Channel (PCH) for
transmitting paging messages, and a downlink Shared Channel (SCH)
for transmitting user traffic or control messages. User traffic or
control messages of a downlink multicast or broadcast service may
be transmitted through the downlink SCH or may be transmitted
through an additional downlink Multicast Channel (MCH). Meanwhile,
uplink transport channels for data transmission from the UE to the
network include a Random Access Channel (RACH) for transmitting
initial control messages and an uplink SCH for transmitting user
traffic or control messages. Logical channels, which are located at
an upper level of the transport channels and are mapped to the
transport channels, include a Broadcast Control Channel (BCCH), a
Paging Control Channel (PCCH), a Common Control Channel (CCCH), a
Multicast Control Channel (MCCH), and a Multicast Traffic Channel
(MTCH).
[0039] FIG. 3 is a diagram showing physical channels used in a 3GPP
system and a general signal transmission method using the same.
[0040] A UE performs an initial cell search operation such as
establishment of synchronization with an eNB when power is turned
on or the UE enters a new cell (S301). The UE may receive a Primary
Synchronization Channel (P-SCH) and a Secondary Synchronization
Channel (S-SCH) from the eNB, establish synchronization with the
eNB, and acquire information such as a cell identity (ID).
Thereafter, the UE may receive a physical broadcast channel from
the eNB to acquire broadcast information within the cell.
Meanwhile, the UE may receive a Downlink Reference Signal (DL RS)
in the initial cell search step to confirm a downlink channel
state.
[0041] Upon completion of the initial cell search, the UE may
receive a Physical Downlink Control Channel (PDCCH) and a Physical
Downlink Shared Channel (PDSCH) according to information included
in the PDCCH to acquire more detailed system information
(S302).
[0042] Meanwhile, if the UE initially accesses the eNB or if radio
resources for signal transmission are not present, the UE may
perform a random access procedure (steps S303 to S306) with respect
to the eNB. To this end, the UE may transmit a specific sequence
through a Physical Random Access Channel (PRACH) as a preamble
(steps S303 and S305), and receive a response message to the
preamble through the PDCCH and the PDSCH corresponding thereto
(steps S304 and S306). In the case of a contention-based RACH, a
contention resolution procedure may be additionally performed.
[0043] The UE which performs the above procedures may receive a
PDCCH/PDSCH (S307) and transmit a Physical Uplink Shared Channel
(PUSCH)/Physical Uplink Control Channel (PUCCH) (S308) according to
a general uplink/downlink signal transmission procedure. Control
information transmitted by the UE to the eNB through uplink or
received by the UE from the eNB through downlink includes a
downlink/uplink Acknowledgement/Negative Acknowledgement (ACK/NACK)
signal, a Channel Quality Indicator (CQI), a Precoding Matrix Index
(PMI), a Rank Indicator (RI), and the like. In the case of the 3GPP
LTE system, the UE may transmit the control information such as
CQI/PMI/RI through the PUSCH and/or the PUCCH.
[0044] FIG. 4 is a diagram showing the structure of a radio frame
used in an LTE system.
[0045] Referring to FIG. 4, the radio frame has a length of 10 ms
(327200 T.sub.s) and includes 10 subframes each having the same
size. Each of the subframes has a length of 1 ms and includes two
slots. Each of the slots has a length of 0.5 ms (15360 T.sub.s). In
this case, T.sub.s denotes a sampling time, and is represented by
T.sub.s=I/(15 kHz.times.2048)=3.2552.times.10.sup.-8 (about 33 ns).
Each slot includes a plurality of OFDM symbols in a time domain and
includes a plurality of Resource Blocks (RBs) in a frequency
domain. In the LTE system, one RB includes 12 subcarriers.times.7
(or 6) OFDM symbols. A Transmission Time Interval (TTI) which is a
unit time for data transmission may be determined in units of one
or more subframes. The above-described structure of the radio frame
is purely exemplary and various modifications may be made in the
number of subframes included in a radio frame, the number of slots
included in a subframe, or the number of OFDM symbols included in a
slot.
[0046] FIG. 5 is a diagram illustrating the structure of an uplink
subframe used in an LTE system.
[0047] As shown in FIG. 5, a 1ms subframe 500, which is a basic
unit of uplink transmission of LTE, includes two 0.5 ms slots 501.
Assuming that it has a normal Cyclic Prefix (CP) length, each slot
includes 7 symbols 502 and one symbol corresponds to one SC-FDMA
symbol. A resource block 503 is a resource allocation unit which
corresponds to 12 subcarriers in the frequency domain and
corresponds to one slot in the time domain. A structure of an
uplink subframe of LTE is mainly divided into a data area 504 and a
control area 505. Here, the data area is a series of communication
resources that are used to transmit data such as audio or a packet
to each UE and corresponds resources other than the control area in
the subframe. The control area is a series of communication
resources that are used to transmit a downlink channel quality
report, an ACK/NACK to a downlink signal, an uplink scheduling
request, or the like from each UE.
[0048] As shown in the example of FIG. 5, a Sounding Reference
Signal (SRS) is transmitted in an interval within a subframe in
which the last SC-FDMA symbol in the subframe is located in the
time domain and is transmitted through a data transmission band in
the frequency domain. SRSs of a number of UEs that are transmitted
through the last SC-FDMA symbol of the same subframe can be
discriminated from each other according to the frequency
location/sequence. SRS generation, physical resource mapping,
multiplexing methods, resource allocation, and the like are
described below in detail with reference to the 3GPP LTE (Release
8).
[0049] An SRS is constructed of a Constant Amplitude Zero Auto
Correlation (CAZAC) sequence. SRSs transmitted from a number of UEs
are CAZAC sequences (r.sup.SRS(n)=r.sub.u,v.sup.(.alpha.)(n))
having different cyclic shift values (.alpha.) according to the
following Expression 1.
.alpha. = 2 .pi. n SRS cs 8 [ Expression 1 ] ##EQU00001##
[0050] Here, n.sub.SRS.sup.cs is a value set for each UE by the
higher layer and has an integer value between 0 and 7.
[0051] Each CAZAC sequence generated from one CAZAC sequence
through cyclic shifting has a zero correlation with other CAZAC
sequences having cyclic shift values different from its cyclic
shift value. Using these characteristics, SRSs of the same
frequency region can be discriminated according to the sequence
CAZAC sequence cyclic shift values. An SRS of each UE is allocated
to a frequency according to a parameter that is set by the eNode B.
The UE performs frequency hopping of the SRS to allow the SRS to be
transmitted over the overall uplink data transfer bandwidth.
[0052] A detailed method for mapping physical resources for
transmitting an SRS in an LTE system is described below.
[0053] First, each SRS sequence r.sup.SRS(n) is multiplied by
.beta..sub.SRS in order to satisfy transmission power P.sub.SRS and
then the SRS sequences, starting from an SRS sequence r.sup.SRS(0),
are sequentially mapped to Resource Elements (REs) whose index is
(k,l) according to the following Expression 2.
a 2 k + k 0 , l = { .beta. SRS r SRS ( k ) k = 0 , 1 , , M sc , b
RS - 1 0 otherwise [ Expression 2 ] ##EQU00002##
[0054] Here, k.sub.0 indicates a frequency region start point of
the SRS and M.sub.ssc,b.sup.RS is the length (i.e., bandwidth) of
an SRS sequence represented in units of subcarriers as defined in
the following Expression 3.
M.sub.sc,b.sup.RS=m.sub.SRS,bN.sub.sc.sup.RB/2 [Expression 3]
[0055] In Expression 3, m.sub.SRS,b is a value signaled from an
eNode B according to an uplink bandwidth N.sub.RB.sup.UL as shown
in the following Tables 1 to 4.
[0056] A cell specific parameter C.sub.SRS which is an integer
value between 0 and 7 and a UE specific parameter B.sub.SRS which
is an integer value between 0 and 3 are required to acquire
m.sub.SRS,b. The values of C.sub.SRS and B.sub.SRS are given by the
higher layer.
TABLE-US-00001 TABLE 1 b.sub.hop = 0, 1, 2, 3, values for the
uplink bandwidth of 6 .ltoreq. N.sub.RB.sup.UL .ltoreq. 40. SRS
bandwidth SRS- SRS- SRS- SRS- configu- Bandwidth Bandwidth
Bandwidth Bandwidth ration B.sub.SRS = 0 B.sub.SRS = 1 B.sub.SRS =
2 B.sub.SRS = 3 C.sub.SRS m.sub.SRS,b N.sub.b m.sub.SRS,b N.sub.b
m.sub.SRS,b N.sub.b m.sub.SRS,b N.sub.b 0 36 1 12 3 4 3 4 1 1 32 1
16 2 8 2 4 2 2 24 1 4 6 4 1 4 1 3 20 1 4 5 4 1 4 1 4 16 1 4 4 4 1 4
1 5 12 1 4 3 4 1 4 1 6 8 1 4 2 4 1 4 1 7 4 1 4 1 4 1 4 1
TABLE-US-00002 TABLE 2 b.sub.hop = 0, 1, 2, 3, values for the
uplink bandwidth of 40 < N.sub.RB.sup.UL .ltoreq. 60. SRS
bandwidth SRS- SRS- SRS- SRS- configu- Bandwidth Bandwidth
Bandwidth Bandwidth ration B.sub.SRS = 0 B.sub.SRS = 1 B.sub.SRS =
2 B.sub.SRS = 3 C.sub.SRS m.sub.SRS,0 N.sub.0 m.sub.SRS,1 N.sub.1
m.sub.SRS,2 N.sub.2 m.sub.SRS,3 N.sub.3 0 48 1 24 2 12 2 4 3 1 48 1
16 3 8 2 4 2 2 40 1 20 2 4 5 4 1 3 36 1 12 3 4 3 4 1 4 32 1 16 2 8
2 4 2 5 24 1 4 6 4 1 4 1 6 20 1 4 5 4 1 4 1 7 16 1 4 4 4 1 4 1
TABLE-US-00003 TABLE 3 b.sub.hop = 0, 1, 2, 3, values for the
uplink bandwidth of 60 < N.sub.RB.sup.UL .ltoreq. 80. SRS
bandwidth SRS- SRS- SRS- SRS- configu- Bandwidth Bandwidth
Bandwidth Bandwidth ration B.sub.SRS = 0 B.sub.SRS = 1 B.sub.SRS =
2 B.sub.SRS = 3 C.sub.SRS m.sub.SRS,0 N.sub.0 m.sub.SRS,1 N.sub.1
m.sub.SRS,2 N.sub.2 m.sub.SRS,3 N.sub.3 0 72 1 24 3 12 2 4 3 1 64 1
32 2 16 2 4 4 2 60 1 20 3 4 5 4 1 3 48 1 24 2 12 2 4 3 4 48 1 16 3
8 2 4 2 5 40 1 20 2 4 5 4 1 6 36 1 12 3 4 3 4 1 7 32 1 16 2 8 2 4
2
TABLE-US-00004 TABLE 4 b.sub.hop = 0, 1, 2, 3, values for the
uplink bandwidth of 80 < N.sub.RB.sup.UL .ltoreq. 110. SRS
bandwidth SRS- SRS- SRS- SRS- configu- Bandwidth Bandwidth
Bandwidth Bandwidth ration B.sub.SRS = 0 B.sub.SRS = 1 B.sub.SRS =
2 B.sub.SRS = 3 C.sub.SRS m.sub.SRS,0 N.sub.0 m.sub.SRS,1 N.sub.1
m.sub.SRS,2 N.sub.2 m.sub.SRS,3 N.sub.3 0 96 1 48 2 24 2 4 6 1 96 1
32 3 16 2 4 4 2 80 1 40 2 20 2 4 5 3 72 1 24 3 12 2 4 3 4 64 1 32 2
16 2 4 4 5 60 1 20 3 4 5 4 1 6 48 1 24 2 12 2 4 3 7 48 1 16 3 8 2 4
2
[0057] As described above, the UE may perform frequency hopping of
the SRS to allow the SRS to be transmitted over the overall uplink
data transfer bandwidth. This frequency hopping is set by a
parameter b.sub.hop having a value of 0 to 3 that is given by the
higher layer.
[0058] When the frequency hopping of the SRS is disabled (i.e.,
when b.sub.hop.gtoreq.B.sub.SRS), the frequency position index
n.sub.b has a specific value as shown in the following Expression
4. In Expression 4, n.sub.RRC is a parameter given by the higher
layer.
n.sub.b=.left brkt-bot.4n.sub.RRC/m.sub.SRS,b.right brkt-bot. mod
N.sub.b [Expression 4]
[0059] On the other hand, when the frequency hopping of the SRS is
enabled (i.e., when b.sub.hop<B.sub.SRS), the frequency position
index n.sub.b is defined according to the following Expressions 5
and 6. In Expression 4, n.sub.RRC is a parameter given by the
higher layer.
n b = { 4 n RRC / m SRS , b mod N b b .ltoreq. b hop { F b ( n SRS
) + 4 n RRC / m SRS , b } mod N b otherwise [ Expression 5 ] F b (
n SRS ) = { ( N b / 2 ) n SRS mod b ' = b hop b N b ' b ' = b hop b
- 1 N b ' + n SRS mod b ' = b hop b N b ' 2 b ' = b hop b - 1 N b '
if N b even N b / 2 n SRS / b ' = b hop b - 1 N b ' if N b odd [
Expression 6 ] ##EQU00003##
[0060] Here, n.sub.SRS is a parameter for calculating the number of
times an SRS has been transmitted as is defined in the following
Expression 7.
n SRS = { 2 N SP n f + 2 ( N SP - 1 ) n s 10 + T offset T offset _
max , for 2 ms SRS periodicity of TDD frame structure ( n f .times.
10 + n s / 2 ) / T SRS , otherwise [ Expression 7 ]
##EQU00004##
[0061] Here, T.sub.SRS denotes a period of the SRS and T.sub.offset
denotes a subframe offset of the SRS. In addition, n.sub.s denotes
a slot number and n.sub.f denotes a frame number.
[0062] UE specific SRS setting indices I.sub.SRS for setting the
period T.sub.SRS and the subframe offset T.sub.offset of the SRS
are shown in the following Tables 5 and 6 respectively for FDD and
TDD.
TABLE-US-00005 TABLE 5 UE Specific SRS Periodicity T.sub.SRS and
Subframe offset Configuration T.sub.offset, FDD. SRS Configuration
SRS Periodicity SRS Subframe Index I.sub.SRS T.sub.SRS (ms) Offset
T.sub.offset 0-1 2 I.sub.SRS 2-6 5 I.sub.SRS-2 7-16 10 I.sub.SRS-7
17-36 20 I.sub.SRS-17 37-76 40 I.sub.SRS-37 77-156 80 I.sub.SRS-77
157-316 160 I.sub.SRS-157 317-636 320 I.sub.SRS-317 637-1023
reserved reserved
TABLE-US-00006 TABLE 6 UE Specific SRS Periodicity T.sub.SRS and
Subframe offset Configuration T.sub.offset, TDD. Configuration SRS
Periodicity SRS Subframe Index I.sub.SRS T.sub.SRS (ms) Offset
T.sub.offset 0 2 0, 1 1 2 0, 2 2 2 1, 2 3 2 0, 3 4 2 1, 3 5 2 0, 4
6 2 1, 4 7 2 2, 3 8 2 2, 4 9 2 3, 4 10-14 5 I.sub.SRS-10 15-24 10
I.sub.SRS-15 25-44 20 I.sub.SRS-25 45-84 40 I.sub.SRS-45 85-164 80
I.sub.SRS-85 165-324 160 I.sub.SRS-165 325-644 320 I.sub.SRS-325
645-1023 reserved reserved
TABLE-US-00007 TABLE 7 k.sub.SRS, TDD subframe index n 1 6 1st
symbol 2nd symbol 1st symbol 2nd symbol of 0 of UpPTS of UpPTS 2 3
4 5 of UpPTS UpPTS 7 8 9 k.sub.SRS in case 0 1 2 3 4 5 6 7 8 9
UpPTS length of 2 symbols k.sub.SRS in case 1 2 3 4 6 7 8 9 UpPTS
length of 1 symbol
[0063] FIG. 6 illustrates a method for transmitting an SRS for each
antenna when antenna selection is applied in an LTE system. In a
conventional LTE system, a UE applies an open-loop antenna
selection or closed-loop antenna selection scheme to switch single
power amplifier output or single antenna transmission based on
single RF power amplifier chain for a plurality of physical
antennas (for example, 2 physical antennas) in the time resource
region when performing uplink transmission.
[0064] Specifically, FIG. 6 illustrates an example in which an SRS
is transmitted using a closed-loop selection transmission method.
More specifically, FIG. 6 illustrates an example in which a
frequency resource region is allocated to an SRS for each antenna
at the timing of SRS transmission in the case where an SRS band
smaller than the entire system band is applied and SRS hopping is
applied. In the case where SRS hopping is not applied, an SRS is
transmitted alternately using each individual antenna at the
position of transmission and the same SRS band for each individual
SRS transmission time. Unlike this method, an uplink transmission
entity (i.e., a UE or a relay node) such as an LTE-A UE can perform
uplink transmission to a plurality of antennas while having a
plurality of transmission antennas and a plurality of RF power
amplifier chains. If it is assumed in this situation that the
method of transmitting an SRS for each individual antenna described
above is applied as an SRS transmission method, there is a problem
in that it is necessary to turn off a power amplifier of an antenna
which does not transmit an SRS in one or more SRS transmission
symbols (for example, OFDM symbols or SC-FDMA symbols) in a
subframe in an LTE-A system to which a simultaneously transmission
scheme which uses a plurality of RF power amplifier chains and a
plurality of antennas is applied. In addition, there may also be a
problem in that the transmission power of an antenna for
transmitting an SRS is limited to 1/(the number of transmission
antennas) relative to single antenna transmission power. In the
case of LTE, an arbitrary UE uses, for SRS transmission, the last
symbol of a subframe at the time of SRS transmission. In the LTE-A
system, a plurality of symbols may be used for SRS transmission and
the positions of the symbols in a subframe may be different from
those in the case of the LTE system although the same number and/or
positions of SRS transmission symbols as those of the LTE system
may also be applied to the LTE-A system. In addition, a method of
configuring SRS transmission and other uplink channel transmission
in an LTE-A uplink transmission scheme which allows non-contiguous
RB transmission and corresponding PUSCH/PUCCH and PUCCH/PUCCH
decoupling (or simultaneous transmission of different channels) may
also be applied in a different manner from that of the LTE system.
In consideration of these facts, a method of transmitting an SRS of
each individual antenna, which is different from the conventional
SRS transmission method, may be defined in the LTE-A system.
[0065] The present invention suggests a method of transmitting an
SRS for the purpose of channel sounding for performing status
information related measurement of channel(s) configured for uplink
transmission in a situation in which an uplink transmission entity
(i.e., a UE or a relay node) in the LTE-A system can perform uplink
transmission to a plurality of antennas while having a plurality of
transmission antennas and a plurality of RF power amplifier chains.
Suggestions of the present invention can be applied to any mobile
communication system in which uplink transmission is simultaneously
performed through each individual antenna through a plurality of RF
power/signal amplifiers and a plurality of transmission antennas
although the present invention has been described with reference to
an LTE-A system throughout this specification.
Embodiment 1
[0066] Method of multiplexing individual SRSs that are generated in
units of transmission antennas (when precoding is not applied to
SRS) or in units of transmission layers (when precoding is applied
to SRS) in a multi-antenna situation.
[0067] {Technology Associated with Allocation of Parts Associated
with SRS Resource Allocation in LTE}
[0068] The following is a summary of information items that are
associated with SRS transmission resource allocation to an
arbitrary UE in the conventional technology described above.
[0069] Transmission Comb k.sub.TC
[0070] k.sub.TC is a parameter used to derive a frequency region
start point of an SRS. One of 0 and 1 is used as an offset value
associated with "transmission comb". This parameter is defined as a
UE-specific RRC parameter and is indicated through UE-specific RRC
signaling. The definition of k.sub.TC is described in section
5.5.3.2 of the 3GPP Technical Specification (TS) 36.211.
[0071] Starting Physical Resource Block Allocation n.sub.RRC
[0072] n.sub.RRC is a UE-specific RRC parameter indicating the
frequency domain position of an SRS and is indicated through
UE-specific RRC signaling. The definition of n.sub.RRC is described
in section 5.5.3.2 of the 3GPP TS 36.211.
[0073] SRS Transmission Duration: Single or Indefinite (Until
Impossible)
[0074] This information is defined as a UE-specific RRC parameter
and is transmitted through UE-specific RRS signaling. In the case
where this parameter is set to "single", an SRS is transmitted only
once and, in the case where this parameter is set to "indefinite",
an SRS continues to be transmitted according to the set
configuration unless in a SRS transmission disabled situation or
unless corresponding signaling is received.
[0075] SRS Configuration Index I.sub.SRS for SRS Periodicity and
SRS Subframe Offset T.sub.offset
[0076] These information items are defined as UE-specific RRC
parameters and are transmitted through UE-specific RRC signaling.
Specifically, these parameters are information indicating the
transmission period of an SRS and an arbitrary subframe offset.
These information items are configured for TDD as shown in Table 5
and are configured for FDD as shown in Table 6. These parameters
are described in section 8.2 of the 3GPP TS 36.211.
[0077] SRS Bandwidth B.sub.SRS
[0078] This information is defined as a UE-specific RRC parameter
and is transmitted through UE-specific RRS signaling. As index
information used to define an SRS bandwidth, this parameter is
specified as one of 0, 1, 2, and 3. This parameter is used for
physical resource mapping as described in section 5.5.3.2 of the
3GPP Technical Specification (TS) 36.211 in the conventional
technology described above.
[0079] Frequency Hopping Bandwidth b.sub.hop
[0080] This information is defined as a UE-specific RRC parameter
and is transmitted through UE-specific RRS signaling. As index
information used to configure frequency hopping of an SRS, this
parameter is specified as one of 0, 1, 2, and 3. This parameter is
used for physical resource mapping as described in section 5.5.3.2
of the 3GPP Technical Specification (TS) 36.211 in the conventional
technology described above.
[0081] Cyclic Shift n.sub.SRS.sup.cs
[0082] This parameter is defined as a UE-specific RRC parameter and
is transmitted through UE-specific RRS signaling. As index
information of cyclic shift of a sequence used to generate an SRS
sequence, this cyclic shift parameter is used as orthogonal
resources in code multiplexing of SRSs for a number of UEs. This
parameter is used to generate an SRS code sequence as described in
section 5.5.3.2 of the 3GPP Technical Specification (TS) 36.211 in
the conventional technology described above.
[0083] Base Sequence Index
[0084] This information characterizes an SRS sequence together with
the cyclic shift when generating an SRS sequence. This information
is derived from a base sequence index of a PUCCH.
[0085] In the LTE system, physical resource mapping and resource
allocation for SRSs of individual UEs are performed based on the
parameters described above. The most important thing, which should
be taken into consideration when designing physical resource
mapping and resource allocation for uplink SRS transmission in the
LTE-A system, is that the LTE-A UE performs uplink transmission
using a plurality of transmission antennas at an arbitrary time
using RF chains and a plurality of power amplifiers while the LTE
UE performs uplink transmission through a single transmission
antenna at an arbitrary time using a single power amplifier. The
following are a summary of important design considerations in main
suggestions of the present invention, focusing upon this fact.
[0086] Compared to a conventional LTE UE, an arbitrary LTE-A UE is
likely to increase the frequency of attempts to perform SRS
transmission for channel sounding for all (physical) antennas of
the UE over a full system band. Therefore, delay may occur in
association with full band channel sounding for all uplink
(physical) antennas and a different delay condition may be applied
when SRS transmission of each layer or each individual antenna is
applied. This may impose limitation to acquisition of optimal
throughput gain when Doppler frequencies are present in association
with channel-dependent scheduling of an eNode B. [0087] In the case
where the LTE-A inherits an LTE scheme in which SRS transmission
symbols are defined according to a TDM scheme in which an SRS is
transmitted in a partial time region of an arbitrary subframe for
the purpose of channel sounding, symbols carrying a PUSCH or a
PUCCH and a symbol(s) carrying an SRS may be discriminated from
each other in a subframe. In this situation, an SRS may be
transmitted using a different number of antennas from the number of
transmission antennas through which a PUSCH or a PUCCH is
transmitted. In this case, a power pooling situation in which power
of a series of transmission antennas which are turned off is
distributed to a transmission antenna(s) that is turned on may
occur when it is possible to turn some transmission antennas on or
off at boundaries between PUSCH/PUCCH transmission symbols and SRS
transmission symbols. It takes time to perform such on/off
switching of power and/or signal amplifiers. To cope with this
situation, it is possible to define a series of guard times using a
series of time sample regions at the last time sample interval of
symbols prior to symbol (e.g., OFDM or SC-FDMA symbol) boundaries
between an SRS transmission symbol(s) and PUSCH or PUCCH
transmission symbols in a subframe (or in a symbol interval) or to
define a series of guard times using a series of time sample
regions at start portions of symbols after the boundaries depending
on the importance of the symbols. In the latter case, there may be
no need to define a separate guard time if a time sample region of
the guard time is defined in a cyclic shift region. However, this
scheme may cause overall throughput degradation. Therefore, as a
different scheme, it is possible to consider an SRS reception
multiplexing allocation scheme in which the number of transmission
antennas used for SRS transmission on an arbitrary LTE-A UE is set
to be as equal to the number of transmission antennas used for
PUSCH or PUCCH transmission in a different symbol interval as
possible without defining such guard times. This can be taken into
account as one important consideration in some suggestions of SRS
transmission resource allocation or multiplexing schemes according
to the present invention. [0088] One of the important
considerations when a receiver of an eNode B/cell performs uplink
channel measurement using an SRS in the case where a UE transmits
an SRS with suggested (or limited) UE transmission power is a
transmission Power Spectral Density (PSD) level in a frequency
region for an SRS transmission signal. Settings associated with
allocation of power for individual SRS transmission while taking
into consideration output power of an arbitrary symbol when
performing SRS transmission resource allocation include setting of
an SRS transmission band and setting of the degree of multiplexing
in which Code Division Multiplexing (CDM) and/or Frequency Division
Multiplexing (FDM) is implemented in an arbitrary frequency
resource region. In addition, another consideration that needs to
be made on an LTE-A UE is the number of uplink transmission
antennas that are simultaneously used. That is, as the total number
of SRS transmissions required in a cell increases as an extended
SRS transmission procedure is required compared to the conventional
SRS transmission in a situation in which an LTE-A UE supports
transmission through multiple antennas at an arbitrary transmission
time, there is a need to provide methods for providing a coverage
in association with SRSs similar to the coverage of the LTE system
and multiplexing and power allocation methods for supporting
reliable measurement of individual SRS transmission. Another
important consideration that should be taken into account is
whether or not an LTE-A UE can perform antenna power pooling when
performing multiple antenna transmission as described above.
[0089] The present invention suggests basic SRS multiplexing and
resource allocation methods for supporting the important
considerations in SRS design of the LTE-A described above.
Embodiment 1
Physical Resource Multiplexing for an SRS in an SRS Transmission
Subframe
[0090] In the case where another series of PUSCHs or PUCCHs is
transmitted in a subframe including an SRS transmission symbol in
an LTE-A system that supports multiple antenna transmission based
on the configuration of RF chains and multiple power amplifiers,
SRS transmission associated with layers (or streams) or physical or
logical antennas (or antenna ports) that are used for PUSCHs or
PUCCHs is performed through SRS transmission symbol(s) allocated to
a subframe such as the channels (i.e., the PUSCHs or PUCCHs). As an
SRS multiplexing method for supporting this SRS transmission, it is
possible to consider CDM, FDM, or CDM/FDM in an SRS transmission
symbol in an arbitrary subframe.
[0091] A factor for determining the basic multiplexing capacity in
CDM is the number of available cyclic shifts in an SRS sequence.
The number of available cyclic shifts may be determined based on a
relation between the length of a Cyclic Prefix (CP) interval of a
transport symbol (for example, an OFDM symbol or an SC-FDMA symbol)
and a delay spread value of the channel. In one example, the number
of available cyclic shifts may be explicitly configured as an RRC
parameter in a higher layer (i.e., the RRC layer) for all or part
of the cyclic shifts that are required for SRS transmission in an
arbitrary LTE-A UE and then may be signaled through UE-specific RRC
signaling. For some cyclic shifts, the number of available cyclic
shifts may be implicitly configured without explicit signaling. As
circumstances require, a base sequence index, which is referred to
as a root index, in an SRS sequence may also be a factor for
determining the multiplexing capacity together with the cyclic
shift. This scheme may be selectively applied depending on the
transmission mode of the UE or the channel environment. The
indication of the scheme may be implicitly or indirectly set
through a series of other signaling information. It is also
possible to define an explicit signaling parameter for indicating
the scheme.
[0092] FIG. 7 illustrates exemplary CDM for the case where an SRS
transmission symbol is the last of the transmission symbols of a
subframe in which an arbitrary LTE-A UE transmits an SRS. Although
FIG. 7 illustrates a situation in which SRSs of an LTE-A UE which
are multiplexed in a CDM manner are transmitted with a limited SRS
transmission band, the SRS transmission band may have a various
size including the full system band.
[0093] As a specific example, it is preferable that CDM be applied
to environments associated with UL coordinated multiple point
(CoMP) transmission and reception and UL/DL CoMP and associated
with LTE-A UEs rather than power-limited environments from the
viewpoint of UE transmission power through power control due to
high geometry. Indication of cyclic shifts of the degree of
application of code division (and indication of base sequence
indices associated with the total or partial number of cyclic
shifts requiring the base sequence indices) may be additionally
defined explicitly as an SRS related RRC parameter in association
with application of CDM or CDM/FDM for SRSs that are to be
transmitted by an arbitrary UE that performs multiple antenna
transmission using multiple power amplifiers and/or RF chains.
Here, examples of the degree of application of code division
include a value associated with the number of code resource units
to be used for transmission. In addition, the number of code
resources that are used according to a UE MIMO transmission mode
may be defined as a preset value. Alternatively, the number of code
resources may be defined as an explicit RRC parameter and cyclic
shift indices of the individual code resources (or base sequence
indices in addition to the cyclic shift indices) and the remaining
values may be implicitly specified using a rule or a series of
offsets using one explicitly specified value.
[0094] As one factor for determining the degree of multiplexing in
an arbitrary SRS transmission symbol when applying the FDM scheme,
it is possible to consider an interval between each subcarrier used
for transmission in an arbitrary frequency region, i.e., both a
discrete comb mapping ratio (which can also be referred to as a
comb division ratio) and a unit SRS transmission band allocated to
an arbitrary UE. For example, in the LTE, the discrete comb mapping
ratio is set to 2 so as to be used for discriminating resources
between full-band soundings and sub-band soundings or for
discriminating resource allocation between even subcarrier indices
and odd subcarrier indices. The SRS transmission band has also been
defined as respective values of various cases for each system band
in a table. In the LTE-A, it is also possible to apply an increased
discrete comb mapping ratio compared to the LTE when taking into
consideration the multiple antenna transmission environment. For
example, as 2*(the number of transmission antennas) or 2*(the
number of transmission layers), the comb division ratio may have a
value of 2 or 4 in the case of 2Tx and may have a value of 2, 4, 6,
or 8 in the case of 4Tx. In the case where the comb division ratio
is increased in this manner or is 2, all or partial comb frequency
offsets may be used multiplexing of an SRS sequence of each
antenna. In association with the SRS transmission band, power of
each antenna of an arbitrary UE that supports multiple antenna
transmission may be reduced by an amount corresponding to the
number of the antennas compared to the single antenna or antenna
selection case. Therefore, in order to secure the coverage of SRS
transmission of each individual antenna (or individual layer) or to
support reliable measurement of the same, it is possible to
additionally define a smaller SRS transmission band in an arbitrary
system band than to the case of an LTE UE that performs single
antenna transmission. That is, it is possible to define smaller SRS
transmission bands in an arbitrary system band than the case where
SRS transmission of the conventional LTE is possible and to add
candidates for the SRS transmission band with higher granularity
than the same case. As a scheme that can be applied independent of
this scheme or in addition to this scheme, it is possible to
specify candidates to be applied in the form of a subset of the
entire set of SRS transmission related parameters (including the
transmission band) configured through RRC parameters for the case
of multiple antenna transmission. The candidates may be specified
through designation of an uplink transmission mode (for example,
UE-specific RRC signaling or L1/L2 control signaling). It is also
possible to define and signal an additional RRC parameter. Through
these schemes, it is possible to maintain a subcarrier power
spectral density (PSD) level that is required from the viewpoint of
measurement quality or the coverage in association with SRS
transmission for each antenna or layer. One method, which can be
applied in parallel with or independent of this scheme, increases
the discrete comb mapping ratio for UEs, each having a plurality of
transmission antennas or for all UEs in a cell (eNode B). In this
method, it is possible to relatively increase the power spectral
density (PSD) of physical resources (i.e., subcarriers or resource
elements (REs)) by reducing, in the frequency domain, the density
of physical resources to which power allocated to an arbitrary
antenna is allocated in a given SRS transmission band. In addition,
it is possible to implement a series of FDM multiplexing by mapping
SRS sequences transmitted through different (physical) transmission
antennas to comb frequency offsets (i.e., unit comb patterns) that
are obtained through the increase of the discrete comb mapping
ratio. Channel measurement performance may be reduced as the
discrete comb mapping ratio increases. In order to prevent the
reduction of channel measurement performance, the discrete comb
mapping ratio may be set to 3 in a situation in which the number of
UE (physical) transmission antennas is 2 or 4. In this case, one
comb pattern may be allocated for a specified range of all or wider
channel soundings and, in the case where the number of transmission
antennas is 2, respective SRS sequences of the antennas may be
differently mapped to 2 remaining comb patterns. On the other hand,
in the case where the number of UE transmission antennas is 4, the
transmission antennas may be grouped to 2 antenna groups, each
including 2 antennas, and the 2 antenna groups may be differently
mapped to the 2 remaining comb patterns. In addition, it is
possible to achieve multiplexing by allocating different frequency
bands or code resources (i.e., cyclic shifts) to 2 transmission
antennas in the antenna group.
[0095] FIG. 8 illustrates exemplary FDM for the case where an SRS
transmission symbol is the last of the transmission symbols of a
subframe in which an arbitrary LTE-A UE transmits an SRS. Although
FIG. 8 illustrates a situation in which SRSs of an LTE-A UE which
are multiplexed in a FDM manner are transmitted with a limited SRS
transmission band, the SRS transmission band may have a various
size including the full system band. Here, it is to be noted that
representations of SRS transmission bands, which are shown as bands
discriminated from each other, may also be applied to the FDM
scheme for discrete physical comb patterns described in the present
invention.
[0096] It is preferable that the FDM or CDM/FDM scheme suggested in
the present invention be applied to a UE which is in a
non-power-limited situation. For example, it is preferable that the
SRS FDM or CDM/FDM scheme enable non-contiguous Resource Block (RB)
allocation through clustered Discrete Fourier
Transform-spread-Orthogonal Frequency Division Multiple Access
(DFT-s-OFDMA) in uplink or that the SRS FDM or CDM/FDM scheme be
applied to a UE that can use component carrier (CC). To accomplish
this, in the case where an indication of the application of the
clustered DFT-s-OFDMA is explicitly or implicitly provided from an
eNode B or an indication of the application of uplink multiple
component subcarriers is explicitly or implicitly provided from an
eNode B, it is possible to apply a multiplexing scheme in the form
of applying FDM or CDM/FDM when multiplexing SRSs based on
signaling of the indication. It is possible to define a parameter
indicating that the SRS configuration is to be changed depending on
the uplink transmission mode of the UE or depending on whether or
not power of the UE is limited and to provide the indication
through UE-specific RRC signaling or L1/L2 control signaling.
[0097] When the CDM/FDM scheme is applied, there is a need to take
into consideration correlations between parameters for determining
multiplexing granularity and capacity of CDM and parameters for
determining multiplexing granularity and capacity of FDM rather
than to take into consideration a simple combination of the two
multiplexing schemes. For example, setting of the discrete comb
mapping ratio for determining the frequency component density and
the multiplexing level of an SRS signal in the FDM scheme has an
influence upon determining the number of available cyclic shifts
associated with the CDM capacity. Specifically, increasing the
discrete comb mapping ratio value has an effect of decreasing the
number of available cyclic shifts in the case of CDM. In addition,
in the case where the base sequence index is set as a code resource
region of CDM, the size of available base sequence index pools is
determined in proportion to the size of an SRS transmission band of
FDM. In the case where CDM/FDM is applied for SRS transmission
multiplexing of LTE-A UEs that supports multiple antenna
transmission using multiple power amplifiers and/or RF chains
taking into consideration this fact, it is possible to define
detailed schemes of CDM/FDM not only basically based on the
efficiency of channel sounding but also based on factors such as
signaling overhead reduction and backward compatibility. For
example, in the case where PUSCH or PUCCH multiplexing is taken
into consideration while achieving a design minimizing additional
indication overhead of used cyclic shifts or decreasing the
capacity of cyclic shifts, it is possible to configure SRS resource
allocation/multiplexing as shown in FIG. 9 under the assumption
that all SRSs are transmitted within an SRS transmission symbol
according to the MIMO transmission mode or according to antennas
configured for the UE.
[0098] FIG. 9 illustrates an example of CDM/FDM in an uplink
subframe of a UE (for example, an LTE-A UE) that transmits an SRS.
Although FIG. 9 illustrates a situation in which SRSs of an LTE-A
UE which are multiplexed in a CDM/FDM manner are transmitted with a
limited SRS transmission band, the SRS transmission band may have a
various size including the full system band. The following is a
more detailed description of the example of FIG. 9. When an
arbitrary LTE-A UE has M SRSs (M>0) that are to be transmitted
in an arbitrary subframe, it is possible to use, as a method of
allocating M SRS resources for SRS transmission, a method of
allocating the number of cyclic shifts and indices to be used
respectively for N used SRS transmission bands in order to optimize
resource utilization. Unlike this method, it is possible to use a
method in which the number and index information of P available
cyclic shift resources (optionally together with a base sequence as
a resource allocation element) and the number and position index
information of N SRS transmission bands as illustrated in FIG. 9 in
order to simplify signaling overhead or configuration. Here, it may
be considered that N and P are specified such that N*P is equal to
or greater than M. As a method of allocating respective resources
for M SRSs, it is possible to apply a band-first assignment scheme
for the SRS transmission band and it is also possible to apply a
code-first assignment scheme for the cyclic shift.
[0099] In addition to the CDM, FDM, or CDM/FDM scheme described
above, it is possible to apply, as other candidates, a series of
SRS resource multiplexing and configurations such as CDM/TDM,
FDM/TDM, and CDM/FDM/TDM to arbitrary LTE-A UEs. The following is a
description of a method of changing the configuration of SRS,
focusing upon the LTE-A. In the case of LTE, when SRS transmission
is enabled, an SRS continues to be transmitted until a transmission
termination event occurs (i.e., until SRS transmission is disabled)
and an RRC parameter for releasing SRS transmission has not been
defined. However, it can be considered that an SRS transmission
release parameter is additionally set for an LTE-A UE. It is also
possible to set the number of transmissions of an SRS or an SRS
transmission time according to period configuration information
after SRS transmission is enabled through UE-specific RRC
signaling. It can also be considered that SRS transmission
configuration information is transmitted using L1/L2 control
signaling (for example, a PDCCH or MAC messaging). For example, it
is possible to trigger SRS transmission through L1/L2 signaling. In
this case, in order to efficiently reduce signaling overhead, L1/L2
control signaling carrying SRS transmission configuration
information may be event-triggered or may have periodic
characteristics. It is possible to employ (but not limited to) an
example in which the number of valid transmissions, a transmission
period, period configuration information, and the like are signaled
while being included in L1/L2 control information. Here, periodic
SRS transmission may be performed every period using a
corresponding subframe and may be performed using consecutive S
subframes, starting from the time of the transmission period. It is
also possible to employ a periodic SRS transmission method in which
a series of offsets are defined and an SRS is transmitted at
intervals corresponding to the offsets. The periodic configuration
information includes a transmission start point, a period, subframe
group allocation information (in the case of periodic transmission
in units of subframe groups), and the like. There is no need to
separately define information regarding the transmission start time
when the method complies with a general grant-to-uplink timing
relation. In the case where SRS transmission is configured through
UE-specific RRC signaling, all or part of the L1/L2 control
information defined according to the present invention as described
above may be defined as an RRC parameter. In addition, in the case
where SRS transmission is enabled or triggered through L1/L2
control signaling, it is possible to additionally define an SRS
transmission release parameter (or message) in L1/L2 control
signaling.
[0100] In the following, as a more detailed scheme of the method
for multiplexing physical resources for an SRS in an arbitrary SRS
transmission subframe described above in the embodiment 1, the
present invention suggests a method for applying an FDM scheme
between antennas and a CDM scheme between UEs.
[0101] Specifically, the present invention suggests an FDM scheme
applied between antennas and a CDM scheme applied between UEs which
reuse the method applied to the conventional LTE sounding channel
and maintains backward compatibility as much as possible.
[0102] i) It is possible to consider a method in which the discrete
comb mapping ratio (or repetition factor (RPF)) described in the
embodiment 1 is increased in proportion to the number of antennas
(or the number of layers or the number of ranks).
[0103] Option 1) RPF=2 used in LTE may be used without change and,
in addition, the RPF for multiple antennas in the LTE-A system
which takes into consideration multiple antennas may be increased
in proportion to the number of antennas (or the number of layers or
the number of ranks). In this case, the length (or duration)
M.sub.sc,b.sup.RS of an SRS sequence may be defined as in the
following Expression 8.
M.sub.sc,b.sup.RS=m.sub.SRS,bN.sub.sc.sup.RB/{2.times.L}
[Expression 8]
[0104] Here, m.sub.SRS,b is a value given for each uplink band
N.sub.RB.sup.UL and is illustrated in Tables 1 to 4. L denotes the
number of transmission antennas (or layers or ranks) for an
SRS.
[0105] When the Number of Transmission Antennas (or Layers or
Ranks) for SRS is 4
[0106] RPF=2 may be applied to the conventional LTE and RPF=4 may
be additionally defined for 4 transmission antennas (or layers or
ranks) in the case of LTE-A.
[0107] In the conventional LTE, the minimum transmission unit of an
SRS for a single antenna is 4 RBs. Accordingly, 6 REs (=4RB*12
subcarriers/(2*4)) are allocated to each antenna (or each layer or
each rank) in the case where distributed FDM is used for
orthogonality between antennas and 4 transmission antennas (or 4
layers or 4 ranks) used in the LTE-A are used, taking into
consideration the minimum RB allocation. Thus, a 6-length sequence
for an SRS is required in the LTE-A. In this case, a CAZAC sequence
(a ZC sequence or a sequence generated based on a truncation or
extension scheme), a DFT based sequence, a PN sequence, or another
type of orthogonal sequence may be used as the 6-length sequence.
As a 6-length sequence, a 6-length computer-generated sequence may
be created and used as it has been suggested and used as an RS
sequence for 1RB (12-length) and 2RB (24-length) in the
conventional LTE.
[0108] In the case where a new length-6 sequence is not defined and
only the smallest 1RB-long (length-12) sequence among sequences
currently used in the LTE is used, it is possible to consider a
method of making a definition such that sounding band allocation of
8 RBs or more is possible using a parameter defined for sounding
channel allocation in the LTE for the case where transmission of 4
Tx antennas (or 4 layers or 4 ranks) is used. For example, it is
possible to consider a method of making a definition such that
sounding band allocation of 8 RBs or more is possible using a 3-bit
SRS band configuration (srs-BandwidthConfig, C.sub.SRS={0, 1, 2, 3,
4, 5, 6, 7}) that is signaled by a higher layer as a cell-specific
parameter and a 2-bit SRS band (srs-BandwidthConfig, B.sub.SRS={0,
1, 2, 3}) that is signaled by a higher layer as a UE-specific
parameter from among the parameters defined in the LTE.
[0109] In addition, it is possible to perform multiplexing for 4
transmission antennas (or layers or ranks) using an FDM scheme for
up to 2 transmission antennas (layers or ranks) and using a CDM
scheme, which allocates cyclic shift indices different from the
indices 1 and 2, for the transmission antennas (layers or ranks) 3
and 4.
[0110] As another method, it is possible to consider a method in
which a sounding channel is transmitted in a TDM manner for each 2
transmission antennas (or layers or ranks) through antenna
switching for multiplexing SRSs for the 4 transmission antennas (or
layers or ranks). In this case, there may be no need to design a
small-length sequence due to an increase in the number of antennas.
In the case where uplink transmission is performed using 4 power
amplifiers and 4 transmission antennas, it is possible to perform
multiplexing of SRSs for 4 transmission antennas (or layers or
ranks) by enabling power-on/off through power control signaling,
higher layer signaling, control signaling, or the like for power
amplifiers of antennas that are not used when applying a 1 or 2
antenna switching scheme.
[0111] When the Number of Transmission Antennas (or Layers or
Ranks) for SRS is 2
[0112] RPF=2 may be applied to the conventional LTE and RPF=4 may
be additionally defined for 4 transmission antennas (or layers or
ranks) in the case of LTE-A.
[0113] The minimum unit for transmitting an SRS for a single
antenna used in the conventional LTE described in the related art
is 4 RBs. Accordingly, 12 REs (=4RB*12 subcarriers/(2*2)) are
allocated to each antenna (or each layer or each rank) when
distributed FDM is used for orthogonality between antennas in the
case where 2 transmission antennas (or layers or ranks) used in the
LTE-A are used, taking into consideration the minimum RB
allocation. In this case, CDM may be performed for UEs, which use
the same band, using a 1-RB computer-generated sequence defined in
the LTE.
[0114] As another method, it is possible to consider a method in
which a sounding channel is transmitted in a TDM manner for each
transmission antennas (or layers or ranks) through antenna
switching for multiplexing SRSs for 2 transmission antennas (or
layers or ranks). In the case where uplink transmission is
performed using a single power amplifier and 2 transmission
antennas, it is possible to perform multiplexing of SRSs for 2
transmission antennas (or layers or ranks) by enabling power-on/off
through power control signaling, higher layer signaling, control
signaling, or the like for power amplifiers of antennas that are
not used when applying a 1-antenna switching scheme.
[0115] Option 2) The same RPF as that of the LTE may be maintained
when the number of antennas (or layers or ranks) for uplink
sounding transmission used in the LTE-A system is 1 and the RPF for
multiple antennas in the LTE-A system may be increased in
proportion to the number of antennas (or the number of layers or
the number of ranks) when the number of antennas (or layers or
ranks) for uplink sounding transmission used in the LTE-A system is
2 or more. In this case, the length (or duration) M.sub.sc,b.sup.RS
of an SRS sequence may be defined as in the following Expression
9.
M.sub.sc,b.sup.RS=m.sub.SRS,bN.sub.sc.sup.RB/2{floor(L/4)+1}
[Expression 9]
[0116] Here, m.sub.SRS,b is a value given for each uplink band
N.sub.RB.sup.UL and is illustrated in Tables 1 to 4. L denotes the
number of transmission antennas (or layers or ranks) for an
SRS.
[0117] When the Number of Transmission Antennas (or Layers or
Ranks) for SRS is 4
[0118] RPF=2 may be applied to the conventional LTE and RPF=4 may
be additionally defined for 4 transmission antennas (or layers or
ranks) in the case of LTE-A.
[0119] The minimum unit for transmitting an SRS for a single
antenna used in the conventional LTE described in the related art
is 4 RBs. Accordingly, 12 REs (=4RB*12 subcarriers/(2*2)) are
allocated to each antenna (or each layer or each rank) in the case
where distributed FDM is used for orthogonality between antennas
and 4 transmission antennas (or 4 layers or 4 ranks) used in the
LTE-A are used, taking into consideration the minimum RB
allocation. In this case, CDM may be performed for UEs, which use
the same band, using a 1-RB computer-generated sequence defined in
the LTE.
[0120] In addition, it is possible to perform multiplexing for 4
transmission antennas (or layers or ranks) using an FDM scheme for
up to 2 transmission antennas (layers or ranks) and using a CDM
scheme, which allocates cyclic shift indices different from the
indices 1 and 2, for the transmission antennas (layers or ranks) 3
and 4.
[0121] As another method, it is possible to consider a method in
which a sounding channel is transmitted in a TDM manner for each 2
transmission antennas (or layers or ranks) through antenna
switching for multiplexing SRSs for the 4 transmission antennas (or
layers or ranks). In this case, there may be no need to design a
small-length sequence due to an increase in the number of antennas.
In the case where uplink transmission is performed using 4 power
amplifiers and 4 transmission antennas, it is possible to perform
multiplexing of SRSs for 4 transmission antennas (or layers or
ranks) by enabling power-on/off through power control signaling,
higher layer signaling, control signaling, or the like for power
amplifiers of antennas that are not used when applying a 1 or 2
antenna switching scheme.
[0122] When the Number of Transmission Antennas (or Layers or
Ranks) for SRS is 2
[0123] RPF=2 may be applied to the conventional LTE and RPF=1 may
be additionally defined for 4 transmission antennas (or layers or
ranks) in the case of LTE-A.
[0124] The minimum unit for transmitting an SRS for a single
antenna used in the conventional LTE described in the related art
is 4 RBs. Accordingly, 24 REs (=4RB*12 subcarriers/(2*1)) are
allocated to each antenna (or each layer or each rank) when
distributed FDM is used for orthogonality between antennas in the
case where 2 transmission antennas (or layers or ranks) used in the
LTE-A are used, taking into consideration the minimum RB
allocation. In this case, CDM may be performed for UEs, which use
the same band, using a 2-RB computer-generated sequence defined in
the LTE.
[0125] As another method, it is possible to consider a method in
which a sounding channel is transmitted in a TDM manner for each
transmission antennas (or layers or ranks) through antenna
switching for multiplexing SRSs for 2 transmission antennas (or
layers or ranks). In the case where uplink transmission is
performed using a single power amplifier and 2 transmission
antennas, it is possible to perform multiplexing of SRSs for 2
transmission antennas (or layers or ranks) by enabling power-on/off
through power control signaling, higher layer signaling, control
signaling, or the like for power amplifiers of antennas that are
not used when applying a 1-antenna switching scheme.
[0126] The following is a more detailed description of additional
aspects of the FDM scheme applied between antennas as a method for
maintaining backward compatibility of the SRS transmission scheme
as much as possible.
[0127] It is possible to consider a method in which an SRS is
transmitted through each antenna while maintaining a band allocated
to each antenna in a disjoint manner by uniformly distributing the
full system band such that a band allocated for each transmission
is proportional to the number of antennas to be used for the
transmission.
[0128] Power-Limited Case
[0129] In the power-limited case, there is a need to perform
transmission so as to maintain a low Cubic Metric (CM) for an SRS
transmitted through each antenna. Accordingly, it is possible to
use a method of performing transmission in a disjoint manner
between antennas. FIGS. 10 and 11 illustrate a case of 2
transmission antennas (or layers or ranks) and FIGS. 12 and 13
illustrate a case of 4 transmission antennas. Referring to FIGS. 10
to 13, SRS bands for different antennas are allocated in a disjoint
manner such that SRS bands of the antennas are at intervals of a
spacing corresponding to the system band/(the number of
transmission antennas (or layers or ranks)).
[0130] Non-power-limited Case (e.g., when clustered DFTs-OFDM,
multiple component carriers, or UL ComP is used)
[0131] In the non-power-limited situation, there is no need to keep
the limitation of having to maintain the same CM as a single
carrier. Accordingly, it is possible to transmit an SRS through
different sounding bands in one symbol. In this case, it is
possible to reduce time resources required to sound the entire
uplink system band.
[0132] Unlike the LTE, the LTE-A supports non-contiguous allocation
using an uplink transmission scheme which is based on clustered
DFTs-OFDM. In the case of a sounding channel, non-power-limited UEs
can transmit a sounding channel using the clustered DFTs-OFDM
scheme. Accordingly, it is possible to allocate multiple resources
to each antenna. However, assuming that the number of frequency
start indices for SRS allocation used in the LTE is maintained at 1
for backward compatibility, it is possible to use a method in which
multiple SRSs are transmitted through each antenna while
maintaining a band allocated to each antenna in a disjoint manner
by applying an RPF equal to the number of antennas (or layers or
ranks) between each antenna and uniformly distributing the full
system band such that a band allocated for each transmission is
proportional to the number of antennas to be used for the
transmission. It is also possible to use a method in which multiple
resources, the amount of which depends on the number of clusters,
are allocated for SRS transmission.
[0133] The methods of option 1) and option 2) of this embodiment
described above may be applied to the method of applying an RPF
between each antenna.
[0134] It is preferable that allocation be performed such that the
CM value for a sequence allocated to an SRS that is transmitted
using multiple resources through each antenna is not significantly
increased compared to the single carrier CM of the LTE. That is,
the CM value of transmission of an SRS through multiple resources
is significantly increased in the case where the same cyclic shift
as the same base sequence is used for each cluster. Accordingly, it
is possible to consider a method in which different cyclic shift
values are allocated to multiple resources or different base
sequences are allocated to multiple resources. As a method of
allocating a cyclic shift index to each cluster, it is possible to
consider a method in which a resource corresponding to each cluster
is allocated using a cyclic shift index that has been defined to be
signaled through higher layer signaling in the LTE.
Embodiment 2
Definition of a Plurality of SRS Transmission Symbols in an SRS
Transmission Subframe
[0135] The LTE-A supports multiple antennas or multilayer
transmission based on the multiple antennas by applying multiple
power amplifiers/RF chains in uplink. Independent of or in parallel
with such multi-antenna transmission, the LTE-A enables access to a
plurality of UL components carriers and enables communication with
a plurality of points through UL CoMP. Accordingly, when
configuring a multi-antenna configuration, it is possible to
configure a plurality of SRS transmissions in order to guarantee
multiplexing capacity, coverage, and measurement reliability in
channel sounding for each individual antenna (or layer), for each
UL component carrier, or for each UL CoMP-based transmission point.
In order to accomplish this, the present invention suggests that a
plurality of SRS transmission symbols be defined in an uplink
subframe of a UE (for example, an LTE-A UE). For ease of
explanation, a description will now be given of two configuration
methods associated with depending on positions in a subframe when
the number of SRS transmission symbols is defined to be 2.
[0136] FIG. 14 illustrates a first method for specifying two SRS
transmission symbols in an uplink subframe according to an
embodiment of the present invention. As shown in FIG. 14, a
position of an SRS transmission symbol that is additionally defined
compared to the conventional LTE may be defined to be located at a
last transmission symbol (for example, OFDM or SC-FDMA symbol) of a
first slot in a subframe that transmits an SRS of a corresponding
UE. To accomplish this, shortened PUCCH formats that have been used
when an SRS is transmitted through two slots in the conventional
LTE may be defined to be still used in the first slot according to
the present invention.
[0137] FIG. 15 illustrates a second method for specifying two SRS
transmission symbols in an uplink subframe according to an
embodiment of the present invention. As shown in FIG. 14, a
position of an SRS transmission symbol that is additionally defined
compared to the conventional LTE may be defined to be located at a
second last transmission symbol (for example, OFDM or SC-FDMA
symbol) of a second slot in a subframe that transmits an SRS of a
corresponding UE. This scheme has an advantage in that the
frequency of occurrences of power transition between an SRS
transmission symbol and a data transmission symbol is the same as
that when one SRS transmission symbol is defined in a subframe as
in the conventional LTE. To accomplish this scheme, there is a need
to additionally define a shortened PUCCH format in which 2 last
transmission symbols are punctured in an arbitrary slot based on
the conventional LTE standard. The method of transmitting control
information through a PUSCH of the conventional LTE uses rate
matching of data and maps Rank Information (RI) to physical
frequency resources of 4 transmission symbols in a subframe. For
example, in the case of a normal CP, the RI is mapped to second and
fifth transmission symbols in each slot of a subframe. In this
case, the position of the fifth transmission symbol of the second
slot to which the RI is mapped overlaps the position of the
additional SRS transmission symbol suggested in the present
invention. Accordingly, to apply this method, it is possible to
consider an RI transmission method which uses three transmission
symbols, excluding the transmission symbol that is defined as the
last symbol in the second slot, among the four transmission symbols
used for RI transmission. In addition, it is possible to consider a
method in which RI is mapped to physical resources, starting from
the first physical resource of the subframe, in a time-first manner
or in which RI is mapped in a reversed order, starting from the
last physical resource. In this case, the RI is mapped to
transmission symbols, excluding or avoiding the transmission symbol
to which an SRS is mapped, in a time-first manner. It is also
possible to consider a method in which the scheme of multiplexing
CQI and data defined in the conventional LTE is additionally
applied to RI such that RI is transmitted in a form of being
multiplexed with data. In this case, RI is mapped to physical
resources of a subframe in a time-first manner.
[0138] In the first and second suggested methods, it is possible to
reduce the burden of having to individually define and signal a
configuration parameter for an SRS transmission symbol for each
slot. In addition, in order to prevent the occurrence of transient
operation of a power amplifier (and/or signal amplifier) of each
individual antenna at boundaries between SRS transmission symbols
and data symbols, it is possible to apply a method in which M SRS
allocations required for a corresponding LTE-A UE are configured on
an individual symbol instead of being divided on a symbol by symbol
basis and the M SRS allocations are repeated in an SRS transmission
symbol defined for each slot such that power allocated to each of
the M SRSs is the sum of powers allocated to two SRS transmission
symbols. It is also possible to employ a configuration in which
individual SRS bands are set at different positions for each slot
while SRS resources are equally allocated to each slot in two SRS
transmission symbols as described above so that two uplink channel
soundings are achieved in an arbitrary uplink subframe. The scheme
in which the same SRS transmission bands are applied, the scheme in
which different SRS transmission bands are applied, the scheme in
which two SRS transmission symbols are used, and the scheme in
which one SRS transmission symbol is used may be selectively
applied individually or in combination depending on the situation
of the UE. Indication information for configuring an SRS may be
explicitly signaled using an additionally defined RRC parameter or
may be explicitly or implicitly applied using L1/L2 control
signaling or may be applied implicitly applied according to setting
information of the transmission mode or the state of the UE. The
transmission mode information may include information indicating
whether or not MIMO transmission is performed, information
indicating whether or not non-contiguous RB allocation based
transmission is performed, and the like.
[0139] As another method, it is possible to configure an overall
multiplexing scheme in which, for two SRS transmission symbols in
an arbitrary SRS transmission subframe, M SRSs that are to be
transmitted by an arbitrary LTE-A UE are transmitted so as to be
discriminated for each SRS transmission symbol by additionally
applying a TDM scheme to the embodiments of the CDM, FDM, and
CDM/FDM described in the present invention in order to reduce the
time required for channel sounding for the entire scheduling band.
Here, code resources of SRS bands and/or cyclic shifts applied to
the two SRS transmission symbols (optionally together with a base
sequence index) may be specified independently in each individual
SRS transmission symbol. Here, as an additional method, the SRS
transmission bands and the code resources may be intentionally
configured so as to be discriminated using different arbitrary
resource values. In consideration of signaling overhead of
SRS-related RRC parameters that need to be additionally defined to
accomplish this scheme, the SRS transmission bands and the code
resources applied to the two SRS transmission symbols may be
commonly allocated (for example, the SRS transmission bands and the
code resources may be configured equally in terms of RRC
parameters, control information, and code and frequency resource
allocation) and indication information used to discriminate
resource allocation of individual SRSs in the two SRS transmission
symbols may be additionally defined in control information in L1/L2
control signaling or in an RRC parameter.
Embodiment 3
Precoded SRS Configuration
[0140] It is possible to consider precoded SRS transmission as a
method for securely reducing the number of SRSs required for a
corresponding UE and for solving the problem of power amplifier
on/off for SRS transmission for LTE-A UEs that support multiple
antenna transmission through multiple power amplifiers/RF chains.
According to this embodiment, even in a situation in which a
plurality of UE transmission antennas is configured, it is possible
to define and use a single SRS resource in the case of rank-1 MIMO
transmission and to define and use a number of SRS resources equal
to a corresponding rank value in the case of higher rank MIMO
transmission when performing Uplink Multiple Input Multiple Output
(UL MIMO). Precoding matrixes used for SRS precoding may be applied
according to precoding matrix index (PMI) information specified in
the most recent uplink grant information. (Here, the same code book
as a code book defined for uplink data transmission is used as a
code book of PMI or Transmit Precoding Matrix Indication (TPMI) for
SRS transmission.) Unlike this method, it is possible to consider a
method in which PMI information for SRS transmission is separately
signaled through a series of L1/L2 control signaling including the
case of UL grant or UE-specific RRC signaling. In addition, it is
possible to configure PMIs applied to all of an SRS or a
DeModulation Reference Signal (DM-RS)/SRS as a code book of PMIs in
a different form from a conventional data transmission code book
for each layer (rank) number and to define signaling information
through UE-specific RRC signaling or L1/L2 control signaling
indicating a PMI to be applied from among the PMIs of the code
book. As another method, it is also possible to apply a method in
which, for uplink data using Transmit Diversity (TxD), one SRS
and/or DM-RS resource is allocated using the PMIs described above
in the same manner as in the case of rank-1 for all of an SRS, a
DM-RS, or an SRS/DM-RS and to transmit the corresponding RS based
on the allocated resource. Here, it is possible to apply a PMI(s)
from among PMIs for a single layer in a code book separately
defined for RS transmission or a data transmission code book as
described above. Taking into consideration the fact that TxD is
associated with open-loop transmission, it is possible to consider
a method in which the eNode B indicates a separate PMI to the UE
through UE-specific RRC signaling or L1/L2 control signaling.
Unlike this method, according to the open-loop characteristics, it
is also possible to apply a series of cycling, shifting, or
permutation schemes through a transmission symbol or a slot level
for a PMI used for a series of subsets or an entire set of single
layer PMIs in a different manner in the time domain or in the
frequency domain. When the operation range of TxD is taken into
consideration, the PMIs to be used may be selected and configured
taking into consideration the Cubit Metric/Peak to Average Power
Ratio (CM/PAPR) characteristics based on single antenna
transmission and may also be configured of PMIs of antenna
selection format in order to prevent beam formation.
[0141] The methods which apply precoding to an SRS (or DM-RS)
according to this embodiment, together with methods which do not
apply precoding, may be selectively applied to an arbitrary LTE-A
UE. Here, as a criterion for selective application, it is possible
to consider whether or not the UE is in a power-limited state, the
UL MIMO transmission mode (rank or TxD/precoding), and the like.
Detailed examples include a scheme in which a precoded SRS (or
DM-RS) is transmitted for the rank 1 which includes or does not
include TxD and a non-precoded SRS (or DM-RS) is transmitted for a
higher rank. In another method, a precoded SRS (or DM-RS) is
transmitted for the rank 1 and the rank 2 which include or do not
include TxD and a non-precoded SRS (or DM-RS) is transmitted for a
higher rank. As another detailed embodiment, it is possible to
consider a scheme in which, for a DM-RS, precoding is applied to
the rank 1 or to both the rank 1 and the rank 2 for data
transmission in a corresponding subframe and a scheme independent
from this scheme in which, for an SRS, precoding is performed with
a PMI based on the rank 1 only in a limited situation or regardless
of the channel state of the UE. As another method, it is also
consider a scheme in which orthogonal resources discriminated in
the spatial domain are defined with PMIs for an arbitrary scheme
among all types of SRS transmission resource allocation and
multiplexing schemes. In this case, a method in which SRSs are
precoded with a series of rank-2 PMIs in a code book for data
transmission or a different code book for SRS transmission may be
applied selectively depending on the situation of the power-limited
UE or may always be applied regardless of the channel condition of
the UE. The PMIs used in this case are PMIs that provide a single
antenna based CM/PAPR and it is possible to define control
information of L1/L2 control signaling or UE-specific signaling for
indicating a PMI to be used for SRS precoding. Unlike this method,
a series of schemes such as cycling, shifting, or permutation
schemes may be applied differently in the time domain or the
frequency domain through a slot level or a transmission symbol for
a PMI set that is applied in an open-loop manner based on an
arbitrary criterion according to the present invention. Here, the
PMI set may be defined as all PMIs or as a series of subsets.
Embodiment 4
SRS Transmission Method in UL Carrier Aggregation Situation
[0142] In the case where a cell eNode B allocates multiple uplink
component carriers to an arbitrary LTE-A UE, RRC parameters
regarding configuration information such as the time of
transmission and SRS resource allocation of each carrier among
individual UL component carriers in association with SRS
transmission may be acquired as independent control information of
each carrier through UE-specific RRC signaling and each independent
SRS transmission scheme may be implemented in each UL component
carrier. As a method for applying an association of inter-carrier
SRS resource allocation and a transmission scheme configuration, it
is possible to apply a method in which a corresponding offset value
between UL component carriers set at the transmission start point
are applied according to an explicit or implicit rule in order to
configure a subframe to be transmitted in units of component
carriers in a staggering manner while applying the same SRS
transmission period to each carrier in order to prevent an increase
in the CM/PAPR for uplink SRS transmission using multiple component
carriers.
Embodiment 5
SRS Transmission Method for Antenna Transmission Mode
[0143] The suggested methods for channel sounding according to the
configuration of a plurality of uplink transmission antennas
according to the present invention have been described mainly with
reference to the case where a signal is transmitted using all
(physical) transmission antennas (i.e., power is loaded to all
(physical) transmission antennas) in an uplink multiple antenna
transmission scheme that is applied to PUSCH or PUCCH transmission
symbols excluding SRS symbol(s) in an SRS transmission subframe.
However, there is a possibility that an antenna selection precoder
is defined on a code book and is applied to corresponding data
transmission symbols or an uplink transmission diversity mode of an
antenna selection or antenna group selection scheme of a
closed-loop mode (for example, a long-term or short-term mode) is
applied in the case of, for example, uplink precoding as the
technology is applied to the system. Basically, it is possible to
apply the multiple antenna channel sounding method suggested in the
present invention in the case where such transmission modes are
introduced. In addition, it is possible to apply methods for
minimizing the occurrence of turning on/off of a series of antenna
power amplifiers and/or signal amplifiers between data transmission
symbols and SRS transmission symbols when implementing detailed
operations and procedures of the multiple antenna channel sounding
method in a transmission mode having such characteristics. In the
following, the present invention suggests methods for applying
channel sounding in the case where only specific (physical)
antennas among all (physical) transmission antennas of the UE
participate in uplink signal transmission.
Embodiment 5-1
Channel Sounding when Antenna Turn-On/Off Precoder is Applied
[0144] In the case where a UE performs uplink transmission using
multiple antennas, antenna gain imbalance (AGI) may occur due to
hand gripping of the user. In this case, transmission signals that
are actually emitted from all or partial transmission antennas
undergo a lost of 6 dB or greater in terms of output power. When
the eNode B has determined that an AGI has occurred in a
transmission antenna signal of a UE by observing a signal (for
example, a DM-RS or an SRS) transmitted from the UE, the eNode B
may provide signaling to allow part of the transmission antennas to
turned off in order to prevent unnecessary power consumption of the
transmission antennas. On the other hand, there is a need for the
eNode B to provide signaling to allow some transmission antennas to
be turned on. To accomplish this, the eNode B may apply turn-on/off
precoders associated with antennas, in which an AGI has occurred,
to a code book and may specify this application of the turn-on/off
precoders through a series of UE-specific L1/L2 control signaling
(for example, indication of a precoder in a DCI format in a UL
grant). As another method, it is possible to make an instruction to
directly turn on/off output power of a transmission antenna, in
which an AGI has occurred, through separate (or additional)
UE-specific RRC signaling or UE-specific L1/L2 control signaling in
a separate control channel DCI format. In this suggestion, when a
power control mechanism is individually defined for each individual
transmission antenna (or layer) or a power control mechanism is
defined for each UE in a PUSCH power control mechanism of the UE,
the power control mechanism may be defined by multiplying an entire
power control mechanism equation by a value of "1" as a signaling
parameter in the "turn-on" case and by a value of "0" as a
signaling parameter in the "turn-off" case. Of course, detailed
equations, which can implement "turn-on/off" using the signaling
parameter, may be included in the suggestions of the present
invention. The following is a summary of methods for preventing the
occurrence of turn-on/off transition of power amplifiers and/or
signal amplifiers at boundaries between data transmission symbols
and SRS transmission symbols in the case where the precoding
transmission mode having such characteristics is applied to the
data transmission symbols. The methods suggested in the following
description may also be applied as SRS transmission-related schemes
when a series of antenna or antenna-group selection precoders,
which are not the antenna turn-on/off precoders introduced due to
causes such as AGI, are applied. First, an embodiment of the
present invention is described below with reference to an antenna
turn-on/off precoder.
[0145] Taking into consideration that an AGI occurs a semi-static
manner, detailed configurations of SRS transmission (for example,
configurations associated with SRS transmission timing, a detailed
multiplexing scheme, an SRS band, and the like) are reconfigured at
the time when the precoder for antenna turn-on/off described above
is applied or when it is applied to power control through signal in
the eNode B and SRS signals for antennas (or power amplifiers and
signal amplifiers) which are in a turn-on state from among all
(physical) transmission antennas of the UE are multiplexed and
transmitted in uplink in SRS transmission symbols according to an
arbitrary scheme among the multiplexing schemes suggested in the
present invention or according to a different multiplexing scheme.
This may prevent the occurrence of turn-on/off transition of power
amplifiers and/or signal amplifiers at boundaries between data
transmission symbols and SRS transmission symbols.
[0146] To allow a cell or an eNode B to monitor semi-static change
of an AGI state in a situation in which channel sounding limited to
some of all antennas (or layers, power amplifiers or signal
amplifiers) of the UE is implemented as in the schemes described
above as an AGI occurs, it is necessary for the UE to perform
channel sounding for all antennas at regular intervals to allow the
cell or eNode B to measure change of the AGI state. To accomplish
this, detailed SRS transmission configurations may be reconfigured
through UE-specific RRC signaling so as to perform channel sounding
in an entire or partial system band for all antennas during a time
duration sufficient for measurement at intervals of an appropriate
period. UE-specific RRC signaling for reconfiguring the detailed
SRS transmission configurations may be performed in a periodic
manner or an event-triggered manner.
[0147] FIG. 16 illustrates an example in which a UE performs
channel sounding through multiple antennas according to an
embodiment of the present invention. In the example of FIG. 16, it
is assumed that an AGI has already occurred such that some antennas
(layers, power amplifiers, or signal amplifiers) of the UE have
been turned off and thus detailed SRS transmission configurations
have been limited to (physical) transmission antennas that are in a
turn-on state. The antenna turn-off state can be applied only to a
specific frequency band or a specific (physical) channel (for
example, a specific SRS transmission symbol). In the case where at
least part of the transmission antennas have been set to a turn-off
state, the eNode B needs to observe a signal transmitted from the
UE in order to check whether or not the UE has escaped from the AGI
situation. To accomplish this, the UE may perform channel sounding
by turning on/off the transmission antennas that have been set to a
turn-off state in a periodic manner or an event-triggered manner.
That is, when at least partial transmission antennas of the UE have
been set to a turn-off state, the UE may perform channel sounding
by temporarily turning the transmission antennas on at intervals of
a specific period or according to a specific event while basically
maintaining the turn-off state of the transmission antennas. For
example, the UE may perform channel sounding of a partial or entire
system band for all (physical) transmission antennas by turning on
all (or partial) (physical) transmission antennas of the UE during
a duration B at intervals of a duration A. To accomplish this, a
turn-on precoder may be applied to an SRS transmission symbol
during the duration B and a turn-off precoder may be applied to an
SRS transmission symbol at a subsequent duration. The duration A
corresponds to a channel sounding transmission period applied to
the antennas that are in a turn-on state. Here, the duration A may
be set to be longer than the channel sounding transmission period
set for the antennas that are in a turn-on state. Specifically, the
duration A may be set to a multiple of the channel sounding
transmission period set for the antennas that are in a turn-on
state. In the case where channel sounding through the duration B is
performed in an event-triggered manner (for example, through L1/L2
control signaling), the duration A may not be separately
defined/signaled.
[0148] In combination with this method, it is possible to prevent
the occurrence of turn-on/off transition of power amplifiers and/or
signal amplifiers at boundaries between data transmission symbols
and SRS transmission symbols in a subframe by turning on all (or
partial) (physical) transmission antennas through UE-specific RRC
signaling, UE-specific L1/L2 control signaling or UE-specific UL
grant PDCCH transmission by a cell or an eNode B in the case where
an antenna turn-off state has been achieved through a power control
mechanism or by allowing precoders other than turn-on/off precoders
to be used in association with the data transmission symbols in the
case where the turn-on/off state of the transmission antennas have
been temporarily transitioned to a turn-on state for channel
sounding (during the duration B). In this scheme, the durations A
and B may be directly defined as a time and may also be set in
units of subframes, each corresponding to, for example, 1 ms, or in
units of radio frames, each corresponding to, for example, 10
ms.
[0149] In another scheme, in the case where the eNode B desires to
perform measurement for checking whether or not the AGI situation
of the UE has changed in an event-triggered manner, the eNode B may
make an instruction to perform channel sound of all (or partial)
(physical) transmission antennas during a preset duration or an
explicitly or implicitly signaled duration (for example, the
duration B) through L1/L2 control signaling (for example, through a
UL grant PDCCH, a power control PDCCH, or a dedicated PDCCH, or the
like). In the case where channel sounding is performed during the
duration B, each precoder for a data transmission symbol may be
specified as a precoder other than an antenna turn-on/off precoder.
This event-triggered signaling may also be specified as UE-specific
RRC signaling. This event-triggered scheme may be implemented by
specifying a precoder in a UL grant DCI format using a precoder of
a data transmission symbol while being tied with reconfiguration of
detailed SRS transmission configurations.
[0150] In this scheme, in the case where precoding is applied to an
SRS and a precoder in a UL grant is specified not only using a
precoder of a data transmission symbol but also using a precoder of
an SRS transmission symbol, antenna turn-on/off of (physical)
transmission antennas that transmit SRSs may be naturally
implemented in a code book. Of course, the suggestions of this
embodiment may also be applied in the case where an SRS is
precoded.
Embodiment 5-2
Channel Sounding in the Case where a Transmission Diversity Scheme
Based on Antenna (Group) Selection is Applied
[0151] All channel sounding schemes suggested in the above
embodiment 5-1 may be applied to this embodiment. This embodiment
differs from the embodiment 5-1 in that UE-specific/cell-specific
RRC control signaling for SRS resetting (or reconfiguration) is
performed in order to perform channel sounding of corresponding
(physical) transmission antennas in a situation in which the
antennas (or power amplifiers or signal amplifiers) are in a
turn-off state when performing detailed SRS transmission
configuration at the time when antenna selection specification for
a series of AGIs or other specific channel information is performed
through UE-specific RRC signaling, a UE-specific UL grant PDCCH, or
a different type of UE-specific dedicated PDCCH. In addition, the
same schemes as the detailed schemes of the embodiment 5-1 may be
applied to parameters that are signaled through a power control
mechanism that is individually defined for a (physical)
transmission antenna or through a power control mechanism of the UE
in association with antenna turn-on/off on the UE.
Embodiment 5-3
Channel Sounding when Dynamic Antenna Selection Precoder is
Applied
[0152] It is possible to apply any of the detailed schemes for SRS
transmission suggested in the embodiment 5-1, taking into
consideration that basic SRS setting is performed in a semi-static
manner in the case where an antenna selection precoder is applied
in a dynamic or semi-static manner. In addition, it is possible to
apply the suggested schemes of the embodiment 5-1, in which the
precoded SRS is applied, and also to consider a scheme in which an
event-triggered-based SRS is used.
Embodiment 5-4
Channel Sounding when an Antenna or Antenna-Group Selection Based
Transmission Mode (which can be Represented as a Type of
Transmission Diversity Scheme) is Applied
[0153] Basically, it is possible to apply any of the schemes
suggested in the embodiment 5-1 in the case where closed-loop or
open-loop antenna selection is implemented using one or more power
amplifiers and (physical) transmission antennas from among power
amplifiers and (physical) transmission antennas provided in an
arbitrary UE in a dynamic or semi-static manner (for example, using
UE-specific RRC setting (signaling)). Here, each (physical)
transmission antenna may be fixedly connected to a specific power
amplifier or may be switchably connected to outputs of a series of
power amplifiers. The following is a more detailed description of a
method for minimizing the occurrence of transition of power
amplifiers and transmission antennas at boundaries of data
transmission symbols and SRS transmission symbols when SRS
transmission is performed and minimizing the impact (or influence)
of the transition of the power amplifiers and the transmission
antennas.
[0154] In a situation in which antenna or antenna group selection
is performed when an antenna or antenna group selection based
transmission mode (which can be represented as a type of
transmission diversity scheme) is applied, the eNode B may
reconfigure detailed SRS transmission configurations (for example,
SRS transmission timing, detailed multiplexing schemes, SRS band,
and the like) and signal reconfigured configurations to the UE at
the time when the transmission mode is applied. On the other hand,
the UE multiplexes and transmits SRSs for antennas (or power
amplifiers and signal amplifiers) which are used for data
transmission from among all (physical) transmission antennas of the
UE in uplink in SRS transmission symbols according to an arbitrary
scheme among the multiplexing schemes suggested in the present
invention or according to a different multiplexing scheme. This may
prevent the occurrence of turn-on/off transition of power
amplifiers and/or signal amplifiers at boundaries between data
transmission symbols and SRS transmission symbols. In this SRS
configuration scheme, it is possible to especially match SRS
settings (configurations) in order to prevent the transition of
power amplifiers and transmission antennas at transmission symbol
boundaries in the case where a special configuration of a single
antenna and power amplifier has been set, as when the UE includes 2
transmission power amplifiers for 4 (physical) transmission
antennas, and in the case where transmission (physical) antennas of
power amplifier output terminals are switched according to the
special configuration.
[0155] In a situation in which channel sounding limited to partial
ones of the (physical) transmission antennas (or layers or power
amplifiers or signal amplifiers) of the UE is implemented, the UE
performs channel sounding on all (or partial) antennas at regular
intervals (or in a periodic manner) to allow the eNode B to measure
channel changes of individual (physical) transmission antennas of
the UE in order to allow the eNode B to select antennas or antenna
groups from the transmission antennas (or layers or power
amplifiers or signal amplifiers) of the UE. To accomplish this, it
is possible to perform selection of antennas or antenna groups upon
data transmission through UE-specific RRC signaling at regular
intervals so as to perform channel sounding of an entire or partial
system band of all (or partial) antennas during a duration
sufficient for measurement at intervals of an appropriate period
and to perform reconfiguration of detailed SRS transmission
configurations suitable for the selection of antennas or antenna
groups.
[0156] The example of FIG. 16 illustrated in association with the
embodiment 5-1 may also be applied to perform channel sounding when
antenna selection is applied according to this embodiment. In this
case, it can be assumed that in the example of FIG. 16 that
detailed SRS transmission configurations have been limited to
(physical) transmission antennas that are in a turn-on state when
specific transmission antennas are used in the case where antenna
or antenna group selection for a series of data transmissions is
applied. In this case, the UE may perform channel sounding by
turning on/off the transmission antennas that have been set to a
turn-off state in a periodic manner or an event-triggered manner.
That is, when at least partial transmission antennas of the UE have
been set to a turn-off state, the UE may perform channel sounding
by temporarily turning the transmission antennas on at intervals of
a specific period or according to a specific event while basically
maintaining the turn-off state of the transmission antennas. For
example, the UE may perform channel sounding of a partial or entire
system band for all (physical) transmission antennas by turning on
all (or partial) (physical) transmission antennas of the UE during
a duration B at intervals of a duration A. To accomplish this, a
turn-on precoder may be applied to an SRS transmission symbol
during the duration B and a turn-off precoder may be applied to an
SRS transmission symbol at a subsequent duration. The duration A
corresponds to a channel sounding transmission period applied to
the antennas that are in a turn-on state. Here, the duration A may
be set to be longer than the channel sounding transmission period
set for the antennas that are in a turn-on state. Specifically, the
duration A may be set to a multiple of the channel sounding
transmission period set for the antennas that are in a turn-on
state. In the case where channel sounding through the duration B is
performed in an event-triggered manner (for example, through L1/L2
control signaling), the duration A may not be separately
defined/signaled.
[0157] In combination with this method, it is possible to apply a
method of temporarily releasing the selection mode to allow all
(physical) transmission antennas of the UE to be applied for
transmission of data transmission symbols. It is also possible to
prevent the occurrence of turn-on/off transition of power
amplifiers and/or signal amplifiers at boundaries between data
transmission symbols and SRS transmission symbols in a subframe by
turning on all (or partial) (physical) transmission antennas
through UE-specific RRC signaling, UE-specific L1/L2 control
signaling or UE-specific UL grant PDCCH transmission by a cell or
an eNode B in the case where an antenna turn-off state has been
achieved through a power control mechanism. In this scheme, the
durations A and B may be directly defined as a time and may also be
set in units of subframes, each corresponding to, for example, 1
ms, or in units of radio frames, each corresponding to, for
example, 10 ms.
[0158] In another scheme, in the case where the eNode B desires to
perform measurement for checking whether or not channel states of
all (physical) transmission antennas of the UE have changed in an
event-triggered manner, the eNode B may make an instruction to
perform channel sound of all (or partial) (physical) transmission
antennas during a preset duration or an explicitly or implicitly
signaled duration (for example, the duration B) through L1/L2
control signaling (for example, through a UL grant PDCCH, a power
control PDCCH, or a dedicated PDCCH, or the like). In the case
where channel sounding is performed during the duration B, each
precoder for a data transmission symbol may be specified as a
precoder other than an antenna turn-on/off precoder. This
event-triggered signaling may also be specified as UE-specific RRC
signaling. This event-triggered scheme may be implemented by
specifying a precoder in a UI grant DCI format using a precoder of
a data transmission symbol while being tied with reconfiguration of
detailed SRS transmission configurations.
[0159] In this scheme, in the case where precoding is applied to an
SRS and a precoder in a UL grant is specified not only using a
precoder of a data transmission symbol but also using a precoder of
an SRS transmission symbol, antenna turn-on/off of (physical)
transmission antennas that transmit SRSs may be naturally
implemented in a code book. Of course, the suggestions of this
embodiment may also be applied in the case where an SRS is
precoded.
[0160] A variety of information for channel sounding may be
dynamically or non-dynamically signaled in the above embodiment 1-5
of the present invention. For example, in the present invention,
information for channel sounding may be signaled in a UE-specific
or a UE-group-specific manner through L1/L2 control signaling. More
specifically, information for channel sounding may be transmitted
from the eNode B (or relay) to the UE through a conventional PDCCH
defined in the LTE system, a separately defined PDCCH, or through a
control channel separately defined for signaling the information
for channel sounding. In the case where the information for channel
sounding is transmitted from the eNode B (or relay) to the UE
through a separately defined PDCCH, an RNTI for an SRS may be
defined or a DCI format may be separately defined. L1/L2 control
signaling for an SRS may be performed at a preset time (for
example, a period or offset) or may be performed in an
event-triggered manner. In the case of a carrier aggregation
system, L1/L2 control signal for channel sounding may be performed
for each downlink component carrier set for the UE or may be
performed only through a specific downlink component carrier (for
example, through an anchor or primary DL component carrier). In
this case, anchor or primary component carriers may be set one by
one for each downlink component carrier group.
[0161] The information for channel sounding includes, but not
limited to, information for newly configuring (or initiating) or
releasing an SRS. For example, in the case where the eNode B has
transmitted an L1/L2 control signaling signal (for example, a
PDCCH) having a specific format/content (for example, a specific
indicator) to the UE, the UE may start or release SRS transmission
after a preset time has elapsed after the signaling is performed or
after the UE has received the L1/L2 control signaling signal. The
information for channel sounding may include configuration
information (SRS transmission configuration information) required
for SRS transmission (for example, an offset, a period, and the
like). When the UE has newly received the SRS transmission
configuration information through the L1/L2 control signaling, the
UE may override (or overwrite) preset configuration information
with the newly received SRS transmission configuration information.
Alternatively, while maintaining the preset configuration
information, the UE may perform channel sounding using the newly
received SRS transmission configuration information only during a
preset time or during a duration in which a preset condition is
satisfied. The information transmitted through the SRS transmission
configuration information may include entire or partial information
required to perform channel sounding. The detailed content included
in the SRS transmission configuration information may set in
various manners depending on the type of signaling, the time of
signaling, the cause of signaling, and the like. Specifically, the
SRS transmission configuration information may include, but not
limited to, at least part of the SRS configuration parameters of
the LTE described above with reference to FIG. 5 and various
parameters that are newly defined or are required to implement the
embodiment 1-5.
[0162] FIG. 17 illustrates an eNode B and a UE to which the
embodiments of the present invention may be applied.
[0163] As shown in FIG. 17, a wireless communication system
includes a Base Station (BS) (or eNode B) 110 and a User Equipment
(UE) 120. In downlink, a transmitter is a part of the BS 110 and a
receiver is a part of the UE 120. In uplink, a transmitter is a
part of the UE 120 and a receiver is a part of the BS 110. The BS
110 includes a processor 112, a memory 114, and a Radio Frequency
(RF) unit 116. The processor 112 may be constructed so as to
implement the procedures and/or methods suggested in the present
invention. The memory 114 is connected to the processor 112 and
stores various information associated with operations of the
processor 112. The RF unit 116 is connected to the processor 112
and transmits or receives a wireless signal. The UE 120 includes a
processor 122, a memory 124, and an RF unit 126. The processor 122
may be constructed so as to implement the procedures and/or methods
suggested in the present invention. The memory 124 is connected to
the processor 122 and stores various information associated with
operations of the processor 122. The RF unit 126 is connected to
the processor 122 and transmits or receives a wireless signal. The
BS 110 and/or the UE 120 may include a single antenna or multiple
antennas.
[0164] The above embodiments are provided by combining components
and features of the present invention in specific forms. The
components or features of the present invention should be
considered optional unless explicitly stated otherwise. The
components or features may be implemented without being combined
with other components or features. The embodiments of the present
invention may also be provided by combining some of the components
and/or features. The order of the operations described above in the
embodiments of the present invention may be changed. Some
components or features of one embodiment may be included in another
embodiment or may be replaced with corresponding components or
features of another embodiment. It will be apparent that claims
which are not explicitly dependent on each other can be combined to
provide an embodiment or new claims can be added through amendment
after this application is filed.
[0165] The embodiments of the present invention have been described
focusing mainly on the data communication relationship between a UE
(or terminal) and a Base Station (BS) (or eNode B). Specific
operations which have been described as being performed by the BS
may also be performed by an upper node as needed. That is, it will
be apparent to those skilled in the art that the BS or any other
network node may perform various operations for communication with
terminals in a network including a number of network nodes
including BSs. The term "base station (BS)" may be replaced with
another term such as "fixed station", "Node B", "eNode B (eNB)", or
"access point". The term "terminal" may also be replaced with
another term such as "user equipment (UE)", "mobile station (MS)",
or "mobile subscriber station (MSS)".
[0166] The embodiments of the present invention can be implemented
by hardware, firmware, software, or any combination thereof. In the
case where the present invention is implemented by hardware, an
embodiment of the present invention may be implemented by one or
more application specific integrated circuits (ASICs), digital
signal processors (DSPs), digital signal processing devices
(DSPDs), programmable logic devices (PLDs), field programmable gate
arrays (FPGAs), processors, controllers, microcontrollers,
microprocessors, or the like.
[0167] In the case where the present invention is implemented by
firmware or software, the embodiments of the present invention may
be implemented in the form of modules, processes, functions, or the
like which perform the features or operations described above.
Software code can be stored in a memory unit so as to be executed
by a processor. The memory unit may be located inside or outside
the processor and can communicate data with the processor through a
variety of known means.
[0168] Those skilled in the art will appreciate that the present
invention may be embodied in other specific forms than those set
forth herein without departing from the spirit of the present
invention. The above description is therefore to be construed in
all aspects as illustrative and not restrictive. The scope of the
invention should be determined by reasonable interpretation of the
appended claims and all changes coming within the equivalency range
of the invention are intended to be embraced in the scope of the
invention.
INDUSTRIAL APPLICABILITY
[0169] The present invention is applicable to a wireless
communication system. Specifically, the present invention is
applicable to a channel sounding method using a plurality of
antennas and an apparatus for the same.
* * * * *