U.S. patent application number 13/880939 was filed with the patent office on 2013-08-15 for method and apparatus for transmitting a sounding reference signal.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is Joon Kui Ahn, Min Gyu Kim, Dong Youn Seo, Suck Chel Yang. Invention is credited to Joon Kui Ahn, Min Gyu Kim, Dong Youn Seo, Suck Chel Yang.
Application Number | 20130208710 13/880939 |
Document ID | / |
Family ID | 45994603 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130208710 |
Kind Code |
A1 |
Seo; Dong Youn ; et
al. |
August 15, 2013 |
METHOD AND APPARATUS FOR TRANSMITTING A SOUNDING REFERENCE
SIGNAL
Abstract
Provided are a method and apparatus for transmitting a sounding
reference signal. A terminal receives, from a base station, a
configuration for periodic channel quality indicator (CQI)
transmission and a configuration for sound reference signal (SRS)
transmission. When a positive SRS request is detected, the terminal
determines an SRS subframe winch satisfies the configuration for
SRS transmission. When the periodically transmitted CQI is
triggered in the SRS subframe, the terminal transmits the SRS in
the SRS subframe to the base station.
Inventors: |
Seo; Dong Youn; (Anyang-si,
KR) ; Kim; Min Gyu; (Anyang-si, KR) ; Yang;
Suck Chel; (Anyang-si, KR) ; Ahn; Joon Kui;
(Anyang-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seo; Dong Youn
Kim; Min Gyu
Yang; Suck Chel
Ahn; Joon Kui |
Anyang-si
Anyang-si
Anyang-si
Anyang-si |
|
KR
KR
KR
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
45994603 |
Appl. No.: |
13/880939 |
Filed: |
October 28, 2011 |
PCT Filed: |
October 28, 2011 |
PCT NO: |
PCT/KR2011/008161 |
371 Date: |
April 22, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61407894 |
Oct 28, 2010 |
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61409066 |
Nov 1, 2010 |
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61409543 |
Nov 3, 2010 |
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61430185 |
Jan 6, 2011 |
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Current U.S.
Class: |
370/336 |
Current CPC
Class: |
H04L 5/0048 20130101;
H04L 1/0026 20130101; H04W 52/346 20130101; H04L 27/2646 20130101;
H04W 24/02 20130101; H04W 52/30 20130101; H04W 72/0473 20130101;
H04W 8/22 20130101; H04L 5/0051 20130101; H04L 5/0007 20130101;
H04L 5/001 20130101; H04L 5/0057 20130101; H04W 72/0446 20130101;
H04W 72/0413 20130101; H04W 48/16 20130101; H04L 1/0027 20130101;
H04W 72/12 20130101; H04L 5/0055 20130101 |
Class at
Publication: |
370/336 |
International
Class: |
H04W 72/04 20060101
H04W072/04 |
Claims
1. A method of transmitting a sounding reference signal in a
wireless communication system, the method comprising: receiving, by
a user equipment, a configuration for periodic channel quality
indicator (CQI) transmission from a base station; receiving, by the
user equipment, a configuration for sounding reference signal (SRS)
transmission from the base station; monitoring, by the user
equipment, a physical downlink control channel (PDCCH) in order to
detect a positive SRS request; upon detecting the positive SRS
request, determining a SRS subframe which satisfies the
configuration for SRS transmission; and if a periodic CQI is also
triggered in the SRS subframe, transmitting a SRS in the SRS
subframe to the base station.
2. The method of claim 1, wherein the periodic CQI is not
transmitted in the SRS subframe.
3. The method of claim 2, wherein the configuration for SRS
transmission includes a SRS periodicity and a SRS subframe offset,
and the configuration for periodic CQI transmission includes a CQI
periodicity and a CQI subframe offset.
4. The method of claim 3, wherein the SRS subframe is determined as
a first subframe which satisfies the configuration for SRS
transmission and n+k, where k.gtoreq.4, when the positive SRS
request is detected in a subframe n.
5. The method of clam 2, wherein the periodic CQI is not
multiplexed with a hybrid automatic repeat request (HARQ)
ACK/NACK.
6. The method of claim 5, wherein the periodic CQI is transmitted
on a physical uplink control channel (PUCCH).
7. The method of claim 5, further comprising: if a periodic CQI
multiplexed with the HARQ ACK/NACK is triggered in the SRS
subframe, transmitting the multiplexed CQI in the SRS subframe to
the base station.
8. The method of claim 7, wherein the multiplexed CQI is
transmitted on a PUCCH.
9. A user equipment configured for transmitting a sounding
reference signal in a wireless communication system, the user
equipment comprising: a radio frequency unit configured to transmit
a radio signal; and a processor operatively coupled with the radio
frequency unit and configured to: receive a configuration for
periodic channel quality indicator (CQI) transmission from a base
station; receive a configuration for sounding reference signal
(SRS) transmission from the base station; monitor a physical
downlink control channel (PDCCH) in order to detect a positive SRS
request; upon detecting the positive SRS request, determine a SRS
subframe which satisfies the configuration for SRS transmission;
and if a periodic CQI is also triggered in the SRS subframe,
transmit a SRS in the SRS subframe to the base station.
10. The user equipment of claim 9, wherein the periodic CQI is not
transmitted in the SRS subframe.
11. The user equipment of claim 10, wherein the configuration for
SRS transmission includes a SRS periodicity and a SRS subframe
offset, and the configuration for periodic CQI transmission
includes a CQI periodicity and a CQI subframe offset.
12. The user equipment of claim 11, wherein the SRS subframe is
determined as a first subframe which satisfies the configuration
for SRS transmission and n+k, where k.gtoreq.4, when the positive
SRS request is detected in a subframe n.
13. The user equipment of clam 10, wherein the periodic CQI is not
multiplexed with a hybrid automatic repeat request (HARQ)
ACK/NACK.
14. The user equipment of claim 13, wherein the processor is
configured to transmit a multiplexed CQI which is multiplexed with
the HARQ ACK/NACK in the SRS subframe to the base station if the
multiplexed CQI is triggered in the SRS subframe.
15. The user equipment of claim 14, wherein the multiplexed CQI is
transmitted on a physical uplink control channel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the invention
[0002] The present invention relates to wireless communications,
and more particularly, to a method and apparatus for transmitting a
sounding reference signal in a wireless communication system.
[0003] 2. Related Art
[0004] Long term evolution (LTE) based on 3.sup.rd generation
partnership project (3GPP) technical specification (TS) release 8
is a promising next-generation mobile communication standard.
[0005] As disclosed in 3GPP TS 36.211 V8.7.0 (2009-05) "Evolved
Universal Terrestrial Radio Access (E-UTRA); Physical Channels and
Modulation (Release 8)", a physical channel of the LTE can be
classified into a downlink channel, i.e., a physical downlink
shared channel (PDSCH) and a physical downlink control channel
(PDCCH), and an uplink channel, i.e., a physical uplink shared
channel (PUSCH) and a physical uplink control channel (PUCCH).
[0006] The PUCCH is an uplink control channel used for transmission
of an uplink control signal such as a hybrid automatic repeat
request (HARQ) positive-acknowledgement
(ACK)/negative-acknowledgement (NACK) signal, a channel quality
indicator (CQI), and a scheduling request (SR).
[0007] An uplink reference signal can be classified into a
demodulation reference signal (DMRS) and a sounding reference
signal (SRS). The DMRS is a reference signal used in channel
estimation for demodulation of a received signal. The SRS is a
reference signal transmitted for uplink scheduling by a user
equipment to a base station. The base station estimates an uplink
channel by using the received SRS, and the estimated uplink channel
is used in uplink scheduling.
[0008] An uplink control signal and an SRS can be allocated
simultaneously in the same duration. Simultaneous transmission of
the uplink control signal and the SRS may cause an increase in
battery consumption by deteriorating a peak-to-average power ratio
(PAPR) property of the user equipment.
[0009] There is a need for a method of scheduling SRS transmission
when SRS transmission is triggered together with uplink control
signal transmission.
SUMMARY OF THE INVENTION
[0010] The present invention provides a method and apparatus for
transmitting an aperiodic sounding reference signal.
[0011] In an aspect, a method of transmitting a sounding reference
signal in a wireless communication system is provided. The method
includes receiving, by a user equipment, a configuration for
periodic channel quality indicator (CQI) transmission from a base
station, receiving, by the user equipment, a configuration for
sounding reference signal (SRS) transmission from the base station,
monitoring, by the user equipment, a physical downlink control
channel (PDCCH) in order to detect a positive SRS request, upon
detecting the positive SRS request, determining a SRS subframe
which satisfies the configuration for SRS transmission, and if a
periodic CQI is also triggered in the SRS subframe, transmitting a
SRS in the SRS subframe to the base station.
[0012] The periodic CQI may not be transmitted in the SRS
subframe.
[0013] The configuration for SRS transmission includes a SRS
periodicity and a SRS subframe offset, and the configuration for
periodic CQI transmission includes a CQI periodicity and a CQI
subframe offset.
[0014] The SRS subframe may be determined as a first subframe which
satisfies the configuration for SRS transmission and n+k, where
k.gtoreq.4, when the positive SRS request is detected in a subframe
n.
[0015] The periodic CQI may not be multiplexed with a hybrid
automatic repeat request (HARQ) ACK/NACK.
[0016] The periodic CQI may be transmitted on a physical uplink
control channel (PUCCH).
[0017] The method may further include transmitting a multiplexed
CQI in the SRS subframe to the base station if a periodic CQI
multiplexed with the HARQ ACK/NACK is triggered in the SRS
subframe.
[0018] The multiplexed CQI may be transmitted on a PUCCH.
[0019] In another aspect, a user equipment configured for
transmitting a sounding reference signal in a wireless
communication system is provided. The user equipment includes a
radio frequency unit configured to transmit a radio signal and a
processor operatively coupled with the radio frequency unit and
configured to receive a configuration for periodic channel quality
indicator (CQI) transmission from a base station, receive a
configuration for sounding reference signal (SRS) transmission from
the base station, monitor a physical downlink control channel
(PDCCH) in order to detect a positive SRS request, upon detecting
the positive SRS request, determine a SRS subframe which satisfies
the configuration for SRS transmission, and if a periodic CQI is
also triggered in the SRS subframe, transmit a SRS in the SRS
subframe to the base station.
[0020] A method of transmitting a sounding reference signal is
provided when an aperiodic sounding reference signal is triggered
together with another uplink transmission. Therefore, a base
station can more correctly perform uplink scheduling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows a downlink radio frame structure in 3.sup.rd
generation partnership project (3GPP) long term evolution
(LTE).
[0022] FIG. 2 shows an example of an uplink subframe in 3GPP
LTE.
[0023] FIG. 3 shows an example of multiple carriers.
[0024] FIG. 4 shows an example of aperiodic sounding reference
signal (SRS) transmission.
[0025] FIG. 5 shows an example of transmission of an SRS and a
physical uplink shared channel (PUSCH).
[0026] FIG. 6 shows an example of resolving a collision of an SRS
and a channel quality indicator (CQI).
[0027] FIG. 7 shows another example of resolving a collision of an
SRS and a CQI.
[0028] FIG. 8 is a flowchart showing an SRS transmission method
according to the embodiment of FIG. 7.
[0029] FIG. 9 is a block diagram showing a wireless communication
system to implement embodiments of the present invention.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0030] A user equipment (UE) may be fixed or mobile, and may be
referred to as another terminology, such as a mobile station (MS),
a mobile terminal (MT), a user terminal (UT), a subscriber station
(SS), a wireless device, a personal digital assistant (PDA), a
wireless modem, a handheld device, etc.
[0031] A base station (BS) is generally a fixed station that
communicates with the UE and may be referred to as another
terminology, such as an evolved node-B (eNB), a base transceiver
system (BTS), an access point, etc.
[0032] FIG. 1 shows a downlink radio frame structure in 3.sup.rd
generation partnership project (3GPP) long term evolution (LTE).
The section 6 of 3GPP TS 36.211 V8.7.0 (2009-05) "Evolved Universal
Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation
(Release 8)" may be incorporated herein by reference.
[0033] A radio frame consists of 20 slots indexed with 0 to 19. One
subframe consists of 2 slots. A time required for transmitting one
subframe is defined as a transmission time interval (TTI). For
example, one subframe may have a length of 1 millisecond (ms), and
one slot may have a length of 0.5 ms.
[0034] One slot may include a plurality of orthogonal frequency
division multiplexing (OFDM) symbols in a time domain. Since the
3GPP LTE uses orthogonal frequency division multiple access (OFDMA)
in a downlink (DL), the OFDM symbol is only for expressing one
symbol period in the time domain, and there is no limitation in a
multiple access scheme or terminologies. For example, the OFDM
symbol may also be referred to as another terminology such as a
single carrier frequency division multiple access (SC-FDMA) symbol,
a symbol period, etc.
[0035] Although it is described that one slot includes 7 OFDM
symbols for example, the number of OFDM symbols included in one
slot may vary depending on a length of a cyclic prefix (CP).
According to 3GPP TS 36.211 V8.7.0, in case of a normal CP, one
slot includes 7 OFDM symbols, and in case of an extended CP, one
slot includes 6 OFDM symbols.
[0036] A resource block (RB) is a resource allocation unit, and
includes a plurality of subcarriers in one slot. For example, if
one slot includes 7 OFDM symbols in a time domain and the RB
includes 12 subcarriers in a frequency domain, one RB can include
7.times.12 resource elements (REs).
[0037] A DL subframe is divided into a control region and a data
region in the time domain. The control region includes up to three
preceding OFDM symbols of a 1.sup.st slot in the subframe. However,
the number of OFDM symbols included in the control region may vary.
A physical downlink control channel (PDCCH) is allocated to the
control region, and a physical downlink shared channel (PDSCH) is
allocated to the data region.
[0038] As disclosed in 3GPP TS 36.211 V8.7.0, the 3GPP LTE
classifies a physical channel into a data channel and a control
channel. Examples of the data channel include a physical downlink
shared channel (PDSCH) and a physical uplink shared channel
(PUSCH). Examples of the control channel include a physical
downlink control channel (PDCCH), a physical control format
indicator channel (PCFICH), a physical hybrid-ARQ indicator channel
(PHICH), and a physical uplink control channel (PUCCH).
[0039] The PCFICH transmitted in a 1.sup.st OFDM symbol of the
subframe carries a control format indicator (CFI) regarding the
number of OFDM symbols (i.e., a size of the control region) used
for transmission of control channels in the subframe. The UE first
receives the CFI through the PCFICH, and thereafter monitors the
PDCCH.
[0040] Unlike the PDCCH, the PCFICH does not use blind decoding,
and is transmitted by using a fixed PCFICH resource of the
subframe.
[0041] The PHICH carries a positive-acknowledgement
(ACK)/negative-acknowledgement (NACK) signal for an uplink hybrid
automatic repeat request (HARQ). The ACK/NACK signal for uplink
(UL) data on a PUSCH transmitted by the UE is transmitted on the
PHICH.
[0042] A physical broadcast channel (PBCH) is transmitted in first
four OFDM symbols in a 2.sup.nd slot of a 1.sup.st subframe of a
radio frame. The PBCH carries system information necessary for
communication between a UE and a BS. The system information
transmitted through the PBCH is referred to as a master information
block (MIB). In comparison thereto, system information transmitted
through the PDCCH is referred to as a system information block
(SIB).
[0043] Control information transmitted through the PDCCH is
referred to as downlink control information (DCI). The DCI may
include resource allocation of the PDSCH (this is referred to as a
DL grant), resource allocation of a PUSCH (this is referred to as a
UL grant), a set of transmit power control commands for individual
UEs in any UE group and/or activation of a voice over Internet
protocol (VoIP).
[0044] The 3GPP LTE uses blind decoding for PDCCH detection. The
blind decoding is a scheme in which a desired identifier is
de-masked from a CRC of a received PDCCH (referred to as a
candidate PDCCH) to determine whether the PDCCH is its own control
channel by performing CRC error checking.
[0045] The BS determines a PDCCH format according to DCI to be
transmitted to the UE, attaches a cyclic redundancy check (CRC) to
the DCI, and masks a unique identifier (referred to as a radio
network temporary identifier (RNTI)) to the CRC according to an
owner or usage of the PDCCH.
[0046] FIG. 2 shows an example of a UL subframe in the 3GPP
LTE.
[0047] The UL subframe can be divided into a control region and a
data region. The control region is a region to which a physical
uplink control channel (PUCCH) carrying UL control information is
assigned. The data region is a region to which a physical uplink
shared channel (PUSCH) carrying user data is assigned.
[0048] The PUCCH is allocated in an RB pair in a subframe. RBs
belonging to the RB pair occupy different subcarriers in each of a
1.sup.st slot and a 2.sup.nd slot. m is a location index indicating
a logical frequency-domain location of the RB pair allocated to the
PUCCH in the subframe. It shows that RBs having the same value m
occupy different subcarriers in the two slots.
[0049] According to 3GPP TS 36.211 V8.7.0, the PUCCH supports
multiple formats. A PUCCH having a different number of bits per
subframe can be used according to a modulation scheme which is
dependent on the PUCCH format.
[0050] Table 1 below shows an example of a modulation scheme and
the number of bits per subframe according to the PUCCH format.
TABLE-US-00001 TABLE 1 PUCCH Format Modulation Scheme Number of
Bits per subframe 1 N/A N/A 1a BPSK 1 1b QPSK 2 2 QPSK 20 2a QPSK +
BPSK 21 2b QPSK + BPSK 22
[0051] The PUCCH format 1 is used for transmission of a scheduling
request (SR). The PUCCH formats 1a/1b are used for transmission of
an ACK/NACK signal. The PUCCH format 2 is used for transmission of
a CQI. The PUCCH formats 2a/2b are used for simultaneous
transmission of the CQI and the ACK/NACK signal. When only the
ACK/NACK signal is transmitted in a subframe, the PUCCH formats
1a/1b are used. When the SR is transmitted alone, the PUCCH format
1 is used. When the SR and the ACK/NACK are simultaneously
transmitted, the PUCCH format 1 is used, and in this transmission,
the ACK/NACK signal is modulated by using a resource allocated to
the SR.
[0052] Now, a multiple-carrier system will be described.
[0053] A 3GPP LTE system supports a case where a DL bandwidth and a
UL bandwidth are set differently only under the assumption that one
component carrier (CC) is used. The 3GPP LTE system supports up to
20 MHz. The UL bandwidth can be different from the DL bandwidth,
but only one CC is supported in each of UL and DL cases.
[0054] Spectrum aggregation (or bandwidth aggregation, also
referred to as carrier aggregation) supports a plurality of CCs.
For example, if 5 CCs are assigned as a granularity of a carrier
unit having a bandwidth of 20 MHz, a bandwidth of up to 100 MHz can
be supported.
[0055] A CC or a CC-pair can correspond to one cell. When a
synchronization signal and a PBCH are transmitted in each CC, one
DL CC may correspond to one cell. Therefore, a UE which
communicates with a BS through a plurality of CCs may receive a
service from a plurality of serving cells.
[0056] FIG. 3 shows an example of multiple carriers.
[0057] Although 3 DL CCs and 3 UL CCs are shown herein, the number
of DL CCs and the number of UL CCs are not limited thereto. In each
DL CC, a PDCCH and a PDSCH are independently transmitted. In each
UL CC, a PUCCH and a PUSCH are independently transmitted. Since
three DL CC-UL CC pairs are defined, it can be said that a UE
receives a service from three serving cells.
[0058] The UE can monitor the PDCCH in a plurality of DL CCs, and
can receive a DL transport block simultaneously through the
plurality of DL CC. The UE can transmit a plurality of UL transport
blocks simultaneously through a plurality of UL CCs.
[0059] It is assumed that a pair of a DL CC #1 and a UL CC #1 is a
1.sup.st serving cell, a pair of a DL CC #2 and a UL CC #2 is a
2.sup.nd serving cell, and a DL CC #3 is a 3.sup.rd serving cell.
Each serving cell can be identified by using a cell index (CI). The
CI may be cell-specific or UE-specific. Herein, CI=0, 1, 2 are
assigned to the 1.sup.st to 3.sup.rd serving cells for example.
[0060] The serving cell can be classified into a primary cell and a
secondary cell. The primary cell operates in a primary frequency,
and is a cell designated as the primary cell when a UE performs an
initial network entry process or starts a network re-entry process
or performs a handover process. The primary cell is also called a
reference cell. The secondary cell operates in a secondary
frequency. The secondary cell can be configured after an RRC
connection is established, and can be used to provide an additional
radio resource. At least one primary cell is configured always. The
secondary cell can be added/modified/released by higher-layer
signaling (e.g., RRC messages).
[0061] The CI of the primary cell may be fixed. For example, a
lowest CI can be designated as a CI of the primary cell. It is
assumed hereinafter that the CI of the primary cell is 0 and a CI
of the secondary cell is allocated sequentially starting from
1.
[0062] Now, sounding reference signal (SRS) transmission will be
described.
[0063] The SRS transmission can be classified into periodic SRS
transmission and aperiodic SRS transmission. The periodic SRS
transmission is when transmission is performed in a subframe
triggered by a periodic SRS configuration. The periodic SRS
configuration includes an SRS periodicity and an SRS subframe
offset. If the periodic SRS configuration is given, a UE can
periodically transmit an SRS in a subframe satisfying the periodic
SRS configuration.
[0064] In the aperiodic SRS transmission, the SRS is transmitted
upon detection of an SRS request of a BS. For the aperiodic SRS
transmission, the SRS configuration is given in advance. The SRS
configuration also includes an SRS periodicity T.sub.SRS and an SRS
subframe offset T.sub.Offset.
[0065] The SRS request for triggering of the aperiodic SRS
transmission may be included in a DL grant or a UL grant on a
PDCCH. For example, if the SRS request is 1 bit, `0` may indicate a
negative SRS request, and `1` may indicate a positive SRS request.
If the SRS request is 2 bits, `00` may indicate a negative SRS
request, and the others may indicate a positive SRS request. In
this case, one of a plurality of SRS configurations for SRS
transmission can be selected.
[0066] If the DL grant or the UL grant does not include a CI, an
SRS can be transmitted in a serving cell of a PDCCH in which an SRS
request is detected. If the DL grant or the UL grant includes the
CI, the SRS can be transmitted in a serving cell indicated by the
CI.
[0067] Assume that a positive SRS request is detected in a subframe
n of a serving cell. Upon detection of the positive SRS request, an
SRS is transmitted in a first subframe satisfying a condition of
n+k where k.gtoreq.4 as well as T.sub.SRS.gtoreq.2 in time division
duplex (TDD) and (10*n.sub.f+k.sub.SRS-T.sub.offset) mod
T.sub.SRS=0 in frequency division duplex (FDD). In FDD, a subframe
index k.sub.SRS is {0, 1, . . ., 9} in a frame n.sub.f. In TDD,
k.sub.SRS is defined by a predetermined table. In TDD of
T.sub.SRS=2, the SRS is transmitted in a first subframe satisfying
a condition of (k.sub.SRS-T.sub.offset)mod5=0.
[0068] Hereinafter, a subframe in which the SRS is transmitted is
called an SRS subframe or a triggered subframe. In periodic SRS
transmission and aperiodic SRS transmission, the SRS can be
determined in an SRS subframe determined UE-specifically.
[0069] An OFDM symbol in which the SRS is transmitted may have a
fixed position in the SRS subframe. For example, the SRS may be
transmitted in a last OFDM symbol of the SRS subframe. The OFDM
symbol in which the SRS is transmitted is called a sounding
reference symbol.
[0070] FIG. 4 shows an example of aperiodic SRS transmission. It is
assumed that an SRS configuration includes an SRS periodicity
T.sub.SRS=5 and an SRS subframe offset T.sub.offset=0.
[0071] It is assumed that a subframe capable of transmitting an SRS
is a subframe n+1 and a subframe n+6 according to the SRS
configuration.
[0072] If an SRS request is detected on a PDCCH of a subframe n,
the SRS is transmitted in the subframe n+6 which is a first
subframe satisfying the SRS configuration after a subframe n+4.
[0073] Now, the proposed multiplexing of an SRS and a PUCCH will be
described.
[0074] An uplink control signal transmitted on a PUCCH includes at
least one of a scheduling request (SR), an ACK/NACK for HARQ, and a
CQI. When the SRS is triggered in the same serving cell or in a
subframe having the same uplink control signal in different serving
cells, the following operation method is proposed.
First Embodiment: Transmission of SRS and PUCCH
[0075] An SRS and a PUCCH can be transmitted simultaneously in the
same subframe. For example, the PUCCH can be transmitted in a
primary cell, and the SRS can be transmitted in a secondary
cell.
[0076] When the PUCCH and the SRS are transmitted simultaneously,
it may be required to regulate transmit power. This is because
total transmit power of the PUCCH and the SRS can exceed maximum
transmit power. This can be expressed by the following
equation.
{ w 1 ( i ) P PUCCH , c ( i ) + w 2 ( i ) c P SRS , c ( i ) }
.ltoreq. P CMAX , c ( i ) [ Equation 1 ] ##EQU00001##
[0077] Herein, P.sub.PUCCH,c(i) denotes transmit power of a PUCCH
in a subframe i of a serving cell c, w.sub.1(i) denotes a scaling
factor of P.sub.PUCCH,c(i), P.sub.SRS,c(i) denotes transmit power
of an SRS in the subframe i of the serving cell c, w.sub.2(i)
denotes a scaling factor of P.sub.SRS,c(i), and P.sub.CMAX,c(i)
denotes maximum transmit power configured in the subframe i of the
serving cell c. Herein, 0.ltoreq.w.sub.1(i).ltoreq.1 and
0.ltoreq.w.sub.2(i).ltoreq.1. At least one PUCCH and at least one
SRS can be transmitted in the subframe i.
[0078] Through the scheduling, the transmit power of the PUCCH can
be readjusted to w.sub.1(i)P.sub.PUCCH,c(i), and the transmit power
of the SRS can be readjusted to w.sub.2(i)P.sub.SRS,c(i).
[0079] When a total transmit power of the PUCCH and the SRS exceeds
maximum transmit power, transmit power of a signal having a low
priority can be decreased by using a priority rule described
below.
[0080] In one embodiment, the PUCCH may have a higher priority than
the SRS. That is, w.sub.1(i)>w.sub.2(i).gtoreq.0. This is
because the PUCCH can carry a control signal (e.g., HARQ ACK/NACK)
which can have a serious effect on communication reliability.
Transmission delay of the HARQ ACK/NACK may cause delay of DL data,
and thus quality of service (QoS) may not be guaranteed.
[0081] In this case, the value w.sub.1(i) can be maintained to 1
until the value w.sub.2(i) becomes a value less than a specific
value (i.e., 1) or becomes 0. That is, the PUCCH transmit power may
not be decreased as long as the SRS transmit power can be
decreased. In addition, the value w.sub.2(i) may have the same
value irrespective of a serving cell. That is, a ratio of
decreasing the SRS transmit power may be identical throughout all
serving cells.
[0082] In another embodiment, the SRS may have a higher priority
than the PUCCH. That is, w.sub.2(i)>w.sub.1(i).gtoreq.0. This is
because, if SRS transmit power is low, a BS cannot correctly
measure a pathloss of a UE and thus may not be able to perform
correct scheduling.
[0083] In this case, the value w.sub.2(i) can be maintained to 1
until the value w.sub.1(i) becomes a value less than a specific
value (i.e., 1) or becomes 0. That is, the SRS transmit power may
not be decreased as long as the PUCCH transmit power can be
decreased.
[0084] In another embodiment, the SRS may have the same priority as
the PUCCH. That is, w.sub.2(i)=w.sub.1(i).
[0085] Meanwhile, the PUSCH may be transmitted in the same subframe
simultaneously with the PUCCH, or simultaneous transmission may not
be allowed.
[0086] If the PUCCH and the SRS are simultaneously triggered in a
mode not allowing PUSCH/PUCCH simultaneous transmission, SRS
transmission may be dropped. Alternatively, by applying a
`shortened format` to the PUCCH, the PUCCH and the SRS can be
prevented from simultaneously transmission in the same OFDM
symbol.
[0087] The aforementioned SRS/PUCCH simultaneous transmission can
be applied in a mode allowing PUSCH/PUCCH simultaneous
transmission.
Second Embodiment: Transmission of SRS and PUSCH
[0088] The SRS and the PUSCH can be simultaneously transmitted in
the same serving cell or in the same subframe of different serving
cells.
[0089] FIG. 5 shows an example of transmission of an SRS and a
PUSCH.
[0090] The PUSCH is transmitted in a serving cell #1. The PUSCH and
the SRS are transmitted in a serving cell #2. The PUSCH is
punctured in a last OFDM symbol of a subframe of the serving cell
#2 in which the SRS is transmitted. However, the PUSCH is not
punctured in a last OFDM symbol of a subframe of the serving cell
#1.
[0091] This is to avoid a data loss caused when the PUSCH is
punctured in another serving cell except for the serving cell in
which the SRS is transmitted, even if a single-carrier property is
not satisfied.
[0092] The puncturing of the PUSCH applies only to the serving cell
in which the SRS is transmitted. The puncturing of the PUSCH is not
performed in a serving cell in which the SRS is not
transmitted.
[0093] When total transmit power of the PUSCH and the SRS exceeds
maximum transmit power, the following operation can be taken into
account.
[0094] First, transmit power of the PUSCH can be preferentially
decreased. This is because a decrease in transmit power of the SRS
may cause a serious error in UL channel estimation performed by a
BS. Alternatively, if the total transmit power of the PUSCH and the
SRS exceeds the maximum transmit power, only the SRS may be
transmitted while dropping PUSCH transmission. Alternatively, if
the total transmit power of the PUSCH and the SRS exceeds the
maximum transmit power, the PUSCH transmission may be dropped when
transmit power of the PUSCH is less than or equal to a specific
value.
[0095] Second, the transmit power of the SRS can be preferentially
decreased. Alternatively, only the PUSCH may be transmitted while
dropping SRS transmission.
[0096] Third, power of the SRS and the PUSCH can be decreased by
the same ratio.
[0097] Examples of the PUSCH may include a PUSCH including only
user data and a PUSCH in which an uplink control signal and the
user signal are multiplexed (such a PUSCH is called a multiplexed
PUSCH). The top priority may be assigned to the multiplexed PUSCH,
and transmit power can be regulated by assigning the same priority
or different priorities to the PUSCH and the SRS.
Third Embodiment: PUSCH/PUCCH/SRS Transmission
[0098] Multiplexing of a UL channel (PUSCH and/or PUCCH) and an SRS
will be proposed.
[0099] First, assume that a UE is set to a mode allowing
simultaneous transmission of the PUSCH and the PUCCH. The PUSCH,
the PUCCH, and the SRS can be transmitted simultaneously.
[0100] Total transmit power of the PUSCH, the PUCCH, and the SRS
can be regulated as follows, so that it does not exceed maximum
transmit power.
{ w 1 ( i ) P PUCCH , c ( i ) + w 2 ( i ) P mPUSCH , c ( i ) + w 3
( i ) c P PUSCH , c ( i ) + w 4 ( i ) c P SRS , c ( i ) } .ltoreq.
P CMAX , c ( i ) [ Equation 2 ] ##EQU00002##
[0101] Herein, P.sub.mPUSCH,c(i) denotes transmit power of a
multiplexed PUSCH in a subframe i of a serving cell c, and
P.sub.PUSCH,c(i) denotes transmit power of a PUSCH in the subframe
i of the serving cell c. w.sub.1(i) denotes a scaling factor of
P.sub.PUCCH,c(i). w.sub.2(i) denotes a scaling factor of
P.sub.mPUSCH,c(i). w.sub.3(i) denotes a scaling factor of
P.sub.PUSCH,c(i). w.sub.4(i) denotes a scaling factor of
P.sub.SRS,c(i).
[0102] Through the scheduling, the transmit power of the PUCCH can
be readjusted to w.sub.1(i)P.sub.mPUSCH,c(i), the transmit power of
the multiplexed PUSCH can be readjusted to
w.sub.2(i)P.sub.mPUSCH,c(i), and the transmit power of the PUSCH
can be readjusted to w.sub.3(i)P.sub.mPUSCH,c(i).
[0103] If the total transmit power exceeds the maximum transmit
power, transmit power of the SRS can be preferentially decreased or
SRS transmission can be dropped. If the total transmit power
exceeds the maximum transmit power even though the transmit power
of the SRS is decreased to be less than or equal to a specific
value or is set to 0, the transmit power of the PUSCH can be
decreased or PUSCH transmission can be dropped.
[0104] In this case, transmit power of a PUSCH not multiplexed with
the control signal can be preferentially decreased or dropped.
Alternatively, irrespective of whether it is the PUCCH multiplexed
with the control signal, transmit power of all PUSCHs can be
decreased by the same ratio or can be dropped. If the transmit
power of the PUSCH exceeds the maximum transmit power even though
the aforementioned method is used, the transmit power of the PUCCH
can be decreased. That is, a power scaling priority is given as
follows.
w.sub.1(i)>w.sub.2(i)>w.sub.3(i)>w.sub.4(i) or
w.sub.1(i)>w.sub.2(i)=w.sub.3(i)>w.sub.4(i)
[0105] Alternatively, if the total transmit power exceeds the
maximum transmit power, the transmit power of the SRS and the PUSCH
not multiplexed with the control signal can be preferentially
decreased by the same ratio or transmission thereof can be dropped.
If the total transmit power exceeds the maximum transmit power even
though the transmit power of the PUSCH not multiplexed with the
control signal and the SRS is decreased to be less than or equal to
a specific value or is set to 0, the transmit power of the PUSCH
multiplexed with the control signal can be decreased or
transmission thereof can be dropped. Alternatively, without having
to distinguish the PUSCH multiplexed with the control signal and
the PUSCH not multiplexed with the control signal, transmit power
can be decreased by the same ratio as the SRS or transmission
thereof can be dropped. If the transmit power of the PUSCH exceeds
the maximum transmit power even though the aforementioned method is
used, the transmit power of the PUCCH can be decreased or PUSCH
transmission can be dropped. That is, a power scaling priority is
given as follows.
w.sub.1(i)>w.sub.2(i)>w.sub.3(i)=w4(i) or
w.sub.1(i)>w.sub.2(i)=w.sub.3(i)=w.sub.4(i)
[0106] If the total transmit power exceeds the maximum transmit
power, the transmit power of the PUSCH can be preferentially
decreased or PUSCH transmission can be dropped. If the total
transmit power exceeds the maximum transmit power even though the
transmit power of the PUSCH is decreased to be less than or equal
to a specific value or is set to 0, the transmit power of the SRS
can be decreased or SRS transmission can be dropped. If the
transmit power of the PUSCH exceeds the maximum transmit power even
though the aforementioned method is used, the transmit power of the
PUCCH can be decreased. That is, a power scaling priority is given
as follows.
w.sub.1(i)>w.sub.4(i)>w.sub.2(i)=w.sub.3(i)
[0107] If the total transmit power exceeds the maximum transmit
power, the transmit power of the PUSCH not multiplexed with the
control signal can be preferentially decreased or transmission
thereof can be dropped. If the total transmit power exceeds the
maximum transmit power even though the transmit power of the PUSCH
is decreased to be less than or equal to a specific value or is set
to 0, the transmit power of the SRS can be decreased or SRS
transmission can be dropped. If the total transmit power exceeds
the maximum transmit power even though the aforementioned method is
used, the transmit power of the PUCCH can be decreased or
transmission thereof can be dropped. If the transmit power of the
PUSCH exceeds the maximum transmit power even though the
aforementioned method is used, the transmit power of the PUCCH can
be decreased. That is, a power scaling priority is given as
follows.
w.sub.1(i)>w.sub.2(i)>w.sub.4(i)>w.sub.3(i)
[0108] In the above description, if the maximum transmit power is
satisfied by decreasing the transmit power of the PUSCH and the
SRS, the remaining transmit power can be re-assigned to the PUSCH
or the SRS.
[0109] In addition, if the PUCCH and the SRS are not simultaneously
transmitted, the above operation can be applied except for the
PUCCH and the w.sub.1(i).
4.sup.th Embodiment: Drop One of SRS and PUCCH
[0110] First, if an aperiodic SRS collides with an SR (i.e., a
PUCCH format 1), only the aperiodic SRS can be transmitted while
dropping SRS transmission.
[0111] The aperiodic SRS may collide with HARQ ACK/NACK (i.e.,
PUCCH format 1a/1b) in the following manner. The HARQ ACK/NACK can
be classified into SPS ACK/NACK for semi-persistent scheduling
(SPS) and dynamic ACK/NACK for dynamic scheduling. The SPS ACK/NACK
is transmitted by using a pre-defined PUCCH resource. The PUCCH
resource can be reported by a BS to a UE through an RRC message.
The dynamic ACK/NACK is transmitted by using a PUCCH resource
acquired from a resource of a PDCCH for carrying a DL grant.
[0112] If the SRS ACK/NACK collides with the aperiodic SRS, only
the aperiodic SRS is transmitted while dropping the SPS ACK/NACK
transmission. This is because it can be seen that the BS
intentionally allows the SPS ACK/NACK and the aperiodic SRS to
collide with each other. If the aperiodic SRS collides with the
dynamic ACK/NACK, the dynamic ACK/NACK is transmitted, and the
aperiodic SRS is dropped.
[0113] Now, a collision of a CQI and an SRS will be described.
[0114] In the conventional 3GPP LTE, the SRS is dropped if a
periodic SRS and a periodic CQI (i.e., a PUCCH format 2) are
triggered in the same subframe.
[0115] However, since the aperiodic SRS is an operation in which a
BS requests SRS transmission at a corresponding time when
necessary, it may not be appropriate to drop the SRS. The present
proposal can be applied when a UE transmits an aperiodic SRS (also
referred to as A-SRS) and CQI in one serving cell, or
simultaneously transmits the aperiodic SRS and CQI in a plurality
of serving cells.
[0116] Since the aperiodic SRS is introduced so that the BS can
perform faster UL channel measurement of the UE, it is not desired
to drop the SRS when it collides with the CQI.
[0117] FIG. 6 shows an example of resolving a collision of an SRS
and a CQI.
[0118] After detection of a positive SRS request, a UE can transmit
the SRS in a first subframe which satisfies an SRS configuration
and which does not collide with periodic CQI transmission.
[0119] Assume that T.sub.SRS=5 and T.sub.offset=0. When an SRS
request is detected on a PDCCH of a subframe n, a first subframe
which satisfies the SRS configuration after a subframe n+4 is a
subframe n+6. However, a periodic CQI is triggered even in the
subframe n+6, and thus the collision of the CQI and the SRS
occurs.
[0120] In the subframe n+6, the SRS is dropped, and only the CQI is
transmitted. The SRS is transmitted in a subframe n+11 which is a
first subframe of a next SRS period which does not collide with a
CQI period.
[0121] FIG. 7 shows another example of resolving a collision of an
SRS and a CQI.
[0122] After detection of a positive SRS request, if a subframe in
which the SRS is triggered is the same as a subframe in which a
periodic CQI is transmitted, a UE can drop periodic CQI
transmission and transmit the SRS.
[0123] Assume that T.sub.SRS=5 and T.sub.offset=0. When an SRS
request is detected on a PDCCH of a subframe n, a first subframe
which satisfies the SRS configuration after a subframe n+4 is a
subframe n+6. However, a periodic CQI is triggered even in the
subframe n+6, and thus the collision of the CQI and the SRS occurs.
The UE drops the CQI, and transmits the SRS. The CQI dropped in
this case is a periodic CQI transmitted with a PUCCH format 2. If
the CQI is transmitted through a PUSCH, the CQI may not be
dropped.
[0124] When the periodic CQI is triggered in the subframe n+6,
ACK/NACK can be multiplexed with the CQI. That is, not the PUCCH
format 2 but the PUCCH formats 2a/2b can collide with an aperiodic
SRS. If the PUCCH format 2 collides with the aperiodic SRS, the
PUCCH format 2 is dropped. If the PUCCH formats 2a/2b collide with
the aperiodic SRS, the SRS is dropped. That is, if transmission of
the CQI multiplexed with the ACK/NACK is triggered, the SRS is
dropped.
[0125] FIG. 8 is a flowchart showing an SRS transmission method
according to the embodiment of FIG. 7.
[0126] A UE receives a CQI configuration for periodic CQI
transmission from a BS (step S810). The CQI configuration may
include a CQI period and a CQI subframe offset. In addition, the
CQI configuration may include information related to a PUCCH
resource for configuring a PUCCH format 2.
[0127] The UE receives the SRS configuration for SRS transmission
from the BS (step S820). The SRS configuration may include an SRS
period and an SRS subframe offset. The UE may receive a plurality
of SRS configurations. One of the plurality of SRS configurations
can be selected by a positive SRS request.
[0128] The UE monitors a PDCCH (step S830). The PDCCH can be
monitored in a UE-specific search space.
[0129] The UE determines whether a positive SRS request is detected
(step S840). A DL grant or UL grant of the PDCCH may include an SRS
request. The SRS request may have one bit or two bits.
[0130] Upon detection of the positive SRS request, the UE
determines an SRS subframe in which SRS transmission is triggered
(step S850).
[0131] The UE determines whether the SRS collides with the CQI in
the SRS subframe (step S860). The UE determines whether the
periodic CQI is triggered in the SRS subframe.
[0132] If the periodic CQI is triggered in the SRS subframe, the
CQI is dropped (step S870).
[0133] The UE transmits the SRS in the SRS subframe (step
S870).
[0134] Meanwhile, in another embodiment, if the aperiodic SRS
collides with the CQI, transmission may be performed with a
`shortened format` instead of the PUCCH format 2. The `shortened
format` is a format acquired by puncturing an OFDM symbol
corresponding to a sounding reference symbol in the PUCCH format
2.
[0135] If the aperiodic SRS collides with the CQI, the SRS may be
dropped and only the CQI may be transmitted. Alternatively, the BS
may indicate whether to simultaneously transmit the CQI and the
SRS. An indicator for indicating whether to perform simultaneous
transmission may be transmitted by the BS to the UE through a PDCCH
or an RRC message.
[0136] The UE may ignore a PDCCH used to detect the SRS request
which collides with CQI transmission. That is, even if the PDCCH
includes a DL grant or a UL grant, it may not be used by being
determined as wrong scheduling. In other words, it can be assumed
that the SRS request which collides with the CQI transmission
cannot be received through the PDCCH.
[0137] When the SRS is transmitted simultaneously with the PUSCH
and/or the PUCCH, dropping can be allowed only when the SRS and the
UL channel (i.e., the PUSCH and/or the PUCCH) are transmitted in
the same antenna port. When transmitted to another antenna port,
the SRS and the UL channels can be both transmitted. Assume that
SRS transmission for a plurality of antenna ports is configured. If
the UL channel and the SRS transmission are triggered in the same
subframe, the SRS may be dropped in an antenna port used by the UL
channel, and the SRS can be transmitted in another antenna
port.
[0138] Assume a case where UL CCs are grouped so that an SRS
included in one UL CC and an SRS (or a PUCCH or a PUSCH) included
in another UL CC are transmitted together. If two UL CCs belong to
the same UL CC group, transmission of one of the two UL CCs can be
dropped. If the two UL CCs belong to different groups, two channels
can be both transmitted. The UL CCs can be grouped to a UL CC
belonging to the same frequency band.
[0139] FIG. 9 is a block diagram showing a wireless communication
system to implement embodiments of the present invention.
[0140] A BS 50 includes a memory 51, a processor 52, and a radio
frequency (RF) unit 53. The memory 51 is coupled to the processor
52, and stores a variety of information for driving the processor
52. The RF unit 53 is coupled to the processor 52, and transmits
and/or receives a radio signal. The processor 52 implements the
proposed functions, procedures, and/or methods. The processor 52
can implement an operation of the BS 50 according to the
aforementioned embodiments. The processor 52 schedules an SRS
configuration, and estimates a channel state on the basis of a
received SRS.
[0141] A UE 60 includes a memory 61, a processor 62, and an RF unit
63. The memory 61 is coupled to the processor 62, and stores a
variety of information for driving the processor 62. The RF unit 63
is coupled to the processor 62, and transmits and/or receives a
radio signal. The processor 62 implements the proposed functions,
procedures, and/or methods. The processor 62 can implement an
operation of the UE 60 according to the aforementioned embodiments.
The processor 62 determines whether an SRS collides with a PUCCH
and/or a PUSCH, and transmits the SRS.
[0142] The processor may include Application-Specific Integrated
Circuits (ASICs), other chipsets, logic circuits, and/or data
processors. The memory may include Read-Only Memory (ROM), Random
Access Memory (RAM), flash memory, memory cards, storage media
and/or other storage devices. The RF unit may include a baseband
circuit for processing a radio signal. When the above-described
embodiment is implemented in software, the above-described scheme
may be implemented using a module (process or function) which
performs the above function. The module may be stored in the memory
and executed by the processor. The memory may be disposed to the
processor internally or externally and connected to the processor
using a variety of well-known means.
[0143] In the above exemplary systems, although the methods have
been described on the basis of the flowcharts using a series of the
steps or blocks, the present invention is not limited to the
sequence of the steps, and some of the steps may be performed at
different sequences from the remaining steps or may be performed
simultaneously with the remaining steps. Furthermore, those skilled
in the art will understand that the steps shown in the flowcharts
are not exclusive and may include other steps or one or more steps
of the flowcharts may be deleted without affecting the scope of the
present invention.
* * * * *