U.S. patent application number 15/886264 was filed with the patent office on 2018-06-07 for apparatus and method for transmitting uplink control information.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Joon Kui Ahn, Eun Sun Kim, Hak Seong Kim, Ki Jun Kim, Han Byul Seo.
Application Number | 20180160412 15/886264 |
Document ID | / |
Family ID | 43826781 |
Filed Date | 2018-06-07 |
United States Patent
Application |
20180160412 |
Kind Code |
A1 |
Kim; Ki Jun ; et
al. |
June 7, 2018 |
APPARATUS AND METHOD FOR TRANSMITTING UPLINK CONTROL
INFORMATION
Abstract
A wireless communication system is disclosed. A method and
apparatus for allowing a user equipment (UE) to transmit uplink
control information through a physical uplink shared channel
(PUSCH) are disclosed. A method for allowing a UE to transmit
uplink control information through a PUSCH in a wireless
communication system includes receiving configuration information
about a plurality of PUSCH feedback modes, identifying information
indicating a specific PUSCH feedback mode for the PUSCH by using
uplink allocation information for the PUSCH, and transmitting the
uplink control information through the PUSCH in accordance with the
specific PUSCH feedback mode
Inventors: |
Kim; Ki Jun; (Anyang-si,
KR) ; Seo; Han Byul; (Anyang-si, KR) ; Kim;
Eun Sun; (Anyang-si, KR) ; Ahn; Joon Kui;
(Anyang-si, KR) ; Kim; Hak Seong; (Anyang-si,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
43826781 |
Appl. No.: |
15/886264 |
Filed: |
February 1, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15410518 |
Jan 19, 2017 |
9924507 |
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15886264 |
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15234714 |
Aug 11, 2016 |
9629137 |
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15410518 |
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13499273 |
Mar 29, 2012 |
9432977 |
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PCT/KR2010/006622 |
Sep 29, 2010 |
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15234714 |
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61246991 |
Sep 30, 2009 |
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61250858 |
Oct 12, 2009 |
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61253481 |
Oct 20, 2009 |
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61312637 |
Mar 10, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 1/1887 20130101;
H04L 1/1819 20130101; H04B 7/0626 20130101; H04W 52/241 20130101;
H04W 72/0413 20130101; H04L 1/0026 20130101; H04W 72/1289 20130101;
H04W 72/042 20130101; H04L 5/001 20130101; H04L 1/0025 20130101;
H04L 1/1861 20130101; H04L 1/06 20130101; H04W 52/146 20130101 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04L 1/00 20060101 H04L001/00; H04L 5/00 20060101
H04L005/00; H04L 1/18 20060101 H04L001/18 |
Claims
1. A method of transmitting aperiodic channel status information
(CSI) at a user equipment (UE) through a physical uplink shared
channel (PUSCH) in a wireless communication system, the method
comprising: receiving a radio resource control (RRC) signal
including configuration information about a plurality of component
carrier sets for aperiodic CSI report, wherein each component
carrier set includes two or more component carriers; receiving
Downlink Control Information (DCI) for the PUSCH through a physical
downlink control channel (PDCCH), the DCI including an indicator
for requesting aperiodic CSI report, wherein the indicator has one
of plural values; and transmitting aperiodic CSI for one of the
plurality of the component carrier sets indicated by the indicator
through the PUSCH scheduled by the DCI.
2. The method of claim 1, wherein the DCI further includes resource
block (RB) assignment information and a hybrid automatic repeat and
request (HARQ) process index for the PUSCH.
3. The method of claim 1, wherein the PUSCH includes the aperiodic
CSI only.
4. The method of claim 1, wherein the PUSCH includes the aperiodic
CSI and data.
5. A method of receiving aperiodic channel status information (CSI)
at a base station (BS) through a physical uplink shared channel
(PUSCH) in a wireless communication system, the method comprising:
transmitting a radio resource control (RRC) signal including
configuration information about a plurality of component carrier
sets for aperiodic CSI report, wherein each component carrier set
includes two or more component carriers; transmitting Downlink
Control Information (DCI) for the PUSCH through a physical downlink
control channel (PDCCH), the DCI including an indicator for
requesting aperiodic CSI report, wherein the indicator has one of
plural values; and receiving aperiodic CSI for one of the plurality
of the component carrier sets indicated by the indicator through
the PUSCH scheduled by the DCI.
6. The method of claim 5, wherein the DCI further includes resource
block (RB) assignment information and a hybrid automatic repeat and
request (HARQ) process index for the PUSCH.
7. The method of claim 5, wherein the PUSCH includes the aperiodic
CSI only.
8. The method of claim 5, wherein the PUSCH includes the aperiodic
CSI and data.
9. A user equipment (UE) configured to transmit aperiodic channel
status information (CSI) through a physical uplink shared channel
(PUSCH) in a wireless communication system, the UE comprising: a
radio frequency (RF) unit; and a processor, wherein the processor
is configured to: receive a radio resource control (RRC) signal
including configuration information about a plurality of component
carrier sets for aperiodic CSI report, wherein each component
carrier set includes two or more component carriers, receive
Downlink Control Information (DCI) for the PUSCH through a physical
downlink control channel (PDCCH), the DCI including an indicator
for requesting aperiodic CSI report, wherein the indicator has one
of plural values, and transmit aperiodic CSI for one of the
plurality of the component carrier sets indicated by the indicator
through the PUSCH scheduled by the DCI.
10. The UE of claim 9, wherein the DCI further includes resource
block (RB) assignment information and a hybrid automatic repeat and
request (HARQ) process index for the PUSCH.
11. The UE of claim 9, wherein the PUSCH includes the aperiodic CSI
only.
12. The UE of claim 9, wherein the PUSCH includes the aperiodic CSI
and data.
13. A base station (BS) configured to receive aperiodic channel
status information (CSI) through a physical uplink shared channel
(PUSCH) in a wireless communication system, the BS comprising: a
radio frequency (RF) unit; and a processor, wherein the processor
is configured to: transmit a radio resource control (RRC) signal
including configuration information about a plurality of component
carrier sets for aperiodic CSI report, wherein each component
carrier set includes two or more component carriers, transmit
Downlink Control Information (DCI) for the PUSCH through a physical
downlink control channel (PDCCH), the DCI including an indicator
for requesting aperiodic CSI report, wherein the indicator has one
of plural values, and receive aperiodic CSI for one of the
plurality of the component carrier sets indicated by the indicator
through the PUSCH scheduled by the DCI.
14. The BS of claim 13, wherein the DCI further includes resource
block (RB) assignment information and a hybrid automatic repeat and
request (HARQ) process index for the PUSCH.
15. The BS of claim 13, wherein the PUSCH includes the aperiodic
CSI only.
16. The BS of claim 13, wherein the PUSCH includes the aperiodic
CSI and data.
Description
TECHNICAL FIELD
[0001] The present invention relates to wireless communication, and
more particularly, to a method and apparatus for transmitting
uplink control information.
BACKGROUND ART
[0002] Wireless communication systems have been diversified in
order to provide various types of communication services such as
voice or data service. In general, a wireless communication system
is a multiple access system capable of sharing available system
resources (bandwidth, transmission power or the like) so as to
support communication with multiple users. Examples of the multiple
access system include a Code Division Multiple Access (CDMA)
system, a Frequency Division Multiple Access (FDMA) system, a Time
Division Multiple Access (TDMA) system, an Orthogonal Frequency
Division Multiple Access (OFDMA) system, a Single Carrier Frequency
Division Multiple Access (SC-FDMA) system, and the like.
DISCLOSURE
Technical Problem
[0003] An object of the present invention devised to solve the
problem lies on a method and apparatus for transmitting uplink
control information.
[0004] Another object of the present invention devised to solve the
problem lies on a method and apparatus for efficiently transmitting
uplink control information through a Physical Uplink Shared Channel
(PUSCH).
Technical Solution
[0005] The object of the present invention can be achieved by
providing a method for allowing a user equipment (UE) to transmit
uplink control information over a physical uplink shared channel
(PUSCH) in a wireless communication system including receiving
configuration information about a plurality of PUSCH feedback
modes, identifying information indicating a specific PUSCH feedback
mode for the PUSCH using uplink allocation information for the
PUSCH, and transmitting the uplink control information through the
PUSCH in accordance with the specific PUSCH feedback mode.
[0006] In another aspect of the present invention, provided herein
is a user equipment (UE) for transmitting uplink control
information through a physical uplink shared channel (PUSCH) in a
wireless communication system, the user equipment (UE) including a
radio frequency (RF) unit, and a processor, wherein the processor
receives configuration information about a plurality of PUSCH
feedback modes, identifies information indicating a specific PUSCH
feedback mode for the PUSCH using uplink allocation information for
the PUSCH, and transmits the uplink control information through the
PUSCH in accordance with the specific PUSCH feedback mode.
[0007] The configuration information about the plurality of PUSCH
feedback modes may be received through Radio Resource Control (RRC)
signaling, and the uplink allocation information may be received
through a physical downlink control channel (PDCCH).
[0008] The information indicating the specific PUSCH feedback mode
may be identified using an index value contained in the uplink
allocation information.
[0009] The information indicating the specific PUSCH feedback mode
may be linked with an index of a resource block (RB) for the
PUSCH.
[0010] The information indicating the specific PUSCH feedback mode
may be linked with a hybrid automatic repeat and request (HARQ)
process for the PUSCH.
[0011] The information indicating the specific PUSCH feedback mode
may be linked with an index of a time interval to which the PUSCH
is transmitted.
[0012] The uplink control information may include first information
indicating a rank during a single-cell operation and second
information indicating a rank during a multi-cell operation.
Advantageous Effects
[0013] According to embodiments of the present invention, it is
possible to efficiently transmit a large amount of uplink control
information in a ratio communication system.
DESCRIPTION OF DRAWINGS
[0014] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention.
[0015] In the drawings:
[0016] FIG. 1 is a diagram showing a network architecture of an
Evolved Universal Mobile Telecommunications System (E-UMTS).
[0017] FIG. 2 is a diagram showing a user/control-plane protocol
for the E-UMTS.
[0018] FIG. 3 is a diagram showing the structure of a radio frame
used in the E-UMTS.
[0019] FIG. 4 is a diagram showing a resource grid of a radio
frame.
[0020] FIG. 5 is a diagram showing the structure of a downlink
subframe.
[0021] FIG. 6 is a diagram showing the structure of an uplink
subframe.
[0022] FIG. 7 is a diagram showing an Uplink Hybrid Automatic
Repeat request (UL HARQ) operation in a Long Term Evolution (LTE)
system.
[0023] FIG. 8 is a diagram showing the configuration of a Multiple
Input Multiple Output (MIMO) system.
[0024] FIG. 9 is a diagram showing channels from N.sub.T
Transmission (Tx) antennas to an i.sup.th Reception (Rx)
antenna.
[0025] FIG. 10 is a diagram showing a Reference Signal (RS) pattern
of an LTE system.
[0026] FIG. 11 is a diagram showing an example of performing
Cooperative Multipoint Transmission/Reception (CoMP).
[0027] FIG. 12 is a diagram showing an example of performing
communication given multiple component carriers.
[0028] FIG. 13 is a diagram showing a downlink scheduling
procedure.
[0029] FIG. 14 is a flow chart showing an example of changing
feedback mode according to an embodiment of the present
invention.
[0030] FIGS. 15 to 19 are examples of feedback format/structure
according to an embodiment of the present invention.
[0031] FIG. 20 is a block diagram showing a base station and a UE
applicable to the present invention.
MODE FOR INVENTION
[0032] The following technologies may be utilized in various radio
access systems such as a Code Division Multiple Access (CDMA)
system, a Frequency Division Multiple Access (FDMA) system, a Time
Division Multiple Access (TDMA) system, an Orthogonal Frequency
Division Multiple Access (OFDMA) system, or a Single Carrier
Frequency Division Multiple Access (SC-FDMA) system. The CDMA
system may be implemented as radio technology such as Universal
Terrestrial Radio Access (UTRA) or CDMA2000. The TDMA system may be
implemented as radio technology such as Global System for Mobile
communications (GSM)/General Packet Radio Service (GPRS)/Enhanced
Data Rates for GSM Evolution (EDGE). The OFDMA system may be
implemented as radio technology such as IEEE 802.11 (Wi-Fi), IEEE
802.16 (WiMAX), IEEE 802-20 or E-UTRA (Evolved UTRA). The UTRA
system is part of the Universal Mobile Telecommunications System
(UMTS). A 3.sup.rd Generation Partnership Project Long Term
Evolution (3GPP LTE) communication system is part of the E-UMTS
(Evolved UMTS), which employs an OFDMA system in downlink and
employs an SC-FDMA system in uplink. LTE-A (Advanced) is an evolved
version of 3GPP LTE.
[0033] In order to clarify the description, the 3GPP LTE/LTE-A will
be focused upon, but the technical scope of the present invention
is not limited thereto.
[0034] FIG. 1 is a diagram showing a network architecture of an
Evolved Universal Mobile Telecommunications System (E-UMTS). The
E-UMTS is an evolved version of a WCDMA UMTS and basic
standardization thereof is in progress under the 3GPP. The E-UMTS
is also referred to as a Long Term Evolution (LTE) system. For
details of the technical specifications of the UMTS and the E-UMTS,
refer to Release 7 and Release 8 of "3rd Generation Partnership
Project; Technical Specification Group Radio Access Network",
respectively.
[0035] Referring to FIG. 1, the E-UMTS mainly includes a User
Equipment (UE) 120, base stations (BSs) (or eNBs or eNode Bs) 110a
and 110b, and an Access Gateway (AG) which is located at an end of
a network (E-UTRAN) and which is connected to an external network.
Generally, the BS can simultaneously transmit multiple data streams
for a broadcast service, a multicast service and/or a unicast
service. One or more cells may exist for one BS. The cell provides
a downlink or uplink transmission service to several UEs using any
one of bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz. Different cells
may be set to provide different bandwidths. A BS controls data
transmission or reception to or from a plurality of UEs. The BS
transmits downlink scheduling information to a UE with respect to
downlink (DL) data so as to inform the UE of time/frequency domain,
coding, data size, Hybrid Automatic Repeat and request (HARQ)
associated information of the data to be transmitted, or the like.
The BS transmits uplink scheduling information to a UE with respect
to uplink (UL) data so as to inform the UE of time/frequency
domain, coding, data size, HARQ associated information used by the
UE, or the like. An interface for transmitting user traffic or
control traffic can be used between BSs. A Core Network (CN) may
include the AG and a network node or the like for user registration
of the UE. The AG manages mobility of a UE on a Tracking Area (TA)
basis. One TA includes a plurality of cells.
[0036] FIG. 2 is a diagram showing a user/control-plane protocol
stack for the E-UMTS. Referring to FIG. 2, protocol layers may be
divided into a first layer (L1), a second layer (L2) and a third
layer (L3) based on the three lower layers of an open system
interconnection (OSI) standard model which is well-known in the art
of communication systems.
[0037] The physical layer PHY, which is the first layer, provides
an information transfer service to a higher layer using a physical
channel. The physical layer is connected with a medium access
control (MAC) layer located at a higher level through a transport
channel, and data is transferred between the MAC layer and the
physical layer via the transport channel. Data is transferred
between physical layers of a transmission side and a reception side
via the physical channel.
[0038] The MAC layer of the second layer (L2) provides services to
a radio link control (RLC) layer, which is a higher layer, via a
logical channel. The RLC layer of the second layer (L2) enables
reliable data transmission. In the case where the MAC layer
performs the RLC function, the RLC layer is included as the
functional block of the MAC layer. The PDCP layer of the second
layer (L2) performs a header compression function that reduces the
size of an Internet protocol (IP) packet header containing
unnecessary control information having a relatively large size in
order to efficiently transmit the IP packets such as IPv4 or IPv6
packets over a radio interface having a limited bandwidth.
[0039] A radio resource control (RRC) layer located at the lowest
portion of the third layer (L3) is only defined in the control
plane and controls logical channels, transport channels and
physical channels in relation to the configuration,
reconfiguration, and release of the radio bearers (RBs). Here, the
RB signifies a service provided by the second layer (L2) for data
transmission between the UE 120 and the E-UTRAN.
[0040] FIG. 3 is a diagram showing the structure of a radio frame
used in the E-UMTS.
[0041] Referring to FIG. 3, the E-UTMS uses a 10 ms radio frame and
one radio frame includes 10 subframes. In addition, one subframe
includes two continuous slots. The length of one slot is 0.5 ms. In
addition, the slot includes a plurality of symbols (e.g., OFDM
symbols or SC-FDMA symbols).
[0042] FIG. 4 is a diagram showing a resource grid for a time
slot.
[0043] Referring to FIG. 4, the time slot includes a plurality of
OFDM symbols or SC-FDMA symbols and includes a plurality of
Resource Blocks (RBs) in a frequency domain. One RB includes
12.times.7(6) resource elements. The number of RBs included in the
time slot depends on frequency bandwidth set in a cell. Each column
of the resource grid indicates minimum resource defined by one
symbol and one subcarrier and is referred to as a Resource Element
(RE). Although the time slot includes 7 symbols and the RB includes
12 subcarriers, in FIG. 4, the present invention is not limited
thereto. For example, the number of symbols included in the time
slot may be changed according to the length of a Cyclic Prefix
(CP).
[0044] FIG. 5 is a diagram showing the structure of a downlink
subframe.
[0045] Referring to FIG. 5, in a downlink subframe of an LTE
system, an L1/L2 control region and a data region are multiplexed
using a Time Division Multiplexing (TDM) method. The L1/L2 control
region includes n (e.g., 3 or 4) first OFDM symbols of the subframe
and the remaining OFDM symbols are used in the data region. The
L1/L2 control region includes a Physical Downlink Control Channel
(PDCCH) for carrying downlink control information and the data
region includes a Physical Downlink Shared Channel (PDSCH) which is
a downlink data channel. In order to receive a downlink signal, a
User Equipment (UE) reads downlink scheduling information from the
PDCCH and receives downlink data on the PDSCH using resource
assignment information indicated by the downlink scheduling
information. Resources (that is, PDSCH) scheduled to the UE are
assigned in units of resource blocks or resource block groups.
[0046] The PDCCH informs the UE of information associated with
resource assignment of a Paging Channel (PCH) and a Downlink-Shared
Channel (DL-SCH), both of which are transfer channels, uplink
scheduling grant, HARQ information and the like. Information
transmitted through the PDCCH is generically called Downlink
Control Information (DCI). The PDCCH has a format which varies
according to information. The DCI format is changed according to
control information. Table 1 shows a DCI format 0 for uplink
scheduling.
TABLE-US-00001 TABLE 1 Field Bits Comment Format 1 Uplink grant or
downlink assignment Hopping flag 1 Frequency hopping on/off RB
assignment 7 Resource block assigned for PUSCH MCS 5 Modulation
scheme, coding scheme, etc. New Data Indicator 1 Toggled for each
new transport block TPC 2 Power control of PUSCH Cyclic shift for 3
Cyclic shift of demodulation reference DMRS signal CQI request 1
Request CQI feedback through PUSCH RNTI/CRC 16 16 bit RNTI
implicitly encoded in CRC Padding 1 Ensure format 0 matches format
1A in size Total 38 -- *MCS: Modulation and Coding Scheme *TPC:
Transmit Power Control *RNTI: Radio Network Temporary Identifier
*CRC: Cyclic Redundancy Check
[0047] The UE to which the PDCCH is transmitted is identified using
the RNTI. For example, it is assumed that a PDCCH is CRC-masked
with an RNTI "A" and uplink radio resource assignment information
"B" (e.g., frequency location) and transmission format information
"C" (e.g., a transmission block size, modulation, coding
information or the like) are transmitted. In this case, UEs located
in a cell monitor the PDCCH using RNTI information and a specific
UE with RNTI "A" performs uplink transmission according to
information about B and C obtained from the PDCCH.
[0048] FIG. 6 is a diagram showing the structure of an uplink
subframe used in the LTE system.
[0049] Referring to FIG. 6, the uplink subframe includes a
plurality of slots (e.g., 2). Each slot may include different
numbers of SC-FDMA symbols according to the length of the CP. The
uplink subframe is divided into a data region and a control region
in a frequency domain. The data region includes a PUSCH and is used
to transmit a data signal such as voice. The control region
includes a PUCCH and is used to transmit uplink control
information. The PUCCH includes RB pairs located at both ends of
the data region on a frequency axis and hops between slots. The
uplink control information includes a Scheduling Request (SR) for
requesting uplink transfer resources, HARQ Acknowledgement
(ACK)/Negative ACK (NACK) for downlink data, downlink channel
(state) information and the like. The downlink channel (state)
information includes a Precoding Matrix Indicator (PMI), a Rank
Indicator (RI) and a Channel Quality Indicator (CQI).
[0050] HARQ
[0051] In a wireless communication system, if plural UEs having
data to be transmitted in uplink/downlink are present, a BS selects
which UE will transmit data in each Transmission Time Interval
(TTI) (e.g., subframe). In particular, in a system operated using
multiple carriers and the like, a BS selects UEs which will
transmit data in uplink/downlink in each TTI and selects a
frequency band used when each UE transmits the data.
[0052] In uplink, UEs transmit reference signals (or pilots) and a
BS checks channel states of the UEs using the reference signals
transmitted from the UEs and selects UEs which will transmit data
in uplink in each unit frequency band. The BS informs the UEs of
the selected results. That is, the base station transmits, to a UE
which is scheduled to perform uplink transmission in a specific
TTI, an uplink assignment message enabling the UE to transmit data
using a specific frequency band. The uplink assignment message is
also called UL grant. The UE transmits data in uplink in response
to the uplink assignment message. The uplink assignment message
includes information about a UE Identity (ID), RB assignment
information, a payload or the like, and may further include an
Incremental Redundancy (IR) version, a New Data Indication (NDI),
and the like.
[0053] In the case where a synchronous non-adaptive HARQ scheme is
applied, when a UE allotted a specific time retransmits data, a
retransmission time is systematically decided in advance (e.g.,
after four subframes from a NACK reception time). Accordingly, a UL
grant message transmitted from a BS to a UE is only transmitted
upon initial transmission and retransmission is performed by an
ACK/NACK signal. In contrast, in the case where an asynchronous
HARQ scheme is applied, since a retransmission time is not decided
in advance, a BS should transmit a retransmission request message
to a UE. In addition, since frequency resources or MCS for
retransmission is changed according to a transmission time, when a
BS transmits a retransmission request message, a HARQ process
index, an IR version and NDI information should be transmitted in
addition to a UE ID, RB assignment information and a payload.
[0054] FIG. 7 is a diagram showing an Uplink Hybrid Automatic
Repeat request (UL HARQ) operation in a Long Term Evolution (LTE)
system. In the LTE system, a UL HARQ scheme uses a synchronous
non-adaptive HARQ scheme. When using 8-channel HARQ, HARQ process
numbers are 0 to 7. One HARQ process operates per TTI (e.g.,
subframe). Referring to FIG. 7, a BS 110 transmits UL grant to a UE
120 through a PDCCH (S700). The UE 120 transmits uplink data to the
BS 110 using an RB and MCS specified by the UL grant four subframes
(e.g., subframe 4) after the UL grant is received (e.g., subframe
0) (8702). The BS 110 decodes the uplink data received from the UE
120 and then generates an ACK/NACK signal. If decoding of the
uplink data fails, the BS 110 transmits a NACK signal to the UE 120
(704). The UE 120 retransmits the uplink data four subframes after
a NACK is received (S706). The initial transmission and
retransmission of the uplink data are performed by the same HARQ
processor (e.g. HARQ process 4).
[0055] MIMO System Modeling
[0056] FIG. 8 is a diagram showing the configuration of a typical
MIMO wireless communication system.
[0057] Referring to FIG. 8, a simultaneous increase in Transmission
(Tx) antennas of a transmitter to N.sub.T and in Reception (Rx)
antennas of a receiver to N.sub.R increases a theoretical channel
transmission capacity in proportion to the number of antennas,
compared to use of a plurality of antennas at only one of the
transmitter and the receiver. Therefore, transmission rate is
increased and frequency efficiency is remarkably increased.
Transmission rate increases up to the product of maximum
transmission rate (R.sub.o) and rate increase (R.sub.i).
R.sub.i=min(N.sub.T,N.sub.R) [Equation 1]
[0058] For instance, a MIMO communication system with four Tx
antennas and four Rx antennas may achieve a four-fold increase in
transmission rate theoretically, relative to a single-antenna
system. Since the theoretical capacity increase of the MIMO system
was proved in the middle 1990's, many techniques have been actively
studied to increase data rate in real implementation. Some of the
techniques have already been reflected in various wireless
communication standards including standards for 3.sup.rd Generation
(3G) mobile communications, future-generation Wireless Local Area
Network (WLAN), etc.
[0059] Concerning the research trend of MIMO up to now, active
studies are underway in many respects of MIMO, inclusive of studies
of information theory related to calculation of multi-antenna
communication capacity in diverse channel environments and multiple
access environments, studies of measuring MIMO radio channels and
MIMO modeling, studies of time-space signal processing techniques
to increase transmission reliability and transmission rate,
etc.
[0060] A communication scheme in the MIMO system will be described
below using a mathematical model. It is assumed that there are
N.sub.T Tx antennas and N.sub.R Rx antennas in the MIMO system.
[0061] Regarding a transmission signal, up to N.sub.T pieces of
information can be transmitted through the N.sub.T Tx antennas, as
expressed as the following vector.
s=[s.sub.1,s.sub.2, . . . ,s.sub.N.sub.T].sup.T [Equation 2]
[0062] A different transmit power may be applied to each piece of
transmission information s.sub.1,s.sub.2, . . . ,s.sub.N.sub.T. Let
the transmit power levels of the transmission information be
denoted by P.sub.1,P.sub.2, . . . ,P.sub.N.sub.T, respectively.
Then the transmit power-controlled transmission information s may
be given as [Equation 3].
s=[s.sub.1,s.sub.2, . . .
,s.sub.N.sub.T].sup.T=[P.sub.1s.sub.1,P.sub.2s.sub.2, . . .
,P.sub.N.sub.Ts.sub.N.sub.T].sup.T [Equation 3]
[0063] s may be expressed as a diagonal matrix P of transmit
power.
s ^ = [ P 1 0 P 2 0 P N T ] [ s 1 s 2 s N T ] = Ps [ Equation 4 ]
##EQU00001##
[0064] Let's consider a case where actual N.sub.T transmitted
signals x.sub.1,x.sub.2, . . . ,x.sub.N.sub.T are configured by
applying a weight matrix W to the transmit power-controlled
information vector s. The weight matrix W functions to
appropriately distribute the transmission information to the Tx
antennas according to transmission channel statuses, etc. These
transmitted signals x.sub.1,x.sub.2, . . . ,x.sub.N.sub.T are
represented as a vector X, which may be determined as
x = [ x 1 x 2 x i x N T ] [ w 11 w 12 w 1 N T w 21 w 22 w 2 N T w i
1 w i 2 w iN T w N T 1 w N T 2 w N T N T ] [ s ^ 1 s ^ 2 s ^ j s ^
N T ] = W s ^ = WPs [ Equation 5 ] ##EQU00002##
where w.sub.ij denotes a weight for a j.sup.th piece of information
s.sub.j transmitted through an i.sup.th Tx antenna and the weights
are expressed as the matrix W. W is also referred to as a precoding
matrix.
[0065] Given N.sub.R Rx antennas, signals received at the Rx
antennas, y.sub.1,y.sub.2, . . . ,y.sub.N.sub.R may be represented
as the following vector.
y=[y.sub.1,y.sub.2, . . . ,y.sub.N.sub.R].sup.T [Equation 6]
[0066] When channels are modeled in the MIMO wireless communication
system, they may be distinguished according to the indexes of Tx
and Rx antennas. A channel between a j.sup.th Tx antenna and an
i.sup.th Rx antenna is represented as h.sub.ij. It is to be noted
herein that the index of the Rx antenna precedes that of the Tx
antenna in h.sub.ij.
[0067] FIG. 9 is a diagram showing channels from N.sub.T TX
antennas to an i.sup.th Rx antenna. Referring to FIG. 2, the
channels from the N.sub.T Tx antennas to the i.sup.th Rx antenna
may be expressed as [Equation 7].
h.sub.i.sup.T=[h.sub.i1,h.sub.i2, . . . ,h.sub.iN.sub.T] [Equation
7]
[0068] Hence, all channels from the N.sub.T Tx antennas to the
N.sub.RRx antennas may be expressed as the following matrix.
H = [ h 1 T h 2 T h i T h N R T ] = [ h 11 h 12 h 1 N T h 21 h 22 h
2 N T h i 1 h i 2 h iN T h N R 1 h N R 2 h N R N T ] [ Equation 8 ]
##EQU00003##
[0069] In the channel matrix H, the number of rows is equal to that
of the Rx antennas, N.sub.R and the number of columns is equal to
that of the Tx antennas, N.sub.T. Thus, the channel matrix H is of
size N.sub.R.times.N.sub.T.
[0070] Actual channels experience the above channel matrix H and
then are added with Additive White Gaussian Noise (AWGN). The AWGN
n.sub.1,n.sub.2, . . . ,n.sub.N.sub.R added to the N.sub.R Rx
antennas is given as the following vector.
n=[n.sub.1,n.sub.2, . . . ,n.sub.N.sub.R].sup.T [Equation 9]
[0071] From the above modeled equations, the received signal is
given as
y = [ y 1 y 2 y i y N R ] = [ h 11 h 12 h 1 N T h 21 h 22 h 2 N T h
i 1 h i 2 h iN T h N R 1 h N R 2 h N R N T ] [ x 1 x 2 x j x N T ]
+ [ n 1 n 2 n i n N R ] = Hx + n [ Equation 10 ] ##EQU00004##
[0072] Meanwhile, the rank of a matrix is defined as the minimum of
the numbers of independent rows or columns. Accordingly, the rank
of the matrix is not larger than the number of rows or columns. For
example, the rank of the channel matrix H, rank(H) is limited as
follows.
rank(H).ltoreq.min(N.sub.T,N.sub.R) [Equation 11]
[0073] If the matrix is eigen value-decomposed, its rank may be
defined as the number of non-zero eigen values. Similarly, in case
of Singular Value Decomposition (SVD), the rank may be defined as
the number of non-zero singular values. In a physical sense,
therefore, the rank of a channel matrix is the maximum number of
different pieces of information that can be transmitted on given
channels.
[0074] Reference Signal (RS)
[0075] In a wireless communication system, since packets are
transmitted through a radio channel, a signal may be distorted
during transmission. In order to enable a reception side to
correctly receive the distorted signal, distortion of the received
signal should be corrected using channel information (or channel
state information). In order to detect the channel information, a
method of transmitting a signal which is known to both the
transmission side and the reception side and detecting channel
information using a distortion degree when the signal is received
through a channel is mainly used. The signal known to both the
transmission side and the reception side is referred to as a pilot
signal or a reference signal (RS). When transmitting or receiving
data using multiple antennas, the channel states between the
transmission antennas and the reception antennas should be detected
in order to correctly receive the signal. Accordingly, each
transmission antenna has an individual RS.
[0076] In the wireless communication system, the RS may be divided
into two signals according to use thereof: an RS used to acquire
channel information (channel measurement RS) and an RS used to
demodulate data (demodulation RS). For convenience, a downlink RS
will be focused upon. Since the channel measurement RS is used to
acquire downlink channel information, the channel measurement RS is
transmitted over the entire band. In addition, even a UE which does
not receive downlink data in a specific subframe should receive and
measure the channel measurement RS. In addition, the channel
measurement RS is used to measure handover or the like. Meanwhile,
the demodulation RS indicates an RS which is sent through resource
together when the BS transmits downlink data. When the UE receives
the demodulation RS, a channel through which data is transmitted
may be estimated and thus the data is demodulated.
[0077] FIG. 10 is a diagram showing a Reference Signal (RS) pattern
of an LTE system.
[0078] Referring to FIG. 10, in the LTE system, two kinds of
downlink RSs are defined for a unicast service: a Common RS (CRS)
(0.about.3) for acquiring channel state information and measuring
handover or the like and a UE-specific RS (D) for data
demodulation. The UE-specific RS is also called a dedicated RS. In
the LTE system, the UE-specific RS is used only for data
demodulation and the CRS is used both for channel information
acquisition and data demodulation. The CRS is a cell-specific
signal and is transmitted on a per subframe basis through the
entire band. Since the LTE system supports a maximum of four
transmission antennas in downlink, CRSs for a maximum of four
antenna ports may be transmitted according to the number of
transmission antennas of a BS. For example, if the number of
transmission antennas of the BS is two, CRSs for antenna ports 0
and 1 are transmitted and, if the number of transmission antennas
is four, CRSs for antenna ports 0 to 3 are transmitted. The
respective CRSs for the antenna ports are multiplexed within RBs
using a Frequency Division Multiplexing (FDM) method.
[0079] An LTE-A system, an evolved form of the LTE system, supports
a maximum of eight transmission antennas in downlink. Accordingly,
RSs for a maximum of eight transmission antennas should be
supported. Since only RSs for a maximum of four antenna ports are
defined as downlink RSs in the LTE system, if a BS has four to
eight downlink transmission antennas in the LTE-A system, RSs for
the antennas should be additionally defined. Channel measurement
RSs and demodulation RSs should be designed as the RSs for a
maximum of eight transmission antenna ports.
[0080] One important consideration in design of the LTE-A system is
backward compatibility. That is, an LTE UE should operate well even
in the LTE-A system and the LTE-A system should support the LTE UE.
In terms of RS transmission, in a time-frequency domain in which
CRSs defined in the LTE system are transmitted, RSs for a maximum
of eight transmission antenna ports should be additionally defined.
However, if an RS pattern for a maximum of eight transmission
antennas is added to the entire band per subframe using the same
method as the existing CRS of the LTE system, RS overhead is
excessively increased in the LTE-A system. Accordingly, RSs newly
designed in the LTE-A system are roughly divided into two types: a
channel measurement RS for selecting an MCS, a Precoding Matrix
Indicator (PMI) or the like (Channel
[0081] State Information RS, Channel State Indication RS (CSI-RS),
etc.) and a Data Demodulation RS (DM-RS). The CSI-RS is used for
channel measurement, whereas the existing CRS is used for channel
measurement or handover measurement. The CSI-RS may also be used
for handover measurement. Since the CSI-RS is transmitted to
acquire a channel state, the CSI-RS need not be transmitted per
subframe, unlike the existing LTE CRS. Accordingly, the CSI-RS may
be intermittently transmitted on a time axis in order to reduce
overhead. For example, the CSI-RS may be periodically transmitted
with a period which is an integral multiple of one subframe or may
be transmitted with a specific transmission pattern. The
transmission period or pattern of the CSI-RS may be configured by a
BS. In order to measure the CSI-RS, a UE should determine
information regarding a time-frequency location of the CSI-RS,
CSI-RS sequence, and CSI-RS frequency shift for each antenna port
of a cell to which the UE belongs. In contrast, the DM-RS is
dedicatedly transmitted to a UE scheduled in a time-frequency
domain for data demodulation. That is, the DM-RS for a specific UE
is transmitted only in a region to which the UE is scheduled, that
is, in a time-frequency domain in which data is received.
[0082] Cooperative Multipoint Transmission/Reception (CoMP)
Method
[0083] Future systems, after the LTE-A system, will employ a method
for enabling cooperation among several cells so as to improve
performance. Such a mode is called Cooperative Multipoint
Transmission/Reception (CoMP). The CoMP method indicates a method
for enabling two or more BSs, access points or cells to cooperate
with each other so as to communicate with a UE, in order to more
smoothly perform communication between a specific UE and a BS, an
access point or a cell. In the present invention, BS, access point
and cell have the same meaning.
[0084] FIG. 11 is a diagram showing an example of performing CoMP.
Referring to FIG. 11, a wireless communication system includes a
plurality of base stations BS1, BS2 and BS3 for performing the CoMP
and a UE. The plurality of base stations BS1, BS2 and BS3 for
performing the CoMP may cooperate with each other so as to
efficiently transmit data to the UE. The CoMP may be roughly
divided into two types depending on whether or not data is
transmitted from each base station for performing the CoMP: Joint
Processing (CoMP Joint Processing (CoMP-JP) and Cooperative
scheduling/beamforming (CoMP-CS)).
[0085] In the CoMP-JP, data transmitted to one UE is simultaneously
transmitted from the base stations, which perform the CoMP, to the
UE and the UE couples the signals from the base stations so as to
improve reception performance. In contrast, in the CoMP-CS, data
transmitted to one UE is transmitted through one base station at a
certain instant and scheduling or beamforming is performed such
that interference with another base station is minimized.
[0086] Carrier Aggregation (CA)
[0087] The LTE-A system uses carrier aggregation or bandwidth
aggregation technology using an uplink/downlink bandwidth greater
than that of a plurality of uplink/downlink frequency blocks in
order to use a wider frequency band. Each frequency block is
transmitted using a Component Carrier (CC). In the present
specification, the CC may be a frequency block and/or a central
carrier of a frequency block for carrier aggregation according to
context.
[0088] FIG. 12 is a diagram showing an example of performing
communication given multiple component carriers. FIG. 11 may
correspond to a communication example of an LTE-A system.
[0089] Referring to FIG. 12, five 20-MHz CCs may be aggregated so
as to support a bandwidth of 100 MHz in uplink/downlink. CCs may be
contiguous or non-contiguous in a frequency domain. FIG. 11 shows
the case where the bandwidth of an uplink CC and the bandwidth of a
downlink CC are equal and symmetrical, for convenience. However,
the bandwidths of the CCs may be independently set. In addition,
asymmetrical carrier aggregation in which the number of uplink CCs
and the number of downlink CCs are different is possible. The
asymmetrical carrier aggregation may occur due to limited
availability of frequency bands or may be artificially generated by
network configuration. For example, although the entire band of the
system includes N CCs, a frequency band in which a specific UE
performs reception may be limited to M (<N) CCs. Various
parameters for carrier aggregation may be set using a cell-specific
method, a UE group-specific method or a UE-specific method.
[0090] Although FIG. 12 shows the case where uplink signals and
downlink signals are transmitted through one-to-one mapped CCs, CCs
over which signals are actually transmitted may be changed
according to network configuration or signal type. For example, if
a scheduling command is transmitted in downlink through a DL CCL1,
data transmitted according to a scheduling command may be
transmitted through another DL CC or UL CC. In addition, uplink
control information may be transmitted in uplink through a specific
UL CC regardless of whether or not mapping between CCs is
performed. Similarly, downlink control information may be
transmitted through a specific DL CC.
[0091] FIG. 13 is a diagram showing a downlink scheduling
procedure.
[0092] Referring to FIG. 13, a BS transmits an RS to a UE (S1200).
The RS includes a channel measurement RS, for example, a CRS or a
CSI-RS. The UE performs channel measurement using the RS received
from the BS (S1202). Thereafter, the UE feeds back downlink channel
information computed through channel measurement to the BS (81204).
The channel information fed back from the UE to the BS includes a
covariance matrix of a channel, an interference and noise signal
level (e.g., a signal-to-noise ratio (SNR), a
signal-to-interference-plus-noise ratio (SINR), a
carrier-to-interference-plus-noise ratio (CINR), or the like),
channel direction information, a Precoding Matrix Indicator (PMI),
a Rank Indicator (RI), a Channel Quality Indicator (CQI), a
Received Signal Strength Indicator (RSSI), a Reference Signal
Received Quality (RSRQ), and the like. Thereafter, the BS may
perform downlink scheduling with respect to the UE using the
downlink channel information received through the feedback
information (S1206).
[0093] Coordinated Multi-Point (CoMP) scheme, (asymmetric) CA
scheme, and Multiple Input Multiple Output (MIMO) scheme supporting
8 downlink (DL) transmission (Tx) antennas have recently been
introduced to a Long Term Evolution-Advanced (LTE-A) system, such
that an amount of uplink control information for supporting the
aforementioned schemes is considerably increased. As an example, in
the CoMP scheme, a user equipment (UE) that has to perform CoMP
needs to measure Channel State Indication-Reference Signals
(CSI-RSs) of both a serving cell for the UE and a neighbor cell
co-operating with the serving cell, and has to provide a base
station (BS) with a feedback result of the measured CSI-RSs.
However, the feedback structure defined in LTE is unable to report
a large amount of newly increased control information via uplink.
Therefore, it is necessary to develop a new uplink control
information feedback scheme.
[0094] In order to solve the above-mentioned problems, the
aperiodic PUSCH-based feedback scheme of the conventional LTE can
be used more effectively than the periodic PUCCH-based feedback
scheme of the conventional LTE. The conventional LTE aperiodic
PUSCH feedback scheme enables a base station (BS) to announce
allocation information of a Resource Block (RB) at which feedback
information will be received, modulation information, etc. through
uplink grant control information in the same manner as in general
uplink data transmission. Feedback information may be transmitted
alone or together with data information through PUSCH.
[0095] The following Table 2 shows some parts of DCI Format 0
indicating aperiodic PUSCH feedback of the LTE. In the DCI Format
0, under the condition that a CQI request field is set to `1`, the
number of Physical Resource Blocks (PRBs) is `4` or less, and
I.sub.MCS indicating an MCS index is set to `29`, the UE only feeds
back channel information (or channel state information (CSI)) of
downlink (DL) through PUSCH. If only the CQI request field is set
to `1`, the UE multiplexes the channel information with UL data and
feeds back them through the PUSCH. If the CQI request field is set
to `0`, the UE does not perform PUSCH feedback but transmits-UL
data only.
TABLE-US-00002 TABLE 2 Bits Aperiodic PUSCH Feedback RB assignment
7 PRB <= 4 MCS 5 I.sub.MCS = 29 CQI request 1 1
Embodiment 1: Dynamic Feedback Mode Adaptation
[0096] The conventional LTE aperiodic PUSCH feedback scheme
announces one feedback mode through RRC signaling, and switches
PUSCH feedback transmission on or off through UL grant information.
In case of the RRC signaling, a time delay of several tens of msec
is required so that the feedback mode switching based on the RRC
signaling is appropriate for simple communication environments or
stable communication environments. However, in complex or rapidly
fluctuating environments, the RRC-based feedback mode switching is
unable to provide appropriate feedback information. In particular,
considering CoMP and carrier aggregation technologies introduced to
the LTE-A system, the conventional aperiodic PUSCH feedback scheme
has limited ability to provide appropriate feedback
information.
[0097] In the case of using CoMP as an example, if a UE's
topographical location is changed, a set of neighbor cells helpful
to the CoMP is changed, such that a feedback mode needs to be
switched. In more detail, when a UE performs CoMP transmission and
reception through 3 cells as shown in FIG. 11, the UE has to feed
back channel information from the cells 1, 2 and 3 so as to perform
the CoMP operation initiated from the cells 1, 2 and 3. However,
provided that only cells 1 and 3 perform the CoMP operation due to
change in UE position or channel environment variation, it is more
efficient for the UE to feed back only channel information of the
cells 1 and 3.
[0098] Therefore, a method for dynamically changing a feedback mode
according to the communication environment or request is needed.
For this purpose, a method for enabling the BS to inform the UE of
configuration information of the corresponding feedback mode and
mode switching information through PDCCH may be devised. In this
case, although dynamic switching between feedback modes is
possible, signaling overhead is unavoidably increased due to
frequent transmission of feedback mode configuration information.
On the other hand, basic information (e.g., measurement set, report
set, etc.) for CoMP, basic information for carrier aggregation, and
basic information for MIMO operations are designated by upper layer
signaling (e.g., RRC signaling), and the designated basic
information is semi-statically maintained. Therefore, in order to
implement not only reduction in the amount of signaling overhead
but also rapid feedback mode switching, the present invention
proposes a two-stage feedback mode designating/switching scheme
which designates basic information about several feedback modes by
upper layer signaling and designates associated CSI content,
format, etc. through physical channel signaling.
[0099] The term "feedback mode designation` for use in the
embodiment of the present invention indicates allocation of
feedback resources. The feedback mode indicates a format of CSI
feedback to be fed back from the UE, scheme and content of the CSI
feedback, and allocation of resources associated with the CSI
feedback. In the present invention, the feedback mode may be simply
used together with a feedback format.
[0100] FIG. 14 is a conceptual diagram illustrating a method for
switching a feedback mode according to an embodiment of the present
invention.
[0101] Referring to FIG. 14, the base station (BS) transmits
information about several feedback modes (i.e., the set of feedback
modes) to the UE through upper layer signaling. (e.g., RRC
signaling) at step S1400. The information about the feedback mode
set may include basic information (e.g., configuration information,
identification (ID) information, mapping information, etc.). For
example, the information about the feedback mode set may include
the size of a used feedback mode set, and detailed information
about individual feedback modes contained in the feedback mode
set.
[0102] Nowadays, the LTE system includes a few channel feedback
modes. For example, the aperiodic feedback transmission scheme of
the LTE is classified into a No-PMI feedback mode, a single-PMI
feedback mode, and a multiple-PMI feedback mode. In addition, the
aperiodic feedback transmission mode is also classified into a
wideband CQI mode, a selected subband CQI mode, and a configured
subband CQI mode. The aforementioned feedback modes are selected to
provide a balance between feedback overhead and the accuracy of
channel information feedback. Therefore, when forming the feedback
mode set using the conventional feedback modes, it is possible to
perform dynamic switching of feedback modes in accordance with
variation in uplink traffic load. That is, the present invention
provides a means for effectively using downlink/uplink (DL/UL)
resources, such that it is possible to perform dynamic switching
between one scheme in which feedback accuracy is high and overhead
is large and the other scheme in which feedback accuracy is low and
overhead is small.
[0103] Table 3 shows one example of a feedback mode set for use in
the CoMP scheme. Table 3 assumes that three cells perform the CoMP
operation as shown in FIG. 11. If the number of CoMP cells is
changed, the feedback mode set may be extended or reduced.
TABLE-US-00003 TABLE 3 Indicator Feedback Mode 0 Single cell
feedback mode: cell 3 1 CoMP-CS mode: cell 1, 3 2 CoMP-CS mode:
cell 2, 3 3 CoMP-CS mode: cell 1, 2, 3 4 CoMP-JP mode: cell 1, 3 5
CoMP-JP mode: cell 2, 3 7 CoMP-JP mode: cell 1, 2, 3
[0104] For convenience of description and better understanding of
the present invention, although Table 3 exemplarily shows the
feedback/format sets for use in the CoMP scheme, the feedback mode
sets for use in the present invention are not limited to CoMP
operations such as a CoMP mode, a CoMP set size, etc., and can be
applied to other examples as necessary.
[0105] Meanwhile, under the condition that the BS performs
scheduling for the UE, assuming that a single-cell operation and a
CoMP operation are dynamically switched or JP (Joint Processing)
and CS/CB (Cooperative Scheduling/Cooperative Beamforming) from
among CoMP operations are dynamically switched, the UE has to feed
back CSI information in such a manner that all cases (single-cell
operation, JP, and CS/CB) are possible. When the UE receives a
downlink (DL) service, feedback resources, content, format, etc.
are changed according to cases, e.g., a case in which the UE
receives the DL service using a single-cell scheme, a case in which
the UE receives the UL service by switching both the single-cell
operation scheme and JP and CS/CB schemes, a case in which the UE
receives the UL service by switching the single-cell operation
scheme and the JP scheme, and a case in which the UE receives the
UL service by switching the single-cell operation scheme and the
CS/CB scheme. Table 4 shows another example of a feedback mode set
taking into consideration the aforementioned CoMP operation.
TABLE-US-00004 TABLE 4 Indicator Feedback Mode 1 CSI in which only
single cell operation is considered 2 CSI in which single cell
operation + JP + CS/CB (PCI (Phase Correction Information)
required) are considered 3 CSI in which single cell operation + JP
(PCI required) are considered 4 CSI in which single cell operation
+ CS/CB are considered
[0106] In addition, the feedback mode set according to the
embodiment of the present invention may be adapted to indicate
channel information about which CC from among several downlink CCs
is fed back under a carrier aggregation (CA) situation. Table 5
exemplarily shows a feedback mode set for use in carrier
aggregation (CA). Table 5 assumes that the number of DL CCs is 3.
If the number of DL CCs is changed, the feedback mode set may be
extended or reduced.
TABLE-US-00005 TABLE 5 Indicator Feedback Mode 0 component carrier
1 1 component carrier 2 2 component carrier 3 3 component carrier
1, 2, 3
[0107] If the feedback mode set between the BS and the UE is
decided, the BS may indicate a feedback mode within the predefined
set through a UL grant message requesting aperiodic PUSCH feedback.
In more detail, a variety of methods 1) to 4) for indicating a
feedback mode through a UL grant message are proposed, and a
detailed description thereof will hereinafter be given.
[0108] 1) Explicit Signaling Method
[0109] A feedback mode indication field may be added to a PDCCH DCI
format for providing UL grant. The UE can recognize a feedback mode
from the corresponding field value upon receiving the UL grant. The
value of the feedback mode indication field may include indication
values shown in Tables 3 to 5 or offset values associated with the
indication values.
[0110] 2) Implicit Signaling Method Using Uplink Assigned RB
Index
[0111] A feedback mode can be indicated/identified using index
functions of UL RBs allocated for aperiodic PUSCH feedback
transmission. That is, information indicating the feedback mode may
be linked with an RB index for PUSCH feedback transmission. For
example, provided that a start index of allocated UL RBs is denoted
by `N_start` and the size of a feedback mode set indicated by RRC
signaling is denoted by `S_set`, a feedback mode can be indicated
and identified using a function of N_start and S_set. Equation 12
shows an example for indicating/identifying a feedback mode.
[Equation 12]
PeedbackModeIndicator=function(RB index) 12-1)
FeedbackModeIndicator=function(N_start) 12-2)
FeedbackModeIndicator=function(N_start,S.sub.--set) 12-3)
FeedbackModeIndicator=function(N_start mod S_set) 12-4).
FeedbackModeIndicator=N_start mod S_set 12-5)
[0112] In Equation 12, `FeedbackModeIndicator` is an indication
value indicating a feedback mode, and `mod` is a
modulo-operation.
[0113] Similarly, a feedback mode may be indicated by an index
function of a specific RB (e.g., final RB) from among allocated UL
RBs. In addition, the feedback mode may be linked with a resource
unit of a control channel used for allocating resources for
aperiodic PUSCH feedback transmission. For example, a feedback mode
may be indicated using a specific CCE (e.g., a first or last CCE)
from among CCEs used for transmitting a PDCCH for UL grant.
[0114] 3) Implicit Signaling Method Using Uplink HARQ Process
Index
[0115] A feedback mode can be indicated/identified using functions
of UL HARQ process indexes (or HARQ process IDs) allocated for
aperiodic PUSCH feedback transmission. That is, information
indicating the feedback mode may be linked with a HARQ process for
PUSCH feedback transmission. For example, provided that an index of
allocated UL HARQ process is denoted by `H` and the size of a
feedback mode set indicated by RRC signaling is denoted by `S_set`,
a feedback mode can be indicated and identified using a function of
the H and S_set parameters. Equation 1e shows an example of
indicating/identifying a feedback mode.
[Equation 13]
FeedbackModeIndicator=function(H) 13-1)
FeedbackModeIndicator=function(H,S_set) 13-2)
FeedbackModeIndicator=function(H mod S_set) 13-3)
FeedbackModeIndicator=H mod S_set 13-4)
[0116] On the other hand, since the LTE system uses the synchronous
HARQ scheme in UL, a UL HARQ process index is mapped one-to-one to
a subframe index. Therefore, the aforementioned scheme may also be
interpreted as a method for indicating a feedback mode as a
function of a subframe index that performs aperiodic PUSCH feedback
transmission. In addition, the aforementioned scheme may also be
interpreted as a method for indicating a feedback mode as a
function of a transmission subframe index of a PDCCH that requests
the aperiodic PUSCH feedback transmission.
[0117] 4) Implicit Signaling Method Using Subframe/Frame Index
[0118] As a modification of the aforementioned scheme (3), a
feedback mode can be indicated by a subframe index, a frame index,
or a System Frame Number (SFN) function to perform the aperiodic
PUSCH feedback transmission. That is, indication information of a
feedback mode may be linked with an index (e.g., a subframe index,
a frame index, SFN index, etc.) of a time interval for PUSCH
feedback transmission. In this case, tables for indicating
individual feedback modes are established by performing the RRC
signaling between the BS and the UE according to an index of a time
interval for PUSCH feedback transmission.
[0119] Next, the UE transmits UL control information to the BS
through PUSCH using the indicated feedback mode at step S1404.
However, the UL control information transmitted via PUSCH feedback
is not limited thereto, and the UL control information may further
include Channel State Information (CSI), for example, a covariance
matrix of a channel, a noise and interference signal level (e.g.,
SNR, SINR, CINR, etc.), channel direction information, PMI, RI, RR
(Rank Request), CQI, RSSI, RSRQ, etc.
Embodiment 2: Feedback Format/Structure
[0120] As CoMP scheme, CA scheme, and MIMO scheme for supporting
many more DL Tx antennas are introduced to the enhanced
communication system such as LTE-A, the amount of UL control
information for supporting the aforementioned schemes is
considerably increased. In addition, owing to a variety of
communication environments, feedback content, format, and an amount
of feedback information to be fed back are changed with time. In
the case of using CoMP as an example, in order to allow the UE to
receive a DL service using the CoMP scheme, it is necessary for
cooperative cells to recognize DL channel information from the
cooperative cells to the corresponding UE. That is, in order to
allow the UE to receive the CoMP service, it is necessary for DL
channels of individual cells to be fed back. If the UE transmits
feedback information about a DL channel to a serving BS, the
serving BS shares the feedback information with a neighbor BS to
cooperate with the serving BS. In association with a first case in
which a single cell provides a service to the UE and a second case
in which several cells collaboratively provide a service to the UE,
feedback content, format, an amount of feedback information, etc.
to be fed back from the UE are changed according to the first and
second cases.
[0121] Next, the feedback format/structure according to the
embodiment of the present invention will hereinafter be described
with reference to the accompanying drawings. For convenience of
description and better understanding of the present invention,
although the drawings and explanation are disclosed on the basis of
the CoMP, the CoMP-based explanation is disclosed for illustrative
purposes only. For example, a BS (or cell) for use in the CoMP
scheme may be replaced with a CC for carrier aggregation (CA), or
may be replaced with an antenna for the MIMO scheme. In addition,
the serving/neighbor BS (or cell) of the CoMP may be replaced with
a primary/secondary CC or antenna.
[0122] The CSI feedback format/structure for multiple cells must be
achieved on the basis of the feedback format/structure of a single
cell. Information required for feedback of a single cell may
include RI (Rank Index, Rank Indication), PMI (Precoding Matrix
Index), CQI (Channel Quality Indication, Channel Quality Index, or
Channel Quality Information), RR (Rank Request), etc. The RR (Rank
Request) is a field that enables the UE to request the increase or
reduction of rank from the BS, such that it is used to request UL
resources for feedback. When the UE feeds back multi-cell CSI, it
is necessary for the UE to basically feed back information about
RI, PMI, CQI, RR, etc. on a per cell basis. According to
cooperative methods of individual cells, i.e., according to a JP
scheme or a CS/CB (Coordinated Scheduling/Coordinated Beamforming)
scheme, feedback resource amount, feedback format/structure,
content, etc. may be changed.
[0123] FIGS. 15 and 16 illustrate examples of the feedback
format/structure for use in multiple cells (multi-cell).
[0124] In FIG. 15, CSI information of the serving cell and CSI
information of the neighbor cell are sequentially combined.
Information and order of cells that need to be actually fed back
from the UE must be engaged between the UE and the BS. In the
feedback format/structure shown in FIG. 15, RI is present in each
reporting cell, and an operation for reporting each RI through CSI
information of a neighbor cell is inefficient. Therefore, as shown
in FIG. 16, it is preferable that the RI be transmitted within only
the CSI feedback area of the serving cell. In this case, the RI
transmitted through the serving-cell feedback may be commonly used
by a neighbor cell 1 and a neighbor cell 2.
[0125] FIGS. 17 and 18 illustrate other examples of the feedback
format/structure for multiple cells.
[0126] In CoMP, if several cells collaborate with one another, it
is necessary for PCI (Phase Correction Indication or Phase
Correction Information) to be additionally fed back, resulting in
increased JP performance or throughput. In this case, since each
neighbor cell requires phase information of the serving cell, the
amount of feedback information is linearly increased in proportion
to the number of cooperative cells. Accordingly, when feedback of a
downlink (DL) channel from each CoMP cell to the UE is performed,
PCI information for each cell has to be added to the feedback.
[0127] FIG. 17 shows an exemplary simple feedback format/structure
when PCI is reported. In FIG. 17, PCI (N1) is phase correction
information of the neighbor cell 1 of the serving cell, and PCI
(N2) is phase correction information of the neighbor cell 2 of the
serving cell. FIG. 18 shows an exemplary feedback format/structure
in which only PCIs are collectively arranged. In the CS/CB-based
CoMP mode, PCI need not be used at all. Thus, if the UE for
receiving the CS/CB-based service continuously transmits the PCI,
inefficient feedback resources may be unavoidably generated. As a
result, PCI may be optionally included according to the CoMP
mode.
[0128] FIG. 19 shows another example of the feedback
format/structure.
[0129] In comparison between a first case in which the UE receives
a service from a single cell and a second case in which the UE
receives a service using the CoMP scheme, the second case has a
higher possibility of changing the corresponding UE rank as
compared to the first case. For example, the UE rank may be set to
2 when receiving the service using the CoMP scheme, whereas the UE
rank is set to 1 when receiving the service from one cell. However,
it is impossible for the conventional CSI feedback format/structure
to represent the change of UE rank.
[0130] Therefore, when CSI feedback for multiple cells is
performed, the present invention proposes a method for informing of
the increase or reduction of rank or the changed rank through
feedback information. For example, a delta RI field is defined in
the feedback format/structure, such that the increase or reduction
of rank or the changed rank can be directly notified. Preferably,
the present invention proposes a method for reusing the RI field
for the delta RI field during the CSI feedback for multiple cells.
For example, some parts (for convenience of description, a
corresponding part is denoted by a delta RI field) of the RI field
may be adapted to indicate the delta rank (i.e., in CoMP, variation
in rank or the increase or reduction of rank). In more detail,
assuming that the RI field is composed of 3 bits, 2 bits may
indicate a rank used when a service is received from a single cell
and 1 bit may indicate a delta rank representing the
increment/decrement of rank. If the rank is set to 1, the delta
rank may be adapted only to indicate the increase/reduction of rank
or no-change of rank.
[0131] Table 6 shows exemplary signaling of the delta rank using
the delta RI field.
TABLE-US-00006 TABLE 6 Delta RI is 1 bit: If Delta RI = 1, then
rank 1 is increased by 1 If else delta RI = 0, then rank is not
changed Delta RI is 2 bits: If delta RI = 00, then rank is not
changed Else if delta RI = 01, then rank is increased by 1 Else if
delta RI = 10, then rank 1 is reduced by 1 Else if delta RI = 11,
reserved
[0132] When the UE feeds back CSI for multiple cells, feedback
information can be generally classified into feedback information
about the serving cell and CSI feedback information about a CoMP
set (i.e., a neighbor cell). CSI information used when only a
single-cell operation is considered and CSI information used when
the CoMP operation is considered need to be added to the feedback
information of the serving cell. That is, an optimum CQI/PMI during
the single-cell operation and an optimum CQI/PMI of the serving
cell during the CoMP operation need to be additionally fed
back.
[0133] As described above, the UE rank may be changed during the
CoMP operation. If the UE rank is changed, a PMI codebook fed back
from the UE is also changed. That is, if the rank is 1, the UE has
to report a specific PMI that is most appropriate amoung the Rank 1
PMI codebook. If the rank is 2, the UE has to report a specific PMI
that is most appropriate among the Rank 2 PMI codebook. Therefore,
if the rank is changed during the CoMP operation, the UE must feed
back information on the changed rank while simultaneously selecting
a PMI codebook in accordance with the changed rank, so that the UE
has to report the most appropriate PMI within the selected PMI
codebook. In addition, a CQI used when the corresponding PMI is
used must also be fed back.
[0134] For example, it is assumed that, under the condition that
the rank is set to 1 at the single-cell operation, the rank is
increased to 2 under the CoMP-based service. In this case, CSI
feedback information about the serving cell must report the most
appropriate PMI from among the Rank 1 codebook in consideration of
the single cell operation, and must also report the most
appropriate PMI from among the Rank 2 codebook in consideration of
the CoMP operation. In addition, a PMI (in the aforementioned
example, Rank 2 Codebook) of a cooperating neighbor cell must be
selected from among the PMI codebook in accordance with the changed
rank, and the selected PMI must be fed back.
[0135] Referring to FIG. 19, PMI(SC) indicates a PMI of the serving
cell under the assumption of the single cell operation, and PMI(MC)
indicates a PMI of the serving cell under the assumption of the
CoMP operation. For the efficiency of feedback, when the UE selects
PMI(MC), the PMI(MC) must be selected from among objects including
PMI(SC). That is, PMI(MC) must be selected from among PMIs, each of
which includes columns (vectors) of the PMI (SC). The
aforementioned PMI selection method is a PMI restriction method to
reduce the number of signaling bits. That is, if the rank is
increased during a multi-cell based service, the added vector space
caused by the multi-cell operation must be orthogonal to a vector
space formed under the conventional single-cell operation. In
addition, only the added vector space is fed back. That is, for
PMI(MC), only changed/added part from the PMI(SC) is fed back. For
example, PMI of Rank=1 and PMI of Rank=2 for use in the current LTE
system will hereinafter be described in detail. Table 7 illustrates
a downlink (DL) codebook defined in the LTE system.
TABLE-US-00007 TABLE 7 Number of layers (Rank) Codebook index 1 2 0
1 2 [ 1 1 ] ##EQU00005## 1 2 [ 1 0 0 1 ] ##EQU00006## 1 1 2 [ 1 - 1
] ##EQU00007## 1 2 [ 1 1 1 - 1 ] ##EQU00008## 2 1 2 [ 1 j ]
##EQU00009## 1 2 [ 1 1 j - j ] ##EQU00010## 3 1 2 [ 1 - j ]
##EQU00011##
[0136] In the single cell operation, if Rank is set to 1 and
PMI(SC) is set to 0 (codebook index: 0) and Rank is changed to 2 by
the CoMP operation, a PMI including a vector in which the codebook
index is 0 is selected as PMI(MC) from among the Rank 2 codebook.
In this example, the codebook index of the PMI(MC) is 1. Therefore,
signaling may be carried out using only one bit. Taking into
consideration the scheme of the present invention, selecting the
PMI(MC), PMI(MC) is directly decided by PMI(SC), such that the BS
can recognize PMI(MC) without receiving the feedback result of the
PMI(MC) from the UE.
[0137] Changing the PMI during the CoMP mode indicates that a CQI
of the corresponding UE is changed. Therefore, information about
the changed CQI must also be fed back. It is assumed that a CQI of
the serving cell under the single-cell operation is denoted by
CQI(SC) and a CQI of the serving cell under the CoMP mode is
denoted by CQI(MC). CQI(MC) indicates a CQI when PMI(MC) is used. A
delta CQI may be denoted by a variation width indicating how much
the CQI(MC) is changed as compared to CQI(SC). In addition, when
CQI of the neighbor cell is fed back from the UE, the UE may
configure and transmit CQI information in such a manner that the
serving cell can calculate/estimate CQI(MC). Therefore, the UE need
not explicitly feed back the delta CQI.
[0138] The aforementioned scheme may also be used as a feedback
scheme for simultaneously supporting SU-MIMO and MU-MIMO in a
single-cell operation. When switching from SU-MIMO to MI-MIMO or
switching from MU-MIMO to SU-MIMO, the UE rank is changed, such
that the aforementioned scheme can be used to switch between
SU-MIMO and MI-MIMO.
[0139] FIG. 20 is a block diagram showing a BS and a UE applicable
to the present invention.
[0140] Referring to FIG. 20, a wireless communication system
includes a BS 110 and a UE 120. In downlink, a transmitter is a
portion of the BS 110 and a receiver is a portion of the UE 120. In
uplink, a transmitter is a portion of the UE 120 and a receiver is
a portion of the BS 110. The BS 110 includes a processor 112, a
memory 114, and a Radio Frequency (RF) module 116. The processor
112 may be configured to implement procedures and/or methods
proposed by the present invention. The memory 114 is connected to
the processor 112 so as to store a variety of information
associated with the operation of the processor 112. The RF module
116 is connected to the processor 112 so as to transmit and/or
receive an RF signal. The UE 120 includes a processor 122, a memory
124 and an RF module 126. The processor 112 may be configured to
implement procedures and/or methods proposed by the present
invention. The memory 124 is connected to the processor 122 so as
to store a variety of information associated with the operation of
the processor 122. The RF module 126 is connected to the processor
122 so as to transmit and/or receive an RF signal. The BS 110
and/or the UE 120 may have a single antenna or multiple antennas.
Although not shown, the UE 120 may further include at least one of
a power management module, a battery, a display, a keypad, a SIM
card (optional), a speaker and a microphone.
[0141] The above-described embodiments are proposed by combining
constituent components and characteristics of the present invention
according to a predetermined format. The individual constituent
components or characteristics should be considered optional on the
condition that there is no additional remark. If required, the
individual constituent components or characteristics need not be
combined with other components or characteristics. Also, some
constituent components and/or characteristics may be combined to
implement the embodiments of the present invention. The order of
operations disclosed in the embodiments of the present invention
may be changed. Some components or characteristics of any
embodiment may also be included in other embodiments, or may be
replaced with those of the other embodiments as necessary. In
addition, embodiments may be configured by combining claims which
do not have an explicit relationship or new claims may be added by
amendment after application.
[0142] The above-mentioned embodiments of the present invention are
disclosed on the basis of a data communication relationship between
a base station and a mobile station. In this case, the base station
is used as a terminal node of a network via which the base station
can directly communicate with the mobile station. Specific
operations to be conducted by the base station in the present
invention may also be conducted by an upper node of the base
station as necessary. In other words, it will be obvious to those
skilled in the art that various operations for enabling the base
station to communicate with the mobile station in a network
composed of several network nodes including the base station will
be conducted by the base station or other network nodes other than
the base station. The term "Base Station" may be replaced with
fixed station, Node-B, eNode-B (eNB), or access point as necessary.
The term "mobile station" may also be replaced with user equipment
(UE), mobile station (MS) or mobile subscriber station (MSS) as
necessary.
[0143] The following embodiments of the present invention can be
implemented by a variety of means, for example, hardware, firmware,
software, or a combination thereof. In the case of implementing the
present invention by hardware, the present invention can be
implemented with application specific integrated circuits (ASICs),
Digital signal processors (DSPs), digital signal processing devices
(DSPDs), programmable logic devices (PLDs), field programmable gate
arrays (FPGAs), a processor, a controller, a microcontroller, a
microprocessor, etc.
[0144] If operations or functions of the present invention are
implemented by firmware or software, the present invention can be
implemented in a variety of formats, for example, modules,
procedures, functions, etc. The software code may be stored in a
memory unit so as to be driven by a processor. The memory unit is
located inside or outside of the processor so as to communicate
with the aforementioned processor via a variety of well-known
parts.
[0145] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
INDUSTRIAL APPLICABILITY
[0146] The present invention is applicable to a wireless
communication system. In detail, the present invention is
applicable to a method and apparatus for transmitting an uplink
control signal in a wireless communication system.
* * * * *