U.S. patent application number 14/844153 was filed with the patent office on 2015-12-31 for cooperative communication method in cellular wireless communication system and terminal for performing the method.
The applicant listed for this patent is Electronics and Telecommunications Research Institute. Invention is credited to Jae Young AHN, Young-Jo KO, Bangwon SEO.
Application Number | 20150381241 14/844153 |
Document ID | / |
Family ID | 43011624 |
Filed Date | 2015-12-31 |
United States Patent
Application |
20150381241 |
Kind Code |
A1 |
KO; Young-Jo ; et
al. |
December 31, 2015 |
COOPERATIVE COMMUNICATION METHOD IN CELLULAR WIRELESS COMMUNICATION
SYSTEM AND TERMINAL FOR PERFORMING THE METHOD
Abstract
Provided is a coordinated communication method in which a
plurality of cells cooperate to perform multi-antenna transmission
and reception in a cellular wireless communication system. A
terminal wirelessly transmits channel state information (CSI)
feedback to a serving cell and at least one coordinating cell. The
serving cell and the coordinating cell perform multi-point
coordinated communication using the CSI feedback. Even if the
serving cell and the coordinating cell belong to different base
stations, information exchange between the cells is minimized, so
that a transmission delay and a traffic increment of a backhaul
network can be prevented.
Inventors: |
KO; Young-Jo; (Daejeon,
KR) ; AHN; Jae Young; (Daejeon, KR) ; SEO;
Bangwon; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Electronics and Telecommunications Research Institute |
Daejeon |
|
KR |
|
|
Family ID: |
43011624 |
Appl. No.: |
14/844153 |
Filed: |
September 3, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13260874 |
Sep 28, 2011 |
9160426 |
|
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PCT/KR2010/002528 |
Apr 22, 2010 |
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14844153 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04B 7/024 20130101;
H04B 7/0626 20130101; H04B 7/0417 20130101; H04L 5/0035 20130101;
H04W 72/1289 20130101 |
International
Class: |
H04B 7/02 20060101
H04B007/02; H04W 72/12 20060101 H04W072/12; H04B 7/06 20060101
H04B007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2009 |
KR |
10-2009-0035844 |
Claims
1. A coordinated communication method of a serving cell in a
cellular wireless communication system including the serving cell
and at least one coordinating cell, comprising: receiving a
measurement result on signals of neighboring cells from a terminal;
transmitting information about the at least one coordinating cell
to the terminal, wherein the at least one coordinating cell is
determined among the neighboring cells by the serving cell based on
the measurement result; receiving channel state information (CSI)
feedback from the terminal; and transmitting data to the terminal
through a coordinated communication performed by the serving cell
and the at least one coordinating cell using the CSI feedback
received from the terminal.
2. The coordinated communication method of claim 1, further
comprising: notifying the at least one coordinating cell of
information about the CSI feedback and downlink scheduling
information of the terminal.
3. The coordinated communication method of claim 1, further
comprising: transmitting, to the terminal, antenna port information
of the serving cell and antenna port information of a neighboring
cell around the terminal.
4. The coordinated communication method of claim 3, wherein the
antenna port information includes the number of antenna ports and
location information of a reference signal used for acquisition of
the CSI in a time-frequency resource space per each antenna
port.
5. The coordinated communication method of claim 3, wherein the
transmitting antenna port information of the serving cell and
antenna port information of a neighboring cell around the terminal
comprises transmitting the antenna port information to the terminal
through a radio resource control (RRC) message.
6. The coordinated communication method of claim 2, wherein the
information about the CSI feedback includes at least one of a
location of an uplink resource used for the CSI feedback and a
feedback transmission format necessary for demodulation, and the
downlink scheduling information of the terminal includes a location
of a downlink resource through which data is transmitted to the
terminal.
7. A coordinated communication method of a coordinating cell in a
cellular wireless communication system including a serving cell and
the coordinating cell, comprising: receiving a measurement result
on signals of neighboring cells from a terminal; receiving channel
state information (CSI) feedback from the terminal; and
transmitting data to the terminal through a coordinated
communication performed by the serving cell and the coordinating
cell using the CSI feedback received from the terminal, wherein the
coordinating cell is determined among the neighboring cells by the
serving cell based on the measurement result, and information about
the coordinating cell is transmitted from the serving cell to the
terminal,
8. The coordinated communication method of claim 7, further
comprising: receiving, from the serving cell, information about the
CSI feedback and downlink scheduling information of the
terminal.
9. The coordinated communication method of claim 8, wherein the
information about the CSI feedback includes at least one of a
location of an uplink resource used for the CSI feedback and a
feedback transmission format necessary for demodulation, and the
downlink scheduling information of the terminal includes a location
of a downlink resource through which data is transmitted to the
terminal.
10. The coordinated communication method of claim 7, further
comprising receiving, from the terminal, information about the CSI
feedback and downlink scheduling information of the terminal when
there is interference between femto cells.
11. The coordinated communication method of claim 10, wherein the
information about the CSI feedback includes at least one of a
location of an uplink resource used for the CSI feedback and a
feedback transmission format necessary for demodulation, and the
downlink scheduling information of the terminal includes a location
of a downlink resource through which data is transmitted to the
terminal.
12. The coordinated communication method of claim 7, wherein
antenna port information of the serving cell and antenna port
information of a neighboring cell around the terminal are
transmitted from the serving cell to the terminal.
13. The coordinated communication method of claim 12, wherein the
antenna port information includes the number of antenna ports and
location information of a reference signal used for acquisition of
the CSI in a time-frequency resource space per each antenna
port.
14. The coordinated communication method of claim 12, wherein the
transmitting antenna port information of the serving cell and
antenna port information of a neighboring cell around the terminal
comprises transmitting the antenna port information to the terminal
through a radio resource control (RRC) message.
Description
RELATED APPLICATIONS FIELD
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/260,874, filed on Sep. 28, 2011, which
claims priority to and the benefit of 35 U.S.C. .sctn.371 national
stage filing of PCT Application No. PCT/KR2010/002528 filed on Apr.
22, 2010, which claims priority to, and the benefit of, Korean
Patent Application No. 10-2009-0035844 filed on Apr. 24, 2009. The
contents of which are hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a cellular wireless
communication technique, and more particularly, to a coordinated
communication method for coordinated communication in a cellular
wireless communication system and a terminal device for performing
the same.
BACKGROUND ART
[0003] In a cellular wireless communication system, terminals
located in a cell boundary are limited in increasing a data
transmission rate due to large interference from other cells.
Multi-cell coordinated communication, a technique for increasing a
data transmission rate of terminals located in a cell boundary, is
one of candidate techniques to be applied to a 3rd Generation
Partnership Project (3GPP) Long Term Evolution (LTE)-Advanced
system. The multi-cell coordinated communication for an Orthogonal
Frequency-Division Multiple Access (OFDMA) downlink which is being
discussed for the LTE-Advanced system can be divided into the
following two fields:
[0004] Joint transmission (joint processing): a terminal receives
data from a plurality of transmission points; and
[0005] Coordinated scheduling: a terminal receives data from one
transmission point. Scheduling, precoding or beam forming of a
terminal is performed through coordination (or cooperation) of
multiple cells.
[0006] In most cases, one cell usually has one transmission
point.
[0007] In a conventional multi-cell coordinated transmission
method, only a serving cell receives channel state information
(CSI) transmitted from a terminal via the uplink, information
necessary for cooperation is extracted from the CSI, and the
extracted information is transmitted to a surrounding coordinating
cell. However, if the serving cell and the coordinating cell belong
to different base stations, there is a problem in that information
exchange between the cells causes a transmission delay and a
traffic increment of a backhaul network.
[0008] As a conventional multi-cell coordinated communication
method, U.S. Pat. No. 7,428,268, entitled "Cooperative MIMO in
multicell wireless networks", discloses a joint transmission
operation under a structure in which the serving cell and the
coordinating cell belong to different base stations. In U.S. Pat.
No. 7,428,268, a method in which a base station of the serving cell
and a base station of the coordinating cell perform joint
transmission is described. However, as described above, if the
serving cell and the coordinating cell belong to different base
stations, there is still a problem in that the transmission delay
and the traffic overhead of the backhaul network are caused at the
time of information exchange between the cells.
DISCLOSURE
Technical Problem
[0009] The present invention is directed to a coordinated
communication method in which a terminal wirelessly transmits CSI
feedback to a serving cell and at least one coordinating cell, and
the serving cell and the coordinating cell perform multi-point
coordinated communication using the CSI feedback.
[0010] The present invention is also directed to a terminal which
performs the coordinated communication.
[0011] The present invention is also directed to a method of
transmitting antenna port information to an LTE terminal or an
LTE-Advanced terminal so that backward compatibility can be
supported in the LTE-Advanced system.
Technical Solution
[0012] One aspect of the present invention provides a coordinated
communication method in a cellular wireless communication system
including a serving cell and at least one coordinating cell,
including: wirelessly transmitting, at a terminal, channel state
information (CSI) feedback to the serving cell and the at least one
coordinating cell; and performing, at the serving cell and the at
least one coordinating cell, coordinated communication using the
CSI feedback received from the terminal.
[0013] The wirelessly transmitting, at the terminal, channel state
information (CSI) feedback to the serving cell and the at least one
coordinating cell may include: wirelessly receiving, at the serving
cell, first CSI feedback from the terminal; and wirelessly
receiving, at the at least one coordinating cell, second CSI
feedback from the terminal.
[0014] The method may further include notifying, at the serving
cell, the coordinating cell of information about the CSI feedback
and downlink scheduling information of the terminal.
[0015] The method may further include notifying the terminal of a
cell ID of a cell which is determined as a coordinating cell by the
serving cell.
[0016] The method may further include determining, at the serving
cell, a cell which acts as the coordinating cell based on a
measurement result of a neighboring cell reported by the terminal,
and notifying the terminal of a cell ID of the cell determined as
the coordinating cell by the serving cell.
[0017] The method may further include notifying, at the serving
cell, the terminal of antenna port information of the serving cell
and antenna port information of a neighboring cell around the
terminal.
[0018] The antenna port information may include the number of
antenna ports and location information of a reference signal used
for acquisition of the CSI in a time-frequency resource space per
each antenna port.
[0019] The notifying the terminal of antenna port information of
the serving cell and antenna port information of a neighboring cell
around the terminal at the serving cell may include, notifying, at
the serving cell, the terminal of the antenna port information
through a radio resource control (RRC) message.
[0020] The information about the CSI feedback may include at least
one of a location of an uplink resource used for the CSI feedback
and a feedback transmission format necessary for demodulation, and
the downlink scheduling information of the terminal includes a
location of a downlink resource through which data is transmitted
to the terminal.
[0021] The terminal may transmit the information about the CSI
feedback and the downlink scheduling information of the terminal to
the coordinating cell when there is interference between femto
cells.
[0022] Another aspect of the present invention provides a terminal
for performing coordinated communication in a cellular wireless
communication system including a serving cell and at least one
coordinating cell. The terminal wirelessly transmits channel state
information (CSI) feedback to the serving cell and the at least one
coordinating cell.
[0023] The terminal may wirelessly transmit first CSI feedback to
the serving cell and wirelessly transmits second CSI feedback to
the at least one coordinating cell.
[0024] The terminal may receive a cell ID of cells which are
determined as a coordinating cell by the serving cell.
[0025] The terminal may receive antenna port information of a
neighboring cell around the serving cell from the serving cell
through a physical broadcast channel (PBCH) or a radio resource
control (RRC) message.
[0026] Still another aspect of the present invention provides a
method of transmitting antenna port information to an LTE terminal
or an LTE-Advanced terminal. The number of antenna ports which
support the LTE terminal is differently set compared with the
number of antenna ports which support the LTE-Advanced terminal
within the same cell, and the method of transmitting antenna port
information to an LTE terminal or an LTE-Advanced terminal
includes: notifying, at each cell, a terminal within the each cell
of the antenna port information of each cell, the antenna port
information of each cell being included in a physical broadcast
channel (PBCH).
[0027] The PBCH may further include time and frequency generation
pattern information of a reference signal for acquisition of
corresponding channel state information in addition to the antenna
port number information.
[0028] The number of antenna ports which support the LTE-Advanced
terminal may be indicated in a reserved bit of the PBCH.
[0029] The antenna port number information among the antenna port
information may be expressed using different mask patterns
depending on the number of antenna ports among the antenna port
information using a CRC bit of the PBCH.
[0030] The multi-cell coordinated communication method according to
exemplary embodiments of the present invention is not limited to a
typical cell. Hereinafter, a term "cell" is used for convenience,
but a cell may include a macro cell, a pico cell, a femto cell, or
a relay node. That is, the multi-cell coordinated communication
method according to exemplary embodiments of the present invention
can be applied to various forms such as coordinated transmission
and reception between cells, coordinated transmission and reception
between relay nodes, and coordinated transmission and reception
between a cell and a relay node. Communication between cells is
necessary for coordinated transmission and reception or coordinated
communication according to the present invention. The communication
between cells may use a backbone network connected to a network, a
dedicated line which directly connects a cell with a cell, or
wireless communication between cells. In the case of the wireless
communication between cells, as a radio resource used for a
communication, part of a frequency band used for communication
between a cell and a terminal or a different frequency band
separated from a frequency band used for communication between a
cell and a terminal may be used.
[0031] Effective inter-cell communication is required to
effectively realize the joint processing or the coordinated
scheduling. Particularly, since the joint processing requires very
fast inter-cell communication, it can be applied to a case in which
cells are connected through a dedicated line. In the case of the
coordinated scheduling, a backbone network (backhaul network)
connected to a network may be used for communication between cells
belonging to different base stations.
Advantageous Effects
[0032] Using a coordinated communication method and a terminal for
performing the same according to exemplary embodiments of the
present invention, it is possible to minimize information exchange
between cells and thereby prevent a transmission delay and a
traffic increment of a backhaul network even in the case in which
the serving cell and the coordinating cell belong to different base
stations.
DESCRIPTION OF DRAWINGS
[0033] FIG. 1 is a conceptual diagram illustrating a case in which
a terminal receives data from a plurality of cells including a
serving cell through downlink joint transmission.
[0034] FIG. 2 is a conceptual diagram illustrating a case in which
a terminal receives data from a plurality of cells including a
serving cell through downlink coordinated scheduling.
[0035] FIG. 3 is a message flowchart illustrating a coordinated
communication method according to an exemplary embodiment of the
present invention.
[0036] FIG. 4 is a table illustrating a physical broadcast channel
(PBCH) cyclic redundancy check (CRC) mask of the LTE.
[0037] FIG. 5 is a table illustrating an example of a PBCH CRC mask
of the LTE-Advanced according to an exemplary embodiment of the
present invention.
[0038] FIG. 6 illustrates an example of a master information block
(MIB) data format of a PBCH according to an exemplary embodiment of
the present invention.
BEST MODE
[0039] Hereinafter, exemplary embodiments of the present invention
will be described in detail. However, the present invention is not
limited to the exemplary embodiments disclosed below, but can be
implemented in various forms. The following exemplary embodiments
are described in order to enable those of ordinary skill in the art
to embody and practice the invention.
[0040] FIG. 1 illustrates a case in which a terminal receives data
from a plurality of cells including a serving cell through joint
transmission. FIG. 2 illustrates a case in which a terminal
receives data from a plurality of cells including a serving cell
through coordinated scheduling. In FIGS. 1 and 2, it is assumed
that a serving cell of a terminal is a cell A. In the case of FIG.
1, neighboring cells B and C transmit data to the terminal A
together with the cell A. In the case of FIG. 2, the terminal A
receives data only from the serving cell, the cell A, and signals
transmitted from the cells B and C function as interference
signals. In FIGS. 1 and 2, a cell may include a macro cell, a pico
cell, or a femto cell, and may include a relay node.
[0041] The terminal needs to feedback downlink CSI to the
neighboring cells as well as the serving cell to which it belongs
for joint transmission or coordinated scheduling.
[0042] Typically, the terminal receives downlink control
information from its serving cell, and the serving cell receives
feedback transmitted via the uplink. In FIGS. 1 and 2, the terminal
can transmit the CSI of the cells B and C under the assumption that
the serving cell, the cell A, receives the CSI.
[0043] FIG. 3 is a message flowchart illustrating a coordinated
communication method according to an exemplary embodiment of the
present invention. The coordinated communication method according
to an exemplary embodiment of the present invention is described
below in connection with the coordinating cell B among a plurality
of coordinating cells B and C in the case in which the cell A is
the service cell in FIGS. 1 and 2.
[0044] Referring to FIG. 3, in order to enable the serving cell A
to determine the coordinating cells, the terminal measures channel
states of the serving cell A and neighboring cells (step 301) and
transmit CSI to the serving cell A (step 303). For example, the
terminal may measure the signal intensity of the neighboring cells
of the terminal and report the signal intensity to the serving cell
A.
[0045] The serving cell A determines the coordinating cell which
will participate in multi-cell coordinated communication with
reference to the measurement result of the neighboring cells which
is reported from the terminal (step 305). For example, the serving
cell A may determine the neighboring cells whose signal intensity
is equal to or more than a predetermined level as coordinating
cells with reference to the measurement result of the neighboring
cells.
[0046] The serving cell A transmits information about the
determined coordinating cells--for example, a cell ID of a cell
constituting the coordinating cell--to the terminal (step 307). The
serving cell A may notify the terminal of antenna port information
of the serving cell A and antenna port information of the
neighboring cells of the terminal. The antenna port information may
include the number of antenna ports and location information of a
reference signal used for acquisition of the CSI in a
time-frequency resource space per each antenna port.
[0047] The serving cell may include the antenna port information in
a radio resource control (RRC) message and transmit the antenna
port information to the terminal. Each cell may transmit a physical
broadcast channel (PBCH) including the antenna port information in
order to notify the terminal within the cell of its antenna port
information. The PBCH or the RRC message may further include
time-frequency generation pattern information of the reference
signal for acquisition of the CSI in addition to the antenna port
number information.
[0048] The serving cell A notifies the coordinating cell A of
information about the CSI feedback of the terminal which is a
target of joint transmission and the downlink scheduling
information of the terminal (step 309) so that the terminal can
wirelessly transmit the CSI feedback to the serving cell A and the
coordinating cell B, and the serving cell A and the coordinating
cell B can cooperate to perform the coordinated communication using
the CSI feedback received from the terminal.
[0049] The information about the CSI feedback may include a
location of an uplink resource used for the CSI feedback of the
terminal and a feedback transmission format necessary for
demodulation. The feedback transmission format necessary for
demodulation may include, for example, a size of a transport block,
a modulation order, and scrambling information.
[0050] The downlink scheduling information of the terminal may
include a location of a downlink resource through which data is
transmitted to the terminal. The downlink scheduling information of
the terminal may include information about a transmission format in
the case of joint processing multi-cell coordinated communication.
The information about the transmission format may include, for
example, a size of a transport block, a modulation order, and
scrambling information. Step 301 is performed by the terminal
before or after receiving information about the determined
coordinating cell or may be performed before the serving cell A
notifies the terminal of the antenna port information of the
serving cell A and the antenna port information of the neighboring
cells around the terminal. The terminal wirelessly transmits first
CSI feedback to the serving cell A (step 311), and second CSI
feedback to the determined coordinating cell B (step 313).
[0051] As described above, the terminal wirelessly transmits the
CSI feedback to the serving cell and one or more coordinating
cells, and the serving cell and the one or more coordinating cells
perform the coordinated communication using the CSI feedback
received from the terminal.
MODE FOR INVENTION
[0052] In the conventional multi-cell coordinated transmission
method, only the serving cell receives the CSI transmitted from the
terminal through an uplink, information necessary for cooperation
is extracted from the CSI, and the extracted information is
transmitted to the coordinating cells around the terminal. However,
in the case in which the serving cell and the coordinating cell
belong to different base stations, there is a problem in that the
information exchange between the cells causes a transmission delay
and a traffic increment of a backhaul network.
[0053] One solution for resolving this problem is to enable the
cells which participate in cooperation as well as the serving cell
to receive the CSI transmitted from the terminal via the uplink. To
this end, the cells which participate in cooperation can receive
the following information as described above in FIG. 3.
[0054] (1) Information about the CSI Feedback of the Terminal
[0055] A location of an uplink resource used for feedback [0056] A
feedback transmission format necessary for demodulation (that is, a
size of a transport block, a modulation order, and scrambling
information)
[0057] (2) Downlink Scheduling Information of the Terminal [0058] A
location of a downlink resource through which data is transmitted
to the terminal [0059] A transmission format in the case of the
joint processing multi-cell coordinated communication (that is, a
size of a transport block, a modulation order, and scrambling
information)
[0060] To this end, the serving cell notifies the coordinating
cells of (1) the information about the CSI feedback of the terminal
and (2) the downlink scheduling information of the terminal as
described above in FIG. 3. In FIGS. 1 and 2, for example, the
serving cell A may transmit the information for the uplink feedback
transmission and the downlink scheduling information about the
terminal as a cooperation target to the neighboring cells B and
C.
[0061] If the coordinating cells are located in different base
stations and communication is performed between the cells via the
backhaul network since they are not connected through a dedicated
line, it is desirable to generate a small amount of information at
a low temporal frequency in order to prevent problems such as the
transmission delay and traffic increment. Thus, it is desirable
that the scheduling information not be frequently temporally
changed. From this point of view, semi persistent scheduling (SPS)
of the LTE release 8 standard is a good scheduling method to which
the above-mentioned method can be applied. In the SPS of the LTE,
if scheduling information such as a radio resource and a modulation
coding scheme (MCS) which is allocated to the terminal is first
relayed via a physical downlink control channel (PDCCH), the same
scheduling information is kept in subsequent transmission without
the PDCCH. Only the first transmission of each packet can be kept
without the PDCCH, and in the case of the retransmission, the
downlink SPS should be allocated via the PDCCH. The SPS can be
applied when a constant amount of traffic is generated at a
constant time interval, as in Voice over IP (VoIP).
[0062] The coordinating cells acquire the CSI directly from the
terminal and participate in the coordinated transmission based on
the CSI.
[0063] In the case of the joint processing multi-cell coordinated
communication, the coordinating cells can apply the precoding to a
transmitting antenna belonging to its cell using the CSI included
in the feedback information of the terminal.
[0064] In the case of the coordinated scheduling multi-cell
coordinated communication, the coordinating cells can select the
precoding which interfere less with the terminal of the neighboring
cell using the CSI included in the feedback information of the
terminal when selecting the precoding applied to the terminal
belonging to its cell.
[0065] Next, a method in which the terminal acquires information
necessary for generating the CSI of the serving cell and the
neighboring cells is described in detail.
[0066] According to the 3GPP LTE release 8 standard, the terminal
can acquire time and frequency synchronization with the neighboring
cells through a neighboring cell search. The terminal may receive
and measure a reference signal of the neighboring cell and report
the measurement result to the serving cell. According to the 3GPP
technical specification (TS) 36.214, the measurement performed by
the terminal with respect to the neighboring cell is carried out
for an antenna port number 0 or antenna port numbers 0 and 1.
[0067] The base station which manages the serving cell may
determine cells which will participate in the multi-cell
cooperation with reference to the measurement result of the
neighboring cells which is reported by the terminal, and the base
station which manages the serving cell may notify the terminal of
cells which are objects for which the terminal generates the CSI
feedback information.
[0068] The terminal should be able to measure the CSI of a certain
neighboring cell as well as the serving cell for the multi-cell
coordinated transmission. For example, in the case of the
coordinated scheduling multi-cell coordinated communication,
terminal feedback information about the neighboring cell having the
following form may be provided. [0069] Precoding index or indices
which give small interference to the terminal [0070] Precoding
index or indices which give large interference to the terminal
[0071] Channel matrix formed by the neighboring cell and the
terminal: when the number of receiving antennas of the terminal is
N.sub.R and the number of transmitting antennas of the cell is
N.sub.T, if a channel matrix of a k-th sub-carrier which is
obtained by the terminal through channel estimation is H.sub.k, it
can be expressed as a matrix of Equation 1 having an size of
N.sub.R.times.N.sub.T.
[0071] H k = [ H k , 11 H k , 1 N T H k , 21 H k , 2 N T H k , N R
, 1 H k , N R , N T ] [ Equation 1 ] ##EQU00001## [0072] A channel
covariance matrix computed from the channel matrix formed by the
neighboring cell and the terminal: a channel covariance matrix
.OMEGA..sub.k of the k-th sub-carrier can be computed by Equation 2
as follows.
[0072] .OMEGA..sub.k=H.sub.k.sup.HH.sub.k [Equation 2] [0073] A
channel specific matrix computed from the channel matrix formed by
the neighboring cell and the terminal and an eigenvalue: a non-zero
eigenvalue and eigen vector elements which are obtained by singular
value decomposition (SVD) of .OMEGA..sub.k.
[0074] In the case of the joint processing multi-cell coordinated
communication, considering the transmitting antenna, it is
necessary to compute the desired precoding indices of all
transmitting antennas possessed by the cells which participate in
the cooperation or feedback the channel matrix, the channel
covariance matrix, and the channel specific matrix.
[0075] Therefore, for the sake of the above-mentioned feedback, the
terminal should know the number of antenna ports of the neighboring
cell around the terminal as well as the serving cell and a location
of s reference signal (a CSI reference signal) of each antenna port
for acquisition of the CSI in the time-frequency resource space.
Such information is referred to as antenna port information. If the
CSI reference signal is known from the antenna port information, it
is possible to receive the reference signal and generate the CSI.
The terminal can acquire the antenna port information of the
serving cell and the neighboring cell by the following methods.
[0076] [Method 1] The terminal can acquire the antenna port
information of the corresponding cell by demodulation of the
PBCH.
[0077] To this end, the PBCH has to include information necessary
for constituting the antenna port information. According to the LTE
release 8 standard TS 36.212, cyclic redundancy check (CRC) bits of
the PBCH are supposed to use different mask patterns depending on
the number of antenna ports. Therefore, the terminal can recognize
the number of antenna ports by checking the CRC bits.
[0078] FIG. 4 is a table illustrating a PBCH CRC mask in the 3GPP
LTE. In the case of the 3GPP LTE, referring to TS 36.212 Section
5.3.1.1, as illustrated in FIG. 4, the 16-bit CRC of the PBCH may
be masked depending on the antenna port information.
[0079] The followings need to be considered in connection with the
antenna port used in the LTE and the LTE-Advanced system. [0080] In
the LTE-Advanced system, a maximum of 8 antenna ports, but more
than the number (1, 2, or 4) of antenna ports which can be used in
the LTE, can be used. [0081] In order to guarantee backward
compatibility, the LTE-Advanced system should be able to support
the LTE terminal.
[0082] For these reasons, in the LTE-Advanced system, it should be
possible to differently set the number of antenna ports which
support the LTE terminal and the number of antenna ports which
support the LTE-Advanced within the same cell.
[0083] In order for the terminal to generate the feedback
information for the multi-cell coordinated transmission, it is
necessary to know the number of antenna ports which support the
LTE-Advanced.
[0084] The PBCH defined in the LTE release 8 standard can
constitute information using a total of 24 bits, 10 bits of which
are reserved bits which are not used in the release 8 for a future
use. If the number of LTE-Advanced antenna ports is indicated using
some of the reserved bits, the terminal can recognize a location of
the CSI reference signal of each antenna port based on the number
of LTE-Advanced antenna ports and the cell ID.
[0085] FIG. 6 illustrates an example of a master information block
(MIB) data format of the PBCH according to an exemplary embodiment
of the present invention. Referring to FIG. 6, the MIB includes a
"DL-bandwidths" field 701, a "PHICH-Config"field 703, a "System
Frame Number" field 705, and "reserved bits" 707. The size of the
transport block of the MIB is 24 bits. As illustrated in FIG. 6,
the number of antenna ports which support the LTE-Advanced terminal
is indicated using the reserved bits 707, 16 bits of "CRC bits" 709
are added to the MIB to constitute a total of 40 bits of the MIB.
The CRC bits of the PBCH are supposed to use different mask
patterns depending on the number of antenna ports. Therefore, the
terminal can recognize the number of antenna ports by checking the
added CRC bits.
[0086] The number of antenna ports for LTE-Advanced and a time and
frequency generation pattern of the CSI reference signal can be
additionally included in the PBCH. In this case, a plurality of
patterns which give a two-dimensional location of the time and
frequency of the reference signal can be defined, and corresponding
patterns according to values of bits included in the PBCH can be
previously defined in the standard.
[0087] Similarly to the method used in the LTE release 8,
information about the antenna port for the LTE-Advanced can be
included in the mask applied to the CRC. FIG. 5 is a table
illustrating an example of a PBCH CRC mask in the LTE-Advanced
according to an exemplary embodiment of the present invention. In
this case, it is necessary to define different mask patterns
depending on the number of antenna ports for LTE and the number of
antenna ports for LTE-Advanced. As illustrated in FIG. 5, in order
to guarantee the backward compatibility, the existing PBCH CRC mask
patterns defined in the LTE release 8 should be included, and
additional PBCH CRC mask patterns can be defined and used to
express the antenna port information for the LTE-Advanced.
[0088] As described above, if information about the number of the
LTE-Advanced antenna ports is added to the PBCH, there is an
advantage that the terminal can easily acquire the antenna port
information of the serving cell and the neighboring cell.
[0089] [Method 2] The base station which manages the serving cell
determines cells which will participate in the multi-cell
cooperation with reference to the measurement result of the
neighboring cell reported by the terminal, and the base station
notifies the terminal of cells which are objects for which the
terminal generates the feedback information. At this time, the
antenna port information of the cells which are targets of the
feedback is relayed together. In this method, differently from
[Method 1], the terminal receives a message transmitted from the
serving cell and acquires the antenna port information of the
neighboring cell even without opening the PBCH.
[0090] While the invention has been shown and described with
reference to certain exemplary embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims.
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