U.S. patent application number 14/335169 was filed with the patent office on 2014-11-06 for method and transmitter for transmitting signal and receiver thereof in wireless communication system.
The applicant listed for this patent is Pantech Co., Ltd.. Invention is credited to Jianjun LI, Kyoungmin Park, Sungjin Suh.
Application Number | 20140328425 14/335169 |
Document ID | / |
Family ID | 43922251 |
Filed Date | 2014-11-06 |
United States Patent
Application |
20140328425 |
Kind Code |
A1 |
LI; Jianjun ; et
al. |
November 6, 2014 |
METHOD AND TRANSMITTER FOR TRANSMITTING SIGNAL AND RECEIVER THEREOF
IN WIRELESS COMMUNICATION SYSTEM
Abstract
A transmitter includes a layer mapper and a precoder. The layer
mapper is configured to map 2 codewords to 3 layers to output a
mapped set of 3 symbols. A first codeword is mapped into one layer,
and a second codeword is mapped into two layers. The precoder is
configured to precode the mapped set of 3 symbols using a precoding
matrix that distributes the mapped set of 3 symbols across 4
antenna ports so that each codeword is distributed across 2 antenna
ports.
Inventors: |
LI; Jianjun; (Seoul, KR)
; Park; Kyoungmin; (Goyang-si, KR) ; Suh;
Sungjin; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pantech Co., Ltd. |
Seoul |
|
KR |
|
|
Family ID: |
43922251 |
Appl. No.: |
14/335169 |
Filed: |
July 18, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13505707 |
May 2, 2012 |
8811518 |
|
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PCT/KR2009/006398 |
Nov 2, 2009 |
|
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14335169 |
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Current U.S.
Class: |
375/267 |
Current CPC
Class: |
H04B 7/0478 20130101;
H04L 2025/03808 20130101; H04B 7/0639 20130101; H04L 2025/03426
20130101; H04L 25/03343 20130101; H04B 7/0447 20130101; H04B 7/0469
20130101 |
Class at
Publication: |
375/267 |
International
Class: |
H04B 7/04 20060101
H04B007/04 |
Claims
1. A method of transmitting a signal from an apparatus, the
apparatus comprising a processor, the method comprising: mapping 2
codewords to 3 layers to output a mapped set of 3 symbols, wherein
a first codeword is mapped into one of the 3 layers, and a second
codeword is mapped into the other two of the 3 layers; precoding,
by the processor, the mapped set of 3 symbols using a precoding
matrix that distributes the mapped set of 3 symbols across 4
antenna ports; and transmitting a signal that comprises the
precoded set of symbols, wherein the precoding matrix is selected
from a set of precoding matrices, wherein each precoding matrix in
the set of precoding matrices includes a first submatrix and a
second submatrix, wherein the first submatrices are 4-by-1
submatrices each having 4 rows and 1 column for the first codeword,
the first submatrices each having 2 non-zero elements and 2 zero
elements, wherein the second submatrices are 4-by-2 submatrices
each having 4 rows and 2 is columns for the second codeword, each
column of the second submatrices having 1 non-zero element and 3
zero elements, wherein the first submatrices are different from
each other, and wherein, in the selected precoding matrix, the 2
non-zero elements of the first submatrix and the 2 non-zero
elements of the second submatrix are arranged in different rows
from each other.
2. The method of claim 1, wherein the first codeword is distributed
across two antenna ports of the 4 antenna ports and the second
codeword is distributed across the other two antenna ports of the 4
antenna ports.
3. The method of claim 1, wherein, in the selected precoding
matrix, the 2 non-zero elements of the first submatrix and the 2
non-zero elements of the second submatrix have the same absolute
value.
4. A wireless communication apparatus, comprising: a layer mapper
to map 2 codewords to 3 layers to output a mapped set of 3 symbols,
wherein a first codeword is mapped into one of the 3 layers, and a
second codeword is mapped into the other two of the 3 layers; a
precoder to precode the mapped set of 3 symbols using a precoding
matrix that distributes the mapped set of 3 symbols across 4
antenna ports; and a transmitter to transmit a signal that
comprises the precoded set of symbols, wherein the precoding matrix
is selected from a set of precoding matrices, wherein each
precoding matrix in the set of precoding matrices includes a first
submatrix and a second submatrix, wherein the first submatrices are
4-by-1 submatrices each having 4 rows and 1 column for the first
codeword, the first submatrices each having 2 non-zero elements and
2 zero elements, wherein the second submatrices are 4-by-2
submatrices each having 4 rows and 2 columns for the second
codeword, each column of the second submatrices having 1 non-zero
is element and 3 zero elements, wherein the first submatrices are
different from each other, and wherein, in the selected precoding
matrix, the 2 non-zero elements of the first submatrix and the 2
non-zero elements of the second submatrix are arranged in different
rows from each other.
5. The wireless communication apparatus of claim 4, wherein the
first codeword is distributed across two antenna ports of the 4
antenna ports and the second codeword is distributed across the
other two antenna ports of the 4 antenna ports.
6. The wireless communication apparatus of claim 4, wherein, in the
selected precoding matrix, the 2 non-zero elements of the first
submatrix and the 2 non-zero elements of the second submatrix have
the same absolute value.
7. A method of receiving a signal from an apparatus, the apparatus
comprising a processor, the method comprising: receiving, from a
transmitter, a signal that comprises a precoded set of symbols
distributed across 4 antenna ports, the precoded set of symbols
being precoded using a precoding matrix of the transmitter;
decoding, by the processor, the precoded set of symbols into a set
of 3 symbols using an inverse matrix of the precoding matrix; and
demapping the decoded set of 3 symbols in 3 layers to 2 codewords,
wherein a first codeword is demapped from one of the 3 layers, and
a second codeword is demapped from the other two of the 3 layers,
wherein the precoding matrix is selected from a set of precoding
matrices, wherein each precoding matrix in the set of precoding
matrices includes a first submatrix and a second submatrix, wherein
the first submatrices are 4-by-1 submatrices each having 4 rows and
1 column for the first codeword, the first submatrices each having
2 non-zero elements and 2 zero elements, wherein the second
submatrices are 4-by-2 submatrices each having 4 rows and 2 columns
for the second codeword, each column of the second submatrices
having 1 non-zero element and 3 zero elements, wherein the first
submatrices are different from each other, and wherein, in the
selected precoding matrix, the 2 non-zero elements of the first
submatrix and the 2 non-zero elements of the second submatrix are
arranged in different rows from each other.
8. The method of claim 7, wherein the first codeword is distributed
across two antenna ports of the 4 antenna ports and the second
codeword is distributed across the other two antenna ports of the 4
antenna ports.
9. The method of claim 7, wherein, in the selected precoding
matrix, the 2 non-zero elements of the first submatrix and the 2
non-zero elements of the second submatrix have the same absolute
value.
10. A wireless communication apparatus, comprising: a receiver to
receive a signal that comprises a precoded set of symbols
distributed across 4 antenna ports, the precoded set of symbols
being precoded using a precoding matrix of a transmitter of the
signal; a post-decoder to decode the precoded set of symbols into a
set of 3 symbols using an inverse matrix of the precoding matrix;
and a layer-demapper to demap the decoded set of 3 symbols in 3
layers to 2 codewords, wherein a first codeword is demapped from
one of the 3 layers, and a second codeword is demapped from the
other two of the 3 layers, wherein the precoding matrix is selected
from a set of precoding matrices, wherein each precoding matrix in
the set of precoding matrices includes a first submatrix and a
second submatrix, wherein the first submatrices are 4-by-1
submatrices each having 4 rows and 1 column for the first codeword,
the first submatrices each having 2 non-zero elements and 2 zero
elements, wherein the second submatrices are 4-by-2 submatrices
each having 4 rows and 2 columns for the second codeword, each
column of the second submatrices having 1 non-zero element and 3
zero elements, wherein the first submatrices are different from
each other, and wherein, in the selected precoding matrix, the 2
non-zero elements of the first submatrix and the 2 non-zero
elements of the second submatrix are arranged in different rows
from each other.
11. The wireless communication apparatus of claim 10, wherein the
first codeword is distributed across two antenna ports of the 4
antenna ports and the second codeword is distributed across the
other two antenna ports of the 4 antenna ports.
12. The wireless communication apparatus of claim 10, wherein, in
the selected precoding matrix, the 2 non-zero elements of the first
submatrix and the 2 non-zero elements of the second submatrix have
the same absolute value.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/505,707, filed on May 2, 2012 which is the
National Stage Entry of International Application No.
PCT/KR2009/006398, filed on Nov. 2, 2009, each of which is hereby
incorporated by reference for all purposes as if fully set forth
herein.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to precoding the signal in
wireless communication system.
[0004] 2. Discussion of the Background
[0005] There are a number of multi-antenna transmission schemes or
transmission such as transit diversity, closed-loop spatial
multiplexing or open-loop spatial multiplexing. Closed-loop MIMO
(CL-MIMO) relies on more extensive feedback from the mobile
terminal.
SUMMARY
[0006] In accordance with an aspect, there is provided a method or
a system, comprising: mapping the (n) number of codewords (n is the
natural number) to the (m) number of layers to output a mapped set
of (m) symbols (m is the natural number more than n and not a
multiple of n) precoding the mapped set of (m) symbols using a
precoding matrix so that all the codewords have the same antenna
ports and antenna correlation property and transmitting a signal
that comprises the precoded set of symbols.
[0007] In accordance with the other aspect, there is provided a
transmitter, comprising: a layer mapper configured to map the (n)
number of codewords (n is the natural number) to the (m) number of
layers to output a set of (m) symbols (m is the natural number more
than n and not a multiple of n) a precoder configured to precode a
codeword based optimized mapping set of (m) symbols using a
precoding matrix so that all the codewords have the same antenna
ports and antenna correlation property.
[0008] In accordance with another aspect, there is provided a
receiver comprising: an estimator configured to estimate a downlink
channel from a received signal, a post-decoder configured to decode
the precoded symbols using a inverse matrix of the precoding matrix
of a transmitter and a layer demapper configured to demap the
decoded symbol streams in a manner complementary to the mapping
performed by the layer mapper of the transmitter to recovers the
original data symbols.
[0009] In accordance with further aspect, there is provided a
method, comprising: mapping the (n) number of codewords (n is the
natural number) to the (m) number of layers to output a mapped set
of (m) symbols (m is the natural number more than n and not a
multiple of n) precoding the mapped set of (m) symbols using a
precoding matrix is U.times. where U is the base matrix for
codebook and is the power allocation matrix, both U and are
optimized for each codeword, not just layers, the U can make all
the codewords have the same antenna ports and antenna correlation
property and the can make optimal power allocation and transmitting
a signal that comprises the precoded set of symbols.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is the block diagram of the wireless communication
system for 4Tx CL-MIMO using closed-loop spatial multiplexing
according to one embodiment.
[0011] FIGS. 2 to 6 are the block diagram of the transmitter of
FIG. 1 for 4Tx CL-MIMO according to the other embodiments.
[0012] FIG. 7 depicts the indexing which we assume in this
contribution (transmitter and receiver).
[0013] FIG. 8 is the block diagram of the transmitter of FIG. 1 for
2nTx (n is the number of codewords) CL-MIMO according to another
embodiment.
[0014] FIG. 9 is the block diagram of the transmitter of FIG. 1 for
6Tx CL-MIMO according to further another embodiment.
[0015] It will be appreciated that for simplicity and clarity of
illustration, elements illustrated in the drawings have not
necessarily been drawn to scale. For example, the dimensions of
some of the elements are exaggerated relative to other elements for
purposes of promoting and is improving clarity and understanding.
Further, where considered appropriate, reference numerals have been
repeated among the drawings to represent corresponding or analogous
elements.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0016] Hereinafter, embodiments of the present invention will be
described in detail with reference to the attached drawings.
[0017] There are a number of multi-antenna transmission schemes or
transmission such as transit diversity, closed-loop spatial
multiplexing or open-loop spatial multiplexing. Closed-loop MIMO
(CL-MIMO) relies on more extensive feedback from the mobile
terminal.
[0018] FIG. 1 is the block diagram of the wireless communication
system for 4Tx CL-MIMO using closed-loop spatial multiplexing
according to one embodiment.
[0019] Referring to FIG. 1, the communication system may be any
type of wireless communication system, including but not limited to
a MIMO system, SDMA system, CDMA system, OFDMA system and OFDM
system, etc. In the communication system, the wireless
communication system using closed-loop spatial multiplexing
according to one embodiment comprises a transmitter 10 and a
receiver 20.
[0020] For the downlink CL MIMO, the transmitter 10 may act as a
base station, while the receiver 20 may act as a subscriber
station, which can be virtually any type of wireless one-way or
two-way communication device such as a cellular telephone, wireless
equipped computer system, and wireless personal digital assistant.
Of course, the receiver/subscriber station 20 can also transmits
signals which are received by the transmitter/base station 10.
[0021] Especially for the uplink CL MIMO, the transmitter 10 may
act as a subscriber station, while the receiver 20 may act as a
base station.
[0022] The signals communicated between the transmitter 10 and the
receiver 20 can include voice, data, electronic mail, video, and
other data, voice, and video signals.
[0023] In operation, the transmitter 10 transmits a signal data
stream through one or more antennas and over a channel to a
receiver 20, which combines the received signal from one or more
receive antennas to reconstruct the transmitted data. To transmit
the signal, the transmitter 10 prepares a transmission signal
represented by the vector for the signal.
[0024] The transmitter 10 comprises a layer mapper 30 and a
precoder 40.
[0025] The layer mapper 30 of the transmitter 10 may map one or two
codewords, corresponding to one or two transport, to the layers
N.sub.L which may range from a minimum of one layer up to a maximum
number of layers equal to the number of antenna ports. In case of
multi-antenna transmission, there can be up to two transport blocks
of dynamic size for each TTI (Transmission Time Interval), where
each transport block corresponds to one codeword in case of
downlink/uplink spatial multiplexing. In other words, the block of
modulation symbols (one block per each transport block) refers to
as a codeword.
[0026] The number of streams capable of being transmitted can be
decided according to rank number. The transmitter 10 measures a
channel status for each layer, selects the best channel having the
best channel status from among several layers, and transmits signal
via the selected channel.
[0027] Rank adaptation may be considered to enhance the performance
according to the change of channel status. For each rank (rank 1 to
4), one mapping relationship between codewords and layers is
allowed. For rank 1, a codeword of CW1 (a first codeword block 1)
can be transmitted one layers. For rank 2, the transmitter 10
simultaneously transmits two codewords via two layers.
[0028] Hereinafter, the rank or the channel rank means the number
of layers that should, preferably, be used for downlink
transmission to the terminal. For example, the rank 3 means three
layers that should, preferably, be used for downlink transmission
to the terminal.
[0029] FIG. 2 to FIG. 6 are the block diagram of the transmitter of
FIG. 1 for 4Tx CL-MIMO according to the other embodiments.
[0030] Referring to FIG. 2, for rank 3, the layer mapper 30 may map
two set of codewords CW1 and CW2 into three layers L1 to L3. The
layer mapper 30 may map one CW1 of codewords into the first layer
L1. The layer mapper 30 may map the other CW2 of codewords into the
second and the third layers L2 and L3 using a serial to parallel
converter 35 as shown in FIG. 3.
[0031] After layer mapping by the layer mapper 30, a set of N.sub.L
symbols (one symbol from each layer) is linearly combined and
mapped to the N.sub.A antenna port by the precoder 40. This
combining/mapping can be described by means of a precoding matrix P
of size N.sub.L.times.N.sub.A.
[0032] For rank 2 (N.sub.L=2) and four transmitting antenna ports
(N.sub.A=4), the precoder 40 precodes N.sub.L symbols and
distributes them across four antenna ports by means of a precoding
matrix P of size 2.times.4.
[0033] For rank 3 (N.sub.L=3) and four transmitting antenna ports
(N.sub.A=4), the precoder 40 precodes N.sub.L symbols and
distributes them across four antenna ports by means of a precoding
matrix P of size 3.times.4.
[0034] For rank 4 (N.sub.L=4) and four transmitting antenna ports
(N.sub.A=4), the precoder 40 precodes N.sub.L symbols and
distributes them across four antenna ports by means of a precoding
matrix P of size 4.times.4.
[0035] The precoder 40 has its own codebook, which is accessed to
obtain a transmission is profile and/or precoding information to be
used to process the input data signal to make best use of the
existing channel conditions for individual receiver stations.
[0036] For Rank 3, there is unbalance on layers allocation to
different codeword. So the codebook design for rank 3 is special.
As shown in FIG. 4, the optimization for rank 3 codebook design is
codeword based. We consider not only the precoding structure from 3
layers to the 4 Tx antennas, but also another structure for the
codeword to layer mapping. We optimize the codebook design by this
two codeword based optimization for every property such as
distance, antenna correlation, power allocation and so on.
[0037] In addition, the receiver 20 includes the same codebook for
use in efficiently transferring information on either the feedback
or feedforward channel.
[0038] distance property and antenna correlation
[0039] In the proposed rank 3 codebook design schemes, the balance
power amplifier is considered for each antenna to make each antenna
the same transmit power. The balance power amplifier should be
fully and equally utilized to ensure this where the vector norm of
each row of a precoding vector/matrix shall be the same.
[0040] The chordal distance between two matrices is defined as
formula 1.
d ( U , V ) = 1 2 UU H - VV H F where U F = V F = 1. [ Math Figure
1 ] ##EQU00001##
[0041] A low CMP (Cubic Matrix-preserving) is a reasonable
criterion for the codebook design in the power limited
scenario.
[0042] One CMP codebook is proposed for UL 4Tx MIMO Rank 3, as
shown in Table 1. Table 1 is Cubic Metric Preserving codebook for
UL 4Tx MIMO Rank 3.
TABLE-US-00001 TABLE 1 [ 1 0 0 0 1 0 x 0 0 0 0 1 ] ##EQU00002## [ 0
1 0 1 0 0 0 0 1 x 0 0 ] ##EQU00003## [ 1 0 0 x 0 0 0 1 0 0 0 1 ]
##EQU00004## [ 0 1 0 0 0 1 1 0 0 x 0 0 ] ##EQU00005## x = { +1, -1,
+j, -j}.
[0043] However, if norms of column vectors are fixed to be same,
Pas (balance power amplifier) lose the balance consequently. If
norms of row vectors are set to be same, layer power imbalance
issue rises. The power ratio of the 3 layers is 2:1:1 for CMP Rank
3 codebook.
[0044] A rank-3 CMF (Cubic Matrix-friendly) precoding matrix can be
written as follows.
W = .PI. [ 1 1 0 x u 0 y 0 1 z 0 v ] [ Math Figure 2 ]
##EQU00006##
[0045] Here, .PI. is a row permutation matrix. The constant
normalization factor is the Frobenius-norm of the matrix W.
[0046] In formula 2, the transmit power across the three layers
(three columns) is equalized via diagonal scaling. It should be
noted that such fixed scaling precludes layer-specific power
control (open or closed loop). Consequently, the scaled CM-friendly
precoding matrix can be written as follows.
W = .PI. [ 1 1 0 x - x 0 y 0 1 z 0 - y * / z * ] [ 1 / 2 0 0 0 1 0
0 0 1 ] [ Math Figure 3 ] ##EQU00007##
[0047] Both cubic metric preserving (CMP), cubic metric friendly
(CMF) and the mixed structure of both are proposed. However, in
their codebook design, they does not consider the special codeword
to layer mapping for rank 3 to optimize the performance. Since the
final system performance is layer based, the previous codebook
design can not achieve the final optimal performance.
[0048] In these embodiments, an optimized rank 3 codebook design
method is proposed based on the rank 3 codeword to layer mapping
for UL 4Tx MIMO. Moreover, the optimized distance property and
antenna correlation by the codeword based optimization with the CMP
or CMF has been taken into account. The codebook should have good
distance properties (e.g. measured by the chordal distance) to
ensure good performances in low correlated scenario.
[0049] For the CMF codeword, the first codeword has 4 Tx antennas
to transmit, and for the second codeword, each layer also has 2 Tx
antennas to transmit. We need optimized the weight for all layers
and codeword, not just antenna selection. Consider the second
codeword has two layers. We put more effort on the second codeword.
If we define the codebook for each codeword is
C.sub.1={W.sub.i.sup.(1)|i=0,1,L,CZ-1} for codeword 1 and.
[0050] C.sub.2={W.sub.i.sup.(2,3)|i=0,1,L,CZ-1} is for codeword
2.
[0051] Where C={W.sub.i|i=0,1,L,CZ-1} is the rank 3 codebook and CZ
is the codebook size.
[0052] W.sub.i.sup.(1) is the first column of the ith matrix in the
codebook.
[0053] W.sub.i.sup.(2,3) is the second and third column of the ith
matrix in the codebook. We can define the codebook size of C1 and
C2 as effective codebook size of codeword 1 and codeword 2.
[0054] In the codebook design, we try to make the effective
codebook size for each codebook the same. And put more priority on
the second codeword so that the final performance is the same.
[0055] The rank 3 codebook is designed by codeword based
optimization. The rank 3 codebook is designed in the form of the
base matrix for codebook U.
[0056] The base matrix for codebook U is optimized by the distance
property and antenna correlation for each codeword.
[0057] The above-described is said that for rank 3, the layer
mapper 30 may map one of codewords into only one layer and the
other of codewords into two layers and the precoder 40 precodes
N.sub.L symbols and distributes them across four antenna ports by
means of a precoding matrix P of size 3.times.4.
[0058] In this case, one of codewords is mapped into only one layer
which is allocated more antenna ports, for example of four
antennas, two antenna ports for balance diversity gain. Antenna
correlation property is also considered to optimize the antenna
allocation especially when cross polarized antenna is used. Usually
the antennas with larger distance and high different polarization
may be allocated to one of codewords and the other is allocated for
the other of codewords.
[0059] For non-uniform antenna configurations such as
dual-polarized arrays, the antenna element indexing is crucial
since it may affect the performance due to the non-uniform
correlation profile.
[0060] FIG. 7 depicts the indexing which we assume in this
contribution (transmitter and receiver).
[0061] The antenna indexing is used to enumerate the spatial
channel coefficients H.sub.n,m where n and m are the receiver and
transmitter antenna indices, respectively.
[0062] The indexing for the 2 pairs of cross-polarized antennas
(FIG. 7(c)) represents the grouping of two antennas with the same
polarization which tend to be more correlated. This is analogous to
the indexing of 2 pairs of ULA in FIG. 7(b).
[0063] Table 2 is the base matrix for codebook U of codeword based
optimization for distance and antenna correlation for FIG. 7(a) and
FIG. 7(b)
TABLE-US-00002 TABLE 2 Index 0~3 1 2 [ 1 0 0 0 1 0 1 0 0 0 0 1 ]
##EQU00008## 1 2 [ 1 0 0 0 1 0 j 0 0 0 0 1 ] ##EQU00009## 1 2 [ 1 0
0 0 1 0 - 1 0 0 0 0 1 ] ##EQU00010## 1 2 [ 1 0 0 0 1 0 - j 0 0 0 0
1 ] ##EQU00011## Index4~7 1 2 [ 0 1 0 1 0 0 0 0 1 1 0 0 ]
##EQU00012## 1 2 [ 0 1 0 1 0 0 0 0 1 j 0 0 ] ##EQU00013## 1 2 [ 0 1
0 1 0 0 0 0 1 - 1 0 0 ] ##EQU00014## 1 2 [ 0 1 0 1 0 0 0 0 1 - j 0
0 ] ##EQU00015##
[0064] By the codebook in Table 2, the codewords to antenna port
are shown in FIGS. 5 and 6 according to index 0.about.3 and index
4.about.7.
[0065] Table 3 is the base matrix for codebook U of codeword based
optimization for distance and antenna correlation for FIG. 7(c)
TABLE-US-00003 TABLE 3 Index 0~3 1 2 [ 1 0 0 0 1 0 0 0 1 1 0 0 ]
##EQU00016## 1 2 [ 1 0 0 0 1 0 0 0 1 j 0 0 ] ##EQU00017## 1 2 [ 1 0
0 0 1 0 0 0 1 - 1 0 0 ] ##EQU00018## 1 2 [ 1 0 0 0 1 0 0 0 1 - j 0
0 ] ##EQU00019## Index 4~7 1 2 [ 0 1 0 1 0 0 1 0 0 0 0 1 ]
##EQU00020## 1 2 [ 0 1 0 1 0 0 j 0 0 0 0 1 ] ##EQU00021## 1 2 [ 0 1
0 1 0 0 - 1 0 0 0 0 1 ] ##EQU00022## 1 2 [ 0 1 0 1 0 0 - j 0 0 0 0
1 ] ##EQU00023##
[0066] Table 3 is the base matrix for codebook U of codeword based
optimization for distance and antenna correlation for FIG. 7(c)
TABLE-US-00004 TABLE 4 Index 0 to 3 [ 1 1 0 - 1 1 0 1 0 1 - 1 0 1 ]
.LAMBDA. ##EQU00024## [ 1 1 0 - 1 1 0 - 1 0 1 1 0 - 1 ] .LAMBDA.
##EQU00025## [ 1 1 0 - 1 1 0 j 0 1 1 0 j ] .LAMBDA. ##EQU00026## [
1 1 0 - 1 1 0 - j 0 1 1 0 - j ] .LAMBDA. ##EQU00027## Index 4 to 7
[ 1 1 0 1 - 1 0 1 0 1 - 1 0 1 ] .LAMBDA. ##EQU00028## [ 1 1 0 1 - 1
0 1 0 1 1 0 - 1 ] .LAMBDA. ##EQU00029## [ 1 1 0 1 - 1 0 1 0 1 - j 0
j ] .LAMBDA. ##EQU00030## [ 1 1 0 1 - 1 0 1 0 1 j 0 - j ] .LAMBDA.
##EQU00031## Index 8 to 11 [ 1 1 0 - j j 0 1 0 1 - 1 0 1 ] .LAMBDA.
##EQU00032## [ 1 1 0 - j j 0 1 0 1 1 0 - 1 ] .LAMBDA. ##EQU00033##
[ 1 1 0 - j j 0 1 0 1 - j 0 j ] .LAMBDA. ##EQU00034## [ 1 1 0 - j j
0 1 0 1 j 0 - j ] .LAMBDA. ##EQU00035## Index 12 to 15 [ 1 1 0 j -
j 0 j 0 1 - j 0 1 ] .LAMBDA. ##EQU00036## [ 1 1 0 j - j 0 j 0 1 j 0
- 1 ] .LAMBDA. ##EQU00037## [ 1 1 0 j - j 0 1 0 1 - j 0 j ]
.LAMBDA. ##EQU00038## [ 1 1 0 - j j 0 1 0 1 j 0 - j ] .LAMBDA.
##EQU00039##
[0067] Table 4 is the base matrix for codebook U of codeword based
optimization for CMF codebook. Where the codebook is optimized the
second codeword has the same effective codebook size as the first
codeword.
[0068] The layer mapper 30 may map one CW1 of codewords into the
first layer L1. the layer mapper 30 may map the other CW2 of
codewords into the second and the third layers L2 and L3 using a
serial to parallel converter 35 as shown in FIG. 3.
[0069] For rank 3 (N.sub.L=3) and four transmitting antenna ports
(N.sub.A=4), the precoder 40 precodes N.sub.L symbols and
distributes them across four antenna ports by means of a precoding
matrix P of size 3.times.4 from the codebook.
[0070] FIG. 8 is the block diagram of the transmitter of FIG. 1 for
6TxCL-MIMO for rank 3 according to further another embodiment.
[0071] For rank 3 (N.sub.L=3), 6 transmitting antenna ports
(N.sub.A=6) and two codewords, the layer mapper 30 may map one CW1
of codewords into the first layer L1. The layer mapper 30 may map
the other CW2 of codewords into the second and the third layers L2
and L3 using a serial to parallel converter 35. The precoder 40
precodes N.sub.L symbols and distributes them is across 6 antenna
ports by means of a precoding matrix P of size 3.times.6 as
follows.
( 1 0 0 1 0 0 1 0 0 0 1 0 0 1 0 0 0 1 ) [ Math Figure 4 ]
##EQU00040##
[0072] In this case, one of codewords is mapped into only one layer
which is allocated three antenna ports for balance diversity gain.
The other of codewords is mapped into two layers which are
allocated three antenna ports.
[0073] FIG. 9 is the block diagram of the transmitter of FIG. 1 for
6Tx CL-MIMO for rank 3 according to further another embodiment.
[0074] For rank 5(N.sub.L=5), 6 transmitting antenna ports
(N.sub.A=6) and two codewords, the layer mapper 30 may map one CW1
of codewords into the first and the second layers L1 and L2 using a
serial to parallel converter 35. The layer mapper 30 may map the
other CW2 of codewords into the third to fifth layers L3 to L5
using a serial to parallel converter 35.
[0075] The precoder 40 precodes 5 symbols and distributes them
across 6 antenna ports by means of a precoding matrix P of size
5.times.6.
[0076] In this case, one of codewords is mapped into only two
layers which are allocated three antenna ports for balance
diversity gain. The other of codewords is mapped into three layers
which are allocated three antenna ports.
[0077] When the number of codewords is more than 3, functions of
the layer mapper 30 and the precoder 40 is the same as described
above.
[0078] Power Allocation
[0079] The power allocation is optimized for each codeword for CMF.
The rank 3 codebook is designed by codeword based optimization. The
rank 3 codebook is designed in the form of U.times., where U is the
base matrix for codebook and is the power allocation matrix. The
base matrix for codebook U is the same as described above.
[0080] The power allocation matrix for each codeword is in the form
of formula 5.
.LAMBDA. = [ .lamda. 1 0 0 0 .lamda. 2 0 0 0 .lamda. 3 ] [ Math
Figure 5 ] ##EQU00041##
[0081] In formula 5, .lamda..sub.1, .lamda..sub.2, .lamda..sub.3
are power allocation factor and
.lamda..sub.1+.lamda..sub.2+.lamda..sub.3=1. .lamda..sub.i is for
the first codeword CW1, and .lamda..sub.2, .lamda..sub.3 is for
second codeword cw2 based on the LTE codeword to layer mapping
pattern. That is to find the optimal power allocation factor in the
way that .lamda..sub.1 Vs. .lamda..sub.2=.lamda..sub.3.
[0082] Table 5 is the rank 3 codebook of U.times. for codeword
based optimization for power allocation.
TABLE-US-00005 TABLE 5 Index 0~3 [ 0.5 0 0 0 1 0 0.5 0 0 0 0 1 ] [
0.4 0 0 0 0.3 0 0 0 0.3 ] ##EQU00042## . . . . . . . . . Index 4~7
. . . . . . . . . . . .
[0083] layer shifting and receiver type
[0084] The codebook is optimized by taking the receiver type and
the layer shifting into account.
[0085] For the MMSE receiver, the above optimization is enough.
Since the SIC receiver is also codeword based, it need to be
considered for another optimization. For rank 3, it is is possible
to detect the second codeword at first since it has two layer
signals. After it removes the second codeword, there will be no
interference any more. So power allocation factor need to be
further optimized for the SIC receiver.
[0086] Moreover, if layer shifting is considered, we also should
re-optimize the codebook design. Because there is also high
diversity for the first codeword, it is better to design the
codebook also in layer shift way as in the example.
[0087] Table 6 is Codebook for codeword based optimization for
layer shifting.
TABLE-US-00006 TABLE 6 Index 1 2 [ 1 0 0 0 1 0 1 0 0 0 0 1 ]
##EQU00043## 1 2 [ 0 1 0 1 0 0 0 1 0 0 0 1 ] ##EQU00044## 1 2 [ 0 0
1 0 1 0 0 0 1 1 0 0 ] ##EQU00045## . . .
[0088] It should be noted that all the optimization in the proposed
algorithm is codeword based, not layer based.
[0089] In the previous rank 3 codebook design for UL MIMO, they
does not consider the special codeword to layer mapping for rank 3
to optimize the performance. Since the final system performance is
layer based, the previous codebook design can not achieve the final
optimal performance.
[0090] In these embodiments, an optimized rank codebook design
method is proposed is based on the rank codeword to layer
mapping.
[0091] Since link adaptation is codeword based in the proposed
codebook design, we optimized the codebook design by allocating
antenna ports, power between different codewords to get the final
optimal performance. Moreover, antenna cross polarized, layer
shifting and receiver type is also considered for the codebook
design.
[0092] To assist the transmitter in selecting a suitable precoding
matrix for transmission by the transmitter 10, the receiver 20 may
report channel information such as a recommended number of layers
(expressed as a Rank Indication, RI) or a recommended precoding
matrix (Precoding Matrix Index, PMI) corresponding to that number
of layers, depending on estimates of the downlink channel
conditions.
[0093] Referring to FIG. 1 again, the receiver 20 comprises a
channel estimator 50, a post-decoder 60 and a layer demapper
70.
[0094] The channel estimator 50 of the receiver 20 estimates the
downlink channel condition. The channel estimator 50 feedbacks at
least one of RI and PMI to the transmitter 10. The channel
estimator 50 may perform many kinds of codebook based PMI
feedback.
[0095] The receiver 20 estimates the channel by the channel
estimator 50. Based on the estimated channel information, then the
receiver 20 selects the precoding matrix for each level from the
corresponding codebooks. Once the precoding matrix for each level
is decided, the receiver 20 separately feedback the PMIs of both
level to the transmitter 10.
[0096] There is codebook based PMI feedback where the receiver 20
feedbacks the precoding matrix index (PMI) of the favorite matrix
in the codebook to the transmitter 10 to is support CL-MIMO (closed
MIMO) operation in wireless communication system.
[0097] The receiver 20 recovers the original data symbols by the
post-decoder 60 with the previous feedback precoding matrices
combination. The post-decoder 60 processes the received signal and
decodes the precoded symbols.
[0098] For example, the post-decoder 60 decodes the precoded
symbols using a inverse matrix of the precoding matrix P, for
example U or UxA as described above.
[0099] The layer demapper 70 may demap the decoded symbol streams
in a manner complementary to the mapping performed by the layer
mapper 30 to recovers the original data symbols.
[0100] The above embodiments are described that the number of
codewords is equal 1 or 2 and the rank number is equal to 3 or 5,
the number of antennas (or antenna ports) is equal to 4 or 6.
[0101] In general, the number of codewords may be n which is the
natural number. The number of layers may be m which is the natural
number more than n and not a multiple of n. the number of antennas
(or antenna ports) may be a multiple of the number of
codewords.
[0102] Therefore, there is a method comprising: mapping the (n)
number of codewords (n is the natural number) to the (m) number of
layers (m is the natural number more than n and not a multiple of
n) and precoding a mapped set of (m) symbols using a precoding
matrix so that all the codewords have the same antenna ports and
antenna correlation property where the number of antenna ports may
be a multiple of the number of codewords.
[0103] The methods and systems as shown and described herein may be
implemented in software stored on a computer-readable medium and
executed as a computer program on a general purpose or special
purpose computer to perform certain tasks. For a hardware
implementation, the elements used to perform various signal
processing steps at the transmitter (e.g., coding and modulating
the data, precoding the modulated signals, preconditioning the
precoded signals, and so on) and/or at the receiver (e.g.,
recovering the transmitted signals, demodulating and decoding the
recovered signals, and so on) may be implemented within one or more
application specific integrated circuits (ASICs), digital signal
processors (DSPs), digital signal processing devices (DSPDs),
programmable logic devices (PLDs), field programmable gate arrays
(FPGAs), processors, controllers, micro-controllers,
microprocessors, other electronic units designed to perform the
functions described herein, or a combination thereof. In addition
or in the alternative, a software implementation may be used,
whereby some or all of the signal processing steps at each of the
transmitter and receiver may be implemented with modules (e.g.,
procedures, functions, and so on) that perform the functions
described herein. It will be appreciated that the separation of
functionality into modules is for illustrative purposes, and
alternative embodiments may merge the functionality of multiple
software modules into a single module or may impose an alternate
decomposition of functionality of modules. In any software
implementation, the software code may be executed by a processor or
controller, with the code and any underlying or processed data
being stored in any machine-readable or computer-readable storage
medium, such as an on-board or external memory unit.
[0104] Although the described exemplary embodiments disclosed
herein are directed to various MIMO precoding systems and methods
for using same, the present invention is not necessarily limited to
the example embodiments illustrate herein. For example, various
embodiments of a MIMO precoding system and design methodology
disclosed herein may be implemented in connection with various
proprietary or wireless communication standards, such as IEEE
802.16e, 3GPP-LTE, DVB and other multi-user MIMO systems. Thus, the
particular is embodiments disclosed above are illustrative only and
should not be taken as limitations upon the present invention, as
the invention may be modified and practiced in different but
equivalent manners apparent to those skilled in the art having the
benefit of the teachings herein. Accordingly, the foregoing
description is not intended to limit the invention to the
particular form set forth, but on the contrary, is intended to
cover such alternatives, modifications and equivalents as may be
included within the spirit and scope of the invention as defined by
the appended claims so that those skilled in the art should
understand that they can make various changes, substitutions and
alterations without departing from the spirit and scope of the
invention in its broadest form.
[0105] Benefits, other advantages, and solutions to problems have
been described above with regard to specific embodiments. However,
the benefits, advantages, solutions to problems, and any element(s)
that may cause any benefit, advantage, or solution to occur or
become more pronounced are not to be construed as a critical,
required, or essential feature or element of any or all the claims.
As used herein, the terms "comprises," "comprising," or any other
variation thereof, are intended to cover a non-exclusive inclusion,
such that a process, method, article, or apparatus that comprises a
list of elements does not include only those elements but may
include other elements not expressly listed or inherent to such
process, method, article, or apparatus.
* * * * *