U.S. patent application number 13/765233 was filed with the patent office on 2019-12-26 for pre-coder selection based on resource block grouping.
This patent application is currently assigned to Texas Instruments Incorporated. The applicant listed for this patent is TEXAS INSTRUMENTS INCORPORATED. Invention is credited to Anand Ganesh DABAK, Eko N. ONGGOSANUSI, Badri VARADARAJAN.
Application Number | 20190393935 13/765233 |
Document ID | / |
Family ID | 51297418 |
Filed Date | 2019-12-26 |
![](/patent/app/20190393935/US20190393935A9-20191226-D00000.png)
![](/patent/app/20190393935/US20190393935A9-20191226-D00001.png)
![](/patent/app/20190393935/US20190393935A9-20191226-D00002.png)
![](/patent/app/20190393935/US20190393935A9-20191226-D00003.png)
![](/patent/app/20190393935/US20190393935A9-20191226-D00004.png)
![](/patent/app/20190393935/US20190393935A9-20191226-M00001.png)
![](/patent/app/20190393935/US20190393935A9-20191226-M00002.png)
United States Patent
Application |
20190393935 |
Kind Code |
A9 |
ONGGOSANUSI; Eko N. ; et
al. |
December 26, 2019 |
PRE-CODER SELECTION BASED ON RESOURCE BLOCK GROUPING
Abstract
The present invention provides a receiver. In one embodiment,
the receiver includes a receive portion employing transmission
signals from a transmitter having multiple antennas and capable of
providing channel estimates. The receiver also includes a feedback
generator portion configured to provide to the transmitter a
pre-coder selection for data transmission that is based on the
channel estimates, wherein the pre-coder selection corresponds to a
grouping of frequency-domain resource blocks. The present invention
also provides a transmitter having multiple antennas. In one
embodiment, the transmitter includes a transmit portion coupled to
the multiple antennas and capable of applying pre-coding to a data
transmission for a receiver. The transmitter also includes a
feedback decoding portion configured to decode a pre-coder
selection for the data transmission that is fed back from the
receiver, wherein the pre-coder selection corresponds to a grouping
of frequency-domain resource blocks.
Inventors: |
ONGGOSANUSI; Eko N.; (Allen,
TX) ; VARADARAJAN; Badri; (Mountain View, CA)
; DABAK; Anand Ganesh; (Plano, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TEXAS INSTRUMENTS INCORPORATED |
Dallas |
TX |
US |
|
|
Assignee: |
Texas Instruments
Incorporated
Dallas
TX
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140226739 A1 |
|
|
US 20180351613 A9 |
December 6, 2018 |
|
|
Family ID: |
51297418 |
Appl. No.: |
13/765233 |
Filed: |
February 12, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11688756 |
Mar 20, 2007 |
10044532 |
|
|
13765233 |
|
|
|
|
60784210 |
Mar 20, 2006 |
|
|
|
60884350 |
Jan 10, 2007 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 25/0228 20130101;
H04L 27/2626 20130101; H04B 7/0456 20130101; H04L 27/2647
20130101 |
International
Class: |
H04B 7/04 20060101
H04B007/04 |
Claims
1. A receiver, comprising: a receive portion employing transmission
signals from a transmitter having multiple antennas and capable of
providing channel estimates; and a feedback generator portion
configured to provide a pre-coder selection for data transmission
to the transmitter that is based on the channel estimates; wherein
the pre-coder selection corresponds to a grouping of
frequency-domain resource blocks.
2. The receiver as recited in claim 1 wherein the pre-coder
selection provides a single pre-coder for each group of contiguous
resource blocks.
3. The receiver as recited in claim 2 wherein a number of
contiguous resource blocks corresponding to each group is varied
and configured by the transmitter employing signaling to the
receiver via a broadcast or a common control channel.
4. The receiver as recited in claim 2 wherein a number of
contiguous resource blocks corresponding to each group is varied
and configured by a network employing signaling to the receiver via
a higher layer signaling.
5. The receiver as recited in claim 1 wherein the pre-coder
selection provides a set of pre-coders corresponding to a subgroup
of resource blocks contained in each group of contiguous resource
blocks.
6. The receiver as recited in claim 1 wherein the pre-coder
selection provides a set of pre-coders corresponding to a
combination of groups of contiguous resource blocks.
7. The receiver as recited in claim 1 wherein the pre-coder
selection is jointly encoded to achieve feedback transmission
compression.
8. The receiver as recited in claim 1 wherein the pre-coder
selection is jointly encoded with a channel quality indicator.
9. The receiver as recited in claim 1 wherein the pre-coder
selection is based on one selected from the group consisting of: a
sum throughput; a worst case throughput; and a specified maximum
error rate.
10. The receiver as recited in claim 1 wherein the grouping of the
resource blocks is variable or fixed based on signaling
support.
11. The receiver as recited in claim 1 wherein the receiver
operates in an OFDM or OFDMA system.
12. A method of operating a receiver, comprising: providing channel
estimates employing transmission signals from a transmitter having
multiple antennas; and feeding back a pre-coder selection for data
transmission to the transmitter that is based on the channel
estimates; wherein the pre-coder selection corresponds to a
grouping of frequency-domain resource blocks.
13. The method as recited in claim 12 wherein the pre-coder
selection provides a single pre-coder for each group of contiguous
resource blocks.
14. The method as recited in claim 13 wherein a number of
contiguous resource blocks corresponding to each group is varied
and configured by the transmitter employing signaling to the
receiver via a broadcast or a common control channel.
15. The method as recited in claim 13 wherein a number of
contiguous resource blocks corresponding to each group is varied
and configured by a network employing signaling to the receiver via
a higher layer signaling.
16. The method as recited in claim 12 wherein the pre-coder
selection provides a set of pre-coders corresponding to a subgroup
of resource blocks contained in each group of contiguous resource
blocks.
17. The method as recited in claim 12 wherein the pre-coder
selection provides a set of pre-coders corresponding to a
combination of groups of contiguous resource blocks.
18. The method as recited in claim 12 wherein the pre-coder
selection is jointly encoded to achieve feedback transmission
compression.
19. The method as recited in claim 12 wherein the pre-coder
selection is jointly encoded with a channel quality indicator.
20. The method as recited in claim 12 wherein the pre-coder
selection is based on one selected from the group consisting of: a
sum throughput; a worst case throughput; and a specified maximum
error rate.
21. The method as recited in claim 12 wherein the grouping of the
resource blocks is variable or fixed based on signaling
support.
22. The method as recited in claim 12 wherein the receiver operates
in an OFDM or OFDMA system.
23-38. (canceled)
39. The receiver as recited in claim 1 wherein the pre-coder
transmission is based on channel estimates and CQI information.
40. The receiver as recited in claim 39, wherein the pre-coder
selection and CQI are computed for the next time the receiver is
scheduled by the transmitter to receive data.
41. The receiver as recited in claim 40, wherein the feedback
decoding portion encodes the pre-coder selection and CQI
information and feeds it back to the transmitter before the data is
transmitted.
42. The receiver as recited in claim 1, wherein each of the
resource blocks represents bandwidth.
43. The receiver as recited in claim 42, wherein each of the
resource blocks represents 180 kHz bandwidth.
44. The receiver as recited in claim 43, wherein each of the
resource blocks represents 180 kHz bandwidth comprising 12
OFDM/OFDMA sub-carriers.
45. The receiver as recited in claim 44, wherein each of the
resource blocks represents 180 kHz bandwidth comprising 12
OFDM/OFDMA sub-carriers thereby giving a group size of 900 kHZ for
each of first, second and third pre-coders selected.
46. The method as recited in claim 12, wherein the pre-coder
transmission is based on channel estimates and CQI information.
47. The method as recited in claim 46, wherein the pre-coder
selection and CQI are computed for the next time the receiver is
scheduled by the transmitter to receive data.
48. The method as recited in claim 47, wherein the feedback
decoding portion encodes the pre-coder selection and CQI
information and feeds it back to the transmitter before the data is
transmitted.
49. The method as recited in claim 31, wherein each of the resource
blocks represents bandwidth.
50. The method as recited in claim 49, wherein each of the resource
blocks represents 180 kHz bandwidth.
51. The receiver as recited in claim 50, wherein each of the
resource blocks represents 180 kHz bandwidth comprising 12
OFDM/OFDMA sub-carriers.
52. The method as recited in claim 51, wherein each of the resource
blocks represents 180 kHz bandwidth comprising 12 OFDM/OFDMA
sub-carriers thereby giving a group size of 900 kHZ for each of
first, second and third pre-coders selected.
Description
CROSS-REFERENCE TO PROVISIONAL APPLICATIONS
[0001] This application is a divisional of prior application Ser.
No. 11/688,756, filed Mar. 20, 2007, which claims the benefit of
U.S. Provisional Application No. 60/784,210 entitled "Evaluation of
Downlink MIMO Pre-coding for E-UTRA with 2-Antenna Node B" to Eko
N. Onggosanusi, Badri Varadarajan and Anand G. Dabak filed on Mar.
20, 2006, which is incorporated herein by reference in its
entirety.
[0002] Additionally, this application claims the benefit of U.S.
Provisional Application No. 60/884,350 entitled "Feedback Reduction
for CL MIMO" to Eko N. Onggosanusi, Badri Varadarajan and Anand G.
Dabak filed on Jan. 10, 2007, which is incorporated herein by
reference in its entirety.
TECHNICAL FIELD OF THE INVENTION
[0003] The present invention is directed, in general, to wireless
communications and, more specifically, to a receiver and a
transmitter and methods of operating a receiver and a
transmitter.
BACKGROUND OF THE INVENTION
[0004] In a cellular network, such as one employing orthogonal
frequency division multiplexing (OFDM) or orthogonal frequency
division multiple access (OFDMA), each cell employs a base station
that communicates with user equipment, such as a cell phone, a
laptop, or a PDA, which is actively located within its cell.
[0005] Initially, the base station transmits reference signals
(synonymous to pilot signals) to the user equipment wherein the
reference signals are basically an agreement between the base
station and the user equipment that at a certain frequency and
time, they are going to receive a known signal. Since the user
equipment knows the signal and its timing, it can generate a
channel estimate based on the reference signal. Of course, there
are unknown distortions such as interference and noise, which
impact the quality of the channel estimate.
[0006] In an OFDM or OFDMA system, different user equipments are
scheduled on different portions of the system bandwidth. The system
bandwidth may be divided into frequency-domain resource blocks of a
certain size (sometime referred as sub-band) wherein a resource
block is the smallest allocation unit available in terms of
frequency granularity that can be allocated to user equipment. Each
resource block consists of N.sub.RB contiguous OFDM/OFDMA
sub-carriers. While the size of different resource blocks can in
general vary, it is preferred to impose the same size across
resource blocks. Otherwise, the resource blocks size shall be as
uniform as possible across the system bandwidth. A different user
could potentially go on each of these resource blocks. In addition,
a user can be scheduled on a portion of the system bandwidth having
adjacent resource blocks inside. Non-adjacent allocation for each
user is also possible.
[0007] The user equipment determines a channel quality indicator
(CQI) for each of the resource blocks based on the channel
estimation performed. The CQI employed can be a signal to
interference noise ratio (SINR) after detection. The CQI can also
be a certain type of quality measure such as mutual information.
Other types of CQI that reflect the quality of transmission channel
are also possible. Furthermore, the CQI for different resource
blocks can also be jointly encoded and compressed. The user
equipment feeds back the CQI for each resource block to the base
station. A higher CQI for a resource block allows a higher data
rate transfer of information from the base station to the user
equipment.
[0008] For systems with multiple transmit and multiple receive
antennas (also termed as multi-input multi-output (MIMO) systems),
improved throughput and/or robustness can be obtained by employing
transmit pre-coding. To apply a pre-coding on a MIMO system means
that a certain transformation (typically linear) is applied to the
data stream(s) prior to transmission via physical antennas. The
number of independent data streams is termed the transmission rank.
With pre-coding, the number of physical antennas does not have to
be equal to the transmission rank. In this case, the pre-coder is a
P.times.R matrix, where P is the number of physical transmit
antennas and R is the transmission rank. Denoting the pre-coder
matrix as W and the R independent data streams as an R-dimensional
vector s, the transmitted signal via the P physical antennas can be
written as: x=Ws.
[0009] Depending on the duplexing scheme, the pre-coder matrix W
can be selected at the transmitter or receiver. For an FDD system
where the uplink and downlink channels are not reciprocal, the
pre-coder matrix W is more efficiently chosen at the receiver (user
equipment) from a finite pre-determined set of matrices, termed the
pre-coding codebook. Based on the channel estimate, the user
equipment determines the pre-coder selection corresponding to the
CQI in each resource block that is needed to allow an optimization
of data throughput, for example. Therefore, the pre-coder is also a
function of the channel and its quality. The same codebook-based
pre-coding scheme can also be used for TDD or half-duplex
TDD/FDD.
[0010] Once this is done, the user equipment will feed back to the
base station for each of its resource blocks, the pre-coder and the
CQI that will be achieved if that pre-coder is used for the
resource block in the transmission of data. For example, in the
context of the 3GPP E-UTRA system deploying a 5-MHz transmission,
10 user equipments having feedback information pertaining to 25
resource blocks requires that 250 units of information be fed back
to the base station, just to schedule them. This requires a high
level of operational overhead information.
[0011] In addition to the CQI and pre-coder selection feedback, the
user equipment shall also select and feed back the transmission
rank. While transmission rank selection may or may not be performed
for each resource block, this constitutes to additional feedback
overhead.
[0012] Accordingly, what is needed in the art is an enhanced way to
reduce the amount of initial feedback required between user
equipment and base station.
SUMMARY OF THE INVENTION
[0013] To address the above-discussed deficiencies of the prior
art, the present invention provides a receiver. In one embodiment,
the receiver includes a receive portion employing transmission
signals from a transmitter having multiple antennas and capable of
providing channel estimates. The receiver also includes a feedback
generator portion configured to provide to the transmitter a
pre-coder selection for data transmission that is based on the
channel estimates, wherein the pre-coder selection corresponds to a
grouping of frequency-domain resource blocks. Pre-coder selection
per group of resource blocks is motivated with the fact that the
pre-coding codebook size is typically kept to a minimum, and hence,
the optimum pre-coder tends to stay the same across multiple
resource blocks.
[0014] The present invention also provides a transmitter having a
plurality of antennas. In one embodiment, the transmitter includes
a transmit portion coupled to the plurality of antennas and capable
of applying pre-coding to a data transmission for a receiver. The
transmitter also includes a feedback decoding portion configured to
decode a pre-coder selection for the data transmission that is fed
back from the receiver, wherein the pre-coder selection corresponds
to a grouping of frequency-domain resource blocks. The grouping
scheme that is used at the transmitter corresponds to the grouping
scheme that is used at the receiver.
[0015] In another aspect, the present invention provides a method
of operating a receiver. In one embodiment, the method includes
providing channel estimates employing transmission signals from a
transmitter having multiple antennas. The method also includes
feeding back a pre-coder selection for data transmission to the
transmitter that is based on the channel estimates, wherein the
pre-coder selection corresponds to a grouping of frequency-domain
resource blocks.
[0016] The present invention also provides a method of operating a
transmitter having a plurality of antennas. In one embodiment, the
method includes extracting a pre-coder selection provided by a
feedback signal from a receiver, wherein the pre-coder selection
corresponds to a grouping of frequency-dependent resource blocks
and applying the pre-coder selection to data to be transmitted to
the receiver based on decoded information corresponding to the
pre-coder selection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] For a more complete understanding of the present invention,
reference is now made to the following descriptions taken in
conjunction with the accompanying drawings, in which:
[0018] FIG. 1A illustrates a system diagram of a receiver as
provided by one embodiment of the present invention;
[0019] FIG. 1B illustrates a system diagram of a transmitter as
provided by one embodiment of the present invention;
[0020] FIG. 2 illustrates a diagram of an exemplary grouping of
resource blocks as provided by one embodiment of the present
invention;
[0021] FIG. 3A illustrates a diagram of a more generalized grouping
of resource blocks corresponding to the exemplary grouping of FIG.
2;
[0022] FIG. 3B illustrates a diagram of a grouping of resource
blocks as provided by an alternative embodiment of the present
invention;
[0023] FIG. 3C illustrates a diagram of a grouping of resource
blocks as provided by another embodiment of the present
invention;
[0024] FIG. 4 illustrates a diagram of an embodiment of a pre-coder
selection that is jointly coded to achieve feedback transmission
compression;
[0025] FIG. 5A illustrates a flow diagram of an embodiment of a
method of operating a receiver carried out according to principles
of the present invention; and
[0026] FIG. 5B illustrates a flow diagram of an embodiment of a
method of operating a transmitter having multiple antennas carried
out according to principles of the present invention.
DETAILED DESCRIPTION
[0027] FIG. 1A illustrates a system diagram of a receiver 100 as
provided by one embodiment of the present invention. In the
illustrated embodiment, the receiver 100 operates in an OFDM
communications system. The receiver 100 includes a receive portion
105 and a feedback generation portion 110. The receive portion 105
includes an OFDM module 106 having Q OFDM demodulators (Q is at
least one) coupled to corresponding receive antenna(s), a MIMO
detector 107, a QAM demodulator plus de-interleaver plus FEC
decoding module 108 and a channel estimation module 109. The
feedback portion 110 includes a pre-coder selector 111, a channel
quality indicator (CQI) computer 112, rank selector 114, and a
feedback encoder 113.
[0028] The receive portion is primarily employed to receive data
from a transmitter based a pre-coder selection that was determined
by the receiver and feedback to the transmitter. The OFDM module
106 demodulates the received data signals and provides them to the
MIMO detector 107, which employs channel estimation and pre-coder
information to further provide the received data to the module 108
for further processing (namely QAM demodulation, de-interleaving,
and FEC decoding). The channel estimation module 109 employs
previously transmitted channel estimation signals to provide the
channel estimates need by the receiver 100. The pre-coder
information can be obtained via an additional downlink signaling
embedded in the downlink shared control channel or in a dedicated
reference signal. Alternatively, the receiver 100 can obtain the
pre-coder information from the previously selected pre-coder. In
addition, the two sources can also be used in conjunction to
further improve the accuracy.
[0029] The pre-coder selector 111 determines the pre-coder
selection for the data transmission based on the channel estimates
and the CQI information provided by the CQI computer 112. These
pre-coder selection and CQI are computed for the next time the user
equipment is scheduled by the transmitter (e.g., a base station) to
receive data. The feedback encoder 113 then encodes the pre-coder
selection and the CQI information and feeds it back to the
transmitter before the data is transmitted. In one embodiment, the
pre-coder selection is jointly encoded to achieve feedback
transmission compression. For improved efficiency, the pre-coder
selection and CQI can be jointly encoded into one codeword.
[0030] The pre-coder selection corresponds to a grouping of
frequency-domain resource blocks employed by the receiver 100. In
the illustrated embodiment, the pre-coder selection provides a
single pre-coder for each group of contiguous resource blocks.
Alternatively, the pre-coder selection may provide a set of
pre-coders corresponding to a subgroup of resource blocks contained
in each group of contiguous resource blocks. Additionally, the
pre-coder selection may provide a set of pre-coders corresponding
to a combination of groups of contiguous resource blocks.
[0031] Actual selection of the pre-coders depends on an "optimality
criterion". A typical optimality criterion may be related to the
sum throughput that a group of resource blocks provides.
Alternatively, a worst case throughput or a specified maximum error
rate for the group of resource blocks may be employed. Of course,
one skilled in the pertinent art will recognize that there may be
other current or future developed optimality criteria applicable to
the present invention.
[0032] The grouping of the resource blocks may be variable or fixed
depending of a level of signaling support available. For example,
the grouping may vary depending on the channel quality afforded by
the resource blocks involved. Or, the grouping may be fixed if the
channel quality is high for the resource blocks involved. Those are
only some examples for the faster variation. Slower variation can
also be employed. For example, the group size (the number of
contiguous resource blocks within each group) is fixed only
throughout the entire communication session, or within each data
frame. For faster variation, the downlink shared control channel
can be used to communicate the change in the grouping scheme. The
slower variation can benefit from the downlink broadcast (common
control) channel, which is transmitted less frequently, or higher
layer signaling.
[0033] In general, the grouping scheme or the group size is
configurable by the network and/or the transmitter (base station).
It is also, possible, however, for the receiver (user equipment) to
request the transmitter and/or the network for changing the
grouping scheme/size. This request can be conveyed via a low-rate
feedback (e.g., sparse physical layer feedback or higher layer
feedback signaling). This is relevant when the downlink
interference characteristic is highly frequency selective.
[0034] FIG. 1B illustrates a system diagram of a transmitter ISO as
provided by one embodiment of the present invention. In the
illustrated embodiment, the transmitter operates in an OFDM
communication system. The transmitter 150 includes a transmit
portion 155 and a feedback decoding portion 160. The transmit
portion 155 includes a modulation and coding scheme module 156, a
pre-coder module 157 and an OFDM module 158 having multiple OFDM
modulators that teed corresponding transmit antennas. The feedback
decoding portion 160 includes a receiver module 166 and a decoder
module 167.
[0035] The transmit portion 155 is employed to transmit data
provided by the MCS module 156 to a receiver based on pre-coding
provided by the pre-coder module 157. The MCS module 156 takes m
codewords (m is at least one) and maps the codeword(s) to the R
layers or spatial streams, where R is the number of transmission
ranks and at least one. Each codeword consists of FEC-encoded,
interleaved, and modulated information bits. The selected
modulation and coding rate for each codeword are derived from the
CQI. A higher CQI implies that a higher data rate may be used. The
pre-coder module 157 employs a pre-coder selection obtained from
the feedback decoding portion 160, wherein the pre-coder selection
corresponds to a grouping of frequency-domain resource blocks
employed by the receiver. The receiver module 166 accepts the
feedback of this pre-coder selection, and the decoder module 157
provides them to the pre-coder module 157.
[0036] Once the R spatial stream(s) are generated from the MCS
module 156, a pre-coder is applied to generate P.gtoreq.R output
streams. Note that P can be equal to R only if R>1 since P>1
and R.gtoreq.1. The pre-coder W is selected from a finite
pre-determined set of possible linear transformations or matrices,
which corresponds to the set that is used by the receiver. Using
pre-coding, the R spatial stream(s) are cross-combined linearly
into P output data streams. For example, if there are 16 matrices
in the pre-coding codebook, a pre-coder index corresponding to one
of the 16 matrices for the resource block (say 5, for example) may
be signaled from the receiver to the transmitter for each group of
resource blocks. The pre-coder index then tells the transmitter 150
which of the 16 matrices to use.
[0037] FIG. 2 illustrates a diagram of an exemplary grouping of
resource blocks 200 as provided by one embodiment of the present
invention. The grouping of resource blocks 200 includes five groups
of five frequency-domain resource blocks wherein a pre-coder
selection provides a single pre-coder for each group, as shown. In
the context of the 3GPP E-UTRA, each of the resource blocks
represents 180 kHz of bandwidth (consisting of 12 OFDM/OFDMA
sub-carriers) thereby giving a group size of 900 kHz for each of
first, second and third pre-coders selected. This grouping may
provide a practical grouping size for many applications. FIGS. 3A,
3B and 3C illustrate generalized alternative embodiments for
pre-coder selection. The resource blocks shown are idealized
representations of the resource blocks shown in FIG. 2, for
simplicity of illustration.
[0038] FIG. 3A illustrates a diagram of a more generalized grouping
of resource blocks 300 corresponding to the exemplary grouping of
FIG. 2. Again, each group of contiguous resource blocks has a
single pre-coder selected for the group. The resource block
grouping 300 corresponds to N groups of M frequency-domain resource
blocks, which represent a total of NM resource blocks for a
channel. The single pre-coder matrix is selected for each of the N
groups wherein the single pre-coder is selected with respect to all
of the M resource blocks in the group. For example, the pre-coder
selected may provide a maximum sum throughput across all resource
blocks within each group. Feedback employs a preferred pre-coding
matrix/vector for each group. That is, only one pre-coder selection
feedback is sent to the transmitter for each group of M
frequency-domain resource blocks. The total feedback in bits may be
represented by NB where each of the N pre-coders employs B bits of
feedback indicator (B=.left brkt-top.log.sub.2 S.sub.PRE.right
brkt-bot.) where S.sub.PRE is the codebook size (the number of
possible pre-coding matrices). Note that these feedback bits are
typically protected with some coding scheme and the NB feedback
bits can be jointly encoded.
[0039] FIG. 3B illustrates a diagram of a grouping of resource
blocks 320 as provided by an alternative embodiment of the present
invention. The resource block grouping 320 employs a pre-coder
selection that provides a set of pre-coders corresponding to a
subgroup of resource blocks contained in each group of contiguous
resource blocks. The resource block grouping 320 corresponds to N'
groups of M' resource blocks that represent a total of N'M'
resource blocks for a channel. An advantage of this embodiment over
that of FIG. 3A is that the group size may typically be increased
to gain pre-coding efficiency.
[0040] This embodiment is group-based and provides the best L out
of M' pre-coders, where 1.ltoreq.L<M'. The L pre-coders are
selected for each of the N' resource groups. Each of the L
pre-coders is selected with respect to one of the M' resource
blocks that satisfies a certain optimality criterion. For example,
if a maximum throughput per resource block is chosen, the L
pre-coders are picked that correspond the L resource blocks with
maximum throughput. In this example, an L equal to one is indicated
in FIG. 3B.
[0041] Feedback employs L preferred pre-coding matrices or vectors
for each group, and pointers are employed to the best L resource
blocks for each group. The total feedback indicator in bits
employing S bits per pre-coder may be represented by equation (1)
below:
( N ' B + N ' log 2 ( M ' L ) ) ( 1 ) ##EQU00001##
These feedback bits can be jointly encoded.
[0042] FIG. 3C illustrates a diagram of a grouping of resource
blocks 340 as provided by another embodiment of the present
invention. The resource block grouping 340 employs a pre-coder
selection that provides a set of pre-coders corresponding to a
combination of groups of contiguous resource blocks. The resource
block grouping 340 corresponds to N groups of M resource blocks
that represent a total of NM resource blocks for a channel. The N
groups are farther partitioned into N/M' "super-groups". An
advantage of this embodiment over those of FIGS. 3A and 33 is that
a further reduction in feedback may be achieved although
performance may suffer.
[0043] This embodiment provides the best L out of M' pre-coders
across an N/M' combination of groups (i.e., super-groups). The L
pre-coders are selected for each of these super-groups. Each of the
pre-coders is selected with respect to one group that satisfies a
certain optimality criterion. For example, a maximum sum (group)
throughput across super-groups may be employed wherein L pre-coders
are selected that correspond to the L groups with maximum
throughput. In this example, a super-group size M' equal to two and
an L equal to one is shown in FIG. 3C.
[0044] Feedback employs a preferred pre-coding matrix/vector for
each group, and pointers are employed to the best l groups for each
super-group. The total feedback in bits employing B bits per
pre-coder may be represented by equation (2) below:
( N M ' B + N M ' log 2 ( M ' L ) ) ( 2 ) ##EQU00002##
Again, these feedback bits can be jointly encoded. Of course, in
each of the embodiments of FIGS. 3A, 3B and 3C, other optimality
criteria may be applied such as a worst case throughput or a
specified maximum error rate, for example.
[0045] FIG. 4 illustrates a diagram of an embodiment of a pre-coder
selection 400 that is jointly encoded to achieve feedback
transmission compression. The pre-coder selection 400 includes L
pre-coder indices that comprise a pre-coder selection. For each
pre-coder grouping scheme, a joint coding scheme may be employed
for a collection of pre-coder indices that is uniquely specified
employing a total number of bits to jointly code the indices.
[0046] For example, assume that four pre-coder indices are fed back
wherein each of them is drawn from a set of three possibilities
(that is, the codebook size of 3). The upper limit needed is, of
course, eight bits. However, if this information is compressed
together, there are only 3.sup.4 or 81 possibilities. This may be
represented by seven bits. There are no two bits that represent
each of the pre-coders directly, and the entire seven bits need to
be decoded to determine the pre-coder information. However,
compression of the feedback information is advantageously achieved.
In general, this embodiment is advantageous not only when the
codebook size is not a power of 2, but also in providing improved
protection due to a more powerful coding. In addition, if a cyclic
redundancy code (CRC) check is used, encoding over a larger number
of bits reduces the overhead due to the CRC parity bits.
[0047] FIG. 5A illustrates a flow diagram of an embodiment of a
method 500 of operating a receiver carried out according to
principles of the present invention. In the illustrated embodiment,
the method 500 is for a receiver that operates in an OFDM or an
OFDMA system and starts in a step 505. Then, in a step 510, channel
estimates are provided employing transmission signals (e.g.,
reference or pilot signals) from a transmitter having a plurality
of antennas. The channel estimates allow channel quality indicators
to be determined for frequency-domain resource blocks that form a
communications channel. As mentioned before, an example of channel
quality indicators are signal to interference noise ratios (SINR)
and mutual information.
[0048] A pre-coder selection is generated that is based on the
channel estimates and corresponds to a grouping of frequency-domain
resource blocks, in a step 515. In the illustrated embodiment, the
pre-coder selection provides a single pre-coder for each group of
contiguous resource blocks. Alternatively, the pre-coder selection
may provide a set of pre-coders corresponding to a subgroup of
resource blocks contained in each group of contiguous resource
blocks or a set of pre-coders corresponding to a combination of
groups of contiguous resource blocks.
[0049] The pre-coder selection is based on an optimality criterion
such as the sum throughput for the grouping of resource blocks that
it represents, a worst case throughput, or a specified maximum
error rate. Additionally, the pre-coder selection may be based on a
grouping of the resource blocks that is variable or fixed depending
on a level of signaling support provided.
[0050] The pre-coder selection for data transmission to the
receiver is fed back to the transmitter in a step 520. The
pre-coder selection is jointly coded to achieve feedback
transmission compression. The channel quality indicators are also
fed back to the transmitter in the step 520. The method 500 ends in
a step 525.
[0051] FIG. 5B illustrates a flow diagram of an embodiment of a
method 550 of operating a transmitter having a plurality of
antennas carried out according to the principles of the present
invention. In the illustrated embodiment, the method 550 is for a
transmitter that operates in an OFDM or an OFDMA system and starts
in a step 555. Then, in a step 560, the transmitter provides a
capability of applying pre-coding to a data transmission for a
receiver. Pre-coding allows the data transmission to be efficiently
applied to the receiver based on channel quality indicators (such
as a signal to interference noise ratio) that are obtained from the
receiver.
[0052] The pre-coder selection for the data transmission is decoded
in a step 565. The pre-coder selection in the step 565 is fed back
from the receiver and corresponds to a grouping of frequency-domain
resource blocks employed by the receiver. In one embodiment, the
pre-coder selection is jointly coded in the feedback to achieve
feedback compression from the receiver.
[0053] In one embodiment, the receiver may provide the pre-coder
selection as a single pre-coder for each group of contiguous
resource blocks. Alternatively, the pre-coder selection may be
provided as a set of pre-coders corresponding to a subgroup of
resource blocks contained in each group of contiguous resource
blocks or as a set of pre-coders corresponding to a combination of
groups of contiguous resource blocks.
[0054] Additionally, the grouping of the resource blocks may be
either variable or fixed based on signaling support provided
between the transmitter and the receiver. In each of these cases,
the pre-coder may be based on a sum throughput, a worst case
throughput or a specified maximum error rate required for each of
resource blocks. The pre-coder selection is applied to the data
transmission to the receiver in a step 570 and the method 550 ends
in a step 575.
[0055] While the methods disclosed herein have been described and
shown with reference to particular steps performed in a particular
order, it will be understood that these steps may be combined,
subdivided, or reordered to form an equivalent method without
departing from the teachings of the present invention. Accordingly,
unless specifically indicated herein, the order or the grouping of
the steps is not a limitation of the present invention.
[0056] For instance, all the pre-coder selection feedback bits
corresponding to the techniques given in this invention can also be
jointly encoded with the channel quality indicator (CQI) bits to
achieve further compression and coding efficiency. It is further
possible to jointly encode the two combinations with at least one
other receiver feedback such as rank selection and/or ACK-NAK
feedback. It is further possible to separately encode the rank
selection feedback bits with the jointly encoded CQI plus pre-coder
selection bits where the rank selection feedback information serves
as the codeword size indicator of the jointly encoded CQI plus
pre-coder selection information.
[0057] While the above embodiments are given in the context of an
OFDM/OFDMA system, it is also possible to apply the techniques
taught in this invention to some other data modulation or multiple
access schemes that utilize some type of frequency-domain
multiplexing. Some examples include but are not limited to the
classical frequency-domain multiple access (FDMA), single-carrier
FDMA (SC-FDMA), and multi-carrier code division multiple access
(MC-CDMA).
[0058] Those skilled in the art to which the invention relates will
appreciate that other and further additions, deletions,
substitutions and modifications may be made to the described
embodiments without departing from the scope of the invention.
* * * * *