U.S. patent application number 12/144535 was filed with the patent office on 2009-02-19 for system and method for acquiring a training matrix for a breamforming acquisition protocol using a butson matrix.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Chiu Ngo, Huaning Niu, Pengfei Xia.
Application Number | 20090046798 12/144535 |
Document ID | / |
Family ID | 40362935 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090046798 |
Kind Code |
A1 |
Xia; Pengfei ; et
al. |
February 19, 2009 |
SYSTEM AND METHOD FOR ACQUIRING A TRAINING MATRIX FOR A
BREAMFORMING ACQUISITION PROTOCOL USING A BUTSON MATRIX
Abstract
A method and system for obtaining and transfer matrix and or
acquiring beamforming vectors using a Butson matrix is disclosed.
In one embodiment, the method includes i) determining the number
(N) of transmitter antennas, ii) obtaining a unitary matrix having
M rows and M columns, wherein M is an greater than or equal to N,
and wherein the elements of the matrix are selected from the group
consisting of: +1, -1, +j, and -j, iii) selecting N rows of the
unitary matrix and iv) generating a training matrix having N rows
and M columns based on the selected N rows. The method may further
include obtaining a source beamforming vector using the training
matrix.
Inventors: |
Xia; Pengfei; (Mountain
View, CA) ; Niu; Huaning; (Milpitas, CA) ;
Ngo; Chiu; (San Francisco, CA) |
Correspondence
Address: |
KNOBBE, MARTENS, OLSON, & BEAR, LLP
2040 MAIN STREET, FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Assignee: |
Samsung Electronics Co.,
Ltd.
Suwon
KR
|
Family ID: |
40362935 |
Appl. No.: |
12/144535 |
Filed: |
June 23, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60955614 |
Aug 13, 2007 |
|
|
|
Current U.S.
Class: |
375/267 |
Current CPC
Class: |
H04B 7/0617 20130101;
H04B 7/086 20130101; H04L 5/0023 20130101; H04B 7/0619
20130101 |
Class at
Publication: |
375/267 |
International
Class: |
H04L 1/02 20060101
H04L001/02 |
Claims
1. A method of obtaining a training matrix for a beamforming
acquisition protocol, the method comprising: determining the number
(N) of transmitter antennas; obtaining a unitary matrix having M
rows and M columns, wherein M is an even number and is greater than
N, and wherein the elements of the matrix comprise both real and
imaginary components; selecting N rows of the unitary matrix;
and
2. generating a training matrix having N rows and M columns based
on the selected N rows. The method of claim 1, wherein each column
of the unitary matrix is orthogonal to other columns of the unitary
matrix, and each row of the unitary matrix is orthogonal to other
rows of the unitary matrix.
3. A system for obtaining a training matrix for a beamforming
acquisition protocol, the system comprising: at least one
transceiver; a memory; and a processor, being in data or signal
communication with the at least one transceiver and the memory,
configured to: i) determine the number (N) of transmitter antennas;
ii) obtain a unitary matrix having M rows and M columns, wherein M
is an even number and is greater than or equal to N, and wherein
the elements of the matrix comprise both real and imaginary
components; iii) select N rows of the unitary matrix; and iv)
generate a training matrix having N rows and M columns based on the
selected N rows.
4. A method of obtaining a training matrix for a beamforming
acquisition protocol, the method comprising: determining the number
(N) of transmitter antennas; obtaining a unitary matrix having M
rows and M columns, wherein M is greater than or equal to N, and
wherein the elements of the matrix are selected from the group
consisting of: +1, -1, +j, and -j; selecting N rows of the unitary
matrix; and generating a training matrix having N rows and M
columns based on the selected N rows.
5. The method of claim 4, wherein each column of the unitary matrix
is orthogonal to other columns of the unitary matrix, and each row
of the unitary matrix is orthogonal to other rows of the unitary
matrix.
6. The method of claim 4, wherein obtaining the unitary matrix
comprises retrieving the matrix from a memory.
7. The method of claim 4, wherein M is the least even number that
is greater than or equal to N.
8. The method of claim 4, wherein M is the least multiple of four
that is greater than or equal to N.
9. The method of claim 4, wherein M is not a multiple of four.
10. The method of claim 4, wherein the selected N rows are the
first N rows of the unitary matrix.
11. The method of claim 4, wherein the selecting comprises using a
computer search algorithm.
12. The method of claim 4, wherein the N rows of the unitary matrix
are selected to minimize the maximum correlation between any two
columns of a matrix formed from the selected rows.
13. The method of claim 4, further comprising obtaining a source
beamforming vector using the training matrix.
14. The method of claim 13, wherein obtaining a source beamforming
vector comprises transmitting M symbols in M time slots from each
of the N transmitter antennas to a receiver station, and wherein
each of the M symbols for a given transmitter antenna is the
element of the training matrix at a row corresponding to the given
transmitter antenna.
15. The method of claim 13, further comprising: modulating a data
signal with the source beamforming vector; and transmitting the
modulated data signal.
16. The method of claim 15, wherein the data signal is a high
definition video data signal.
17. The method of claim 16, wherein the high definition video data
is uncompressed.
18. A system for obtaining a training matrix for a beamforming
acquisition protocol, the system comprising: at least one
transceiver; a memory; and a processor, being in data or signal
communication with the at least one transceiver and the memory,
configured to: i) determine the number (N) of transmitter antennas;
ii) obtain a unitary matrix having M rows and M columns, wherein M
is greater than or equal to N, and wherein the elements of the
matrix are selected from the group consisting of: +1, -1, +j, and
-j; iii) select N rows of the unitary matrix; and iv) generate a
training matrix having N rows and M columns based on the selected N
rows.
19. The system of claim 18, wherein each column of the unitary
matrix is orthogonal to other columns of the unitary matrix, and
each row of the unitary matrix is orthogonal to other rows of the
unitary matrix.
20. The system of claim 18, wherein the memory is configured to
store the unitary matrix.
21. The system of claim 18, wherein the processor is further
configured to obtain a source beamforming vector using the training
matrix and the at least one transceiver.
22. The system of claim 21, wherein the processor is further
configured to transmit M symbols in M time slots from each of N
transmitter antennas to a receiver station, and wherein each of the
M symbols for a given transmitter antenna corresponds to the values
in the training matrix at a given row.
23. The system of claim 18, wherein at least one of the memory and
the processor is contained within the transceiver.
24. A system for obtaining a training matrix for a beamforming
acquisition protocol, the system comprising: means for determining
the number (N) of transmitter antennas; means for obtaining a
unitary matrix having M rows and M columns, wherein M is greater
than or equal to N, and wherein the elements of the matrix are
selected from the group consisting of: +1, -1, +j, and -j; means
for selecting N rows of the unitary matrix; and means for
generating a training matrix having N rows and M columns based on
the selected N rows.
25. The system of claim 24, wherein M is the least even number that
is greater than or equal to N.
26. The system of claim 24, further comprising means for obtaining
a source beamforming vector using the training matrix.
27. One or more processor-readable storage devices having
processor-readable code, the processor-readable code for
programming one or more processors to perform a method of obtaining
a training matrix for a beamforming acquisition protocol, the
method comprising: determining the number (N) of transmitter
antennas; obtaining a unitary matrix having M rows and M columns,
wherein M is greater than or equal to N, and wherein the elements
of the matrix are selected from the group consisting of: +1, -1,
+j, and -j; selecting N rows of the unitary matrix; and generating
a training matrix having N rows and M columns based on the selected
N rows.
28. A method of obtaining a training matrix for a beamforming
acquisition protocol, the method comprising generating a training
matrix based on at least a portion of a unitary matrix, wherein the
elements of the unitary matrix are selected from the group
consisting of: +1, -1, +j, and -j.
29. The method of claim 28, further comprising obtaining a source
beamforming vector using the training matrix.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C. 119(e)
of U.S. Provisional Application No. 60/955,614, filed on Aug. 13,
2007, which is incorporated by reference in its entirety.
[0002] This application also relates to U.S. patent application
Ser. No. 11/864,707, filed on Sep. 28, 2007, entitled "System and
Method for Wireless Communication of Uncompressed High Definition
Video Data Using a Beamforming Acquisition Protocol" and U.S.
patent application Ser. No. 11/864,721, filed on Sep. 28, 2007,
entitled "System and Method for Wireless Communication of
Uncompressed High Definition Video Data Using a Transfer Matrix for
Beamforming Estimation," which are herein incorporated by reference
in their entirety. This application also relates to U.S. patent
application (Attorney Docket Number: SAMINF.125A) entitled "System
and Method for Acquiring Beamforming Vectors Using Training
Sequences with Adaptive Spreading Gains," which is concurrently
filed with this application and is incorporated herein by
reference.
BACKGROUND
[0003] 1. Field
[0004] The present invention relates to acquiring beamforming
vectors, and in particular, to acquiring beamforming vectors for
high-speed wireless data and video communications using antenna
arrays at both transmitter and receiver.
[0005] 2. Description of the Related Technology
[0006] With the proliferation of high quality video, an increasing
number of electronic devices, such as consumer electronic devices,
utilize high definition (HD) video which can require about 1 Gbps
(gigabits per second) in bandwidth for transmission. As such, when
transmitting such HD video between devices, conventional
transmission approaches compress the HD video to a fraction of its
size to lower the required transmission bandwidth. The compressed
video is then decompressed for consumption. However, with each
compression and subsequent decompression of the video data, some
data can be lost and the picture quality can be reduced.
[0007] The High-Definition Multimedia Interface (HDMI)
specification allows transfer of uncompressed HD signals between
devices via a cable. While consumer electronics makers are
beginning to offer HDMI-compatible equipment, there is not yet a
suitable wireless (e.g., radio frequency) technology that is
capable of transmitting uncompressed HD video signals. Wireless
local area network (WLAN) and similar technologies can suffer
interference issues when several devices, which do not have the
bandwidth to carry the uncompressed HD signals, are connected
together.
SUMMARY OF CERTAIN INVENTIVE ASPECTS
[0008] One aspect of the invention is a method of obtaining a
training matrix for a beamforming acquisition protocol, the method
comprising determining the number (N) of transmitter antennas,
obtaining a unitary matrix having M rows and M columns, wherein M
is an even number and is greater than N, and wherein the elements
of the matrix comprise both real and imaginary components,
selecting N rows of the unitary matrix and generating a training
matrix having N rows and M columns based on the selected N
rows.
[0009] Another aspect of the invention is a system for obtaining a
training matrix for a beamforming acquisition protocol, the system
comprising at least one transceiver, a memory, and a processor,
being in data or signal communication with the at least one
transceiver and the memory, configured to i) determine the number
(N) of transmitter antennas, ii) obtain a unitary matrix having M
rows and M columns, wherein M is an even number and is greater than
or equal to N, and wherein the elements of the matrix comprise both
real and imaginary components, iii) select N rows of the unitary
matrix, and iv) generate a training matrix having N rows and M
columns based on the selected N rows.
[0010] Another aspect of the invention is a method of obtaining a
training matrix for a beamforming acquisition protocol, the method
comprising determining the number (N) of transmitter antennas,
obtaining a unitary matrix having M rows and M columns, wherein M
is an greater than or equal to N, and wherein the elements of the
matrix are selected from the group consisting of: +1, -1, +j, and
-j, selecting N rows of the unitary matrix and generating a
training matrix having N rows and M columns based on the selected N
rows.
[0011] Another aspect of the invention is a system for obtaining a
training matrix for a beamforming acquisition protocol, the system
comprising at least one transceiver, a memory, and a processor,
being in data or signal communication with the at least one
transceiver and the memory, configured to i) determine the number
(N) of transmitter antennas, ii) obtain a unitary matrix having M
rows and M columns, wherein M is greater than or equal to N, and
wherein the elements of the matrix are selected from the group
consisting of: +1, -1, +j, and -j, iii) select N rows of the
unitary matrix, and iv) generate a training matrix having N rows
and M columns based on the selected N rows.
[0012] Yet another aspect of the invention is a system for
obtaining a training matrix for a beamforming acquisition protocol,
the system comprising means for determining the number (N) of
transmitter antennas, means for obtaining a unitary matrix having M
rows and M columns, wherein M is an greater than or equal to N, and
wherein the elements of the matrix are selected from the group
consisting of: +1, -1, +j, and -j, means for selecting N rows of
the unitary matrix and means for generating a training matrix
having N rows and M columns based on the selected N rows.
[0013] Yet another aspect of the invention is one or more
processor-readable storage devices having processor-readable code,
the processor-readable code for programming one or more processors
to perform a method of obtaining a source beamforming vector for
transmission of a data signal over a wireless communications
channel, the method comprising determining the number (N) of
transmitter antennas, obtaining a unitary matrix having M rows and
M columns, wherein M is an greater than or equal to N, and wherein
the elements of the matrix are selected from the group consisting
of: +1, -1, +j, and -j, selecting N rows of the unitary matrix and
generating a training matrix having N rows and M columns based on
the selected N rows.
[0014] Still another aspect of the invention is a method of
obtaining a training matrix for a beamforming acquisition protocol,
the method comprising generating a training matrix based on at
least a portion of a unitary matrix, wherein the elements of the
unitary matrix are selected from the group consisting of: +1, -1,
+j, and -j.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a functional block diagram of a wireless network
that implements uncompressed HD video transmission between wireless
devices according to one embodiment of the invention.
[0016] FIG. 2 is a functional block diagram of an example
communication system for transmission of uncompressed HD video over
a wireless communications channel, according to one embodiment of
the invention.
[0017] FIG. 3 is a diagram demonstrating an exemplary beamforming
scheme of a wireless HD video communication system according to one
embodiment of the invention.
[0018] FIG. 4 is a block diagram illustrating the transmitter and
receiver of a wireless HD video communication system according to
one embodiment of the invention.
[0019] FIG. 5a is a flowchart which shows an exemplary iterative
beamforming acquisition procedure according to one embodiment of
the invention.
[0020] FIG. 5b is a flowchart which shows an exemplary iterative
beamforming acquisition procedure according to another embodiment
of the invention.
[0021] FIG. 6 is a diagram demonstrating the typical convergence
behavior of signal-to-noise ratio as a function of iteration in an
iterative beamforming acquisition procedure.
[0022] FIG. 7a is a flowchart which shows an exemplary iterative
beamforming acquisition procedure from the point-of-view of a
source of data.
[0023] FIG. 7b is a flowchart which shows an exemplary iterative
beamforming acquisition procedure from the point-of-view of a
destination of data.
[0024] FIG. 8 is a collection of exemplary matrices, where
2/pi*log(B) is displayed element by element, where B is a Butson
matrix whose elements take the values +1, -1, +j, and -j.
[0025] FIG. 9 is a flowchart which shows a method of obtaining a
training matrix.
DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS
System Overview
[0026] Example implementations of the embodiments in a wireless
high definition (HD) audio/video (A/V) system will now be
described. FIG. 1 shows a functional block diagram of a wireless
network 100 that implements uncompressed HD video transmission
between A/V devices such as an A/V device coordinator and A/V
stations, according to certain embodiments. In other embodiments,
one or more of the devices can be a computer, such as a personal
computer (PC). The network 100 includes a device coordinator 112
and multiple A/V stations 114 (e.g., Device 1, Device 2, . . . ,
Device N). The A/V stations 114 utilize a low-rate (LR) wireless
channel 116 (dashed lines in FIG. 1), and may use a high-rate (HR)
channel 118 (heavy solid lines in FIG. 1), for communication
between any of the devices. The device coordinator 112 uses a
low-rate channel 116 and a high-rate wireless channel 118, for
communication with the stations 114.
[0027] Each station 114 uses the low-rate channel 116 for
communications with other stations 114. The high-rate channel 118
supports single direction unicast transmission over directional
beams established by beamforming, with e.g., multi-giga bps
bandwidth, to support uncompressed HD video transmission. For
example, a set-top box can transmit uncompressed video to a HD
television (HDTV) over the high-rate channel 118. The low-rate
channel 116 can support bi-directional transmission, e.g., with up
to 40 Mbps throughput in certain embodiments. The low-rate channel
116 is mainly used to transmit control frames such as
acknowledgement (ACK) frames. For example, the low-rate channel 116
can transmit an acknowledgement from the HDTV to the set-top box.
It is also possible that some low-rate data like audio and
compressed video can be transmitted on the low-rate channel between
two devices directly. Time division duplexing (TDD) is applied to
the high-rate and low-rate channel. At any one time, the low-rate
and high-rate channels cannot be used in parallel for transmission,
in certain embodiments. Beamforming technology can be used in both
low-rate and high-rate channels. The low-rate channels can also
support omni-directional transmissions.
[0028] In one example, the device coordinator 112 is a receiver of
video information (hereinafter "receiver 112"), and the station 114
is a sender of the video information (hereinafter "sender 114").
For example, the receiver 112 can be a sink of video and/or audio
data implemented, such as, in an HDTV set in a home wireless
network environment which is a type of WLAN. In another embodiment,
the receiver 112 may be a projector. The sender 114 can be a source
of uncompressed video or audio. Examples of the sender 114 include
a set-top box, a DVD player or recorder, digital camera, camcorder,
other computing device (e.g., laptop, desktop, PDA, etc.) and so
forth.
[0029] FIG. 2 illustrates a functional block diagram of an example
communication system 200. The system 200 includes a wireless
transmitter 202 and wireless receiver 204. The transmitter 202
includes a physical (PHY) layer 206, a media access control (MAC)
layer 208 and an application layer 210. Similarly, the receiver 204
includes a PHY layer 214, a MAC layer 216, and an application layer
218. The PHY layers provide wireless communication between the
transmitter 202 and the receiver 204 via one or more antennas
through a wireless communications channel 201.
[0030] The application layer 210 of the transmitter 202 includes an
A/V pre-processing module 211 and an audio video control (AV/C)
module 212. The A/V pre-processing module 211 can perform
pre-processing of the audio/video such as partitioning of
uncompressed video. The AV/C module 212 provides a standard way to
exchange A/V capability information. Before a connection begins,
the AV/C module negotiates the A/V formats to be used, and when the
need for the connection is completed, AV/C commands are used to
stop the connection.
[0031] In the transmitter 202, the PHY layer 206 includes a
low-rate (LR) channel 203 and a high rate (HR) channel 205 that are
used to communicate with the MAC layer 208 and with a radio
frequency (RF) module 207. In certain embodiments, the MAC layer
208 can include a packetization module (not shown). The PHY/MAC
layers of the transmitter 202 add PHY and MAC headers to packets
and transmit the packets to the receiver 204 over the wireless
channel 201.
[0032] In the wireless receiver 204, the PHY/MAC layers 214, 216
process the received packets. The PHY layer 214 includes a RF
module 213 connected to the one or more antennas. A LR channel 215
and a HR channel 217 are used to communicate with the MAC layer 216
and with the RF module 213. The application layer 218 of the
receiver 204 includes an A/V post-processing module 219 and an AV/C
module 220. The module 219 can perform an inverse processing method
of the module 211 to regenerate the uncompressed video, for
example. The AV/C module 220 operates in a complementary way with
the AV/C module 212 of the transmitter 202.
General Beamforming
[0033] Transmit and/or receive beamforming has the potential of
improving link quality substantially in wireless communications.
For typical multiple-input/multiple-output (MIMO) systems, transmit
and/or receiver beamforming are implemented in the digital domain,
before a digital-to-analog conversion (DAC) operation at a
transmitter side and after an analog-to-digital conversion (ADC)
operation at a receiver side. The good performance of digitally
beamformed systems comes at a cost of N|M RF chains, where N is the
number of transmitter antennas and M is the number of receiver
antennas. The cost may become formidable, especially when the
sampling frequency increases. When cost-effectiveness becomes a
dominant system design issue, analog beamforming is more favorable,
as it generally requires only one RF chain.
[0034] Analog beamforming for MIMO orthogonal frequency division
multiplex (OFDM) systems will be mainly described, while the same
scheme can be applied to MIMO single carrier modulated systems as
well. Suppose that K is the number of sub-carriers for OFDM
modulation, N is the number of transmitter antennas, and M is the
number of receiver antennas. Also, it is assumed that the transmit
beamforming vector (hereinafter will be interchangeably referred to
as "source beamforming vector") is w.sup..rho.=[w.sub.1, w.sub.2, .
. . , w.sub.N].sup.T and the receive beamforming vector
(hereinafter will be interchangeably referred to as "destination
beamforming vector") is .nu..sup..rho.=[.nu..sub.1, .nu..sub.2, . .
. , .nu..sub.N].sup.T. Also, let L+1 be the maximum number of
multipath channel taps for each pair of transmit and receive
antennas. Without loss of generality, it is reasonable to have
K>>L+1 (i.e., the number of OFDM sub-carriers is much greater
than the maximum number of multipath channel taps between any pair
of transmitter and receiver antennas). Further, let
h.sup..rho..sub.ij=[h.sub.ij (0) h.sub.ij (1) h.sub.ij (2) .LAMBDA.
h.sub.ij 0 (L) 0 .LAMBDA. 0].sup.T be the multipath channel impulse
response between the ith receive and jth transmit antenna, appended
with zeros such that each vector h.sup..rho..sub.ij of size
K.times.1. There are altogether M.times.N such channel vectors,
with each one corresponding to one transmit and receive antenna
pair. Let S=diag(s.sub.1,s.sub.2, . . . ,s.sub.K) be a diagonal
matrix containing all the K data sub-carriers in an OFDM system.
Thus, the transmitted vector (over an OFDM symbol duration) on a
jth transmitter antenna after beamforming is
[w.sub.js.sub.1,w.sub.js.sub.2, . . . ,w.sub.js.sub.K], for j=1, 2,
. . . , N. Because OFDM modulation diagonalizes the multipath
channel, the received vector (over an OFDM symbol duration) on the
ith receive antenna can be written as
y i .PI. = j = 1 N w j S c .rho. ij , ##EQU00001##
where c.sup..rho..sub.ij=F.sub.Kh.sup..rho..sub.ij is the frequency
channel response corresponding to the time-domain channel
h.sup..rho..sub.ij, w.sub.j is the jth transmit beamforming
coefficient, and F.sub.K is a K.times.K Fourier transform
matrix.
[0035] At the receiver side, the received vectors y.sup..rho..sub.i
across all M receiver antennas will be combined by receive
beamforming vectors .nu..sup..rho.=[.nu..sub.1,.nu..sub.2, . . .
,.nu..sub.N].sup.T, where .nu..sub.i is the ith receive beamforming
coefficient. For this reason, the combined signal vector can be
written as
z .rho. = i = 1 M v i y .rho. i = i = 1 M v i j = 1 N w j S c .rho.
ij = S i = 1 M v i j = 1 N w j c .rho. ij z .rho. = S i = 1 M v i A
i w .rho. z .rho. = SA v .rho. ##EQU00002##
where the K.times.N matrix A.sub.i is defined as A.sub.i=.left
brkt-bot.c.sup..rho..sub.i1,c.sup..rho..sub.i2,.LAMBDA.,c.sup..rho..sub.i-
N.right brkt-bot., and the K.times.N matrix A is defined as
A = i = 1 M v i A i . ##EQU00003##
Similarly, the received signal vector can be written as
z .rho. = S j = 1 N w j i = 1 M v i c .rho. ij z .rho. = S j = 1 N
w j B j v .rho. z .rho. = SB w .rho. ##EQU00004##
where the K.times.M matrix B.sub.j is defined as B.sub.j=.left
brkt-bot.c.sup..rho..sub.1j,c.sup..rho..sub.2j,.LAMBDA.,c.sup..rho..sub.M-
j.right brkt-bot., and the K.times.M matrix B is defined as
B = j = 1 N w j B j . ##EQU00005##
To optimize the transmit and receive beamforming vectors, one
embodiment of the invention finds the transmit and receive
beamforming vectors that jointly minimize the pairwise error
probability (PEP) between two arbitrary information codes. To
obtain the above, one embodiment of the invention solves the
following two problems simultaneously:
maximize .nu..sup..rho..sup.II B.sup.II B.nu..sup..rho.
subject to .parallel..nu..sup..rho..parallel.=1
and
maximize w.sup..rho..sup.H A.sup.H Aw.sup..rho.
subject to .parallel.w.sup..rho..parallel.=1.
[0036] It is noticed that the matrix A is dependent upon vector
.nu..sup.w, while the matrix B is dependent upon vector .nu..sup.w.
For this reason, the above two problems cannot be solved
easily.
[0037] FIG. 3 is a diagram demonstrating an exemplary beamforming
scheme of a wireless HD video communication system, as applied to
an MIMO OFDM system. The FIG. 3 scheme can also be applied for
non-OFDM modulated schemes, such as single carrier modulated
systems. In one embodiment, the system 300 is for the
implementation of analog beamforming. The system 300 includes a
transmitter 310 and a receiver 320. The transmitter 310 includes i)
a module 302 which can perform an inverse Fourier transform, ii) a
module 303 which can perform digital-to-analog conversion and
mixing, iii) a transmitter beamformer 305, and iv) transmitter
antennas 221. The receiver 320 includes i) a module 312 which can
perform a Fourier transform, ii) a module 313 which can perform
analog-to-digital conversion and mixing, iii) a receiver beamformer
315, and iv) receiver antennas 222. The transmitter 310 and
receiver 320 can perform beamforming in conjunction with each
other. It is appreciated that certain elements of the system 300
may be omitted, or combined with or incorporated into other
elements of the system 300. In another embodiment, a certain
element may be broken into a plurality of sub-elements. Also, the
order of certain elements in the system 300 may change. In
addition, certain elements, not shown in FIG. 3, may be added to
the system 300. Furthermore, specific features of each element
shown in FIG. 3 are merely examples and many other modifications
may also be possible.
[0038] On the transmitter side, high definition (HD) video data,
denoted by the vector s.sup..rho., is input into the system 300. In
one embodiment, the HD video data is uncompressed. After an inverse
Fourier transform (IFFT) in the module 302, as well as
digital-to-analog conversion and mixing in the module 303, the
modified video data is input into the transmitter beamformer 305.
The weights of the transmitter beamformer 305 are denoted by the
variables w.sub.i, for i=1, 2, . . . , N, where N is the number of
the transmitter antennas 221. After being weighted by the
transmitter beamformer 305, the data is transmitted by the
transmitter antennas 221 through the wireless channel 201, where it
is received by the receiver antennas 222. The receiver beamformer
315 acts upon the received data to demodulate it. The weights of
the receiver beamformer 315 are denoted by the variables .nu..sub.i
for i=1, 2, . . . , M, where M is the number of the receiver
antennas 222. After being processed by the receiver beamformer 315,
the received data is input through the mixer and analog-to-digital
converter 313. Also, a Fourier transform is performed by the module
312 on the data to obtain the final received HD video data 311,
denoted by the vector z.sup.92.
[0039] FIG. 4 is an exemplary block diagram illustrating the
transmitter and receiver of a wireless HD video communication
system according to one embodiment of the invention. A system 400
includes two stations, denoted by STA1 401 and STA2 411,
respectively. Each station 401, 411 includes a processor 402, 412
as well as a memory for storage 403, 413. Each of the stations 401,
411 also includes a transceiver structure that further includes a
transmitter 404, 414 and a receiver 405, 415 which connect to an
antenna or set of antennas 406, 416. The system 400 may perform at
least one of procedures 500, 550, 700, 750, and 900 shown in FIGS.
5a, 5b, 7a, 7b and 9 (described below in greater detail), for
iteratively acquiring beamforming vectors.
[0040] In one embodiment, at least one of the procedures 500, 550,
700, 750, and 900 is implemented in a conventional programming
language, such as C or C++ or another suitable programming
language. In one embodiment of the invention, the program is stored
on a computer accessible storage medium of the transmitter 401
and/or the receiver 411, for example, such as the memory 403 and/or
413. In another embodiment, the program can be stored in other
system locations so long as it can perform at least one of the
procedures 500, 550, 700, 750, and 900 according to embodiments of
the invention. The storage medium may include any of a variety of
technologies for storing information. In one embodiment, the
storage medium includes a random access memory (RAM), hard disks,
floppy disks, digital video devices, compact discs, video discs,
and/or other optical storage mediums, etc.
[0041] In another embodiment, the processor 402 and/or 412 can be
configured to or programmed to perform at least one of the
procedures 500, 550, 700, 750, and 900. The program may be stored
in the processor 402 and/or 412 or the memory 403 and/or 413. In
various embodiments, the processor 402, 412 may have a
configuration based on Intel Corporation's family of
microprocessors, such as the Pentium family and Microsoft
Corporation's Windows operating systems such as Windows
95/98/2000/XP or Windows NT. In one embodiment, the processor is
implemented with a variety of computer platforms using a single
chip or multichip microprocessors, digital signal processors,
embedded microprocessors, microcontrollers, etc. In another
embodiment, the processor is enabled by a wide range of operating
systems such as Unix, Linux, Microsoft DOS, Microsoft Windows
2000/9x/ME/XP, Macintosh OS, OS/2 and the like. In another
embodiment, at least one of the procedures 500, 550, 700, 750, and
900 can be implemented with embedded software or firmware.
Iteratively Acquiring Beamforming Vectors
[0042] One embodiment provides a method of determining the transmit
beamforming vector and the receive beamforming vector. FIG. 5a is
an exemplary iterative beamforming acquisition procedure 500
according to one embodiment of the invention. Depending on the
embodiments, additional states may be added, others removed, or the
order of the states changes in FIG. 5a. This applies to the
remaining schemes shown in FIGS. 5b, 7a, 7b and 8. This procedure
500 involves a transmitter 501 (also referred to as STA1, or
source) and a receiver 502 (also referred to as STA2, or
destination). The first stage for the transmitter 501 involves
entering beamforming acquisition mode to begin beamforming vector
acquisition (510).
[0043] At this point, since this is the first iteration, the
iteration counting variable, n, is set to one. The transmitter
initializes the source beamforming vector, w.sup..rho..sub.1 (511).
The initialization may be chosen randomly, or the initial
beamforming vector can be an omnidirectional beamforming vector.
Other initialization methods may be used. The transmitter 501
spreads a training signal using a spreading sequence of spreading
gain S.sub.n (512). Let C.sub.1 be a spreading sequence of
spreading gain S.sub.1, wherein each element of the spreading
sequence is chosen from {1, -1} or from {1, -1, j, -j}. Then, if an
element 1 in the training signal is to be transmitted, the whole
sequence C.sub.1 is transmitted. If an element -1 in the training
signal is to be transmitted, the whole sequence -C.sub.1 is to be
transmitted. That is, the opposite of each element of the sequence
C.sub.1 is to be transmitted. Similarly, if the element j is to be
transmitted, then the sequence jC.sub.1 is to be transmitted. That
is, a sequence comprising each element of the sequence C.sub.1 is
multiplied by the imaginary variable j. Finally, if the element -j
is to be transmitted, then the sequence -jC.sub.1 is to be
transmitted. In one embodiment, for a given iteration, each element
of the training signal is subjected to the same spreading sequence.
In another embodiment, for a given iteration, the training signal
transmitted from different antennas may be spread using different
spreading sequences.
[0044] The transmitter transmits the spread training signal using
the current source beamforming vector, w.sup..rho..sub.n (514). In
the first iteration, the source beamforming vector is the
initialized transmit beamforming vector, w.sup..rho..sub.1. In
later iterations, the source beamforming vector may be different.
The receiver 502 receives this transmitted signal and based on this
received signal computes a destination beamforming vector,
.nu..sup..rho..sub.n (516). In one embodiment, different algorithms
can be used to compute the destination beamforming vector. In one
embodiment, the receiver spreads a training signal using a
spreading sequence of spreading gain Q.sub.n (518). In some
embodiments, S.sub.n and Q.sub.n may be different spreading gains.
The receiver 502 (STA2) then transmits the spread training signal
back to STA1 501 using the calculated destination beamforming
vector, .nu..sup..rho..sub.n (520). At this point in the process,
the iteration counting variable, n, is increased by one, i.e.,
n=n+1. STA1 601 receives the transmitted signal and computes a new
source beamforming vector, w.sup..rho..sub.n (522). In one
embodiment, the transmitter 501 makes a determination as to whether
or not the final source beamforming vector is acquired (524). In
one embodiment, this determination may involve counting the number
of times the source beamforming vector has been recalculated. In
another embodiment, this determination may involve comparing the
new source beamforming vector to previous source beamforming
vectors.
[0045] If it is determined that the final source beamforming vector
has not been acquired, stages 512, 514, 516, 518 520, 522, and 524
are repeated until it is determined that the final beamforming
vectors have been acquired. When it has been determined that the
final beamforming vectors have been acquired, the transmitter 501
then enters data transmission mode and begins to transmit HD video
data (526). The receiver 502 enters data reception mode and begins
to receive high definition video data (528).
[0046] FIG. 5b is a flowchart which shows an exemplary iterative
beamforming acquisition procedure 550 according to another
embodiment of the invention. The main difference between the
embodiments of FIGS. 5a and 5b is that the determining whether or
not the final beamforming vectors are acquired is performed by the
receiver in FIG. 5b. The first stage of the transmitter 551 is to
enter beamforming acquisition mode to begin beamforming vector
acquisition (560). The transmitter 551 then initializes the source
beamforming vector, w.sup..rho..sub.1 (561). Then, the transmitter
551 spreads a training signal using a spreading sequence of
spreading gain S.sub.n (562). The transmitter 551 uses the source
beamforming vector to send the spread training signal to the
receiver 552 (564). The receiver 552 receives the signal and uses
it to compute the destination beamforming vector,
.nu..sup..rho..sub.n (566). It is determined in the receiver 552
whether or not the final source and destination beamforming vectors
have been acquired (574). In one embodiment, the determination may
include the number of times the source or destination beamforming
vector has been computed. In another embodiment, the determination
may include a comparison between the current source or destination
beamforming vector and previous beamforming vectors. In another
embodiment, the determination may involve setting a threshold for
the signal-to-noise level and determining whether the current
beamforming vectors would provide a signal-to-noise level above the
threshold. If the source and destination beamforming vectors are
not acquired, the receiver/STA2 552 spreads a training signal using
a spreading sequence of spreading gain Q.sub.n (568) and transmits
back to the transmitter/STA1 551 using the computed destination
beamforming vector, .nu..sup..rho..sub.n (570). STA1 551 then
receives this signal and computes a new source beamforming vector,
w.sup..rho..sub.n (572). Stages 562, 564, and 566 are then
repeated. A determination of whether or not the final source
beamforming vector has been acquired is again performed (574),
resulting in either a repetition of stages 568, 570, 572, 562, 564,
and 566 or progressing to stages 576 and 578. Upon acquiring the
final source beamforming vector, the transmitter 551 enters data
transmission mode and begins to transmit HD video data (576). The
receiver 552 enters data reception mode and begins to receive HD
video data (578).
[0047] It can be noticed that acquisition of the source beamforming
vector and the destination beamforming vector can take a few signal
exchanges, and possibly take a long time. This may be unacceptable
overhead if such a procedure is needed for each and every data
packet. One embodiment uses such a procedure for each and every
data packet. Alternatively, if the wireless channel is not
changing, the procedure would not be needed for every packet.
[0048] In one embodiment of the invention, the spreading sequence
C.sub.n is the same for each iteration. In this embodiment, the
spreading gain of C.sub.n, i.e., S.sub.n, is the same from
iteration to iteration. FIG. 6 is a diagram demonstrating the
typical convergence behavior of signal-to-noise ratio as a function
of iteration in an iterative beamforming acquisition procedure. The
axis of abscissas 610 of FIG. 6 shows the index of iterations (n),
and the axis of ordinates 620 shows the achieved signal-to-noise
ratio (SNR) enabled by the beamforming vectors of the nth iteration
in linear scale. It may be noted that the achieved SNR saturates
quickly as iteration progresses, corroborating the effectiveness of
the iterative acquisition protocol. One method to take advantage of
this fact is to apply a strong spreading gain (corresponding to a
long spreading sequence) during the first stage to compensate for
the relatively low SNR in the initial stage. As iteration
progresses, one may use a relatively smaller spreading gain for
later stages, as the beamforming vectors are more and more
effective in themselves bridging the wireless link between the
transmitter and receiver.
[0049] One embodiment of the invention is an iterative training
protocol with an adaptive spreading scheme. During the n stages of
the entire iteration protocol, each stage may employ a different
spreading gain. In some embodiments, the first stage employs the
largest spreading gain with the longest spreading sequence, while
later stages employ a smaller spreading gain with shorter spreading
sequences.
[0050] FIG. 7a is a flowchart which shows an exemplary iterative
beamforming acquisition procedure 700 from the point-of-view of a
source of data. In the procedure 700, the eventual source of data
obtains a source beamforming vector (710). This source beamforming
vector is used to perform beamforming to modulate a training signal
having a spreading gain of S.sub.n (712). After modulation, the
modulated training signal is transmitted (714) to the eventual
destination of data. A response signal, which may comprise a
modulated training signal having a spreading gain of Q.sub.n, is
received (716) from, for example, the eventual destination of data.
In other embodiments, a response signal is received (716) from a
device which is not the eventual destination of data, for example,
an antenna controlling device separated from the eventual
destination of data. Once the response signal is received (716), a
determination is made (720) whether or not to use the current
source beamforming vector to transmit data. This determination may
be done in a number of ways. For example, it may be determined to
use the source beamforming vector if the number of iterations meets
or exceeds some threshold. It may be determined to use the source
beamforming vector if the current source beamforming vector is
similar to a previously obtained source beamforming vector,
indicating convergence of the iterative process. The determination
may also be done by analyzing the response signal. If it is
determined to use the source beamforming vector, the next stage of
the process is to modulate data using the source beamforming vector
and transmit the modulated data (722). If it is determined that the
source beamforming vector should not be used, the process repeats
by returning to stage 710 and obtaining a new source beamforming
vector.
[0051] FIG. 7b is a flowchart which shows an exemplary iterative
beamforming acquisition procedure 750 from the point-of-view of a
destination of data. In the procedure 750, the eventual destination
of data receives a modulated training signal (760). In some
embodiments, the modulated training signal is received from the
eventual source of data. Based on the training signal, the eventual
destination of data obtains or updates a destination beamforming
vector (762). The destination beamforming vector may be obtained in
a number of ways. For example, the destination beamforming vector
may be calculated using maximal ratio combining. In another
embodiment, the destination beamforming vector can be selected from
a finite set of candidate beamforming vectors. With the destination
beamforming vector, a response signal, which may comprise a
training sequence having a spreading gain of Q.sub.n, is modulated
(764). In some embodiments, the response signal bears resemblance
to the training signals transmitted by the eventual source of data.
The response signal is transmitted (766) and it is determined
whether to use the destination beamforming vector to receive data
(770). As described above in reference to the transmitter, the
determining may be performed in a number of ways. If it is
determined to use the destination beamforming vector, the next
stage of the process is to demodulate received data using the
destination beamforming vector (772). If it is determined that the
destination beamforming vector should not be used, the process
repeats by returning to stage 770 and receiving a modulated
training signal.
[0052] The calculation of S.sub.n for use in spreading the training
sequence for each iteration may be done in a number of ways. In
some embodiments, the number is pre-programmed within the
transmitter and/or receiver. In another embodiment, after each
iteration, the receiver may feedback to the transmitter an estimate
of the overall SNR improvement relative to the previous stage,
which may be denoted by K. This value, K, would be the maximum
possible spreading gain deduction ratio. That is, the spreading
gain of the spreading sequence of the next iteration may be
proportional or inversely proportional to K. This feedback may be
transmitted on top of any other feedback, if any.
[0053] For example, in an iterative beamforming acquisition process
with four iterations, there may be a three-fold gain in SNR on the
second iteration relative to the first iteration. In the embodiment
in which the spreading gain is fixed, the four iterations would
require time and power on the order of four times the spreading
gain of the initial spreading sequence, i.e. 4 S.sub.1. In the
embodiment in which the spreading gain is variable, due to the
three-fold gain in SNR, the spreading gain of the second, third,
and fourth iterations would be one-third the spreading gain of the
initial spreading sequence (or less). Thus, the time and power
consumed would be on the order of two times the spreading gain of
the initial spreading sequence, i.e. 2 S.sub.1, achieving about 50%
savings in time and power without sacrificing the acquisition
performance. Furthermore, at least one embodiment can significantly
improve the efficiency of the existing training protocols.
[0054] This technology can be applied to most iterative antenna
training protocol and can safely coexist with most other
technologies.
Discrete Matrix Element Antenna Training
[0055] In another embodiment of the invention, the antenna type
(phased array, switched antenna, or single antenna) and number of
antennas may be exchanged between the transmitter and receiver in
advance such that the beamforming acquisition algorithm can be
conducted based on both antenna type and number of antennas.
[0056] To illustrate, let STA1 be a station with a phased array
having N antennas and let STA2 have a sectored antenna. An
embodiment described herein discloses the training of the N antenna
of STA1. During the training of the antenna of STA1, in one
embodiment, the direction of the antenna of STA2 should stay the
same. For example, a sector antenna may remain pointed in the same
direction, a switched antenna may use the same candidate
beamforming vector, or a fully adaptive antenna array may keep the
weights of each antenna fixed.
[0057] In such an embodiment, the signals transmitted from the STA1
antennas during the training have an effect on the resultant
beamforming vectors and the performance of the beamforming vectors
on signal-to-noise ratio. The training patterns can be realized as
a matrix P having N rows and t columns, where N is number of STA1
antennas and t is the number of time slots to complete the training
of the STA1 antennas. It can be shown that the minimum t required
to train N antenna is, in fact, N. In other words, in order to
train N antennas on the STA1 side, a minimum of N time slots are
needed. In one embodiment, N time slots are chosen so that no
overhead is involved in performing the training. Thus, the training
matrix is a square matrix. In some embodiments, this square matrix
is an orthogonal or unitary matrix. For example, the training
matrix may be a Fourier matrix.
[0058] In analog beamforming, the phaser on each antenna element
typically has a finite alphabet. For example, each antenna may only
be capable of phasing the transmitted value at angles of 0 and pi.
As another example, each antenna may only be capable of phasing the
transmitted values at four values, such as 0, pi/2, pi, and 3*pi/2.
Using a Fourier matrix as the training pattern may violate a finite
alphabet condition for some values of N.
[0059] In some embodiments, the training matrix is a Hadamard
matrix, which is a square orthogonal matrix with binary values +1
and -1, corresponding to phase values of 0 and pi. Such an
embodiment would be well-suited to an analog phaser having an
alphabet with two elements. Hadamard matrices having N rows and N
columns exist only when N is a multiple of four. Thus, for an
arbitrary N, as may be the case in practice, it is sometimes
impossible to find a Hadamard matrix having N rows and N columns.
In one embodiment of the invention, a Hadamard matrix having M rows
and M columns, where M the smallest multiple of four not less than
N is created. This Hadamard matrix is abridged by selecting N rows
to create a training pattern of M symbols for each of the N
antennas of STA1. This incurs an overhead of M-N, which is one of
0, 1, 2, or 3 symbols.
[0060] In other embodiments, the training matrix is a Butson-type
complex Hadamard matrix, or Butson matrix, which is a square
unitary matrix with four values, typically +1, -1, +j, and -j,
corresponding to phase values of 0, pi, pi/2, and 3*pi/2. Such an
embodiment would be well-suited to an analog phaser having an
alphabet with four elements. Butson matrices having N rows and N
columns exist only when N is a multiple of two. Thus, for an
arbitrary N, as may be the case in practice, it is sometimes very
difficult to find a Butson matrix having N rows and N columns. In
one embodiment of the invention, a Butson matrix having M rows and
M columns, where M is the smallest even number not less than N is
created. This Butson matrix is abridged by selecting N rows to
create a training pattern of M symbols for each of the N antennas
of STA1. This incurs an overhead of M-N, which is either 0 or 1
symbols. FIG. 8 is a collection of exemplary matrices, where
2/pi*log(B) is displayed element by element, where B is a Butson
matrix whose elements take the values +1, -1, +j, and -j.
[0061] FIG. 9 shows a procedure 900 of obtaining a training matrix.
The first stage of the procedure is to determine the number of
antennas (N) of STA1 (902). STA1 may be, for example, a source of
data such as uncompressed high definition video data. Using N, the
number M is determined, where M is the smallest number not less
than N that satisfies a given constraint (904). In one embodiment,
that constraint may be that the next stages are capable of being
performed using M. For example, if the training matrix is to be
based on a Hadamard matrix, M is selected as a multiple of four. As
another example, if the training matrix is to be based on a Butson
matrix, M is selected as an even number. A unitary matrix having M
rows and M columns is then constructed (906). The unitary matrix is
used to create a training matrix have N rows and M columns (908).
The N rows may be selected as the first N rows of the unitary
matrix, the last N rows of the unitary matrix, a random or
arbitrary selection of N rows of the unitary matrix, or the N rows
may be selected to maximize a performance metric. For example, the
N rows may be selected such that the M columns of the resulting
training matrix are maximally uncorrelated. A computer search
algorithm may be used in the selection of the N rows. At least one
embodiment can minimize the overhead due to finite alphabet
training.
[0062] While the above description has pointed out novel features
of the invention as applied to various embodiments, the skilled
person will understand that various omissions, substitutions, and
changes in the form and details of the device or process
illustrated may be made without departing from the scope of the
invention. For example, although embodiments of the invention have
been described with reference to uncompressed video data, those
embodiments can be applied to compressed video data as well.
Embodiments of the invention can also be applied to non-video data.
Therefore, the scope of the invention is defined by the appended
claims rather than by the foregoing description. All variations
coming within the meaning and range of equivalency of the claims
are embraced within their scope.
* * * * *