U.S. patent application number 11/418661 was filed with the patent office on 2006-11-09 for mimo pgrc system and method.
Invention is credited to Anand G. Dabak, Eko N. Onggosanusi, Timothy M. Schmidl, Badri N. Varadarajan.
Application Number | 20060250941 11/418661 |
Document ID | / |
Family ID | 37393912 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060250941 |
Kind Code |
A1 |
Onggosanusi; Eko N. ; et
al. |
November 9, 2006 |
MIMO PGRC system and method
Abstract
A method of transmitting a wireless signal (FIGS. 3A-3C) is
disclosed. A data stream is divided (306) into a first data stream
and a second data stream. The first data stream is encoded (300) at
a first data rate. The second data stream is encoded (320) at a
second data rate different from the first data rate. A first part
of the encoded first data stream is transmitted from a first
transmit antenna (308). A second part of the encoded first data
stream is transmitted from a second transmit antenna (312).
Inventors: |
Onggosanusi; Eko N.; (Allen,
TX) ; Dabak; Anand G.; (Plano, TX) ; Schmidl;
Timothy M.; (Dallas, TX) ; Varadarajan; Badri N.;
(Dallas, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Family ID: |
37393912 |
Appl. No.: |
11/418661 |
Filed: |
May 5, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60678471 |
May 6, 2005 |
|
|
|
Current U.S.
Class: |
370/208 |
Current CPC
Class: |
H04W 8/30 20130101; H04B
7/0697 20130101; H04W 24/08 20130101; H04J 11/00 20130101; H04L
1/0009 20130101; H04L 47/2458 20130101; H04B 7/0691 20130101; H04B
7/0848 20130101; H04B 17/336 20150115; H04B 7/0854 20130101; H04L
1/0003 20130101; H04L 27/2601 20130101; H04B 17/382 20150115 |
Class at
Publication: |
370/208 |
International
Class: |
H04J 11/00 20060101
H04J011/00 |
Claims
1. A method of transmitting a wireless signal, comprising the steps
of: receiving a data stream; dividing the data stream into a first
data stream and a second data stream; encoding the first data
stream at a first data rate; encoding the second data stream at a
second data rate different from the first data rate; transmitting a
first part of the encoded first data stream from a first transmit
antenna; and transmitting a second part of the encoded first data
stream from a second transmit antenna.
2. A method as in claim 1, comprising the steps of: transmitting a
first part of the encoded second data stream from a third transmit
antenna; and transmitting a second part of the encoded second data
stream from a fourth transmit antenna.
3. A method as in claim 2, comprising the steps of: converting the
encoded first data stream to a first symbol constellation; and
converting the encoded second data stream to a second symbol
constellation different from the first symbol constellation.
4. A method as in claim 2, comprising the steps of: converting the
encoded first part of the first data stream to a first symbol
constellation; converting the encoded second part of the first data
stream to a second symbol constellation; converting the encoded
first part of the second data stream to a third symbol
constellation; and converting the encoded second part of the second
data stream to a fourth symbol constellation, wherein at least two
of the first through fourth symbol constellations are
different.
5. A method as in claim 2, comprising the steps of: applying the
first and second parts of the first data stream to two of the first
through fourth transmit antennas having a best channel quality
indication; and applying the first and second parts of the second
data stream to two of the first through fourth transmit antennas
having a worst channel quality indication.
6. A method as in claim 2, comprising the step of multiplying the
encoded first and second parts of the first data stream and
multiplying the encoded first and second parts of the second data
stream by a linear basis matrix.
7. A method as in claim 6, wherein the linear basis matrix is
unitary.
8. A method as in claim 6, wherein the linear basis matrix is
non-unitary.
9. A method as in claim 1, wherein at least one of the encoded
first and second data steams comprise orthogonal frequency division
multiplex (OFDM) symbols.
10. A method as in claim 1, wherein the data stream comprises data
for at least two different wireless receivers.
11. A method as in claim 1, wherein the data stream comprises data
for a single wireless receiver.
12. A method as in claim 1, wherein each of the first and second
data rates are selected in response to a channel quality
indication.
13. A wireless transmitter, comprising: a first serial-to-parallel
circuit arranged to convert a data stream into a first data stream
and a second data stream; a first encoder circuit arranged to
encode the first data stream; a second encoder circuit arranged to
encode the second data stream; a group circuit arranged to apply a
first part of the first data stream to a first transmit antenna, a
second part of the first data stream to a second transmit antenna,
a first part of the second data stream to a third transmit antenna,
and a second part of the second data stream to a fourth transmit
antenna, wherein each of the first and second transmit antennas
have a better channel quality indication than each of the third and
fourth transmit antennas.
14. A wireless transmitter as in claim 13, wherein the first
encoder circuit encodes the first data stream at a first data rate,
and wherein the second encoder circuit encodes the second data
stream at a second data rate different from the first data
rate.
15. A wireless transmitter as in claim 14, wherein each of the
first and second data rates is selected in response to a channel
quality indication.
16. A wireless transmitter as in claim 13, comprising: a first
interleaver circuit arranged to interleave the first data stream;
and a second interleaver circuit arranged to interleave the second
data stream.
17. A wireless transmitter as in claim 13, comprising: a first
symbol mapper circuit arranged to convert the first data stream to
a first symbol constellation; and a second symbol mapper circuit
arranged to convert the second data stream to a second symbol
constellation.
18. A wireless transmitter as in claim 17, comprising: a second
serial-to-parallel circuit arranged to apply the first symbol
constellation to one of the first and second transmit antennas; and
a third serial-to-parallel circuit arranged to apply the second
symbol constellation to one of the third and fourth transmit
antennas.
19. A wireless transmitter as in claim 13, wherein the group
circuit multiplies the encoded first and second parts of the first
data stream and the encoded first and second parts of the second
data stream by a linear basis matrix.
20. A wireless transmitter as in claim 19, wherein the linear basis
matrix is unitary.
21. A wireless transmitter as in claim 19, wherein the linear basis
matrix is non-unitary.
22. A wireless transmitter as in claim 13, wherein at least one of
the encoded first and second data steams comprise orthogonal
frequency division multiplex (OFDM) symbols.
23. A wireless transmitter as in claim 13, wherein the data stream
comprises data for at least two different wireless receivers.
24. A wireless transmitter as in claim 13, wherein the data stream
comprises data for a single wireless receiver.
25. A wireless transmitter as in claim 13, comprising more than
four transmit antennas.
26. A method of receiving a wireless signal, comprising the steps
of: receiving a plurality of signals from a plurality of remote
transmit antennas; detecting a first signal from a first group of
the plurality of remote transmit antennas, the first group having a
first code rate; receiving a second signal from a second group of
the plurality of remote transmit antennas, the second group having
a second code rate different from the first code rate; and
producing a channel quality indication for the first signal.
28. A method as in claim 26, wherein the step of receiving a
plurality of signals comprises receiving a plurality of signals at
a plurality of receive antennas.
29. A method as in claim 28, wherein the plurality of receive
antennas comprises at least four receive antennas.
30. A method as in claim 28, wherein the plurality of receive
antennas comprises more than four receive antennas.
31. A method as in claim 26, wherein the step of detecting a first
signal comprises Mean Minimum Square Error (MMSE) detection.
32. A method as in claim 26, wherein the step of producing a
channel quality indication comprises producing a
signal-to-interference+noise ratio (SINR).
33. A method as in claim 26, comprising the steps of: producing a
channel rotation estimate; and transmitting the channel quality
indication and the channel rotation estimate to a remote
transmitter.
34. A method as in claim 26, wherein the plurality of signals
comprises orthogonal frequency division multiplex (OFDM)
symbols.
35. A method as in claim 26, wherein the plurality of signals
comprises data for at least two different wireless receivers.
36. A method as in claim 26, wherein the plurality of signals
comprises data for a single wireless receiver.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit, under 35 U.S.C.
.sctn.119(e)(1), of U.S. Provisional Application No. 60/678,471
(TI-60504PS), filed May 6, 2005, and incorporated herein by this
reference.
BACKGROUND OF THE INVENTION
[0002] The present embodiments relate to wireless communications
systems and, more particularly, to Multiple-input Multiple-output
(MIMO) communication with Per Group Rate Control (PGRC).
[0003] Wireless communications are prevalent in business, personal,
and other applications, and as a result the technology for such
communications continues to advance in various areas. One such
advancement includes the use of spread spectrum communications,
including that of code division multiple access (CDMA) which
includes wideband code division multiple access (WCDMA) cellular
communications. In CDMA communications, user equipment (UE) (e.g.,
a hand held cellular phone, personal digital assistant, or other)
communicates with a base station, where typically the base station
corresponds to a "cell." CDMA communications are by way of
transmitting symbols from a transmitter to a receiver, and the
symbols are modulated using a spreading code which consists of a
series of binary pulses. The code runs at a higher rate than the
symbol rate and determines the actual transmission bandwidth. In
the current industry, each piece of CDMA signal transmitted
according to this code is said to be a "chip," where each chip
corresponds to an element in the CDMA code. Thus, the chip
frequency defines the rate of the CDMA code. WCDMA includes
alternative methods of data transfer, one being frequency division
duplex (FDD) and another being time division duplex (TDD), where
the uplink and downlink channels are asymmetric for FDD and
symmetric for TDD. Another wireless standard involves time division
multiple access (TDMA) apparatus, which also communicate symbols
and are used by way of example in cellular systems. TDMA
communications are transmitted as a group of packets in a time
period, where the time period is divided into time slots so that
multiple receivers may each access meaningful information during a
different part of that time period. In other words, in a group of
TDMA receivers, each receiver is designated a time slot in the time
period, and that time slot repeats for each group of successive
packets transmitted to the receiver. Accordingly, each receiver is
able to identify the information intended for it by synchronizing
to the group of packets and then deciphering the time slot
corresponding to the given receiver. Given the preceding, CDMA
transmissions are receiver-distinguished in response to codes,
while TDMA transmissions are receiver-distinguished in response to
time slots.
[0004] Referring to FIG. 4, there is a wireless communication
system or the prior art including a transmitter and user equipment
450-454. The transmitter includes a separate buffer 440-444 for
each respective user equipment 450-454. Data from these buffers is
applied to serial-to-parallel converter circuit 410. The
serial-to-parallel circuit 410 converts the serial data streams
into parallel data words which are then applied to modulation code
scheme (MCS) circuits 400 and 404. The modulation code scheme
circuits 400 and 404 transmit the signals via respective antennas
402 and 406 to user equipment within the wireless system. For
example, a signal 462 from antenna 402 is transmitted to UE 1 450.
Likewise, a signal 468 is transmitted from antenna 406 to UE 3 454.
Antennas 402 and 406, however, also transmit respective
interference signals 466 and 464. These interference signals
degrade the intended data signal at the user equipment.
[0005] Wireless communications are also degraded by the channel
effect. For example, the transmitted signals 462 and 468 in FIG. 4
are likely reflected by objects such as the ground, mountains,
buildings, and other things that it contacts. Thus, when the
transmitted communication arrives at the receiver, it has been
affected by the channel effect as well as interference signals.
Consequently, the originally-transmitted data is more difficult to
decipher. Various approaches have been developed in an effort to
reduce or remove the channel effect from the received signal so
that the originally-transmitted data is properly recognized. In
other words, these approaches endeavor to improve
signal-to-interference+noise ratio (SINR), thereby improving other
data accuracy measures (e.g., bit error rate (BER), frame error
rate (FER), and symbol error rate (SER)).
[0006] One approach to improve SINR is referred to in the art as
antenna diversity, which refers to using multiple antennas at the
transmitter, receiver, or both. For example, in the prior art, a
multiple-antenna transmitter is used to transmit the same data on
each antenna where the data is manipulated in some manner
differently for each antenna. One example of such an approach is
space-time transmit diversity (STTD). In STTD, a first antenna
transmits a block of two input symbols over a corresponding two
symbol intervals in a first order while at the same time a second
antenna transmits, by way of example, the complex conjugates of the
same block of two symbols and wherein those conjugates are output
in a reversed order relative to how they are transmitted by the
first antenna and the second symbol is a negative value relative to
its value as an input.
[0007] Another approach to improve SINR combines antenna diversity
with the need for higher data rate. Specifically, a Multiple-input
Multiple-output (MIMO) system with transmit diversity has been
devised, where each transmit antenna transmits a distinct and
respective data stream. In other words, in a MIMO system, each
transmit antenna transmits symbols that are independent from the
symbols transmitted by any other transmit antennas for the
transmitter and, thus, there is no redundancy either along a single
or with respect to multiple of the transmit antennas. The advantage
of a MIMO scheme using distinct and non-redundant streams is that
it can achieve higher data rates as compared to a transmit
diversity system.
[0008] Communication system performance demands in user equipment,
however, are often dictated by web access. Applications such as
news, stock quotes, video, and music require substantially higher
performance in downlink transmission than in uplink transmission.
Thus, MIMO system performance may be further improved for
High-Speed Downlink Packet Access (HSDPA) by Orthogonal Frequency
Division Multiplex (OFDM) transmission. With OFDM, multiple symbols
are transmitted on multiple carriers that are spaced apart to
provide orthogonality. An OFDM modulator typically takes data
symbols into a serial-to-parallel converter, and the output of the
serial-to-parallel converter is considered as frequency domain data
symbols. The frequency domain tones at either edge of the band may
be set to zero and are called guard tones. These guard tones allow
the OFDM signal to fit into an appropriate spectral mask. Some of
the frequency domain tones are set to values which will be known at
the receiver, and these tones are termed pilot tones or symbols.
These pilot symbols can be useful for channel estimation at the
receiver. An inverse fast Fourier transform (IFFT) converts the
frequency domain data symbols into a time domain waveform. The IFFT
structure allows the frequency tones to be orthogonal. A cyclic
prefix is formed by copying the tail samples from the time domain
waveform and appending them to the front of the waveform. The time
domain waveform with cyclic prefix is termed an OFDM symbol, and
this OFDM symbol may be upconverted to an RF frequency and
transmitted. An OFDM receiver may recover the timing and carrier
frequency and then process the received samples through a fast
Fourier transform (FFT). The cyclic prefix may be discarded and
after the FFT, frequency domain information is recovered. The pilot
symbols may be recovered to aid in channel estimation so that the
data sent on the frequency tones can be recovered. A
parallel-to-serial converter is applied, and the data is sent to
the channel decoder. Just as with HSDPA, OFDM communications may be
performed in an FDD mode or in a TDD mode.
[0009] One approach to improve spatial diversity of a multipath
channel for MIMO communications systems is the vertical BLAST (Bell
Laboratories Layered Space Time) or V-BLAST system as shown at FIG.
1. The V-BLAST system uses a vertically layered space-time
architecture as described by Wolniansky et al., "V-BLAST: An
Architecture for Realizing Very High Data Rates Over the
Rich-Scattering Wireless Channel" (ISSSE, October 1998) and by
Wolniansky et al., "Detection algorithm and initial laboratory
results using V-BLAST space-time communication architecture" ( IEEE
Vol. 35, No. 1, January 1999). The modulation code scheme (MCS) of
the V-BLAST circuit includes encoder 100, interleaver 102, and
symbol mapper 104. Encoder 100 of the V-BLAST system encodes a
serial data stream which is subsequently applied to interleaver
circuit 102. The resulting interleaved data is then applied to
symbol mapper 104 to produce a desired symbol constellation. The
resulting symbols are then applied to serial-to-parallel circuit
106 and transmitted to remote user equipment via antennas 108. The
V-BLAST system, therefore, improves communication with a single MCS
by dividing a data stream into sub-streams that propagate
differently over the wireless channel. The improvement, however,
depends on the relative independence of these sub-streams. When
there is a high correlation between the sub-streams, data may not
be properly detected at the remote user equipment.
[0010] A further improvement over the V-BLAST system is shown in
the per antenna rate control (PARC) circuit of FIG. 2. The PARC
circuit includes four separate MCS circuits. Each MCS circuit
includes an encoder 200, and interleaver 202, and a symbol mapper
204. The serial-to-parallel circuit 206 divides a data stream into
four separate sub-streams. Each sub-stream is applied to a
respective encoder circuit 200. Each encoder preferably allocates a
different data rate according to the channel quality of each
corresponding transmit antenna 208. For CDMA applications, each
encoder circuit 200 may also multiply each sub-stream by a
spreading code corresponding to the intended user equipment. The
encoded sub-streams are subsequently interleaved, symbol mapped,
and transmitted over transmit antennas 208. The PARC system,
therefore, improves communication by dividing a data stream into
sub-streams that propagate differently over the wireless channel
and allocating specific data rates to each sub-stream corresponding
to the quality of the respective wireless channel. The improvement,
however, significantly increases signal processing complexity. A
separate MCS circuit is required for each respective transmit
antenna. Moreover, remote PARC receivers must identify and report
the SINR for each transmit antenna.
[0011] While the preceding approaches provide steady improvements
in wireless communications, the present inventors recognize that
still further improvements may be made, including by addressing
some of the drawbacks of the prior art. In particular, embodiments
of the present invention improve communication quality and
significantly reduce signal processing complexity compared to the
PARC system. Some of these issues are described in co-pending U.S.
patent application Ser. No. 10/230,003 (docket: TI-33494), filed
Aug. 28, 2002, entitled, "MIMO HYBRID-ARQ USING BASIS HOPPING", and
incorporated herein by reference. In this referenced application,
multiple independent streams of data are adaptively transmitted
with a variable basis selected to improve signal quality. Further,
a receiver is provided that decodes the transmitted signals
including the multipaths therein. While this improvement therefore
provides various benefits as discussed in the referenced
application, the inventors also recognize still additional benefits
that may be achieved with such systems. Accordingly, the preferred
embodiments described below are directed toward these benefits as
well as improving upon the prior art.
BRIEF SUMMARY OF THE INVENTION
[0012] In a first preferred embodiment, a wireless transmitter
receives a data stream for transmission. The data stream is divided
into first and second data streams. The first data stream is
encoded at a first data rate. The second data stream is encoded at
a second data rate different from the first data rate. A first part
of the encoded first data stream is transmitted from a first
transmit antenna. A second part of the encoded first data stream
from a second transmit antenna. A first part of the encoded second
data stream is transmitted from a third transmit antenna. A second
part of the encoded second data stream is transmitted from a fourth
transmit antenna. In a preferred embodiment, transmitter circuitry
is reduced by using two modulation code schemes for four transmit
antennas.
[0013] In a second preferred embodiment, a wireless receiver
receives a plurality of signals from a plurality of remote transmit
antennas. The wireless receiver detects a first signal from a first
group of the plurality of remote transmit antennas. Signals in the
first group are encoded at a first code rate. The wireless receiver
receives a second signal from a second group of the plurality of
remote transmit antennas. Signals in the second group are encoded
at a second code rate different from the first code rate. The
wireless receiver produces a quality of signal indication for the
first signal. In a preferred embodiment, receiver complexity is
reduced by reporting a quality of signal for only the first group
of remote transmit antennas.
[0014] Other devices, systems, and methods are also disclosed and
claimed.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0015] FIG. 1 is a block diagram of a V-BLAST transmitter of the
prior art;
[0016] FIG. 2 is a block diagram of a PARC transmitter of the prior
art;
[0017] FIG. 3A is a block diagram of a first embodiment of a PGRC
transmitter of the present invention;
[0018] FIG. 3B is a block diagram of a second embodiment of a PGRC
transmitter of the present invention;
[0019] FIG. 3C is a block diagram of a third embodiment of a PGRC
transmitter of the present invention adapted for OFDM
transmission;
[0020] FIG. 4 is a simplified block diagram of a multiuser PARC
wireless communication system of the prior art;
[0021] FIG. 5 is a block diagram of a PGRC transmitter as in FIG.
3A for multiuser transmission;
[0022] FIG. 6A is a block diagram of a PARC receiver of the present
invention;
[0023] FIG. 6B is a block diagram of a PARC receiver of the present
invention adapted for OFDM reception; and
[0024] FIGS. 7A and 7B are simulations of the present invention,
V-BLAST, and PARC for zero channel correlation and 50% channel
correlation, respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The preferred embodiments of the present invention provide
circuit simplification for a wireless communication system. The
wireless communication system preferably provides for the Long Term
Evolution of High-Speed Downlink Packet Access (HSDPA) and
Multiple-input Multiple-output (MIMO) as will be explained in
detail. A simplified block diagram of a wireless transmitter of the
present invention for such a system is shown in FIG. 3A. The
wireless transmitter includes two separate modulation code schemes
(MCS) and four transmit antennas. Each MCS preferably includes an
encoder, an interleaver, and a symbol mapper.
[0026] The wireless transmitter of FIG. 3A receives an input data
stream from a baseband processor (not shown). This data stream may
include pilot signals, control signals, and data signals for
synchronization and control of remote wireless user equipment (UE).
The data stream is divided into first and second data streams by
serial-to-parallel circuit 306. Both first and second data streams
are separately encoded based on channel quality information (CQI).
The particular code may be a low density parity code, turbo code,
Hamming code, Reed Solomon code, or other code as is known in the
art. Moreover, the particular code may be different for each
encoder 300 and 320. The CQI corresponding to each encoder 300 and
320 is preferably fed back from a remote UE in a previous
communication. A particular code rate for each encoder is selected
to reduce data errors and minimize retransmission of data. In
general, a code rate of N/M indicates that N input data bits
produce M encoded output data bits. In practical wireless
communication systems, the code rate may vary from 1/8 for low CQI
to for high CQI. The first data stream is encoded at a first data
rate by encoder 300. The second data stream is encoded at a second
data rate by encoder 320. Interleavers 302 and 322 interleave their
respective encoded data streams which are then applied to
respective symbol mappers 304 and 324. The symbol mappers convert
the interleaved data streams to respective symbol constellations.
These symbol constellations may be, for example, QPSK (2 bit),
16-QAM (4 bit), or 64-QAM (16 bit). An appropriate symbol
constellation is preferably selected in response to the CQI. For a
low CQI, the symbol mapper may produce a QPSK symbol.
Alternatively, for a high CQI, the symbol mapper may produce a
64-QAM symbol.
[0027] Data symbols from symbol mapper 304 are applied to
serial-to-parallel circuit 310 to produce two parallel symbol
streams. Likewise, data symbols from symbol mapper 324 are applied
to serial-to-parallel circuit 330 to produce two parallel symbol
streams. These four parallel symbol streams are applied to group
circuit 330. Group circuit 330 then applies the parallel symbol
streams having the highest data rate to the two best transmit
antennas having the highest CQI. Group circuit 330 applies the
remaining parallel symbol streams having the lowest data rate to
the remaining two transmit antennas having the lowest CQI. The MCS
with maximum data throughput or code rate, therefore, is applied to
the transmit antennas having the best CQI. The MCS with a lesser
data throughput or code rate is applied to the transmit antennas
having a lesser CQI. Alternative grouping schemes, such as strong
and weak transmit antennas, necessarily limit data throughput of
each MCS to that of the weakest transmit antenna having the minimum
CQI. In a preferred embodiment of the present invention, group
circuit 330 also pre-codes the parallel symbol streams. Pre-coding
preferably multiplies each symbol stream by a matrix V to correct
or counteract the anticipated channel gain and rotation prior to
transmission. The matrix V can be unitary or non-unitary. Here, a
square matrix is unitary when the conjugate transpose V.sup.H is
equal to the matrix inverse V.sup.-1. When V is unitary, V may be
generated using Givens or Householder constructions. In a preferred
embodiment of the present invention, matrix V of group circuit 330
is unitary. The anticipated channel rotation or an indication of
the chosen matrix V is preferably fed back from a remote UE
together with CQI. The present invention, therefore, advantageously
tailors each MCS code rate and symbol mapping scheme to the CQI for
respective transmit antennas. Moreover, circuit complexity is
reduced by half as compared to 4-antenna PARC circuits of the prior
art while providing approximately the same performance as will be
explained in detail.
[0028] Turning now to FIG. 3B, there is another embodiment of a
transmitter of the present invention. Like numbered circuit blocks
perform substantially the same functions as previously described
with regard to the transmitter of FIG. 3A. However, interleaved
data streams from blocks 302 and 322 are applied directly to
serial-to-parallel circuits 340 and 342, respectively. Each
serial-to-parallel circuit produces two parallel interleaved data
streams. The two parallel data streams from serial-to-parallel
circuit 340 are applied to symbol mapper circuits 350 and 352.
Likewise, the two parallel data streams from serial-to-parallel
circuit 342 are applied to symbol mapper circuits 354 and 356. Each
of symbol mapper circuits 350-356 may produce any combination of
symbol constellations. Thus, each MCS of FIG. 3B may advantageously
produce two different code rates as well as two different symbol
constellations for each respective code rate. The additional symbol
mapper circuits, therefore, advantageously provide a finer
resolution of data throughput in response to the CQI than the
circuit of FIG. 3A for slightly greater circuit complexity.
[0029] Referring now to FIG. 3C, there is another embodiment of the
present invention. Like numbered circuit blocks perform similar
functions as previously described with regard to the transmitter of
FIG. 3B. Orthogonal frequency division multiplex (OFDM)
transmitters 360-366 are added to transmit OFDM symbols from
respective transmit antennas 308, 312, 328, and 332. Symbol mapper
circuits 350-356 receive respective data streams from
serial-to-parallel converter circuits 340 and 342 and produce
frequency domain data symbols. Group circuit 330 then applies the
frequency domain data symbols having the highest data rate to the
OFDM transmitters corresponding to the two best transmit antennas
having the highest CQI. The remaining frequency domain data symbols
having the lowest data rate are applied to the remaining OFDM
transmitters corresponding to the two transmit antennas having the
lowest CQI. An inverse fast Fourier transform (IFFT) converts the
frequency domain data symbols into time domain waveforms. The IFFT
structure allows the frequency tones to be orthogonal. The OFDM
symbols are upconverted to RF and transmitted by respective OFDM
transmitters 360-366 on multiple carriers that are spaced apart to
provide orthogonality. The present invention, therefore,
advantageously provides two MCS data rates and four selectable
symbol mapper circuits for maximum data throughput. Furthermore,
the present invention is compatible with OFDM transmission.
[0030] Referring now to FIG. 5, there is yet another embodiment of
the present invention adapted to multiuser transmission. The
wireless transmitter of FIG. 5 receives multiple data input streams
from user buffers 540-544. Data from these input buffers is applied
to serial-to-parallel circuit 506 and divided into first and second
data streams. The first data stream is applied to the upper MCS
including encoder 500, interleaver 502, and symbol mapper 504. The
second data stream is applied to the lower MCS including encoder
520, interleaver 522, and symbol mapper 524. Both first and second
data streams are separately encoded based on channel quality
information (CQI) as previously described with regard to FIG. 3A.
For the multiuser case, however, a single MCS may be assigned to a
user with higher data throughput requirements. Other users with
lower throughput requirements may be assigned to the remaining MCS.
For example, UE 1 buffer 504 may be sending High-Speed Downlink
Packet Access (HSDPA). UE 2 542 and UE 3 544 may be sending voice,
stock quotes, or other low speed data. UE 1 buffer 540 is
preferably assigned to the upper MCS, and UE 2 542 and UE 3 544
buffers are assigned to the lower MCS. Each encoder is 500 and 520
selects a code rate compatible with the CQI. Interleavers 502 and
522 interleave their respective encoded data streams which are then
applied to respective symbol mappers 504 and 524. The symbol
mappers convert the interleaved data streams to respective symbol
constellations. These symbol constellations may be, for example,
QPSK (2 bit), 16-QAM (16 bit), or 64-QAM (64 bit). An appropriate
symbol constellation is preferably selected in response to the CQI
as previously described with respect to FIG. 3A.
[0031] Data symbols from symbol mappers 504 and 524 are applied to
serial-to-parallel circuits 510 and 530, respectively, to produce
four parallel symbol streams. These four parallel symbol streams
are applied to group circuit 530. Group circuit 530 then applies
the parallel symbol streams having the highest data rate to the two
best transmit antennas having the highest CQI. Group circuit 530
applies the remaining parallel symbol streams having the lowest
data rate to the remaining two transmit antennas having the lowest
CQI. The MCS with maximum data throughput or code rate, therefore,
is applied to the transmit antennas having the best CQI. The MCS
with a lesser data throughput or code rate is applied to the
transmit antennas having a lesser CQI. In a preferred embodiment of
the present invention, group circuit 530 also pre-codes the
parallel symbol streams as previously described. Pre-coding
multiplies each symbol stream by a matrix V to correct or
counteract the anticipated channel gain and rotation prior to
transmission. The matrix V can be unitary or non-unitary. When V is
unitary, V may be generated using Givens or Householder
constructions. In a preferred embodiment of the present invention,
matrix V of group circuit 330 is unitary. The anticipated channel
rotation or an indication of the chosen matrix V is preferably fed
back from a remote UE together with CQI. The present invention,
therefore, advantageously tailors each MCS code rate and symbol
mapping scheme to the CQI for respective transmit antennas. MCS
allocation is determined by data throughput requirements for each
UE. Moreover, circuit complexity is reduced by half as compared to
4-antenna PARC circuits of the prior art while providing
approximately the same performance.
[0032] Referring to FIG. 6A, there is a simplified block diagram of
a wireless receiver of the present invention. Inventive features of
the previously described transmitters of the present invention are
included in the receiver for compatibility. Antennas 630-636
receive signals from a remote transmitter. In a preferred
embodiment, there are two, four, or more antennas 630-636. Received
signals at each antenna 630-636 include signals from each transmit
antenna of a remote transmitter. For example, antenna 630 receives
signals from transmit antennas 308-332 (FIG. 3A) in a single user
environment. Antenna 630 also receives signals from transmit
antennas 508-532 (FIG. 5) in a multiuser environment. However, in
the multiuser environment, signals from transmit antenna 508 may be
intended for the receiver of FIG. 6A while signals from transmit
antennas 512-532 may be interference. Received signals from
antennas 630-636 are applied to Mean Minimum Square Error (MMSE)
detection circuit 602. The MMSE detection circuit detects user data
streams from receive antennas 630-636. Alternative detection
circuits utilizing match filter, zero forcing, or least square
algorithms as are known in the art may also be used in lieu of MMSE
detection. For CDMA applications, the received signals may be
despread with user-specific spreading codes. Circuit 614 extracts
pilot signals from these user data streams. These pilot signals may
have a power boost relative to data signals. The extracted pilot
signals are applied to circuit 610 to compute an effective channel
matrix representing the channel effect between the receiver and
remote transmitter. The outputs of the MMSE detection circuit 602
are applied to the multi-antenna processing circuit 604 and
corrected by the effective channel matrix from circuit 610.
Different types of multi-antenna processing can be used such as
linear, decision feedback, or maximum likelihood. These signals are
subsequently converted to a serial data stream by
parallel-to-serial converter 606. The serial data stream is then
demapped, deinterleaved, and, decoded in circuit 608 and applied to
a baseband processor (not shown). An optional feedback loop 612
from circuit 608 to circuit 604 allows a decision feedback
operation which can improve the estimation of data bits. The
decision feedback operation may include successive interference
cancellation (SIC) wherein each detected signal is successively
removed from the composite received signal.
[0033] Circuit 608 also calculates a group SINR from the received
signal which is subsequently retransmitted to the remote
transmitter as a CQI. The group SINR corresponds to a particular
transmitter MCS that produced the intended user signal. In a single
user environment, the receiver preferably reports an SINR for each
MCS of the transmitter of FIG. 3A. By way of contrast, MIMO
receivers of the prior art are required to report a separate SINR
for each transmit antenna of a PARC transmitter. Thus, the present
invention advantageously reduces the SINR reporting overhead by
half in a single user environment. Alternatively, for a multiuser
environment, the receiver of FIG. 6A reports a single SINR for the
remote transmitter MCS producing the intended user data stream.
[0034] Referring now to FIG. 6B, there is a simplified block
diagram of another embodiment of a wireless receiver of the present
invention. Like numbered circuit blocks perform substantially the
same functions as previously described with regard to the receiver
of FIG. 6A. Antennas 630-636 receive signals from a remote
transmitter. In a preferred embodiment, there are two, four, or
more antennas 630-636. Received signals at each antenna 630-636
include signals from each transmit antenna of a remote transmitter
as previously described. These received signals are applied to
respective OFDM receiver circuits 620-626. The OFDM circuits
perform an FFT on each OFDM data stream to convert received signals
to a stream of OFDM signals or tones in the frequency domain. The
OFDM tones are applied to Mean Minimum Square Error (MMSE)
detection circuit 602. As with the circuit of FIG. 6A, alternative
detection circuits utilizing match filter, zero forcing, or least
square algorithms as are known in the art may also be used in lieu
of MMSE detection. The MMSE detection circuit detects user data
streams from OFDM receivers 620-626. Circuit 614 extracts pilot
tones from these user data streams. The extracted pilot tones are
applied to circuit 610 to compute the effective channel matrix
between the receiver and remote transmitter. The outputs of the
MMSE detection circuit 602 are applied to the multi-antenna
processing circuit 604 and corrected by the effective channel
matrix from circuit 610. Different types of multi-antenna
processing can be used such as linear, decision feedback, or
maximum likelihood. These signals are subsequently converted to a
serial data stream by parallel-to-serial converter 606. The serial
data stream is then demapped, deinterleaved, and, decoded in
circuit 608 and applied to a baseband processor. As previously
described, an optional feedback loop 612 from circuit 608 to
circuit 604 allows a decision feedback operation which can improve
the estimation of data bits. The decision feedback operation may
include successive interference cancellation (SIC) wherein each
detected signal is successively removed from the composite received
signal.
[0035] Referring now to FIGS. 7A and 7B there are simulations of
the present invention and circuits of the prior art. The simulation
of FIG. 7A is based on a spatial correlation value of zero
(.rho.=0). This represents an ideal case of orthogonal signals
where a receiver correctly identifies each signal from each
transmit antenna. The simulation of FIG. 7A is based on a spatial
correlation value of zero (.rho.=0). By way of comparison, the
simulation of FIG. 7B represents a worst case where received
signals correlate 50% of the time (.rho.=0.5). Both simulations
assume a 10 user scheduler maximum carrier-to-interference (MCI)
ratio, a low doppler rate, and 5 MHz channel bandwidth for OFDM
transmission with iterative MMSE detection. The vertical axis of
each simulation is throughput in units of
bits-per-second/Hz/sector. The horizontal axis is a ratio of
received signal power (IOR) to total channel power (IOC) in dB.
This is comparable to a SINR as previously described. In view of
the foregoing, only the curves of FIG. 7A will be described in
detail.
[0036] The simulation of FIG. 7A includes eight curves. Numbers in
the legend indicate a number of transmit and receive antennas,
respectively, in the communication system. For example, the
1.times.1 curve indicates a prior art communication system with a
single transmit antenna and a single receive antenna. This curve
establishes a baseline for comparison of performance of the present
invention with circuits of the prior art. The 1.times.1 curve
increases throughput from 0 to 4.5 with IOR/IOC increasing from -10
dB to 15 dB. No substantial improvement is seen for values of
IOR/IOC above 15 dB for this curve or any of the other seven
curves. A second group of 2.times.2 curves shows a significant
improvement over the 1.times.1 curve. This second group includes
V-BLAST (2.times.2 VBLAST), single user PARC (2.times.2 SU-PARC),
and multiuser PARC (2.times.2 MU-PARC). The second group
approximately doubles the throughput of the 1.times.1 system to 9.0
at 15 dB. The multiuser (2.times.2 MU-PARC) shows a slight
advantage in throughput over the other two systems. A third group
of 4.times.4 curves shows a significant improvement over the
1.times.1 curve and the second group of 2.times.2 curves. This
third group includes V-BLAST (4.times.4 VBLAST), single user PGRC
(4.times.4 SU-PGRC), multiuser PARC (4.times.4 MU-PARC), and
multiuser PGRC (4.times.4 MU-PGRC). The third group approximately
doubles the throughput of the 2.times.2 system to 18.0 at 15 dB.
The multiuser (4.times.4 MU-PGRC) shows a consistent advantage in
throughput over the single user (4.times.4 SU-PGRC) system.
However, performance of the multiuser PGRC (4.times.4 MU-PGRC)
system of the present invention is virtually identically to the
multiuser PARC (4.times.4 MU-PARC) system of the prior art
throughout the simulation range. Thus, the present invention
greatly simplifies circuit complexity and reduces uplink SINR
reporting relative to PARC systems of the prior art while offering
virtually identical throughput.
[0037] Still further, while numerous examples have thus been
provided, one skilled in the art should recognize that various
modifications, substitutions, or alterations may be made to the
described embodiments while still falling with the inventive scope
as defined by the following claims. For example, the present
invention may be applied to any number of antennas greater than
four. When 6 antennas are present, they may be grouped into 3
groups of 2 antennas each or 2 groups of 3 antennas each. Likewise,
when 8 antennas are present, they may be grouped into 2 groups of 4
antennas each or 4 groups of 2 antennas each. Other combinations
will be readily apparent to one of ordinary skill in the art having
access to the instant specification.
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