MIMO PGRC system and method
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).
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This application claims the benefit, under 35 U.S.C. §119(e)(1), of U.S. Provisional Application No. 60/678,471, filed May 6, 2005, and under 35 U.S.C. §120, of U.S. Nonprovisional application Ser. No. 10/131,742, now U.S. Pat. No. 7,929,631, filed Apr. 22, 2002, and issued Apr. 19, 2011, and incorporated herein in their entirety by this reference.
BACKGROUND OF THE INVENTIONThe present embodiments relate to wireless communications systems and, more particularly, to Multiple-input Multiple-output (MIMO) communication with Per Group Rate Control (PGRC).
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.
Referring to
Wireless communications are also degraded by the channel effect. For example, the transmitted signals 462 and 468 in
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.
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.
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.
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
A further improvement over the V-BLAST system is shown in the per antenna rate control (PARC) circuit of
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, 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 INVENTIONIn 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.
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.
Other devices, systems, and methods are also disclosed and claimed.
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
The wireless transmitter of
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 VH is equal to the matrix inverse V−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.
Turning now to
Referring now to
Referring now to
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.
Referring to
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
Referring now to
Referring now to
The simulation of
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.
Claims
1. A method of transmitting a wireless signal from a wireless transmitter, 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 in response to a first channel quality indication;
- encoding the second data stream separately from the first data stream in response to a second channel quality indication;
- converting a first part of the encoded first data stream to a first symbol;
- converting a second part of the encoded first data stream to a second symbol;
- multiplying the encoded first and second symbols by a linear basis matrix to produce first and second product symbols; and
- transmitting the product symbols from at least two transmit antennas of the wireless transmitter.
2. The method of claim 1, comprising the steps of:
- converting a first part of the encoded second data stream to a third symbol;
- converting a second part of the encoded second data stream to a fourth symbol;
- multiplying the encoded third and fourth are basis matrix to produce third and fourth product symbols; and
- transmitting the third and fourth product symbols from the at least two transmit antennas.
3. The method of claim 1 wherein the linear basis matrix is unitary.
4. The method of claim 1, wherein the linear basis matrix is non-unitary.
5. The method of claim 1, wherein at least one of the encoded first and second data steams comprise orthogonal frequency division multiplex (OFDM) symbols.
6. The method of claim 1, wherein the data stream comprises data for at least two different wireless receivers.
7. The method of claim 1, wherein the data stream comprises data for a single wireless receiver.
8. 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 at a first data rate;
- a second encoder circuit arranged to encode the second data stream at a second data rate greater than the first data rate;
- a first symbol mapper arranged to produce a first and a second symbol from the first data stream;
- a second symbol mapper arranged to produce a third and a fourth symbol from the second data stream; and
- a group circuit arranged to multiply the encoded first, second, third, and fourth symbols by a linear basis matrix to produce a plurality of product symbols.
9. The wireless transmitter of claim 8, comprising applying the plurality of product symbols to a plurality of transmit antennas.
10. The wireless transmitter of claim 9, wherein the data stream comprises data for at least two different wireless receivers.
11. The wireless transmitter of claim 9, comprising more than four transmit antennas.
12. The wireless transmitter of claim 8, wherein each of the first and second data rates is selected in response to a channel quality indication.
13. The wireless transmitter of claim 8, comprising:
- a first interleaver circuit arranged to interleave the first data stream; and
- a second interleaver circuit arranged to interleave the second data stream.
14. The wireless transmitter of claim 8, wherein the group circuit applies the plurality of product symbols to a plurality of transmit antennas.
15. The wireless transmitter of claim 8, wherein the linear basis matrix is unitary.
16. The wireless transmitter of claim 8, wherein the linear basis matrix is non-unitary.
17. The wireless transmitter of claim 8, wherein the symbols comprise orthogonal frequency division multiplex (OFDM) symbols.
18. The wireless transmitter of claim 8, wherein the data stream comprises data for a single wireless receiver.
19. A method of receiving a signal at a wireless receiver, comprising the steps of:
- receiving at the wireless receiver a plurality of symbols from a plurality of remote transmit antennas;
- detecting the plurality of symbols;
- receiving a plurality of pilot signals from the remote transmit antennas;
- computing an effective channel matrix in response to the received pilot signals;
- multiplying the plurality of symbols by the effective channel matrix to produce a plurality of product symbols; and
- decoding the plurality of product symbols.
20. The method of claim 19, wherein the step of receiving a plurality of symbols comprises receiving a plurality of symbols at a plurality of receive antennas.
21. The method of claim 20, wherein the plurality of receive antennas comprises at least four receive antennas.
22. The method of claim 20, wherein the plurality of receive antennas comprises more than four receive antennas.
23. The method of claim 19, wherein the step of detecting comprises Mean Minimum Square Error (MMSE) detection.
24. The method of claim 19, comprising producing a channel quality indication.
25. The method of claim 19, comprising the steps of:
- producing a channel rotation estimate; and
- transmitting the channel quality indication and the channel rotation, estimate to a remote transmitter.
26. The method of claim 19, wherein the plurality of symbols comprises orthogonal frequency division multiplex (OFDM) symbols.
27. The method of claim 19, wherein the plurality of symbols comprises data for at least two different users.
28. The method of claim 19, wherein the plurality of symbols comprises data for a single user.
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Type: Grant
Filed: May 5, 2006
Date of Patent: Feb 23, 2016
Patent Publication Number: 20060250941
Assignee: TEXAS INSTRUMENTS INCORPORATED (Dallas, TX)
Inventors: Eko N. Onggosanusi (Allen, TX), Anand G. Dabak (Plano, TX), Timothy M. Schmidt (Dallas, TX), Badri N. Varadarajan (Dallas, TX)
Primary Examiner: Mark Rinehart
Assistant Examiner: Gbemileke Onamuti
Application Number: 11/418,661
International Classification: H04J 11/00 (20060101); H04L 1/00 (20060101); H04B 7/06 (20060101); H04B 7/08 (20060101); H04B 17/336 (20150101); H04B 17/382 (20150101); H04L 27/26 (20060101);