Space-time processing for wireless systems with multiple transmit and receive antennas

• US 20040208258A1
• Filed: 05/11/2004
• Published: 10/21/2004
• Est. Priority Date: 08/18/2000
• Status: Active Grant

• Current Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Original Assignee: Angel Lozano, Farrokh Rashid-Farrokhi, Reinaldo A. Valenzuela
• Inventors: Valenzuela, Reinaldo A., Lozano, Angel, Rashid-Farrokhi, Farrokh
• Granted Patent: US 7,113,558 B2
• Time in Patent Office: Days
• US Class Current: 375/295
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04B 7/065 Variable contents, e.g. long-term or short-short
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• CPC Class Codes: H04B 7/0837 using pre-detection combining H04B7/0868 takes precedence

Abstract

Signals are developed for use in a wireless system with multiple transmit and multiple receive antennas so that even in the face of some correlation the most open-loop capacity that can be achieved using a substantially open-loop system with a channel of that level of correlation is obtained. In accordance with the principles of the invention, the signals transmitted from the various antennas are processed so as to improve their ability to convey the maximum amount of information. More specifically, the data to be transmitted is divided into M+1 substreams, where M is the number of transmit antennas. Each transmit antenna is supplied with a combination signal that is made up of a weighted version of a common one of the substreams and a weighted version of a respective one of the substreams that is supplied uniquely for that antenna, so that there are M transmit signals. A receiver having N antennas receives the M transmit signals as combined by the channel and reconstitutes the original data therefrom. This may be achieved using successive decoding techniques. Advantageously, the capacity, i.e., the rate of information that can be conveyed with an arbitrarily small probability of error when the instantaneous forward channel condition is unknown to the transmitter, is maximized.

Claims

1. A method for transmitting a data signal in communications over a forward channel, the method comprising the steps of:

demultiplexing said data signal into M+1 data substreams, M≧

2;

weighting the first M of said data substreams with a first weight to produce M first weighted substreams;

weighting the remaining M+1^th data substream with a second weight to produce one second weighted data substream;

combining each respective one of said M first weighted substreams with said second weighted data substream to produce M combined weighted data substreams.

2. The invention as defined in claim 1 further comprising the step of transmitting each of said combined weighted data substreams from a respective one of M transmit antennas.

3. The invention as defined in claim 1 further comprising the step of receiving a weight parameter via a reverse channel and developing therefrom said first and second weights.

4. The invention as defined in claim 1 wherein said first and second weights are determined as a function of forward channel statistics received from a receiver via a reverse channel.

5. The invention as defined in claim 1 further including the step of converting said combined weighted data substreams into radio frequency signals.

6. The invention as defined in claim 1 wherein said first and second weights are determined by solving

7. The invention as defined in claim 6 wherein

8. Apparatus for transmitting a data signal in a communications system over a forward channel, the apparatus comprising:

means for demultiplexing said data signal into M+1 data substreams, M≧

2;

means for weighting the first M of said data substreams with a first weight to produce M first weighted substreams;

means for weighting the remaining M+1^th data substream with a second weight to produce one second weighted data substream;

means for combining each respective one of said M first weighted substreams with said second weighted data substream to produce M combined weighted data substreams.

9. The invention as defined in claim 8 wherein said apparatus comprises means for developing said weights.

10. The invention as defined in claim 8 wherein said apparatus comprises means for storing said weights.

11. The invention as defined in claim 8 wherein said apparatus further comprises:

means receiving a weight parameter via a reverse channel; and

means for developing said first and second weights from said weight parameter.

12. The invention as defined in claim 8 further comprising means for transmitting each of said combined weighted data substreams as a radio frequency signal from a respective one of M transmit antennas.

13. The invention as defined in claim 8 wherein said first and second weights are determined by means for solving

14. A transmitter for transmitting a data signal in communications system over a forward channel, the transmitter comprising:

a demultiplexer that divides said data signal into M+1 data substreams, M≧

2;

multipliers for weighting the first M of said data substreams with a first weight to produce M first weighted substreams;

multipliers for weighting the remaining M+1^th data substream with a second weight to produce one second weighted data substream;

adders for combining each respective one of said M first weighted substreams with said second weighted data substream to produce M combined weighted data substreams.

15. The invention as defined in claim 14 further comprising a radio frequency converter for converting each of said combined weighted substreams to radio frequency for broadcast by a respective one of M transmit antennas.

16. The invention as defined in claim 14 wherein said weights are determined in said transmitter in response to a weight parameter received from a receiver over a reverse channel.

17. The invention as defined in claim 14 wherein said weights are determined in said transmitter in response to channel statistics received over a reverse channel from a receiver.

18. The invention as defined in claim 14 wherein said wherein said first and second weights are determined by solving

19. The invention as defined in claim 14 wherein said transmitter and receiver communicate using time division duplexing (TDD) and said weights are determined in said transmitter using an estimate of the correlation among the channel components that is determined by a receiver of a reverse link for said transmitter.

20. A receiver for use in a MIMO system, comprising:

N forward channel receive antennas;

N radio frequency (RF) converters, each RF converter downconverting a signal it receives from a respective associated one of said N antennas to an analog baseband signal and converting said analog baseband signal to a digital representation;

an estimator, responsive to said digital representations, for estimating channel statistics for a forward channel being received by said receiver; and

a transmitter for a reverse channel for transmitting said channel statistics from time to time to a receiver for said reverse channel.

21. A receiver for use in a MIMO system, comprising:

an estimator, responsive to N digital representations of signals of a forward channel received by N respective antennas, for determining an estimate of the average signal-to-interference-and-noise ratio (SINR) for said forward channel being received by said receiver;

an estimator, responsive to N digital representations of signals of a forward channel recited by N respective antennas, for determining an estimate of a correlation among the channel components for said forward channel being received by said receiver; and

a transmitter for transmitting over a reverse channel said estimate of the average SINR and said estimate of a correlation among the channel components.

22. A receiver for use in a MIMO system, comprising:

an estimator, responsive to N digital representations of signals of a forward channel received by N respective antennas for determining an estimate of the average signal-to-interference-and-noise ratio (SINR) for a forward channel being received by said receiver;

an estimator for determining an estimate of a correlation among the channel components for a forward channel being received by said receiver; and

a weight calculator for calculating at least one weight for use by a transmitter of said forward channel to transmit data substreams to said receiver as a function of said estimates of SINR and correlation among the channel components

23. The invention as defined in claim 22 further including a transmitter for a reverse channel for transmitting said at least one weight to a receiver for said reverse channel.

24. A receiver for use in a MIMO system, comprising:

N receive antennas;

N radio frequency (RF) converters, each RF converter downconverting a signal it receives from a respective associated antenna to an analog baseband signal and converting said analog baseband signal to a digital representation;

an estimator, responsive to said digital representations, for determining an estimate of the average signal-to-interference-and-noise ratio (SINR) for a forward channel being received by said receiver;

an estimator for determining an estimate of a correlation among the channel components for a forward channel being received by said receiver; and

a weight calculator for calculating at least one weight for use by a transmitter of said forward channel to transmit data substreams to said receiver as a function of said estimates of SINR and correlation among the channel components, said at least one weight being determined in said weight calculator by solving at least one equation of the set consisting of

$\begin{array}{c}{\mathrm{\alpha <br><br>}}_1=\sqrt{\frac{P_T}{M}-{\mathrm{\alpha <br><br>}}_2^2}\\ {\mathrm{\alpha <br><br>}}_2=\sqrt{\frac{P_T<br><br>\mathrm{\eta <br><br>}}{\mathrm{\rho <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>N<br><br>\left(1-\mathrm{\eta <br><br>}\right)<br><br>\left(M<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\eta <br><br>}+1-\mathrm{\eta <br><br>}\right)}}\end{array}$

where

α

₁ and α

₂ are first and second weights, respectively,

P_T is the total available transmit power

ρ

is an estimate of the average signal-to-interference-and-noise ratio (SINR), and

η

is the correlation among the channel components,

M is the number of transmit antennas, and

N is the number of receiver antennas.

25. A method for transmitting a data signal in communications over a forward channel, the method comprising the steps of:

demultiplexing said data signal into two data substreams;

weighting the first of said two data substreams with a first weight to produce a first weighted substream;

weighting the second of said two data substreams with a second weight to produce a second weighted substream;

demultiplexing said second weighted data substream into M weighted data substreams, M≧

2;

combining each respective one of said M weighted substreams with said first weighted data substream to produce M combined weighted data substreams.

26. The invention as defined in claim 25 further comprising the step of transmitting each of said combined weighted data substreams from a respective one of M transmit antennas.

27. The invention as defined in claim 25 wherein said first and second weights are determined by solving

28. Apparatus for transmitting a data signal in a communications system over a forward channel, the apparatus comprising:

means for demultiplexing said data signal into two data substreams;

means for weighting the first of said two data substreams with a first weight to produce a first weighted substream;

means for weighting the second of said two data substreams with a second weight to produce a second weighted substream;

means for demultiplexing said second weighted data substream into M weighted data substreams, M≧

2;

means for combining each respective one of said M weighted substreams with said first weighted data substream to produce M combined weighted data substreams.

29. The invention as defined in claim 28 further comprising means for transmitting each of said combined weighted data substreams as a radio frequency signal from a respective one of M transmit antennas.

30. The invention as defined in claim 28 wherein said first and second weights are determined by means for solving

31. A transmitter for transmitting a data signal in communications system over a forward channel, the transmitter comprising:

a first demultiplexer that divides said data signal into two data substreams;

multipliers for weighting the first of said two data substreams with a first weight to produce a first weighted substream;

multipliers for weighting the second of said two data substreams with a second weight to produce a second weighted substream;

a second demultiplexer that divides said second weighted data substream into M weighted data substreams, M≧

2;

M adders for combining each respective one of said M weighted substreams with said first weighted data substream to produce M combined weighted data substreams.

32. The invention as defined in claim 31 further comprising the step of transmitting each of said combined weighted data substreams from a respective one of M transmit antennas.

33. The invention as defined in claim 31 wherein said first and second weights are determined by solving