Channel aware optimal space-time signaling for wireless communication over wideband multipath channels

• US 7,110,378 B2
• Filed: 10/03/2001
• Issued: 09/19/2006
• Est. Priority Date: 10/03/2000
• Status: Active Grant

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Sayeed, Akbar Muhammad, Onggosanusi, Eko Nugroho, Van Veen, Barry Dean
• Primary Examiner(s): Vu, Huy D.
• Assistant Examiner(s): Mattis, Jason
• Application Number:
  US09/970,460
• Publication Number:
  US 20020114269A1
• Time in Patent Office: 1,812 Days
• Field of Search: 370/334, 370/329, 370/332
• US Class Current: 370/334
• CPC Class Codes: H04L 1/0618 Space-time coding

Abstract

A method and system is described for more optimally managing the usage of a wideband space-time multipath channel. The wideband space-time multipath channel is decomposed into a plurality of orthogonal sub-channels, where the orthogonal sub-channels having the best signaling characteristics are used for transmitting one or more signal streams. For purposes of decomposing the wideband space-time multipath channel into a plurality of orthogonal sub-channels, channel estimates are determined for each signal propagation path. A closed-form singular value decomposition of the channel corresponding to each receive antenna before coherent combining is utilized to obtain an orthogonal decomposition of the overall effective space-time channel after coherent combining. By using the overall effective space-time channel after coherent combining rather than before coherent combining, the complexity and correspondingly the resources required for obtaining the orthogonal sub-channels is significantly reduced. The method and system further provide for transmit power to be allocated between the selected sub-channels in order to minimize the effective bit-error rate for a fixed average throughput or to maximize average throughput for a fixed minimum effective bit-error rate.

Claims

1. A method for managing the usage of a wideband space-time multipath channel having plural orthogonal sub-channels in a communication system including a transmitter having one or more transmit antennas, a receiver having one or more receive antennas, and one or more signal propagation paths between each of said one or more transmit antennas and each of said one or more receive antennas, and having channel state information available at the transmitter, said method comprising:

estimating a channel for each signal propagation path;

coherently combining a received signal using the channel estimates across all the receive antennas;

obtaining a closed-form orthogonal decomposition of the overall effective space-time channel after coherently combining the channel estimates, thereby determining one or more orthogonal sub-channels; and

selecting one or more of the determined orthogonal sub-channels for communicating information between the transmitter and the receiver.

2. The method according to claim 1, wherein said estimating channel, coherently combining, and obtaining a closed-form orthogonal decomposition is performed for each of a plurality of available signal frequencies.

3. The method according to claim 1, wherein estimating channel includes determining the signal gain, which includes its amplitude and phase, and propagation delay for each signal propagation path.

4. The method according to claim 1, wherein the channel state information is determined at both the transmitter and the receiver.

5. The method according to claim 1, wherein the channel state information is determined at the transmitter.

6. The method according to claim 1, wherein the channel state information is determined at the receiver and signaled to the transmitter via a feedback channel.

7. The method according to claim 1, wherein selecting the one or more of the determined orthogonal sub-channels includes determining a frequency index and a beamformer vector.

8. The method according to claim 7, wherein the frequency index and the beamformer vector are computed at both the transmitter and the receiver.

9. The method according to claim 7, wherein the frequency index and the beamformer vector are computed at the transmitter and signaled to the receiver.

10. The method according to claim 7, wherein the frequency index and the beamformer vector are computed at the receiver and signaled to the transmitter via a feedback channel.

11. The method according to claim 1, wherein a number of orthogonal sub-channels selected correspond to a number of separate channels needed to communicate data at the desired data rate.

12. The method according to claim 1, wherein the orthogonal sub-channels are selected based upon the sub-channels having an acceptable signal to noise ratio.

13. The method according to claim 1, wherein the orthogonal sub-channels are selected based upon the sub-channels having the best gain.

14. The method according to claim 1, further comprising, after selecting orthogonal sub-channels, allocating available transmit power to each of the selected sub-channels.

15. The method according to claim 14, wherein each of the selected sub-channels is adapted for receiving a variable amount of transmit power.

16. The method according to claim 14, wherein a maximum sum of the power allocated to the selected sub-channels is fixed.

17. The method according to claim 14, wherein a maximum sum of the power allocated to the selected sub-channels is fixed, and a separate amount of power allocated to each of the selected sub-channels is variable and is selected to optimize one or more general signal transmission characteristics.

18. The method according to claim 17, wherein the amount of power allocated to each of the selected sub-channels is selected to maximize average data throughput for a given bit-error rate.

19. The method according to claim 17, wherein the amount of power allocated to each of the selected sub-channels is selected to minimize bit-error rate for a given average data throughput.

20. The method according to claim 19, wherein the amount of power allocated to each of the selected sub-channels is determined based upon a comparison of an exact bit error rate for each of the selected sub-channels.

21. The method according to claim 19, wherein the amount of power allocated to each of the selected sub-channels is determined based upon a comparison of a Chernoff bound-based minimum effective bit error rate for each of the selected sub-channels.

22. The method according to claim 1, further comprising, after selecting orthogonal sub-channels, transmitting a data stream via each of the selected orthogonal sub-channels.

23. The method according to claim 22, wherein transmitting a data stream via each of the selected orthogonal sub-channels includes transmitting a plurality of data streams via a plurality of parallel sub-channels.

24. The method according to claim 23, wherein the plurality of parallel sub-channels are allocated between a plurality of users.

25. A channel state processing unit for use in a communication system including a transmitter having one or more transmit antennas, a receiver having one or more receive antennas, and one or more signal propagation paths between each of said one or more transmit antennas and each of said corresponding one or more receive antennas, said channel state processing unit comprising:

a channel state information estimator including;

circuitry configured to determine channel state information,

circuitry configured to estimate a channel for each receive antenna,

circuitry configured to coherently combine a received signal using the channel estimates across all the receive antennas,

and circuitry configured to obtain a closed-form orthogonal decomposition of the coherently combined channel estimates for each receive antenna, thereby determining one or more orthogonal sub-channels; and

sub-channel selection circuitry configured to select one or more of the orthogonal sub-channels for communicating information between the transmitter and the receiver.

26. The channel state processing unit according to claim 25, wherein said sub-channel selection circuitry includes a frequency index selector and a beamformer weight determiner configured to select a frequency index and corresponding set of beamformer weights for each selected sub-channel.

27. The channel state processing unit according to claim 25, further comprising a transmit power allocator configured to distribute available transmit power between selected sub-channels.

28. The channel state processing unit according to claim 25, further comprising one or more digital signal processors configured to execute a computer program including one or more sets of operational instructions and corresponding data.

29. The channel state processing unit according to claim 28, wherein at least one of said digital signal processors is used as part of said channel state information estimator.

30. The channel state processing unit according to claim 28, wherein at least one of said digital signal processors is used as part of said sub-channel selection circuitry.