Ordered successive interference cancellation receiver processing for multipath channels

• US 20050008092A1
• Filed: 08/11/2004
• Published: 01/13/2005
• Est. Priority Date: 04/09/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Kadous, Tamer
• Granted Patent: US 7,194,041 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H04L 1/0618 Space-time coding

Abstract

Techniques to process a number of “received” symbol streams in a Multiple-Input Multiple-Output (MIMO) system with multipath channels such that improved performance may be achieved when using successive interference cancellation (SIC) processing. In an aspect, metrics indicative of the quality or “goodness” of a “detected” symbol stream are provided. These metrics consider the frequency selective response of the multipath channels used to transmit the symbol stream. For example, the metrics may relate to (1) an overall channel capacity for all transmission channels used for the symbol stream, or (2) an equivalent signal-to-interference noise ratio (SNR) of an Additive White Gaussian Noise (AWGN) channel modeling these transmission channels. In another aspect, techniques are provided to process the received symbol streams, using SIC processing, to recover a number of transmitted symbol streams. The particular order in which the symbol streams are recovered is determined based on the metrics determined for symbol streams detected at each SIC processing stage.

Claims

1. In a multiple-input multiple-output (MIMO) communication system with multipath channels, a method for processing a plurality of received symbol streams to recover a plurality of transmitted symbol streams, comprising:

processing the received symbol streams to provide a plurality of detected symbol streams, wherein each detected symbol stream is an estimate of a corresponding transmitted symbol stream;

determining a metric for each of the plurality of detected symbol streams, wherein the metric considers frequency selective response of one or more transmission channels used to transmit the detected symbol stream; and

selecting the detected symbol stream associated with a best metric for recovery;

processing the selected detected symbol stream to recover the symbol stream and obtain data transmitted for the symbol stream.

2. The method of claim 1, further comprising:

deriving a plurality of modified symbol streams having estimated interference due to the recovered symbol stream approximately removed; and

processing the modified symbol streams to recover another transmitted symbol stream.

3. The method of claim 1, wherein the metric for each detected symbol stream relates to an overall channel capacity of the one or more transmission channels used to transmit the detected symbol stream.

4. The method of claim 1, wherein the metric for each detected symbol stream relates to an equivalent signal-to-noise-and-interference ratio (SNR) for an AWGN channel that models the one or more transmission channels used to transmit the detected symbol stream.

5. The method of claim 1, wherein the metric for each detected symbol stream is determined based on post-detection signal-to-noise-and-interference ratio (SNRs) of the one or more transmission channels used to transmit the detected symbol stream.

6. The method of claim 1, wherein the determining the metric for each detected symbol stream includes:

estimating a post-detection signal-to-noise-and-interference ratio (SNR) of each of the one or more transmission channels used to transmit the detected symbol stream;

determining a channel capacity of each transmission channel based on the post-detection SNR; and

accumulating channel capacities of the one or more transmission channels to obtain an overall channel capacity associated with the detected symbol stream;

wherein the detected symbol stream associated with a highest overall channel capacity is selected for recovery.

7. The method of claim 6, wherein the channel capacity of each transmission channel is determined based on an unconstrained capacity function.

8. The method of claim 6, wherein the channel capacity of each transmission channel is determined based on a constrained capacity function.

9. The method of claim 6, wherein the determining the metric for each detected symbol stream further includes:

determining an equivalent SNR for an Additive White Gaussian Noise (AWGN) channel based on the overall channel capacity associated with the detected symbol stream;

wherein the detected symbol stream associated with a highest equivalent SNR is selected for recovery.

10. The method of claim 1, wherein the plurality of detected symbol streams correspond to a plurality of data streams with same rates.

11. The method of claim 1, wherein the plurality of detected symbol streams correspond to a plurality of data streams with a non-uniform distribution of rates.

12. The method of claim 11, wherein the metric for each detected symbol stream further considers the rate of the corresponding data stream.

13. The method of claim 1, wherein the metric for each detected symbol stream relates to a margin between a required signal-to-noise-and-interference ratio (SNR) and an equivalent SNR for an Additive White Gaussian Noise (AWGN) channel that models the one or more transmission channels used to transmit the detected symbol stream.

14. The method of claim 13, wherein the detected symbol stream with a highest margin is selected for recovery.

15. The method of claim 1, wherein the received symbol streams are processed based on spatial or space-time receiver processing to provide the plurality of detected symbol streams.

16. The method of claim 1, wherein the MIMO communication system implements orthogonal frequency division multiplexing (OFDM).

17. The method of claim 16, wherein each of the plurality of transmitted symbol streams is transmitted on all frequency subchannels of a respective transmit antenna.

18. The method of claim 16, wherein the determining the metric for each detected symbol stream includes:

estimating a post-detection signal-to-noise-and-interference ratio (SNR) of each frequency subchannel used to transmit the detected symbol stream;

determining a channel capacity of each frequency subchannel based on the post-detection SNR; and

accumulating channel capacities for all frequency subchannels used to transmit the detected symbol stream to obtain an overall channel capacity associated with the detected symbol stream;

wherein the detected symbol stream associated with a highest overall channel capacity is selected for recovery.

19. The method of claim 18, wherein the determining the metric for each detected symbol stream further includes:

determining an equivalent SNR for an AWGN channel based on the overall channel capacity associated with the detected symbol stream;

wherein the detected symbol stream associated with a highest equivalent SNR is selected for recovery.

20. The method of claim 16, wherein the plurality of transmitted symbol streams are derived for a plurality of transmitted data streams having same rates.

21. The method of claim 16, wherein the plurality of transmitted symbol streams are derived for a plurality of transmitted data streams having different rates.

22. In a multiple-input multiple-output (MIMO) communication system that implements orthogonal frequency division multiplexing (OFDM), a method for processing a plurality of received symbol streams to recover a plurality of transmitted symbol streams, comprising:

performing spatial or space-time processing on the received symbol streams to provide a plurality of detected symbol streams;

determining a metric for each of the plurality of detected symbol streams, wherein the metric considers frequency selective response of a plurality of frequency subchannels used to transmit each detected symbol stream;

selecting the detected symbol stream associated with a best metric for recovery;

processing the selected detected symbol stream to recover the symbol stream and obtain data transmitted for the symbol stream;

deriving a plurality of modified symbol streams having estimated interference due to the recovered symbol stream approximately removed; and

processing the modified symbol streams to recover another transmitted symbol stream.

23. The method of claim 22, wherein the determining the metric for each detected symbol stream includes:

estimating a post-detection signal-to-noise-and-interference ratio (SNR) of each frequency subchannel used to transmit the detected symbol stream;

determining a channel capacity of each frequency subchannel based on the post-detection signal-to-noise-and-interference ratio (SNR); and

accumulating channel capacities for the plurality of frequency subchannels used to transmit the detected symbol stream to obtain an overall channel capacity associated with the detected symbol stream;

wherein the detected symbol stream associated with a highest overall channel capacity is selected for recovery.

24. A method for deriving a metric indicative of a received quality of a symbol stream transmitted via a multipath channel, comprising:

estimating a signal-to-noise-and-interference ratio (SNR) of each of a plurality of frequency bins used to transmit the symbol stream;

transforming the SNR of each frequency bin to an intermediate value based on a particular function; and

accumulating intermediate values for the plurality of frequency bins to obtain the metric indicative of the received quality of the symbol stream.

25. The method of claim 24, wherein the metric is used to select a specific symbol stream at a stage of a successive interference cancellation receiver for recovery.

26. A method for deriving a metric indicative of a received quality of a symbol stream transmitted via a multipath channel in a multiple-input multiple-output (MIMO) communication system, comprising:

estimating a post-detection signal-to-noise-and-interference ratio (SNR) of each of a plurality of frequency bins used to transmit the symbol stream;

determining a channel capacity of each frequency bin based on the post-detection SNR; and

accumulating channel capacities of the plurality of frequency bins to obtain an overall channel capacity indicative of the received quality of the symbol stream.

27. The method of claim 26, wherein the post-detection SNR is indicative of a received signal quality after spatial or space-time processing at a receiver to isolate the symbol stream.

28. The method of claim 26, wherein the channel capacity of each frequency bin is determined based on an unconstrained capacity function.

29. The method of claim 26, wherein the channel capacity of each frequency bin is determined based on a constrained capacity function.

30. The method of claim 26, further comprising:

determining an equivalent SNR for an Additive White Gaussian Noise (AWGN) channel based on the overall channel capacity, wherein the equivalent SNR is indicative of the received quality of the symbol stream.

31. The method of claim 30, further comprising:

determining a required SNR for the symbol stream; and

determining a margin between the required SNR and the equivalent SNR as the metric for the symbol stream.

32. The method of claim 26, wherein the metric is used to select a specific detected symbol stream at a particular stage of a successive interference cancellation receiver for recovery.

33. A digital signal processing device (DSPD) capable of interpreting digital information to:

process a plurality of received symbol streams at a receiver of a multiple-input multiple-output (MIMO) communication system to provide a plurality of detected symbol streams, wherein each detected symbol stream is an estimate of a corresponding transmitted symbol stream;

determine a metric for each detected symbol stream, wherein the metric considers frequency selective response of one or more transmission channels used to transmit the detected symbol stream;

select the detected symbol stream associated with a best metric for recovery;

process the selected detected symbol stream to recover the symbol stream and obtain data transmitted for the symbol stream;

derive a plurality of modified symbol streams having estimated interference due to the recovered symbol stream approximately removed; and

process the modified symbol streams to recover another transmitted symbol stream.

34. An apparatus in a multiple-input multiple-output (MIMO) communication system, comprising:

means for processing a plurality of received symbol streams to provide a plurality of detected symbol streams;

means for determining a metric for each detected symbol stream, wherein the metric considers frequency selective response of one or more transmission channels used to transmit the detected symbol stream;

means for selecting the detected symbol stream associated with a best metric for recovery; and

means for processing the selected detected symbol stream to recover the symbol stream and obtain data transmitted for the symbol stream.

35. The apparatus of claim 34, further comprising:

means for deriving a plurality of modified symbol streams having estimated interference from the recovered symbol stream approximately removed; and

means for processing the modified symbol streams to recover another transmitted symbol stream.

36. The apparatus of claim 34, further comprising:

means for estimating a post-detection signal-to-noise-and-interference ratio (SNR) of each of the one or more transmission channels used to transmit the detected symbol stream;

means for determining a channel capacity of each transmission channel based on the post-detection SNR; and

means for accumulating channel capacities of the one or more transmission channels to obtain an overall channel capacity associated with the detected symbol stream;

wherein the detected symbol stream associated with a highest overall channel capacity is selected for recovery.

37. The apparatus of claim 34, wherein the plurality of detected symbol streams correspond to a plurality of data streams with same rates.

38. The apparatus of claim 34, wherein the plurality of detected symbol streams correspond to a plurality of data streams with a non-uniform distribution of rates.

39. The apparatus of claim 38, wherein the metric for each detected symbol stream further considers the rate of the corresponding data stream.

40. The apparatus of claim 34, wherein the MIMO system implements orthogonal frequency division multiplexing (OFDM).

41. An access point in the MIMO system comprising the apparatus of claim 34.

42. A wireless terminal in the MIMO system comprising the apparatus of claim 34.

43. A receiver unit in a multiple-input multiple-output (MIMO) communication system, comprising:

a spatial processor operative to process a plurality of received symbol streams based on successive interference cancellation (SIC) processing, wherein for each stage of the SIC processing, the receiver processor is operative to perform spatial or space-time processing on a plurality of input symbol streams for the stage to provide one or more detected symbol streams, wherein the input symbol streams for the first stage are the received symbol streams, and wherein each detected symbol stream is an estimate of a corresponding transmitted symbol stream;

a data processor operative to, for each stage of the SIC processing, process a selected detected symbol stream to recover the symbol stream and obtain data transmitted for the symbol stream; and

a third processor operative to, for each stage of the SIC processing except for a last stage, determine a metric for each of a plurality of detected symbol streams, select the detected symbol stream associated with a best metric for recovery in the stage, and provide an indication of the selected detected symbol stream for the stage, wherein the metric for each detected symbol stream considers frequency selective response of one or more transmission channels used to transmit the detected symbol stream.

44. The receiver unit of claim 43, wherein the third processor is further operative to determine the metric for each detected symbol stream by receiving an estimated post-detection signal-to-noise-and-interference ratio (SNR) of each of the one or more transmission channels used to transmit the detected symbol stream, determine a channel capacity of each transmission channel based on the post-detection SNR, and accumulate channel capacities of the one or more transmission channels to obtain an overall channel capacity associated with the detected symbol stream.

45. The receiver unit of claim 43, wherein the plurality of detected symbol streams for each stage except for the last stage correspond to a plurality of data streams with same rates.

46. The receiver unit of claim 43, wherein the plurality of detected symbol streams for each stage except for the last stage correspond to a plurality of data streams with a non-uniform distribution of rates.

47. The receiver unit of claim 46, wherein the metric for each detected symbol stream further considers the rate of the corresponding data stream.