Iterative Interference Cancellation for MIMO-OFDM Receivers

• US 20100208854A1
• Filed: 02/17/2010
• Published: 08/19/2010
• Est. Priority Date: 11/15/2005
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC
• Original Assignee: Rambus Inc.
• Inventors: Scharf, Louis L., Guess, Tommy, McCloud, Michael L.
• Granted Patent: US 8,218,697 B2
• Time in Patent Office: Days
• US Class Current: 375/347
• CPC Class Codes: H04L 1/0048 in conjunction with detection of multiuser or interfering signals, e.g. iteration between CDMA or MIMO detector and FEC decoder for spatial equalizer H04L25/03286
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0631 Receiver arrangements
• CPC Class Codes: H04L 25/0328 with interference cancellation circuitry adaptations for interference cancellation within a sequence estimator H04L25/03305; interference related aspects of direct sequence spread spectrum H04B1/7097; interference related aspects of frequency hopping spread spectrum H04B1/715; see also H04B1/10
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

An OFDMA-MIMO receiver performs a recursive interference cancellation across several correlated subbands and several receive antenna elements to demodulate complex source symbols for several users that have been coded across several subbands and transmit antennas. The iterative parallel interference canceller (PIC) is configured to work in the presence of both spatial and frequency structure introduced by the transmitter space-frequency mapping and the actual frequency selective wireless channel. The interference canceller uses mixed decisions, confidence weights, and stabilizing step sizes in a PIC receiver, which may be used with a successive decoding architecture in a receiver that employs a combination of modulation level interference cancellation with successive decoding.

Claims

1. An iterative interference canceller comprising:

a soft-weighting module configured for applying soft weights to each of a plurality of input symbol estimates for an initial iteration, and to each of a plurality of updated symbol estimates for at least one subsequent iteration for producing a plurality of weighted symbol estimates,

a channel-mapping module configured for synthesizing constituent signals from the plurality of weighted symbol estimates, and producing a combined signal therefrom,

a subtraction module configured for subtracting the combined signal from the received signal to produce an error signal,

a stabilizing step size module configured for scaling the error signal by a stabilizing step size to produce a scaled error signal,

a channel-matching module configured for resolving the scaled error signal onto user space-frequency channel mapping functions to produce interference-cancelled symbol estimates, and

a mixed-decision module configured for performing a mixed decision comprising a hard decision or a soft decision on each of the interference-cancelled symbol estimates to produce the plurality of updated symbol estimates.

2. The canceller recited in claim 1, wherein the canceller is employed in a OFDMA-MIMO receiver whereby a plurality of streams of independently encoded data in a received signal employing a common set of transmit antennas and frequency subbands are separated.

3. The canceller recited in claim 1, further configured to process each of a plurality of frequency subbands dedicated to a user of interest.

4. The canceller recited in claim 1, wherein the canceller is further configured to employ a steepest-descent iterative approximation to Normal Equations of LMMSE filtering for space-frequency filtering.

5. The canceller recited in claim 1, wherein the canceller is further configured to employ a conjugate gradient iterative approximation to Normal Equations of LMMSE filtering for space-frequency filtering.

6. The canceller recited in claim 1, further comprising a successive decoding architecture to separate the plurality of streams of independently encoded data.

7. The canceller recited in claim 1, wherein the canceller is employed in a space-time multiplexed receiver whereby a plurality of streams of independently encoded data in a received signal employing a common set of transmit antennas and temporal subbands are separated.

8. The canceller recited in claim 7, whereby the channel-mapping module and the channel-matching module are further configured to process frequency correlations introduced by transmitter space-frequency mapping.

9. The canceller recited in claim 8, whereby the temporal subbands comprise coded modulations.

10. The canceller recited in claim 8, whereby the channel-mapping module and the channel-matching module are further configured to process spatial and temporal structure introduced by a transmitter space-time mapping and a frequency-selective wireless channel.

11. An iterative interference cancellation method comprising:

providing for applying a soft weight to each of a plurality of input symbol estimates for an initial iteration, and to each of a plurality of updated symbol estimates for at least one subsequent iteration for producing a plurality of weighted symbol estimates,

providing for channel mapping the plurality of weighted symbol estimates to synthesize constituent signals, and producing a combined signal therefrom,

providing for subtracting the combined signal from the received signal to produce an error signal,

providing for scaling the error signal by a stabilizing step size to produce a scaled error signal,

providing for channel matching the scaled error signal onto user space-frequency channel mapping functions to produce interference-cancelled symbol estimates, and

providing for performing a mixed decision comprising a hard decision or a soft decision on each of the interference-cancelled symbol estimates to produce the plurality of updated symbol estimates.

12. The method of recited in claim 11, wherein the method is employed with a plurality of streams of independently encoded data in a received OFDMA-MIMO signal employing a common set of transmit antennas and frequency subbands and wherein said streams of independently encoded data are separated.

13. The method of recited in claim 11, wherein the method is employed with a plurality of streams of independently encoded data in a received space-time multiplexed signal employing a common set of transmit antennas and temporal subbands and wherein said streams of independently encoded data are separated

14. The method recited in claim 11, whereby providing for channel mapping and providing for channel matching further comprises processing frequency correlations introduced by transmitter space-frequency mapping.

15. The method recited in claim 11, further comprising processing each of a plurality of frequency subbands dedicated to a user of interest.

16. The method recited in claim 11, further comprising employing a steepest-descent iterative approximation to Normal Equations of LMMSE filtering for space-frequency filtering.

17. The method recited in claim 11, further comprising employing a conjugate gradient iterative approximation to Normal Equations of LMMSE filtering for space-frequency filtering.

18. The method recited in claim 11, further comprising providing for successive decoding to separate the plurality of streams of independently encoded data.

19. The method recited in claim 13, whereby the temporal subbands comprise coded modulations.

20. The method recited in claim 13, whereby providing for channel mapping and providing for channel matching further comprises processing spatial and temporal structure introduced by a transmitter space-time mapping and a frequency-selective wireless channel.

21. The method recited in claim 13, further comprising processing each of a plurality of temporal subbands dedicated to a user of interest.

22. The method recited in claim 13, further comprising processing a plurality of temporal subbands dedicated to a user of interest.

23. A space-frequency receiver configured to separate a plurality of streams of independently encoded data in a received signal employing a common set of transmit antennas and frequency subbands, the space-frequency receiver comprising:

an

iterative interference canceller configured to process an input signal comprising a plurality of independently encoded data streams, the iterative interference canceller comprising;

a soft-weighting module configured for applying soft weights to each of a plurality of input symbol estimates for an initial iteration, and to each of a plurality of updated symbol estimates for at least one subsequent iteration for producing a plurality of weighted symbol estimates,

a channel-mapping module configured for synthesizing constituent signals from the plurality of weighted symbol estimates, and producing a combined signal therefrom,

a subtraction module configured for subtracting the combined signal from the received signal to produce an error signal,

a stabilizing step size module configured for scaling the error signal by a stabilizing step size to produce a scaled error signal,

a channel-matching module configured for resolving the scaled error signal onto user space-frequency channel mapping functions to produce interference-cancelled symbol estimates, and

a mixed-decision module configured for performing a mixed decision comprising a hard decision or a soft decision on each of the interference-cancelled symbol estimates to produce the plurality of updated symbol estimates, and

a successive decoder, comprising;

a demapper and a decoder configured to process the plurality of updated symbol estimates for producing an estimated data stream for one of the plurality of independently encoded data streams,

a synthesis module configured for re-encoding and remapping the estimated input information sequence for producing its estimated contribution to the received signal, and

a second subtraction module configured for subtracting the estimated contribution from the received signal for producing an updated input signal comprising one less than the plurality of independently encoded data streams, for coupling back to the iterative interference canceller, wherein the iterative interference canceller is configurable for processing the updated input signal until the updated input signal comprises only one independently encoded data stream.

24. The receiver recited in claim 23, whereby the channel-mapping module and the channel-matching module are further configured to process frequency correlations introduced by transmitter space-frequency mapping.

25. The receiver recited in claim 23, further configured to process each of a plurality of frequency subbands dedicated to a user of interest.

26. The receiver recited in claim 23, wherein the canceller is further configured to employ a steepest-descent iterative approximation to Normal Equations of LMMSE filtering for space-frequency filtering.

27. The receiver recited in claim 23, wherein the canceller is further configured to employ a conjugate gradient iterative approximation to the Normal Equations of LMMSE filtering for space-frequency filtering.

28. The receiver recited in claim 23, further comprising a successive decoding architecture to separate the plurality of streams of independently encoded data.

29. A space-time receiver configured to separate a plurality of streams of independently encoded data in a received signal employing a common set of transmit antennas and temporal subbands, the space-time receiver comprising:

an iterative interference canceller configured to process an input signal comprising a plurality of independently encoded data streams, the iterative interference canceller comprising;

a soft-weighting module configured for applying soft weights to each of a plurality of input symbol estimates for an initial iteration, and to each of a plurality of updated symbol estimates for at least one subsequent iteration for producing a plurality of weighted symbol estimates,

a channel-mapping module configured for synthesizing constituent signals from the plurality of weighted symbol estimates, and producing a combined signal therefrom,

a subtraction module configured for subtracting the combined signal from the received signal to produce an error signal,

a stabilizing step size module configured for scaling the error signal by a stabilizing step size to produce a scaled error signal,

a channel-matching module configured for resolving the scaled error signal onto user space-time channel mapping functions to produce interference-cancelled symbol estimates, and a mixed-decision module configured for performing a mixed decision comprising a hard decision or a soft decision on each of the interference-cancelled symbol estimates to produce the plurality of updated symbol estimates, and

a successive decoder, comprising;

a demapper and a decoder configured to process the plurality of updated symbol estimates for producing an estimated data stream for one of the plurality of independently encoded data streams,

a synthesis module configured for re-encoding and remapping the estimated input information sequence for producing its estimated contribution to the received signal, and

a second subtraction module configured for subtracting the estimated contribution from the received signal for producing an updated input signal comprising one less than the plurality of independently encoded data streams, for coupling back to the iterative interference canceller, wherein the iterative interference canceller is configurable for processing the updated input signal until the updated input signal comprises only one independently encoded data stream.

30. The receiver recited in claim 29, whereby the channel-mapping module and the channel-matching module are further configured to process time-domain correlations introduced by transmitter space-time mapping.

31. The receiver recited in claim 29, further configured to process each of a plurality of temporal subbands dedicated to a user of interest.

32. The receiver recited in claim 29, wherein the canceller is further configured to employ a steepest-descent iterative approximation to Normal Equations of LMMSE filtering for space-time filtering.

33. The receiver recited in claim 29, wherein the canceller is further configured to employ a conjugate gradient iterative approximation to the Normal Equations of LMMSE filtering for space-time filtering.

34. The receiver recited in claim 29, further comprising a successive decoding architecture to separate the plurality of streams of independently encoded data.