Iterative interference canceler for wireless multiple-access systems with multiple receive antennas

• US 8,121,176 B2
• Filed: 10/29/2010
• Issued: 02/21/2012
• Est. Priority Date: 11/15/2005
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC
• Original Assignee: Rambus Inc.
• Inventors: Guess, Tommy, McCloud, Michael L., Nagarajan, Vijay, Lamba, Gagandeep Singh
• Primary Examiner(s): Lugo, David
• Application Number:
  US12/916,389
• Publication Number:
  US 20110044378A1
• Time in Patent Office: 480 Days
• Field of Search: 375/144, 375/147, 375/148, 375/260, 375/267, 375/346, 375/347, 375/349, 375/350
• US Class Current: 375/148
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04B 7/0894 using different delays between antennas
• CPC Class Codes: H04J 11/0063 of multipath interference, e.g. Rake receivers

Abstract

This invention teaches to the details of an interference canceling receiver for canceling intra-cell and inter-cell interference in coded, multiple-access, spread spectrum transmissions that propagate through frequency selective communication channels to a multiplicity of receive antennas. The receiver is designed or adapted through the repeated use of symbol-estimate weighting, subtractive cancellation with a stabilizing step-size, and mixed-decision symbol estimates. Receiver embodiments may be designed, adapted, and implemented explicitly in software or programmed hardware, or implicitly in standard RAKE-based hardware either within the RAKE (i.e., at the finger level) or outside the RAKE (i.e., at the user or subchannel symbol level). Embodiments may be employed in user equipment on the forward link or in a base station on the reverse link. It may be adapted to general signal processing applications where a signal is to be extracted from interference.

Claims

1. An interference canceller for canceling at least one of inter-cell and intra-cell interference in multiple-access communication signals received by a plurality of antennas, comprising:

a front-end processing module configured for generating input symbol decisions; and

one or more interference cancellation units configured for processing the input symbol decisions, each of the one or more interference cancellation units comprising one or more of a soft-weighting module, a mixed-decision module, and a stabilizing step-size module to convert the input symbol decisions into updated symbol decisions;

wherein at least one of the one or more interference cancellation units comprises a stabilizing step-size module, the stabilizing step-size module comprising;

a stabilizing step size calculation module configured to generate a stabilizing step size having a magnitude indicative of how far the input symbol decisions are from desired interference-cancelled symbol decisions in an iteration of an iterative cancellation process; and

a weighting module configured for weighting one or more error signals with the stabilizing step size.

2. The interference canceller of claim 1, wherein at least one of the interference cancellation units comprises two or more of a soft-weighting module, a mixed-decision module, and a stabilizing step-size module to convert the input symbol decisions into updated symbol decisions.

3. The interference canceller of claim 1, wherein the calculation module is configured to calculate the stabilizing step size as a ratio of distance measures between received signals combined across the plurality of antennas and synthesized received signals combined across the plurality of antennas.

4. The interference canceller of claim 1, wherein the stabilizing step size is characterized by

5. The interference canceller of claim 1, wherein the calculation module is configured to calculate the stabilizing step size as a ratio of distance measures between received signals combined across the plurality of antennas and two differently synthesized received signals for each antenna that are combined across the plurality of antennas.

6. The interference canceller of claim 5,

wherein the stabilizing step size comprises a ratio, the ratio comprising a numerator and a denominator;

wherein the one or more error signals each correspond to one of the plurality of antennas and are evaluated as a difference between a received signal on one of the plurality of antennas and a first synthesized received signal;

wherein the denominator of the ratio is calculated by;

scaling the first total error vector with one or more soft weights to produce a scaled error vector;

producing synthesized signals that would be received on the antennas in response to elements of the scaled error vector if employed as symbols at the one or more transmit sources using a signal basis for the one or more transmit sources;

integrating square magnitudes of the synthesized signals to produce integrated signals; and

summing the integrated signals; and

wherein the numerator of the ratio is calculated as an inner product between the first total error vector scaled by the one or more soft weights and the second total error vector.

7. The interference canceller of claim 5, wherein the calculation module further is configured for:

resolving each of the one or more error signals onto a signal basis for one or more transmit sources to produce one or more first error vectors, each first error vector corresponding to one of the plurality of antennas;

summing the one or more first error vectors to produce a first total error vector;

scaling the input symbol decisions by a square of one or more soft weights to produce scaled input symbol decisions;

synthesizing signals that would be received by the plurality of antennas in response to the scaled input symbol decisions if employed as symbols at the one or more transmit sources using a signal basis for all symbol sources in the channel;

evaluating for each of the plurality of antennas, a difference between the received signal and the synthesized signal to produce an error signal for each antenna;

resolving the error signal for each antenna onto a signal basis for the one or more transmit sources to produce one or more second error vectors; and

summing together the one or more second error vectors to produce a second total error vector.

8. The interference canceller of claim 5, wherein the stabilizing step size is characterized by

9. The interference canceller of claim 1, wherein the stabilizing step is measured as a function of channel quality parameters.

10. The interference canceller of claim 9, wherein the stabilizing step size is characterized by

11. The interference canceller of claim 1, wherein the stabilizing step is set equal to a predetermined fixed value.

12. The interference canceller of claim 1, wherein the front-end processing module comprises:

a combiner configured for combining the received signals from each of one or more transmission sources across the plurality of antennas for producing a combined signal;

a despreader configured for resolving the combined signal onto a signal basis for the one or more transmission sources to produce soft symbol estimates from the one or more transmission sources; and

a symbol estimator configured for performing a mixed decision on each of the soft symbol estimates to generate the input symbol decisions.

13. The interference canceller of claim 12, further configured for canceling interference from each of a plurality of base stations.

14. The interference canceller of claim 12, wherein each of the one or more interference-cancellation units is configured for processing signals received by each of the plurality of antennas to produce a plurality of resolved error signals.

15. The interference canceller of claim 14, wherein the plurality of resolved error signals is produced by adding constituent signals for each of the plurality of antennas to corresponding scaled error signals to produce error signals for the one or more transmission sources, and resolving the error signals for the one or more transmission sources across the plurality of antennas onto the signal basis for the one or more transmission sources.

16. The interference canceller of claim 15, wherein the constituent signals comprise Rake-finger signals.

17. The interference canceller of claim 16, further comprising:

a synthesizer configured for synthesizing estimated Rake finger signals for each antenna that would be received if weighted symbol decisions were employed at the one or more transmission sources; and

a subtraction module configured for performing per-antenna subtraction of a sum of synthesized Rake finger signals from that antenna'"'"'s received signal to produce an error signal.

18. The interference canceller of claim 14, wherein the constituent signals comprise received signals associated with each of the one or more transmission sources.

19. The canceller of claim 12, further comprising:

a despreader configured to resolve each of a plurality of error signals corresponding to each of a plurality of antennas onto a signal basis for the one or more transmission sources for producing a plurality of resolved error signals;

a first combiner configured for combining the resolved error signals across antennas for producing a combined signal;

a stabilizing step-size module configured to scale the combined signal by a stabilizing step size for producing a scaled signal; and

a second combiner configured for combining the combined signal with a weighted input vector.

20. The canceller of claim 12, configured to reside in at least one of a set of devices, the set comprising a subscriber-side device configured for processing forward-link signals and a server-side device for processing reverse-link signals.

21. An interference cancellation method for canceling at least one of inter-cell and intracell interference in multiple-access communication signals received by a plurality of antennas, the method comprising:

processing one or more received signals in a front-end processor to generate input symbol decisions; and

performing iterative interference cancellation to process the input symbol decisions, the iterative interference cancellation comprising one or more of soft weighting, performing mixed decisions, and scaling by a stabilizing step-size to convert the input symbol decisions into updated symbol decisions;

wherein the step of iterative interference cancellation comprises scaling by a stabilizing step-size, scaling by a stabilizing step size comprising;

generating a stabilizing step size having a magnitude indicative of how far the input symbol decisions are from desired interference-cancelled symbol decisions in an iteration of the iterative interference cancellation; and

weighting an error signal with the stabilizing step size.

22. The method of claim 21, wherein the step of performing iterative interference cancellation comprises two or more of soft weighting, performing mixed decisions, and scaling by a stabilizing step-size to convert the input symbol decisions into updated symbol decisions.

23. The method of claim 21, wherein generating a stabilizing step size comprises calculating the stabilizing step size as a ratio of distance measures between received signals combined across the plurality of antennas and synthesized received signals combined across the plurality of antennas.

24. The method of claim 23, wherein the stabilizing step size comprises a ratio, the ratio comprising a numerator and a denominator,

wherein the numerator of the ratio is calculated by:

evaluating for a particular antenna an error signal as a difference between a received signal on the particular antenna and a synthesized received signal for the particular antenna;

resolving the error signal onto a signal basis for one or more transmit sources by employing Rake reception;

maximal ratio combining;

despreading to produce an error vector;

summing together error vectors from the plurality of antennas to produce a total error vector; and

summing square magnitudes of elements of the total error vector; and

wherein the denominator is calculated by;

synthesizing for each of the plurality of antennas, a signal that would be received in response to elements of the total error vector being employed as symbols at the one or more transmit sources, using a signal basis for the one or more transmit sources;

evaluating an integral of square magnitude for each synthesized antenna signal for producing a plurality of integrals; and

summing together the integrals over the plurality of antennas.

25. The method of claim 24, wherein the stabilizing step size is characterized by

26. The method of claim 21, wherein generating a stabilizing step size is configured to calculate the stabilizing step size as a ratio of distance measures between received signals combined across the plurality of antennas and two differently synthesized received signals for each antenna that are combined across the plurality of antennas.

27. The method of claim 26,

wherein the stabilizing step size comprises a ratio, the ratio comprising a numerator and a denominator;

wherein the error signal comprises a plurality of error signals, each corresponding to one of the plurality of antennas and being evaluated as a difference between a received signal on one of the plurality of antennas and a first synthesized received signal;

wherein the denominator of the ratio is calculated by;

scaling the first total error vector with the soft weights to produce a scaled error vector;

producing synthesized signals that would be received on the antennas in response to elements of the scaled error vector if employed as symbols at the one or more transmit sources using a signal basis for the one or more transmit sources; and

integrating square magnitudes of the synthesized signals to produce integrated signals and summing the integrated signals; and

wherein the numerator of the ratio is calculated as an inner product between the first total error vector scaled by the soft weights and the second total error vector.

28. The method of claim 26, wherein the calculation module further is configured for

resolving each of the plurality of error signals onto a signal basis for one or more transmit sources to produce one or more error vectors, each error vector corresponding to one of the plurality of antennas;

summing the one or more error vectors to produce a first total error vector;

scaling the input symbol decisions by a square of the soft weights;

synthesizing signals that would be received by the plurality of antennas in response to the scaled input symbol decisions if employed as symbols at the one or more transmit sources using a signal basis for all symbol sources in the channel;

evaluating for each of the plurality of antennas, a difference between the received signal and the synthesized signal to produce an error signal for each antenna;

resolving the error signal onto a signal basis for the one or more transmit sources to produce a second error vector; and

summing together a plurality of second error vectors from the plurality of antennas to produce a second total error vector.

29. The method of claim 26, wherein the stabilizing step size is characterized by

30. The method of claim 21, wherein the stabilizing step is measured as a function of channel quality parameters.

31. The method of claim 30, wherein the stabilizing step size is characterized by

32. The method of claim 21, wherein the stabilizing step is set equal to a predetermined fixed value.

33. The method of claim 21, wherein the step of processing further comprises:

combining one or more received signals from each of one or more transmission sources across the plurality of antennas to produce one or more combined signals;

resolving the one or more combined signals onto a signal basis for the one or more transmission sources to produce soft symbol estimates from the one or more transmission sources; and

performing a mixed decision on each of the soft symbol estimates to generate the input symbol decisions.

34. The method of claim 33, further configured for canceling interference from each of a plurality of base stations.

35. The method of claim 33, wherein processing by iterative interference cancellation is configured for processing signals received by each of the plurality of antennas, wherein constituent signals for each of the plurality of antennas are added to corresponding scaled error signals to produce antenna error signals for the one or more transmission sources, followed by resolving the antenna error signals for the one or more transmission sources across the plurality of antennas onto the signal basis for the one or more transmission sources.

36. The method of claim 35, wherein the constituent signals comprise Rake-finger signals.

37. The method of claim 36, further comprising:

synthesizing estimated Rake finger signals for each antenna that would be received if weighted symbol decisions were employed at the one or more transmission sources; and

performing per-antenna subtraction of a sum of synthesized Rake finger signals from that per-antenna received signal to produce one or more antenna error signals.

38. The method of claim 35, wherein the constituent signals comprise received signals associated with each of the one or more transmission sources.

39. The method of claim 33, further comprising:

resolving each of one or more error signals each corresponding to one of the plurality of antennas onto a signal basis for the one or more transmission sources for producing a one or more of resolved error signals;

combining the one or more resolved error signals across antennas for producing a combined signal;

scaling the combined signal by a stabilizing step size to producing a scaled signal; and

combining the combined signal with a weighted input vector.