Interference cancellation in variable codelength systems for multi-access communication

• US 20070263704A1
• Filed: 05/11/2006
• Published: 11/15/2007
• Est. Priority Date: 05/11/2006
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC (Intellectual Ventures LLC)
• Original Assignee: Rambus Inc.
• Inventors: Nagarajan, Vijay, Scharf, Louis, Narayan, Anand
• Granted Patent: US 7,697,595 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• 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 2201/70703 using multiple or variable rates
• CPC Class Codes: H04B 2201/709727 GRAKE type RAKE receivers

Abstract

A receiver employs low-rate processing to synthesize the effect of high-rate interference in a received multi-rate signal. Each high-rate subchannel is analyzed on its low-rate descendents to produce symbol estimates for each low-rate symbol interval. The symbol estimates are applied to low-rate descendent subchannels, which are then combined to synthesize the effects of the high-rate interference. An interference canceller processes the synthesized interference with the received signal for producing an interference-cancelled signal. Alternatively, analogous steps may be applied at high-rate to analyze, synthesize, and cancel the effects of low-rate interference in a multi-rate signal.

Claims

1. A receiver configured for cancelling interference effects of at least one high-rate subchannel at a low rate in a multi-rate communication system, the receiver comprising:

an analysis module configured to analyze the at least one high-rate subchannel on its low-rate surrogate subchannels for generating low-rate surrogate symbol estimates,

a synthesis module configured to synthesize the interference effects of the at least one high-rate channel by applying the low-rate surrogate symbol estimates to synthesized low-rate surrogate subchannels for generating surrogate low-rate interferences, and

a combiner configured to combine the surrogate low-rate interferences into a composite interference signal that models the interference from a sequence of high rate transmissions.

2. The receiver recited in claim 1, wherein the at least one high-rate subchannel comprises a code-multiplexed subchannel having a low spreading factor, and the low-rate surrogate subchannels comprise code-multiplexed subchannels having a high spreading factor.

3. The receiver recited in claim 1, wherein the analysis module and the synthesis module comprises a Rake receiver comprising a plurality of Rake fingers, each of the plurality of Rake fingers assigned to a particular multipath component of a received signal, a combiner configured to combine a plurality of Rake signals, a despreader, a symbol estimator, and a synthesizer configured for synthesizing the surrogate low-rate interferences from weighted low-rate surrogate symbol estimates applied to subchannel signals.

4. The receiver recited in claim 1, wherein the analysis module is configured to sample the at least one high-rate signal to ensure that amplitudes of a received signal do not change significantly over a predetermined time interval.

5. A method for cancelling interference effects of at least one high-rate subchannel at a low rate in a multi-rate communication system, the method comprising:

providing for analyzing the at least one high-rate subchannel on its low-rate surrogate subchannels for generating low-rate surrogate symbol estimates,

providing for synthesizing the interference effects of the at least one high-rate subchannel by applying the low-rate surrogate symbol estimates to synthesized low-rate surrogate subchannels to generate surrogate low-rate interferences, and

combining the surrogate low-rate interferences into a composite interference signal that models interference from a sequence of high rate transmissions.

6. The method recited in claim 5, wherein the at least one high-rate subchannel comprises a code-multiplexed subchannel having a low spreading factor, and the low-rate surrogate subchannels comprise code-multiplexed subchannels having a high spreading factor.

7. The method recited in claim 5, wherein providing for analyzing and providing for synthesizing comprise Rake processing for each of the plurality of multipath components of a received signal to produce a plurality of Rake signals, combining the plurality of Rake signals to produce a combined signal, despreading the combined signal to produce a despread signal, providing symbol estimates from the despread signal, and synthesizing interference from weighted symbol estimates applied to subchannel signals.

8. The method recited in claim 5, wherein providing for analyzing comprises sampling the at least one high-rate signal to ensure that amplitudes of a received signal do not change significantly over a predetermined time interval.

9. The method recited in claim 5, wherein providing for analyzing further comprises performing mixed-mode processing that uses hard and soft decisions, including comparing a subchannel rate for each subchannel in a received signal to a predetermined processing rate, followed by generating a mix of hard and soft decisions for subchannels having a rate equal to the processing rate and soft-decisions for subchannels having a rate greater than or lesser than the processing rate.

10. A chipset configured to perform the method recited in claim 5.

11. A digital computer system programmed to perform the method recited in claim 5.

12. A computer-readable medium storing a computer program implementing the method of claim 5.

13. A base station configured to perform the method of claim 5.

14. A handset configured to perform the method of claim 5.

15. A system configured for cancelling interference effects of at least one high-rate subchannel at a low rate in a multi-rate communication system, the system comprising:

an analysis means configured for analyzing the at least one high-rate subchannel on its low-rate surrogate subchannels for generating low-rate surrogate symbol estimates,

an interference-cancellation means configured for synthesizing the interference effects of the at least one high-rate channel by applying the low-rate surrogate symbol estimates to synthesized low-rate surrogate subchannels to generate surrogate low-rate interferences, and for combining the surrogate low-rate interferences to produce a composite interference signal that models interference from a sequence of high rate transmissions.

16. The system recited in claim 15, wherein the at least one high-rate subchannel comprises a code-multiplexed subchannel having a low spreading factor, and the low-rate surrogate subchannels comprise code-multiplexed subchannels having a high spreading factor.

17. The system recited in claim 15, wherein the analysis means comprises a Rake receiver having a plurality of Rake fingers, each of the plurality of Rake fingers assigned to a particular multipath component of a received signal for generating one of a plurality of Rake signals, a combining means configured to weight and combine the plurality of Rake signals to generate a combined signal, a despreading means for generating a despread signal from the combined signal, a symbol-estimating means configured for generating the low-rate surrogate symbol estimates from the combined signal, the interference-cancellation means configured for weighting the low-rate surrogate symbol estimates to produce weighted symbol estimates, and synthesizing interference-cancelled Rake finger signals from the weighted symbol estimates applied to the synthesized low-rate surrogate subchannels.

18. The system recited in claim 15, wherein the analysis means comprises a sampling means configured for sampling the at least one high-rate signal to ensure that amplitudes of a received signal do not change significantly over a predetermined time interval.

19. The system recited in claim 15, wherein the analysis means includes a mixed-mode processing means, configured for comparing a subchannel rate for each subchannel in a received signal to a predetermined processing rate, followed by generating a mix of hard and soft decisions for subchannels having a rate equal to the processing rate and soft-decisions for subchannels having a rate greater than or lesser than the processing rate.

20. A method for determining a presence of at least one of high-rate subchannels and low-rate subchannels, comprising:

providing for performing at least one of a high-rate analysis and a low-rate analysis for a plurality of subchannels in a received baseband signal,

providing for calculating a signal-to-interference-and-noise ratio (SINR) for each of the plurality of subchannels, and

providing for employing a function of the SINR for determining the presence of high-rate and low-rate subchannels in the received baseband signal.

21. The method recited in claim 20, wherein providing for employing the function comprises estimating a variance of the SINR and determining whether the variance is zero or non-zero.

22. The method recited in claim 20, wherein providing for calculating an SINR is configured for calculating a plurality of low-rate SINRs for a plurality of low-rate subchannels and at least one high-rate SINR for at least one high-rate subchannel, the method further comprising combining the plurality of low-rate SINRs to produce a summed SINR and scaling the at least one high-rate SINR by a ratio of the high rate and the low rate to account for spreading gain due to non-normalized spreading codes.

23. The method recited in claim 22, further comprising generating first-order statistics from symbol estimates of the plurality of subchannels, and processing the first-order statistics to determine the presence of at least one of a high-rate subchannel and a low-rate subchannel.

24. The method recited in claim 20, further comprising comparing instantaneous symbol estimates to at least one predetermined value for determining the presence of the at least one of high-rate subchannels and low-rate subchannels.

25. A chipset configured to perform the method recited in claim 20.

26. A digital computer system programmed to perform the method recited in claim 20.

27. A computer-readable medium storing a computer program implementing the method of claim 20.

28. A base station configured to perform the method of claim 20.

29. A handset configured to perform the method of claim 20.

30. An apparatus configured for determining a presence of at least one of a high-rate subchannel and a low-rate subchannel in a received baseband signal, comprising:

an analysis module configured for performing at least one of a high-rate analysis and a low-rate analysis for a plurality of subchannels in the received baseband signal,

a signal-to-interference-and-noise ratio (SINR) module configured for calculating an SINR for each of the plurality of subchannels, and

a decision module configured for employing a function of the SINR for determining the presence of at least one of high-rate subchannels and low-rate subchannels in the received baseband signal.

31. The apparatus recited in claim 30, further comprising a variance calculator configured for estimating an SINR variance and determining whether the SINR variance is zero or non-zero.

32. The apparatus recited in claim 30, wherein the SINR module is configured for calculating a plurality of low-rate SINRs for a plurality of low-rate subchannels and at least one high-rate SINR for at least one high-rate subchannel, the apparatus further comprising a combiner configured to sum the plurality of low-rate SINRs to produce a summed SINR and a scaling module configured to multiply the at least one high-rate SINR by a ratio of the high rate and the low rate, to account for spreading gain of non-normalized spreading codes.

33. The apparatus recited in claim 30, wherein the analysis module comprises a low-rate analysis block configured to process the received baseband signal for producing low-rate symbol estimates of low-rate descendants of a high-rate subchannel, and a high-rate analysis block configured to process the received baseband signal at the high rate for producing high-rate symbol estimates.

34. The apparatus recited in claim 33, further comprising at least one first-order statistics block configured for processing at least one of the low-rate symbol estimates and the high-rate symbol estimates for generating first-order statistics, the decision module further configured for employing the first-order statistics for determining the presence of high-rate subchannels and low-rate subchannels in the received baseband signal.

35. The apparatus recited in claim 30, wherein the decision module is configured to compare instantaneous symbol estimates from the analysis module to at least one predetermined value for determining the presence of at least one of high-rate subchannels and low-rate subchannels in the received baseband signal.

36. A system configured for determining a presence of at least one of a high-rate subchannel and a low-rate subchannel in a received baseband signal, comprising:

an analysis means for performing at least one of a high-rate analysis and a low-rate analysis for a plurality of subchannels in a received baseband signal,

an SINR-calculation means for calculating a signal-to-interference-and-noise ratio (SINR) for each of the plurality of subchannels, and

a detection means for employing a function of the SINR for detecting the presence of high-rate and low-rate subchannels in the received baseband signal.

37. The system recited in claim 36, wherein the detection means is configured for calculating a variance of the SINR and determining whether the variance is zero or non-zero.

38. The system recited in claim 36, wherein the SINR-calculation means is configured for calculating a plurality of low-rate SINRs for a plurality of low-rate subchannels and at least one high-rate SINR for at least one high-rate subchannel, the system further comprising a combining means for combining the plurality of low-rate SINRs to produce a summed SINR and a scaling means configured for scaling the at least one high-rate SINR by a ratio of the high rate and the low rate to account for spreading gain of non-normalized spreading codes.

39. The system recited in claim 38, wherein the analysis means is configured to produce low-rate symbol estimates and high-rate symbol estimates, the system further comprising a first-order statistics means configured for processing at least one of the low-rate symbol estimates and the high-rate symbol estimates for generating first-order statistics, the detection means further configured for employing the first-order statistics for determining the presence of at least one of high-rate subchannels and low-rate subchannels in the received baseband signal.

40. The system recited in claim 36, wherein the detection means is configured to compare instantaneous symbol estimates produced by the analysis means to at least one predetermined value for determining the presence of at least one of high-rate subchannels and low-rate subchannels in the received baseband signal.

41. A receiver configured for cancelling interference effects of at least one low-rate subchannel at a high rate in a multi-rate communication system, the receiver comprising:

an analysis module configured for analyzing the at least one low-rate subchannel on its high-rate ancestor subchannel for generating surrogate symbol estimates,

a synthesis module configured for applying weighted surrogate symbol estimates to synthesized high-rate ancestor subchannel to generate a plurality of high-rate interference signals, and using a sequence of the plurality of high-rate interference signals to model the interference effects from a low-rate transmissions.

42. The receiver recited in claim 41, wherein the at least one low-rate subchannel comprises a code-multiplexed subchannel having a high spreading factor, and the high-rate ancestor subchannel comprise a plurality of code-multiplexed subchannels, each having a low spreading factor.

43. The receiver recited in claim 41, wherein the synthesis module is configured to employ a function of merit of the surrogate symbol estimates for calculating weights used to produce the weighted surrogate symbol estimates.

44. The receiver recited in claim 43, wherein the function of merit is a function of SINR for the high-rate ancestor subchannel.

45. A method for cancelling interference effects of at least one low-rate subchannel at a high rate in a multi-rate communication system, the method comprising:

providing for analyzing the at least one low-rate subchannel on its high-rate ancestor subchannel for generating surrogate symbol estimates,

providing for applying weighted surrogate symbol estimates to synthesized high-rate ancestor subchannel to generate a plurality of high-rate interference signals, and using a sequence of the plurality of high-rate interference signals to model the interference effects from a low-rate transmissions.

46. The method recited in claim 45, wherein the at least one low-rate subchannel comprises a code-multiplexed subchannel having a high spreading factor, and the high-rate ancestor subchannel comprise a plurality of code-multiplexed subchannels, each having a low spreading factor.

47. The method recited in claim 45, wherein providing for applying weighted surrogate symbol estimates is configured to employ a function of merit of the surrogate symbol estimates for calculating weights used to produce the weighted surrogate symbol estimates.

48. The method recited in claim 47, wherein the function of merit is a function of SINR for the high-rate ancestor subchannel.

49. A chipset configured to perform the method recited in claim 45.

50. A digital computer system programmed to perform the method recited in claim 45.

51. A computer-readable medium storing a computer program implementing the method of claim 45.

52. A base station configured to perform the method of claim 45.

53. A handset configured to perform the method of claim 45.