Interference cancellation in variable codelength systems for multi-access communication

• US 7,697,595 B2
• Filed: 05/11/2006
• Issued: 04/13/2010
• Est. Priority Date: 05/11/2006
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC (Intellectual Ventures LLC)
• Original Assignee: TensorComm, Inc. (Rambus Inc.)
• Inventors: Nagarajan, Vijay, Narayan, Anand P, Scharf, Louis L
• Primary Examiner(s): Tran, Khai
• Application Number:
  US11/432,580
• Publication Number:
  US 20070263704A1
• Time in Patent Office: 1,433 Days
• Field of Search: 375/148, 375/347, 375/342, 375/267, 375/152, 375/349, 370/209, 370/335, 370/337, 370/342, 455/132, 455/137, 455/138
• 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 for calculating at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel in a received signal, and

an interference canceller configured for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

wherein the analysis module is configured to sample the at least one high-rate subchannel to ensure that amplitudes of the received signal do not change significantly over a predetermined time interval.

2. 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 a received signal to produce at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel, and

providing for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

wherein providing for analyzing comprises sampling the at least one high-rate subchannel to ensure that amplitudes of the received signal do not change significantly over a predetermined time interval.

3. 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 a received signal to produce at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel, and

providing for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

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 the 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.

4. 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 received signal to produce at least one low-rate symbol estimate calculated from at least one low-rate descendant subchannel of the at least one high-rate subchannel, and

an interference-cancellation means configured for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel.

5. The system recited in claim 4, wherein the at least one high-rate subchannel comprises at least one code-multiplexed subchannel having a low spreading factor, and the at least one low-rate descendant subchannel comprises at least one code-multiplexed subchannel having a high spreading factor.

6. The system recited in claim 4, wherein the analysis means comprises a Rake-processing means for generating one of a plurality of signals, a combining means configured to weight and combine the plurality of signals to generate a combined signal, a despreading means for generating a despread signal from the combined signal, and a symbol-estimating means configured for generating the at least one low-rate symbol estimate from the combined signal.

7. The system recited in claim 4, wherein the analysis means comprises a sampling means configured for sampling the at least one high-rate subchannel to ensure that amplitudes of a received signal do not change significantly over a predetermined time interval.

8. The system recited in claim 4, 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.

9. The system recited in claim 4, wherein the interference-cancellation means comprises coupling the interference-cancelled signal back to the analysis means to perform iterative interference cancellation.

10. The system recited in claim 4,

wherein the interference-cancellation means comprises a synthesis means comprising

a weighting means for weighting the at least one low-rate symbol estimate for producing at least one weighted symbol estimate,

a spreading means for spreading the at least one weighted symbol estimate to produce at least one spread signal,

a channel-emulation means for performing channel emulation on the at least one spread signal to produce an estimated received signal, and

a combining means for combining a plurality of components of the estimated received signal.

11. A method for processing at least one of high-rate subchannels and low-rate subchannels, the method comprising:

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

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

providing for employing a function of the SINR for processing high-rate and low-rate subchannels in the received baseband signal,

wherein providing for employing the function comprises calculating a variance of the SINR and determining whether the variance is substantially zero or substantially non-zero.

12. The method recited in claim 11, 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.

13. The method recited in claim 12, 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.

14. The method recited in claim 11, 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.

15. An apparatus configured for processing 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,

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

a variance calculator configured for estimating an SINR variance and determining whether the SINR variance is substantially zero or substantially non-zero.

16. The apparatus recited in claim 15,

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.

17. The apparatus recited in claim 15,

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.

18. The apparatus recited in claim 17, 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 processing the high-rate subchannels and low-rate subchannels in the received baseband signal.

19. The apparatus recited in claim 15,

wherein the decision module is configured to compare instantaneous symbol estimates from the analysis module to at least one predetermined value for processing the high-rate subchannels and low-rate subchannels in the received baseband signal.

20. The apparatus recited in claim 15, wherein the analysis module comprises a means for equalization configured to generate the at least one low rate symbol estimate from the combined signal.

21. A system configured for processing 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 processing the high-rate and low-rate subchannels in the received baseband signal,

wherein the detection means is configured for calculating a variance of the SINR and determining whether the variance is substantially zero or substantially non-zero.

22. The system recited in claim 21, 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.

23. The system recited in claim 22, 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 processing the high-rate subchannels and low-rate subchannels in the received baseband signal.

24. The system recited in claim 21, wherein the detection means is configured to compare instantaneous symbol estimates produced by the analysis means to at least one predetermined value for processing the high-rate subchannels and low-rate subchannels in the received baseband signal.

25. 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 symbol estimates,

providing for applying weighted symbol estimates to at least one 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 transmission,

wherein the at least one low-rate subchannel comprises a code-multiplexed subchannel having a high spreading factor, and the high-rate ancestor subchannel comprises a plurality of code-multiplexed subchannels, each having a low spreading factor.

26. 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 for calculating at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel in a received signal, and

an interference canceller configured for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

wherein the interference canceller comprises a synthesis module configured to synthesize the interference by applying the at least one low-rate symbol estimate to at least one synthesized low-rate subchannel.

27. 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 for calculating at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel in a received signal, and

an interference canceller configured for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

where the analysis module comprises at least one equalizer to generate the symbol estimate.

28. 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 a received signal to produce at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel, and

providing for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

wherein providing for analyzing comprises performing equalization in order to produce the at least one symbol estimate.

29. 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 for calculating at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel in a received signal, and

an interference canceller configured for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

wherein the analysis 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 the received signal and configured to produce a plurality of despread signals, and

wherein the Rake receiver comprises a combiner configured to combine the plurality of despread signals.

30. 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 for calculating at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel in a received signal, and

an interference canceller configured for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

wherein the interference canceller comprises at least one weighting module, at least one spreading module, at least one channel emulator, and a combiner.

31. 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 a received signal to produce at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel, and

providing for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

wherein providing for processing further comprises synthesizing the interference by applying the at least one low-rate symbol estimate to at least one synthesized low-rate subchannel.

32. 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 a received signal to produce at least one low-rate symbol estimate from at least one low-rate descendant subchannel of the at least one high-rate subchannel, and

providing for processing the at least one low-rate symbol estimate with the received signal to cancel interference contributed by the at least one high-rate subchannel,

wherein providing for processing comprises coupling the interference-cancelled signal back to the step of providing for analyzing to perform iterative interference cancellation.