Iterative interference suppression using mixed feedback weights and stabilizing step sizes

• US 8,953,723 B2
• Filed: 06/03/2013
• Issued: 02/10/2015
• Est. Priority Date: 04/07/2005
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC
• Original Assignee: III Holdings 1, LLC
• Inventors: Guess, Tommy, McCloud, Michael L, Nagarajan, Vijay, Lamba, Gagandeep Singh
• Primary Examiner(s): Kim, Kevin
• Application Number:
  US13/908,264
• Publication Number:
  US 20130336363A1
• Time in Patent Office: 617 Days
• Field of Search: 375/346
• US Class Current: 375/346
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71072 Successive interference cancellation
• 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 1/715 Interference-related aspects
• CPC Class Codes: H04L 2025/03375 Passband transmission
• CPC Class Codes: H04L 25/03006 Arrangements for removing intersymbol interference

Abstract

A receiver is configured for canceling intra-cell and inter-cell interference in coded, multiple-access, spread-spectrum transmissions that propagate through frequency-selective communication channels. The receiver employs iterative symbol-estimate weighting, subtractive cancellation with a stabilizing step-size, and mixed-decision symbol estimate. Receiver embodiments may be implemented explicitly in software of 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 of subchannel symbol level).

Claims

1. A receiver, comprising:

a front-end configured to receive a signal and generate symbol estimates from the received signal;

an iterative interference suppressor configured to iteratively;

produce a synthesized signal from the symbol estimates;

subtract the synthesized signal from the received signal to obtain an error signal;

calculate a stabilizing step size having a magnitude that is a function of at least the received signal and the synthesized signal;

weight the error signal with the stabilizing step size to obtain a scaled error signal; and

combine the scaled error signal and the symbol estimates to obtain interference-suppressed symbol estimates.

2. The receiver of claim 1, wherein the front-end comprises a plurality of Rake receivers configured to generate the symbol estimates from the received signal.

3. The receiver of claim 1, wherein the iterative interference suppressor is further configured to de-bias the symbol estimates using a non-negative de-biasing constant and apply a mixed-decision map to the de-biased symbol estimates to update the symbol estimates.

4. The receiver of claim 1, wherein the iterative interference suppressor is further configured to weight the symbol estimates using soft weights, wherein each soft weight reflects a confidence measure of accuracy for a respective symbol estimate.

5. The receiver of claim 1, wherein the iterative interference suppressor is further configured to weight the symbol estimates using soft weights, wherein each soft weight is derived from a signal-to-interference-plus-noise ratio (SINR) measure for a respective symbol estimate.

6. The receiver of claim 1, wherein the iterative suppressor is further configured to determine the stabilizing step size based on proximity of the symbol estimates to a desired interference-cancelled symbol decision.

7. The receiver of claim 1, wherein the iterative suppressor is further configured to set the stabilizing step size to a fixed value.

8. A method for iteratively computing interference-suppressed symbol estimates, the method comprising:

producing a synthesized signal from symbol estimates for a received signal;

subtracting the synthesized signal from the received signal to obtain an error signal;

calculating a stabilizing step size having a magnitude that is a function of at least the received signal and the synthesized signal;

weighting the error signal with the stabilizing step size to obtain a scaled error signal; and

combining the scaled error signal and the symbol estimates to obtain interference-suppressed symbol estimates.

9. The method of claim 8, further comprising:

de-biasing the symbol estimates using a non-negative de-biasing constant; and

applying a mixed-decision map to the de-biased symbol estimates to update the symbol estimates.

10. The method of claim 8, further comprising weighting the symbol estimates using soft weights, wherein each soft weight reflects a confidence measure of accuracy for a respective symbol estimate.

11. The method of claim 8, further comprising weighting the symbol estimates using soft weights, wherein each soft weight is derived from a signal-to-interference-plus-noise ratio (SINR) measure for a respective symbol estimate.

12. The method of claim 8, further comprising determining the stabilizing step size based on proximity of the symbol estimates to a desired interference-cancelled symbol decision.

13. The method of claim 8, further comprising setting the stabilizing step size to a fixed value.

14. A non-transitory computer-readable storage medium, comprising a plurality of instructions, that in response to being executed, cause a receiver to:

produce a synthesized signal from symbol estimates for a received signal;

subtract the synthesized signal from the received signal to obtain an error signal;

calculate a stabilizing step size having a magnitude that is a function of at least the received signal and the synthesized signal;

weight the error signal with the stabilizing step size to obtain a scaled error signal; and

combine the scaled error signal and the symbol estimates to obtain interference-suppressed symbol estimates.

15. The non-transitory computer-readable storage medium of claim 14, wherein the plurality of instructions, in response to being executed, further cause the receiver to:

de-bias the symbol estimates using a non-negative de-biasing constant; and

apply a mixed-decision map to the de-biased symbol estimates to update the symbol estimates.

16. The non-transitory computer-readable storage medium of claim 14, wherein the plurality of instructions, in response to being executed, further cause the receiver to weight the symbol estimates using soft weights, wherein each soft weight reflects a confidence measure of accuracy for a respective symbol estimate.

17. The non-transitory computer-readable storage medium of claim 14, wherein the plurality of instructions, in response to being executed, further cause the receiver to weight the symbol estimates using soft weights, wherein each soft weight is derived from a signal-to-interference-plus-noise ratio (SINR) measure for a respective symbol estimate.

18. The non-transitory computer-readable storage medium of claim 14, wherein the plurality of instructions, in response to being executed, further cause the receiver to determine the stabilizing step size based on proximity of the symbol estimates to a desired interference-cancelled symbol decision.

19. The non-transitory computer-readable storage medium of claim 14, wherein the plurality of instructions, in response to being executed, further cause the receiver to set the stabilizing step size to a fixed value.