Iterative interference suppression using mixed feedback weights and stabilizing step sizes
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).
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.