Iterative interference suppressor for wireless multiple-access systems with multiple receive antennas
This invention teaches to the details of an interference suppressing receiver for suppressing 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 suppression 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.
1. An interference suppressor for suppressing 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 receiving constituent signals of the received multiple-access communications signals and generating input symbol decisions; and
one or more interference suppression units configured for processing the input symbol decisions into updated symbol decisions, each of the one or more interference suppression units 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.
2. The interference suppressor of claim 1 , wherein each of the one or more interference suppression units is configured to convert the input symbol decisions into updated symbol decisions.
3. The interference suppressor of claim 1 , wherein the front-end processing module comprises:
a combiner configured for combining the received multiple-access communications 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.
4. The interference suppressor of claim 3 , further configured for suppressing interference from each of a plurality of base stations.
5. The interference suppressor of claim 3 , 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.
6. The interference suppressor of claim 1 , wherein the constituent signals comprise Rake-finger signals.
7. The interference suppressor of claim 6 , 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.
8. The interference suppressor of claim 1 , wherein the constituent signals comprise received signals associated with each of the one or more transmission sources.
9. An interference suppression method for suppressing 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 suppression to process the input symbol decisions, wherein said performing iterative interference suppression includes:
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 for producing a scaled signal; and
combining the combined signal with a weighted input vector.
10. The method of claim 9 , wherein said performing iterative interference suppression further includes converting the input symbol decisions into updated symbol decisions.
11. The method of claim 9 , wherein said scaling by a stabilizing step-size comprises:
generating a stabilizing step size having a magnitude indicative of how far the input symbol decisions are from desired interference-suppressed symbol decisions in an iteration of the iterative interference suppression; and
weighting an error signal with the stabilizing step size.
12. The method of claim 11 , wherein said 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.
13. The method of claim 11 , wherein said 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 two differently synthesized received signals for each antenna that are combined across the plurality of antennas.
14. The method of claim 11 , further comprising measuring the stabilizing step as a function of channel quality parameters.
15. The method of claim 11 , further comprising setting the stabilizing step equal to a predetermined fixed value.
16. The method of claim 9 , wherein said 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.
17. The method of claim 16 , further comprising suppressing interference from each of a plurality of base stations.
18. The method of claim 9 , wherein:
said processing comprises receiving constituent signals received by the plurality of antennas; and
the constituent signals comprise Rake-finger signals.
19. The method of claim 18 , 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.
20. The method of claim 9 , wherein:
said processing comprises receiving constituent signals received by the plurality of antennas; and
the constituent signals comprise received signals associated with each of the one or more transmission sources.