MULTIPLE INPUT MULTIPLE OUTPUT COMMUNICATIONS OVER NONLINEAR CHANNELS USING ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING

1 . A System comprising:

an orthogonal frequency division multiplexing (OFDM) receiver comprising a nonlinearity compensation circuit and a soft-input-soft-output (SISO) forward error correction (FEC) decoder which are operated iteratively, wherein for a particular iteration:

said nonlinearity compensation circuit is operable to generate estimates of constellation points transmitted on each of a plurality of bins of a received signal, wherein:

each of said bins corresponds to a respective one of a plurality of subcarrier and spatial stream combinations; and

said estimates are generated based on decoded soft bit decisions generated by said SISO FEC decoder during a previous iteration;

said SISO FEC decoder is operable to generate soft bit decisions generated from said estimates to generate decoded soft bit decisions for said particular iteration.

2 . The system of claim 1 , comprising a demapper operable to:

generate said soft bit decisions from estimates of said bins; and

output said generated soft bit decisions for decoding by said SISO FEC decoder.

3 . The system of claim 1 , comprising a multiple-input-multiple-output (MIMO) equalizer and decoder.

4 . The system of claim 3 , wherein said MIMO equalizer and decoder is operable to:

generate said soft bit decisions from estimates of said bins; and

output said generated soft bit decisions for decoding by said SISO FEC decoder.

5 . The system of claim 3 , wherein said MIMO equalizer and decoder is operable to:

receive said estimates from said nonlinearity compensation circuit; and

for each of said plurality of subcarrier and spatial stream combinations, generate a corresponding one of a plurality of lists of candidates to be used for calculation of said soft bit decisions.

6 . The system of claim 5 , wherein each one of said plurality of lists of candidates is generated independently of each other one of said plurality of lists of candidates.

7 . The system of claim 5 , wherein said MIMO equalizer and decoder is operable to perform linear decoding.

8 . The system of claim 5 , wherein said MIMO equalizer and decoder is operable generate said plurality of lists of candidates based on a cost function that is based on a model of nonlinearity of a transmitter from which a signal being decoded was received.

9 . The system of claim 7 , wherein said MIMO equalizer and decoder is operable to generate said plurality of lists of candidates using a gradient method to solve for one subcarrier at a time while the other subcarriers are fixed to said estimates generated by said nonlinearity compensation circuitry.

10 . The system of claim 1 , wherein said nonlinearity compensation circuit is operable to generate said estimates based on a cost function that is based on a model of nonlinearity of a transmitter from which a signal being decoded was received.

11 . The system of claim 10 , wherein:

said cost function does not completely account for correlation between noise components over different spatial streams of a particular subcarrier; and

said OFDM receiver comprises a MIMO decoder operable to extract said correlation between noise components over said different spatial streams of said particular subcarrier.

12 . The system of claim 1 , wherein said generation of said estimates is based on a measure of distance that is either: between a function of said received signal and a synthesized version of said received signal, or between said estimates and said decoded soft bit decisions.

13 . The system of claim 1 , wherein:

said iterative operation of said nonlinearity compensation circuit and said SISO FEC decoder comprises processing comprises a plurality of outer iterations and a plurality of inner iterations;

said particular iteration is one of said plurality of outer iterations; and

said previous iteration is another one of said plurality of outer iterations.

14 . The system of claim 13 , wherein for each of said inner iterations for said particular iteration, said SISO FEC decoder is operable to generate variable-node-to-check-node messages based on said estimates.

15 . The system of claim 13 , wherein:

for a first one of said inner iterations for said particular iteration, said FEC decoder is operable to generates variable-node-to-check-node messages based on check-node-to-variable-node messages generated during a last one of said inner iterations for said previous iterations.

16 . The system of claim 15 , comprising circuitry operable to: for said previous iterations, halt said inner iterations before said FEC decoder converges.

17 . The system of claim 13 , comprising circuitry operable to:

categorize said decoded soft bit decisions from said previous iteration; and

adjust said decoded soft bit decisions based on a category into which they are placed, wherein:

said adjustment results in adjusted soft bit decisions; and

said estimates for said particular iteration are generated based on said adjusted soft bit decisions.

18 . The system of claim 13 , comprising circuitry operable to:

for a particular one of said outer iterations, calculate an expectation using said decoded soft bit decisions, wherein said generation of said estimates is based on said expectation.

19 . The system of claim 13 , wherein said generation of said estimates is a refinement of estimates generated during said previous iteration.

20 . The system of claim 19 , wherein:

said refinement is limited by one or more constraints; and

said constraints are determined based on said decoded soft bit decisions.