SINGLE CARRIER COMMUNICATIONS HARNESSING NONLINEARITY
A single-carrier receiver comprises a (FEC) decoder and a nonlinearity compensation circuit. The nonlinearity compensation circuit is operable to generate estimates of constellation points transmitted on a received signal based on soft decisions from the FEC decoder and based on a model of nonlinear distortion introduced by a transmitter from which the received signal was received. The generation of the estimates may be based on a measure of distance between a function of the received signal and a synthesized version of the received signal. The generation of the estimates may comprise iterative processing of symbols of the received signal, and the iterative processing may comprise a plurality of outer iterations and a plurality of inner iterations.
1 . A System comprising:
an single carrier receiver comprising a forward error correction (FEC) decoder and a nonlinearity compensation circuit, wherein:
said nonlinearity compensation circuit is operable to generate estimates of constellation points transmitted on a received signal; and
said generation of said estimates is based on:
soft decisions from said FEC decoder; and
a model of nonlinear distortion introduced by a transmitter from which said received signal was received.
2 . 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 decoder soft values.
3 . The system of claim 1 , wherein:
said generation of said estimates comprises iterative processing of symbols of said received signal; and
said iterative processing comprises a plurality of outer iterations and a plurality of inner iterations.
4 . The system of claim 3 , wherein:
said estimates are an output of said nonlinearity compensation circuit during a first particular outer iteration; and
said soft decisions are an output of said FEC decoder during a second particular outer iteration preceding said first particular outer iteration.
5 . The system of claim 3 , wherein:
said estimates are an output of said nonlinearity compensation circuit during a first particular outer iteration; and
for each of said inner iterations for said particular outer iteration, said FEC decoder generates variable-node-to-check-node messages based on said estimates.
6 . The system of claim 3 , wherein:
for a first one of said inner iterations for a first particular one of said outer iterations, said FEC decoder 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 a second particular one of said outer iterations.
7 . The system of claim 6 , wherein, for said second particular one of said outer iterations, said inner iterations are halted before said FEC decoder converges.
8 . The system of claim 3 , wherein:
for a particular one of said outer iterations, said soft decisions from a previous one of said outer iterations are categorized and adjusted based on a category into which they are placed, said adjustment resulting in adjusted soft decisions; and
said estimates for said particular one of said iterations are generated based on said adjusted soft decisions.
9 . The system of claim 3 , wherein:
for a particular one of said outer iterations, an expectation is calculated using said soft decisions from a previous one of said outer iterations; and
said generation of said estimates is based on said expectation.
10 . The system of claim 3 , wherein said nonlinearity compensation circuitry is operable to:
during each successive outer iteration, refine one or more of said estimates generated during a previous outer iteration based on said soft decisions output by said FEC decoder during said previous outer iteration.
11 . The system of claim 10 , wherein:
said refinement is limited by one or more constraints; and
said constraints are determined based on said soft decisions.
12 . The system of claim 11 , wherein said constraints are updated for each successive one of said outer iterations.
13 . The system of claim 10 , wherein said generation of said estimates of said transmitted constellation points is based on a metric of distance between symbol estimation and said expectation, and said metric is affected from soft reliability measures.
14 . The system of claim 1 , wherein:
said nonlinearity compensation circuit is operable to generate said model based on a training sequence transmitted by said transmitter; and
said training sequence has a peak to average power ratio that causes an output of said power amplifier of said transmitter to compress and introduce nonlinear distortion.
15 . The system of claim 14 , wherein said training sequence comprises multiple permutations of a determined sequence of symbols.
16 . The system of claim 1 , wherein, for processing a particular received symbol, said nonlinearity compensation circuit is operable to determine said model of nonlinear distortion based on a first training sequence that preceded said particular received symbol and a second training sequence that followed said particular received symbol.
17 . The system of claim 16 , wherein said nonlinearity compensation circuitry is operable to use said first training sequence and said second training sequence to estimate phase noise present in said received signal.
18 . The system of claim 1 , wherein each of said soft decisions corresponds to only one of: a real dimension of said received signal and an imaginary dimension of said received signal.
19 . The system of claim 1 , wherein said estimate of nonlinear distortion introduced by said transmitter accounts for a digital nonlinear function implemented in said transmitter.
20 . The system of claim 19 , wherein said digital nonlinear function is a protective clip.