Reduced state sequence estimation with soft decision outputs
A receiver may be operable to receive an inter-symbol correlated (ISC) signal, and generate a plurality of soft decisions as to information carried in the ISC signal. The soft decisions may be generated using a reduced-state sequence estimation (RSSE) process. The RSSE process may be such that the number of symbol survivors retained after each iteration of the RSSE process is less than the maximum likelihood state space. The plurality of soft decisions may comprise a plurality of log likelihood ratios (LLRs). Each of the plurality of LLRs may correspond to a respective one of a plurality of subwords of a forward error correction (FEC) codeword.
1. A system comprising:
signal processing circuitry and sequence estimation circuitry, wherein:
said signal processing circuitry is operable to receive an inter-symbol correlated signal resulting from a transmitted plurality of symbols, each of said plurality of symbols corresponding to a plurality of subwords;
said signal processing circuitry is operable to output samples of said received inter-symbol correlated signal to said sequence estimation circuitry;
said sequence estimation circuitry is operable to process said samples using a sequence estimation process in which each iteration of said sequence estimation process comprises generation of multiple survivor vectors; and
said sequence estimation circuitry is operable to generate soft-decisions as to values of said plurality of symbols and/or said plurality of subwords based on a count of occurrences of a particular symbol and/or subword value in said multiple survivor vectors.
2. The system of claim 1 , wherein:
a weight is applied to each one of said occurrences during generation of said count of occurrences; and
said weight is based on which one of said multiple survivor vectors said one of said occurrences is in.
3. The system of claim 2 , wherein said weight applied to said one of said occurrences is based on a metric calculated for said one of said multiple survivor vectors.
4. The system of claim 1 , wherein:
when said one of said multiple survivor vectors is a first survivor vector having a first metric, said weight applied to said one of said occurrences is a first weight based on said first metric; and
when said one of said multiple survivor vectors is a second survivor vector having a second metric, said weight applied to said one of said occurrences is a second weight based on said second metric.
5. The system of claim 1 , wherein said count of occurrences includes multiple decision delays in said multiple survivor vectors.
6. The system of claim 5 , wherein:
a weight is applied to each one of said occurrences during generation of said count of occurrences; and
said weight is based on which one of said multiple decision delays said one of said occurrences is at.
7. The system of claim 6 , wherein:
when said one of said occurrences is at a first one of said decision delays, said weight is a first weight; and
when said one of said occurrences is at a second one of said decision delays, said weight is a second weight.
8. The system of claim 1 , wherein said sequence estimation circuitry is operable to process said soft-decisions using a signal-to-noise ratio (SNR)-dependent function.
9. The system of claim 1 , wherein one of said soft-decisions corresponding to one of said plurality of symbols or said plurality of subwords is based on a ratio of said count of occurrences of said particular symbol and/or subword value in said multiple survivor vectors to a count of occurrences of one or more other symbol and/or subword values in said multiple survivor vectors.
10. The system of claim 1 , wherein each of said plurality of symbols is a quadrature amplitude modulation (QAM) symbol and each of said plurality of subwords is a bit.
11. A method comprising:
performing in a receiver comprising signal processing circuitry and sequence estimation circuitry:
receiving, by said signal processing circuitry, an inter-symbol correlated signal resulting from a transmitted plurality of symbols, each of said plurality of symbols corresponding to a plurality of subwords;
outputting, by said signal processing circuitry, samples of said received inter-symbol correlated signal to said sequence estimation circuitry;
processing, by said sequence estimation circuitry, said samples using a sequence estimation process in which each iteration of said sequence estimation process comprises generating multiple survivor vectors; and
generating, by said sequence estimation circuitry, soft-decisions as to values of said plurality of symbols and/or said plurality of subwords based on a count of occurrences of a particular symbol and/or subword value in said multiple survivor vectors.
12. The method of claim 11 , comprising: applying, by said sequence estimation circuitry, a weight to each one of said occurrences as part of generating said count of occurrences, wherein said weight is based on which one of said multiple survivor vectors said one of said occurrences is in.
13. The method of claim 12 , wherein said weight applied to said one of said occurrences is based on a metric calculated for said one of said multiple survivor vectors.
14. The method of claim 11 , wherein:
when said one of said multiple survivor vectors is a first survivor vector having a first metric, said weight applied to said one of said occurrences is a first weight based on said first metric; and
when said one of said multiple survivor vectors is a second survivor vector having a second metric, said weight applied to said one of said occurrences is a second weight based on said second metric.
15. The method of claim 11 , wherein said count of occurrences includes multiple decision delays in said multiple survivor vectors.
16. The method of claim 15 , comprising:
applying, by said sequence estimation circuitry, a weight to each one of said occurrences as part of generating of said count of occurrences, wherein said weight is based on which one of said multiple decision delays said one of said occurrences is at.
17. The method of claim 16 , wherein:
when said one of said occurrences is at a first one of said decision delays, said weight is a first weight; and
when said one of said occurrences is at a second one of said decision delays, said weight is a second weight.
18. The method of claim 11 , comprising processing, by said sequence estimation circuitry, said soft-decisions using a signal-to-noise ratio (SNR)-dependent function.
19. The method of claim 11 , wherein one of said soft-decisions corresponding to one of said plurality of symbols or said plurality of subwords is based on a ratio of said count of occurrences of said particular symbol and/or subword value in said multiple survivor vectors to a count of occurrences of one or more other symbol and/or subword values in said multiple survivor vectors.
20. The method of claim 11 , wherein each of said plurality of symbols is a quadrature amplitude modulation (QAM) symbol and each of said plurality of subwords is a bit.