Joint sequence estimation of symbol and phase with high tolerance of nonlinearity
A method and system for a sequence estimation in a receiver, such as for use when receiving a sample of a received inter-symbol correlated (ISC) signal corresponding to a transmitted vector of L symbols, with L being a integer greater than 1, and with symbol L being a most-recent symbol and symbol 1 being least recent symbol of the vector. A plurality of candidate vectors may be generated, wherein element L−m of each candidate vector holding one of a plurality of possible values of the symbol L−m, with m is an integer greater than or equal to 1, and elements L−m+1 through L of each candidate vectors holding determined filler values. A plurality of metrics may be generated based on the plurality of candidate vectors, and based on the generated plurality of metrics, a best one of the possible values of the symbol L−m may be selected.
1. A system comprising:
a sequence estimation circuit operable to:
generate a plurality of candidate vectors, wherein:
each of said plurality of candidate vectors comprises a plurality of elements ranging from a least-recent element to a most-recent element;
each of said plurality of candidate vectors contains, in an element other than its said most-recent element, a respective one of a plurality of symbol values to be searched; and
each of said plurality of candidate vectors contains, in its said most-recent element, a respective one of a corresponding plurality of filler values;
calculate a plurality of branch metrics corresponding to the plurality of candidate vectors; and
select, based on said plurality of branch metrics, one of said plurality of candidate vectors to be output for use by another circuit.
2. The system of claim 1 , wherein:
said plurality of candidate vectors consists of M, an integer, candidate vectors; and
each of said plurality of symbol values to be searched corresponds to a respective one of M values of an M-QAM constellation.
3. The system of claim 1 , wherein, as part of said calculation of said plurality of branch metrics, said sequence estimation circuit is operable to convolve each of said plurality of candidate vectors with a plurality of tap coefficients to generate a corresponding plurality of candidate partial response vectors.
4. The system of claim 3 , wherein, as part of said calculation of said plurality of branch metrics, said sequence estimation circuit is operable to apply a non-linearity model to each of said plurality of candidate partial response vectors to generate a corresponding one of a plurality of partial response reconstructed candidates.
5. The system of claim 4 , wherein, as part of said calculation of said plurality of branch metrics, said sequence estimation circuit is operable to calculate a Euclidean distance between each of said plurality of partial response reconstructed candidates and a corresponding one of a plurality of vectors generated from a signal whose values are to be estimated by said sequence estimation circuit.
6. The system of claim 1 , wherein said sequence estimation circuit is operable to perform an inverse calculation to determine each of said plurality of filler values.
7. The system of claim 6 , wherein said inverse calculation uses a model of non-linearity experienced by a signal whose values are to be estimated by said sequence estimation circuit.
8. The system of claim 1 , wherein:
said sequence estimation circuit is operable to determine each of said plurality of filler values; and
for any particular one of said plurality of candidate vectors, determining a corresponding one of said plurality of filler values comprises insertion of a zero into said most-recent element of said particular one of said plurality of candidate vectors to generate a zero-filled vector.
9. The system of claim 8 , wherein, as part of said determination of said corresponding one of said plurality of filler values, said sequence estimation circuit is operable to determine a contribution of a most-recent symbol of a received signal based on said zero-filled vector.
10. The system of claim 9 , wherein, as part of said determination of said contribution of said most-recent symbol of said received signal, said sequence estimation circuit is operable to perform a slicing operation.
11. A method comprising:
in a sequence estimation circuit of a receiver:
generating a plurality of candidate vectors, wherein:
each of said plurality of candidate vectors comprises a plurality of elements ranging from a least-recent element to a most-recent element;
each of said plurality of candidate vectors contains, in an element other than its said most-recent element, a respective one of a plurality of symbol values to be searched; and
each of said plurality of candidate vectors contains, in its said most-recent element, a respective one of a corresponding plurality of filler values;
calculating a plurality of branch metrics corresponding to the plurality of candidate vectors; and
selecting, based on said plurality of branch metrics, one of said plurality of candidate vectors to be output for use by another circuit.
12. The method of claim 11 , wherein:
said plurality of candidate vectors consists of M, an integer, candidate vectors; and
each of said plurality of symbol values to be searched corresponds to a respective one of M values of an M-QAM constellation.
13. The method of claim 11 , wherein said calculating of said plurality of branch metrics comprises convolving each of said plurality of candidate vectors with a plurality of tap coefficients to generate a corresponding plurality of candidate partial response vectors.
14. The method of claim 13 , wherein said calculating said plurality of branch metrics comprises applying a non-linearity model to each of said plurality of candidate partial response vectors to generate a corresponding one of a plurality of partial response reconstructed candidates.
15. The method of claim 14 , wherein said calculating said plurality of branch metrics comprises calculating a Euclidean distance between each of said plurality of partial response reconstructed candidates and a corresponding one of a plurality of vectors generated from a signal whose values are to be estimated by said sequence estimation circuit.
16. The system of claim 11 , comprising performing an inverse calculation to determine each of said plurality of filler values.
17. The system of claim 16 , wherein said inverse calculation uses a model of non-linearity experienced by a signal whose values are to be estimated by said sequence estimation circuit.
18. The method of claim 11 , comprising:
determining each of said plurality of filler values, wherein for any particular one of said plurality of candidate vectors, determining a corresponding one of said plurality of filler values comprises inserting a zero into said most-recent element of said particular one of said plurality of candidate vectors to generate a zero-filled vector.
19. The method of claim 18 , wherein said determining said corresponding one of said plurality of filler values comprises determining a contribution of a most-recent symbol of a received signal based on said zero-filled vector.
20. The method of claim 19 , wherein said determining said contribution of said most-recent symbol of said received signal comprises performing a slicing operation.