Serial turbo trellis coded modulation using a serially concatenated coder
Serial concatenated trellis coded modulation (SCTCM) includes an outer coder, an interleaver, a recursive inner coder and a mapping element. The outer coder receives data to be coded and produces outer coded data. The interleaver permutes the outer coded data to produce interleaved data. The recursive inner coder codes the interleaved data to produce inner coded data. The mapping element maps the inner coded data to a symbol. The recursive inner coder has a structure which facilitates iterative decoding of the symbols at a decoder system. The recursive inner coder and the mapping element are selected to maximize the effective free Euclidean distance of a trellis coded modulator formed from the recursive inner coder and the mapping element. The decoder system includes a demodulation unit, an inner SISO (soft-input soft-output) decoder, a deinterleaver, an outer SISO decoder, and an interleaver.
1. A method, comprising:
receiving a set of input information, wherein the set of input information corresponds to a stream of symbols transmitted by an encoder system configured to perform a trellis coded modulation (TCM), wherein the TCM includes an inner encoding and a mapping, wherein the inner encoding encodes a first set of data to generate an intermediate set of data according to a rate 1 recursive code, wherein the mapping generates the stream of symbols from the intermediate set of data according to a first map, wherein the rate 1 recursive code and the first map maximize the effective free Euclidean distance of the inner encoding;
performing a first SISO decoding operation on the set of input information to generate a first set of decoded information, wherein the first SISO decoding operation is for reversing the effects of the TCM encoding of the encoder system;
generating a deinterleaved version of the first set of decoded information; and
performing a second SISO decoding operation on the deinterleaved version of the first set of decoded information to generate a set of output information.
2. The method of claim 1 , further comprising:
generating, from the set of output information, an estimate of original data bits in the first set of data.
3. The method of claim 2 , wherein performing the second SISO decoding operation also generates a first set of feedback information;
wherein the method further comprises:
interleaving the first set of feedback information to generate a second set of feedback information;
repeating the first and second SISO decoding operations, wherein the repeated first SISO decoding operation uses the second set of feedback information and the repeated second SISO decoding operation uses a deinterleaved version of decoded information generated by the repeated first SISO decoding operation.
4. The method of claim 1 , wherein the symbols of said stream are symbols of a quadrature amplitude modulation (QAM) constellation having 2 2m points, wherein m is greater than one.
5. The method of claim 1 , wherein the symbols of said stream correspond to a phase shift keying (PSK) modulation having a constellation with 2 m points, wherein m is greater than one.
6. The method of claim 1 , wherein the encoder system is configured to perform an outer encoding in addition to said TCM, wherein the outer encoding encodes original data bits to produce outer coded data, wherein the first set of data is an interleaved version of the outer coded data, wherein the second SISO decoding operation is based on the outer encoding.
7. The method of claim 6 , wherein the outer encoding has rate b/(b+1), wherein b is an integer greater than or equal to one.
8. An apparatus, comprising:
a inner SISO decoding unit configured to receive, at an input, input information and generate intermediate decode information therefrom, wherein the input information corresponds to a stream of symbols transmitted by an encoder system configured to perform a trellis coded modulation (TCM), wherein the TCM includes an inner encoding and a mapping, wherein the inner encoding encodes a first set of data to generate an intermediate set of data according to a rate 1 recursive code, wherein the mapping generates the stream of symbols from the intermediate set of data according to a first map, wherein the rate 1 recursive code and the first map maximize the effective free Euclidean distance of the inner encoding, wherein the inner SISO decoding unit is configured according to the TCM of the encoder system, and wherein the inner SISO decoding unit is configured to reverse the effects of the TCM encoding;
a deinterleaver unit configured to generate a deinterleaved version of the intermediate decode information; and
an outer SISO decoding unit configured to generate output information from the deinterleaved version of the intermediate decode information.
9. The apparatus of claim 8 , wherein the apparatus is configured to generate, from the output information, an estimate of original data bits in the first set of data.
10. The apparatus of claim 9 , wherein the outer SISO decoding unit is configured to generate feedback information, wherein the apparatus further comprises an interleaver unit configured to generate an interleaved version of the feedback information.
11. The apparatus of claim 10 , wherein the inner SISO decoding unit and the outer SISO decoding unit are configured to generate the estimate by performing iterative decoding operations.
12. The apparatus of claim 11 , wherein the inner SISO decoding unit is configured to generate subsequent sets of intermediate decode information from input information and interleaved versions of the feedback information.
13. The apparatus of claim 8 , wherein the symbols of said stream are symbols of a quadrature amplitude modulation (QAM) constellation having 2 2m points, wherein m is greater than one.
14. The apparatus of claim 8 , wherein the symbols of said stream correspond to a phase shift keying (PSK) modulation having a constellation with 2 m points, wherein m is greater than one.
15. The apparatus of claim 8 , wherein the encoder system is configured to perform an outer encoding in addition to said TCM, wherein the outer encoding encodes original data bits to produce outer coded data, wherein the first set of data is an interleaved version of the outer coded data, wherein a SISO decoding operation performed by the outer SISO decoder unit is based on the outer encoding.
16. The apparatus of claim 15 , wherein the outer encoding has rate b/(b+1), wherein b is an integer greater than or equal to one.
17. A decoding apparatus, comprising:
a first soft-input soft-output (SISO) module configured to receive input information corresponding to symbols transmitted by an encoding apparatus, wherein the encoding apparatus is configured to perform an outer encoding on source data in order to generate first intermediate source data, and to perform an inner trellis coded modulation (TCM) on an interleaved version of the first intermediate source data to generate the transmitted symbols, wherein the first SISO module is configured to compute intermediate decode information from the input information based on an inner trellis used by said inner TCM of the encoder system, and wherein the first SISO module is configured to reverse the effects of the TCM encoding; and
a second SISO module configured to compute output information from a deinterleaved version of the intermediate decode information based on an outer trellis used by the outer encoding of the encoding system;
wherein the inner TCM performed by the encoder system includes an inner encoding and a mapping, wherein the inner encoding encodes the interleaved version of the first intermediate source data to generate second intermediate source data according to a rate 1 recursive code, wherein the mapping generates the output symbols from the second intermediate source data according to a first map, wherein the rate 1 recursive code and the first map maximize the effective free Euclidean distance of the inner TCM.
18. The decoding apparatus of claim 17 , further comprising:
an interleaver module; and
a deinterleaver module configured to generate the deinterleaved version of the intermediate decode information;
wherein the second SISO module is configured to generate feedback information from the deinterleaved version of the intermediate decode information; and
wherein the interleaver module is configured to generate an interleaved version of the feedback information, and wherein the first SISO module is further configured to generate the intermediate decode information from the interleaved version of the feedback information.
19. The decoding apparatus of claim 18 , wherein the inner trellis is a 4-state trellis.
20. The decoding apparatus of claim 18 , wherein the inner trellis is a 2-state trellis.