Methods, apparatus, and systems for coding with constrained interleaving

Abstract

Serially-concatenated codes are formed in accordance with the present invention using a constrained interleaver. The constrained interleaver cause the minimum distance of the serial concatenated code to increase above the minimum distance of the inner code alone by adding a constraint that forces some or all of the distance of the outer code onto the serially-concatenated code. This allows the serially-concatenated code to be jointly optimized in terms of both minimum distance and error coefficient to provide significant performance advantages. Constrained interleaving can be summarized in that it: 1) uses an outer code that is a block code or a non-recursive convolutional code, and as such, there are multiple codewords present in the constrained interleaver, 2) selects a desired MHD, 3) selects an interleaver size and a set of predefined interleaver constraints to prevent undesired (low-distance) error events so as to achieve the desired MHD, and 4) performs uniform interleaving among the allowable (non-constrained) positions, to thereby maximize or otherwise improve the interleaver gain subject to the constraints imposed to maintain the desired MHD.

What we claim is: 
     
         1 . A communications apparatus, comprising:
 an outer encoder configured to transform a sequence of input bits to a sequence of outer encoded bits, wherein the sequence of outer-encoded bits is encoded in accordance with an outer code that is a member of the group consisting of a Reed Solomon code, a low density parity check (LDPC) code, a block code and a non-recursive convolutional code;   a constrained interleaver that is configured to implement a permutation function to permute the order of the outer-encoded bits to produce a constrained-interleaved sequence of outer-encoded bits, wherein the permutation function corresponds to a reordering of the outer-encoded bits subject to one or more pre-defined constraints; and   a signal mapper configured to transform the constrained-interleaved sequence of outer-encoded bits to a sequence of bit interleaved coded modulation symbols, wherein each bit interleaved coded modulation symbol corresponds to a 2 r -ary symbol, where r is an integer, and r>1;   wherein the outer code has a minimum distance of d o  and the pre-defined constraints are selected to ensure that at least a pre-specified number of bit interleaved coded modulation symbols will be different for any two valid transmitted sequences.   
     
     
         2 . The communications apparatus of  claim 1 , wherein the pre-specified number of bit interleaved coded modulation symbols is equal to d o . 
     
     
         3 . The communications apparatus of  claim 1 , wherein the permutation function is pseudo randomly selected from among a set of permutation functions that meet the one or more pre-defined constraints. 
     
     
         4 . The communications apparatus of  claim 1 , wherein the permutation function is implemented using a row-column structure with r number of rows. 
     
     
         5 . The communications apparatus of  claim 4 , wherein the constrained interleaver ensures that a pre-specified number of outer encoded coded bits of each outer encoded codeword are placed into different columns of the row-column structure. 
     
     
         6 . The communications apparatus of  claim 5 , wherein pre-specified number is equal to d o . 
     
     
         7 . The communications apparatus of  claim 5 , wherein the constrained interleaver places outer encoded bits into pseudo randomly selected locations from among the possible remaining unconstrained locations in the row-column structure that meet the one or more pre-defined constraints. 
     
     
         8 . The communications apparatus of  claim 1 , wherein each 2 r -ary symbol corresponds to a phase shift keyed (PSK) symbol. 
     
     
         9 . The communications apparatus of  claim 8 , wherein r=3 and each 2 r -ary symbol corresponds to an 8-PSK symbol. 
     
     
         10 . The communications apparatus of  claim 1 , wherein the outer code corresponds to a member of the group consisting of an single parity check (SPC) code, a Hamming code, and a shortened Hamming code. 
     
     
         11 . A method for use in a communications apparatus, the method comprising:
 transforming a sequence of input bits to a sequence of outer encoded bits, wherein the sequence of outer-encoded bits is encoded in accordance with an outer code that is a member of the group consisting of a Reed Solomon code, a low density parity check (LDPC) code, a block code and a non-recursive convolutional code;   reordering, in accordance with a permutation function that is subject to one or more pre-defined constraints, the order of the outer-encoded bits to produce a constrained-interleaved sequence of outer-encoded bits; and   transforming the constrained-interleaved sequence of outer-encoded bits to a sequence of bit interleaved coded modulation symbols, wherein each bit interleaved coded modulation symbol corresponds to a 2 r -ary symbol, where r is an integer, and r>1;   wherein the outer code has a minimum distance of d o  and the pre-defined constraints are selected to ensure that at least a pre-specified number of bit interleaved coded modulation symbols will be different for any two valid transmitted sequences.   
     
     
         12 . The communications apparatus of  claim 10 , wherein the pre-specified number of bit interleaved coded modulation symbols is equal to d o . 
     
     
         13 . The communications apparatus of  claim 10 , wherein the permutation function is pseudo randomly selected from among a set of permutation functions that meet the one or more pre-defined constraints. 
     
     
         14 . The communications apparatus of  claim 10 , wherein the permutation function is implemented using a row-column structure with r number of rows. 
     
     
         15 . The communications apparatus of  claim 14 , wherein the constrained interleaver ensures that a pre-specified number of outer encoded coded bits of each outer encoded codeword are placed into different columns of the row-column structure. 
     
     
         16 . The communications apparatus of  claim 15 , wherein pre-specified number is equal to d o . 
     
     
         17 . The communications apparatus of  claim 14 , wherein the constrained interleaver places outer encoded bits into pseudo randomly selected locations from among the possible remaining unconstrained locations in the row-column structure that meet the one or more pre-defined constraints. 
     
     
         18 . The communications apparatus of  claim 10 , wherein each 2 r -ary symbol corresponds to a phase shift keyed (PSK) symbol. 
     
     
         19 . The communications apparatus of  claim 18 , wherein r=3 and each 2 r -ary symbol corresponds to an 8-PSK symbol. 
     
     
         20 . The communications apparatus of  claim 10 , wherein the outer code corresponds to a member of the group consisting of an single parity check (SPC) code, a Hamming code, and a shortened Hamming code.