Interleaver pruning for construction of variable length turbo codes

The issue of pruning (i.e., shortening) a given interleaver in a parallel concatenated convolutional code (PCCC or turbo codes) employing recursive systematic convolutional (RSC) constituent codes has been addressed. The encoder uses two RSC codes coupled with an interleaver represented by the permutation vector. Since the encoding and decoding delay associated with turbo codes are essentially dominated by the block length (interleaver length), it is of considerable practical interest to be able to modify it in order to obtain a variable length block code. Most other interleaver construction techniques do not have a recursive build nature and as a consequence, each time the interleaver length is modified, the interleaver itself must be redesigned. In the case of turbo codes, it is desirable to identify a technique that would allow any interleaver performing a given permutation to be reduced in size with gradual performance degradation of the resulting PCCC, but without the need for changing almost completely the operation of the interleaver.