Computing the free distance of turbo codes and seriallyconcatenated codes with interleavers: algorithms and applications

摘要

We present a new algorithm for computing the free distancendfree of parallel and serially concatenated codes withninterleavers, the parameter that dominates the code performance at verynhigh signal-to-noise ratios (SNRs). The knowledge of dfreenallows one to analytically estimate the error floor, which may preventnthe use of concatenated codes in applications requiring very low errornrates. The algorithm is based on the new notion of constrained subcodes,nand permits the computation of large distances for large interleaversnwithout a constraint on the input sequence weight (e.g., up tondfree=40 for a rate-1/3 turbo code with interleaver lengthnN=3568). Applications to practical cases of relevant interest, i.e., (1)nthe new Consultative Committee for Space Data Systems (CCSDS) standardnfor deep-space telemetry and (2) the new UMTS/3GPP standard fornthird-generation personal communications, are presented for the firstntime. Other related aspects, like a study on the free distancendistribution of turbo codes with small/medium interleaver length, and ancomparison between parallel and serial concatenation behavior, are alsondiscussed