Interleavers for digital communications

摘要

An improved method and apparatus for interleaving block codes exploits helical symmetry whereby correspondingly positioned code symbols of code words of length n interleaved to depth i, i<n, are separated on the channel by alpha i+ beta symbol intervals where 1+ gamma >/=i is averaged over the i correspondingly positioned symbols and alpha and ¦ beta ¦ are integers >1. The requirement for synchrony is reduced to a period counted modulo n instead of mod (nxi). For the case i=n-1, the total interleaving delay is reduced to 2(n-1)n and phase dependence of burst error onset is minimized. The performance of the de-interleaver is enhanced through a pseudo fade detector implemented by creating erasures prior to decoding, at certain positions for codewords subsequent to confirmed error. Synchronization of interleaver and de-interleaver is accomplished in apparatus which inspects all c contiguous bit patterns corresponding to a c bit synch symbol. To each c contiguous bit pattern of the data stream there is associated a probability counter for incrementing when the synch pattern is detected and decremented otherwise. Maximum probability establishes synch.