Turbo-decoder synchronisation procedure: application to the CAS5093 integrated circuit

Recently, a new family of error correcting codes called turbo-codes, has been developed. An original auto-synchronisation method for these turbocodes is reported. This method ensures the timing synchronisation necessary to trigger the internal functions of turbo-decoders like interleaving or deinterleaving. This technique also takes into account elementary decoder synchronisation to remove any ambiguities about the position and/or the inversion of the symbols coming from the channel. The ambiguities due to demodulation are removed in the case of base band, BPSK and and PSK modulations. The two types of synchronisation are performed at the same time without any synchronisation word or any loss in the coding rate. A pseudo-syndrome concept for decoder supervision in the tracking phase is presented. The decoder is thus able to detect out-of-synchronisation reception and to start a new synchronisation search phase