Adaptive SNR turbo decoding algorithm and stop criterion

The sensitivity of the iterative maximum a posteriori probability (MAP) decoder to the initial channel values is investigated and a simple adaptive signal-to-noise (SNR) algorithm operating within the delta variances from two MAP decoders is proposed. The exact SNR values estimated from the turbo decoders are considered. It can bring the initialization of channel values towards optimization. Therefore, we may improve the BER by about 0.3 dB with a simple additional lookup table from the conventional BCJR decoder. Furthermore, since the closest SNR values are estimated, the proposed algorithm can be exploited to efficient make stop criterion for reducing the delay and computation time.