Modified branch metric for turbo codes using PSA technique in Rician fading channels

The authors study a log-maximum a posteriori (MAP) algorithm for use with turbo-coded systems incorporated with pilot-symbol-aided (PSA) transmission in the satellite mobile channels. The channel probability used in a conventional log-MAP algorithm assumes the channel is memoryless white Gaussian noise. If this same channel probability is used in the log-MAP algorithm for decoding turbo-coded signals with fading compensation in the satellite mobile channels, which are Rician-faded, performance degradation occurs. A new channel probability for use in the log-MAP algorithm to decode turbo-coded signals incorporated with PSA transmission on Rician fading channels is derived. Monte Carlo simulation results have shown that the proposed log-MAP algorithm can give substantial improvements in the bit-error-rate performances of a turbo-coded quarternary-phase-shift-keyed (QPSK) signal over the conventional log-MAP and other log-MAP algorithms