Decision directed coherent detection of 16-QAM on fading channels

A coherent detector for differentially encoded 16-QAM on Rayleigh fading channels is presented. An FIR-filter with previous received samples as the input delivers an MMSE estimate of the fading process, providing the carrier reference needed for coherent detection. This estimation is assisted by previous decisions. The bit error performance of the detector proposed is analysed for the first-event bit error case, providing a performance lower bound for the BER in more realistic cases. According to the analysis, the proposed detector exhibits a performance degradation of only 8 dB compared to an ideal coherent detector for 16-QAM at a BER of 1% for a normalized Doppler frequency of 0.05. This is better than other published results than we know of. The impact of error propagation is investigated by simulations. A two branch diversity detector, using the same channel estimation method, is also proposed. Simulated performance for this case is also shown.