Performance analysis of LDPC codes for time-selective complex fading channels

Low-density parity-check (LDPC) codes are analyzed using density evolution techniques for a frequency-nonselective, time-selective fading channel where the fading affects both the amplitude and the phase of the transmitted signal. To aid the channel estimation process, pilot symbols are transmitted periodically. The performance of several message-passing estimation/decoding algorithms is investigated, and the optimal energy allocation between the pilot and coded symbols is evaluated. The results show that optimal power allocation can improve the performance by more than 1 dB for moderate channel dynamics. Finally, necessary and sufficient conditions for the convergence to error-free transmission are derived that take into account the channel coherence time.