Analysis and design of LDPC codes for time-selective complex-fading channels

Pilot-symbol-assisted (PSA) 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. The performance of several message-passing estimation/decoding receivers is investigated, and the optimal energy allocation between pilot and coded symbols is evaluated. Several message-passing estimation/decoding receivers are shown to fall under a single unifying description which leads to significant simplification of the analysis and design of the PSA LDPC codes and receivers. The immediate surprising result is that for the described class of receivers, the best codes for the case of perfect channel state information (CSI) at the receiver are also the best codes when no CSI is available at the receiver, regardless of the channel dynamics. A class of more elaborate receivers that perform iterative joint decoding/estimation is also presented and it is shown that codes designed specifically for these receivers provide an additional performance gain.