Low-density parity-check codes with power reallocation

Power reallocation among the code symbols in a codeword is investigated for regular low-density parity-check (LDPC) codes. The motivation is that when error-control coding is employed, the received SNR need not be equally maintained for all symbols in a codeword because a certain number of errors within the error-correction capability can be corrected regardless of the received SNR for those erroneous symbols. We propose allocating no power to symbols experiencing a less favorable channel and reallocating the saved power to the remaining symbols experiencing a more favorable channel in order to receive them with an even higher reliability. At the receiver, the truncated symbols are tagged with erasures and errors-and-erasures correction decoding is performed. The simulation results show that the proposed power reallocation provides a power gain of 1.7-1.8 dB over equal allocation of power resources among the code symbols in a Rayleigh fading channel.