Impact of Bit-Channel Reliability Disparity on the Performance of LDPC Codes

This work investigates Low-Density Parity-Check (LDPC) codes in short block-length regimes, which are highly relevant for future communication systems. Although LDPC codes are known for their near-capacity performance, their efficiency can be limited when the code length is reduced, particularly in scenarios involving heterogeneous bit-channel reliabilities. Recently, Smith et al. have considered an LDPC coding technique to improve the error performance by exploiting the unequal bit-channel reliabilities. Reliability classes for variable nodes were defined, with constraints so the most reliable bits support the least reliable ones. The present study reveals that there is an optimum gap between these two extreme reliabilities that maximizes the performance gain. Initial simulation results showing this principle are presented, shedding light on short LDPC-Polar code concatenation.