LDPC-Coded Modulations: Performance Bounds and a Novel Design Criterion

In this paper, we present a novel design criterion for low-density parity-check (LDPC)-coded modulations based on the concatenation of an LDPC code with a coded modulator (CM) tailored for the specific transmission channel. Although we use an analysis based on extrinsic information transfer (EXIT) charts, we focus on the bit error rate (BER) performance as opposed to the convergence threshold. First, we characterize the convergence behavior of the decoding process as a function of the LDPC code degree distributions. Then, the BER performance is accurately estimated by deriving upper and lower bounds as functions of the extrinsic information.