Design and Analysis of Delayed Bit-Interleaved Coded Modulation with LDPC Codes

TL;DR

This paper presents an optimized design for delayed bit-interleaved coded modulation with LDPC codes, enhancing spectral efficiency and error protection by leveraging capacity properties and joint code-interleaver optimization.

Contribution

It introduces a novel delay scheme optimization and LDPC code design methodology for DBICM, improving performance over traditional BICM systems.

Findings

Significant spectral efficiency gains with optimized delay schemes.

Enhanced LDPC code performance through joint design and capacity-aware optimization.

Demonstrated superior error correction compared to standard BICM systems.

Abstract

This paper investigates the design and performance of delayed bit-interleaved coded modulation (DBICM) with low-density parity-check (LDPC) codes. For Gray labeled square $M$-ary quadrature amplitude modulation (QAM) constellations, we investigate the optimal delay scheme with the largest spectrum efficiency of DBICM for a fixed maximum number of delayed time slots and a given signal-to-noise ratio. When analyzing the capacity of DBICM, we find two important properties: the capacity improvement due to delayed coded bits being mapped to the real and imaginary parts of the transmitted symbols are independent of each other; a pair of delay schemes with delayed coded bits having identical bit-channel capacity lead to equivalent DBICM capacity. Using these two properties, we efficiently optimize the delay scheme for any uniform Gray-QAM systems. Furthermore, these two properties enable efficient LDPC code designs regarding unequal error protection via bit-channel type classifications. Moreover, we use protograph-based extrinsic information transfer charts to jointly optimize degree distributions and channel assignments of LDPC codes and propose a constrained progressive edge growth like algorithm to jointly construct LDPC codes and bit-interleavers for DBICM, taking distinctive bit-channel's capacity into account. Simulation results demonstrate that the designed LDPC coded DBICM systems significantly outperform LDPC coded BICM systems.