Threshold of Protograph-Based LDPC Coded BICM for Rayleigh Fading

Abstract

Protograph-based bit-interleaved coded modulation (BICM) provides an elegant way of designing coded modulation over Rayleigh faded channels, however, to date the available designs have been limited to specific modulations and the corresponding decoding thresholds have not been known for Rayleigh faded channels. In this work, we present a simple method for designing protograph-based BICM that is general and applies to any modulation, and furthermore we calculate the iterative decoding thresholds of the protograph codes while mapped to higher order modulations. This general coding framework can support not only multiple rates but also adaptive modulation. We report that certain families of protograph codes achieve a threshold within a gap of approximately 0.2 − 0.4 dB of BICM capacity limit across a wide range of rates and modulations.

Improving soft FEC performance for higher-order modulations via optimized bit channel mappings

“…The approaches in [15][16][17] can be recovered by considering only nonfractional assignments, i.e., a i, j ∈ {0, 1}. In that case, VNs of the original protograph [15,16] or an intermediate protograph [17] are directly assigned to the modulation bits.…”

“…The approach proposed here relies on a modified P-EXIT analysis which allows for a fractional allocation between protograph nodes and modulation bits. This approach is, to the best of our knowledge, novel in the context of protograph-based codes and different from the approaches described in [15][16][17]. In particular, a fractional allocation allows for an unrestricted matching of protographs and modulation formats and additionally does not suffer from an increased design complexity due to a larger intermediate protograph.…”

“…This idea is extended in [16], where the authors exhaustively search over all possible nonequivalent connections between protograph nodes and modulation bits showing performance improvements over VDMM. As pointed out in [17], the above approaches are somewhat restrictive in the sense that only certain protographs can be used with certain modulation formats. A more flexible approach is proposed in [17], which is in principle suitable for any protograph structure and modulation but relies on a larger intermediate protograph.…”

“…As pointed out in [17], the above approaches are somewhat restrictive in the sense that only certain protographs can be used with certain modulation formats. A more flexible approach is proposed in [17], which is in principle suitable for any protograph structure and modulation but relies on a larger intermediate protograph.…”

Interleaver Design for Small-Coupling-Length Spatially Coupled Protograph LDPC-Coded BICM Systems Over Wireless Fading Channels

“…In PLDPC-coded BICM systems, the interleaver design can be considered as another important technique to enable additional performance gains by exploiting the unequal-error-protection (UEP) characteristic of high-order modulations. For instance, an interleaving scheme, called variable-degree matched mapping (VDMM), has been proposed for Gray-mapped BICM systems over additive white Gaussian noise (AWGN) channels [10] and Rayleigh fading channels [11]. Furthermore, an exhaustive-search-based method has been incorporated into VDMM so as to find the best permutation between the variable nodes (VNs) and the labeling bit positions [12].…”