Spatially-Coupled Protograph LDPC-Coded Hierarchical Modulated BICM-ID Systems: A Promising Transmission Technique for 6G-Enabled Internet of Things

As a spectral-efficiency technique for unequal error
protection (UEP), hierarchical modulated (HM) bit-interleaved
coded modulation (BICM) with iterative decoding (ID) has attracted
interests in wireless communication community. In this paper, we
conduct an investigation on spatially coupled (SC) protograph lowdensity
parity-check (P-LDPC)-coded M-ary quadrature amplitude
modulation (QAM) HM-BICM-ID systems. We first develop an
information-theoretic methodology to calculate (log2M)=2 types of
constellation-constrained average mutual information (AMI), which
can be used to characterize the performance limits of different
layers in the HM-BICM systems. We further propose a two-stage
design approach to construct a novel type of constellations, called
as structural quadrant (SQ) constellations, and develop a quadrantbased
harmonic mean analysis to evaluate the non-feedback and
iterative-feedback asymptotic performance of the proposed constellations.
In addition, we conceive a performance-analysis tool,
referred to as multi-stream-based extrinsic information transfer (MSEXIT)
algorithm, for predicting the decoding thresholds of all
individual coded-bit streams in the proposed SC P-LDPC-coded
HM-BICM-ID systems. Simulation results not only agree well with
the theoretical analyses, but also indicate that the proposed SC PLDPC-
coded HM-BICM-ID systems are remarkably superior to the
state-of-the-art counterparts. Thereby, the proposed SC P-LDPCcoded
HM-BICM-ID systems are competent to provide diverse
quality-of-service (QoS) for future wireless applications, such as
6G-enabled Internet of Things (IoT).