  As a typical example of bandwidth-efficient techniques, bit-interleaved coded
modulation with iterative decoding (BICM-ID) provides desirable spectral
efficiencies in various wireless communication scenarios. In this paper, we
carry out a comprehensive investigation on tail-biting (TB) spatially coupled
protograph (SCP) low-density parity-check (LDPC) codes in BICM-ID systems.
Specifically, we first develop a two-step design method to formulate a novel
type of constellation mappers, referred to as labeling-bit-partial-match (LBPM)
constellation mappers, for SC-P-based BICM-ID systems. The LBPM constellation
mappers can be seamlessly combined with high-order modulations, such as M-ary
phase-shift keying (PSK) and M-ary quadrature amplitude modulation (QAM).
Furthermore, we conceive a new bit-level interleaving scheme, referred to as
variable node matched mapping (VNMM) scheme, which can substantially exploit
the structure feature of SC-P codes and the unequal protection-degree property
of labeling bits to trigger the wave-like convergence for TB-SC-P codes. In
addition, we propose a hierarchical extrinsic information transfer (EXIT)
algorithm to predict the convergence performance (i.e., decoding thresholds) of
the proposed SC-P-based BICM-ID systems. Theoretical analyses and simulation
results illustrate that the LBPM-mapped SC-P-based BICM-ID systems are
remarkably superior to the state-of-the-art mapped counterparts. Moreover, the
proposed SC-P-based BICM-ID systems can achieve even better error performance
with the aid of the VNMM scheme. As a consequence, the proposed LBPM
constellation mappers and VNMM scheme make the SC-P-based BICM-ID systems a
favorable choice for the future-generation wireless communication systems.
