Nested Root-Protograph LDPC-Coded Multilevel-Priority IR-HARQ Systems: A New Design for Multi-Stream Transmissions with Non-Ergodic Block Fading

To enhance the adaptability and performance of multi-stream transmissions over non-ergodic block fading (BF) channels, this paper studies a multilevel-priority incremental-redundancy hybrid ARQ (MP-IR-HARQ) system with nested root-protograph-based low-density parity-check (NRP-LDPC) codes. Specifically, we analyze the performance of traditional RP-LDPC codes and reveal that they are unable to achieve full diversity in the IR-HARQ system over non-ergodic BF channels. To address this limitation, we propose a design methodology to construct a family of NRP-LDPC codes having the full-diversity property, throughput-limit-approaching property, outage-limit-approaching performance, and rate compatibility tailored for the IR-HARQ system. Additionally, we incorporate a multilevel-priority design composed of the adaptive modulation, adaptive detection, and successive decoding into the traditional IR-HARQ framework. The designed MP-IR-HARQ system can support the transmission of multiple data streams while providing unequal error protection (UEP) across them. The outage-boundary analyses, throughput analyses, and word-error-rate (WER) simulations demonstrate that the proposed NRP-LDPC-coded MP-IR-HARQ system can not only significantly outperform prior-art counterparts over non-ergodic BF channels, but also enable the multi-data-stream-based UEP transmission.