Zhaojie Yang

This paper is concerned with sparse code multiple access (SCMA) with protograph-based low-density parity-check (P-LDPC) codes over Rayleigh fading channels. To be specific, we first propose a two-step design method consisting of both low-density factor graph (LDFG) and energy-based constellation superposition (ECS) principles to construct a new type of non-uniform codebooks (CBs), which have superior robustness against inter-user interference. We also develop a new segment-wise interleaved transmission (SWIT) scheme, which features a systematic optimization among repetition coding, resource mapping, and cross-slot data coupling, to further improve the performance of P-LDPC-coded SCMA. Additionally, we conceive a decoding-threshold-guided multi-objective optimization (DT-MOO) method to construct protograph-based enhanced multi-user codes (EMUCs), which exhibit excellent error-rate performance under both turbo and non-turbo decoding compared to traditional single-user and existing multi-user codes. Theoretical and simulated results validate the superiorities of proposed non-uniform SCMA scheme with SWIT and EMUCs compared to state-of-the-art benchmarks. Owing to the above advantages, the proposed designs are competent to provide massive connectivity and energy-efficient transmission for simultaneous wireless information and power transfer (SWIPT) applications in 6G networks.

The study of anytime codes over non-ergodic block-fading (BF) channels remains largely unexplored. To address this gap, we propose a novel root-protograph-based anytime (RP-anytime) coding framework and develop modified density evolution (DE) equations. Leveraging these equations, we introduce two performance metrics to evaluate the asymptotic behavior of RP-anytime codes under the assumption of infinite frame length: the average asymptotic bit error rate (BER), which characterizes anytime reliability, and the anytime outage region, which reflects the code’s ability to achieve full diversity. Using these metrics, we analyze the performance of the proposed RP-anytime codes and compare them with both root-protograph LDPC codes and conventional anytime codes. The results demonstrate the superiority of the RP-anytime structure in terms of reliability and diversity over non-ergodic BF channels. Furthermore, we employ a multi-objective differential evolution (MODE) algorithm to design optimized RP-anytime codes. Simulation results confirm that the newly designed codes achieve excellent anytime reliability, full diversity, and near-outage-limit error performance—significantly outperforming prior-art root-protograph LDPC codes and anytime codes.

This letter investigates the joint design of constellation mapping and protograph low-density parity-check (PLDPC) code for power-domain non-orthogonal multiple access (PD-NOMA) downlink systems. Specifically, we first propose a multi-priority design method to generate a type of symmetric-Hamming (SH) constellation mappings, and then verify their merits through a modified harmonic mean analysis. Furthermore, we construct a new type of non-punctured and punctured PLDPC codes by a mutual-information-guided threshold estimation to resist the inter-user interference. Simulation results demonstrate that the proposed designs achieve better performance than the existing benchmark schemes over Rayleigh fading channels.

This letter introduces an orthogonal frequency division multiplexing differential chaos shift keying (OFDM-DCSK) waveform for communication-centric integrated sensing and communication (ISAC), which simultaneously enables reliable noncoherent communication and robust sensing capabilities. To further address the high peak-to-average power ratio (PAPR) issue of OFDM-based waveforms, a Riemann matrix–based group selected mapping (G-SLM) scheme is incorporated to reduce PAPR under ISAC sensing constraints. The proposed G-SLM achieves significant PAPR improvement compared with conventional SLM methods while requiring no side information at the receiver. Closed-form expressions are derived for the ambiguity function and bit error rate (BER) in the proposed systems with and without G-SLM. Both analytical and simulation results verify that the OFDM-DCSK waveform integrated with G-SLM maintains communication reliability and sensing accuracy compared to the conventional OFDM-DCSK waveform, while reducing the PAPR with only slight main lobes broadening and modest side lobes elevation. These features make the proposed scheme particularly suitable for ISAC applications in complex wireless environments under low and moderate mobility conditions.

This work investigates iterative receiver and code design for protograph-coded overloaded sparse code multiple access (SCMA) systems. As a type of non-orthogonal multiple access (NOMA) technology, SCMA relies on an iterative detection and decoding (IDD) receiver to eliminate inter-user interference and channel noise. However, the existing IDD receiver requires a larger number of iterations to achieve successful convergence. To overcome this limitation, we propose a ranked successive detection and decoding (R-SDD) receiver, which dynamically allocates computational resources to bottleneck users with the lowest reliability. This approach accelerates information convergence and improves error performance without increasing overall complexity. Moreover, we introduce a factor-graph-based (FG) interleaving scheme for the proposed SCMA systems, which outperforms the existing interleaver. To further enhance the error-correction capability for overloaded multi-user scenarios, we propose a new protograph design principle tailored for SCMA systems and develop two high-performance protograph low-density parity-check (LDPC) codes, achieving over 0.3 dB improvement compared with the state-of-the-art alternatives. Owing to the salient advantages of the new iterative receiver and code design, the proposed SCMA system offers a promising solution for future high-bandwidth, high-reliability communication networks.

This paper studies the design of protograph low-density parity-check (PLDPC) coded sparse code multiple access (SCMA) systems with power-imbalanced multi-level decoding (PI-MLD) scheme. Specifically, by exploiting the protograph extrinsic information transfer (PEXIT) analysis, we first design two enhanced PLDPC (E-PLDPC) codes with the lowest decoding thresholds for the SCMA system over a Rayleigh fading channel. Furthermore, we conceive a new PI-MLD scheme, which is composed of level classification, power-imbalanced allocation (PIA), and power-oriented MLD, to further eliminate the SCMA inter-user interference. In particular, level classification and PIA can assign different powers to the users accessing the same resource, while the power-oriented MLD implements the sequential decoding according to a high-to-low power order among users. Analyses and simulation results show that the SCMA system with the proposed E-PLDPC codes and PI-MLD scheme is significantly superior to the prior art.