The proliferation of smart vehicles and resource-hungry applications has imposed challenges to on-board systems. By exploiting the clustered vehicles in neighbor-following network (NFN), the multi-hop vehicular network (MHVN) enables cooperative communication among multiple vehicles, making it promising for vehicular edge computing (VEC). Nonetheless, to the best of our knowledge, the joint task offloading and resource allocation strategies in MHVN remains open due to challenges arising from the prevalence of link disruptions, the substantial variability in channel states, and the limited computational resource. With the above considerations, in this work, the task offloading and resource allocation are jointly optimized in the MHVN to minimize the offloading cost and maximize the task completion rate (TCR). However, the optimization problem turns out to be a mixed integer nonlinear programming (MINLP) problem. To this end, the problem is decoupled into two subproblems, which are solved by graph theory and improved water-filling algorithm, respectively. Furthermore, an iterative optimization algorithm is designed to mitigate the impact of the relaxation of delay constraints. Simulations are conducted to confirm the effectiveness of the proposed scheme.

Chaotic waveforms, characterized by their noise-like properties and potential security advantages, have emerged as a promising solution for physical layer security (PLS) in wireless communication schemes. However, conventional differential chaos shift keying (DCSK) schemes suffer from limitations such as low data rate, energy inefficiency, and vulnerability to frequency-selective fading (FSF) channels. To address these challenges, this paper proposes a new matrix index technique for multi-carrier DCSK scheme, referred to asMIT-MC-DCSKscheme, tailored for robust and secure transmission over FSF channels. The proposed MIT-MC-DCSK scheme enables time-frequency diversity to mitigate the negative effect of fading while enhancing bit error rate (BER) performance. Theoretical BER expressions of the proposed scheme are rigorously derived over FSF channels, which are validated by extensive Monte Carlo simulations. Experimental results demonstrate that the proposed MIT-MC-DCSK scheme achieves superior BER performance and higher transmission efficiency than the state-of-the-art benchmark schemes. Furthermore, the proposed MIT-MC-DCSK scheme significantly reduces information leakage and improves secrecy capacity by leveraging matrix reconstruction technique, making it resilient against eavesdropping. Thanks to these advancements, the MIT-MC-DCSK scheme appears to be a robust candidate for secure and reliable communication in FSF scenarios.

In this paper, we propose an integrated sensing and backscatter communication system utilizing high scanning-rate slot array antennas (SAAs) in a frequency-diverse configuration, leveraging an inverse scattering approach. This system employs a frequency diversity scheme to facilitate rapid spatial data acquisition, significantly outperforming traditional mechanical and electronic scanning methods in terms of speed and cost-efficiency. The proposed integrated system achieves simultaneous localization, identification, and backscatter communication of tags within cluttered environments. Our approach analyzes backscatter process based on the structural and antenna modes of tags, as well as the presence of clutter scatterers. By modulating the tags between open-circuit and short-circuit states, we effectively extract the structural and antenna mode components. The structural mode component allows us to sense both the tags and the surrounding clutter scatterers, while the antenna mode component is used for precise tag identification by incorporating both inverse scattering and compressive sensing (CS) algorithms. During these processes, channel state information (CSI) is gathered through the antenna mode, enhancing the backscatter communication capability of the system. Additionally, the efficacy of backscatter communication is assessed using the bit error rate (BER) with the maximum ratio combining (MRC) technique. Simulations and experimental results demonstrate that our proposed system can accurately sense and identify tags amidst clutter scatterers while maintaining robust backscatter communication over a 40 MHz bandwidth within the 3.98-4.02 GHz range. These results highlight the significant advantages of employing the proposed frequency-diverse antennas and the inverse scattering approach in integrated backscatter communication and sensing applications.

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.

Bit-interleaved coded modulation with iterative decoding (BICM-ID) is a key technology enabling communication systems to realize high-throughput and high-reliability. In contrast to previous studies focused exclusively on uniformly distributed sources, this work investigates irregular mapping (IM)-based BICM-ID systems for sources with non-uniform distributions. First, a density evolution (DE) algorithm based on Gaussian weighted mixture approximation (GWMA) is put forward to estimate the convergence performance of the IM-BICM-ID systems with non-uniform sources, where the probability density function of the log-likelihood ratio messages output from the bit-level channels in this system is neither Gaussian nor symmetric. Then, by employing the GWMA-DE algorithm and the achievable system rates analysis, a design strategy for optimal IM labelings is established, which utilizes the inherent redundancy in non-uniform sources to achieve shaping gains. Furthermore, channel codes tailored to the proposed IM labelings are designed to further improve the bit error rate performance. Both analytical results and simulations indicate that the proposed labelings and codes outperform existing counterparts in IM-BICM-ID systems with non-uniform sources.

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 aranked 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 afactor-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 proposes an innovative framework that integrates electromagnetic inverse scattering with improved quadrature spatial modulation (IQSM) to simultaneously accomplish sensing, identification, and backscatter communication. Specifically tailored for energy- and spectrum-efficient wireless operations in highly cluttered environments, the proposed system employs distinct load impedance modulation at the tags to effectively separate structural and antenna mode signatures. Structural mode signals are processed using inverse scattering combined with compressive sensing techniques, enabling precise localization of both tags and surrounding clutter. Concurrently, antenna mode signals are utilized for accurate tag identification. In addition, the antenna mode enables the acquisition of the reliable channel state information (CSI), facilitating the integration of IQSM schemes into the backscatter communication module. Furthermore, we present a theoretical analysis by deriving the bit error probability (BEP) for the proposed system. The proposed system is validated through a proof-of-concept experimental setup consisting of transmit and receive arrays, each configured as a 3×3 uniform linear antenna array (ULA). Both simulation and experimental results confirm that the inverse scattering-based approach achieves high-precision sensing and accurate identification of tags individually or in combination. Additionally, the integration of IQSM significantly enhances spectral efficiency (SE) and data throughput, compared with the state-of-the-art systems that do not incorporate spatial modulation (SM) techniques. These findings highlight the effectiveness and practical viability of the proposed integrated sensing and communication system for challenging clutter-rich scenarios.

The escalating storage density of three-dimensional (3D) NAND flash memory introduces heightened channel noise, significantly degrading channel quality and exacerbating the raw bit error rate (RBER). The fixed and unchangeable code rate of the traditional global coupled low-density-parity-check (GC-LDPC) codes fails to address the performance mismatch arising from the stochastic temporal and spatial fluctuations in 3D NAND flash channels. To address the above issue efficiently, in this paper we investigate high-rate-compatible LDPC codes in 3D NAND flash memory. Firstly, we analyze the flash memory channel characteristics from the FPGA test platform and model the 3D triple-level cell (TLC) NAND flash channel. Subsequently, we propose a novel High-Rate-Compatible Algebraic GC-LDPC (HRC-A-GC-LDPC) code and conduct a comprehensive theoretical analysis of its structure and performance. Specifically, the HRC-A-GC-LDPC code features an information bit length of 4 KB and supports dynamic adjustment to multiple code rates, enabling it to match the varying characteristics of 3D NAND flash channels. This paper also examines and analyzes various construction methods for the HRC-A-GC-LDPC code corresponding to different column weights (CWs), providing insights into its design flexibility. Simulation results demonstrate that, in 3D TLC NAND flash memory, the proposed HRC-A-GC-LDPC code outperforms conventional GC-LDPC codes in both error correction capability and extended memory lifetime, validating its suitability for high-density 3D NAND flash applications.

LoRa is a widely recognized modulation technology in the field of low power wide area networks (LPWANs). However, the data rate of LoRa is too low to satisfy the requirements of Internet of Things applications. To address this issue, we propose a novel high-data-rate LoRa scheme based on the spreading factor index (SFI). In the proposed SFI-LoRa scheme, the starting frequency bin of a chirp signal is used to transmit information bits, while the combinations of spreading factors are exploited as a set of indices to convey additional information bits. Moreover, the theoretical symbol error rate, data rate, transmission throughput, complexity and energy efficiency of the proposed SFI-LoRa scheme are carefully analyzed. Simulation results not only verify the accuracy of our theoretical analysis, but also demonstrate that the proposed SFI-LoRa scheme can improve the transmission throughput of existing LoRa schemes without sacrificing the BER performance over additive white Gaussian noise, Rayleigh fading, and multipath flat-fading channels. Therefore, the proposed SFI-LoRa scheme is a potential solution for applications requiring a high data rate in the LPWAN domain.

In unsourced random access (URA) system, user pilot collisions are a key challenge when multiple users select identical pilot sequences, leading to poor activity detection and decoding performance. To address this issue, this paper develops a two-stage segmented pilot (TSSP) design for collision-resilient URA in massive multiple-input multiple-output (MIMO) system. The proposed scheme enables a substantial enlargement of the effective pilot space without increasing the physical codebook size and detection complexity. First, we construct a probabilistic collision model by leveraging the birthday-problem analogy, which provides theoretical characterization of collision events and closely matches the simulation results. Second, we propose a segmented pilot mapping and decoding framework in which the pilot bits are divided into two interconnected parts linked by common pilot bits. This structured segmentation allows the system to resolve partial collisions and reduce missed detection in high-density access scenarios. Third, we develop a joint-covariance linear minimum mean square error (JC-LMMSE) scheme that exploits the segmented pilot structure to suppress pilot contamination and improve estimation accuracy. Monte Carlo simulations show that the proposed TSSP framework achieves up to 3.5 dB gain in collision scenarios and approximately 1 dB gain in collision-free cases over existing methods, while maintaining comparable computational complexity.

The growth of maritime activities has boosted the demand for efficient marine communications and computation offloading. Mobile edge computing (MEC)-powered space-air–ground-sea integrated network (SAGSIN) is a promising solution to satisfy these demands. To the best of our knowledge, the existing research on high altitude platforms (HAPs) in SAGSIN remains open. To exploit the HAPs’ advantages of facilitating communication at shorter distances and more stable computing services than terrestrial base stations, this work considers multi-HAP-assisted computation offloading in SAGSIN and formulates an optimization problem, which turns out to be a mixed integer nonlinear programming (MINLP) due to the joint optimization among task-HAP association, computational resource allocation of HAPs and task-satellite association. To this end, the problem is decoupled into three single-variable subproblems by relaxing the delay constraint, and the subproblems are solved by graph theory, the Lagrange multiplier method with Karush-Kuhn–Tucker (KKT) constraints, and the alternating optimization, respectively. Simulation results demonstrate the efficiency of the proposed scheme with superior performances compared to benchmark schemes.

In this paper, we design a novel joint receiver that iteratively performs channel estimation (CE) and symbol detection for channel-coded multi-user multiple-input multiple-output systems with orthogonal time frequency space modulation (MIMO-OTFS). In particular, we first propose a two-stage CE method based on a single superimposed pilot (SP) with inter-user interference canceling (ICCE). The delay-Doppler domain SP is used to estimate path delays, Doppler shifts, and other channel parameters. Then the detected user symbols are utilized to update the channel parameters with mitigating inter-user and multipath interferences. Second, we construct a joint CE and signal detection scheme based on the expectation propagation (EP) algorithm (EP-ICCE). We exploit the relationship between CE and symbol detection, refining the estimated channel matrix with the detected data symbols. Finally, simulation results shows the proposed EP-ICCE can achieve performance gains up to 2 dB over the conventional methods for the different MIMO and modulations.

This work studies the transceiver design and convergence performance analysis for the hierarchical modulation (HM) systems with protograph-based low-density parity-check (P-LDPC) codes. Specifically, we first conceive new source-constrained (SC) coding scheme and inter-layer-cascaded (ILC) decoding scheme tailored for the HM-based transmitter and receiver, respectively. Both the proposed SC coding and ILC decoding schemes form an enhanced version of bit-interleaved-coded HM (BIC-HM) systems, namely source-constrained HM (SC-HM) systems, providing a more reliable and flexible multi-data transmission solution. Moreover, according to the SC coding principle, we conceive a novel variable-node-degree-based (VND) multiplexing scheme to further improve the performance of the proposed SC-HM systems. Additionally, based on the ILC decoding framework, we devise a novel mutual information (MI) analysis tool, namely ILC-based extrinsic-information-transfer (ILC-EXIT) algorithm, to predict the decoding thresholds of the proposed P-LDPC-coded SC-HM systems. Theoretical and simulation results demonstrate that the proposed SC-HM systems significantly outperform the existing benchmarks in terms of error performance, decoding latency, and transmission-rate adaptation.

With the continuous improvement of data memory density, as the common solution for error correction of NAND flash, the low-density-parity-check (LDPC) code faces more challenges, such as the increasing code length requirements, the worse raw bit error rates (RBER), and the frequently varied channels. In this paper, a new (37536,33672) spatially coupled and globally coupled LDPC (SC-GC-LDPC) code is constructed to address the above challenge, which outperforms the traditional globally coupled LDPC (GC-LDPC) code with the gaps of 0.065 dB and 0.08 dB by exploiting the layered sum-product algorithm (SPA) and the layered normalized min-sum (NMS) algorithm, respectively. In the flash channel, the SC-GC-LDPC code also shows superior error correction performance than the conventional GC-LDPC codes with 25% improvement. Due to its special structure of the check matrix, an improved two-level decoding algorithm (ITLA) and an improved two-phase decoding algorithm (ITPA) are proposed in this paper. Specifically, the algorithms exploit the adjacent subcodes to correct the faulty ones, which reduces the number of check-node-updating (CNU). For the case of single subcode errors, the simulation results show that the number of CNU is reduced by ranging from 6.64% to 31.14% by applying our proposed algorithms, leading to significant improvement of throughput. Compared with the conventional algorithms, the ITLA and ITPA only show slight performance loss. Moreover, ITPA also provides high flexibility of decoding in the NAND flash memory, which can achieve the balance between the error-correction performance and the throughput.

Recent studies have shown that analog joint source-channel coding (AJSCC) is capable of approaching the optimum performance theoretically attainable (OPTA). However, it would be costly to transmit the continuous output of AJSCC. This paper proposes a two-dimensional (2D) quantization-based modulation scheme to map the discrete-time real-valued source encoder output into a finite set of 2D constellation points for modulated transmission. To minimize the resultant quantization distortion, the constellation is optimized by constructing a centroidal Voronoi diagram that can best match the distribution of the source encoder output under power transformation. Based on a comprehensive analysis of effects of encoder configuration and power transformation in connection with the channel condition, an algorithm is presented for jointly optimizing the source encoder and the constellation, with the objective of maximizing the system performance in terms of the end-to-end signal-to-distortion ratio (SDR) with respect to the channel condition in terms of signal-to-noise ratio (SNR). Simulation results show that under joint optimization, the modulated AJSCC system improves as the modulation order increases, and it tends to approach the benchmark performance of the unmodulated system that is close to the OPTA. More practically, the modulated AJSCC system is robust to tolerate imperfect channel estimation to some extent. This work provides a promising way of enabling a source-oriented AJSCC system to access digital communication networks.

Due to the duality between source coding and channel coding, high-performance channel codes are often adopted for addressing source coding problems. In this paper, we investigate the design and analysis of protograph low-density parity-check (P-LDPC) codes in lossy source coding systems. First, we propose a novel lossy source coding architecture based on P-LDPC codes, and empirically verify that although high-performance channel codes perform exceptionally well in their intended domain, they are not inherently optimal for lossy compression. To facilitate analysis, we introduce the lossy compression protograph extrinsic information transfer (LC-PEXIT) algorithm, which aids in evaluating the rate-distortion (RD) performance of P-LDPC codes. Additionally, the LC-PEXIT algorithm allows for the prediction of key parameters, such as the prior coefficientPand the reinforcement rateR, both of which critically influence system performance. We further propose a design algorithm for lossy P-LDPC codes and provide two sets of design examples. Experimental results show strong alignment between the predicted and actual values ofPandRf, with the designed P-LDPC codes exhibiting superior RD performance compared to classical P-LDPC and state-of-the-art ultra-sparse LDPC (US-LDPC) codes. In particular, the designed P-LDPC codes over benchmark codes increases the system coding efficiency of up to approximate 70% and achieves a performance gain of 1.69 ~ 3.26 dB, making it highly effective for lossy compression applications.

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.

As the number of stacked layers in 3D NAND flash memory increases, the channels experience more complex noise, leading to significant fluctuations in the error detection rate. Error-correcting codes with varying error correction capabilities (ECC) are required at different flash stages. To address this issue, we investigate multi-high-rate low-density parity-check (LDPC) codes for 3D NAND flash memory in this paper. Firstly, we mathematically model the 3D triple-level cell (TLC) NAND flash channel based on the obtained data from the test platform. Then we propose a multi-high-rate structured algebraic quasi-cyclic LDPC (MHR-SA-QC-LDPC) code. Specifically, the MHR-SA-QC-LDPC code contains the fixed number of information bits and can be adjusted to various rates according to the characteristics of NAND flash channels. Both additive and multiplicative group construction methods are analyzed in the prime field. Simulation results demonstrate that the proposed LDPC codes outperform existing benchmarks in 3D TLC NAND flash channels, improving both ECC performance and device lifetime.

Rate-splitting multiple access (RSMA), space division multiple access (SDMA), and non-orthogonal multiple access (NOMA) have gained significant popularity and are extensively utilized across various domains. However, it is still unclear whether hybridRSMA-SDMA-NOMA (HybridRDN) would seamlessly combine the advantages of RSMA, SDMA, and NOMA to contribute to the computation offloading of autonomous vehicle systems. To address the above issue, this paper introduces a novel HybridRDN-assisted computation offloading fleet (COF) scheme tailored for autonomous vehicle systems. First, we propose a stochastic-geometry-aided method to model the offloading framework. Afterwards, the task vehicles (TVs) ingeniously employ the proposed HybridRDN scheme to offload tasks to the resource vehicles (RVs) in each COF to relieve their computational burden. Diverging from the sole optimization of the task segmentation ratio or the transmission rate, a joint optimization problem involving the transmission weighting factor, the HybridRDN precoding matrix, the common rate, and the task segmentation ratio, is formulated, which aims to minimize the average delay of the COF system while approaching the rate performance of the ideal HybridRDN. Furthermore, a delay-optimal alternating optimization algorithm (DOAOA) is developed to obtain the solution for the optimization problem. Experimental results validate the plausibility and superiority of the proposed framework compared to the state-of-the-art schemes.

A new search method named two-dimensional greedy search (TDGS) is proposed to progressively determine each element within an exponent matrix, so as to generate quasi-cyclic (QC) low-density parity-check (LDPC) codes without 4-cycles and 6-cycles. By applying four different two-dimensional scanning orders to the TDGS, a design framework is formulated to unify several existing and novel explicit constructions for short (3,$L$)-regular QC-LDPC codes without 4-cycles and 6-cycles. Through equivalence analysis between the exponent matrices greedily found by the TDGS and directly defined by explicit constructions, novel girth properties of (and connections between) these existing explicit constructions are also revealed.

In this article, we investigate the performance of physical-layer network coding (PNC) with hierarchical modulation (HM) over a two-way relay channel (TWRC). While Gray mapping is the optimal for the bit-interleaved coded modulation (BICM) systems in point-to-point communications, the superimposed constellation at the relay in PNC transmission does not maintain the same characteristics as the original Gray mapping at the users. Thus, to address this issue and obtain the optimal mapping for PNC, we propose a Pseudo-Gray (Pe-Gray) constellation for the user-end hierarchical quadrature amplitude modulation (H-QAM). In particular, we develop the design criterion for the user constellation to avoid demodulation ambiguity and more importantly, to ensure that the superimposed constellation can be Gray-mapped. The achievable rate analysis and simulation results show that the proposed Pe-Gray can achieve significant performance gains of up to 2 dB over the conventional Gray, M3, and MSED constellations in power-imbalanced HM-BICM-PNC. The performance superiority of the Pe-Gray is further demonstrated over the power-imbalanced channels, which also suggests its enhanced robustness in wireless fading channels.

In this paper, we propose a polarization-aided polar coding scheme over non-orthogonal multiple access channels operated with physical-layer network coding (PN-NOMA), where M users adopt polar coding for transmission. By exploiting the characteristic of PNC and polar encoding, we found that the polar code at the users can be seen as nested codes and sub-codeword of a larger polar code. It enables us to construct a single (virtual) polar code at the receiver, which has the length M times longer than that of the original user codes. In this way, we can decode all the user messages within this single polar code. The channel polarization effect as well as the decoding performance can be improved. We further propose a Monte Carlo-based code construction for the virtual polar code with user channel coefficients, and short nested user codes can be individually derived from this code. Simulation results show that the proposed PN-NOMA can achieve significant performance gains of more than 0.5 dB as compared to conventional polar-coded NOMA (PC-NOMA) over power-imbalanced channels, and this gain is more than 2 dB over Rayleigh fading channels.

Both massive multiple-input and multiple-output (MIMO) and physical-layer network coding (PNC) techniques can effectively improve the network throughput. However, for PNC-aided massive MIMO systems, the high-order modulations superimposed at the relay particularly bring computational burden and performance degradation to the signal detection. Thus, this letter proposes an iterative MIMO-PNC detector from double expectation propagation (DEP) as a high-accuracy solution in this large-scale system. By exploiting the PNC characteristic, the summation and difference (SD) information of the user pair messages are first linearly formed and iteratively updated between the DEP detector and the channel decoder. Simulation results show that the proposed iterative method can achieve significant performance gains of 2 dB in various massive MIMO systems, as compared to the non-iterative one and traditional linear minimum mean square error (LMMSE) detector.

A three-dimensional constellation-basedM-ary differential chaos shift keying modulation system, referred to as3D-M-DCSK system, is proposed in this paper. In particular, we exploit the excellent cross-correlation properties of chaotic signals to intelligently combine the 3D constellation mapping and the DCSK scheme, thus increasing the minimum Euclidean distance (MED) between the adjacent mapped symbols. In this way, the date rate and transmission reliability of conventional two-dimensional constellation mapping can be effectively improved. The theoretical expressions for the symbol error rate (SER) of the proposed 3D-M-DCSK system are derived under the additive white Gaussian noise (AWGN) channel as well as the multipath Rayleigh fading channel. Additionally, the peak-to-average-power-ratio (PAPR) performance of the proposed 3D-M-DCSK system is carefully analyzed. Simulation results show that the proposed 3D-M-DCSK system achieves outstanding improvement in terms of transmission reliability and PAPR performance compared to the state-of-the-artM-DCSK system in both AWGN and multipath Rayleigh fading channels.

This paper is centered on multiple-input multiple-output visible light communication (MIMO-VLC) systems with protograph-based low-density parity-check (P-LDPC) codes. We propose a two-step design method, which is composed of spatial-domain (SpD)-based Gray-like (GL) principle and signal-domain (SiD)-based energy-optimization (EO) principle, to construct a novel class of generalized spatial modulation (GSM) schemes, referred to asGLEOGSM schemes, to enhance the system performance. We also introduce a novel internal-stopping (IS) principle into the conventional joint detection and decoding (JDD) architecture, the resultant IS-aided JDD (IS-JDD) algorithm significantly reduces the computational overhead. Inspired by the proposed IS-JDD architecture, we further conceive a low-complexity IS-aided extrinsic-information-transfer (IS-EXIT) algorithm to analyze the convergence performance of P-LDPC-coded MIMO-VLC systems. Both theoretical and simulation results verify that our proposed designs can remarkably outperform the existing benchmark schemes in terms of capacity, convergence and complexity.

Orbital angular momentum (OAM) is a mode division multiplexing (MDM) technique enabling simpler implementation and higher capacity than conventional multiple-input multiple-output (MIMO) over line-of-sight (LoS) channels. This paper studies the joint design of protograph low-density parity-check (PLDPC) codes and shaping index modulation (IM) in OAM systems. To begin with, we analyze the distribution of extrinsic log-likelihood-ratios (LLRs) for coded bits output from channel detector, and then propose a customized Box-Cox transformation (CBCT) to make the distribution achieve symmetry and Gaussian features. We also devise a CBCT-based protograph extrinsic information transfer (CBCT-PEXIT) algorithm to predict the convergence performance of PLDPC-coded OAM systems. Furthermore, with the aid of such an algorithm, we construct two new types of improved PLDPC codes tailored for OAM systems, including unpunctured codes and rate-compatible punctured codes. In addition, we present a two-step design method, which seamlessly combines the shaping technique and index rule into a novel modulation scheme, calledshaping index. Both theoretical analyses and simulation results demonstrate that the proposed PLDPC-coded OAM systems with shaping index significantly outperform state-of-the-art counterparts.

In this paper, we propose a reconfigurable intelligent surface (RIS)-assisted frequency-modulated (FM) differential chaos shift keying (DCSK) scheme with simultaneous wireless information and power transfer (SWIPT), called RIS-FM-DCSK-SWIPT scheme, for low-power, low-cost, and high-reliability wireless communication networks. In particular, the proposed scheme is developed under a non-linear energy-harvesting (EH) model which can accurately characterize the practical situation. The proposed RIS-FM-DCSK-SWIPT scheme has an appealing feature that it does not require channel state information, thus avoiding the complex channel estimation. We further derive the closed-form theoretical expressions for the energy shortage probability and bit error rate (BER) of the proposed scheme over the multipath Rayleigh fading channel. In addition, we investigate the influence of key parameters on the performance of the proposed transmission scheme in two different scenarios, i.e., RIS-assisted access point (RIS-AP) and dual-hop communication (RIS-DH). Finally, we carry out various Monte-Carlo experiments to verify the accuracy of the theoretical derivation, illustrate the performance advantage of the proposed scheme, and give some design insights for future study.

To achieve reliable and efficient transmissions in free-space optical (FSO) communication, this paper designs a new protograph low-density parity-check (PLDPC) coded generalized spatial multipulse position modulation (GSMPPM) system over weak turbulence channels. Specifically, we investigate the PLDPC code, generalized space shift keying (GSSK) modulation, and MPPM constellation. First, we propose a type of novel GSMPPM constellations that intelligently integrates the GSSK into MPPM, referred to as asymmetric dual-mode (ADM) constellations, so as to improve the performance of the PLDPC-coded GSMPPM system. Furthermore, exploiting a protograph extrinsic information transfer (PEXIT) algorithm, we construct a type of improved PLDPC code, referred to as I-PLDPC code, which outperforms the existing PLDPC codes over weak turbulence channels. Analytical and simulation results show that the proposed ADM constellations and the proposed I-PLDPC code can obtain noticeable performance gains over their counterparts. Therefore, the proposed PLDPC-coded GSMPPM system with ADM constellations is competent to satisfy the high-reliability requirement for FSO applications.

The huge amount of data produced in the 6G networks not only brings new challenges to the reliability and efficiency of mobile devices but also drives rapid development of new storage techniques. With the benefits of fast access speed and high reliability, NAND flash memory has become a promising storage solution for the 6G networks. In this paper, we investigate a protograph-coded bit-interleaved coded modulation with iterative detection and decoding (BICM-ID) utilizing irregular mapping (IM) in the NAND flash-memory systems. First, we propose an enhanced protograph-based extrinsic information transfer (EPEXIT) algorithm to facilitate the analysis of protograph codes in the IM-BICM-ID systems. With the use of EPEXIT algorithm, a simple design method is conceived for the construction of a family of high-rate protograph codes, called irregular-mapped accumulate-repeat-accumulate (IMARA) codes, which possess excellent decoding thresholds and linear-minimum-distance-growth property. Furthermore, motivated by the voltage-region iterative gain characteristics of IM-BICM-ID systems, a novel read-voltage optimization scheme is developed to acquire accurate read-voltage levels, thus minimizing the decoding thresholds (in dB) of protograph codes. Analyses and simulations indicate that the proposed IMARA-aided IM-BICM-ID scheme and read-voltage optimization scheme remarkably improve the convergence and decoding performance of flash-memory systems. Thus, the proposed protograph-coded IM-BICM-ID can be viewed as a reliable and efficient storage solution for the new-generation mobile networks, such as Internet of Vehicles.

As one of the most promising solutions, edge caching is emerging to reduce the content retrieval latency and relieve the huge burden on the backhaul links in the 6th generation (6G) millimeter wave (mmWave) intelligent vehicular networks. In this paper, we first formulate the optimization problem in terms of request hit probability and investigate two crucial factors, which impact the effectiveness of cache placement in device-to-device (D2D) enabled mmWave vehicular networks. Then, the general mathematical expressions for optimization of the request hit probability with the constraints of caching capacity are derived. Moreover, a group caching scheme (GCS) is proposed to obtain the sub-optimal results by utilizing relaxation method and Karush-Kuhn-Tucker (KKT) conditions. Inspired from the Matern hard-core processes and by exploiting the spatially correlated characteristics of users distribution, hard-cored based caching algorithm (HCCA) is proposed to avoid the simultaneous caching for a particular file. In addition, a joint caching and scheduling strategy is investigated which maximizes the number of concurrent transmissions by D2D enabled vehicle pairs matching and antennas adjustment. Comprehensive simulations validate our theoretical analysis and demonstrate that the proposed scheme can achieve higher performance in terms of request hit probability and the number of concurrent transmissions compared to the existing methods. Consequently, the proposed caching scheme has great potential in future intelligent vehicular applications.

In this work, we develop a pair of rate-diverse encoder and decoder for a two-user Gaussian multiple access channel (GMAC). The proposed scheme enables the users to transmit with the same codeword length but different coding rates under diverse user channel conditions. First, we propose the row-combining (RC) method and row-extending (RE) method to design practical low-density parity-check (LDPC) channel codes for rate-diverse GMAC. Second, we develop an iterative rate-diverse joint user messages decoding (RDJD) algorithm for GMAC, where all user messages are decoded with a single parity-check matrix. In contrast to the conventional network-coded multiple access (NCMA) and compute-forward multiple access (CFMA) schemes that first recover a linear combination of the transmitted codewords and then decode both user messages, this work can decode both the user messages simultaneously. Extrinsic information transfer (EXIT) chart analysis and simulation results indicate that RDJD can achieve gains up to 1.0 dB over NCMA and CFMA in the two-user GMAC. In particular, we show that there exists an optimal rate allocation for the two users to achieve the best decoding performance given the channel conditions and sum rate.

A new differential chaos shift keying scheme with multidimensional index modulation, referred to as MIM-DCSK scheme, is proposed in this paper. This design objective of the proposed MIM-DCSK scheme is to enhance the data rate, energy efficiency, and spectral efficiency of traditional DCSK scheme. In the proposed MIM-DCSK scheme, in addition to the information bits allocated for physical transmission, multidimensional transmission entities, namely the time slot, carrier, and Walsh code are simultaneously considered as indices to convey additional information bits, thus achieving high data rate, spectral efficiency, and energy efficiency. The theoretical bit-error-rate (BER) expressions of the MIM-DCSK scheme are derived over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels. Furthermore, the data rate, complexity, spectral efficiency, and energy efficiency of the MIM-DCSK scheme are analyzed. Simulation results verify the accuracy of the theoretical analysis and illustrate the superiority of the proposed scheme. The proposed MIM-DCSK scheme is a promising solution for low-power and low-cost short-wireless communications.

In this paper, we investigate the performance of space-time block-coded multiple-input-multiple-output (STBCMIMO) LoRa system over Nakagami-m and Ricean fading channels with perfect and imperfect channel state information (CSI). Specifically, we derive the closed-form bit-error-rate expressions and analyze the diversity order of the STBC-MIMO LoRa system with perfect and imperfect CSI, where two common channel estimation error models are considered. Moreover, we perform simulations to evaluate the coverage performance of the system and to verify the accuracy of the theoretical analyses.

As an attempt to tackle the low-data-rate issue of the conventional LoRa systems, we propose two novel frequency-bin-index (FBI) LoRa schemes. In scheme I, the indices of starting frequency bins (SFBs) are utilized to carry the information bits. To facilitate the actual implementation, the SFBs of each LoRa signal are divided into several groups prior to the modulation process in the proposed FBI-LoRa system. To further improve the system flexibility, we formulate a generalized modulation scheme and propose scheme II by treating the SFB groups as an additional type of transmission entity. In scheme II, the combination of SFB indices and that of SFB group indices are both exploited to carry the information bits. We derive the theoretical expressions for bit error rate (BER) and throughput of the proposed FBI-LoRa system with two modulation schemes over AWGN and Rayleigh fading channels. Simulation results not only verify the accuracy of theoretical BER and throughput analyses but also show that the proposed FBI-LoRa schemes can significantly increase the transmission throughput compared with the existing LoRa systems at the expense of a slight loss in BER performance. The proposed FBI-LoRa system is a promising alternative for high-data-rate Internet of Things (IoT) applications.

Owing to the effect of data retention noise in multi-level-cell NAND flash memory, the initial threshold-voltage distributions and read voltages can no longer be used to accurately calculate log-likelihood ratios (LLRs) as the retention time increases, thus causing retention errors. To solve this problem, we first utilize the so-called “correction factors” to optimize the LLR accuracy by maximizing the achievable rate of a flash-memory system without introducing extra memory-sensing operations. We further prove that the optimization of the correction factors is a convex optimization problem and can be solved analytically. To obtain the optimal correction factors, we propose two retention-error correction schemes, referred to as offline maximum-achievable-rate correction (MARC) algorithm and online MARC algorithm, which enable the flash-memory controller to utilize the corrected LLRs that are stored in a look-up table and correct the inaccurate LLRs in real time, respectively. Motivated by the variation characteristics of the threshold-voltage distributions, we also propose an enhanced expectation–maximization (EM) algorithm to reestimate their corresponding parameters, and then adjust the read voltages. By combining the enhanced EM algorithm with the MARC algorithms, an enhanced EM-based correction strategy is developed to further boost the retention-error endurance of flash memory while avoiding excessive memory-sensing overhead. Theoretical analyses and simulation results illustrate the superiority of the proposed correction mehtods in terms of the robustness against retention errors.

The differential chaos shift keying with code index modulation (CIM-DCSK) using Walsh codes can increase the data rate, but error rate performance degrades over practical multipath channel with high delay spread. To tackle this drawback, this paper proposes a parallel CIM-DCSK (PT-CIM-DCSK), where the first time slot is used to transmit the chaotic reference sequence, and the second slot is used to transmit the multiple sequences carrying data bits. In particular, multiple$q$chaotic sequences are added for data transmission in parallel, and each sequence is modulated by CIM-DCSK with$m_{c}$bits. By exploiting the quasi-orthogonal characteristics of permuted chaotic signals, the interference between$q$sequences can be remarkably suppressed. In this way, given the data rate, PT-CIM-DCSK can achieve a larger length of Walsh segment than the CIM-DCSK, since its parallel transmission compensates the rate. In addition, the error performance of the proposed scheme over the multipath Rayleigh fading channel is theoretically analyzed. The theoretical and consistent simulation results demonstrate that the PT-CIM-DCSK can obtain significant performance gains over the conventional CIM-DCSK, and the gain can be up to 5 dB in multipath fading channel with high delay. This is because the larger Walsh segment of PT-CIM-DCSK provides the enhanced robustness against multipath effect. The performance superiority of the proposed scheme is further verified in practical ultra-wideband (UWB) wireless industrial scenarios, which suggests promising for low-cost and low-complexity wireless communication applications.

To realize high energy-efficient, high spectrum-efficient, and high-throughput data transmission, a multi-carrier differential chaos shift keying communication system with hybrid index modulation, referred to asHIM-MC-DCSK system, is proposed in this paper. In the HIM-MC-DCSK system, we intelligently integrate the carrier-number-index technique and carrier-index technique into the MC-DCSK modulation in order to significantly boost the transmission efficiency in wireless communication systems. Especially, we use a pair of orthogonal signals to represent the active and inactive subcarriers in the HIM-MC-DCSK system so as to exploit all the subcarriers to transmit information bits. In addition, the theoretical bit-error-rate (BER) expressions of the HIM-MC-DCSK system are derived over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels. Also, the data rate, spectrum efficiency, energy efficiency, and complexity of the proposed system are carefully analyzed. Monte-Carlo simulations not only verify the accuracy of the theoretical analysis but also illustrate the superiority of the proposed system.

In conventional star-topology LoRa networks, the gateways are expected to collect the data from all the nodes nearby. However, a major challenge for the conventional LoRa system is the performance degradation due to the long-range communication over fading channels. To resolve the challenging issue, this paper investigates a two-hop amplify-and-forward relaying LoRa network in a two-dimension plane, where random nodal distances are considered. Moreover, a relay-selection mechanism is developed for the proposed system. Based on the best relay-selection protocol, the analytical bit-error-rate (BER) and asymptotic BER expressions, achievable diversity order, coverage probability, and throughput of the proposed system are derived over the Nakagami-$m$fading channel. Furthermore, to maximize the throughput of the proposed system, a two-dimensional resource allocation optimization problem (i.e., the spread factor selection and power allocation optimization) is formulated and investigated. The proposed optimal spread factor selection and power allocation scheme is verified to outperform the two baseline schemes. Simulation and numerical results show that although the proposed system reduces the throughput compared to the conventional LoRa system, it significantly improves the BER and coverage probability. Hence, the proposed system can be considered as a promising technique for low-power, long-range and highly reliable Internet-of-Things applications.

2D position information of input tokens is essential for transformer-based semantic segmentation models, especially on high-resolution aerial images. However, recent transformer-based segmentation methods use the position encoding to record position information and most position encoding methods encode the 1D positions of tokens. Therefore, we propose a two-dimensional semantic transformer model (2DSegFormer) for semantic segmentation on aerial images. In 2DSegFormer, we design a novel 2D positional attention to accurately record the 2D position information required by the transformer. Furthermore, we design the dilated residual connection and use it instead of skip connection in the deep stages to get a larger receptive field. skip connections are used in the shallow stages of 2DSegFormer to pass the details to the corresponding stages in the decoder. Experimental results on UAVid, Vaihingen and AeroScapes data sets demonstrate the effectiveness of 2DSegFormer. Compared with the state-of-the-art methods, 2DSegFormer shows better performance and great robustness on three different data sets. In particular, 2DSegFormer-B2 achieves first place in the public ranking on the UAVid test set.

As a spectral-efficiency technique for unequal error protection (UEP), hierarchical modulation (HM) bit-interleaved coded modulation (BICM) with iterative decoding (ID) has attracted interests in the wireless communication community. In this article, we conduct an investigation on spatially coupled (SC) protograph low-density 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 quadrant-based harmonic mean analysis to evaluate the nonfeedback and iterative-feedback asymptotic performance of the proposed constellations. In addition, we conceive a performance-analysis tool, referred to as multistream-based extrinsic information transfer (MS-EXIT) 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 P-LDPC-coded HM-BICM-ID systems are remarkably superior to the state-of-the-art counterparts. Thereby, the proposed SC P-LDPC-coded 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).

Code index modulated multi-carrier M-ary differential chaos shift keying (CIM-MC-M-DCSK) system not only inherits low-power and low-complexity advantages of the conventional DCSK system, but also significantly increases the transmission rate. This feature is of particular importance to Internet of Things (IoT) with trillions of low-cost devices. In particular, for e-health IoT applications, an efficient transmission scheme is designed to solve the challenge of the limited battery capacity for numerous user equipments served by one base station. In this paper, a new multiple-input-single-output simultaneous wireless information and power transfer (MISO-SWIPT) scheme for CIM-MC-M-DCSK system is proposed by utilizing orthogonal characteristic of chaotic signals with different initial values. The proposed system adopts power splitting mode, which is very promising for simultaneously providing energy and transmitting information of the user equipments without any external power supply. In particular, the new system can achieve desirable anti-multipath-fading capability without using channel estimator. Moreover, the analytical bit-error-rate expression of the proposed system is derived over multipath Rayleigh fading channels. Furthermore, the spectral efficiency and energy efficiency of the proposed system are analyzed. Simulation results not only validate the analytical expressions, but also demonstrate the superiority of the proposed system.

This letter proposes a polarization mapping (PM) for polar coded modulation with physical network coding (PM-PNC) over two-way relay channels (TWRC). The achievable information rates (AIRs) of the mapped bits within a XOR symbol from bit-wise XOR of two user symbols are significantly different, since the users adopt non-uniform PAM modulation to avoid mapping ambiguity. In the polar-coded PM-PNC, the original channels associated with the split information bit channel are mapped to the XOR bit stream with a larger AIR. In this way, the achieved rate of the split information channels can be maximized and is illustrated in distribution of split bit channel AIRs. Simulation results show that the proposed PM-PNC can achieve significant performance gains of more than 0.5 dB as compared to the bit-interleaved coded modulation (BICM) and multilevel coded (MLC) PNC systems over Gaussian and block fading channels.

LoRa is a modulation technology for low power wide area networks (LPWAN) with enormous potential in 5G era. However, the performance of LoRa system deteriorates seriously in fading-channel environments. To tackle this problem, in this paper we introduce multiple-input-multiple-output (MIMO) configuration employing space-time block coding (STBC) schemes into the LoRa system to formulate an STBC-MIMO LoRa system. Then, we investigate the theoretical performance of the proposed system over Rayleigh fading channels. To this end, we derive the distribution of the decision metric for the demodulator in the proposed system. Based on the above distribution, we propose a closed-form approximate BER expression of the proposed system when perfect and imperfect channel state information (CSI) are considered. Furthermore, we analyze the diversity order and the throughput of the proposed system. The results of the diversity analysis demonstrate that the diversity order of the system in the imperfect CSI scenario with fixed channel estimate error variance is zero. However, in the imperfect CSI scenario with a decreasing channel estimate error variance and the perfect CSI scenario, the system can achieve full diversity. In addition, the results of the throughput analysis show that the throughput of the proposed system is little affected by CSI conditions. Simulation results verify the accuracy of the theoretical analysis and the excellent performance of the proposed system. Due to such superiority, the proposed STBC-MIMO LoRa system can be considered as a good scheme for LPWAN.

In this letter, we conduct an insightful study on protograph-low-density parity-check (PLDPC)-code-assisted deterministic measurement matrices for compressed sensing applications. As is well known, the recovery performance of conventional PLDPC sparse matrices (PLDPC-SM) will be dramatically degraded as the ratio of N to M increases, where M × N is the size of the matrices. To address the above issue, we propose a novel construction method to formulate a class of extended PLDPC-SM (EPLDPCSM) by intelligently inserting part of Hadamard matrices into the conventional PLDPC-SM. The proposed EPLDPC-SM not only can realize more flexible sizes with respect to the existing counterparts, but also can be amenable to lower coherence without costing more storage resources. Both coherence analyses and experiment results demonstrate that the proposed EPLDPC-SM are superior to the well-performing deterministic measurement matrices (i.e., PLDPCSM) and random matrices (i.e., random Gaussian matrices (R-GM) and random sparse matrices (R-SBM)) for various values of N/M1.

In this letter, we propose a new hyperspectral image (HSI) classification approach, called the random subspace ensemble with enhanced feature (RSE-EF), which trains several individual classifiers with enhanced spatial information. The proposed approach aims to address two common issues: the curses of the imbalanced training samples and high feature-to-instance ratio. Specifically, we first propose a similar-neighboring-sample-search (SNSS) method to address the issue of imbalanced training samples. Afterward, we generate the enhanced random subspaces (ERSs) that possess relatively lower dimensionality and more distinctive information compared with the original random subspaces (RSs) so as to alleviate the curse of high feature-to-instance ratio more effectively. Furthermore, a shallow neural network kernel-based extreme learning machine (KELM) is applied to the RSE-EF to classify image pixels. Experimental results on two public hyperspectral data sets illustrate that the proposed RSE-EF approach outperforms the state-of-the-art HSI classification counterparts.

Adaptive link selection for buffer-aided relaying can achieve significant performance gain compared with the conventional relaying with fixed transmission criterion. However, most of the existing link-selection strategies are designed based on perfect channel state information (CSI), which are very complex by requiring channel estimator. To solve this issue, in this paper, we investigate a buffer-aided differential chaos-shift-keying based simultaneous wireless information and power transfer (DCSK-SWIPT) relay system, where a decode-and-forward protocol is considered and the relay is equipped with a data buffer and an energy buffer. In particular, we propose two link-selection protocols for the proposed system based on harvested energy, data-buffer status and energy-shortage status, where the CSI is replaced by the harvested energy to avoid the channel estimation and the practical problem of the decoding cost at the relay is considered. Furthermore, the bit-error-rate (BER) and average-delay closed-form expressions of the proposed protocols are derived over multipath Rayleigh fading channels, which are validated via simulations. Finally, results demonstrate that both the proposed protocols not only provide better BER performance than the conventional DCSK system and DCSK-SWIPT relay system but also achieve better BER performance and lower average delay in comparison to the conventional signal-to-noise-ratio-based buffer-aided DCSK-SWIPT relay systems.

With the continual increase of storage density, NAND flash memory cells are particularly vulnerable to channel noise, which significantly degrades the storage reliability. To overcome this issue, low‐density parity check (LDPC) codes have been considered as a preferable choice for flash memory systems. To further improve the efficiency of the decoder, the convergence speed and the error‐rate performance are the key performance indicators for LDPC‐coded NAND flash memory. In this study, a threshold‐voltage‐drift‐aware scheduling for belief propagation (BP) decoding of LDPC‐coded NAND flash memory is introduced to improve the convergence speed and the error‐rate performance. The basic idea of the proposed scheduling is to find an appropriate updated order of variable nodes according to their corresponding locations of threshold voltages. Since the proposed scheduling updates less reliable variable nodes with higher priority, it can improve the efficiency of BP decoding. Simulation results show that the proposed scheduling not only significantly improves the convergence speed, but also obtains better error‐rate performance than the conventional serial scheduling.

Nowadays, the serious security threat of industrial control system and sensors has become a major challenge with the rapid development of Industrial Internet of Things (IIoT). Man-in-the-middle (MITM) attack is a very common intrusion method, which will make a great security threat in the application of IIoT. In IIoT scenario, the lightweight safety certification can play a very important role in the development of data-intensive and decentralized applications running on billions of sensors and devices, preserving their security. Therefore, in this paper, a low-latency high-reliability security mechanism is proposed to avoid the MITM attack in IIoT scenario. First, combining the radio frequency fingerprint (RFF) technology with IIoT applications, a lightweight IIoT security architecture is proposed. Based on the proposed IIoT security architecture, the process of device access authentication and communication service is illustrated. Second, according to the requirement of IIoT identification method, an access authentication method of the device is proposed based on the RFF. The method of feature extraction, classifier designing, and the access authentication process is discussed in detail. Finally, the simulation results show that the identification rate of devices can reach 95% under SNR = 6 dB, and can nearly reach 100% under SNR = 15 dB. Through the new process of access authentication, the access authentication rate can reach 95% under SNR = 15 dB. Therefore, according to the simulation results, the new security mechanisms based on RFF can be used to avoid the MITM attack in IIoT scenario.

As a bandwidth-efficient technique, bit-interleaved coded modulation with iterative demapping and decoding (BICM-ID) has attracted much research attention in the field of wireless communication. In this paper, we put forth a joint design of root-protograph (RP) low-density parity-check (LDPC) codes and BICM-ID, referred to as RP-based BICM-ID (RP-BICM-ID), over block-fading (BF) channels so as to boost the throughput under limited bandwidth. To preserve the full-diversity property of RP codes, we propose an efficient modulation strategy for the RP-BICM-ID system by taking the fading-block length into consideration. We also analyze the outage-probability limit of the RP-BICM-ID systems to establish the fundamental lower-limit on their word-error-rate (WER) performance. Moreover, we conceive a multi-level protograph extrinsic information transfer (ML-PEXIT) algorithm to derive the asymptotic WER and bit error rate (BER) of the RP-BICM-ID systems over BF channels. As a further insight, we develop a novel unequal-error-protection (UEP) bit-to-symbol (B2S) mapping scheme for the RP-BICM-ID systems, which gives rise to an additional performance improvement. Analyses and simulations show that the proposed RP-BICM-ID systems can not only realize desirable spectral efficiency, but also obtain near-outage-limit performance over BF channels. Therefore, the proposed RP-BICM-ID systems are very promising in achieving high-reliability and high-rate transmissions under slow-fading wireless-communication environments.

In this paper, we consider the constructions of type-II quasi-cyclic (QC) low-density parity-check (LDPC) codes with girth eight from a Sidon sequence. We first derive the necessary and sufficient conditions guaranteeing a girth-eight type-II QC-LDPC code. By combining these conditions with the concept of the Sidon sequence, three classes of type-II QC-LDPC codes are subsequently proposed with girth eight. To the best of our knowledge, the second and the third classes we proposed are the first series of systematic and algebraic constructions for the girth-eight type-II QC-LDPC codes that have rates being greater than a half and, at the same time, have distance upper bounds being not limited to 12. Via simulations, we show the promising performance of the proposed type-II QC-LDPC codes with girth eight. In addition, a set of general bounds and explicit/random constructions without using a Sidon sequence are also presented for the type-II QC-LDPC codes with girth six or eight. We observe that the proposed codes perform better than or equally well as the random QC-LDPC codes from PEG and quadr.-congr. methods, while the novel codes possess both highly structured parity-check matrices and very flexible choices in circulant size.

Frequency-modulated differential chaos shift keying ultrawideband (FM-DCSK UWB) system has attracted more and more attention in recent years because of its low-complexity and low-power advantages. Nevertheless, its system performance is severely degraded in the presence of narrowband interference (NBI), which further limits its practical applications. In this paper, an enhanced energy-based detector (EED) is proposed for the FM-DCSK UWB system to tackle this problem. Compared with the conventional energy detector (ED), the proposed EED significantly enhances the anti-NBI capability while maintaining the low-power and low-complexity feature. As a further insight, the analytical bit-error-rate (BER) expression of the proposed EED-based FM-DCSK UWB system is derived over additive white Gaussian noise as well as IEEE 802.15.4a multipath fading channels. Moreover, simulation results are carried out to demonstrate the accuracy of the theoretical analysis and the merit of the proposed EED. It is illustrated that the proposed EED achieves better performance than the conventional ED in various transmission scenarios. Thanks to the above-mentioned advantages, the proposed EED-based FM-DCSK UWB system appears to be an excellent candidate for low-power and low-complexity tactile Internet-of-Things applications, e.g., wireless sensor networks and wireless body area networks.

The lattice L(A) of a full-column rank matrix A ∈ Rm×nis defined as the set of all the integer linear combinations of the column vectors of A. The successive minima λi(A), 1 ≤ i ≤ n, of lattice L(A) are important quantities since they have close relationships with the following problems: shortest vector problem, shortest independent vector problem, and successive minima problem. These problems arise from many practical applications, such as communications and cryptography. This paper first investigates some properties of λi(A). Specifically, we develop lower and upper bounds on λi(A), where A are, respectively, the Cholesky factor of G1+ G2and (G1+ G2)-1for two given symmetric positive definitive matrices G1and G2. The bounds are, respectively, expressed as the successive minima of L(A1) and L(A2), and L(A1) and L(A2), where A1, A2, A1and A2are, respectively, the Cholesky factors of G1, G2, G1-1, and G2-1. Then, we show how some properties of λi(A) are used to design a suboptimal integer-forcing strategy for cloud radio access network. Our approach provides much higher time efficiency while keeping the same achievable rate as the algorithm reported by Bakoury and Nazer (I. E. Bakoury and B. Nazer, “Integer-forcing architectures for uplink cloud radio access networks,” in Proc. 55th Annu. Allerton Conf. Commun. Control Comput., Oct. 2007, pp. 67-75). Simulation tests are performed to illustrate our main results.

Coded modulation (CM) is a bandwidth efficient framework to approach the capacity limit of the differential chaos shift keying (DCSK) systems. In this paper, we propose an M-ary DCSK system operated with CM based on nonbinary protograph low-density parity-check (LDPC) codes over Rayleigh fading channels. First, we investigate the performance of the proposed nonbinary channel coded DCSK (CM-DCSK) and bit-interleaved coded DCSK (BICM-DCSK). In particular, we show that CM-DCSK outperforms BICM-DCSK over Rayleigh fading channels in terms of capacity limit. Compared with BICM-DCSK, CM-DCSK can simplify the receiver structure, since it does not require turbo iteration between the noncoherent detector and channel decoder. Second, guided by the modified extrinsic information transfer (EXIT) analysis, we put forth two new types of nonbinary protograph LDPC codes to approach the capacity limit of CM-DCSK. Both EXIT analysis and simulation results demonstrate that the proposed protograph-coded CM-DCSK achieves a better error performance than BICM-DCSK even with iterative decoding. Furthermore, we show the performance superiority of nonbinary protograph-coded CM-DCSK over a practical ultra-wideband channel. Hence, we conclude that this proposed scheme offers a good alternative for wireless local area network applications.

This paper investigates the performance of nonbinary low-density parity-check (LDPC) channel coded M-ary differential chaos shift keying (DCSK) modulation systems over Rayleigh fading channels. The receiver adopts non-coherent detector for DCSK modulation and sum-product algorithm (SPA) for channel coding. Unlike that the previous binary channel coded M-ary DCSK system uses turbo iterative decoding between the detector and the channel decoder, the nonbinary coded DCSK system does not require turbo iteration, which simplifies the receiver implementation and reduces the decoding latency, because that soft information from M-ary detector can be directly used by M-ary channel decoder. The simulation result shows that the proposed nonbinary coded M-ary DCSK system has much better error performance than the binary coded one.

This paper studies protograph low-density paritycheck coded cooperation (CC) schemes for two-hop multi-relay systems with L relays over Nakagami-m quasi-static fading (QSF) channels. We propose two CC schemes, namely schemes I and II, with different maximum code rates to satisfy different transmission requirements. We further design a family of distributed rate-compatible root-protograph (RCRP) codes to achieve full diversity in CC-based multi-relay QSF channels. In particular, our RCRP codes with L + 1 sub-codewords can realize full diversity in scheme I, and our RCRP codes with two sub-codewords can achieve full diversity in scheme II with a maximum-ratio combiner. In addition, we estimate the asymptotic word error rate and bit error rate of our RCRP codes using a generalized protograph extrinsic information transfer algorithm, which is able to characterize the error performance of finite-length codewords accurately. Analysis and simulation show that our RCRP codes can achieve outage-limit-approaching performance in both multi-relay CC architectures. This makes the RCRP coding framework extremely attractive for multirelay cooperative communication applications with slow-varying fading.

For two-way relay channel-coded physical network coding (CPNC) systems with sufficiently low code rate, the separate complete decoding (SCD) scheme outperforms the joint channel-physical network coding (JCNC) scheme. Hence, this paper addresses the design of protograph LDPC codes to approach the SCD-based CPNC capacity. In fact, due to virtual erasures induced by CPNC transmission, the conventional protograph that approaches point to point (P2P) AWGN capacity may not perform well in SCD-based CPNC channel in terms of error rates. We then use the finite-length EXIT chart to calculate iterative decoding threshold of a joint code graph formed by two codes in the SCD. Furthermore, we investigate the serial separate complete decoding (S-SCD) and parallel separate decoding (P-SCD). Simulation results show that with the S-SCD, the proposed protograph codes have within 0.9 dB of their capacity limits for rates from 1/3 to 3/5.

The authors study the performance of protograph low‐density parity‐check (LDPC) codes over two‐dimensional (2D) intersymbol interference (ISI) channels in this study. To begin with, the authors propose a modified version of finite‐length (FL) extrinsic information transfer (EXIT) algorithm so as to facilitate the convergence analysis of protograph codes. Exploiting the FL‐EXIT analyses, the authors observe that the protograph codes optimised for 1D ISI channels, e.g. the 1D‐ISI protograph code, cannot maintain their advantages in the 2D‐ISI scenarios. To address this problem, the authors develop a simple design scheme for constructing a family of rate‐compatible improved protograph (RCIP) codes particularly for 2D‐ISI channels, which not only outperform the 1D‐ISI protograph code, but also are superior to the regular column‐weight‐3 code and optimised irregular LDPC codes in terms of the convergence speed and error performance. More importantly, such RCIP codes benefit from relatively lower error‐floor as well as linear encoding and fast decoding. Thanks to these advantages, the proposed RCIP codes stand out as better alternatives in comparison with other error‐correction codes for ultra‐high‐density data storage systems.

In this paper, we investigate the performance of the protograph low-density parity-check (LDPC) codes concatenated with space-time block code (STBC) over Rayleigh fading channels. We firstly extend the modified protograph extrinsic information transfer (PEXIT) algorithm in order to analyze the convergence performance of protograph codes. Based on the extended PEXIT algorithm and Gaussian approximation, we further derive the asymptotic bit-error-rate (BER) expression of protograph codes. Utilizing the PEXIT algorithm, theoretical and simulated BERs, we compare the performance of two classical protograph codes, i.e., accumulate-repeat-by-3-accumulate (AR3A) code and accumulate-repeat-by-4-jagged-accumulate (AR4JA) code, regular LDPC code, and optimized irregular LDPC codes, and illustrate that the AR3A code is superior to other three codes. Additionally, we discuss the impact of the number of receive antennas (i.e., NR) on the system performance and verify that the theoretical analyses hold as NR varies. As a result, the AR3A code stands out as a good candidate for wireless communication applications with multiple antennas.

This letter considers the design of measurement matrices with low complexity, easy hardware implementation and good sensing performance for practical compressed sensing applications. We construct a class of sparse binary measurement matrices from protograph Low-density parity-check (LDPC) codes, which can satisfy these features simultaneously. The optimal performance of proposed matrices is analyzed from the mutual coherence aspect. Moreover, we obtain a sufficient condition for optimal construction of the matrices using proposed algorithm. Simulation experiments also demonstrate that orthogonal matching pursuit (OMP) algorithm performs better using the constructed matrices as compared with several state-of-the-art measurement matrices, such as random Gaussian matrices.

We investigate the performance of the protograph low-density parity-check (LDPC) codes over Nakagami block-fading (BF) channels with multiple receive antennas. Using the modified protograph extrinsic information transfer (PEXIT) algorithm, we observe that the existing protograph LDPC codes, which have been shown to possess excellent error performance over additive white Gaussian noise channels, cannot perform well over non-ergodic BF channels. To address this problem, a simple design scheme is proposed to construct three new root-protograph (RP) LDPC codes, i.e., the regular RP code, the improved RP1 (IRP1) code, and the IRP2 code. The convergence analysis, error-performance analysis, and simulated results show that the three proposed RP codes outperform the existing protograph LDPC codes and regular quasi-cyclic LDPC code. Furthermore, the IRP1 code and the IRP2 code are superior to the regular RP code and the regular root-LDPC code and exhibit outage-limit-approaching error performance. Consequently, these two proposed IRP codes appear to be better alternatives as compared to other error-correction codes for slowly-varying wireless communication systems.

In this paper1, we propose a novel cooperative scheme to enhance the performance of multiple-access (MA) differential-chaos-shift-keying (DCSK) systems. We provide the bit-error-rate (BER) performance and throughput analyses for the new system with a decode-and-forward (DF) protocol over Nakagami-m fading channels. Our simulated results not only show that this system significantly improves the BER performance as compared to the existing DCSK non-cooperative (DCSK-NC) system and the multiple-input multiple-output DCSK (MIMO-DCSK) system, but also verify the theoretical analyses. Furthermore, we show that the throughput of this system approximately equals that of the DCSK-NC system, both of which have prominent improvements over the MIMO-DCSK system. We thus believe that the proposed system can be a good framework for chaos-modulation-based wireless communications.

In this study, the authors investigate the error performance of the protograph (low‐density parity check) codes over Nakagami‐ m fading relay channels. The authors first calculate the decoding thresholds of the protograph codes over such channels with different fading depths (i.e. different values of m ) by exploiting the modified protograph extrinsic information transfer (PEXIT) algorithm. Furthermore, based on the PEXIT analysis and using Gaussian approximation, the authors derive the bit‐error‐rate (BER) expressions for the error‐free (EF) relaying protocol and decode‐and‐forward (DF) relaying protocol. The authors finally compare the threshold with the theoretical BER and the simulated BER results of the protograph codes. It reveals that the performance of DF protocol is approximately the same as that of EF protocol. Moreover, the theoretical BER expressions, which are shown to be reasonably consistent with the decoding thresholds and the simulated BERs, are able to evaluate the system performance and predict the decoding threshold with lower complexity as compared with the modified PEXIT algorithm. As a result, this work can facilitate the design of the protograph codes for the wireless communication systems.

This letter develops a log-likelihood-ratio-based decoder for a generalized joint channel-coding-and-physical-network coding used in a two-way relay system. Assuming that the same low-density parity-check codes are used at the source nodes, the proposed decoder shows identical error performance as the probability-domain-based decoder but with a much lower computational complexity.

In wireless communications, spatial diversity techniques, such as space-time block code and single-input multiple-output (SIMO), are employed to strengthen the robustness of the transmitted signal against channel fading. This article studies the performance of protograph-based low-density parity-check (LDPC) codes with receive antenna diversity. The authors first propose a modified version of the protograph extrinsic information transfer algorithm and use it for deriving the threshold of the protograph codes in a SIMO system. The authors then calculate the decoding threshold and simulate the bit-error rate (BER) of two protograph codes (accumulate-repeat-by-3-accumulate (AR3A) code and accumulate-repeat-by-4-jagged-accumulate (AR4JA) code), a regular (3,6) LDPC code and two optimised irregular LDPC codes. The results reveal that the irregular codes achieve the best error performance in the low signal-to-noise-ratio (SNR) region and the AR3A code outperforms all other codes in the high-SNR region. Utilising the theoretical analyses and the simulated results, the authors further discuss the effect of the diversity order on the performance of the protograph codes. Accordingly, the AR3A code stands out as a good candidate for wireless communication systems with multiple receive antennas.

We investigate the performance of the protograph low-density parity-check (LDPC) codes, which have been shown to possess simple structures and outstanding error performance over additive white Gaussian noise (AWGN) channels, over partial response (PR) channels using the finite-length extrinsic information transfer (EXIT) algorithm. Due to the intersymbol interference (ISI) caused by the PR channels, we observe that the conventional protograph LDPC codes do not perform well in terms of error rates. We further propose a new design scheme and construct three new types of protograph LDPC codes. Unlike conventional protograph LDPC codes in which the highest-degree variable nodes are punctured, the new protograph LDPC codes have their lowest-degree variable nodes punctured. Moreover, some edge re-connections are made in one of the proposed codes. The EXIT-chart analysis, the convergence analysis and the bit-error-rate simulation have shown that all three new codes outperform the conventional protograph LDPC codes. Moreover, two of the proposed codes are superior to the regular column-weight-3 LDPC code and thus they are good alternatives compared to other error-correction codes for use in data storage systems.