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.

Scene Text Recognition (STR) is challenging in extracting effective character representations from visual data when text is unreadable. Permutation language modeling (PLM) is introduced to refine character predictions by jointly capturing contextual and visual information. However, in PLM, the use of random permutations causes training fit oscillation, and the iterative refinement (IR) operation also introduces additional overhead. To address these issues, this paper proposes the Hierarchical Attention autoregressive Model with Adaptive Permutation (HAAP) to enhance position-context-image interaction capability, improving autoregressive LM generalization. First, we propose Implicit Permutation Neurons (IPN) to generate adaptive attention masks that dynamically exploit token dependencies, enhancing the correlation between visual information and context. Adaptive correlation representation helps the model avoid training fit oscillation. Second, the Cross-modal Hierarchical Attention mechanism (CHA) is introduced to capture the dependencies among position queries, contextual semantics and visual information. CHA enables position tokens to aggregate global semantic information, avoiding the need for IR. Extensive experimental results show that the proposed HAAP achieves state-of-the-art (SOTA) performance in terms of accuracy, complexity, and latency on several datasets.

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.

This paper presents a novel multi-carrier differential chaos shift keying modulation with permutation index (PI-MC-DCSK) over wireless multipath fading channels, since the conventional multi-carrier DCSK (MC-DCSK) suffers from low spectral efficiency and loss of system performance. In this system, the predefined subcarriers can carry multiple data bits according to permutation indexes, while only a single subcarrier is used as the chaotic reference and shared by data subcarriers. Thus, the transmission energy is saved and the data rate can be enhanced. Moreover, the low cross-correlation property of permuted chaotic sequences is exploited in PI-MC-DCSK to effectively suppress inter-subcarrier interference. The theoretical analysis and consistent simulation results show that the proposed system can obtain significant performance gains of more than 2 dB than the conventional MC-DCSK over Rayleigh multipath channels. This performance gain can be up to 4 dB in typical ultra-wideband (UWB) channels, which proves its feasibility in practical applications. Therefore, this new design can be viewed as a low-complexity solution for chaos-based wireless communications, such as short-range Internet of Things (IoT) applications of transmitted-reference communications.

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.

Non-local similarity (NLS) has been successfully applied to point cloud denoising. However, existing non-local methods either involve high algorithmic complexity in capturing NLS or suffer from diminished accuracy in estimating low-rank matrices. To address these problems, we propose a Point Cloud Denoising framework using $\gamma$γ-norm minimization based on Curvature Entropy (PCD-$\gamma$γCE) for efficiently removing noise. First, we develop a structure descriptor, which exploits Curvature Entropy (CE) to accurately capture shape variation details of Non-Local Similar Structure (NLSS), and employs Angle Subdivision (AS) of NLSS to control the complexity of initial normal matrix construction. Second, we introduce $\gamma$γ-norm to construct a low-rank denoising model for initial normal matrix, thereby providing a nearly unbiased estimation of rank function with better robustness to noise. Extensive experiments on synthetic and raw scanned point clouds show that our approach outperforms the popular denoising methods, with a 99.90% time reduction and gains in Mean Square Error (MSE) and Chamfer Distance (CD) compared with the Weighted Nuclear Norm Minimization (WNNM) method.

Non-coherent chaotic communication has gained increasing attention as it provides an efficient solution for reliable communications without requiring channel state information. In this paper, we propose a non-coherent reconfigurable intelligent surface (RIS)-empowered differential chaos shift keying scheme with two-level nested index modulation (RIS-DCSK-TLNIM). In the proposed RIS-DCSK-TLNIM scheme, the reference index and information index are nested to form two-level nested index modulation. This design enhances both the spectral efficiency and bit error rate (BER) performance of RIS-DCSK-TLNIM, albeit at the expense of slightly increased complexity. Furthermore, we propose a joint detection algorithm to recover the information bits transmitted via the reference index, information index, and two distinct-mode signals. We then extend RIS-DCSK-TLNIM into an enhanced system to achieve higher spectral efficiency. Subsequently, we analyze the BER performance, spectral efficiency, and system complexity of RIS-DCSK-TLNIM, and compare these metrics with those of benchmark systems. Comparison results demonstrate that the proposed RIS-DCSK-TLNIM, when configured with a small number of time slots, can achieve more than twice the spectral efficiency and at least a 6 dB gain in BER performance compared to benchmark systems.

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.

In this paper, we develop a non-coherent differential chaos shift keying based index modulation by using initial value index (IVI-DCSK) to convey additional information for wireless communications. In the proposed scheme,mcmapped bits are carried by 2mcchaotic sequences by exploiting the quasi-orthogonality of different chaotic signals, while the modulated bit is carried by DCSK. To diminish the multiuser interference, the references allocated to different users are sent in individual time slots, while the information-bearing sequences for the mapped bits of users are sent simultaneously. We then derive the bit error rate (BER) expression of multi-user IVI-DCSK over multipath Rayleigh fading channels. The theoretical and consistent simulation results show that the proposed IVI-DCSK achieves significant gains over the conventional chaotic-based index modulations, i.e., permutation index DCSK (PI-DCSK) and code index modulation DCSK (CIM-DCSK). This gain can be more than 4 dB in fading channels with high multipath delay. In addition, it achieves higher energy and spectral efficiencies over the latter ones. The superiority of the proposed scheme is further verified in practical ultra-wideband (UWB) communications. Thus, this proposed scheme is efficient and promising for chaotic-based low-complexity communications, such as in wireless local area network (WLAN) and indoor applications.

Low-density parity-check (LDPC) codes with protograph-based raptor-like (PBRL) structure have been chosen as the data channel coding scheme for the fifth-generation (5G) enhanced mobile broad band (eMBB) services. However, these 5G LDPC codes are not optimized for the scenarios of Ultra Reliable and Low Latency Communications (URLLC) and massive Machine Type Communications (mMTC) in which small transport block sizes are usually used. In this paper, a new method is proposed to construct PBRL LDPC codes for URLLC and mMTC. This method incorporates degree-distribution optimization, base matrix derived from parity-check matrix of quadratic residue codes, masking technique and modified progressive-edge-growth (PEG) algorithm. Simulation results show that the proposed PBRL LDPC codes outperform 5G LDPC short codes in terms of error-correcting performance.

For moving cameras, the video content changes significantly, which leads to inaccurate prediction in traditional inter prediction and results in limited compression efficiency. To solve these problems, first, we propose a camera pose-based background modeling (CP-BM) framework that uses the camera motion and the textures of reconstructed frames to model the background of the current frame. Compared with the reconstructed frames, the predicted background frame generated by CP-BM is more geometrically similar to the current frame in position and is more strongly correlated with it at the pixel level; thus, it can serve as a higher-quality reference for inter prediction, and the compression efficiency can be improved. Second, to compensate the motion of the background pixels, we construct a pixel-level motion vector field that can accurately describe various complex motions with only a small overhead. Our method is more general than other motion models because it has more degrees of freedom, and when the degrees of freedom are decreased, it encompasses other motion models as special cases. Third, we propose an optical flow-based depth estimation (OF-DE) method to synchronize the depth information at the codec, which is used to build the motion vector field. Finally, we integrate the overall scheme into the High Efficiency Video Coding (HEVC) and Versatile Video Coding (VVC) reference software HM-16.7 and VTM-10.0. Experimental results demonstrate that in HM-16.7, for in-vehicle video sequences, our solution has an average Bjøntegaard delta bit rate (BD-rate) gain of 8.02% and reduces the encoding time by 20.9% due to the superiority of our scheme in motion estimation. Moreover, in VTM-10.0 with affine motion compensation (MC) turned off and turned on, our method has average BD-rate gains of 5.68% and 0.56%, respectively.

Vehicular fog computing (VFC) that supports inter-vehicular task offloading emerges as a promising complement to handle the explosive growth of computation-intensive tasks in Intelligent Transportation Systems (ITS). Nonetheless, as the fog access points (F-APs) in crowed areas are often overloaded, the conventional single F-AP VFC may become incompetent and energy-inefficient. To tackle the issue, a novel scheme of non-orthogonal multiple access (NOMA)-enabled multi-F-AP VFC with partial offloading is proposed in this work. However, the corresponding energy minimization turns out to be a highly non-trivial non-linear mixed-integer programming problem. To this end, the optimal power allocation is derived by exploiting monotonicity while good task splitting ratio and user association are found through successive convex approximation (SCA)-based interior-point method and game theoretic approach, respectively. Extensive simulations based on MATLAB show that, in the considered scenarios, the proposed scheme can fulfill a more balanced offloading and better exploit the available computing resources, thereby leading to an approximately 30% energy consumption reduction compared to the baselines.

With the advent of the Internet of vehicles (IoV), the explosive growth of data from vehicular sensors places a heavy computing burden on green-enabled intelligent transportation systems. In this study, a paradigm of vehicular fog computing (VFC) is introduced, which is able to offload computation tasks to the nearby fog nodes. In addition, considering the advantage of non-orthogonal multiple access (NOMA), a NOMA-enabled VFC is proposed, in which a task vehicle, a main fog access point (F-AP), an idle vehicle, and other cooperative F-APs are involved to process the task. By jointly optimizing NOMA power allocation, task allocation ratio, bandwidth allocation and time slot allocation, the offloading data maximization problem is investigated. After simplifying the problem through mathematical analysis, the offloading data maximization problem is solved by the proposed interior-point method based on successive convex approximation (SCA). Simulation results show that the proposed offloading scheme performs better than other existing schemes in terms of offloading data.

Abstract Arbitrary shape text detection is a challenging task in scene text recognition. Driven by deep learning and large‐scale data sets, the detection method based on connected component (CC) has increasingly gained popularity. However, there are still problems of unclear separation of text instances and incorrect component links. Thus, in this paper, the authors propose a novel component connection method, that is, Fragmented Affinity Reasoning Network of Text Instances (FARNet), for arbitrary shape text detection. The network consists of a Weighted Feature Fusion Pyramid Network (WFFPN), Text Fragments Subgraph (TFS), and Dense Graph Attention Network (DGAT), which can be trained end‐to‐end. The WFFPN is used to generate text fragments, TFS and DGAT jointly construct an affinity reasoning network. Since the neighbouring boundaries between text instances may blend them into a single instance, the core idea is to use the WFFPN to divide the text instance into a series of rectangular fragments, the affinity reasoning network infers the affinity between fragments and then links them to rebuild text instances. Extensive experiments on seven challenging datasets (ICDAR2015, MSRA‐TD500, Totaltext, CTW‐1500, ICDAR 2019MLT, ICDAR2019 ArT, and DAST‐1500) demonstrate that the proposed text detector achieves state‐of‐the‐art performance in both on polygon datasets and quadrilateral datasets. The code is available at https://github.com/giganticpower/FARNet .

Device-to-device (D2D) communication is one of the most promising technologies for relieving the pressure of demands in the 5G mobile networks. However, due to randomness of user request, limitation of storage space and transmission capacity, it is still a challenge for channel allocation to optimize the successful delivery ratio of contents. Thus, in this article, we first consider the link selection problem for mobile users in multi-D2D (MD2D)-based content delivery networks. We establish a content delivery utility that combines physical and social aspects, taking into account energy consumption, user mobility, and trust relationships. Second, we model the content delivery link selection as the maximum weighted matching problem. For this NP-hard problem, by relaxing the integer constraints, we propose a BnB-CDLS algorithm based on the branch-and-bound method for the proposed content delivery scheme. Furthermore, we prove that the problem can be computationally reduced to a monotone submodular problem subject to matroid and knapsack constraints, which can be solved by a greedy GA-CDLS algorithm. Numerical results show that as compared with the existing schemes, the proposed scheme can significantly improve the successful delivery ratio of contents.

For the double protograph low-density parity-check (DP-LDPC) code pair, indicating the source and channel codes utilized in the joint source channel coding, the coding optimization is generally implemented by the differential evolution searching with high complexity. In this paper, a new structured design of the DP-LDPC code pair is proposed based on Graph theory to reduce the searching complexity, namely mesh model-based merging (M3) method. Firstly, four basic mesh models are designed to merge the protographs at any dimension. According to the different structures of the source and channel codes, the merging boundary constraint is statistically established to limit the using number of basic models. Then, a prior sorting algorithm is proposed to arrange the selection priorities of basic models for source and channel codes, respectively, which greatly refines the merging accuracy. Since most of the degrees are symmetric and predetermined in the merged protographs, the searching complexity is significantly reduced when the merged protographs are used as the initial input. Finally, simulation results demonstrate that the merging DP-LDPC code pairs show better performances compared to the existing code pairs. Furthermore, the proposed M3 method is hardware-friendly in Internet of Things because of its simple structure.

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.

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.

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.

The protograph low‐density parity‐check (LDPC) codes possess many attractive properties, such as the low encoding/decoding complexity and better error floor performance, and hence have been successfully applied to different types of communication and data storage channels. In this study, the authors design protograph LDPC codes for communication systems corrupted by the impulsive noise, which are modelled as additive white symmetric alpha‐stable noise (AWS SN) channels. They start by presenting a novel simulation‐based protograph extrinsic information transfer analysis to derive the iterative decoding threshold of the protograph codes. By further applying the asymptotic weight distribution analysis, the authors design new protograph codes for the AWS SN channel. Both theoretical analysis and simulation results demonstrate that the proposed protograph codes can provide better error rate performance than the prior art AR4JA code, the irregular codes optimised for the AWGN channel, as well as the irregular codes optimised for the AWS SN channel.

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.

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.

This paper presents novel soft-decision decoding (SDD) of error correction codes (ECCs) that substantially improve the reliability of DNA-based data storage system compared with conventional hard-decision decoding (HDD). We propose a simplified system model for DNA-based data storage according to the major characteristics and different types of errors associated with the prevailing DNA synthesis and sequencing technologies. We compute analytically the error-free probability of each sequenced DNA oligonucleotide (oligo), based on which the soft-decision log-likelihood ratio (LLR) of each oligo can be derived. We apply the proposed SDD algorithms to the recently proposed DNA Fountain scheme. Simulation results show that SDD achieves an error rate improvement of two to three orders of magnitude over HDD, thus demonstrating its potential to improve the information density of DNA-based data storage systems.

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 considers a multiuser communication network, where a receiver is set to compute functions of the messages from K users. All user nodes and the receiver are equipped with multi-antenna. We propose a space-time (ST) coded multiple-input multiple-output (MIMO) linear physical-layer network coding (LPNC) scheme that promises full-rate and full-diversity, while achieving the maximum coding gain of LPNC. In the proposed framework, the users' messages are encoded by the same linear dispersion ST code and transmitted simultaneously. The receiver exploits the MIMO LPNC mapping in reconstructing an arbitrary number of linearly network-coded (NC) messages. We derive the NC generator matrix that leads to the greatest coding gain and minimized error probability at the receiver. On top of that, we analytically show that the proposed ST coded LPNC scheme guarantees the full-diversity and full-rate transmission. The proposed method applies to a wide range of network configurations. Two case studies on: (1) MIMO two-way relay network and (2) MIMO multiple-access relay network are presented in this paper. For both case studies, numerical results are shown to demonstrate the performance improvement of the proposed scheme over conventional schemes by more than 4 dB, while the full-rate and full-diversity behaviors are in line with our analysis.

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.

With the rapid development of narrow band power-line communications (NPLC) in recent years, many effective modulation schemes have been proposed for it. In this paper, we propose M-ary differential chaotic shift keying (M-DCSK) for Narrow Band (NB) PLC. Firstly, which improves the bandwidth efficiency compared with DCSK scheme. The performance of M-DCSK scheme is analyzed over PLC channels where background, impulsive and phase noise exist. Simulation results verifiy the accuracy of the derived theoretic performance. Due to the inner properties of chaotic carrier, M-DCSK shows good robustness against multipath fadings and phase noises, which are very common in PLC channels. Besides, comparing with the traditional direct sequence M-ary differential phase shift keying (DS-MDPSK) scheme, M-DCSK can achieve better bit error rate (BER) performances.

This paper presents several soft decision iterative decoding schemes for physical-layer network coding (PNC) operated with coded modulation (CM) and bit-interleaved coded modulation (BICM). With respect to PNC operated with CM, we consider network coding-based channel decoding (NC-CD) and multi-user complete decoding (MUD-NC) for PNC decoding at the relay. Their BICM counterparts are XOR-based channel decoding (XOR-CD) and MUD-XOR, respectively. First, we show that, when the decoding is non-iterative, there is a gap between the BICM capacities of both XOR-CD and MUD-XOR under Gray mapping and the capacities of their CM counterparts, NC-CD, and MUD-NC. This is in contrast to the conventional point-to-point communication system, for which the BICM capacity with Gray mapping is known to be very close to the CM capacity, without the need for iterative decoding. Second, we investigate the error performance of iteratively decoded BICM XOR-CD and MUD-XOR. Extrinsic information transfer chart analysis and simulation results indicate that for these Gray-mapped BICM PNC systems, iterative decoding can achieve considerable gains over non-iterative decoding. Again, this is in contrast to the Gray-mapped BICM point-to-point communication system, for which iterative decoding provides little gain over non-iterative decoding. We further show that Gray mapping gives rise to best PNC rate for MUD-XOR and XOR-CD systems among several bits-to-symbol mappings under study. Overall, our results indicate that BICM PNC systems exhibit different decoding behavior from conventional BICM point-to-point systems. This paper serves as a first foray into the investigation of this issue.

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.

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 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.