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This paper provides a comprehensive performance comparison between a current robust military waveform; namely, MIL-STD-188-110D, Waveform 0, and a filter bank multicarrier spread-spectrum (FBMC-SS) waveform proposed for communications through ionospheric/skywave HF channels. Waveform 0 is effectively a direct sequence spread spectrum waveform that uses Walsh multi-codes to enhance the information transmission rate. It may thus be referred to as Walsh-DSSS. FBMC-SS, on the other hand, makes use of filter banks to provide excellent performance when the received signal is subject to partial band interference. Successful application of FBMC-SS for communications across skywave HF channels has been previously demonstrated, both theoretically and through experimental work. However, very little has been done to contrast FBMC-SS against Walsh-DSSS. The goal of this paper is to first add new features to FBMC-SS to bring it on par with Walsh-DSSS. These features include: (i), introduction of multi-codes that achieve a comparable (or better) data rate to Walsh-DSSS; and (ii), addition of a scrambling step applied to the multi-codes to make the receiver detection robust against widely spread multipaths. With this established, in the second part of the paper, we examine the performance of the developed FBMC-SS against Walsh-DSSS when both are applied for communications across skywave HF channels. The two waveforms are compared both through a theoretical study and through experimental works across several skywave channels ranging from hundreds to thousands of kilometers. [ABSTRACT FROM AUTHOR]

Spinal codes are a new family of rateless codes which have been proved to be capacity-achieving over both the additive white Gaussian noise (AWGN) channel and the binary symmetric channel (BSC). However, over the Rayleigh fading channel between the vehicle nodes, the error performance of Spinal codes is not satisfactory since the tail message blocks of Spinal codes are prone to error. To solve this issue, this paper proposes a new practical partial self-concatenation coding structure of Spinal codes, named $N$ tail-protected Spinal codes, to pointedly protect tail message blocks of Spinal codes over the flat Rayleigh fading channel. Theoretical performance analysis and simulation results are also provided to validate and verify the effectiveness of the proposed $N$ tail-protected Spinal codes. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the design and analysis of the Analog Fountain Code (AFC) for short packet communications. We first propose a density evolution (DE) based framework, which tracks the evolution of the probability density function of the messages exchanged between variable and check nodes of AFC in the belief propagation decoder. Using the proposed DE framework, we formulate an optimisation problem to find the optimal AFC code parameters, including the weight-set, which minimises the bit error rate at a given signal-to-noise ratio (SNR). Our results show the superiority of our AFC code design compared to existing designs of AFC in the literature and thus the validity of the proposed DE framework in the asymptotically long block length regime. We then focus on selecting the precoder to improve the performance of AFC at short block lengths. Simulation results show that lower precode rates obtain better realised rates over a wide SNR range for short information block lengths. We also discuss the complexity of the AFC decoder and propose a threshold-based decoder to reduce the complexity. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel generalized space-code index modulation (GSCIM) scheme for spectrum-efficient and energy-saving transmission. In our proposed scheme, the input information bits are transmitted not only by modulated symbols, but also by the activated transmit antennas pattern and the selected spreading code patterns for the in-phase and quadrature components. Due to the increase of the index dimension, more information bits can be implicitly transmitted, which can improve energy efficiency and have a higher data rate compared with spatial modulation (SM), generalized SM (GSM), generalized CIM-aided SM (GCIM-SM) and CIM-aided quadrature spatial modulation (CIM-QSM). In order to further reduce the complexity of despreading-based maximum likelihood (ML) detection, we propose an enhanced low-complexity detector that can achieve near-ML error performance. An analytical upper bound on the average bit error probability associated with the optimal ML detection is derived, which is verified by simulation results. Simulation results also show that the proposed GSCIM scheme outperforms SM, GSM, GCIM-SM and CIM-QSM schemes in terms of error performance. [ABSTRACT FROM AUTHOR]

Combining powerful error-correction codes (ECCs) with multipulse pulse-position modulation (MPPM) has great potential to realize high-throughput and high-reliability transmissions in free-space optical (FSO) communication systems. This paper conducts an insightful investigation on protograph low-density parity-check (PLDPC)-coded MPPM systems over Poisson channels. To be specific, we first put forward a novel type of constellations, referred to as irregular pulse-distribution (IPD) constellations, for MPPM. We also conceive a bit-level rate-adaptive (RA) scheme, which can exploit the structural property of the IPD constellations to significantly improve the convergence performance at the price of transmission-rate loss. Furthermore, with the aid of a modified protograph extrinsic information transfer (PEXIT) algorithm, we construct three enhanced PLDPC codes with code rates $1/2, 2/3$ and $3/4$ that exhibit excellent decoding thresholds over Poisson channels. The proposed PLDPC-coded MPPM systems with the use of the IPD constellations, RA scheme, and enhanced PLDPC codes are superior to the state-of-the-art counterparts. [ABSTRACT FROM AUTHOR]

A quadrature spatial modulation with the fourth order transmit diversity (FO-QSM) scheme is presented in this paper. In this scheme, two dispersion-matrix (DM) sets are assigned at the transmitter, and $P$ out of $Q$ DMs are activated in each set to extend the real and imaginary parts of $P$ QSM signals respectively, to large number of transmit antennas. The two DM sets are constructed by performing Kronecker product between two simple extension matrices and the DMs of Sezginer-Sari-Biglieri (SSB) code. The framework designs of FO-QSM and the two DM sets make FO-QSM possess the properties: 1) it guarantees the fourth order transmit diversity without requiring any parameter optimization; 2) it has higher spectral efficiency than the newly proposed generalized space-time block coded spatial modulation (GSTBC-SM) scheme. Furthermore, a repeated computation reduced sphere decoding (RCR-SD) is proposed. RCR-SD is very suitable for the schemes constructed by a large number of DMs, including FO-QSM. By sorting the index vectors, the RCR-SD detector can efficiently reduce the repeated computations in the SD searching, which significantly reduces the decoding complexity without sacrificing optimal decoding performance. Simulation results show that FO-QSM has obvious better bit error rate (BER) performance than GSTBC-SM. [ABSTRACT FROM AUTHOR]

The paper proposes a multiple-input multiple-output-based power line communication (PLC) system subject to Rayleigh fading and corrupted by additive cyclostationary Gaussian noise. The proposed coherent receiver structure employs a block reception rule at the reception unit for detecting the space-time block-coded transmitted data symbols. A closed-form expression for the pairwise error probability (PEP) is derived using a characteristic function approach. Exact and asymptotic expressions for the average PEP are obtained for the special case of Alamouti code transmission which show that the PLC system under consideration offers full diversity. Numerical results depict the improvement in the system performance with increase in the number of receive diversity branches and the average signal-to-noise ratio per branch and decrease in the correlation value between the noise samples. [ABSTRACT FROM AUTHOR]

The internet of vehicles needs mobile communication systems for efficient communications. On the physical downlink control channel (PDCCH) of 5G, blind detection is performed to identify the downlink control information (DCI). Due to the uncertainty of DCI formats and PDCCH formats, the existing two-stage blind detection schemes separately decode every PDCCH code block under different DCI formats, leading to a high decoding complexity in the first stage. To reduce the detection complexity, this paper proposes an efficient DCI detection method, where a significance-test strategy is designed to detect the DCI formats. The significance-test strategy can forecast the DCI lengths without separately decoding the whole codeword, thus reducing the decoding complexity by several times. Moreover, the accuracy of the DCI detection is analyzed, with which the test scope of the test statistic is optimized for minimizing the decoding complexity on condition of meeting the detection accuracy requirements. Simulation results show that the proposed method significantly reduces the decoding complexity relatively to the existing two-stage detection schemes. [ABSTRACT FROM AUTHOR]

Modern vehicle-based distributed storage networks need to provide efficient data recovery services due to the high mobility nature of storage vehicles. Compared with the simple replication scheme, erasure codes have been increasingly deployed in practical systems to achieve better storage performance. Specifically, fractional repetition (FR) codes are a class of repair efficient erasure codes characterized by the features of uncoded exact repair and minimum repair bandwidth. In this paper, we consider the capacity of FR codes, which is the maximum amount of information that can be obtained by any user contacting $k$ out of $n$ storage nodes in the code based system. We present several families of FR codes that achieve a tight upper bound on the FR capacity, which are derived from combinatorial designs. The proposed constructions extend the parameter values of capacity-achieving FR codes to larger sets, and the resulting codes are of practical interest for vehicle-based distributed storage systems. [ABSTRACT FROM AUTHOR]

Batched sparse (BATS) coding is a promising new technique designed for reliable transmissions over erasure networks, which can achieve asymptotic bandwidth optimality. However, the decoder of the conventional BATS codes begins to recover the source packets only after receiving a sufficient number of encoded packets which induces delay. Moreover, the larger the source block size is, the longer the time delay will be. In this paper, we propose a scheme by using expanding window applied over BATS codes, termed the expanding-window BATS codes, which divide the source data into smaller blocks for reducing delay. Furthermore, for improving the decoding performance we design an adaptive encoder which encodes the source packets with dynamic encoding probabilities. Because the performance of BATS codes highly depends on the degree distribution, we further optimize the degree distributions for the proposed expanding-window BATS codes with linear programming and the performances have been verified by the simulation results. [ABSTRACT FROM AUTHOR]

Highmobility is an important scenario for the 5G wireless communications. However, the high mobility results in serious time-varying fading, bringing challenges to the reliabilities of wireless transmission. Diversity technique is an essential method to overcome the effect of fading. It is noted that an LDPC (low-density parity-check) code is a concatenation of single parity-check codes (SPC) and repetition codes (REP) by a random interleaver, and a REP can be viewed as a typical example for achieving time/frequency diversity. Thus, it is appealing to jointly consider LDPC codes and diversity techniques. This paper presents parity-check coding transmit diversity (PCTD) schemes based on half-rate invertible LDPC codes, which are capable of achieving both diversity and coding gains from the time-varying fading channels. Besides, we investigate two types of PCTD schemes, and take into consideration two transmission modes, which are single-carrier (SC) and orthogonal frequency division multiplexing (OFDM) transmission modes. A chase combining based message passing algorithm (CC-MPA) is proposed for the proposed schemes, which can take full advantages of signal processing and coding gains. Furthermore, the Shannon limits of time-varying fading channels with BPSK signaling are deduced. Simulation results show that the proposed PCTD with CC-MPA algorithm can provide better BER performances than the classical time-domain diversity scheme in time-varying fading channels, which is appealing for the high mobility communications. [ABSTRACT FROM AUTHOR]

The development of smart vehicles and rich cloud services have led to the emergence of vehicular edge computing. To perform the distributed computation tasks efficiently, Coded Distributed Computing (CDC) was proposed to reduce communication costs and mitigate the straggler effects through the use of coding techniques. In this paper, we propose a double auction mechanism to allocate the resources of the edge servers to the vehicles in order to complete the CDC tasks. Specifically, the vehicles use the PolyDot codes to manage the tradeoff between communication costs and recovery threshold. Given the requirements of various vehicles, the double auction mechanism matches the edge servers with the required resources to the vehicles. Besides, the double auction mechanism also determines the prices that the vehicles need to pay for the resources of the edge servers. The analyses show that the double auction mechanism satisfies the properties of individual rationality, incentive compatibility and budget-balance. From the simulation, the utility of auctioneer increases when the number of vehicles and edge servers increases. [ABSTRACT FROM AUTHOR]

This paper presents a cross-layer design of error-control protocols with rate adaptation for free-space optical (FSO) burst transmission in satellite communication systems. While the prior works mostly focused on the design of error-control protocols for terrestrial-based FSO communications, using either hybrid automatic repeat request (HARQ) based stop-and-wait mechanism or pure sliding window ARQ, we instead propose a design of HARQ-based sliding window mechanism for the high data-rate and long-distance of FSO-based satellite systems. In particular, we model and analyze the performance of low-earth orbit (LEO) satellite-to-ground FSO systems over atmospheric turbulence channels when truncated incremental redundancy (IR) HARQ protocols, which combine the rate-compatible punctured convolutional (RCPC) codes and sliding window ARQ, are employed. For this purpose, the time-varying behavior of atmospheric turbulence channels is first captured by a finite-state Markov chain. Then, the channel model is used to develop the burst loss model to analytically derive the system performance metrics, including throughput, energy efficiency, and average frame delay. The results quantitatively demonstrate the impact of atmospheric turbulence and pointing error on the system performance and support the optimal selection of parameters. Additionally, the effectiveness of the proposed system is numerically confirmed. Monte Carlo simulations are also performed to validate the accuracy of theoretical derivations. [ABSTRACT FROM AUTHOR]

Coded Slotted ALOHA (CSA) is a random access scheme based on the application of packet erasure correcting codes to transmitted packets and the use of successive interference cancellation at the receiver. CSA has been widely studied and a common assumption is that interference cancellation can always be applied perfectly. In this paper, we study the design of CSA protocol, accounting for a non-zero probability of error due to imperfect interference cancellation (IC). A classical method to evaluate the performance of such protocols is density evolution, originating from coding theory, and that we adapt to our assumptions. Analyzing the convergence of density evolution in asymptotic conditions, we derive the optimal parameters of CSA, i.e., the set of code selection probabilities of users that maximizes the channel load. A new parameter is introduced to model the packet loss rate of the system, which is non-zero due to potential IC errors. Multi-packet reception (MPR) and the performance of 2-MPR are also studied. We investigate the trade-off between optimal load and packet loss rate, which sheds light on new optimal distributions that outperform known ones. Finally, we show that our asymptotic analytical results are consistent with simulations obtained on a finite number of slots. [ABSTRACT FROM AUTHOR]

In this paper, we propose clustering-based blind detection methods with the aid of systematic convolutional low density generator matrix (SC-LDGM) codes. Inspired by the fact that the received signals naturally fall into clusters in the block-fading channels, we develop a system constrained Gaussian mixture model (SCGMM) by taking into account the inherent characteristics of communication systems, in which the parameters can be estimated by the expectation-maximization (EM) algorithm. We also present an initialization method for the proposed SCGMM to accelerate convergence. After clustering, a decoding algorithm of SC-LDGM codes is designed to resolve the centroid ambiguity. To further improve the detection performance in the low signal-to-noise (SNR) and deep fading scenarios, we propose an improved label-assisted (ILA) method, which integrates the label-assisted (LA) information into the blind detection algorithm. Numerical results show that the performance of our methods can closely approach the performance with perfect channel state information (CSI). The simulation results also show that the performance can be improved by increasing the encoding memory. [ABSTRACT FROM AUTHOR]

In this paper, an improved Quadrature Multi-carrier Differential Chaos Shift Keying (QMC-DCSK) based on Chaotic Shape-forming Filter (CSF) and Cross Correction (CC) is proposed. The chaotic signal generated by CSF is used as reference spreading sequence in QMC-DCSK. Quadrature multi-carriers are used to carry the reference and multiple information bearing signals simultaneously in order to improve the Bit Transmission Rate (BTR). By this way, the proposed system is able to transmit $2M-1$ bits Traditional Data Stream (TDS) during one traditional DCSK bit duration, where $M$ is the number of carrier frequencies. Meanwhile, the reference signal transmits Additional Data Stream (ADS) encoded by CSF together with $2M-1$ identical or inverse data stream carried by the rest $2M-1$ channels (information bearing signals). By this system configuration, the channel redundance can be used to improved bit error rate (BER) performance of ADS, after decoding TDS. In turn, the TDS reliability can also be improved by checking most ADS polarity of the corresponding carrier. This process is referred to as CC. The contribution of this work lies in the CC operation, by which the reliability of both TDS and ADS is improved significantly. It is the CSF and multi-carrier that make CC possible. The analytical BER is derived for the proposed method. The merits of the proposed system include, first, it improves the BTR as compared to that of QMC-DCSK, because ADS conveys more information bits; second, the ADS reliability is improved dramatically because the $\text{2}\,M$ duplication can be used to improve the signal to noise ratio; third, the TDS reliability is improved as well because the information bits conveyed by each carrier frequency is enhanced and corrected by the $\text{2}\,M$ repetitions. By this way, not only TDS and ADS are transmitted (i.e., the higher BTR is achieved), but also both reliability are improved (i.e. the lower BER is achieved). In order to testify the feasibility and superiority of the proposed method, simulation and wireless open-access research platform (WARP) experiment are conducted. The simulation and experiment results show that the proposed method is superior to other comparison methods. [ABSTRACT FROM AUTHOR]

In this paper, we propose a general carrier index assisted dual-mode differential chaos shift keying with full mapping (GCI-DM-DCSK-FM) system, where a pair of distinguishable modem-mode signals is designed with the aid of general carrier index modulation. Specifically, the selected and unselected subcarriers are used to carry differential chaos shift keying (DCSK) and quadrature chaos shift keying (QCSK) signals, respectively, thereby obtaining higher data rate and spectral efficiency. To tackle the issue of discarding the subcarrier activation pattern (SAP), an effective full mapping method is proposed for the GCI-DM-DCSK-FM system to harvest better bit error rate (BER) performance and higher data rate. Moreover, a noise decontamination method is designed for the GCI-DM-DCSK-FM system to enhance the BER performance. To confirm the validness for our proposed systems, we derive the BER expressions of the GCI-DM-DCSK-FM system over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels. Finally, plenty of simulation results show the excellent BER performance of the GCI-DM-DCSK-FM system. [ABSTRACT FROM AUTHOR]

In this paper, we design a kind of robust rateless multi-user code, which is called spatially coupled repeat-accumulate-repeat (SC-RA-R) code, for the interleave-division multiple-access (IDMA) system. The code is constructed by serially concatenating a fixed outer spatially coupled repeat-accumulate (SC-RA) code with an adjustable inner irregular repetition code. It achieves rateless property by simply adjusting the parameters of the inner repetition code. The IDMA system with the proposed SC-RA-R multi-user codes can adapt to varying channel qualities and varying number of users via rateless property while keeping encoder and decoder implementation unchanged. Analytical extrinsic information transfer (EXIT) functions are derived to determine belief propagation (BP) decoding thresholds of SC-RA-R codes on the IDMA system. The optimization expression is also given under the constraint that repeat parameters are monotonically non-decreasing with the sum rate decreasing. The numerical results show that the maximum achievable sum rates of the SC-RA-R codes can be close to the Shannon bound for arbitrary channel qualities. Besides, our proposed SC-RA-R codes have better BP thresholds and bit-error-rate (BER) performances than the conventional optimal parallel-concatenate codes (PCC) and the optimal partially repeated spatially coupled low-density parity-check (PR-SC-LDPC) codes on IDMA systems. [ABSTRACT FROM AUTHOR]

Mobile storage systems (MSSs) which store popular content in mobile devices can reduce the heavy traffic burden on the base station (BS). To deal with data loss caused by the mobility of devices, erasure codes are widely used in practice to improve system reliability. The duration to repair all lost data is defined the repair delay. However, the repair delay via device-to-device communications is usually large due to intermittent contacts among devices within a given communication range, which causes files to be irreparable and permanently lost. This paper focuses on analyzing the repair delay of the MSSs through D2D communications. We adopt a coded repair process running periodically and derive analytical expressions of the average repair delay by taking into account factors, i.e., limited communication range, device mobility, and coded repair scheme. Moreover, considering that devices need multipath contacts to repair lost data for large files, we propose a relay cooperation repair scheme, in which some mobile devices can act as relay nodes to transmit data cooperatively. Furthermore, we design a heuristic algorithm to optimize the number of relay devices and the amount of data allocated to each path, with the objective of minimizing the average repair delay. We find that maximum distance separable codes can yield smaller average repair delays for small files, and the average repair delay can be reduced by selecting faster moving devices to participate. With the file size increasing, the relay cooperation repair scheme can significantly improve repair efficiency in MSSs using the proposed heuristic algorithm. [ABSTRACT FROM AUTHOR]

A novel permuted fast successive-cancellation list decoding algorithm with fast Hadamard transform (FHT-FSCL) is presented. The proposed decoder initializes $L$ $(L\geq 1)$ active decoding paths with $L$ random codeword permutations sampled from the full symmetry group of the codes. The path extension in the permutation domain is carried out until the first constituent RM code of order 1 is visited. Conventional path extension of the successive-cancellation list decoder is then utilized in the information bit domain. The simulation results show that for a RM code of length 512 with 46 information bits, by running 20 parallel permuted FHT-FSCL decoders with $L=4$ , we reduce 72% of the computational complexity, 22% of the decoding latency, and 84% of the memory consumption of the state-of-the-art simplified successive-cancellation decoder that uses 512 permutations sampled from the full symmetry group of the code, with similar error-correction performance at the target frame error rate of $10^{-4}$. [ABSTRACT FROM AUTHOR]

Sparse code multiple access (SCMA) is a promising multiuser communication technique for the enabling of future massive machine-type networks. Unlike existing codebook design schemes assuming uniform power allocation, we present a novel class of SCMA codebooks which display power imbalance among different users for downlink transmission. Based on the Star-QAM mother constellation structure and with the aid of genetic algorithm, we optimize the minimum Euclidean distance (MED) and the minimum product distance (MPD) of the proposed codebooks. Numerical simulation results show that our proposed codebooks lead to significantly improved error rate performances over Gaussian channels and Rayleigh fading channels. [ABSTRACT FROM AUTHOR]

Satellite high-mobility communications can provide global communication services for mobile terminals, which plays a vital role in today's world of wireless communications. Different from traditional terrestrial-satellite communications, high-mobility terminals impose more challenges on the direct sequence spread spectrum (DSSS) signal acquisition in satellite communications. On the one hand, the spread spectrum sequence used in satellite communication systems is relatively long, which inevitably increases the computational complexity. On the other hand, high Doppler frequency offsets and time-varying Doppler rates caused by high-mobility terminals make satellite DSSS signal acquisition become the bottleneck. To solve such a problem in high-mobility satellite communications, we propose a new acquisition algorithm based on the new factor graph where time-varying Doppler rate is modeled by the random walk model, named the turbo iterative acquisition algorithm. It consists of the constraint-detection loop and the Doppler-estimation loop. By means of soft messages passed between these loops, the negative influence of time-varying Doppler frequency offsets can be eliminated effectively. Simulation results show that, compared with traditional algorithms, the proposed algorithm improves acquisition performance more than 1.3 dB with low computational complexity, which demonstrates the superiority of the proposed algorithm in terms of acquisition performance and complexity. [ABSTRACT FROM AUTHOR]

The demand for multimedia services is growing day by day in vehicular ad hoc networks (VANETs), resulting in high spectral usage and network congestion. Non-orthogonal multiple access (NOMA) is a promising wireless communication technique to solve the problems related to spectral efficiency effectively. The index coding (IC) is a powerful method to improve spectral utilization, where a sender aims to satisfy the needs of multiple receivers with a minimum number of transmissions. By combining these two approaches, in this work, we propose a novel technique called index coded NOMA (IC-NOMA), where we apply NOMA techniques on index coded data to reduce the number of transmissions further. This work shows that the IC-NOMA system demands a specific design for index codes to reap the advantages of NOMA. We have done the feasibility analysis of the proposed method in a general scenario and proposed an index code design to integrate IC over NOMA for the best efficiency. Through detailed analytical studies it is validated that the proposed transmission system provides improved spectral efficiency and power saving compared to conventional IC systems. [ABSTRACT FROM AUTHOR]

Since a novel diversity technique called a space–time line code (STLC) was invented, previous studies have focused on the analysis of a rate-1 STLC assuming two receive antennas. For the state-of-the-art STLCs with transmit antenna selection (TAS), in this study, the ergodic capacities of TAS-STLC systems with various code rates are mathematically derived, not only for a TAS-STLC system with two receive antennas but also for those with three or four. To this end, the probability density function of the instantaneous signal-to-noise ratio was characterized. The accuracy of the mathematical analysis was validated by a numerical simulation. This study is significant for investigating the fundamental performance of TAS-STLC systems. [ABSTRACT FROM AUTHOR]

Embedded index coding problem is a variant of index coding problems, where each user functions as both broadcast sender and receiver. Consider a set of the messages, the indices of which form an ordered set. Each user owns a subset of these messages known as side information and tries to meet the demands of one another with a minimum number of transmissions. The side information is said to be consecutive if the elements of the index set of side information at a user are consecutive. We consider a practical vehicular ad-hoc network where the embedded index coding could be applied. In the scenario considered, the receiver demands all messages it does not possess, and the side-information is consecutive. Under this setup, a lower bound on the number of transmissions is determined. We present an optimal solution to achieve the bound. The constructed codes work over any field size, including binary. [ABSTRACT FROM AUTHOR]

Hybrid multiple access schemes are considered potential technologies towards achieving optimal spectrum sharing for future heterogeneous networks. Multiple users are multiplexed on a single resource unit in the code domain for sparse code multiple access (SCMA) or power domain for power domain non-orthogonal multiple access (PD-NOMA) and in both domains for the hybrid power domain sparse code non-orthogonal multiple access (PD-SCMA). This allows for effective spectrum usage but comes at a cost of increased detection complexity resulting in loss of performance in terms of outages. It is therefore imperative to determine the user multiplexing capacity for effective performance. This work investigates codebook capacity bounds in small cells, pairing and power capacity bounds for the number of small cell user equipment’s (SUEs) and macro cell user equipment’s (MUEs) that can be multiplexed on a codebook for the developed PD-SCMA technology. Closed-form solutions for codebook, pairing and power multiplexing capacity bounds are derived. The performance of the system results into low outage when the system’s point of operation is within the multiplexing bounds. To alleviate the resource allocation (RA) challenges of such a system at the transmitter, dual parameter ranking (DPR) and alternate search method (ASM) based RA schemes are proposed. The results show significant capacity gain with DPR-RA in comparison with conventional schemes. [ABSTRACT FROM AUTHOR]

A forward error correction (FEC) and unity-rate coded (URC) autoencoder (AE)-assisted communication system is proposed for the first time, which relies on soft iterative decoding for attaining a vanishingly low error probability. The AE-demapper is specifically designed for directly calculating the extrinsic logarithmic likelihood ratios (LLRs), which can be directly entered into the URC decoder for soft iterative decoding. This avoids the potential degradation due to the conversion of symbol probabilities to bit LLRs. A comprehensive capacity analysis of the AE is performed, which demonstrates the capacity advantage of the AE-aided constellation design over its conventional quadrature amplitude modulation (QAM)/ phase shift keying (PSK) counterpart. Furthermore, we carry out its EXtrinsic Information Transfer (EXIT) chart analysis, which indicates that as a benefit of our URC, the EXIT curve always reaches the [1,1] point of perfect convergence, leading to a vanishingly low error probability. More explicitly, our bit error ratio (BER) and block error ratio (BLER) results demonstrate that the proposed FEC-URC-AE system achieves significant iterative gains both in additive white Gaussian noise (AWGN) and Rayleigh channels, outperforming both its model-based FEC-AE and its conventional coded QAM/QPSK counterparts. [ABSTRACT FROM AUTHOR]

In an orthogonal frequency division multiplexing (OFDM) system, cyclic prefix (CP) has to be added to eliminate multipath-induced inter-symbol interference (ISI) with a severely sacrificed bandwidth efficiency. Peak-to-average ratio (PAPR) may impair its performance further if a large number of carriers are used. On the other hand, traditional multi-carrier modulation suffers a prohibitive complexity, which can not be implemented with colorred current available silicon technologies. This work proposes a cost-effective way to implement multi-carrier modulation, namely multi-layer quadrature (MLQ) modulation, which requires only two oscillators. As an application example, we apply MLQ modulation to a complementary coded code division multiple access (MLQ-CC-CDMA) system, whose multi-carrier transmission is based on MLQ modulation to mitigate ISI and multi-user interference (MUI) with ideal auto- and cross-correlations of complementary codes. Compared to a frequency domain (FD) CC-CDMA system, MLQ-CC-CDMA has a lower RF complexity. Compared to OFDM direct sequence (DS) CDMA and single carrier frequency division multiple access (SC-FDMA) CDMA schemes, MLQ-CC-CDMA achieves a higher spectrum efficiency (SE) and a lower bit error rate with Rake and minimum mean square error (MMSE) detection due to its powerful multipath and multi-carrier diversity gains. [ABSTRACT FROM AUTHOR]

This work focuses on the impact of finite-blocklength (FBL) regimes on performance of hybrid automatic repeat request (HARQ) protocols under the proposed conditions of outdated channel state information (oCSI) severity, generalised-Rician fading and maximal-ratio-combining deployment. The outage probability (OP)|defined as the probability of erroneous HARQ short-packet transmissions and the OP is a key performance indicator in this work|will be derived in compact form under the proposed conditions. Compact expressions are obtained, which depict the OP under these practical conditions and present certain trade-off among latency, blocklength and the OP. A brief review of existing results is performed. Penalty of increasing information capacity and the dominance of system coherence are shown, which justifies this work. [ABSTRACT FROM AUTHOR]

Electromagnetic interference causes considerable performance degradation on wireless communication systems. The performance degradation is largely affected by the characteristics of the interference. Impulse interference commonly occurs in industrial and automotive environments, where many closely located systems and electronic equipment coexist. In this work, we propose two novel algorithms for adaptive demodulation in impulse noise. The proposed methods compute appropriate log-likelihood ratios based on interference classification and estimation of Middleton’s Class A noise model as well as the symmetric $\alpha$ -Stable (S $\alpha$ S) model. The analytical complexity and intractability of the S $\alpha$ S probability density function (PDF) makes real-time applications unfeasible. Therefore, the proposed algorithms are developed using two different techniques for approximating the S $\alpha$ S PDF. The approximations are achieved through interpolation via i) approximate closed-form expressions of the PDF for a specific parameter set and ii) via numerically pre-calculated look-up tables of the PDF for arbitrary parameter choices. The proposed adaptive techniques are shown to provide a performance gain in terms of bit error rate (BER) of up to 20 dB energy per bit to noise power ratio (Eb/N0), in comparison to traditional, non-adaptive, methods for varying levels of impulse interference. The performance loss of approximating the PDF in comparison to exact calculations amount to less than 8 dB Eb/N0, which is small in relation to the performance gain achieved in comparison to traditional methods. However, the complexity in terms of simulation execution time of the proposed approximate algorithms is reduced by up to a factor 250, compared to methods based on exact computation. The algorithms are validated using regular low density parity check (LDPC) codes, in addition to quasi-cyclic (QC)-LDPC and turbo codes. The proposed adaptive demodulation techniques can be used to improve decoding and demodulation performance in many real-life situations where non-Gaussian interference commonly occurs. [ABSTRACT FROM AUTHOR]

Spectrum efficiency is a critical performance metric in wireless communications due to an increasing demand for radio spectrum to support high data rate applications. Direct sequence spread spectrum technology enables a code division multiple access (CDMA) system a strong anti-interference capability but with a relatively low spectrum efficiency. To address this issue, complementary coded scrambling multiple access (CCSMA) (X. Liu et al., in 2018) was proposed to use three-dimensional (space-time-frequency) resources for performance enhancement. However, in a CCSMA system, if the number of multipath returns is larger than the number of transmit (Tx) antennas, a code reuse problem occurs to degrade bit error rate performance significantly. This work designs a new scrambling code, namely generalized complementary coded scrambling multiple access (GCCSMA) codes, to overcome the code reuse problem in CCSMA. GCCSMA uses complementary codes, scrambling modulation, and multiple-input-multiple-output (MIMO) techniques jointly, which works well even in multipath channels with more paths than the number of Tx antennas. The analysis and simulations are conducted to validate the effectiveness of the proposed GCCSMA system. [ABSTRACT FROM AUTHOR]

Low-complexity detectors are conceivedfor the spatial modulation-aided sparse code-division multiple-access (SM-SCDMA). Firstly, the approximate message passing (AMP) algorithm is adapted for the detection of SM-SCDMA, which has less than 1% detection complexity of the state-of-the-art message passing-aided (MPA) detection albeit at a bit error ratio (BER) degradation. Therefore, inspired by the benefits of interference cancellation (IC) and the unique characteristics of SM, an enhanced AMP (EAMP) detector is proposed for mitigating BER degradation without increasing the detection complexity. Finally, the classic expectation propagation (EP) is intrinsically amalgamated with our EAMP detector, leading to a novel EAMP-EP detector, which further reduces the detection complexity of the EAMP algorithm. The three detectors are compared both in terms of their coded and uncoded BER, as well as complexity. [ABSTRACT FROM AUTHOR]

In future wireless communications, the Internet of Things (IoT) is a promising paradigm which is expected to connect massive number of devices while satisfying ultra-reliable and low latency communications (URLLC). In this article, we consider a multi-device IoT network supporting URLLC, where the data transmission process from the devices perform blind Automatic Repeat-reQuest (ARQ) or Hybrid ARQ (HARQ) via shared radio resources. We leverage recent advances in the characterization of coding rates and error probability in the finite blocklength regime to investigate the reliability and goodput performances of such network with both ARQ and HARQ schemes. Furthermore, both reliability-oriented and goodput-oriented designs are proposed for ARQ and HARQ schemes, respectively. In particular, we provide the optimal solutions for the error probability minimization problem, while efficient sub-optimal solutions for the goodput maximization problem are introduced, which show a tight performance in comparison to exhaustive search. Via simulation, the analytical results are validated and the system performance for both schemes are evaluated under variant setups with respect to total resources, packet sizes and SNR. [ABSTRACT FROM AUTHOR]

A novel index modulation with spherical code and its constellation mapping are proposed. We derive the closed form of the approximation bound of the bit error rate (BER) of the OFDM-IM system based on four-dimensional spherical code. Our derived BER is very close to the simulation results. And different constellation mapping method have different BER performance and the gap is less than 0.2 dB. To reduce the detection complexity which is caused by the high-dimensional modulation, a DNN-based receiver with partial-connected layer is proposed. Simulation results show that our proposed DNN-based receiver can greatly reduce the complexity while its BER performance is close to the classical maximum likelihood detection method. [ABSTRACT FROM AUTHOR]

We consider multi-input convolutional codes with unequal error protection (UEP) among the inputs. Using conventional metrics including the free input distance and free input sum weight as a measure for UEP degree, we design efficient and optimal algorithms to evaluate these metrics for any number of inputs. Next, we discuss several ambiguities arisen from using these metrics to estimate convolutional code UEP property and propose two new metrics, the average weight per path and the ant colony system UEP (ACS-UEP) index. The ACS-UEP index can accurately and consistently capture UEP properties over all ranges of SNR. Using these metrics, we propose an algorithmic process for designing convolutional codes with bounded external degree complexity to minimize a weighted sum of input error probabilities. We analyze the effectiveness of the design approach and show significant improvements over existing UEP convolutional code designing approach in terms of both the absolute and UEP input error protections. Our proposed algorithms for designing multi-input convolutional codes with UEP are flexible, adaptable, and provide high performance codes within the specified complexity. [ABSTRACT FROM AUTHOR]