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In this contribution, the performance of wideband code-division multiple-access (W-CDMA) systems using space-time-spreading- (STS-) based transmit diversity is investigated, when frequency-selective Nakagami-m fading channels, multiuser interference, and background noise are considered. The analysis and numerical results suggest that the achievable diversity order is the product of the frequency-selective diversity order and the transmit diversity order. Furthermore, both the transmit diversity and the frequency-selective diversity have the same order of importance. Since W-CDMA signals are subjected to frequency-selective fading, the number of resolvable paths at the receiver may vary over a wide range depending on the transmission environment encountered. It can be shown that, for wireless channels where the frequency selectivity is sufficiently high, transmit diversity may be not necessitated. Under this case, multiple transmission antennas can be leveraged into an increased bitrate. Therefore, an adaptive STS-based transmission scheme is then proposed for improving the throughput of W-CDMA systems. Our numerical results demonstrate that this adaptive STS-based transmission scheme is capable of significantly improving the effective throughput of W-CDMA systems. Specifically, the studied W-CDMA system's bitrate can be increased by a factor of three at the modest cost of requiring an extra 0.4 dB or 1.2 dB transmitted power in the context of the investigated urban or suburban areas, respectively.

The efficiency of link adaptation in wireless communications relies greatly on the accuracy of channel knowledge and transmission mode selection. In this paper, a novel deep learning based link adaptation framework is proposed for the orthogonal frequency-division multiplexing (OFDM) systems with compressed-sensing-assisted index modulation, termed as OFDM-CSIM, communicating over millimeter-wave (mmWave) channels. To achieve link adaptation, a novel multi-layer sparse Bayesian learning (SBL) algorithm is proposed for accurately and instantaneously providing the required channel state information. Meanwhile, a deep neural networks (DNN)-assisted adaptive modulation algorithm is proposed to choose the best possible transmission mode to maximize the achievable throughput. Simulation results show that the proposed multi-layer SBL algorithm enables more accurate channel estimation than the conventional techniques. The DNN-based adaptive modulator is capable of achieving a higher throughput than the learning-assisted solution based on the $k$ nearest neighbor ($k$ -NN) algorithm, and also the classic average signal-to-noise ratio (SNR)-based solutions. Moreover, analysis shows that both the multi-layer SBL algorithm and the DNN-assisted adaptive modulator achieve better performance than their respective conventional counterparts while at a significantly lower computational complexity cost. [ABSTRACT FROM AUTHOR]

This paper investigates the uplink performance of a high-capacity direct-sequence code-division multiple-access (DS-CDMA) wireless communication system, where numerous antennas are distributed in the area covered by the system. Following the description of the system, typical characteristics of the distributed-antenna DS-CDMA (DA/DS-CDMA) system are summarized, in comparison with conventional DS-CDMA systems that employ centralized base station (BS) antennas. Then, the bit error rate (BER) performance of the DA/DS-CDMA system without using power control is investigated when the low-complexity correlation and minimum mean square error (MMSE) detectors are employed and when composite transmission pass loss, lognormal shadowing slow fading, and Nakagami-m fast fading are considered. Our analytical and numerical results suggest that the DA/DS-CDMA system constitutes a high-power-efficiency wireless system. For the same set of system parameters, the DA/DS-CDMA system is capable of providing a much higher capacity than the conventional DS-CDMA system. The DA/DS-CDMA system can be free from power control. Furthermore, the hand-over in the DA/DS-CDMA system is also very simple. Index Terms--Code-division multiple access (CDMA), distributed antennas, large-scale fading, multiple input-multiple output (MIMO), multiuser detection (MUD), single-user detection (SUD), small-scale fading.

This article discusses the self-sustainability of reconfigurable intelligent surface (RIS) in wireless powered Internet of Things (IoT) networks. Our vision is that RIS helps improve energy harvesting and data transmission capabilities simultaneously, without the extra utilization of RF spectrum and energy consumption. The inherent properties of RIS are first discussed to unveil its distinctive features, followed by a broader range of use cases motivated by RIS as their enabling technology. The focus is on the application of RIS in the wireless powered IoT networks, and its potential to interconnect and support these practical use cases. Such an application is then thoroughly evaluated in a case study of an RIS-assisted wireless powered sensor network, with system throughput, energy transmission time consumption, and energy harvesting as the key performance metrics. The comprehensive performance evaluation showcases the self-sustainable property of RIS being unlocked in the considered scenario, identifying a clear pathway toward the future wireless powered IoT networks. We further pave the way by exploring research challenges and open issues related to emerging technological development. [ABSTRACT FROM AUTHOR]

In this paper we investigate a turbo detection scheme designed for robust video transmission over an uncorrelated Rayleigh fading channel. We first introduce a novel block error-correcting code, referred to as an extrinsic information transfer (EXIT)-chart optimized block code (ECOBC), which benefits from soft decision decoding. The ECOBC exploits both the residual redundancy which manifests itself in terms of the non-uniform probability distribution of K-bit strings inherent in the video encoded bit-stream, as well as the intentional redundancy imposed by the ECOBC for mitigating the effects of transmission errors. As our first novel contribution, we address the design of ECOBCs by formulating the necessary and sufficient condition, which ensures that the EXIT function of the sof-tbit ECOBC decoder reaches the (1,1) point in the EXIT chart. Secondly, we propose a novel real-valued free-distance metric for characterizing the ECOBC's performance. Furthermore, the attainable performance and the computational complexity imposed by the ECOBC are investigated. The effects of the interleaver delay on the ECOBC's performance are also quantified. As an additional result, we demonstrate that at a fixed system bandwidth, the turbo detection scheme using the H.264 video codec with the error concealment tools disabled but amalgamated with the proposed ECOBC as well as an additional generalized low-density parity-check (GLDPC) code may lead to an approximately 2.5 dB signal-to-noise ratio gain in comparison to the benchmarker having the same total bit rate, which operated the H.264 scheme with the error concealment tools enabled hence resulting in a higher video rate and amalgamated with the same-rate GLDPC code, but dispensing with our novel ECOBC. Index Terms--Error resilient video compression, extrinsic information transfer charts (EXIT), EXIT-chart optimized block code, generalized low-density parity-check (GLDPC) codes, H.264 standard, softbit APP decoding.

Subspace-based blind and group-blind space-time (ST) multiuser detection (MUD) is invoked for a smart-antenna-aided generalized multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) system communicating over a dispersive ST Rayleigh fading channel, where the channel estimates are attained by using subspace-based blind techniques. Smart antennas are employed to provide increased degrees of freedom and, hence, to improve both the attainable single-user performance and the multiuser capacity. Furthermore, two adaptive subspace-tracking algorithms, i.e., the Projection Approximation Subspace-Tracking deflation (PASTd) algorithm and the Noise-Averaged Hermitian--Jacobi Fast Subspace Tracking (NAHJ-FST) algorithm, are employed for the sake of reducing the computational complexity imposed by eigenvalue decomposition. When employing the NAHJ-FST algorithm, the group-blind MUD employing an antenna array having M = 2 elements exposed to uncorrelated fading achieved a 4.2-dB signal-to-noise-ratio (SNR) gain at a bit error rate (BER) of [10.sup.-4] compared with that employing a single antenna, which is an explicit benefit of its increased computational complexity. Index Terms--Blind multiuser detection, frequency-domain spreading, generalized MC-CDMA, group-blind multiuser detection, MUD, time-domain spreading.

We employ the Mellin transform to facilitate the bit error ratio (BER) analysis of a fast frequency hopping (FFH)-assisted, M-ary frequency-shift keying (MFSK) using product combining (PC) when the transmitted signal is subjected to both Rayleigh fading and partial-band noise jamming. Exploiting the fact that the Mellin transform of the product of independent random variables is the product of their Mellin transforms, we derive the probability density function (PDF) of the PC's output. The derivation of the PDF then allows the computation of the system's BER. It is shown that the Mellin transform substantially simplifies the analysis of the PC receiver and hence facilitates, for the first time, the analysis of the FFH-MFSK PC receiver for modulation orders of M > 2. Index Terms--Fast frequency hopping (FFH), Mellin transform, partial-band noise jamming (PBNJ), probability density function (PDF), product combining (PC), Rayleigh fading, residues.

In this letter a multiuser transmitter preprocessing (MUTP) approach is proposed for downlink wireless communications, such as in spatial-division multiple-access (SDMA) or direct-sequence code-division multiple-access (DS-CDMA) system. In the proposed MUTP the preprocessing matrix is obtained by constructing a subspace that is orthogonai to the interference subspace without relying on eigen-analysis. The proposed MUTP fully removes the downlink multiuser interference, resulting in the zero-forcing (ZF) solution. It is capable of achieving the same bit error rate (BER) performance as the conventional ZF-based MUTP (ZF-MUTP). Index Terms--Pre-filtering, preprocessing, zero-forcing, multiple-input multiple-output, space-division multiple-access, direct-sequence code-division multiple-access, orthogonal subspace.

A novel ant colony optimization (ACO)-based multiuser detector (MUD) is designed for the synchronous multifunctional antenna array (MFAA)-assisted multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) uplink, which supports both receiver diversity and receiver beamforming. The ACO-based MUD aims to achieve a bit-error-rate performance approaching that of the optimum maximum-likelihood (ML) MUD, without carrying out an exhaustive search of the entire MC DS-CDMA search space constituted by all possible combinations of the received multiuser vectors. We will demonstrate that regardless of the number of the subcarriers or of the MFAA configuration, the system employing the proposed ACO-based MUD is capable of supporting 32 users with the aid of 31-chip Gold codes used as the T-domain spreading sequence without any significant performance degradation when compared to the single-user system. As a further benefit, the number of floating-point operations per second imposed by the proposed ACO-based MUD is a factor of [10.sup.8] lower than that of the ML MUD. We will also show that at a given increase of the complexity, the MFAA will allow the ACO-based MUD to achieve a higher signal-to-noise ratio gain than the single-input-single-output MC DS-CDMA system. Index Terms--Ant colony optimization (ACO), multicarrier direct-sequence code-division multiple access (MC DS-CDMA), multifunctional antenna array (MFAA), multiuser detector (MUD), near-maximum-likelihood detection (near-MLD), uplink (UL).

In this paper, the achievable performance of Reed-Solomon (RS)-coded slow-frequency-hopping assisted M-ary frequency-shift keying using various erasure-insertion (EI) schemes is investigated when communicating over uncorrelated Rayleigh fading channels in the presence of multitone jamming. Three different E1 schemes are considered, which are based on the output threshold test, on the ratio threshold test, and on the joint maximum output--ratio threshold test. The relevant statistics of these EI schemes are investigated mathematically, and based on these statistics, their performance is evaluated in the context of RS error-and-erasure decoding (EED). It is demonstrated that the system performance can be significantly improved by using EED, invoking the EI schemes considered. Index Terms--Error-and-erasure decoding (EED), maximum output-ratio threshold test (MO-RTT), output threshold test (OTT), ratio threshold test (RTT), slow frequency hopping (SFH), tone jamming (TJ).

A time-hopping multicarrier code-division multiple-access (TH/MC-CDMA) scheme is proposed and investigated. In the proposed TH/MC-CDMA, each information symbol is transmitted by a number of time-domain pulses with each time-domain pulse modulating a subcarrier. The transmitted information at the receiver is extracted from one of the, say, M possible time-slot positions, i.e., assuming that M-ary pulse-position modulation is employed. Specifically, in this paper, we concentrate on the scenarios such as system design, power spectral density (PSD) and single-user-based signal detection. The error performance of the TH/MC-CDMA system is investigated when each subcarrier signal experiences flat Nakagami-m fading in addition to additive white Gaussian noise. According to our analysis and results, it can be shown that the TH/MC-CDMA signal is capable of providing a near ideal PSD, which is flat over the system bandwidth available, while decreasing rapidly beyond that bandwidth. Explicitly, signals having this type of PSD are beneficial to both broadband and ultrawide-bandwidth communications. Furthermore, our results show that when optimum user address codes are employed, the single-user detector considered is near-far resistant, provided that the number of users supported by the system is lower than the number of subcarriers used for conveying an information symbol. Index Terms--Code-division multiple access (CDMA), frequency-time matrix, multicarrier (MC), multiuser detection, Nakagami fading channels, power spectral density (PSD), time-hopping (TH), ultrawide-bandwidth (UWB) radio.

In this paper, the authors will investigate the performance of a loosely synchronized (LS) code-based space-time spreading (STS) scheme in comparison to that of classic Walsh code and pseudonoise code-based STS when communicating over dispersive Nakagami-m multipath channels. Closed-form formulas are derived for characterizing the bit-error-rate performance as a function of the number of resolvable paths L and the number of users K. Our numerical results suggest that the employment of LS code-based STS scheme is beneficial in a low-user-load and low-dispersion channel scenario, where a near-single-user performance can be achieved without a multiuser detector. Index Terms--Code-division multiple access (CDMA), Gaussian approximation, interference-free window (IFW), large area synchronized (LAS) codes, loosely synchronized (LS) codes, Nakagami-m fading.

The novel family of redundant residue number system (RRNS) codes is studied. RRNS codes constitute maximum-minimum distance block codes, exhibiting identical distance properties to Reed-Solomon codes. Binary to RRNS symbol-mapping methods are proposed, in order to implement both systematic and non-systematic RRNS codes. Furthermore, the upper-bound performance of systematic RRNS codes is investigated, when maximum-likelihood (ML) soft decoding is invoked. The classic Chase algorithm achieving near-ML soft decoding is introduced for the first time for RRNS codes, in order to decrease the complexity of the ML soft decoding. Furthermore, the modified Chase algorithm is employed to accept soft inputs, as well as to provide soft outputs, assisting in the turbo decoding of RRNS codes by using the soft-input/soft-output Chase algorithm. Index Terms--Redundant residue number system (RRNS), residue number system (RNS), turbo detection.

A burst-by-burst (BbB) adaptive speech transceiver is proposed, which can drop its source coding rate and speech quality under transceiver control in order to invoke a more error resilient modem mode among less favorable channel conditions. The adaptive multirate (AMR) speech eodec is operated at bit rates of 4.75 and 10.2 kb/s and combined with source sensitivity-matched redundant residue number system (RRNSI based channel codes. BbB adaptive joint detection aided code division multiple access is used for supporting the dual rate speech codec. Both the objective and subjective speech quality assessments favored the proposed BbB adaptive transceiver. Index Terms--AMR voice codec, HSDPA, RNS, RRNS.

In this contribution, we study a reduced-complexity multiuser detection aided multicarrier direct-sequence code-division multipleaccess (MC DS-CDMA) scheme, which employs both time (T)-domain and frequency (F)-domain spreading. We investigate the achievable detection performance in the context of synchronous TF-domain spread MC DS-CDMA when communicating over an additive white Gaussian noise (AWGN) channel. Five detection schemes are investigated, which include the single-user correlation based detector, the joint TF-domain decorrelating multiuser detector (MUD), the joint TF-domain MMSE MUD, the separate TF-domain decorrelating/MMSE MUD, and the separate TF-domain MMSE/decorrelating MUD. Our simulation results show that the separate TF-domain MUD schemes are capable of achieving a similar bit error rate (BER) performance to that of the significantly more complex joint TF-domain MUD schemes. Index Terms--Code-division multiple-access (CDMA), decorrelating, frequency-domain spreading, joint detection, minimum mean square error (MMSE), multicarrier (MC), multiuser detection, separate detection, time-domain spreading.

In multicarrier code-division multiple-access (MC-CDMA), the total system bandwidth is divided into a number of subbands, where each subband may use direct-sequence (DS) spreading and each subband signal is transmitted using a subcarrier frequency. In this paper, we divide the symbol duration into a number of fractional subsymbol durations also referred to here as fractions, in a manner analogous to subbands in MC-CDMA systems. In the proposed MC-CDMA scheme, the data streams are spread at both the symbol-fraction level and at the chip level by the transmitter, and hence the proposed scheme is referred to as the fractionally spread MC-CDMA arrangement, or FS MCCDMA. Furthermore, the FS MC-CDMA signal is additionally spread in the frequency (F)-domain using a spreading code with the aid of a number of subcarriers. In comparison to conventional MC-CDMA schemes, which are suitable for communications over frequency-selective fading channels, our study demonstrates that the proposed FS MC-CDMA is capable of efficiently exploiting both the frequency-selective and the time-selective characteristics of wireless channels. Index Terms--Broadband communications, code-division multiple access (CDMA), fractionally spreading, frequency-domain spreading, multicarrier modulation, Nakagami fading, time-domain spreading.

A novel sequential estimation method is proposed for the initial synchronization of pseudonoise (PN) signals derived from m-sequences. This sequential estimation method is designed based on the principle of recursive soft-in/soft-out (SISO) decoding, and we refer to it as the recursive soft sequential estimation (RSSE) acquisition scheme. The RSSE acquisition scheme exhibits a complexity similar to that of a conventional m-sequence generator, which increases only linearly with the number of stages in the m-sequence generator. Our simulation results also show that the acquisition time of the proposed RSSE acquisition scheme is also linearly dependent on the number of stages in the m-sequence generator. Owing to the above properties, the employment of the proposed RSSE acquisition scheme is beneficial for the acquisition of long m-sequences. Index Terms--Acquisition, initial synchronization, maximum-likelihood (ML) estimation, m-sequence, pseudonoise (PN) signals, recursive decoding, sequential estimation, soft-in/soft-out (SISO) decoding, spread-spectrum signals.

In this contribution, adaptive rate transmissions are investigated in the context of direct-sequence code-division multiple-access (DS-CDMA) systems using variable spreading factors (VSFs). In the context of the recently established family of adaptive rate-transmission schemes, the transmission rate is typically adapted in response to the channel's fading-induced quality fluctuation. By contrast, in this contribution the transmission rate is adapted in response to the multiuser interference fluctuations encountered. We present the philosophy of the proposed adaptive rate-transmission scheme and analyze the effective throughput as well as the achievable bit error rate (BER) performance, when communicating over additive white Gaussian noise channels. Our study shows that by employing the proposed VSF-assisted adaptive rate-transmission scheme, the effective throughput may be in creased by up to 40%, when compared to that of DS-CDMA systems using constant spreading factors. This increased throughput is achieved without wasting power, without imposing extra interference upon other users, and without increasing the BER. Index Terms--Adaptive rate transmissions, code-division multiple access (CDMA), Markov chain, matched filter receiver, multiuser interference, throughput, variable spreading factors (VSFs).

In this letter, we extend our investigation of generalized multicarrier direct-sequence code-division multiple access by considering two additional types of chip waveforms, namely, the time-domain half-sine and raised-cosine chip waveforms, in addition to the rectangular chip waveform. A range of closed-form equations are provided for quantifying the effect of both the multipath interference and the multiuser interference, when using partially overlapping subcarriers. These closed-form formulas allow us to evaluate the bit-error rate performance of arbitrary code-division multiple access schemes using overlapping subbands with the aid of the standard Gaussian approximation. Index Terms--Code-division multiple access (CDMA), multicarrier, frequency-selective fading.

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]

This paper investigates the first resource management problem for vehicular-to-infrastructure (V2I) networks under the in-band full-duplex (IBFD) backhauling scheme with guaranteed ultra-reliable and low-latency (URLLC) service. The considered networks suffers from interference caused by three node transmission in IBFD scheme and the mobility of vehicular user equipments (VUEs). The resource allocation problem is formulated to jointly optimize VUE association, resource block assignment (RA) and power allocation (PA), while satisfying the reliability and latency constraints at the same time. The formulated problem is a mixed integer non-linear problem with non-convex objective function and constraints. Finding globally optimal solution for this type of problem is still an open problem. To develop tractable solutions, the original problem is firstly simplified using derived equivalent expression for the objective function. The proposed method then decomposed it into RA and PA sub-problems. In each iteration, the PA sub-problem is solved for a set of given PA solution; while the solution for PA sub-problem is searched under determined RA results. The RA and PA sub-problems are solved iteratively until the converging condition is achieved. Theoretical analysis proves that the proposed method achieves Nash-stable equilibrium and local optimality for RA and PA sub-problems respectively. Simulation results verify the effectiveness of the derived performance analysis and demonstrate that the proposed algorithm outperforms the state-of-the-art algorithms in the literatures. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surfaces (RIS) constitute a revolutionary technique of beneficially reconfiguring the smart radio environment. However, despite the fact that wireless propagation is of time-varying nature, most of the existing RIS contributions focus on time-invariant scenarios for the following reasons. Firstly, it becomes impractical to instantaneously feed back the control signal based on the doubly selective non-line-of-sight (NLoS) fading scenario. Secondly, channel estimation conceived for the high-mobility and high-dimensional RIS-assisted links has to take into account the spatial-domain (SD), time-domain (TD), and frequency-domain (FD) correlations imposed by the angle-of-arrival/departure (AoA/AoD), the Doppler and the orthogonal frequency-division multiplexing (OFDM) operations, respectively, where none of the existing solutions can be directly applied. Thirdly, it is far from trivial to maximize the NLoS channel powers on all subcarriers by a common set of RIS reflecting coefficients. Fourthly, in the face of double selectivity, it becomes inevitable to encounter either inter-symbol interference (ISI) or inter-channel interference (ICI) during the signal detection in the TD or in the FD, respectively. Against this background, firstly, we focus our attention on line-of-sight (LoS) dominated unmanned aerial vehicle (UAV) scenarios. Secondly, we conceive new minimum mean squared error (MMSE) channel estimation methods for doubly selective fading, which perodically transmit pilot symbols embedded into the TD and FD over the SD in order to beneficially exploit the correlations in the three domains. Thirdly, the RIS coefficients are optimized by a low-complexity algorithm based on the LoS representation of the end-to-end system model. Fourthly, tailor-made interference cancallation techniques are devised for improving the signal detection both in the FD and in the TD. Our simulation results are examined in six frequency bands licensed in 5 G, which confirms that the employment of RIS is capable of achieving substantial performance improvements. [ABSTRACT FROM AUTHOR]

A novel signaling scheme is presented, where a set of orthogonal signals is transmitted in parallel. The signals are selected according to the so-called residue number system (RNS). Hence the system is essentially a multiple code parallel communication scheme using high modulation alphabets. It is demonstrated that the system's performance can be substantially improved by exploiting a number of advantageous properties of the RNS arithmetic. In Part I of this paper, we focus our attention on the system's description and on the associated background of the RNS arithmetic, as well as on the performance evaluation of the residue number system arithmetic, using both nonredundant and redundant moduli based orthogonal signaling schemes, over an additive white Gaussian noise (AWGN) channel. Redundant RNS codes are introduced in order to protect the transmitted information. The detection techniques used in this novel system are different from conventional detectors. Specifically, a novel decision algorithm, referred to as a ratio statistic test, is designed, which implies dropping some of the lowest reliability demodulation outputs before the residue digits are transformed back to binary symbols. This improves the system's performance. This dropping technique is different from the conventional 'errors and erasures' decoding, where the erased symbols (or bits) should be computed and filled during decoding. We argue that the demodulated/decoded information can be obtained by decoding the retained or undiscarded symbols upon exploiting the properties of the RNS arithmetic. Our numerical results show that the proposed scheme constitutes a high-efficiency parallel transmission method for high-bit-rate communication, achieving a coding gain of 2 dB at a bit error rate of [10.sup.-6] over AWGN channels. Index Terms--Code-division multiple access (CDMA), error control, orthogonal signalling, parallel signalling, ratio statistic test, redundant residue number system (RRNS), residue number system (RNS).

A novel signaling scheme is presented, where a set of orthogonal signals is transmitted in parallel. The signals are selected according to the so-called residue number system (RNS). Hence the system is essentially a multiple code parallel communication scheme using high-modulation alphabets. It is demonstrated that the system performance can be substantially improved by exploiting a number of advantageous properties of the RNS arithmetic. The model treated in Part I of this paper is extended here to account for the effects of the multipath Rayleigh fading channel when using noncoherent demodulation. Diversity reception techniques with equal gain combining (EGC) or selection combining (SC) are concerned. The related performance is evaluated for both nonredundant and redundant RNS-based orthogonal signaling. Interleaving and forward error-correction techniques are introduced for enhancing the system's bit error rate (BER) performance. The concept of concatenated coding with a Reed-Solomon (RS) code as the outer code and a redundant RNS code as the inner code is presented, and the performance of the proposed concatenated code is evaluated. Expressions of the error probability for the above-mentioned scenarios are presented, and the associated BER performance is evaluated numerically with respect to specific system parameters. Without concatenated coding, coding gains up to 8.5 or 11 dB are achieved at a BER of [10.sup.-6] using the lowest reliability dropping technique of Part I and one or two redundant moduli, respectively. The BER is substantially higher than that over the additive white Gaussian noise channel reported in Part I. With the aid of RS coding, an additional 7.5-dB coding gain is achieved. Index Terms--Code-division multiple access (CDMA), concatenated coding, forward error correction, joint demodulation/decoding, M-ary orthogonal signaling, redundant residue number system (RRNS), residue number system (RNS).

In band full duplex (IBFD) has the potential to not only double spectral efficiency (SE) but also greatly reduce transmission latency. However, the immaturity of existing self-interference cancellation (SIC) techniques renders IBFD impractical for near-future wireless applications. To inherit the merits of FD but with practical SIC requirements, multicarrier-division duplex (MDD) was recently proposed and studied. In this article, we demonstrate the advantages of MDD over the IBFD mode and the conventional half-duplex (HD) modes of frequency-division duplex (FDD) and time-division duplex (TDD) from several essential aspects, including SIC capability, resource integration, and the support for high-mobility communications. Several numerical results are included to show that MDD outperforms IBFD in terms of energy efficiency (EE) and SIC. Compared with the HD modes, MDD is capable of efficiently integrating DL/UL resources to achieve higher SE and significantly outperforms TDD when communicating over fast time-varying channels. Finally, some implementation challenges of MDD systems are discussed. [ABSTRACT FROM AUTHOR]

Differential frequency hopping (DFH) technique is widely used in wireless communications by exploiting its capabilities of mitigating tracking interference and confidentiality. However, electronic attacks in wireless systems become more and more rigorous, which imposes a lot of challenges on the DFH sequences designed based on the linear congruence theory, fuzzy and chaotic theory, etc. In this article, we investigate the sequence design in DFH systems by exploiting the equivalence principle between the G-function algorithm and the encryption algorithm, in order to achieve high security. In more details, first, the novel G-function is proposed with the aid of the Government Standard algorithm and the Rivest–Shamir–Adleman algorithm. Then, two sequence design algorithms are proposed, namely, the G-function-assisted sequence generation algorithm, which takes the full advantages of the symmetric and asymmetric encryption algorithms, and the high-order G-function-aided sequence generation algorithm, which is capable of enhancing the correlation of the elements in a DFH sequence. Moreover, the security and ergodicity performance of the proposed algorithms are analyzed. Our studies and results show that the DFH sequences generated by the proposed algorithms significantly outperform the sequences generated by the reversible hash algorithm and affine transformation in terms of the uniformity, randomness, complexity, and the security. [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]

Message passing (MP) aided detectors are designed for orthogonal time frequency space (OTFS) modulated system. We first characterize the transmit-receive relationship of our OTFS-modulated system in the delay-Doppler (DD) domain by designing a joint factor graph. Based on this joint factor graph, we then conceive a joint message passing aided (JMPA) detector. Furthermore, a novel low-complexity Gaussian approximate MP (GA-MP) detector is also conceived, which models the a posteriori probabilities propagated through the proposed joint factor graph by Gaussian distributions. Finally, we demonstrate that the proposed GA-MP detector outperforms the state-of-the-art MP detector by at least 1.5 dB at a bit error ratio (BER) of $10^{-4}$ , while keeping the same complexity order. [ABSTRACT FROM AUTHOR]

Low complexity approximate message passing (AMP) orthogonal frequency division multiplexing combined with index modulation (OFDM-IM) detection algorithms are proposed, which exploit the sparse structure of the frequency domain (FD) OFDM-IM symbols. To circumvent the high root mean square error (RMSE) in the conventional AMP algorithm, a minimum mean square error (MMSE) denoiser is proposed based on the classic Bayesian approach and on the state evolution of AMP. Our simulation results demonstrate that it is capable of improving both the RMSE as well as the convergence rate. However, in practice, the channel's diagonal FD matrix may be a non-Gaussian sensing matrix, hence a damping strategy is conceived. In conclusion, the proposed MMSE denoiser based damping-assisted AMP-aided detector strikes a compelling bit error ratio vs. complexity trade-off. [ABSTRACT FROM AUTHOR]

In-band full-duplex (IBFD) systems require promising resource allocation (RA) strategies to fully exploit the available time-frequency resources. Furthermore, the acquisition of channel state information and signal reception in IBFD systems are significantly impacted by insufficient self-interference cancellation (SIC), impeding the applications of IBFD in practical wireless systems. Multicarrier-division duplex (MDD), which benefits low-budget SI mitigation in digital domain and flexible subcarrier assignment, is expected to be a promising transitional technique from half-duplex (HD) to IBFD. To demonstrate the advantages of MDD over HD, this paper first compares the upper-bound performance of MDD and HD by applying unfair greedy RA. Then, considering the millimeter-wave (mmWave) with hybrid beamforming, we propose the RA optimization with the quality-of-service constraints on both downlink (DL) and uplink (UL) mobile-stations (MSs). To solve this non-convex RA problem, we divide it into a suboptimal subcarrier allocation problem solved by the proposed improved fair greedy (IFG) algorithm, and a convex power allocation problem. Furthermore, we design two general hybrid precoder based on matrix factorization and direct approach, and a combiner having high SIC capability. Our results show that the proposed RA algorithm can achieve the performance near the upper-bound achieved by the unfair greedy algorithm, while guaranteeing the proportional fairness among all DL/UL MSs. The performance of the two precoding schemes is depended on the number of radio frequency chains supported. Finally, the proposed SIC algorithm is able to provide sufficient SI mitigation, which can be implemented without impacting the RA operation. [ABSTRACT FROM AUTHOR]

Space-time coded generalized spatial modulation-aided sparse code division multiple access (STC/GSM-SCDMA) is proposed, which exploits the two-dimensional transmit diversity potential of both the spatial and of the frequency domain. Hence, it constitutes a promising solution for the pervasive connectivity of devices in next-generation nonorthogonal multiple access (NOMA) systems. More explicitly, our STC/GSM scheme achieves diversity in the spatial-domain, while the sparse signal-spreading action of SCDMA results in frequency-domain (FD) diversity. A single-user bit error rate (BER) bound is derived as the benchmark of the BER performance of our STC/GSM-SCDMA system. Furthermore, a pair of novel detectors, namely a bespoke message passing aided (MPA) detector and a tailor-made approximate message passing (AMP) detector are conceived by designing a new factor graphs for our proposed STC/GSM-SCDMA system. The performance of these detectors is characterized in terms of their BER vs. complexity. Our simulation results show that the proposed AMP detector is capable of operating within 2 dB of the MPA detector’s signal-to-noise ratio (SNR) requirement, while supporting a normalized user load of 150%, despite its appealing low complexity, which is about 1000 times lower than the MPA detector. [ABSTRACT FROM AUTHOR]

This paper is focused on code-domain non-orthogonal multiple access (CD-NOMA), which is an emerging paradigm to support massive connectivity for future machine-type wireless networks. We take a comparative approach to study two types of overloaded CD-NOMA, i.e., sparse code multiple access (SCMA) and dense code multiple access (DCMA), which are distinctive from each other in terms of their codebooks having sparsity or not. By analysing their individual diversity orders (DO) in Rayleigh fading channels, it is found that DCMA can be designed with the aid of generalized sphere decoder (i.e., a nonlinear multiuser detector) to enjoy full DO which is equal to the maximum number of resource nodes in the system. This is in contrast to SCMA whose error rate suffers from limited DO equal to the codebook sparsity (i.e., the effective number of resource nodes occupied by each user). We conduct theoretical analysis for the codebook design criteria and propose to use generalized sphere decoder for DCMA detection. We numerically evaluate two types of multiple access schemes under “4 × 6” (i.e., six users communicate over four subcarriers) and “5 × 10” NOMA settings and reveal that DCMA gives rise to significantly improved error rate performance in Rayleigh fading channels, whilst having decoding complexity comparable to that of SCMA. [ABSTRACT FROM AUTHOR]

This paper proposes a novel transmission policy for a wireless powered sensor network (WPSN) assisted by an intelligent reflecting surface (IRS) to enhance the performance of wireless energy transfer (WET) and wireless information transfer (WIT) with certain phase shifts. To achieve its self-sustainability, IRS collects energy from the energy station to support its own control circuit operation. Our proposed policy for the considered WPSN is called IRS assisted harvest-then-transmit time switching (IRS-HTT-TS), which is capable to schedule the transmission time slots by switching between energy collection and energy reflection modes. We provide a joint design of the transmission time slots, the power allocation as well as the discrete phase shifts of the WET and WIT, aiming to maximize the system sum throughput. This formulates a problem as a mixed-integer non-linear program (MINLP), which is NP-hard and non-convex. To effectively solve this problem, we first relax it to the one with continuous phase shifts, and then propose a two-step approach and decompose the original problem into two sub-problems. We address the first sub-problem in closed form with respect to the phase shifts of the WIT. For the second sub-problem, we apply the Lagrange dual method and Karush-Kuhn-Tucker conditions to derive the optimal closed-form transmission time slots, power allocation, and phase shift of the WET, respectively. The optimal discrete phase shifts can be obtained by quantizing the continuous values. Numerical results demonstrate the effectiveness of the proposed policy and validate the beneficial role of the IRS in comparison to the benchmark schemes. [ABSTRACT FROM AUTHOR]

An edge-cancellation-aided iterative detection and decoding (EC-IDD) algorithm is proposed for polar-coded sparse code multiple access (SCMA), which jointly performs Gaussian-approximated message passing (GA-MP) detection of SCMA supported by the soft list decoding (SLD) of polar codes. A reduced-edge factor graph is formulated in each consecutive iteration with the aid of the cyclic redundancy check (CRC) and EC. Based on the simplified factor graph, the EC-IDD gradually reduces its complexity in each subsequent iteration, while improving the bit error rate (BER) performance, compared to the state-of-the-art joint detection and decoding (JDD) of polar-coded SCMA. Furthermore, an embedded decision-directed channel estimator (DD-CE) is proposed for our polar-coded SCMA system under realistic imperfect channel state information (CSI). Our simulation results demonstrate that the proposed EC-IDD achieves better BER performance than the state-of-the-art JDD under both perfect and imperfect CSI, despite achieving a complexity reduction of 92%. Finally, the BER of the proposed joint DD-CE and EC-IDD algorithm under imperfect CSI converges to that of EC-IDD operating under perfect CSI. [ABSTRACT FROM AUTHOR]

Polar coding has been ratified for employment in the 3GPP New Radio standard and several soft-decision decoders achieved comparable performance to that of the state-of-the-art successive cancellation list decoder. Aiming for further improving the performance of the soft-decision polar decoders, we propose a soft-output successive cancellation stack (SSCS) polar decoder, which jointly exploits the benefits of the depth-first search of the stack decoder and the soft information output of the belief propagation decoder. This has the substantial benefit of facilitating soft-input soft-output (SISO) decoding and seamless iterative information exchange in turbo-style receivers. As a further contribution, we intrinsically amalgamate our SSCS decoder into polar-coded large-scale multiple-input multiple-output (MIMO) systems and conceive an iterative turbo receiver, operating on the basis of logarithmic likelihood ratios (LLRs). Our simulation results show that the proposed SSCS decoder is capable of outperforming the state-of-the-art SISO polar decoders, despite requiring a lower complexity at moderate to high signal-to-noise ratios (SNRs). Additionally, compared with the non-iterative hard-output SCS decoder, our SSCS scheme attained 1.5 dB SNR gain at a bit error ratio level of 10−5, when decoding the [256,512] polar code of a (64 × 64) MIMO system. [ABSTRACT FROM AUTHOR]

For improving the throughput while simultaneously enhancing the security in aeronautical ad-hoc networking (AANET), a channel quality indicator (CQI)-mapped spatially modulated sparse code multiple access (SM-SCMA) scheme is proposed in this paper. On one hand, we exploit the joint benefits of spatial modulation and SCMA for boosting the data rate. On the other hand, a physical-layer secret key is generated by varying the SM-SCMA mapping patterns based on the instantaneous CQI in the desired link. This guarantees the security of AANETs, since this secret key is not exchanged between the source aeroplane and its destination. Due to the line-of-sight (LoS) propagation in the AANET, other aeroplanes or eavesdroppers may detect the signals delivered in the desired link. However, they are unable to translate the detected signals into the original confidential information, even if multiple copies of the signals are recoined over multiple hops of the AANET, because they have no knowledge of the CQI-based SM-SCMA mapping pattern. The performance of the CQI-mapped SM-SCMA is evaluated in terms of both its bit error rate and its ergodic secrecy rate, which substantiates that the proposed scheme secures the confidential information exchange in the multi-hop AANET. [ABSTRACT FROM AUTHOR]