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For several years, the completion time and the decoding delay problems in instantly decodable network coding (IDNC) were considered separately and were thought to act completely against each other. Recently, some works have aimed to balance the effects of these two important IDNC metrics, but none of them studied a further optimization of one by controlling the other. This paper investigates the effect of controlling the decoding delay to reduce the completion time below its currently best known solution in both perfect and imperfect feedback with persistent erasure channels. To solve the problem, the decoding-delay-dependent expressions of the users' and overall completion times are derived in the complete feedback scenario. Although using such expressions to find the optimal overall completion time is NP-hard, this paper proposes two novel heuristics that minimize the probability of increasing the maximum of these decoding-delay-dependent completion time expressions after each transmission through a layered control of their decoding delays. Afterward, this paper extends the study to the imperfect feedback scenario, in which uncertainties at the sender affect its ability to anticipate accurately the decoding delay increase at each user. This paper formulates the problem in such an environment and derives the expression of the minimum increase in the completion time. Simulation results show the performance of the proposed solutions and suggest that both heuristics achieve a lower mean completion time, as compared with the best known heuristics for completion time reduction in perfect and imperfect feedback. The gap in performance becomes more significant as the erasure of the channel increases. [ABSTRACT FROM PUBLISHER]

This paper presents a multiple-input–multiple-output (MIMO) precoder with a compensated QR decomposition (CQRD) combination for coordinated multipoint (CoMP) downlink transmission. Unlike conventional QR decomposition (QRD) combination, CQRD combination adopts compensated channel matrix orderings. This paper first proposes CQRD combination for CoMP scenarios. The statistics for combined spatial subchannel gains with a CQRD combination of two coordinated base stations (BSs) are derived, and these statistics show that more balanced subchannel gains are generated with a CQRD combination than with a QRD combination. Furthermore, this paper proposes a generalized CQRD combination scheme with a joint sorting strategy that can be applied to scenarios with more than two coordinated BSs. Unlike the unsorted strategy, the joint sorting strategy determines an enhanced compensated combination to further increase spatial subchannel gains; therefore, the performance can be upgraded. Because conventional Tomlinson–Harashima precoding (THP) cannot be used in the CQRD combination, interference presubtraction and vector precoding (VP) is adopted. Theoretical analysis and simulation results are both provided to demonstrate the advantages of balanced spatial subchannel gains and enhanced bit-error-rate (BER) performance in the proposed CQRD-based schemes. Compared with existing QRD-based MIMO precoders in CoMP scenarios, the proposed CQRD-based schemes have substantial signal-to-noise ratio (SNR) improvements of 2–5 dB. [ABSTRACT FROM PUBLISHER]

This paper investigates the scenario in which a weak desired signal reaches a poorly selective receiver along with a high-powered pulsed radar occupying a neighboring channel. Traditionally, an automatic gain control (AGC) is used to fit the high-powered radar into the dynamic range of the receiver. However, this approach desensitizes the receiver because it also sacrifices the signal-to-noise ratio (SNR) of the desired signal. We propose the use of an auxiliary receive path to address this problem of strong neighboring channel signals. In this method, receiver gain is not lowered to avoid clipping. Instead, the strong signal is allowed to clip and distort the desired signal. This paper shows that only a subset of the symbols contained in the desired signal will be distorted; hence, redundancy within the desired signal (due to forward error correction) can be exploited to “fill the gaps” created by the distortion. The auxiliary path samples the envelope of the strong neighboring-channel signal and informs the decoder about which symbols are distorted (or “bad”) and which symbols are not distorted (or “good”). This additional information is shown to improve the estimation performance of the decoder in the presence of high-powered neighboring-channel radar. Using simulation and hardware-based experiments, it is shown that auxiliary-path-based receivers can obtain a significantly better throughput performance than AGC-based receivers. [ABSTRACT FROM AUTHOR]

Aerial base stations (ABSs) are expected to be important supplementary components for the 5G-and-beyond communication systems to achieve global Internet of Everything. To fully exploit the advantages of the ABSs seamless connection, in this paper, we propose a high altitude platform (HAP) and low altitude platforms (LAPs) cooperated network architecture. Specifically, the HAP can extend the network coverage and LAPs can act as relays to improve the transmission performance for hot spots. In the considered network, we investigate the sum rate maximization problem by optimizing the downlink and the uplink transmissions, respectively. In the downlink, we adopt the orthogonal frequency division multiple access technique and take the basic rate requirement into account. In addition, we optimize the height of LAPs and the spectrum allocation between the HAP and LAPs, and between the LAP and users. Then, we decouple the downlink sum rate maximation problem as three subproblems. An alternating optimization framework is designed to deal with these non-convex optimization problems, where the height and spectrum allocation are tackled in turn. In the uplink, we adopt the non-orthogonal multiple access technique, and consider the decoding threshold of the successive interference cancellation technique. Afterward, we optimize the power allocation of each user, and the spectrum allocation between users and the LAP, and between LAPs and the HAP. Finally, simulation results show the effects of spectrum allocation, height optimization and power allocation on network performance, which verify that the proposed scheme can achieve higher sum rate on both downlink and uplink in comparison with the current works. [ABSTRACT FROM AUTHOR]

This paper investigates collaborative spectrum sharing (CSS) for which a cognitive secondary transmitter acts as a decode-and-forward (DF) relay for two primary users (PUs) occupying an interfering multiple-access channel. PUs are assumed to send their signals simultaneously; hence, interference between the primary signals exists due to the multiple-access nature. The secondary user (SU) selects and forwards one of the PU's signals to a desired destination, and at the same time, the SU also transmits its own signal only if it is not harmful to PUs. The selection of a primary signal to relay is investigated, depending on SU's knowledge of two primary source–destination channels, for which closed-form outage probabilities for PUs and SU are provided accordingly. With the help of the closed-form PU's outage probability, an optimal selection strategy between the primary signals and an optimal power allocation between the primary and secondary signals are also obtained in closed form, which minimizes SU's outage probability while keeping the PU's outage performance at an SU-free level. Numerical investigation is used to verify and illustrate the analysis given in this paper. Numerical results also show that the SU's performance can vary significantly according to the amount of channel knowledge that the SU can have. [ABSTRACT FROM PUBLISHER]

The joint transmission scheme of polar codes and sparse code multiple access (SCMA) has been regarded as a promising technology for future wireless communication systems. However, most of the existing polar-coded SCMA (PC-SCMA) systems suffer from high latency caused by the feedback iteration and list decoding. In addition, the error performance of PC-SCMA systems is unsatisfactory for ultra-reliable transmission. Inspired by the compelling benefits of non-binary polar codes, in this paper, we design a non-binary polar-coded SCMA (NB-PC-SCMA) system with a free order matching strategy to address the issues of delay and reliability. Specifically, we first formulate a joint factor graph for NB-PC-SCMA and propose a non-binary successive cancellation list (NB-SCL) and damping based joint iterative detection and decoding (NSD-JIDD) multiuser receiver to improve the BER and latency performance. Then, a lazy-search based NB-SCL (L-NB-SCL) decoding is proposed to reduce the computational complexity by simplifying the path search pattern of the list decoder. After that, we modify the update of user nodes for SCMA detection to improve the convergence error and finally propose the improved NSD-JIDD (ISD-JIDD) algorithm, which can avoid redundant operations by exploiting L-NB-SCL decoding. Simulation results show that the proposed NB-PC-SCMA system achieves better bit error rate (BER) performance and considerable latency gain when compared to its counterparts. In particular, the proposed ISD-JIDD can achieve similar BER performance of NSD-JIDD with less complexity. [ABSTRACT FROM AUTHOR]

Ultra-reliable low-latency communication (uRLLC) emerges as one of the three service categories in fifth-generation (5G) wireless networks, with a potential to support multiple advanced services for latency-sensitive communications. The inherent openness of the wireless environment makes security in 5G unprecedentedly urgent to be addressed. Accordingly, the physical layer security (PLS) technique exploits the randomness characteristics of the wireless channel to fulfill security and confidentiality of information transmission. Different from many current works, which ignored the significance of security in uRLLC, this paper studies secrecy improvement strategy design in uRLLC scenarios. First, we propose suitable performance metrics for evaluating PLS of uRLLC and make a compromise between reliability, latency, and security, while maximizing the network throughput. Next, we identify the key challenging issues for achieving PLS in the context of uRLLC, and discuss the role of cooperative communication and mobility in terms of possible solutions. To the best of our knowledge, this is the first paper to make a trade-off among reliability, security and network throughput. Simulations validate the theoretical analyses. [ABSTRACT FROM AUTHOR]

This paper proposes a channel code for vector perturbation (VP) precoded transmission in multiuser downlink and examines its achievable sum-rate performance. In particular, we first find the most suitable outer convolutional code (CC) for VP precoded transmission under bit-interleaved coded modulation with iterative decoding (BICM-ID) by applying a semi-analytic technique based on extrinsic information transfer charts. We then study the achievable sum rate of the proposed BICM-ID-based VP precoded system, and we compare it with the sum capacity of the dirty paper coding (DPC) scheme. Our investigation shows that under perfect channel state information (CSI), the sum rate of the proposed system grows linearly over the number of users, which is the same growth of the DPC. Under quantized CSI and finite-rate feedback, a linear increase in feedback overhead per user is necessary to maintain such a linear sum-rate growth. [ABSTRACT FROM PUBLISHER]

In this paper, we analyse a secure transmission scheme using rateless codes (RC) in a delay constrained system. By using RC, secrecy is achieved if the legitimate receiver can accumulate required number of packets before an eavesdropper does. To achieve this, we employ transmit antenna selection (TAS) at the base station to improve the main channel and, artificial noise (AN) is generated by the use of a cooperative jammer to degrade the eavesdropper's channel. Quality of violation probability (QVP) which consists of both the delay violation probability and the intercept probability is used as a performance metric. A closed-form expression for QVP is derived. We show that using TAS for reducing QVP is effective only at lower signal to noise ratio (SNR). We also observe that on increasing number of antennas at the source ($N_{A}$) while using TAS along with AN, QVP decreases for delay sensitive services, whereas, in case of delay tolerant applications, increasing $N_{A}$ is effective at low SNR. [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]

This paper designs and analyzes the bit-interleaved coded modulation with iterative demapping and decoding (BICM-ID) framework under color-shift-keying (CSK) modulation to achieve spectrally efficient transmissions in visible light communication (VLC) systems. Specifically, we investigate the protograph low-density parity-check (LDPC) codes, bit-to-symbol mapping schemes, and constellation labeling rules in higher-order CSK-aided VLC systems. To fully explore the BICM-ID benefit, we propose an irregular CSK mapping, in which an $M$ -ary standardized constellation (called “Standard constellation”) and a new $M$ -ary constellation (called “Target constellation”) are separately applied to modulate two different coded sub-blocks in a codeword to optimize the error performance of the CSK-aided VLC systems. Furthermore, using a modified protograph extrinsic information transfer (PEXIT) algorithm, we construct two types of protograph LDPC codes (i.e., unpunctured and punctured protograph LDPC codes) that outperform the conventional protograph LDPC codes. Both analytical and simulation results show that the proposed irregular-CSK-mapped BICM-ID employing the new protograph LDPC codes and Target constellation is capable of achieving outstanding performance, and is a promising transmission solution for high-speed VLC applications. [ABSTRACT FROM AUTHOR]

This paper examines the queueing performance of communication systems that transmit encoded data over unreliable channels. A fading formulation suitable for wireless mobile applications is considered, where errors are caused by a discrete channel with correlated behavior over time. For carefully selected channel models and arrival processes, a tractable Markov structure composed of queue length and channel state is identified. This facilitates the analysis of the stationary behavior of the system, leading to evaluation criteria such as bounds on the probability of the queue exceeding a threshold. Specifically, this paper focuses on system models with scalable arrival profiles, which are based on Poisson processes, and finite-state channels with memory. These assumptions permit the rigorous comparison of system performance for codes with arbitrary block lengths and code rates. Based on the resulting characterizations, it is possible to select the best code parameters for delay-sensitive applications over various channels. Random codes and BCH codes are then employed as a means to study the relationship between code parameter selection and the queueing performance of point-to-point data links. The methodology introduced herein offers a new perspective on the joint queueing–coding analysis of finite-state channels with memory, and it is supported by numerical simulations. [ABSTRACT FROM PUBLISHER]

This paper investigates the capacity of radio channels when iterative channel estimation, data detection, and decoding are employed. Knowing the capacity gain from iterative detection versus purely pilot-based channel estimation helps a designer compare the performance of an iterative receiver against a noniterative receiver and select the best balance between performance and cost. A bound is put on the linear minimum mean square error (LMMSE) channel estimation error, based on which a bound on the capacity is obtained. The attainable capacity is related to the channel estimation error of the receiver. The bounds take into account the uncertainty in symbol detection on channel estimation and incorporate the effect of channel estimation error on channel capacity. The interaction between the symbol detector and the decoder is analytically characterized and depicted in an extrinsic information transfer (EXIT) chart, where a bound on the detector curve is found. With optimal LMMSE pilot-based channel estimation, the results of this paper demonstrate that iterative channel estimation provides insignificant capacity advantage at fading rates below 1% of the symbol rate, although a computational-cost gain is still available. Iterative channel estimation provides a capacity benefit if suboptimal pilot signaling is used to provide initial channel estimates. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a channel transformation technique for joint decoding of desired and interfering signals in an interference alignment scenario consisting of $K$ users with multiple antennas. Our technique, i.e., pseudo-lattice treatment, is based on the compute-and-forward framework. Our technique can be implemented to provide decoding gains with low complexity for subspace aligned interference signals. We evaluate the performance of the system through simulations that show the performance gain attained by using our pseudo-lattice method over subspace decoding techniques for interference alignment in low- and medium-SNR conditions. [ABSTRACT FROM AUTHOR]

Device-to-device (D2D) communication permits direct communication between devices, thereby it provides performance gain for traditional cellular networks. In this paper, we investigate how to improve the performance of D2D communication while satisfying the delay constraint for practical applications. Closed-form expressions are derived for trade-offs among system performance, such as successful transmission probability, transmission capacity, delay constraint, and energy consumption. In addition, two schemes are proposed to improve the performance for D2D communication under a given delay constraint. First, an optimal transmission scheme is proposed in which the transmission of user equipment (UE) can be scheduled adaptively to have the best successful transmission probability, whereas the D2D link satisfies the delay constraint. Second, a delay assignment scheme is proposed in which delay is adaptively assigned for each hop to achieve the maximum capacity when the network employs multihop D2D communication. Simulation results show that the adaptive transmission scheme improves the successful transmission probability (e.g., increased by 13 times when the source density is \text10^-4) compared with the fixed-probability transmission scheme, although it can satisfy the delay constraints for different applications. Furthermore, compared with the fixed delay assignment scheme, the network capacity can be improved up to 50% by the proposed scheme with proper delay assignment for each hop. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new clustered structure for a multiway relay network (MWRN) with $G$ clusters, $N$ users per cluster, one intracluster relay per cluster, and a single intercluster relay. The proposed structure allows private information exchange among users within a certain cluster through the corresponding intracluster relay and only public information exchange among users in different clusters through the intercluster relay. In this paper, we quantify the dominating error events in the proposed clustered MWRN and derive the expressions for the probability of these error events. Then, we use these expressions to derive the average bit error rate (BER) of a clustered MWRN. It is shown that clustering in an MWRN improves the error performance by reducing the number of dominating error events and, in effect, reducing error propagation, compared with the nonclustered counterpart. The analysis proves that the average BER of a clustered MWRN is minimized when the number of clusters and the number of users per cluster are chosen to be the closest possible factors of the total number of users, i.e., $L=GN$. Finally, numerical simulation results are provided to verify the validity of the analysis. [ABSTRACT FROM AUTHOR]

The growing demand for high-speed data, quality of service (QoS) assurance, and energy efficiency has triggered the evolution of fourth-generation (4G) Long-Term Evolution-Advanced (LTE-A) networks to fifth generation (5G) and beyond. Interference is still a major performance bottleneck. This paper studies the application of physical-layer network coding (PNC), which is a technique that exploits interference, in heterogeneous cellular networks. In particular, we propose a rate-maximizing relay selection algorithm for a single cell with multiple relays assuming the decode-and-forward (DF) strategy. With nodes transmitting at different powers, the proposed algorithm adapts the resource allocation according to the differing link rates, and we prove theoretically that the optimization problem is log-concave. The proposed technique is shown to perform significantly better than the widely studied selection-cooperation technique. We then undertake an experimental study—on a software radio platform—of the decoding performance of PNC with unbalanced signal-to-noise ratios (SNRs) in the multiple-access transmissions. This problem is inherent in cellular networks, and it is shown that, with channel coding and decoders based on multiuser detection and successive interference cancellation, the performance is better with power imbalance. This paper paves the way for further research on multicell PNC, resource allocation, and the implementation of PNC with higher order modulations and advanced coding techniques. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a general centralized feedback model for interference alignment (IA) algorithms of which precoders and decoders are designed with quantized channel state information (CSI) at a central unit and then fed back to corresponding transmitters and receivers via finite-rate links. The significant difference of this model from existing models is that all the realizations of channels, precoders, and decoders are fed back by finite rates. The signal-to-interference-plus-noise ratio (SINR) characteristic of this model is analyzed, which helps derive an upper bound of average throughput loss relative to perfect IA. The upper bound is shown to be tight by simulation, particularly in the high-feedback regime. Based on this result, the scaling laws of feedback bits for channels, precoding, and decoding vectors to obtain full degree of freedom are derived, which are backward compatible to the existing results for quantized CSI only or quantized precoder only. Simulation results show that the system is interference limited at a high signal-to-noise ratio (SNR) if the three scaling laws are not simultaneously satisfied, and the throughput performance is dominantly limited by the worst feedback links among the channels, precoders, and decoders. [ABSTRACT FROM PUBLISHER]

In this paper, resource allocation for a multi-carrier uplink non-orthogonal multiple access (NOMA) system is studied. Unlike the existing works on multi-carrier uplink NOMA, in which each user is assumed to access only one subcarrier, we consider a more general scenario where the number of subcarriers allocated to a single user is not constrained. We first aim to maximize the system's sum rate, which requires selecting the appropriate subcarriers for each user and distribute the transmission power. The formulated non-convex problem is transformed into a convex one, and further, an optimal and low-complexity iterative water-filling solution is proposed. Nonetheless, it is shown that maximum transmit power is employed by each user to maximize the sum rate. Motivated by the fact that the users are power constrained, the energy efficiency (EE) maximization problem is also studied. Based on fractional programming, the EE maximization problem is transformed into a series of sum rate maximization subproblems, and the proposed iterative water-filling solution is applied to each subproblem. The proposed schemes are compared with other NOMA-based and orthogonal multiple access based algorithms, and its superiority is fully validated. [ABSTRACT FROM AUTHOR]

In this correspondence paper, a variable-rate coding scheme is proposed for an uplink NOMA system. Specifically, each user employs a multilevel irregular repeat-accumulate (IRA) coding scheme, which consists of multiple common component IRA encoders. The variable-rate coding scheme is realized by flexibly adjusting the number of component IRA encoders allocated to each user. We design this common component IRA encoder based on extrinsic information transfer analysis to achieve an overall good multi-user decoding performance. The advantages of our proposed scheme are as follows: first, simple implementation of rate variation, second, flexible design of multilevel IRA coding, i.e., the well-designed component IRA encoders does not need to be re-designed when any user changes its rate, third, fair decoding convergence of each user, and finally, capacity-approaching performance. [ABSTRACT FROM AUTHOR]

An iterative detection and decoding (IDD) technique has recently received much attention due to its capacity approaching performance and manageable complexity for (parallel) turbo-coded systems. The existing IDD receivers process indiscriminately the a priori information of the systematic bits and the parity bits generated by the turbo decoder in the front-end detection. In this paper, we first show that the parity bits of the parallel turbo codes are inherently less protected than the systematic bits, which leads to suboptimality for the IDD receivers. Based on this observation, we then propose an unequal-error-correcting-capability-aware technique to mitigate the associated performance loss. As an illustrative example, the minimum-mean-square-error (MMSE) filtering and soft interference cancelation (MMSE-SIC)-aided iterative receiver for parallel-turbo-coded multiple-input–multiple-output (MIMO) systems is employed in this paper. Numerical results manifest that the MMSE-SIC-aided iterative receiver based on the proposed paradigm achieves noticeable performance gains over the conventional unequal-error-correcting-capability-agnostic one even with reduced computational complexity. The extension of the proposed principle to other iterative algorithms for parallel-turbo-coded data transmission is straightforward. [ABSTRACT FROM PUBLISHER]

This paper analyzes the performance of generalized multirelay cooperation (GMRC) protocols, which generalize the conventional single- and multiple-relay cooperative protocols, by allowing the number of relays employed in a cooperative cycle to vary with the instantaneous channel condition. Two variants of GMRC protocols are studied, including the output-detection GMRC (OD-GMRC) based on a decoding result and the output-threshold-test GMRC (OT-GMRC) relying on a threshold test. For both protocols, we derive the average outage probability and the average delay for completing a cooperative cycle, assuming uncoded decode-and-forward (DF) relays with multiple receiving antennas. Through numerical results, we validate the analysis accuracy and identify the ideal operational mode of GMRC under different network configurations. [ABSTRACT FROM PUBLISHER]

With low-density parity-check (LDPC) codes and polar codes selected as the standard codes for the fifth generation (5 G) enhanced Mobile Broad Band scenario (eMBB), a decoding architecture that can simultaneously support the decoding of control and data plane becomes necessary at the terminal side to meet the raising requirement for 5 G network deployment. Due to the special structure of LDPC codes according to the Release 15 (R15) 5 G standard, a straight-forward extension of the existing reconfigurable scheme is in general difficult. Therefore in this paper, a unified decoding architecture is proposed that can be reconfigured to either LDPC codes or polar codes. Due to various differences between the two codes such as parity-check matrices, codeword lengths and iterative methods, a joint decoding algorithm is introduced by reordering basic decoding operations to the unified add-comparison-add pattern for both codes. Then, a pipelined structure of reconfigurable decoding unit (RDU) is presented correspondingly which is fully compatible with all decoding patterns of the R15 standard. And finally, a reconfigurable decoder is proposed with multiple levels of parallelism, and the reconfiguration scheme is introduced to improve the hardware utilization and decoding efficiency. The proposed decoder is implemented in FPGA and ASIC, respectively, and has achieved state-of-the-art performance in throughput and area efficiency compared to LDPC-only and polar-only decoders. [ABSTRACT FROM AUTHOR]

This paper proposes a Hierarchical Rate Splitting (HRS)-based and Macro Base Station (MBS)-assisted cooperative content delivery scheme for Cache-enabled Cloud Radio Access Networks (C $^{2}$ -RANs). In this scheme, a user is served by a cluster of Small Base Stations (SBSs) that cache contents. If the user-requested content is missing in its cache, the SBS retrieves it from the central processor (backhaul link) and the MBS (wireless broadcast). We minimize the total delay of this system. We thus optimize user grouping, decoding order, RS variables, BS clustering, and beamforming subject to the transmit power and backhaul capacity constraints. This process formulates a non-convex problem, which we decouple into three subproblems. First, we must pair users to reduce intra-group interference. We thus develop a Low-Complexity User Pairing (LCUP) algorithm. Second, we optimize the decoding order to minimize the broadcast link delay. We, therefore, propose a Dynamic Delay-based Decoding Order Update (D $^{3}$ OU) algorithm. Third, we jointly design the RS variables, beamforming, and BS clustering. We use surrogate optimization via the Quadratic Transform (QT), Woodbury matrix identity, and Taylor expansion. We then recast this problem to a Two-Tier Alternating (TTA) problem, which we solve with closed-form (outer tier) and convex (inner tier) formulations. We integrate these algorithms to propose an overall algorithm. It achieves significant performance gains and a 3-fold reduction in time-complexity over the standard Semi-Definite Relaxation (SDR)-based algorithm and several benchmark schemes. [ABSTRACT FROM AUTHOR]

In this paper, we derive an upper bound on load-threshold of coded slotted ALOHA (CSA) for slot erasure channel (SEC) and that for packet erasure channel (PEC), respectively. In SEC, by exploiting the analogy between Gaussian elimination of solving linear equations and the iterative successive interference-cancellation (SIC) decoding procedure of CSA, we derive the upper performance bound for SEC. Subsequently, in PEC, utilizing density evolution to track the average probability of packet-decoded failure within the SIC decoding process, we obtain the upper bound for PEC. Moreover, we propose a numerical search algorithm of these bounds under a given calculating precision. The numerical results indicate that the asymptotic upper limit on load-threshold of CSA over SEC is always less than that over PEC with any given erasure probability and average transmission rate. [ABSTRACT FROM AUTHOR]

Resource allocation is an important strategy to optimize system performance in multiuser cooperative orthogonal frequency-division multiple-access (OFDMA) systems. In this paper, we jointly consider three different transmission modes in cooperative OFDMA systems, i.e., direct transmission (DT) mode, half-duplex (HD) relay cooperative transmission (HDRCT) mode, and full-duplex (FD) relay transmission (FDRT) mode. The joint optimization problem of transmission mode selection, subcarrier assignment, relay selection, subcarrier pairing, and power allocation (PA) is investigated. In this paper, we transform the binary assignment problem into a maximum-weighted bipartite matching problem, which can be solved by the classical Hungarian method. Based on the dual method, we solve the joint PA and binary assignment problem iteratively. Specifically, since the direct link is considered interference in the FD relay transmission mode, the PA problem in FD relay transmission mode is nontrivial. Thus, we provide a novel hierarchical dual method to solve the PA problem in FD relay transmission mode. In addition, in HDRCT mode, the joint transmission of both the source and relay is taken into account, and we provide a simple and insightful PA scheme. Simulation results show that the proposed algorithms can significantly enhance the overall system throughput, compared with previous works. [ABSTRACT FROM AUTHOR]

This paper proposes two new data detection algorithms for decode-and-forward alternate-relaying cooperative communication systems. These algorithms are discussed in the context of bit-interleaved coded modulation transmission with a multiple-antenna destination. The interference signal, resulting from the concurrent transmission of the source and one of the relays, is exploited as a beneficial resource to develop an optimal data detection algorithm. We show that the optimal algorithm can be implemented by parallel demappers, each based on a family of Bahl, Cocke, Jelinek, and Raviv algorithms, connected to parallel decoders in an iterative way. Due to the need to buffer the entire frame before decoding, the optimal algorithm suffers from long processing time. A suboptimal algorithm is also proposed to avoid this problem, where each packet is decoded by using two consecutive received packets. The suboptimal algorithm reduces processing time, complexity, bandwidth loss, and memory size with a slight increase in the bit error rate (BER). The BER performance of the proposed algorithms is evaluated via Monte Carlo simulations, and the results indicate their effectiveness in improving the BER performance. [ABSTRACT FROM AUTHOR]

In this paper, we design and analyze an improved bit-interleaved coded modulation (CM) scheme with a pseudorandom sequence (BICM-P). For the proposed scheme, the pseudorandom sequence is introduced into a systematic encoder at the transmitter and serves as side information at the receiver. With this design, the receiver can enjoy the benefit of increased Hamming distance when applying this side information at the receiver. In particular, we present a new constellation mapping principle to take advantage of the side information in the modulator, which leads to different signal constellations for the information bits and the parity-check bits. We then analytically derive the constellation-constrained capacity for BICM-P and quantify its gain as a nonlinear function associated with the two constellations. For the practical use of BICM-P, this paper indicates that the side information makes the regular low-density parity-check (LDPC) code irregular. Accordingly, the density evolution analysis tool is developed to design and optimize the regular LDPC code for BICM-P. The performance of LDPC-coded BICM-P on additive white Gaussian noise (AWGN) channels and fast Rayleigh fading channels is analyzed using extensive simulations. We observe that, at high code rates (\geqslant \mbox1/\mbox2), LDPC-coded BICM-P has a substantial gain (0.1117–0.6558 dB) compared with LDPC-coded BICM on the AWGN channel. The performance gains will become more significant (0.7541–2.3481 dB) on the fast Rayleigh fading channel. [ABSTRACT FROM PUBLISHER]

Study of polar codes in fading channels is of great importance when applying polar codes in wireless communications. Channel estimation is a fundamental step for communication to be possible in fading channels. Construction of both systematic and nonsystematic polar codes is based on an information set and the known frozen bits. Efficient implementation of systematic and nonsystematic polar codes exists. When it comes to channel estimation or channel tracking, additional pilot symbols are inserted in the codeword traditionally. In this paper, to improve the performance of polar codes in the finite domain, pilot symbols are selected from the coded symbols themselves. In order to keep the existing efficient structure of polar code encoding, pilot selection is critical since not all selections can reuse the existing structure. In this paper, two pilot selections denoted as Uneven Pilot Selection (UEPS) and Even Pilot Selection (EPS) are proposed, which do not change the efficient polar encoding structure. The proposed UEPS and EPS are proven to satisfy the efficient construction condition. The performance of EPS is shown in this paper to outperform both the UEPS and the traditional pilot insertion scheme. The simulation results provided verify the performance of the proposed pilot selection schemes. [ABSTRACT FROM AUTHOR]

This paper presents the first network-coded multiple access (NCMA) system prototype operated on high-order modulations up to 16-QAM. NCMA jointly exploits physical-layer network coding (PNC) and multiuser decoding (MUD) to boost throughput of multipacket reception systems. Direct generalization of the existing NCMA decoding algorithm, originally designed for BPSK, to high-order modulations, will lead to huge performance degradation. The throughput degradation is caused by the relative phase offset between received signals from different nodes. To circumvent the phase offset problem, this paper investigates an NCMA system with multiple receive antennas at the access point, referred to as MIMO-NCMA. We put forth a low-complexity symbol-level NCMA decoder that, together with MIMO, can substantially alleviate the performance degradation induced by relative phase offset. To demonstrate the feasibility and advantage of MIMO-NCMA for high-order modulations, we implemented our designs on software-defined radio. Our experimental results show that the throughput of QPSK MIMO-NCMA is double that of both BPSK NCMA and QPSK MUD at SNR = 10 dB. For higher signal-to-noise ratios at which 16-QAM can be supported, the throughput of MIMO-NCMA can be as high as 3.5 times that of BPSK NCMA. Overall, this paper provides an implementable framework for high-order modulated NCMA. [ABSTRACT FROM PUBLISHER]

In this paper, a robust uplink transmission scheme combining beamforming (BF) with rate splitting multiple access is proposed to improve the spectrum efficiency of a multibeam satellite system. By assuming that only imperfect channel state information is available, we first formulate an optimization problem to minimize the total transmit power under the constraints of individual transmit power budget and users’ rate requirements. Then, based on the successive convex approximation and difference-of-convex, we present an approach to convert the nonconvex constraints into convex ones, and obtain the BF vectors and power control parameters through iterative procedure. Finally, numerical results confirm the validity and superiority of our proposed scheme. [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]

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]

In this paper, we propose a framework of the mutual information-maximizing (MIM) quantized decoding for low-density parity-check (LDPC) codes by using simple mappings and fixed-point additions. Our decoding method is generic in the sense that it can be applied to LDPC codes with arbitrary degree distributions, and can be implemented based on either the belief propagation (BP) algorithm or the min-sum (MS) algorithm. In particular, we propose the MIM density evolution (MIM-DE) to construct the lookup tables (LUTs) for the node updates. The computational complexity and memory requirements are discussed and compared to the LUT decoder variants. For applications with low-latency requirement, we consider the layered schedule to accelerate the convergence speed of decoding quasi-cyclic LDPC codes. In particular, we develop the layered MIM-DE to design the LUTs based on the MS algorithm, leading to the MIM layered quantized MS (MIM-LQMS) decoder. An optimization method is further introduced to reduce the memory requirement for storing the LUTs. Simulation results show that the MIM quantized decoders outperform the state-of-the-art LUT decoders in the waterfall region with both 3-bit and 4-bit precision over the additive white Gaussian noise channels. For small decoding iterations, the MIM quantized decoders also achieve a faster convergence speed compared to the benchmarks. Moreover, the 4-bit MIM-LQMS decoder can approach the error performance of the floating-point layered BP decoder within 0.3 dB in the moderate-to-high SNR regions, over both the AWGN channels and the fast fading channels. [ABSTRACT FROM AUTHOR]

Secure transmission in full-duplex relay networks is considered in this paper. To ensure security, we propose a network coding assisted relaying scheme, where all the messages are encoded by the transmitter and the full-duplex relay respectively. Specifically, the encoding at the transmitter makes sure that all the coded messages are required to decode a private message. Consequently, security is achieved if the eavesdropper loses one or more coded messages. The encoding at the relay is operated by introducing a public auxiliary message, which changes the eavesdropper's decoding method from combining-before-decoding to combining-after-decoding, and thus decreases the eavesdropper's signal-noise-ratio (SNR) obviously. Intercept probability is used to measure the security, and results show that the proposed scheme can significantly improve the security performance of full-duplex relay networks. [ABSTRACT FROM AUTHOR]

Ultra-reliable and low-latency communications (URLLC) partakes a major role in 5 G networks for mission-critical applications. Sparse vector coding (SVC) appears as a strong candidate for future URLLC networks by enabling superior performance in terms of bit error rate (BER). SVC exploits the virtual digital domain (VDD) and compressed sensing (CS) algorithms to encode and decode its information through active symbol indices. In this paper, first, a clever encoding/decoding algorithm is proposed for the SVC scheme, which allows the use of all possible activation patterns (APs) resulting in increasing spectral efficiency. Second, a novel solution is proposed to convey additional information bits by further exploiting index modulation (IM) for the codebooks of the SVC scheme. Computer simulation results reveal that our low-complexity algorithm and novel IM solution provide not only a superior BER performance but also an increase in the number of bits conveyed by IM compared to the ordinary SVC approach. [ABSTRACT FROM AUTHOR]

This paper presents a novel transmission scheme to support massive machine-type communications (MTC) devices sending very short packets for Internet-of-Things (IoT) applications. The proposed scheme, termed as pilot-less one-shot (PLOS) transmission, does not require the pilot signaling. The key idea behind PLOS is to encode information into the inter-block nonzero positions and intra-block nonzero positions of a sparse vector. In the receiver, we propose a deep neural network-based scheme, referred to as deep learning-based PLOS (DL-PLOS) to recover the nonzero positions of the sparse vector. From the simulations results, we demonstrate that PLOS is effective in the short packet transmission and DL-PLOS outperforms the conventional greedy algorithms. [ABSTRACT FROM AUTHOR]

Fountain coding is a new paradigm for enhancing wireless communications security. In this paper, we investigate how to dynamically construct the fountain code to prevent information leakage and reduce the decoding delay at the legitimate receiver. To be specific, a method is developed to determine how many source packets should be used and which source packets should be chosen to participate in the fountain coding process, taking into account the channel quality, delay constraint, as well as the priorities of various source packets. We also apply the proposed scheme to practical image transmission, and demonstrate the advantages of our scheme via numerical simulations. [ABSTRACT FROM AUTHOR]

A key challenge of enabling massive machine type communications (mMTC) is to support infrequent small data transmission from a large number of machine type devices (MTDs). Random access with spatial successive decoding allows a packet to be received by multiple receivers and decoded with successive interference cancellation (SIC) across receivers, increasing not only throughput but also reliability, which is a promising random access protocol for mMTC. However, its theoretical throughput analysis is still an open issue. To address this issue, an innovative bipartite graph based throughput analysis framework is proposed in this paper, in which multiple receivers serve as sum nodes, active users serve as burst nodes, independent on-off fading channels are used to model edges connecting sum nodes and burst nodes. With this bipartite graph representation, an and-or tree iteration with binomial distributed node perspective degree distribution is formalized to evaluate the asymptotic throughput of random access with spatial successive decoding. Moreover, as a byproduct theorem, an alternative simplified proof is given to derive the analytical throughput of random access with spatial diversity but without successive decoding. Comprehensive numerical results are provided to illustrate their critical performance characteristics and verify the advantages of including spatial diversity and successive decoding for random access. [ABSTRACT FROM AUTHOR]

In this paper, we propose an enhanced random access (RA) with a distributed pilot orthogonalization (ERA-DPO) for mitigating packet collisions in Step3 during the RA procedure in cellular internet-of-things (IoT) networks. Even though each IoT device experiences a preamble collision in Step1, it can avoid the packet collision in Step3 by differentiating uplink pilot with the proposed technique, which provides an opportunity for the collided packets to be separated in spatial domain by multiple receive antennas. We also mathematically analyze the performance of the proposed scheme in terms of packet collision probability, throughput, and resource efficiency, based on a Markov chain model. Simulation results reveal that the proposed scheme significantly reduces the packet collision probability and increases resource efficiency compared to the conventional scheme. [ABSTRACT FROM AUTHOR]

The 5th-generation (5G) mobile networks and beyond need to support massive machine-type communications (MTC) devices with limited available radio resources. In this paper, we study the power-domain non-orthogonal multiple access (NOMA) technology to support energy-efficient massive MTC networks, where MTC devices exchange information using sporadic and low-rate short packets. We investigate the subchannel allocation and power control policy to maximize the achievable effective energy efficiency (EE) for uplink NOMA-based massive MTC networks, taking into account of short-packet communication characteristics. We model the subchannel allocation problem as a multi-agent Markov decision process and propose an efficient Q-learning algorithm to solve it. Furthermore, we obtain the optimal transmission power policy by approximating the achievable effective rate of uplink NOMA-based short packet communications. Compared with the existing OFDMA scheme, simulations validate that the proposed scheme can improve the achievable effective EE of massive MTC networks with 5.93%. [ABSTRACT FROM AUTHOR]

Low latency and high reliability are key features of the fifth-generation (5G) machine-type communications. In this paper, we provide a stringently delay-constrained model for multi-user interference channel, and formulate the rate and power allocation problem based on Markov decision process (MDP), which is solved by value iteration algorithm. In particular, to make timely transmission of each packet after being encoded, we characterize the delay constraint on sum of buffering delay and transmission delay. Then, the rate splitting and group decoding are employed at transmitters and receivers, respectively, which can offer significant improvement of achievable rate region. In addition, we also consider the receiving latency and propose novel delay-constrained partial group decoding (DC-CPGD), where all desired messages can be decoded within allowable interference cancellation steps to effectively control this latency. Two rate allocation algorithms are proposed with limited information exchange. Numerical results demonstrate that the proposed DC-CPGD can perform close to exhaustive search, and the proposed MDP-based adaptive transmission combined with DC-CPGD can significantly reduce the transmission cost under stringent delay requirement. [ABSTRACT FROM AUTHOR]

It is well known that spinal codes can essentially approach channel capacity for equiprobable source, and achieve seamless rate adaptation at the same time. But how to design an optimal spinal codes for non-equiprobable source is still an open problem. This paper proposes a novel Sparse Spinal (S-Spinal) codes design, which can essentially approach channel capacity for non-equiprobable and compressible source, and its seamless rate adaptation is also preserved. The main idea is to utilize source distribution information at the spinal decoder. The sparser the source is, the less symbols the receiver needs. The rateless feature of spinal codes can provide fine-grain compression ratio. The different decoder designs for Binary Symmetrical Channel (BSC) and Additive White Gaussian Noise (AWGN) channel are proposed, since their priori information is different. We also analyze and prove the S-Spinal codes with a practical pruning decoder can essentially achieve the channel capacity. The experimental results show that the proposed S-Spinal is very close to channel capacity of both BSC and AWGN channel for non-equiprobable source, and can achieve seamless rate adaption in practical system. [ABSTRACT FROM AUTHOR]

Due to rapid changes in the environment, vehicular communication channels no longer satisfy the assumption of wide-sense stationary uncorrelated scattering. The non-stationary fading process can be characterized by assuming local stationarity regions with finite extent in time and frequency. The local scattering function (LSF) and channel correlation function (CCF) provide a framework to characterize the mean power and correlation of the non-stationary channel scatterers, respectively. In this paper, we estimate the LSF and CCF from measurements collected in a vehicle-to-infrastructure radio channel sounding campaign in a suburban environment in Lille, France. Based on the CCF, the stationarity region is evaluated in time as 567 ms and used to capture the non-stationary fading parameters. We obtain the time-varying delay and Doppler power profiles from the LSF, and we analyze the corresponding root-mean-square delay and Doppler spreads. We show that the distribution of these parameters follows a lognormal model. Finally, application relevance in terms of channel capacity and diversity techniques is discussed. Results show that the assumption of ergodic capacity and the performance of various diversity techniques depend on the stationarity and coherence parameters of the channel. The evaluation and statistical modeling of such parameters can provide a way of tracking channel variation, hence, increasing the performance of adaptive schemes. [ABSTRACT FROM AUTHOR]

In this paper, we study the problem of multirate packet delivery in heterogeneous packet erasure broadcast networks. The technical challenge is to enable users receive packets at different rates, as dictated by the quality of their individual channel. We present a new analytical framework for characterizing the delivery rate and delivery delay performance of a previously proposed non-block-based network coding scheme in the literature. This scheme was studied in homogeneous network settings. We show for the first time, via new theoretical analysis and simulations that it can actually achieve multirate packet delivery. Using acknowledgments from each user, we show that the user with the highest link capacity achieves the maximum possible throughput. Also, a non-zero packet delivery rate is possible for other users, and the delivery rate depends on the difference between the packet arrival rate at the sender and the link capacity of each user. The accuracy of our analytical framework is confirmed by comparing the results with simulations for different settings of packet arrival rate at the sender and link capacities. [ABSTRACT FROM AUTHOR]

In this paper, we propose short-packet communications (SPCs) with non-orthogonal multiple access (NOMA) for coordinated and direct relay transmission (CDRT) Internet-of-Things (IoT) networks to enhance spectrum utilization and system performance. In this system, a source transmits its packets to a near IoT user via direct transmission and a far IoT user via selective relaying transmission under practical conditions of imperfect successive interference cancellation and cochannel interference. We derive the closed-form and asymptotic expressions for the average block-error-rate (BLER), throughput, and the goodput of the considered system over Rayleigh fading channels. To further improve the considered system, we formulate the system throughput maximization problem. Numerical results show that our proposed system outperforms the orthogonal multiple access and conventional NOMA-CDRT ones in terms of both BLER, system throughput, and goodput. In addition, by jointly optimizing power allocation coefficients and channel coding ratios, the system throughput performance is maximized. Furthermore, for a given block-length, the proposed system with short messages achieves superior latency and reliability compared to the long-message one. Monte Carlo simulations are presented to confirm the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, we study an uplink non-orthogonal multiple access (NOMA) wireless system with short-packet communications (SPC) in the presence of channel estimation errors and residual transceiver hardware impairments. Two NOMA decoding schemes are considered, namely fixed-order decoding (i.e., mean-power based decoding) and dynamic-order decoding (i.e., instantaneous-power based decoding). We first derive the closed-form exact and asymptotic expressions of the cumulative distribution functions (CDF) of the signal-to-interference-plus-noise ratio (SINR) associated with the two decoding schemes. Based on this, we analyze the average block error-rate (BLER) achieved in the finite block-length regime. Next, we formulate maximum throughput optimization problems with respect to the length of the packet. This problem is shown to be quasi-concave, which facilitates the finding of the optimal block-length via a search algorithm. Analytical comparisons between the NOMA-SPC system and its OMA-SPC counterpart are also performed. Simulation results are provided to validate the analysis. [ABSTRACT FROM AUTHOR]

This paper studies the performance of intelligent reflecting surface (IRS)-aided short-packet non-orthogonal multiple access (NOMA) systems under perfect and imperfect successive interference cancellation. Closed-form expressions for the average block error rate (BLER) with random and optimal phase shifts are derived. To gain some useful insights, an asymptotic analysis is carried out, based on which the diversity gain is achieved. Numerical results show that, at high signal-to-noise ratio, users with random phase shift achieve significant performance improvements in the performance gap between direct and non-direct links from a source when compared with that of the optimal phase shift. In addition, the proposed system outperforms its orthogonal multiple access counterpart in terms of both BLER and throughput. Furthermore, optimal channel coding rates of users can maximize the system throughput performance. Monte Carlo simulations are presented to corroborate the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the diversity performance of source–relay joint precoding in spatial multiplexing (SM) multiple-input–multiple-output (MIMO) amplify-and-forward (AF) relaying systems with channel coding. First, we evaluate the achievable diversity order of singular-value-decomposition-based precoding schemes as a function of a code rate. Then, we show that a significant diversity improvement can be obtained by utilizing signal space diversity. Our analysis provides helpful insights on the tradeoff between the code rate and the diversity order in SM MIMO AF relaying systems. Simulation results demonstrate that our analytical expressions match well with the numerical results. [ABSTRACT FROM PUBLISHER]

This paper considers the problems of minimizing the completion time and reducing decoding complexity for relay-aided wireless broadcast. Both network coding and scheduling problems are considered. A deterministic network coding algorithm is designed to select innovative encoding vectors, which is applicable to both the base station and the relay. The proposed algorithm can reduce decoding complexity significantly by selecting sparse encoding vectors. Integrating with the proposed network coding algorithm, a scheduling scheme based on dynamic programming is proposed, which is proved to be optimal in terms of minimizing expected completion time. Considering the size of state space and computational complexity of dynamic programming, a greedy scheduling algorithm is also proposed for practical implementation. Simulation shows that the proposed network coding algorithm and scheduling schemes work very well both in reducing completion time and in decoding complexity. [ABSTRACT FROM PUBLISHER]