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In this article, a new expression for the joint moment generating function (MGF) of the signal-to-noise ratio (SNR) considering correlated $\eta$ - $\mu$ fading is determined. Based on this result, a new closed-form expression is presented for the bit error probability (BEP) of the rectangular quadrature amplitude modulation ($R$ -QAM) scheme, considering frequency non-selective channel subject to cascaded double correlated $\eta$ - $\mu$ fading and a receiver with dual branch maximum ratio combining (MRC). The signal is received from two links with correlated cascaded double fading in the second link. In addition, a new expression for the outage probability (OP) is derived. All expressions determined in this paper are new and corroborated by simulations performed with Monte Carlo method. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surface (RIS) is considered as a promising technology, which can effectively control the phase of signals with low-cost reflective elements. In this paper, we investigate the RIS-assisted D2D communication system under Nakagami- $m$ fading. Overlay mode and underlay mode are discussed respectively. To characterize the performance of proposed communication system, we propose novel closed-form analytical expressions for outage probability under two modes, respectively. Based on the analytical results, we derive the diversity order of outage probability. We show that under overlay D2D mode, the diversity order depends on the number of elements and fading parameters. For the underlay D2D case, 0 diversity order is obtained due to the existence of interference. Furthermore, we study the ergodic achievable rate for each mode and the corresponding tight bounds are derived in closed form. High SNR slopes achieved by users under two modes are also discussed. We observe a high SNR slope of order 1 for overlay D2D mode and 0 for underlay D2D mode. In addition, we also investigate the energy efficiency (EE) of the considered system. Numerical results show that the optimal phase shift proposed in our paper enhance system performance effectively comparing to the traditional D2D communication and random phase shift scheme. Significant EE gains can be obtained for low to middle SNR region by passive reflectors with reconfigurable phase. Unlike relay system, the nearer RIS to the D2D transmitter/receiver, the better performance is obtained. [ABSTRACT FROM AUTHOR]

The amount of sensitive data, which is transmitted wirelessly will increase with future technologies. This raises many questions about secure data transmission. Besides cryptography, information-theoretic security gained increasing attention over the recent years. Among others, it deals with the problem of secure data transmission on the physical layer to a legitimate receiver (Bob) in the presence of an eavesdropper (Eve). In this work, we investigate upper and lower bounds on the secrecy outage probability for slowly-fading wiretap channels with an arbitrary dependency structure between the fading channels to Bob and Eve. Both cases of absence of channel-state information at the transmitter (CSI-T) and availability of CSI-T of only the main channel to the legitimate receiver are considered. Furthermore, we derive explicit expressions for the upper and lower bounds for Rayleigh fading and compare them to the case of independent channels. The joint distribution of the legitimate and eavesdropper channels has a tremendous impact on the achievable secrecy outage probability. The bounds enable developing guaranteed secrecy schemes by only measuring the marginal channel distributions. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of wireless systems that employ finite-blocklength channel codes for transmission and operate under queuing constraints in the form of limitations on buffer overflow or delay violation probabilities. A block fading model, in which fading stays constant in each coherence block and changes independently between blocks, is considered. It is assumed that channel coding is performed over multiple coherence blocks. A simple ARQ scheme with error-free feedback without any delay is considered. The channel coding rate with given maximal error probability is considered as the service rate and is incorporated into the effective capacity formulation, which characterizes the maximum constant arrival rate that can be supported under statistical queuing constraints. Performances of variable-rate and fixed-rate transmissions are studied. The optimum error probability for variable-rate and fixed-rate transmissions is shown to be unique. The limiting performance as the number of blocks increases is characterized. The tradeoffs and the interactions between the throughput, the number of coherence blocks over which channel coding is performed, error probabilities, channel coherence duration, and queuing constraints are identified. [ABSTRACT FROM AUTHOR]

In this paper, a distributed cognitive underlay single carrier system is investigated. A secondary users’ network consists of a control unit (CU) and a group of secondary user remote radio heads (S-RRHs). To effectively access the radio spectrum licensed to the primary users, a distributed cyclic delay diversity (dCDD) scheme is employed between the CU and S-RRHs as the transmit diversity scheme. Multiple primary user transmitters (PTXs) are assumed to be located isotropically within the secondary users’ network, so that a mixture of line-of-sight (LoS) and non-line-of-sight (nLoS) paths from the PTXs to the secondary user receiver is considered. In addition, a mixture of LoS and nLoS paths is considered in the secondary users’ network. For a new transmit diversity scheme and channel model, the performance of the secondary users’ network achieved by the dCDD in the presence of isotropically distributed multiple PTXs is investigated. The dCDD enables the CU to use multiple S-RRHs at the same time, so that determining the effects of a different number of S-RRHs in the presence of a new channel model is an open research issue. To this end, a new closed-form expression for the outage probability is derived, and then its accuracy is verified by link-level simulations. [ABSTRACT FROM AUTHOR]

Multi-connectivity (MCo) is considered to be a key strategy for enabling reliable transmissions and enhanced data rates in fifth-generation mobile networks, as it provides multiple links from source to destination. In this paper, we quantify the communication performance of MCo in terms of outage probability and throughput. For doing so, we establish a simple, yet accurate analytical framework at high signal-to-noise ratio (SNR), in which the number of links, the spectral efficiency, the path loss, and the SNR are incorporated, giving new insights into the potentials of MCo as compared with the single-connectivity (SCo). These are our main contributions: 1) finding the exact coding gain of the outage probability for parallel block-fading channels; 2) quantifying the performance improvement of MCo over SCo in terms of SNR gain; and 3) comparing optimal and suboptimal combining algorithms for MCo at the receiver side, namely joint decoding, selection combining, and maximal-ratio combining, also in terms of SNR gain. In addition, we apply our analytical framework to real field channel measurements and thereby illustrate the potential of MCo to achieve high reliability and high data rates in real cellular networks. [ABSTRACT FROM AUTHOR]

This paper investigates the physical-layer security of the modify-and-forward (MF) protocol in multi-relay and multi-eavesdropper networks. Three relay selection critera are developed according to the channel state information (CSI) acquisition. Criterion I requires the CSI of all main channels for relay selection. Criteria II and III rely only on the CSI of the source-relay and relay-destination channels, respectively. We derive the exact secrecy outage probability (SOP), probability of nonzero secrecy capacity, and the ergodic secrecy rate in the closed forms. The $\epsilon$ -outage secrecy capacity is also evaluated. Asymptotic analysis of the SOP explicitly reveals that the secrecy diversity order of criterion I depends on the total number of relays, whereas those of criteria II and III are 2 and 1, respectively. The probability of nonzero secrecy capacity asymptotically decreases with the SNR of the wiretap channel as the eavesdropper is close to the source and relays. Criterion I is always superior to criteria II and III in terms of the ergodic secrecy rate and $\epsilon$ -outage secrecy capacity. Simulations results also demonstrated that the $\epsilon$ -outage secrecy capacity deteriorates as the SNR of the eavesdropper's channel increases. [ABSTRACT FROM AUTHOR]

Energy efficiency of three common hybrid automatic repeat request (HARQ) schemes, including Type I HARQ, HARQ with chase combining (HARQ-CC) and HARQ with incremental redundancy (HARQ-IR), is analyzed and joint power allocation and rate selection to maximize the energy efficiency is investigated in this paper. Unlike prior literature, time-correlated fading channels are considered and two widely concerned quality of service (QoS) constraints, i.e., outage and goodput constraints, are also considered in the optimization, which further differentiates this paper from prior ones. Using a unified expression of asymptotic outage probabilities, optimal transmission powers and optimal rate are derived in closed forms to maximize the energy efficiency while satisfying the QoS constraints. These closed-form solutions then enable a thorough analysis of the maximal energy efficiencies of various HARQ schemes. It is revealed that with low-outage constraint, the maximal energy efficiency achieved by Type I HARQ is $\frac{1}{4\ln 2}$ b/J, while HARQ-CC and HARQ-IR can achieve the same maximal energy efficiency as $\frac{\kappa _\infty }{4\ln 2}$ b/J, where $\kappa _\infty = 1.6617$. Moreover, time correlation in the fading channels has a negative impact on the energy efficiency, whereas large maximal allowable number of transmissions is favorable for the improvement of energy efficiency. The effectiveness of the energy-efficient optimization is verified by extensive simulations and the results also show that HARQ-CC can achieve the best tradeoff between energy efficiency and spectral efficiency among the three HARQ schemes. [ABSTRACT FROM AUTHOR]

In contrast to the traditional assumption of the independent and identically distributed fading channels, this paper studies the achievable rate of the multiuser two-way full-duplex (FD) relay system under the independent and nonidentically distributed (i.ni.d.) fading channels, which leads to the different selection probabilities and different weighted rates of different user pairs contributing to the overall system achievable rate as well. To be specific, we first derive the user pair selection probabilities of the max–min scheduling scheme for the i.ni.d. channels. Then, based on the selection probabilities, we solve the hard problem of the weighted rate derivation of each pair. Finally, according to the total probability theorem, the general expressions of the system achievable rate are obtained. In addition, theoretical evaluations and numerical simulations are conducted. The results verify the accuracy of the theoretical analysis and reveal the superiority of the FD mode especially within the low transmitting power regime. [ABSTRACT FROM PUBLISHER]

In this paper, we study the performance of a downlink non-orthogonal multiple access-based cooperative relay system with a single relay over Nakagami- $m$ fading channels, where both decode-and-forward (DF) and amplify-and-forward (AF) protocols are considered. We assume that only statistical channel state information is available to the system and used to determine the decoding order of cell-edge users’ data. For DF relaying, both ergodic sum rate and outage probability are solved in closed form. For AF relaying, closed-form asymptotic ergodic sum rate and outage probability are provided. Numerical results verify the accuracy of the analysis and demonstrate that the DF protocol significantly outperforms the AF one in terms of ergodic sum rate even the channel’s near–far effect weakens. In addition, the DF protocol exhibits better outage performance than the AF one at low signal-to-noise ratio (SNR), though the superiority becomes negligible with the increasing SNR. [ABSTRACT FROM PUBLISHER]

This paper investigates a distributed cyclic delay diversity (CDD) transmission scheme for cyclic-prefixed single carrier systems in non-identically and identically distributed frequency selective fading channels. The distinguishable feature of the proposed scheme lies in providing a transmit diversity gain while reducing the burden of estimating the channel state information, which is a challenging task in distributed and cooperative systems. To effectively use the distributed CDD scheme at the transmitters, two sufficient conditions are derived to eliminate the intersymbol interference at the receiver and leveraged to convert the multi-input single-output channel into a single-input single-output channel. These conditions allow the system to achieve the maximum diversity for frequency selective fading channels at a full rate. To achieve this maximum diversity, a fixed number of CDD transmitters are selected based on the channel conditions, symbol block size, and maximum time dispersion of the channel, and a new two-stage transmission mode is proposed. Based on the distributed CDD and the proposed selection schemes, a new expression for the signal-to-noise ratio at the receiver is obtained with the aid of order statistics, and then closed-form expressions for the outage probability and average symbol error rate (ASER) are derived. As far as the identically distributed frequency selective fading channel model is concerned, the achievable maximum diversity gain is proved, with the aid of asymptotic analysis, to be equal to the product of the total number of transmitters in the system and the number of multipath components. Link-level simulations are also conducted to validate the analytical expressions for outage probability, ASER, and maximum achievable diversity gain. [ABSTRACT FROM PUBLISHER]

We investigate the performance of three-node lossy-forward (LF) relaying over independent block Nakagami- $m$ fading channels. Based on the theorem of source coding with side information, the exact outage probability expression for arbitrary values of the shape factor $m$ is derived under the assumptions of both the Gaussian codebook capacity and the constellation constrained capacity. The difference in outage probability between the two codebook models of capacity is found to be very minor. Furthermore, an accurate high signal-to-noise ratio approximation for the outage probability is obtained. It clearly identifies the equivalent diversity order and coding gain of the LF relaying. It is shown that the LF relaying is superior to conventional decode-and-forward relaying in terms of the outage probability and the $\epsilon$ -outage achievable rate. Moreover, with the LF relaying, the optimal location for the relay (R), which minimizes the outage probability, is found to be the point having same distance to the source (S) and the destination (D) when the S-R and R-D links experience the same level of fading. The accuracy of the analytical results is verified by a series of Monte Carlo simulations. [ABSTRACT FROM PUBLISHER]

This paper quantifies the impact of correlated fading on secure communication of multiple amplify-and-forward (AF) relaying networks. In such a network, the base station (BS) is equipped with multiple antennas and communicates with the destination through multiple AF relays, while the message from the relays can be overheard by an eavesdropper. We focus on the practical communication scenario, where the main and eavesdropper’s channels are correlated. In order to enhance the transmission security, transmit antenna selection is performed at the BS, and the best relay is chosen according to the full- or partial-relay selection criterion, which relies on the dual-hop relay channels or the second-hop relay channels, respectively. For these criteria, we study the impact of correlated fading on the network secrecy performance, by deriving an analytical approximation for the secrecy outage probability and an asymptotic expression for the high main-to-eavesdropper ratio. From these results, it is concluded that the channel correlation is always beneficial to the secrecy performance of full relay selection. However, it deteriorates the secrecy performance if partial-relay selection is used, when the number of antennas at the BS is less than the number of relays. [ABSTRACT FROM PUBLISHER]

The outage probability (OP) of the signal-to-interference-plus-noise ratio (SINR) is an important metric that is used to evaluate the performance of wireless systems. One difficulty toward assessing the OP is that, in realistic scenarios, closed-form expressions cannot be derived. This is, for instance, the case of the Log-normal environment, in which evaluating the OP of the SINR amounts to computing the probability that a sum of correlated Log-normal variates exceeds a given threshold. Since such a probability does not admit a closed-form expression, it has thus far been evaluated by several approximation techniques, the accuracies of which are not guaranteed in the region of small OPs. For these regions, simulation techniques based on variance reduction algorithms are a good alternative, being quick and highly accurate for estimating rare event probabilities. This constitutes the major motivation behind this paper. More specifically, we propose a generalized hybrid importance sampling scheme, based on a combination of a mean shifting and a covariance matrix scaling, to evaluate the OP of the SINR in a Log-normal environment. We further our analysis by providing a detailed study of two particular cases. Finally, the performance of these techniques is performed both theoretically and through various simulation results. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a novel distributed cooperative sensing algorithm for connected vehicles. The adaptive energy detection threshold, which is used to decide whether the channel is busy, is optimized in this paper by using a computationally efficient numerical approach. The proposed optimization approach minimizes the probability of an incorrect detection as a function of both the probability of false alarm and the probability of missed detection. By considering both probabilities when computing the probability of incorrect detection, to the best of the authors' knowledge, the proposed approach is novel. During the energy detection process, large-scale fading, multipath fading, Doppler effect, and transmission errors affecting the control messaging process are accounted for in order to provide a practical solution for connected vehicles. Once the available channels have been detected, the vehicles share this information using broadcast control messages. Each vehicle evaluates the available channels by voting on the information received from one-hop neighbors, where the credibility of each neighbor is weighted during the voting process. An interdisciplinary approach referred to as entropy-based weighting is used to define the neighbor, as well as the vehicle's own credibility. The voting mechanism is switched between the proposed voting mechanism and the traditional voting approach obtained from the current state of the art in order to maintain a balance between the computational cost/latency and robust spectrum sensing. Experimental results show that by using the proposed distributed cooperative spectrum sensing mechanism, spectrum detection error converges to zero. [ABSTRACT FROM AUTHOR]

The Gamma–Gamma distribution has recently emerged in a number of applications ranging from modeling scattering and reverberation in sonar and radar systems to modeling atmospheric turbulence in wireless optical channels. In this respect, assessing the outage probability achieved by some diversity techniques over this kind of channels is of major practical importance. In many circumstances, this is related to the difficult question of analyzing the statistics of a sum of Gamma–Gamma random variables. Answering this question is not a simple matter. This is essentially because outage probabilities encountered in practice are often very small, and hence, the use of classical Monte Carlo methods is not a reasonable choice. This lies behind the main motivation of this paper. In particular, this paper proposes a new approach to estimate the left tail of the sum of Gamma–Gamma variates. More specifically, we propose robust importance sampling schemes that efficiently evaluates the outage probability of diversity receivers over Gamma–Gamma fading channels. The proposed estimators satisfy the well-known bounded relative error criterion for both maximum ratio combining and equal gain combining cases. We show the accuracy and the efficiency of our approach compared with naive Monte Carlo via some selected numerical simulations. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze the performance of an overlay multiuser two-way relay network with $N$ th-user selection by employing a three-phase cooperative spectrum sharing (3PCSS) scheme. Hereby, a one-end primary user (PU) communicates with the arbitrary (which may be the $N$ th best) selected other-end PUs with the cooperation of a secondary user (SU) in three transmission phases. By splitting up its available power, the SU assists in bidirectional primary transmissions and accesses the spectrum for its own transmission, based on satisfying the primary system outage constraint. Considering the involved $N$ th-order statistics with correlation, we derive the outage probability expressions for both primary and secondary systems over general fading channels. Based on these expressions, we compute the total system throughput of the 3PCSS scheme and compare it with other competitive schemes. We illustrate that the 3PCSS scheme can effectively realize spectrum sharing by harnessing additional cooperative diversity and achieving spectral efficiency at par with the primary two-phase direct transmission system. Numerical and simulation results substantiate our theoretical findings. [ABSTRACT FROM PUBLISHER]

The incomplete moment generating function (IMGF) has paramount relevance in communication theory, since it appears in a plethora of scenarios when analyzing the performance of communication systems. We here present a general method for calculating the IMGF of any arbitrary fading distribution. Then, we provide exact closed-form expressions for the IMGF of the very general $\kappa $ - $\mu $ shadowed fading model, which includes the popular $\kappa $ - $\mu $ , $\eta $ - $\mu $ , Rician shadowed, and other classical models as particular cases. We illustrate the practical applicability of this result by analyzing several scenarios of interest in wireless communications: 1) physical layer security in the presence of an eavesdropper; 2) outage probability analysis with interference and background noise; 3) channel capacity with side information at the transmitter and the receiver; and 4) average bit-error rate with adaptive modulation, when the fading on the desired link can be modeled by any of the aforementioned distributions. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the achievable coverage and the information rate of an aerial base station. The air-to-ground link is analysed by considering random fading and shadowing effects impairing the wireless transmission, together with a homogeneous spatial distribution of the terrestrial users. The distribution of the buildings in the underlying coverage region is modeled using the International Telecommunication Union-Recommendation statistical city model. For a given urban environment/region, we analytically quantify the achievable coverage probability and the information rate of users on the ground at a particular base station altitude. Furthermore, we analytically find the optimal altitude of the aerial base station to maximise the terrestrial coverage given a certain service region. Simulations are conducted to verify our analysis, and a close match between the analytical and simulation results is observed. [ABSTRACT FROM AUTHOR]

In this paper, the secrecy performance of finite-sized cooperative cyclic prefixed single carrier systems with multiple eavesdroppers and unreliable wireless backhaul connections across multiple transmitters is investigated. For nonidentical frequency-selective fading channels between the relay and destination nodes, secrecy performance metrics including the secrecy outage probability, ergodic secrecy rate, and probability of nonzero achievable secrecy rate are derived. Furthermore, the existence of performance limits on the secrecy outage probability and probability of non-zero achievable secrecy rate are verified for various backhaul scenarios. These limits are found to be exclusively determined by the backhaul reliability. For imperfect backhaul connections, it is found that the diversity gain promised by cooperative cyclic prefixed single-carrier systems cannot be achieved in the conventional asymptotic high signal-to-noise ratio region. Link-level simulations are conducted to verify the derived impact of backhaul reliability on the secrecy performance. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a framework to analyze the performance of buffer-aided (BA) relaying under time-correlated fading channels in terms of the queueing behavior of packets at the relay's buffer. Unlike independent and identically distributed (i.i.d.) fading, correlated fading brings challenges in performance analysis since the state transition probabilities of buffer occupancy become time variant. To overcome this issue, we first establish an aggregate quasi-birth-death (QBD) Markov chain integrating both the buffer occupancy process and the channel fading process, then analyze the stationary distribution of the aggregate chain, and finally extract the stationary distribution of buffer occupancy from it. Using the stationary distribution of buffer occupancy, system throughput, end-to-end delay, and outage probability are derived. Numerical results verify our analyses and show that the throughput of BA relaying under correlated fading channels can approach the one under i.i.d. fading only for loose delay constraints or high fading margins. For stringent delay constraints and low fading margins, correlated fading causes great degradation of throughput. In particular, a throughput loss of about 16% under an infinite buffer (28% under a finite buffer) is observed for the requirement of an average delay of 20 slots and a fading margin of 5 dB. This means that the designs based on i.i.d. fading are not always feasible for correlated fading. According to these observations, some insights on performance degradation and guidelines on redesigning improved policies under correlated fading are provided. [ABSTRACT FROM PUBLISHER]

In this paper, the energy efficiency (EE) of multihop relaying over Nakagami- $m$ fading channels is investigated. The “consumption factor” (CF), which is adopted as a metric to evaluate the EE, is derived for both amplify-and-forward and decode-and-forward relaying strategies. Then, based on the obtained expressions, we propose a power-allocation (PA) strategy maximizing the CF. In addition, a suboptimal low-complexity PA algorithm is proposed and analyzed, and the obtained PA scheme is compared in terms of EE with other PA schemes from the literature. Analytical and simulation results confirm the accuracy of our derivations and assess the performance gains of the proposed approach. [ABSTRACT FROM PUBLISHER]

In this paper, we present a comprehensive framework for quadrature spatial modulation (QSM) in generalized fading channels. In particular, the performance analysis of QSM systems in the presence of imperfect channel knowledge and under correlated fading channels is presented. A simple and closed-form expression for the pairwise error probability (PEP) is provided. Based on the obtained PEP, a closed-form upper bound expression for the average bit error probability (BEP) is obtained. The analysis is unified in the sense that it is applicable for any fading channel once its envelope and phase distributions are available. As such, different generalized fading distribution models, namely, $\eta $ – $\mu $ , $\kappa $ – $\mu $ , and $\alpha $ – $\mu $ distributions, are considered. The obtained results clearly show the influence of the fading parameters on the average BEP. In the case of the $\alpha $ – $\mu $ fading channels, increasing $\alpha $ has larger negative impact on the average BEP compared with increasing $\mu $ . For the $\kappa $ – $\mu $ channels, increasing $\mu $ results in increasing the average BEP dramatically when compared with increasing $\kappa $ . In the same context, in $\eta $ – $\mu $ fading channels, as $\mu $ increases the average BEP degrades whereas increasing $\eta $ slightly improves the average BEP. In addition, it is demonstrated that transmit-antenna correlation significantly deteriorate the average BEP when compared with receive-antenna correlation. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of the point-to-point multiple-input–multiple-output (MIMO) systems in the presence of a large but finite numbers of antennas at the transmitters and/or receivers. Considering the cases with and without hybrid automatic repeat request (HARQ) feedback, we determine the minimum numbers of the transmit/receive antennas, which are required to satisfy different outage probability constraints. Our results are obtained for different fading conditions and the effect of the power amplifiers efficiency/feedback error probability on the performance of the MIMO–HARQ systems is analyzed. Then, we use some recent results on the achievable rates of finite block-length codes, to analyze the effect of the codewords lengths on the system performance. Moreover, we derive closed-form expressions for the asymptotic performance of the MIMO–HARQ systems when the number of antennas increases. Our analytical and numerical results show that different outage requirements can be satisfied with relatively few transmit/receive antennas. [ABSTRACT FROM PUBLISHER]

Prior results on exact error rates and outage probabilities of diversity receptions over arbitrarily correlated fading channels involve intractable nested integrals, which makes the performance analyses challenging to carry out. In this paper, we derive asymptotic expressions and asymptotically tight bounds for error rates and outage probabilities of diversity receptions (including maximal-ratio combining, selection combining, and equal-gain combining) over arbitrarily correlated Beckmann fading channels. These new asymptotic performance expressions reveal insights into the diversity systems over arbitrarily correlated Beckmann fading channels, and the accuracy of the asymptotic performance expressions is explicitly quantified by the performance bounds. Using these analytical tools, one can assess the performance of the diversity reception systems over arbitrarily correlated Beckmann fading channels without resorting to time-consuming Monte Carlo simulation or numerical multifold integration. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a two-way relaying system where two users communicate with each other with the help of multiple relays and in which every node is equipped with a single antenna. We assume that the relay employs the amplify-and-forward protocol and propose the $N$th worst relay selection scheme. We intend to analyze the system performance of our considered system under two different fading models: lognormal shadowing channels and generalized- {\cal K} fading channels. More specifically, the outage probability and bit-error-rate expressions of the proposed scheme are derived. Finally, numerical results are provided to verify and illustrate our mathematical analysis. [ABSTRACT FROM PUBLISHER]

In this paper, the product of two independent and nonidentically distributed (i.n.i.d.) \alpha \- \mu variates is considered. Exact reasonably simple closed-form expressions for the probability density function (pdf), the cumulative distribution function (cdf) , and the moments of the resulting random variable (RV) are derived. These results find a wide range of applications in a number of fields, such as radar communications, multihop systems, multiple-input–multiple-input links, and cascaded communications in general. In particular, they are used here to describe a novel \alpha \-\mu/\alpha \- \mu composite multipath–shadowing fading model. Because the \alpha \- \mu model alone comprises a substantial number of useful fading environments, its \alpha \-\mu/\alpha \- \mu composite version leads to a variety and an immense amount of composite fading distributions. The novel expressions for this rather flexible scenario compute instantaneously, constituting a powerful tool to characterize wireless fading channels. [ABSTRACT FROM PUBLISHER]

In this paper, we propose two relay antenna selection (RAS) schemes in multiple-input–multiple-output (MIMO) two-way relay networks, where an NA-antenna source and an NB-antenna source exchange information via an NR-antenna amplify-and-forward (AF) relay. The proposed RAS schemes maximize the minimum of the two overall end-to-end signal-to-noise ratio (SNR) values. In the first RAS scheme, transmit and receive beamforming (BF) is adopted at the two sources using all antennas. In the second RAS scheme, transmit and receive antenna selection (AS) is adopted at the two sources using one antenna. To conduct a performance comparison of the proposed RAS-BF and RAS-AS schemes, we first derive new expressions for the exact outage probability over independent but not necessarily identically distributed Nakagami- m fading channels. We then derive new closed-form lower and upper bounds on the outage probability to offer an efficient computation. We further derive new compact expressions for the asymptotic outage probability to characterize the performance in the high-SNR regime. Notably, we demonstrate that RAS-BF and RAS-AS achieve the full outage diversity order of \min\{N_{\rm A}N_{\rm R}m_{\rm A}, N_{\rm B}N_{\rm R}m_{\rm B}\}, where m_{\rm A} and mB denote the Nakagami- m fading parameters between the NA-antenna source and relay and between the NB-antenna source and relay, respectively. Based on asymptotic results, we determine a concise solution for the optimal power allocation among the sources and the relay to maximize the performance under the assumption that both the sources have the same transmit power. To quantify the effect of spatial correlation at the sources, we derive new closed-form expressions for the asymptotic outage probability over correlated Nakagami- $m$ fading channels. The results indicate that the spatial correlation has no impact on the outage diversity order but significantly deteriorates the outage array gain. [ABSTRACT FROM PUBLISHER]

A (layered) broadcast approach is studied for the fading wiretap channel without the channel state information (CSI) at the transmitter. Two broadcast schemes, based on superposition coding and embedded coding, respectively, are developed to encode information into a number of layers and use stochastic encoding to keep the corresponding information secret from an eavesdropper. The layers that can be successfully and securely transmitted are determined by the channel states to the legitimate receiver and the eavesdropper. The advantage of these broadcast approaches is that the transmitter does not need to know the CSI to the legitimate receiver and the eavesdropper, but the scheme still adapts to the channel states of the legitimate receiver and the eavesdropper. Three scenarios of block fading wiretap channels with stringent delay constraints are studied, in which either the legitimate receiver's channel, the eavesdropper's channel, or both channels are fading. For each scenario, the secrecy rate that can be achieved via the broadcast approach developed in this paper is derived, and the optimal power allocation over the layers (or the conditions on the optimal power allocation) is also characterized. A notion of probabilistic secrecy, which characterizes the probability that a certain secrecy rate of decoded messages is achieved during one block, is also introduced and studied for scenarios when the eavesdropper's channel is fading. Numerical examples are provided to demonstrate the impact of the CSI at the transmitter and the channel fluctuations of the eavesdropper on the average secrecy rate. These examples also demonstrate the advantage of the proposed broadcast approach over the compound channel approach. [ABSTRACT FROM AUTHOR]

This paper studies a multi-relay adaptive turbo-coded cooperative diversity scheme over Nakagami- m fading channels. In the underlying scheme, after receiving a fraction of the codeword determined by a tradeoff parameter denoted by f, all the relays decode, and only the reliable relays forward the rest of the codeword to the destination. We assume binary phase-shift keying modulation and analyze the scheme under study in terms of bit error rate (BER) and outage probability. Union bounds on the BER are derived using the transfer function bounding and the limit-before-average techniques. Furthermore, we examine the asymptotic behavior of the system in the high-signal-to-noise-ratio (SNR) regime using the derived pairwise error probability (PEP). We also derive a closed-form expression for the outage probability of the system and its high-SNR approximation to evaluate the achievable diversity order. Simulations are provided to assess the accuracy of our analytical work. [ABSTRACT FROM PUBLISHER]

In this paper, the performance of interference-limited wireless networks in an asynchronized environment is analyzed. A modified model is proposed to calculate precisely the amount of interference by carefully addressing the overlap of transmissions, which results due to frequency reuse in the network. For the proposed model, taking medium-access-control (MAC) constraints into account, the probability of a node being in the guard zone and the effective number of interferers are calculated. Closed-form expressions are derived for a specific case. Here, a link-probability-based range is used in place of a unit disk model (UDM), and a two-slope (TS) path-loss model is used to account for path-loss conditions. Outage performance is analyzed using the proposed interference model. Effects of antenna height on network performance are also investigated through simulations. [ABSTRACT FROM PUBLISHER]

We investigate the performance of a dual-hop amplifyand-forward (AF) multi-relay system over independent and identically distributed (i.i.d.) Nakagami-m fading channels, where all nodes in the system are equipped with multiple antennas, and space–time block codes are used in both transmissions. By assuming that the number of source–relay spatial subchannels is equal to the number of relay–destination subchannels, new analytical expressions for the most important figures of merit, namely, outage probability, symbol error probability (SEP), and average channel capacity, are derived for arbitrary signal-to-noise ratios (SNRs) and for arbitrary values of the m parameter. We also present simplified expressions in the high-SNR regime that enable us to quantify the system performance in terms of diversity order and coding gain. Two different scenarios have been considered. First, each relay and destination combine the received signal, and then, the harmonic mean of the source–relay and relay–destination channels is computed. After that, the relay with the best harmonic mean is selected. In the second scenario, each relay and destination combine the received signal, and then, the relay with the best source–relay SNR is selected. After that, the harmonic mean of the source-to-selected-relay channel and selected-relay-to-destination channel is computed. For both considered scenarios, some special cases of interest (e.g., Nakagami-0.5 and Rayleigh) are examined. Our results explicitly demonstrate that the first scheme has higher diversity order than the second scheme, whereas the coding gain of the second scheme is always greater for the multi-relay case [ABSTRACT FROM PUBLISHER]

This paper provides an analytical framework for the performance evaluation of dual-hop decode-and-forward (DF) cooperative systems operating over \eta– \mu fading channels in the presence of cochannel interference (CCI) and additive white Gaussian noise (AWGN). The interferers are subject to independent but not necessarily identically distributed \eta– \mu fading. For the considered system, assuming multiple interferers at both the relay and the destination, simple accurate analytical expressions for the outage probability (OP), average bit error probability (ABEP), and average capacity are derived. Various numerically evaluated results accompanied with Monte Carlo simulations are presented to corroborate the accuracy of the proposed approximations. [ABSTRACT FROM PUBLISHER]

Cooperative communication networks can exploit the spatial diversity inherent in a multiuser system by allowing users to cooperate and relay other users' messages to a destination. Avoiding the multiple-access interference (MAI) while taking full advantage of the multiuser cooperative multiple-input–multiple-output (Co-MIMO) is still an interesting problem. In this paper, we propose a relay scheme that combines the source user's two antennas and the relay user's two antennas to form a virtual-four-antenna space–time cyclic delay transmit diversity (STCDTD), and explore 2-D block-spread code-division multiple access (CDMA) to achieve MAI-free uplink transmission. The theoretical error probability of the proposed scheme is described, when a signal is transmitted through a multiple-access Rayleigh fading channel. Computer simulations indicate that the proposed scheme is able to avoid the MAI over a slow fading channel and to improve the bit error rate (BER) significantly. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze the outage probability and finite-SNR diversity–multiplexing tradeoff (f-DMT) performance for two-way relay channels (TWRCs). Both amplify-and-forward (AF) and decode-and-forward (DF) relay protocols are considered. The two source nodes are equipped with single antenna, and the relay is equipped with single or multiple antennas. First, we derive lower bounds of outage probability for single- and multiantenna relay AF, upper and lower bounds for multiantenna relay DF, and the exact closed-form expression for single-antenna DF. These results are suitable for arbitrary time-sharing and rate allocation for DF and arbitrary rate allocation for AF. Numerical results show that the derived lower bounds approximate very well the actual outage performance obtained by Monte Carlo simulation. Based on the tight lower bounds, we further derive estimates of the f-DMTs. We find that AF always outperforms DF in terms of f-DMT in all SNR regimes. However, the comparison result of outage performance between AF and DF depends on channel conditions. Finally, we also discuss the impact of relay location, time-sharing, and rate allocation on the outage and f-DMT via numerical examples. [ABSTRACT FROM AUTHOR]

This paper considers point-to-point secure communication over flat fading channels under an outage constraint. More specifically, we extend the definition of outage capacity to account for the secrecy constraint and obtain sharp characterizations of the corresponding fundamental limits under two different assumptions on the transmitter channel state information (CSI). First, we find the outage secrecy capacity assuming that the transmitter has perfect knowledge of the legitimate and eavesdropper channel gains. In this scenario, the capacity achieving scheme relies on opportunistically exchanging private keys between the legitimate nodes. These keys are stored in a key buffer and later used to secure delay sensitive data using the Vernam's one time pad technique. We then extend our results to the more practical scenario where the transmitter is assumed to know only the legitimate channel gain. Here, our achievability arguments rely on privacy amplification techniques to generate secret key bits. In the two cases, we also characterize the optimal power control policies which, interestingly, turn out to be a judicious combination of channel inversion and the optimal ergodic strategy. Finally, we analyze the effect of key buffer overflow on the overall outage probability. [ABSTRACT FROM AUTHOR]

In dense radio frequency identification (RFID) systems, reader-to-reader interference may appear among readers operating nearby. When the anticollision algorithm is Frame Slotted Aloha (FSA), a usual solution is to multiplex the frames of interfering readers by means of a central controller. The scenario studied considers RFID tags attached to objects carried by conveyor belts or vehicles so that each tag crosses, in constant motion, one reader's interrogation region. The problem addressed consists of determining the length of the multiplexed FSA frames such that each object is successfully identified, with high probability, before exiting its interrogation region. In this paper, we develop a mathematical model, based on dynamic system theory, allowing us to obtain the configurations attaining the desired reliability objective, to show that some configurations present multiple equilibrium points and should be avoided, and to define the operating boundaries of the system. The model can also incorporate fading and capture effects. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the design of artificial-noise-aided secure multi-antenna transmission in slow fading channels. The primary design concerns include the transmit power allocation and the rate parameters of the wiretap code. We consider two scenarios with different complexity levels: 1) the design parameters are chosen to be fixed for all transmissions; and 2) they are adaptively adjusted based on the instantaneous channel feedback from the intended receiver. In both scenarios, we provide explicit design solutions for achieving the maximal throughput subject to a secrecy constraint, given by a maximum allowable secrecy outage probability. We then derive accurate approximations for the maximal throughput in both scenarios in the high signal-to-noise ratio region, and give new insights into the additional power cost for achieving a higher security level while maintaining a specified target throughput. In the end, the throughput gain of adaptive transmission over non-adaptive transmission is also quantified and analyzed. [ABSTRACT FROM PUBLISHER]

The outage probability of a multiuser two-hop amplify-and-forward relaying system employing opportunistic scheduling is investigated. A practically important case where there are cochannel interference signals present at the network is considered for the analysis. Exact expressions and closed-form lower bounds are derived for the outage probability. Exact closed-form expressions are derived for the system outage probability when interference signals are present at the relay and at the destination separately. A closed-form lower bound is derived for the outage probability when the relay and the destination nodes are affected by interference simultaneously. The effects of channel state information feedback delay are investigated for special cases. In addition, asymptotic outage probability results are derived to obtain useful insights on the effects of interference and feedback delay. The novel expressions can be used by practicing engineers to obtain reliable and realistic performance estimates for dual-hop multiuser relay networks. The results are useful for understanding the capabilities of the feedback channel required in this system. [ABSTRACT FROM AUTHOR]

In this paper, we derive exact closed-form expressions for the bivariate Nakagami-m cumulative distribution function (CDF) with positive integer fading severity index m in terms of a class of hypergeometric functions. Particularly, we show that the bivariate Nakagami-m CDF can be expressed as a finite sum of elementary functions and bivariate confluent hypergeometric Φ_3 functions. Direct applications which arise from the proposed closed-form expression are the outage probability (OP) analysis of a dual-branch selection combiner in correlated Nakagami-m fading, or the calculation of the level crossing rate (LCR) and average fade duration (AFD) of a sampled Nakagami-m fading envelope. [ABSTRACT FROM AUTHOR]

We consider the restless multiarmed bandit problem with unknown dynamics in which a player chooses one out of N arms to play at each time. The reward state of each arm transits according to an unknown Markovian rule when it is played and evolves according to an arbitrary unknown random process when it is passive. The performance of an arm selection policy is measured by regret, defined as the reward loss with respect to the case where the player knows which arm is the most rewarding and always plays the best arm. We construct a policy with an interleaving exploration and exploitation epoch structure that achieves a regret with logarithmic order. We further extend the problem to a decentralized setting where multiple distributed players share the arms without information exchange. Under both an exogenous restless model and an endogenous restless model, we show that a decentralized extension of the proposed policy preserves the logarithmic regret order as in the centralized setting. The results apply to adaptive learning in various dynamic systems and communication networks, as well as financial investment. [ABSTRACT FROM AUTHOR]

In wireless networks, communication links may be subject to random fatal impacts: for example, sensor networks under sudden power losses or cognitive radio networks with unpredictable primary user spectrum occupancy. Under such circumstances, it is critical to quantify how fast and reliably the information can be collected over attacked links. For a single channel subject to random attacks, named as a dying channel, we model it as a block-fading (BF) channel with a finite and random channel length. For this channel, we first study the outage capacity and the outage probability when the data frame length is fixed and uniform power allocation is assumed. Furthermore, we discuss the optimization over the frame length and/or the power allocation over the constituting data blocks to minimize the outage probability. In addition, we extend the results from the single dying channel to the parallel multi-channel case where each sub-channel is a dying channel, and investigate the asymptotic behavior of the overall outage probability as the number of sub-channels goes to infinity with two different attack models: the independent-attack case and the m-dependent-attack case. It is shown that the asymptotic outage probability diminishes to zero for both cases as the number of sub-channels increases if the rate per unit cost is less than a certain threshold. The outage exponents are also studied to reveal how fast the outage probability improves with the number of sub-channels. [ABSTRACT FROM PUBLISHER]

In this paper exact closed-form expressions are derived for the outage probability (OP) in scenarios where the signal of interest (SoI) experiences η-μ or κ-μ fading, the interfering signals are subject to η-μ fading and the background noise can be neglected. With the only assumption that the μ parameter is a positive integer number for the interfering signals, the derived expressions when the SoI is either η-μ or κ-μ distributed are given in elementary terms for maximal ratio combining (MRC) with independent branches. If the pre-combining SoI power signals are η-μ distributed with their corresponding μ parameters being positive integer or half-integer numbers, the previous analysis is extended for spatially correlated MRC at the receiver. [ABSTRACT FROM PUBLISHER]

In this paper, a transmit antenna selection scheme, which is based on shadowing side information, is investigated. In this scheme, the selected single transmit antenna provides the highest shadowing coefficient between a transmitter and a receiver. By the proposed technique, the frequency of the usage of the feedback channel from the receiver to the transmitter and channel estimation complexity at the receiver can be reduced. We study the performance of our proposed technique, and in the analysis, we consider an independent but not identically distributed generalized-K composite fading model. More specifically, exact and closed-form expressions for the outage probability, the moment-generating function, the moments of signal-to-noise ratio, and the average symbol error probability (SEP) are derived. In addition, asymptotic outage probability and SP expressions are also presented to investigate the diversity order and the array gain. Finally, our theoretical performance results are validated by Monte Carlo simulations. [ABSTRACT FROM PUBLISHER]

In this paper, we demonstrate that the sampling property of a delta function can be used to quantify integration dynamically. The proposed approach reduces integration to a sampling. The sampling point is obtained in terms of a constant or fading parameter. We illustrate an example using Rayleigh fading channel. We investigate the dynamic behavior of the sampling error probability, relative error and sampling point error of the proposed integration. We extend the result to the general order rectangular QAM with Nakagami-n fading. The significance of the proposed method is that the dynamic integration can be used to find integrals with no available antiderivative. [ABSTRACT FROM PUBLISHER]

A new theoretical method, the generalized transformed characteristic function (GTCF) approach gives an exact, integral solution for the probability density function of the end-to-end received signal-to-noise ratio in multihop amplify-and-forward relaying systems. In turn, the GTCF approach is used to obtain exact integral solutions for the ergodic capacity, outage probability and average symbol error probability of multihop amplify-and-forward relaying systems. The results are precise for any number of hops and can accommodate any channel fading distribution. The theory provides the first exact theoretical solutions for numbers of hops larger than 2. [ABSTRACT FROM AUTHOR]

This paper studies the differentially amplitude- and phase-encoded quadrature amplitude modulation (DAPE QAM) transmission for the amplify-and-forward multiple-relay system using the fixed-relay-gain mechanism over independent Rician and Nakagami-m fading links. In the multiple-relay system, the destination collects signals from the source and multiple relays in distinct phases. Operating over two successively received symbols, an equal-gain combining (EGC) receiver and a weighted-gain combining (WGC) receiver are developed to noncoherently combine received signals from direct and multiple-relay links and thereby achieve cooperative diversity. The EGC receiver operates without any link-side information, whereas the knowledge of average signal-to-noise ratios (SNRs) on source–relay and relay–destination links is required for realizing the WGC receiver. Based on Beaulieu's convergent series approach, efficient computation formulas of the bit error probability (BEP) upper bounds are derived for both receivers. Numerical and simulation results on 16- and 64-point signal constellations show that the WGC receiver exhibits better BEP performance than the EGC receiver when link SNR estimates are not significantly large in error. The WGC receiver for DAPE QAM is also shown to outperform, in terms of BEP, the conventional receiver for differentially detecting the differential phase-shift keying modulation signal with the same constellation size. [ABSTRACT FROM PUBLISHER]

In opportunistic selection (OS)-based systems, outdated channel state information (CSI) is encountered due to channel variation between the instants of channel estimation and actual data transmission. This will result in unreliable CSIs employed in OS, which greatly degrades the system performance. To address this issue, a novel metric is proposed to evaluate the transmission quality of a channel suffering from Nakagami-m fading, taking both outdated CSI and fading statistics into consideration. Moreover, its suboptimized counterpart is also proposed to significantly reduce computational complexity. We then use this metric to select users (sources) in a multiuser scheduling model and evaluate its outage performance. Both analytical and simulation results show that our proposals outperform the existing alternatives in terms of outage probability. [ABSTRACT FROM PUBLISHER]

The performance of uplink cooperative code-division multiple-access (CDMA) systems using adaptive decode-and-forward (DF) relaying is investigated over Nakagami-m fading channels. A closed-form expression for the outage probability for a multirelay system with relay selection is derived. Our method is based on the moment-generating function (MGF) for the total signal-to-noise ratio (SNR) at the base station where the cumulative density function (cdf) is obtained. We also examine the asymptotic performance of the system at high SNR from which we evaluate the achievable diversity gain for different system parameters. Both simulations and analytical results are presented for performance evaluation. [ABSTRACT FROM PUBLISHER]

A novel analytical framework for evaluating the statistics of the product of independent random variables is proposed. Compared with other methods, which use either infinite series or special functions, the new method provides simple and efficient closed-form approximations, in terms of elementary functions, such as powers and exponentials. Numerical results, which are used to check the accuracy of the new approximations, show that it is quite accurate in most regions of interest. As an application, the proposed analytical results can be efficiently used in wireless communications theory to evaluate in closed form the outage probability of cascaded fading channels, as well as the rate offset of the hybrid automatic repeat request (H-ARQ) transmission. Numerical examples show that the derived expressions provide significant insights on the behaviors of important system parameters as the outage probability and the rate offset. [ABSTRACT FROM PUBLISHER]