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The Internet of Things (IoT) is a new para-digm for achieving ubiquitous connectivity by enormously deploying physical objects like sensors, actuators, and controllers. Wireless communication is one of the main enabling technologies that make the IoT a reality. However, due to the open nature of wireless communication and constraints on energy consumption, this raises concerns about the security of the IoT. Eavesdropping is a major threat to the wireless communications security. To counteract such an attack, physical layer security is among the promising solutions. The aim of this work is to evaluate the secrecy performance of two-hop wireless communication systems. This evaluation is done in the presence of potential eavesdropping threats over Nakagami-m and mixed Rayleigh–Nakagami-m fading channels. To enhance the security of the system, the use of cooperative jamming and opportunistic relaying has been considered. In particular, based on classical probability theory, we first analyze the secrecy outage performance for scenario 1, where all channels (S-R, R-D, R-R, S-E, R-E) experience Nakagami-m fading. Then, we examine the secrecy performance for scenario 2, where the channel coefficients for links (S-R, R-D, S-E, R-E) are subject to Nakagami-m fading and the channel coefficients for the link (R-R) follow Rayleigh fading. Finally, simulation and numerical results are presented to validate our theoretical achievements. The results suggest that as the fading parameter m increases, the probability of secrecy outages decreases, leading to an improvement in the security performance of the wireless IoT data collection process. [ABSTRACT FROM AUTHOR]

Summary: In this paper, we have presented the outage probability analysis of multiple intelligent reflecting surface (IRS)‐assisted single‐input‐single‐output (SISO) system with switched diversity schemes. The switched diversity is simpler than the selection combining diversity technique, which can help in reducing the channel estimation overhead. There are two main types of switch diversity schemes, namely, switch and stay combining (SSC) and switch and examine combining (SEC). We consider a SISO wireless scenario in which a single transmitting antenna is sending its message to the receiving antenna with the aid of multiple IRS panels. This communication scenario will arise as a typical application of uplink scenario for future 6G wireless systems. The outage probability (OP) expressions for dual‐IRS‐panel‐aided SSC system and multiple‐IRS‐panel‐aided SEC system are analyzed, respectively, over Rician fading channels. We derive tight approximate OP expressions in closed form for a large number of IRS elements. Further, we derive a simple asymptotic OP for studying diversity order and coding gain. The OP performance with respect to each system parameter is thoroughly explored. Several numerical OP results are presented with corresponding simulated OP results to validate the accuracy of the presented analytical analysis. [ABSTRACT FROM AUTHOR]

This paper proposes an overlay network wherein a pair of licensed source (LS) and licensed destination (LD) is adaptively assisted by a pair of unlicensed source (US) and unlicensed destination (UD). By processing adaptively at US and UD relied on the decoding statuses of LD and US, licensed communication is always supported with a high diversity gain from which unlicensed communication also benefits from removing licensed interference as well as transmitting with the highest available power, eventually improving reliability of both unlicensed and licensed communication. This paper also proposes closed-form formulas of outage probabilities at LD and UD for prompt reliability evaluation over κ - μ shadowed fading channels. Multiple results illustrate the superiority of the proposed adaptive processing scheme as compared to its counterpart. Further, the reliability of the suggested scheme can be flexibly controlled and optimized with setting specifications reasonably. [ABSTRACT FROM AUTHOR]

The IEEE 802.11ah standard, marketed as Wi-Fi Halow, introduces a new channel access mechanism called the Restricted Access Window (RAW), aiming to provide connectivity for the Internet of Things (IoT) applications over broad areas. RAW aspires to alleviate the contention by splitting the channel access into periods and allocating each period to a given group of stations. This paper develops an analytical framework based on Probability and Renewal theories for modeling and evaluating an IEEE 802.11ah-based network implementing the RAW mechanism. We consider a Rayleigh-fading channel with the presence of the capture effect: a realistic scenario for IoT networks deployed in dense urban environments. Considering a single-hop scenario of stations randomly distributed around an Access Point (AP) and the power attenuation of transmitted packets, we model the channel access under capture awareness. As the RAW mechanism presents a time-limited contention for channel access, we develop a counting process that tracks transmissions up to the end of the contention time interval. Henceforth, we evaluate the network performance in terms of throughput. We meticulously validate the derived analytical results through extensive campaigns of discrete-event simulations. Our study evaluates the impact of different parameters on the overall performance, including the contention time, the number of stations, the number of groups, and the capture threshold. We henceforth study the impact of the capture effect on enhancing the network performance under the grouping feature introduced by the RAW mechanism. This work contributes to developing an analytical modeling framework to evaluate the performance of time-limited random access mechanisms accurately and can be an excellent basis for proposing practical scheduling algorithms to configure the RAW mechanism under non-ideal channel conditions. [ABSTRACT FROM AUTHOR]

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]

As one of key technologies of future networks, vehicle-to-everything (V2X) communication has recently been proposed to improve conventional vehicle systems in terms of traffic and communications. Main benefits of using V2X are efficient and safe traffic as well as low-latency communications and reliable massive connections. Non-orthogonal multiple access (NOMA) scheme was introduced as a promising solution in the fifth-generation (5G) mobile communications, by which quality-of-service (QoS) requirements of many 5G-enabled applications are satisfied as a result of improved network throughput and lower accessing and transmission latency. In this paper, we study NOMA-based communications between vehicles equipped with multiple antennas over Nakagami-m fading channels in V2X networks, in which uplink and downlink transmission between two vehicles with upper controller are supported by a road side unit (RSU) to increase the capacity rather than simply be connected to the base station. In the NOMA-V2X system under study, the outage probability depends on the power allocation factor of RSU transmission and the operation of successive interference cancellation (SIC) at vehicles. Analyses and simulations verify that the outage performance of NOMA-V2X system are mainly affected by fading parameters, levels of imperfect SIC, and power allocation factors. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) is a major candidate technology for the future radio networks due to its potential to have high spectral efficiency and to support massive connections. It is also an important advantage for the NOMA to be very compatible with the other physical layer techniques. The relay-aided-NOMA which consists of the interplay between cooperative communication and NOMA, offers very large coverage area besides the high spectral efficiency and the massive connectivity. Hence, the relay-aided-NOMA has great recent attention. Most of these studies are devoted to reveal outage probability and the overall system capacity performances of the systems. However, the bit error performances have been ignored. In this paper, theoretical end-to-end (E2E) average bit error probability (ABEP) expressions are derived for the relay-aided-NOMA using a relay with the decode-forward (DF) protocol. The derived expressions are validated through Monte Carlo simulations. The E2E error performance of the system are examined for different system parameters. Moreover, by considering user fairness in terms of error performance, it is discussed how the optimum power allocation should be done. And finally, a sub-optimum power allocation algorithm is presented according to the proportional fairness index. [ABSTRACT FROM AUTHOR]

As the core technology of 5G communication, D2D plays a vital role in meeting user communication needs and increasing the number of users connected. In view of the high system outage probability of traditional reuse algorithm and the large consumption of user resources, this paper proposed a D2D resource allocation algorithm based on exhaustive search method. The algorithm used the exhaustive search method to preliminarily determine the user's transmission power, at the same time, it referenced cellular and D2D user's status to determine the reuse combination. It applied the power adjustment step to reduce the outage probability. The simulation results show that the D2D resource allocation algorithm based on the exhaustive search method compares to the traditional algorithm when the number of cellular users is small, the connectivity probability average increases 15. 7 % in the case of more D2D users, and the user 's energy consumption average decreases 10. 5 %. [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]

Abstract The present work covers the wide range of distributions and proposes the moment generating function (MGF) based analytical framework to derive the average symbol error probability (SEP), the average probability of detection (PD), and the average area under the receiver operating characteristic curve (AUC) for the wireless system with maximal ratio combining (MRC) diversity. The proposed solutions are expressed in terms of Fox's H and bivariate Fox's H-functions which are widely being used in the current literature. Finally, the analytical framework, thus proposed has been used in applications, such as ultra-wideband (UWB) single-input-single-output (SISO) and multiple-input-multiple-output (MIMO) system and the impact of the number of transmitting and receiving antennas for MIMO system over the average SEP has been analysed. The correctness of the proposed solutions has been corroborated by comparing them with Monte-Carlo simulation. [ABSTRACT FROM AUTHOR]

In order to solve the security problem for fading channel, a pragmatic physical layer encryption (PLE) scheme is proposed, which utilises diversity technique elaborately. Different from the conventional PLE schemes based on phase rotation for the modulated symbol, the proposed scheme changed phase and amplitude together for a block of symbols each time, which can be defined as multi-dimensional PLE (MPLE). Unconventional constellation obfuscates eavesdropper, which can be seen as the first level security in the physical layer. The correct probability based on chosen plaintext attacks and known plaintext attacks is deduced. It can be seen from the simulation results that the MPLE scheme can achieve lower attack success probability because of multi-level security and better performance based on diversity under fading channel. [ABSTRACT FROM AUTHOR]

In this article, mixture gamma (MG) distribution is used for analysing the performance of L-Hoyt/lognormal composite fading channel. To overcome small-scale fading effect, micro-diversity using maximum ratio combining (MRC) is used at the receiver. Due to mathematical complexity, performance analysis of composite (L-Hoyt/lognormal) fading models is not present in closed form. The analytical expressions for the performance measure are derived in the form of received signal-to-noise ratio (SNR). The impact of system parameters on the energy detector (ED) performance is studied in terms of receiver operating characteristic (ROC) and area under the ROC curve (AUC). Further, the detection threshold parameter is optimised by minimising the total probability of error for L-Hoyt/lognormal channel. The accuracy of the proposed closed-form expressions is validated by comparing all the results with the Monte-Carlo/exact simulations. [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]

Several power allocation algorithms for cooperative relay networks are presented in the literature. These contributions assume perfect channel knowledge and capacity achieving codes. However in practice, obtaining the channel state information at a relay or at the destination is an estimation problem and can generally not be error free. The investigation of the power allocation mechanism in a wireless network due to channel imperfections is important because it can severely degrade its performance regarding throughput and bit error rate. In this paper, the impact of imperfect channel state information on the power allocation of an adaptive relay network is investigated. Moreover, a framework including Automatic Repeat reQuest (ARQ) mechanism is provided to make the power allocation mechanism robust against these channel imperfections. For this framework, the end-to-end SNR is calculated considering imperfect channel knowledge using ARQ analytically. The goal is to emphasize the impact of imperfect channel knowledge on the power allocation mechanism. In this paper, the simulation results illustrate the impact of channel uncertainties on the average outage probability, throughput, and consumed sum power for different qualities of channel estimation. It is shown that the presented framework with ARQ is extremely robust against the channel imperfections. [ABSTRACT FROM AUTHOR]

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]

The real-world wireless channels are accurately modeled by the composite multipath fading and shadowing channel models. The performance of a typical cognitive spectrum sharing (SS) network under a composite fading and shadowing model is rarely analyzed, and hence, needs considerable attention. In this paper, a cognitive SS network is considered having multiantenna at the secondary/cognitive receiver (SR), and the signals received at different antennas are combined using maximal ratio combining scheme. The channels at SR are considered to be spatially correlated κ - μ shadowed distributed. The analytical expressions for the outage probability and the ergodic capacity are derived under peak interference power constraint (PIPC) of the primary receiver (PR). It is shown that the performance of the SS network degrades as the spatial correlation increases at SR. It is also observed that the severity of fading/shadowing at the interfering link is favorable to the secondary user’s communication up to a certain value of PIPC of PR. [ABSTRACT FROM AUTHOR]

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]

In this paper, we investigate the impact of hardware impairments on the outage performance and the instantaneous capacity of dual-hop decode-and-forward (DF) satellite relay networks in the presence of co-channel interference. Specifically, the exact closed-form expression for the outage probability and the analytical expression for the instantaneous capacity of the system are derived over a shadowed-Rician fading channel, which provides a fast means to evaluate the impact of hardware impairments on the system performance. Our results demonstrate that the outage floor occurs and the capacity upper bound appears when the hardware impairments exist. In addition, simulation results were provided to verify the correctness of the analytical results. [ABSTRACT FROM AUTHOR]

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]

We investigate outage performance of fixed-gain and variable-gain amplify-and-forward (AF) full-duplex (FD) relaying systems under residual loop-interference (LI) in non-identical Nakagami- m fading channels. New exact outage probability expressions are derived analytically in a single-integral form by using the cumulative distribution function approach. Moreover, tight lower-bound and asymptotic outage probability expressions are derived in closed-form for the evaluated systems. It is shown that the fixed-gain AF-FD relaying outperforms the variable-gain AF-FD relaying when LI power and/or signal-to-noise ratio increase. The analytical results are verified by Monte-Carlo simulations. [ABSTRACT FROM AUTHOR]

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 outage probability of an arbitrary branch equal gain combining (EGC) receiver with carrier phase error in the presence of co-channel interference in composite generalized gamma (GG) and composite generalized K (KG) fading environment is derived. Mathematical expressions for the outage probability of the EGC receiver for these fading channels have been obtained. The obtained expressions for the outage probability are numerically evaluated. Numerical results for different degrees of phase errors is plotted with the simulation results. Simulation results closely match with the numerical results. [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, the end-to-end performance of decode and forward relaying over an independent, asymmetrical and generalized fading channels are analyzed. We consider a dual hop mixed fading channel, one hop is subject to η - μ fading and the other hop is subject to κ - μ fading. We derived an exact expression of symbol error rate (SER) for non-coherent detection, outage probability, outage capacity and an approximate expression of SER for coherent detection. In addition, we compared the SER performance over different η , μ 1 , κ , μ 2 which corresponds to different fading effects and validated the arrived expressions through Monte-Carlo simulation. [ABSTRACT FROM AUTHOR]

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]

In Rician-fading scenario, cognitive radio networks (CRNs) with a source in a secondary system transmitting its confidential information to a legitimate destination in the presence of an eavesdropper, are considered in this paper. Under CRNs, the interference power reaching at primary user (PU) is limited by some pre-defined threshold. Secrecy outage not only occurs when the achievable secrecy capacity for source-destination link is smaller than a target rate, but also occurs in the case that the interference power at PU is greater than that threshold. Analytical expression for secrecy outage probability has been derived and verified with simulation results. In addition, we have also derived the analytical expression for probability of non-zero secrecy capacity. [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 investigate the detection performance of cooperative spectrum sensing (CSS) using energy detector in several fading scenarios. The fading environments comprise relatively less-studied Hoyt and Weibull channels in addition to the conventional Rayleigh, Rician, Nakagami-mand log-normal shadowing channels. We have presented an analytical framework for evaluating different probabilities related to spectrum sensing, i.e. missed detection, false alarm and total error due to both of them, for all the fading/shadowing models mentioned. The major theoretical contribution is, however, the derivation of closed-form expressions for probability of detection. Based on our developed framework, we present performance results of CSS under various hard decision fusion strategies such as OR rule, AND rule and Majority rule. Effects of sensing channel signal-to-noise ratio, detection threshold, fusion rules, number of cooperating cognitive radios (CRs) and fading/shadowing parameters on the sensing performance have been illustrated. The performance improvement achieved with CSS over a single CR-based sensing is depicted in terms of total error probability. Further, an optimal threshold that minimises total error probability has been indicated for all the fading/shadowing channels. [ABSTRACT FROM PUBLISHER]

The work focuses on the max link selection (MLS) schemes of buffer-aided relaying over the independent and non-identically distributed (i.ni.d) Nakagami- m fading channels in terms of outage probability, average packet delay, and improved diversity-delay trade-off schemes. By modeling the transition of buffer states as a Markov chain, we first obtain the outage probability and average packet delays for MLS schemes, which are given with closed-form expressions. The achieved results show that the i.ni.d fading channels impose severe loss in the diversity and coding gains of MLS schemes. Especially, when the disparity among the channel powers is very large, the diversity order provided by the MLS schemes is less than the ones provided by the traditional best relay selection (T-BRS) and max-max link selection (MMLS) schemes even if the buffers' size is large enough. For the average packet delay of MLS schemes, our results show that they are impacted by the transmit power and the fading severity factors. In general, in the low transmit power, the average packet delays are varying with the transmit power. However, in the high transmit power, the average packet delays approach the stationary values. Besides of this, it is also achieved that the i.ni.d fading makes the average packet delays of MLS schemes at all relays are different. When the powers of relay-destination links are greater than the ones of source-relay links, the average packet delays can be reduced evidently. Motivated by the observations, a weight-based MLS (W-MLS) diversity-delay trade-off scheme is proposed. The proposed W-MLS diversity-delay trade-off schemes not only have the low packet delays at all relays but also provide enough diversity and coding gains over T-BRS and MMML, which can overcome the performance loss caused by non-identical distribution on MLS schemes. [ABSTRACT FROM AUTHOR]

This paper proposes exact and limit outage probability expressions for thoroughly evaluating the performance of cooperative cognitive networks with opportunistic relay selection under imperfect channel information, independent and non-identical (i.n.i.) Rayleigh fading channels, maximum transmit power constraint, and interference power constraint. The proposed derivations can be straightforwardly extended to corresponding analysis in dual-hop cognitive networks with opportunistic relay selection to investigate how much performance gain can be achieved from using the direct channel between the source and the destination in relaying communications. Numerous results illustrate significant outage performance degradation and performance saturation due to channel information imperfection but the degradation and saturation level can be remedied by increasing the number of relays. Also, the channel direct brings a considerable performance improvement without any additional expense of system resources such as power and bandwidth. Moreover, channel information imperfection can cause interference power at primary users to exceed a pre-defined level, deteriorating the quality of service of primary users. [ABSTRACT FROM AUTHOR]

In this paper, we consider the effect of interference on the coverage and connectivity of an ad hoc network that operates in the presence of fading and shadowing. We assume that the number of interfering signals at each receiving node of a wireless network is a random variable that belongs to a Matern Hard-core point process (MPP). The aggregate interference at the receiver is approximated using the shifted Gamma distribution. We derive closed-form expressions for node isolation probability using a moment matching method. This performance measure is useful for evaluating the overall network connectivity in a wireless channel with co-channel interference and noise. The analysis does not assume knowledge of the fading distribution for the desired or interfering signals. The analytical results are verified with computer simulations. [ABSTRACT FROM AUTHOR]

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]

A wireless system consisting of a finite number of heterogeneous users transmitting packets over a slotted ALOHA Rayleigh-fading channel is investigated in this paper. In this system, each user tries to minimize its number of transmission attempts while meeting the throughput demand. The user interaction in such an ALOHA network is modeled as a random access game. A novel technique to better exploit the channel state information (CSI) named adaptive CSI transmission method is proposed. Benchmarking with the no-CSI method and threshold-based CSI method, it is revealed that the proposed adaptive CSI method can yield up to 9.9% more throughput and 12.3% power reduction. Two simple yet effective guidelines on selecting among these CSI-related methods are formulated for systems with different SNRs and capture ratios. A distributed algorithm is proposed to find the optimal transmission probability. Both analytical and simulation results show that the algorithm exhibits fast convergence speed and is robustness against changes on the number of active nodes in the network. [ABSTRACT FROM AUTHOR]

In this paper the broadcast relay channel, where the source communicates with multiple destinations with the help of a single relay is studied. Five different transmission protocols, direct transmission, multihop (MH), multihop with link combination (MHLC), path selection (PS) and path selection with link combination (PSLC) are investigated. In MH and MHLC, the relay decodes the source message and assists both destinations. In PS and PSLC, the relay can perform partial decoding and has the option to help only one of the destinations. Under long-term power constraint, power allocation for delay-limited transmission is performed to minimize common outage probability and individual outage probability region. For comparison, lower bounds on both common and individual outage probabilities are found. Numerical results suggest that path selection significantly lowers outage probabilities, while enforcing the relay to help both destinations simultaneously is limiting the system performance. [ABSTRACT FROM AUTHOR]