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This paper reports throughput maximization over various fading channels for cluster-based cooperative spectrum sensing in cognitive radio. For that purpose, the secondary users are grouped into clusters and effect of different fusion rules on throughput over Nakagami, Weibull, Rayleigh and Rician fading channels is investigated. Inside each cluster, i.e., for intra fusion, OR ( m = 1 ) and AND ( m = K ) fusion rules are considered. Further, a formula is proposed for optimal number of clusters which maximize throughput over fading channels. This expression is derived for two different inter-cluster fusion rules (fusion rule between cluster head and fusion centre) given as OR ( p = 1 ) and AND ( p = N ). Simulation results are carried out for OR-AND ( m = 1 , p = N ) and AND-OR ( m = K , p = 1 ) fusion rules for given cluster size (number of users inside a cluster), and number of clusters are optimized over Weibull and Nakagami fading channels. The proposed expressions for the optimal number of clusters are validated by the results. It is found that for given fixed parameters, the number of clusters at which throughput is maximum are N = 6 and N = 5 over Nakagami and Weibull fading channels respectively for AND-OR fusion rule. In case of OR-AND fusion rule, maximum throughput is achieved for N = 5 and N = 6 over Nakagami and Weibull fading channels respectively. [ABSTRACT FROM AUTHOR]

In cooperative spectrum sensing (CSS), in order to maximise the energy efficiency (EE) of cognitive radio (CR) users, users are divided into clusters. In this paper, the optimal inter-fusion rule threshold formula for different number of clusters and users is proposed for maximum EE in cluster-based CSS (CB-CSS). Different fusion rules are investigated for this purpose over Nakagami and Rician fading channel conditions. Simulations are conducted for different number of clusters and users using AND and OR intra-fusion rules and inter-fusion rule threshold is optimised in CB-CSS over the Nakagami-m fading channel and the Rician fading channel. The obtained mathematical expression for the inter-fusion rule threshold is verified by the results. It is investigated that when number of clusters are P = 4 and number of users in a cluster are K = 6 , OR-AND ( n = 1 , r = P) fusion rule achieves 2.46% more EE than AND-OR ( n = K , r = 1) fusion rule in case of Nakagami fading channel and 5.06% more EE than AND-OR fusion rule in case of Rician fading channel. Further, EE with respect to number of users is compared between additive white gaussian noise (AWGN) channel and Nakagami and Rician fading channels. [ABSTRACT FROM AUTHOR]

This paper presents the secrecy outage probability of relay and user (RU) selection in the antenna selection (AS)-amplify and forward (AF) system over integer-valued m Nakagami fading channels for the physical layer security. This work derives the lower bound (LB) and asymptotic cumulative density functions (CDFs) of the signal to noise ratio (SNR) for the RU selection in the AS-AF system. This study also considers the impact of the two types of receivers, i.e., maximal ratio combining (MRC), selection combining (SC) for the authorized system and eavesdropper. Using the lower bound CDFs, the LB expressions of the secrecy outage probability are derived for various scenarios. Applying the asymptotic CDFs, the diversity order of the secrecy performance is also quantified for each case. From analysis results, we show that the diversity order of the secrecy outage probability in the proposed system is only affected by authorized system's parameters, not by eavesdropper's parameters. Further, the relay and user nodes with the MRC receiver provide the SNR gain compared to the SC receiver regardless of eavesdropper's receiver type. Finally, the secrecy outage probability of the proposed RU system with the SC eavesdropper has the SNR gain compared to the MRC eavesdropper, while the diversity order is identical to each other. [ABSTRACT FROM AUTHOR]

In this paper, we propose an asymmetric adaptive modulation scheme for a heterogeneous two-way relay network (TWRN). In this scheme, due to the heterogeneity of the TWRN, different modulation schemes with different bit rates are assigned to the source nodes. Due to the mismatch between the bit rates of the two opposite traffic flows, the conventional XOR-based network coding is not applicable to this scheme. To cope with this heterogeneity at the relay node, we propose a network coding scheme in which the two data streams are combined at the level of symbol. We optimize the pair of modulation schemes and bit rates such that the instantaneous transmission rate is maximized under the constraint that a quality-of-service requirement in terms of the end-to-end BER is satisfied. To find the solution of this multi-dimensional problem, we propose a simple procedure with very low computational complexity by reducing the problem dimension to one. We analyze the system performance in terms of the average end-to-end BER, the average transmission rate, and the outage probability over Nakagami fading channel. Our analysis shows that this scheme not only achieves high spectral efficiency but also mitigates error propagation from the relay to the transceivers. [ABSTRACT FROM AUTHOR]

In this paper, we consider a radio-frequency identification (RFID) backscatter system with two scenarios: single input multiple output (SIMO) and multiple input single output (MISO). We investigate the impact of channel correlation between the forward and backscatter links on the symbol error rate (SER), and we compare the performance of SIMO and MISO RFID systems with maximum ratio combining reception over arbitrarily correlated Nakagami- $m$ fading channels. In order to gain an insight for the system design, closed-form expressions for the asymptotic SER and an upper bound are derived for $M$ -ary phase-shift keying and quadrature amplitude modulation. The diversity order in the fully correlated cases, revealed from these expressions, is half of that in the partially correlated and uncorrelated cases. Finally, simulations are performed to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) is currently considered as a promising technology for the next-generation wireless networks. In this paper, the error rate performance of NOMA systems is investigated over Nakagami- $m$ fading channels, while considering imperfect successive interference cancelation. In particular, this paper focuses on the pairwise error probability (PEP) analysis, where exact PEP expressions are derived to characterize the performance of all users under different fading conditions. The obtained PEP expressions are then used to derive an exact union bound on the bit error rate (BER). Through the derived PEP expressions, the asymptotic PEP analysis is presented to investigate the maximum achievable diversity gain of NOMA users. Moreover, using the derived BER bound, the power allocation problem for all users in NOMA systems is considered under average power and users BER constraints, which allows realizing the full potential of NOMA. Monte Carlo simulation and numerical results are presented to corroborate the derived analytical expressions and give valuable insights into the error rate performance of each user and the achievable diversity gain. [ABSTRACT FROM AUTHOR]

Link adaptation (LA) schemes maximize average spectral efficiency (ASE) using accurate channel state information (CSI) and knowledge of signal to noise ratio (SNR) distribution. In practical systems, partial CSI is available at the transmitter through feedback of modulation and coding scheme index, often known as channel quality indicator (CQI). However, parameters of SNR distribution (${\Theta }$) are not known or only assumed to be known. We propose two LA schemes, for execution at the receiver and transmitter, respectively, each without prior knowledge about ${\Theta }$. In the receiver centric schemes, parametric estimation of SNR distribution is performed using unquantized SNR samples. In the transmitter centric scheme, we estimate ${\Theta }$ from CQI samples using an iterative joint quantization-estimation algorithm. These parametric estimates form long-term SNR distribution, which is used to compute SNR switching thresholds. Using these thresholds, rate and power adaptation decisions are made based on instantaneous SNR. We have derived the maximum-likelihood estimator and Cramer–Rao lower bound for the proposed estimator using CQI feedback for Nakagami- $m$ fading channels and demonstrate that near optimal ASE can be achieved while using the proposed schemes as in an ideal scenario, where perfect knowledge about CSI and SNR distribution are available a priori. [ABSTRACT FROM AUTHOR]

We propose a power-and rate-adaptation scheme for cloud radio access networks (C-RANs), where each radio remote head (RRH) is connected to the baseband unit pool through optical links. The RRHs jointly support the users by efficiently exploiting the enhanced spatial degrees of freedom. Our proposed scheme aims at maximizing the effective capacity (EC) of the user subject to both per-RRH average- and peak-power constraints, where the EC is defined as the maximum arrival rate that can be supported by the C-RAN under the statistical delay requirement. We first transform the EC maximization problem into an equivalent convex optimization problem. By using the Lagrange dual decomposition method and solving the Karush–Kuhn–Tucker equations, the optimal transmission power of each RRH can be obtained in the closed form. Furthermore, an online tracking method is provided for approximating the average power of each RRH. For the special case of two RRHs, the expression of the average power of each RRH can be calculated in the explicit form. Hence, the Lagrange dual variables can be computed in advance in this special case. Furthermore, we derive the power allocation for two important extreme cases: first, no delay constraint and, second, extremely stringent delay requirements. Our simulation results show that the proposed scheme significantly outperforms the conventional algorithm without considering the delay requirements. Furthermore, when appropriately tuning the value of the delay exponent, our proposed algorithm is capable of guaranteeing a delay outage probability below $10^{-9}$ when the maximum tolerable delay is 1 ms. This is suitable for the future ultra-reliable low-latency communications. [ABSTRACT FROM AUTHOR]

Using a well-known wire-tap model, novel wireless secrecy analyses under dual correlated Nakagami- $m$ fading with a real fading parameter $m$ are reported. Infinite summations for incomplete gamma functions are employed to derive compact expressions for secrecy capacity and secrecy outage probability (SOP) under noninteger $m$. Independently, using finite summations, corresponding closed-form findings for integer $m$ are also derived. In the current literature, finite summations for the incomplete gamma functions, whose first arguments and hence $m$ must be an integer, are employed to obtain closed-form expressions for, first, the SOP (with an unknown passive wire-tapper's channel state information), and second, ergodic secrecy capacity (with partially known active wire-tapper's channel state information under slow fading). The new secrecy results for noninteger $m$ generalize the proposed findings for integer $m$ , and existing findings under dual correlated Rayleigh fading for $m=1$. The new findings can thus be comprehensively employed for wireless secrecy computation under dual correlated Nakagami- $m$ fading for real $m$. Infinite-summation convergence and cross verification are also obtained for a finite number of terms, which shows the practicality and consistency of the new findings. For the first time, secrecy analyses employing an adaptive encoder with on/off transmission are performed under dual correlated Nakagami- $m$ fading for real $m$ to not only improve wireless secrecy, but also achieve the eventual successful transmission from a source to a destination. The new SOP results for real $m$ can be employed as lower bounds and complete theoretical secrecy analyses, for SOP under dual correlated Nakagami- $m$ fading with integer $m$. Simulation results are employed to show matching between the proposed findings and existing findings. [ABSTRACT FROM AUTHOR]

For buffer-aided tandem networks consisting of relay nodes and multiple channels per hop, we consider two traffic allocation schemes, namely local allocation and global allocation, and investigate the end-to-end latency of a file transfer. We formulate the problem for generic multi-hop queuing systems and subsequently derive closed-form expressions of the end-to-end latency. We quantify the advantages of the global allocation scheme relative to its local allocation counterpart, and we conduct an asymptotic analysis on the performance gain when the number of channels in each hops increases to infinity. The traffic allocations and the analytical delay performance are validated through simulations. Furthermore, taking a specific two-hop network with millimeter-wave (mm-wave) as an example, we derive lower bounds on the average end-to-end latency, where Nakagami- $m$ fading is considered. Numerical results demonstrate that, compared with the local allocation scheme, the advantage of global allocation grows as the number of relay nodes increases, at the expense of higher complexity that linearly increases with the number of relay nodes. It is also demonstrated that a proper deployment of relay nodes in a linear mm-wave network plays an important role in reducing the average end-to-end latency, and the average latency decays as the mm-wave channels become more deterministic. These findings provide insights for designing multi-hop mm-wave networks with low end-to-end latency. [ABSTRACT FROM AUTHOR]

In this paper, we provide a global framework analysis of a dual-hop mixed radio frequency (RF)/free space optical (FSO) system with multiple branches/relays wherein the first and second hops, respectively, consist of RF and FSO channels. To cover various cases of fading, we propose generalized channels’ models for RF and FSO links that follow the Nakagami-m and the double generalized gamma distributions, respectively. Moreover, we suggest channel state information (CSI)-assisted relaying or variable relaying gain based amplifiy-and-forward amplification. Partial relay selection with outdated CSI is assumed as a relay selection protocol based on the knowledge of the RF CSI. In order to derive the end-to-end signal-to-interference-plus-noise ratio statistics, such as the cumulative distribution function, the probability density function, the higher order moments, the amount of fading and the moment generating function, the numerical values of the fading severity parameters are only valid for integer values. Based on these statistics, we derive closed-forms of the outage probability, the bit error probability, the ergodic capacity, and the outage capacity in terms of Meijer-G, univariate, bivariate, and trivariate Fox-H functions. Capitalizing on these expressions, we derive the asymptotic high SNR to unpack valuable engineering insights of the system performance. Monte Carlo simulation is used to confirm the analytical expressions. [ABSTRACT FROM AUTHOR]

In this Letter, performance of multiple users in downlink of non-orthogonal multiple access (NOMA) network considering the general α − κ − μ shadowed fading model which was proposed in recent years is studied. In particular, main metrics including the outage probability, ergodic rate related to ordered channels are derived in novel and exact expressions for arbitrary values of the fading parameters. Moreover, numerical simulations are carried out in order to exhibit further insights on how the system performance is affected by the fading parameters. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the ergodic capacity (EC) of a downlink multiuser hybrid satellite-terrestrial amplify-and-forward relay network (HSTAFRN) using a fixed-gain relaying protocol in the presence of co-channel interference. Herein, we employ opportunistic scheduling of terrestrial users by considering outdated channel state information over Nakagami-m fading channels of pertinent links. By deploying multiple antennas at the satellite, we derive a novel and accurate analytical expression of the achievable EC by making use of the complementary moment generating function transform. More importantly, we carry out the EC analysis under both uncorrelated and correlated shadowed-Rician fading channels of satellite links. Our numerical and simulation results attest the accuracy of the proposed analysis and reveal the impact of various system/channel parameters on EC of the considered HSTAFRN. [ABSTRACT FROM PUBLISHER]

We here introduce an extension and natural generalization of both the $\kappa$-$\mu$ shadowed and the classical Beckmann fading models: the Fluctuating Beckmann (FB) fading model. This new model considers the clustering of multipath waves on which the line-of-sight (LoS) components randomly fluctuate, together with the effect of in-phase/quadrature power imbalance in the LoS and non-LoS components. Thus, it unifies a variety of important fading distributions as the one-sided Gaussian, Rayleigh, Nakagami- $m$, Rician, $\kappa$ -$\mu$, $\eta$- $\mu$, $\eta$ -$\kappa$, Beckmann, Rician shadowed, and the $\kappa$- $\mu$ shadowed distribution. The chief probability functions of the FB fading model, namely probability density function, cumulative distribution function, and moment generating function are derived. The second-order statistics such as the level crossing rate and the average fade duration are also analyzed. These results can be used to derive some performance metrics of interest of wireless communication systems operating over FB fading channels [ABSTRACT FROM PUBLISHER]

In this paper, we study a cooperative vehicle-to-vehicle (V2V) interference-limited communication system with decode-and-forward relaying operating over double-Nakagami (DN) fading channels. This distribution has been proposed as a fading model for scenarios where both the transmitter and the receiver are in motion, as is the case in V2V communications. For the purposes of our analysis, we introduce the bivariate DN distribution and derive statistical metrics for this distribution, such as the probability density function, the cumulative distribution function, and the moments. The new expressions have been employed to model the outdated channel state information (CSI) that is due to the fast time-varying nature of the wireless medium and the delay naturally existing between relay selection and data transmission instances. The analysis considers two relay selection schemes, according to the relay-destination channel quality, namely the well-known best relay selection (BRS) and a new one termed as threshold-based relay selection, which offers lower complexity than BRS. Using our analytical framework, exact and asymptotic performance results are obtained for the outage and the average symbol error probabilities, while the diversity order has been also evaluated. The numerical and simulation results corroborate our theoretical ones and quantify the impact of the outdated CSI, level of interference, and varying distances between the relay nodes and the final destination on the system's performance. [ABSTRACT FROM PUBLISHER]

The Nakagami-m distribution plays an important role in problems related to communication engineering. This distribution can also be used for modeling reliability data as its hazard rate (mean residual life) function presents increasing (decreasing) or bathtub (unimodal) shapes. In this study, a Bayesian inference considering objective priors for the Nakagami-m distribution parameters is presented. We propose a theorem with sufficient and necessary conditions so that a general class of posteriors are proper. The impropriety of these posteriors can be observed by the behavior of the objective priors. This theorem is applied to different objective priors such as Jeffreys’ rule, Jeffreys prior, maximal data information prior, and reference priors. Simulation studies were conducted to investigate the performance of the Bayes estimators. Finally, our methodology is illustrated using two real lifetime datasets showing that the Nakagami-m distribution can be used to describe lifetime data. [ABSTRACT FROM PUBLISHER]

In this paper we present a bivariate Rician shadowed fading model where the shadowing is assumed to follow a Nakagami-$m$ distribution. We derive exact expressions involving a single integral for both the joint probability density function (PDF) and the joint cumulative distribution function and we also derive an exact closed-form expression for the moment generating function. As a direct consequence we obtain a closed-form expression for the power correlation coefficient between Rician shadowed variables as a function of the correlation coefficient between the underlying variables of the model. Additionally, in the particular case of integer $m$ we show that the PDF can be expressed in closed form in terms of a sum of $m$ Meijer G-functions of two variables. Results are applied to analyze the outage probability of a dual-branch selection combiner in correlated Rician shadowed fading and the evaluation of the level crossing rate and average fade duration of a sampled Rician shadowed fading envelope. [ABSTRACT FROM PUBLISHER]

We investigate the system performance of a nonorthogonal multiple access (NOMA) based downlink amplify-and-forward relay network over Nakagami-$m$ fading channels with imperfect channel state information, where the base station and all users are provided with multiple antennas, while the relay is equipped with a single antenna. Two special conditions of interest (e.g., Nakagami-1, i.e., Rayleigh and Nakagami-2) are analyzed, and closed-form expression for the system outage probability is derived. Moreover, tight lower and upper bounds of the outage probability, and the outage probability in the high signal-to-interference-and-noise ratio regime, i.e., in the presence of error floor, which exists due to the channel estimation errors, are obtained. Finally, computer simulations are conducted to verify the accuracy of the numerical analysis and to confirm the superiority of the antenna selection and NOMA scheme. [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]

Small cells deployment is one of the most significant long-term strategic policies of the mobile network operators. In heterogeneous networks (HetNets), small cells serve as offloading spots in the radio access network to offload macro users (MUs) and their associated traffic from congested macrocells. In this paper, we perform analytical analysis and investigate how the radio channel propagation impairments such as multipath fading, shadowing, and small cell base station density affect MUs’ offloading to small cells network (SCN). In particular, we exploit composite fading channels in our evaluation when an MU is offloaded to SCN with varying small cell base station density in the stochastic geometry HetNets framework. We derive the expressions for service outage probability (equivalently service coverage probability) of the MU in macro cell network and SCN under two different composite fading scenarios, viz., Nakagami-Lognormal channel fading and time-shared (combined) shadowed/unshadowed channel fading. We propose efficient approximations for the probability density functions of the channel fading (power) for the aforementioned composite fading distributions that do not have closed-form expressions employing Gauss–Hermite integration and finite exponential series, respectively. Finally, the service outage probability performance of MU with and without offloading services is analyzed under various system parameters and channel fading conditions. [ABSTRACT FROM PUBLISHER]

This paper investigates and optimizes the performance of simultaneous wireless information and power transfer (SWIPT) in wireless sensor networks over Nakagami- $m$ fading channels. In the considered system, there is one mobile reader ( $R$ ), which is equipped with one transmit antenna and one receive antenna, and a group of passive sensors. The information delivery includes two stages: 1) $R$ broadcasts a command with radio-frequency energy to the sensors, which adopt time splitting (TS)/power splitting (PS) schemes to harvest energy and 2) sensors deliver their information to $R$ over orthogonal channels by using the harvested energy. In this paper, we propose a unified framework to study and optimize the impact of SWIPT on the system performance with both TS and PS schemes. First, we characterize the probability density function and cumulative distribution function of the signal-to-interference-plus-noise-ratio in high signal-to-noise ratio region, then we study the outage and ergodic capacity performance of the backward links. The approximated closed-form expressions for the outage probability and ergodic capacity are derived and validated through Monte Carlo simulations. Finally, we also evaluate the energy efficiency of the target system, and propose an optimal splitting scheme for TS and PS to maximize the throughput of the target system. [ABSTRACT FROM PUBLISHER]

The performance of $L$- branch scan-and-wait combining (SWC) reception systems over arbitrarily correlated and not necessarily identically distributed Nakagami- $m$ fading channels is analyzed and evaluated. First, a fast convergent infinite series representation for the SWC output signal-to-noise ratio (SNR) is presented. This expression is used to obtain analytical expressions in the form of infinite series for the average error probability performance of various modulation schemes for integer values of $m$ as well as the average number of paths estimation and the average waiting time (AWT) of $L$-branch SWC receivers for arbitrary values of $m$. The numerically obtained results have shown that the performance expressions converge very fast to their exact analytical values. It was found that the convergence speed depends on the correlation and operating SNR values as well as the Nakagami $m$- parameter. In addition to the analytical results, complementary computer simulated performance evaluation results have been obtained by means of Monte Carlo error counting techniques. The match between these two sets of results has verified the accuracy of the proposed mathematical analysis. Furthermore, it is revealed that, at the expense of a negligible AWT, the average error probability performance of SWC receivers is always superior to that of switch-and-examine combining receivers and, in certain cases, to that of maximal-ratio combining receivers. [ABSTRACT FROM PUBLISHER]

This paper considers a multiple-input–multiple-output (MIMO) cognitive wiretap system over Nakagami- $m$ channels with generalized selection combining (GSC), where confidential messages transmitted from a multiple-antenna transmitter to a multiple-antenna legitimate receiver are overheard by a multiple-antenna eavesdropper. Depending on whether the source node has the global channel state information (CSI) of both the main and wiretap channels, we investigate the secrecy outage performances of optimal antenna selection (OAS) and suboptimal antenna selection (SAS) schemes for MIMO underlay cognitive radio systems over Nakagami- $m$ channels, and we compare them with the space-time transmission (STT) scheme. The closed-form expressions for the exact and asymptotic secrecy outage probability (SOP) for various schemes are derived. Simulations are conducted to validate the accuracy of our derived analytical results. [ABSTRACT FROM PUBLISHER]

This paper investigates the physical layer security problem of cognitive decode-and-forward relay networks over Nakagami- $m$ fading channels. We consider the relaying communication between one secondary user (SU) source and one SU destination by using an opportunistic relay selection from multiple SU relays and sharing the licensed spectrum of multiple primary users (PUs) in the underlay network. While the transmission between the SUs imposes interference on each PU, the relayed transmission is intercepted by one SU eavesdropper. In the absence of the eavesdropper’s channel state information, the relay selection is based on the largest channel gain of relay-to-destination link, which is assumed to be outdated due to feedback delay. We derive the exact probability of non-zero secrecy capacity and the exact secrecy outage probability (SOP) in the closed form. Furthermore, we derive the asymptotic SOP in two different cases, and explicitly show the effects of system parameters on the secrecy diversity order and the secrecy diversity gain, respectively. Both asymptotic analysis and simulation results show that the secrecy performance can be improved by increasing either the number of relays or the Nakagami parameter of the legitimate relay channels, whereas the secrecy diversity gain deteriorates as the number of the PUs increases. [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]

Nonorthogonal multiple access (NOMA), which can improve the spectrum efficiency and system throughput compared with conventional orthogonal multiple access (OMA), has been regarded as a promising technique for the fifth-generation (5G) mobile communication network. In this paper, we consider a NOMA-based relaying networks over Nakagami-$m$ fading channels, where the base station communicates with multiple mobile users simultaneously through the help of an amplify-and-forward (AF) relay. First, we study the system outage behavior, and closed-form expressions for the exact outage probability and simple bounds of the outage probability are obtained, respectively. The analytical results are further evaluated in the high-signal-to-noise-ratio (SNR) regime to explicitly characterize the diversity order of the network. Next, the ergodic sum rate achieved by the network is investigated, and expressions for the lower and upper bounds of the ergodic sum rate are derived. Finally, numerical examples are conducted to confirm the validity of our analysis and show a comparison of NOMA against conventional OMA networks. NOMA is reported to outperform conventional OMA and provide better spectral efficiency and user fairness. [ABSTRACT FROM PUBLISHER]

This paper considers a single-input–multiple-output underlay cognitive wiretap system over Nakagami-$m$ channels with generalized selection combining, where confidential messages transmitted from a single-antenna transmitter to a multiple-antenna legitimate receiver are overheard by a multiple-antenna eavesdropper. Passive eavesdropping scenario is considered in this work, while the channel state information of the eavesdropping channel is not available at the secondary transmitter. We derived the closed-form expression for the exact secrecy outage probability. Simulations are conducted to validate the accuracy of our proposed analytical models. [ABSTRACT FROM PUBLISHER]

Future wireless networks are expected to handle a huge number of devices, including sensors, within a low energy consumption. In this scope, we present, in this paper, performance of wireless sensor networks (WSN). Specifically, we aim at finding the optimal transmit power of a node communicating with multiple receivers in a cognitive radio (CR) spectrum sharing framework, i.e., existence of an active primary user. We first present the optimal power with single secondary receiver, under instantaneous or average transmission rate constraints. Then, we propose a suboptimal solution for an easier, yet efficient, implementation and perform insightful asymptotical analysis for both schemes with Rayleigh fading. Afterwards, we extend our results to a multiple secondary receives CR scenario and present the corresponding optimal and suboptimal transmit power while satisfying independent peak/average and sum of peak/average transmission rate constraints. The corresponding numerical results are provided for Rayleigh and Nakagami-m fading channels. We characterize some transmission outage events depending on system parameters. [ABSTRACT FROM AUTHOR]

Although there has been a growing interest on the study of diversity-multiplexing tradeoff (DMT), the existing works are mostly restricted to the outcomes reported for Rayleigh, Rician, and Nakagami fading channels. In this paper, we investigate the optimal tradeoff in the presence of log-normal fading, which provides an accurate model for indoor wireless, optical wireless, and ultra-wideband channels. We consider a multiple-input multiple-output (MIMO) log-normal channel, derive the outage probability expression, and then present the asymptotical DMT expression. It is shown that the asymptotical maximum diversity gain tends to infinity with logarithm of signal-to-noise ratio (SNR). To have further insight, we normalize the DMT with that of single-input single-output case and express the relative asymptotical DMT of the MIMO log-normal channel as a function of the number of transmit and receive antennas. We further study DMT for finite SNRs and demonstrate convergence to the asymptotical case. Extensive numerical results are provided to corroborate the analytical derivation. [ABSTRACT FROM AUTHOR]

SUMMARY An expression for the average symbol error probability of coherent orthogonal M-ary frequency shift keying in generalized fading was recently reported by Chandra, Poram, and Bose. We show that the expression is only exact for M = 2; it does, however, provide an accurate approximation for M > 2. By modifying the derivation of the reported expression, we derive a lower bound for M ⩽5 that has the same complexity as the reported expression, and we illustrate that, for M > 2, the expression of the derived bound provides an approximation that is also more accurate.Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A novel metric to assess whether the standard Gaussian approximation of a single interferer underestimates or overestimates the link bit error rate is derived. The standard Gaussian approximation is newly constructed by a nonlinear transformation. The proposed metric is a function of the interference statistics; however, it is otherwise independent of the statistics of the desired signal. A closed-form expression for the proposed metric is obtained for the Nakagami distributed interference fading amplitude. Numerical results confirming validity of the proposed metric are provided for the case of Nakagami and lognormally distributed interference fading amplitudes. [ABSTRACT FROM PUBLISHER]

The symbol pairwise error probability performance of the Alamouti space‐time block code (STBC‐Alamouti) and the STBC from the coordinate interleaved orthogonal design (STBC‐CIOD) over Nakagami‐m fading channels is investigated, especially with residual phase estimation error (PEE). The derived union upper bounds on the average BER are utilised to evaluate the effect of the residual PEE on error performance. Rigorous numerical results demonstrate that both STBCs can asymptotically achieve full‐diversity even with the adverse effect of PEE in the high SNR regime. [ABSTRACT FROM AUTHOR]

Energy‐efficiency (EE) in antenna selection multi‐input–multi‐output (MIMO) systems over Nakagami‐m fading channels is investigated. An EE metric is defined as the number of successfully received bits per unit of energy consumption, which takes into account several important system parameters such as channel coding and modulation. An optimisation problem that maximises the EE metric subject to an error‐performance constraint is formulated. On the basis of an analysis of this problem, the optimal value of the average energy per transmitted data symbol is obtained, such that the EE in the system is maximised. Simulation results are provided to validate the analysis. [ABSTRACT FROM AUTHOR]

Spectrum sensing is the important aspect of cognitive radio (CR). In order to use the vacant spectrum, cognitive radio user must be able to identify the presence of empty spectrum efficiently. A non-cooperative spectrum sensing faces the problem of shadowing and hidden terminal due to which the CR user fails to monitor the vacant spectrum. To solve the problem of hidden terminal and shadowing in non-cooperative spectrum sensing, cooperative spectrum sensing (CSS) is used. CSS can be divided in two categories, centralised and distributed. In this paper comparison of centralised and distributed CSS is presented and a cluster based distributed CSS is proposed over fading channel with different fusion rules and effect of number of CR users and number of clusters on the performance has been investigated. It is investigated that if number of users and number of cluster increases, user cooperation increases and chances of detection of empty spectrum increases. Detection probability increases 134% for SNR = 0 dB when total number of CR users in a cluster is fixed at 2 and number of clusters are varied from 2 to 8 and it increases 97% when total number of clusters are 3 and number of CR users in a cluster is varied from 2 to 8. [ABSTRACT FROM AUTHOR]