Ensuring timely information delivery is of paramount importance for mission-critical applications in the Internet of Things (IoT). The age of information (AoI), which measures the time elapsed from data generation to reception, is critical for assessing information freshness in time-sensitive scenarios. This work focuses on the AoI analysis of cooperative IoT systems with decode-and-forward relaying mode, where automatic repeat request (ARQ) and truncated ARQ (TARQ) protocols are employed to enhance the reliability of short packet communications. The source and relay nodes have limited battery capacity, thereby harvesting energy from the charging towers. We derive analytical expressions for the average AoI and the average peak AoI for the proposed ARQ-assisted and TARQ-assisted protocols. Simulation results validate our theoretical analysis and explore the impact of system parameters on AoI performance. Our findings highlight the existence of the optimal packet length and retransmission time that minimize AoI, providing valuable insights for designing efficient IoT systems.

This work addresses the challenge of achieving covert communication in cooperative wireless systems, which consist of a source, a decode-and-forward relay, and a destination. The direct link between the source and the destination is often impaired by deep fading, necessitating the use of a relay to forward signals. The relay also attempts to transmit its covert signal to the destination over the same spectrum, complicating the source’s detection capabilities. To tackle this issue, we propose two power allocation schemes: 1) fixed power allocation (FPA) and 2) dynamic power allocation (DPA). The FPA scheme maintains a constant power allocation for the source’s message, while the DPA scheme adjusts power based on the channel quality from the relay to the destination. Considering noise uncertainty at the source, we derive closed-form expressions for false alarm probability, miss detection probability, and minimum detection error probability, which are crucial for evaluating the source’s detection performance while ensuring Quality of Service for both source and relay messages. Simulation results demonstrate that the DPA scheme outperforms the FPA scheme in terms of covert throughput, especially under conditions of higher transmission rate thresholds and improved channel conditions.

In the sixth-generation (6G) Internet of Things (IoT) networks, unmanned aerial vehicle (UAV)-mounted base stations and reconfigurable intelligent surfaces (RISs) have been considered key technologies to enhance coverage, flexibility, and security in nonterrestrial networks (NTNs). In addition to aerial networks enabled by NTN technologies, the integration of underwater networks with 6G IoT can be considered one of the most innovative challenges in future IoT. Along with such trends in IoT, this study investigates the secrecy performance of IoT networks that integrate radio frequency (RF) UAV-based NTNs and underwater optical wireless communication (UOWC) with RISs. Under three potential eavesdropping scenarios, i.e., overhearing of RF signal, UOWC signal, and both signals, we derive closed-form expressions for secrecy performance metrics, including average secrecy capacity, secrecy outage probability, probability of strictly positive secrecy capacity, and effective secrecy throughput. Extensive numerical analyses and Monte Carlo simulations elucidate the impact of system parameters, such as fading severity, the number of RIS reflecting elements, underwater turbulence, pointing errors, and detection techniques on system security. The findings offer comprehensive design guidelines for network deployment aiming to enhance secrecy performance and ensure secure communication in diverse and challenging environments.

This study investigates the secrecy performance of a rate-splitting multiple-access system inspired by cognitive radio principles, where the primary user takes on the role of a potential eavesdropper seeking to intercept the secondary user's message. The on-off scheme is utilized to guarantee the transmission of the primary user. We provide closed-form expressions for critical metrics, including the transmission probability of the system under consideration, the secrecy outage probability, and the reliable outage probability of the cognitive user. Monte Carlo simulation results are presented to substantiate our findings and explore the impact of system parameters, such as transmit power and the number of antennas at the base station, on system performance.

Cyber resilience quantification is the process of evaluating and measuring an organisation’s ability to withstand, adapt to, and recover from cyber-attacks. It involves estimating IT systems, networks, and response strategies to ensure robust defence and effective recovery mechanisms in the event of a cyber-attack. Quantifying cyber resilience can be difficult due to the constantly changing components of IT infrastructure. Traditional methods like vulnerability assessments and penetration testing may not be effective. Measuring cyber resilience is essential to evaluate and strengthen an organisation’s preparedness against evolving cyber-attacks. It helps identify weaknesses, allocate resources, and ensure the uninterrupted operation of critical systems and information. There are various methods for measuring cyber resilience, such as evaluating, teaming and testing, and creating simulated models. This article proposes a cyber resilience quantification framework for IT infrastructure that utilises a simulation approach. This approach enables organisations to simulate different attack scenarios, identify vulnerabilities, and improve their cyber resilience. The comparative analysis of cyber resilience factors highlights pre-configuration’s robust planning and adaptation (61.44%), buffering supported’s initial readiness (44.53%), and network topologies’ robust planning but weak recovery and adaptation (60.04% to 77.86%), underscoring the need for comprehensive enhancements across all phases. The utilisation of the proposed factors is crucial in conducting a comprehensive evaluation of IT infrastructure in the event of a cyber-attack.

Millimeter-wave (mmWave) communication is one of the effective technologies for the next generation of wireless communications due to the enormous amount of available spectrum resources. Rate splitting multiple access (RSMA) is a powerful multiple access, interference management, and multiuser strategy for designing future wireless networks. In this work, a multiple-input-single-output mmWave RSMA system is considered wherein a base station serves two users in the presence of a passive eavesdropper. Different eavesdropping scenarios are considered corresponding to the overlapped resolvable paths between the main and the wiretap channels under the considered transmission schemes. The analytical expressions for the secrecy outage probability (SOP) are derived respectively through the Gaussian–Chebyshev quadrature method. Monte Carlo simulation results are presented to validate the correctness of the derived analytical expressions and demonstrate the effects of system parameters on the SOP of the considered mmWave RSMA systems.

In the realm of the Internet of Things, reconfigurable intelligent surfaces (RISs) have emerged as a pivotal technology, offering unprecedented opportunities to enhance signal quality, coverage, and energy efficiency as part of the ongoing pursuit to overcome the limitations of conventional wireless communication systems. In this context, this paper focuses on the analysis of performance in an integrated air-to-underwater network under the amplified-and-forward relay with variable gain, specifically examining the impact of RISs on a mixed terahertz-underwater optical communication system. This study utilizes the α-μ distribution to characterize the fading effects and pointing error on the THz signal. On the other hand, the underwater turbulence on the optical signal is modeled using the mixture of Exponential Generalized Gamma distribution with pointing error impairments. To provide a basis for comparison, the heterodyne detection technique and the intensity modulation with the direct detection technique are also incorporated. Therefore, analytical expressions of outage probability, average bit error rate, and average channel capacity are demonstrated in terms of the Meijer-G function. To provide more insights, high signal-to-noise approximations of these metrics are also presented. Furthermore, the impact of various modulation schemes, fading severity, pointing errors, atmospheric turbulence conditions, and receiver detection techniques are inspected on the system performance. Finally, the analytical findings are validated through Monte-Carlo simulations, ensuring the robustness of the results.

As air-to-ground links tend to exhibit a high probability of being line-of-sight (LoS), unmanned aerial vehicles (UAVs) are widely used to improve the performance of wireless communications. The design of the UAV flight path plays a pivotal role in determining the effectiveness of UAV communication systems. However, the air-to-ground links with a high probability of LoS introduce a heightened risk of eavesdropping, posing a significant security challenge. In this work, we investigate the problem of ensuring secure data acquisition for quadrotor UAV-based communication systems in the presence of multiple location-uncertain terrestrial eavesdroppers. The bandwidth allocation and the three-dimensional trajectory of the UAV are jointly designed to maximize the system’s overall fair secrecy rate. This design also considers the UAV’s energy consumption during flight and aims to ensure fairness among users. Solving this problem poses a challenge since it is a non-convex and involves multiple variables, making it difficult to address using conventional optimization methods. Therefore, a deep reinforcement learning algorithm is developed based on the deep deterministic policy gradient algorithm. Simulation results are given to verify the effectiveness of the proposed algorithm in improving the security of aerial Internet of Things systems.

Semi-grant-free (SGF) transmission scheme enables grant-free (GF) users to utilize resource blocks allocated for grant-based (GB) users while maintaining the quality of service of GB users. This work investigates the secrecy performance of non-orthogonal multiple access (NOMA)-aided SGF systems. First, analytical expressions for the exact and asymptotic secrecy outage probability (SOP) of NOMA-aided SGF systems with a single GF user are derived. Then, the SGF systems with multiple GF users and the best-user scheduling scheme is considered. By utilizing order statistics theory, analytical expressions for the exact and asymptotic SOP are derived. Monte Carlo simulation results are provided and compared with two benchmark schemes. The effects of system parameters on the SOP of the considered system are demonstrated and the accuracy of the developed analytical results is verified. The results indicate that both the outage target rate for GB and the secure target rate for GF are the main factors of the secrecy performance of SGF systems.

In this work, a mixed underwater acoustic/optical wireless transmission system under both amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols is proposed. Assuming pointing errors and both heterodyne detection (HD) as well as intensity modulation/direct detection (IM/DD) techniques in the underwater optical link, we deduce the exact analytical formulas for the outage probability (OP), average bit error rate (ABER), and average capacity of the system under consideration. Also, we further derive the corresponding asymptotic expressions to gain intuitive physical insights about the system and channel models under consideration. Additionally, we extend the analysis to a more general multi-sensor system. Finally, we check the analytical results by Monte Carlo simulations.

This contribution quantifies the achievable physical layer security of wireless transmission over realistic composite fading conditions in the presence of multiple eavesdroppers (Eves). To this end, exact closed-form analytic expressions are derived for the achievable secure outage probability (SOP) and the probability of strictly positive secrecy capacity (SPSC) for the case of$\mathcal{F}$composite fading channels. The derived expressions are tractable and their validity is justified through comparisons with respective computer simulation results. In addition, they allow for the development of useful theoretical and practical insights on the effect of the presence of numerous eavesdroppers under different multipath fading and shadowing conditions, as these are encountered in realistic wireless communication scenarios.

In this contribution we evaluate the transmission of confidential information over ${\mathcal{F}}$ composite fading channels in the presence of an eavesdropper (Eve) who also experiences ${\mathcal{F}}$ composite fading. Upon obtaining tractable closed-form expressions for the secure outage probability and the probability of strictly positive secrecy capacity, we analyze extensively the achievable physical layer security performance in the context of mm-wave communications. This is realized with the aid of extensive measurement results from realistic communication scenarios, which show the behavior of composite ${\mathcal{F}}$ fading channels in device-to-device communication scenarios. The offered results provide meaningful insights of theoretical and practical importance that are expected to be useful in the design of mm-wave based communication systems.

In the uplink cognitive radio-inspired nonorthogonal multiple access (CR-NOMA) systems, the successive interference cancellation (SIC), and power control (PC) schemes were designed to enhance the outage performance but they lack the capability of protecting signals from being eavesdropped. This work investigates the secrecy performance of uplink CR-NOMA systems with the hybrid SIC and PC (HSIC-PC) scheme in the presence of a passive eavesdropper. Furthermore, through transmitting artificial noise (AN), a new scheme is proposed to improve the security of the cognitive user with HSIC-PC without deteriorating the primary user’s quality of service. Specifically, the primary and secondary users transmit AN cooperatively to enhance the security of the secondary user. The secrecy performance of the proposed scheme is analyzed based on the relationship between the maximum interference power that the primary user can tolerate and the secondary user’s channel gain. The analytical expressions for the secrecy outage probability (SOP) are derived, and the effect of parameters on the SOP is discussed. We also derive the analytical expressions of the asymptotic SOP in the high-power region to obtain further insights. Monte Carlo simulation results are performed to verify the analytical results. The results demonstrate that the proposed scheme performs better than the benchmarks.

Unmanned aerial vehicles (UAVs) have been widely employed to enhance the end-to-end performance of wireless communications since the links between UAVs and terrestrial nodes are Line-of-Sight (LoS) with high probability. However, the broadcast characteristics of signal propagation in LoS links make them vulnerable to being wiretapped by malicious eavesdroppers, which poses a considerable challenge to the security of wireless communications. In this work, we investigate the security of aerial underlay Internet of Things (IoT) systems by jointly designing trajectory and user scheduling. An airborne base station transmits confidential messages to secondary users utilizing the same spectrum as the primary network. An aerial jammer transmits jamming signals to suppress the eavesdropper to enhance secrecy performance. The uncertainty of eavesdropping node locations is considered, and the average secrecy rate of the secondary user is maximized by optimizing multiple users’ scheduling, the UAVs’ trajectory, and transmit power. To solve the nonconvex optimization problem with a mixed multi-integer variable problem, we propose an iterative algorithm based on block coordinate descent and successive convex approximation. Numerical results verify the effectiveness of our proposed algorithm and demonstrate that our scheme is beneficial in improving the secrecy performance of aerial underlay IoT systems.

This paper proposes a new scheme to enhance the secrecy performance of non-orthogonal multiple access (NOMA)-based coordinated direct relay transmission (CDRT) systems with an untrusted relay. The physical-layer network coding (PNC) and the NOMA schemes are combined to improve spectrum efficiency. Furthermore, inter-user interference and friendly jamming signals are utilized to suppress the eavesdropping ability of the untrusted relay without compromising the acceptance quality of legitimate users. Specifically, the far user in the first slot and the near user in the second slot act as jammers that generate jamming signals to ensure secure transmissions of confidential messages. We investigate the secrecy performance of the NOMA-based CDRT systems with the PNC scheme and derive the closed-form expression for the ergodic secrecy sum rate. The asymptotic analysis at a high signal-to-noise ratio is performed to obtain more insights. Finally, simulation results are presented to demonstrate the proposed scheme’s effectiveness and the theoretical analysis’s correctness.

The time-reversal division multiple access (TRDMA) system employs multipath channels to realize multi-user transmission via time-reversal filtering. The performance of TRDMA is affected by the correlation among users’ channels. When the correlation is high, inter-user interference (IUI) in the TRDMA system will be serious and the system capacity will be severely restricted. In this paper, we propose an uplink multiple access scheme time-reversal non-orthogonal multiple access (TR-NOMA), wherein TRDMA and power-domain non-orthogonal multiple access are combined. The base station employs a TR filter for each user to suppress IUI and applies successive interference cancellations in the detection process of users’ signals. Users’ transmit power and TR filters are jointly optimized to promote system capacity. The original optimization problem is non-convex. We decompose the optimization problem into two sub-problems: the design of TR filters and the allocation of users’ transmit power, which is solved by utilizing generalized eigenvalue decomposition and successive lower bound convex approximation, respectively. The solution to the original optimization problem is obtained by the iterative solution between the two sub-problems. Simulation results demonstrate that the sum rate of the optimized TR-NOMA system is significantly higher than that of the TRDMA system.

Millimeter-wave (mmWave) communication has attracted considerable attention from academia and industry, providing multi-gigabits per second rates due to the substantial bandwidth. Rate splitting multiple access (RSMA) is an effective technology that provides a generalized multiple access framework. Regarding the new propagation characteristics of the mmWave, we investigate the outage performance of the mmWave RSMA multiple-input-single-output system with a fixed-located user and a randomly-located user. Based on the spatial correlation of the paired users, the user’s paths are divided into overlapped and non-overlapped paths. Two beamforming schemes are proposed to improve the reliability of the mmWave RSMA system. The common stream is transmitted on the overlapped paths or all the paths. By utilizing stochastic geometry theory, the closed-form expressions of the outage probability (OP) with proposed schemes are derived. To obtain more insights, the expressions for the asymptotic OP are derived. Monte Carlo simulation results are presented to validate the analysis and the effects of the system parameters, such as power allocation coefficients and the number of resolvable paths, on the outage performance are investigated.

In this article, we study the secure communication performance of nonorthogonal multiple access (NOMA) communication systems with aerial eavesdroppers. First, the ground-to-ground NOMA communications systems are considered wherein the near user is uniformly distributed in an inner disc and the far user is uniformly distributed in an outer ring within cell coverage of a base station (BS) at the center. A single eavesdropper is uniformly distributed outside the protected zone or multiple eavesdroppers are randomly dispersed and modeled as a 3-D homogeneous Poisson point process. Subsequently, the secrecy performance of the ground-to-air NOMA communications systems is investigated wherein the near user is uniformly distributed in an internal 3-D spherical cap and the far user is uniformly distributed in an external 3-D spherical cap. To enhance secrecy performance, a protected zone is introduced around the ground BS. Novel exact expressions for the secrecy outage probability (SOP) for both scenarios are derived. Finally, Monte Carlo simulation results are presented to validate the correctness of the derived analytical expressions and demonstrate the effects of system parameters on SOP of the considered system.

In this paper, we study the secure communication performance of nonorthogonal multiple access (NOMA) communication systems in presence of aerial eavesdroppers. The security of ground-to-air NOMA communication systems is investigated wherein, utilizing stochastic geometry, the near user is uniformly distributed in an internal three-dimensional (3D) spherical cap and the far user is uniformly distributed in an external 3D spherical cap. To enhance secrecy performance, a protection zone and directional antenna are introduced. The scenarios of both a single eavesdropper and multiple eavesdroppers are considered and new exact expressions for the secrecy outage probability (SOP) under both scenarios are derived. Monte Carlo simulation results are presented to verify the correctness of the derived analytical expressions and the effects of system parameters on SOP of the considered system are investigated.

The use of bivariate Fox H-functions (BFHFs) in performance analyses of wireless communication systems has gained considerable attention in past few decades. However, the non-existence of robust built-in routines for evaluating such functions in standard computing systems poses numerous challenges in numerical experiments and simulations. Motivated by the apparent need to circumvent these difficulties in performance analyses of cooperative wireless communications, this work presents an alternative method for obtaining the exact, approximate and asymptotic BFHF-free cumulative distribution function (CDF) of the end-to-end (e2e) signal-to-noise ratio (SNR) of multi-hop amplify-and-forward (AF) relaying wireless communication systems. As an illustration, the e2e performance analysis of an all-optical dual-hop free-space optical (FSO) transmission system over Gamma-Gamma turbulence in the presence of pointing errors is revisited. Specifically, new mathematical formulae for the statistical characteristics of the e2e SNR for systems with AF fixed-gain relaying as well as channel-state-information(CSI)-assisted using heterodyne detection (HD) or intensity modulation with direct detection (IM/DD) are derived in terms of mathematically malleable and uniformly convergent infinite series of weighted Meijer G-functions. The usefulness of the derived CDFs is illustrated through derivation of traditional system performance metrics. The accuracy of the derived analytical formulae is verified via Monte Carlo simulations in MATLAB®. Finally, based on results observed in this paper, useful expansions of common BFHFs in terms of easily computable univariate hypergeometric functions are proposed.

The recent pandemic of COVID-19 has changed the way people socially interact with each other. A huge increase in the usage of social media applications has been observed due to quarantine strategies enforced by many governments across the globe. This has put a great burden on already overloaded cellular networks. It is believed that direct Device-to-Device (D2D) communication can offload a significant amount of traffic from cellular networks, especially during scenarios when residents in a locality aim to share information among them. WiFi Direct is one of the enabling technologies of D2D communications, having a great potential to facilitate various proximity-based applications. In this work, we propose power saving schemes that aim at minimizing energy consumption of user devices across D2D based multi-hop networks. Further, we provide an analytical model to formulate energy consumption of such a network. The simulation results demonstrate that a small modification in the network configuration, such as group size and transmit power can provide considerable energy gains. The observed energy consumption is reduced by 5 times for a throughput loss of 12%. Additionally, we measure the energy per transmitted bit for different configurations of the network. Furthermore, we analyze the behavior of the network, in terms of its energy consumption and throughput, for different file sizes.

Unmanned aerial vehicles (UAVs) will be extensively utilized in various Internet of Things (IoT) scenarios due to their flexible mobility and rapid on-demand deployment. It becomes necessary and urgent to investigate the secrecy performance of the UAV IoT communication systems because of the open characteristics of wireless channels. In this article, the physical layer security of UAV IoT communication systems is studied, in which a ground IoT device transmits some confidential messages to a UAV hovering in the air, while a random number of eavesdroppers are randomly positioned around the ground source. The ground-to-air channel is assumed to experience Rician fading for the case of line-of-sight propagation and Rayleigh fading for the case of nonline-of-sight propagation, respectively. In addition, in order to improve the security of the system, we also investigate the secrecy performance of the UAV IoT system with a friendly UAV that generates jamming signals to distract the eavesdroppers. Utilizing the stochastic geometry theory, the cumulative distribution functions for the signal-to-interference-plus-noise ratio of the main and eavesdropping links are derived, and then the analytical expressions of the secrecy outage probability and the average secrecy rate are obtained. Finally, the accuracy of the analytical results is verified by Monte Carlo simulation.

In this work, we investigate the relationship between the reliability and security of a typical two-user downlink non-orthogonal multiple access (NOMA) communication system. The level of successive interference cancellation on NOMA user is considered. Firstly, the impact of various key parameters on transmit signal-to-noise ratio (SNR) of the NOMA users with the reliability outage probability (ROP) constraint is discussed. Taking the minimum of transmit SNR for ROP into account, the secrecy outage performance of the downlink NOMA systems is studied and the analytical expressions of the secrecy outage probability of the NOMA system are derived under two cases of eavesdropping capability. Furthermore, the sum effective secrecy throughput of the NOMA system under two scenarios with considering ROP constraint is derived. Monte Carlo simulations are provided to verify the accuracy of our analysis.

In this work, we analyze the secrecy outage performance of a dual-hop relay system composed of multipleinput- multiple-output radio-frequency (RF) links and a freespace optical (FSO) link while a multiple-antenna eavesdropper wiretaps the confidential information by decoding the received signals from the source node. The channel state information (CSI) of the RF and FSO links is considered to be outdated and imprecise, respectively. We propose four transmit antenna selection (TAS) schemes to enhance the secrecy performance of the considered systems. The secrecy outage performance with different TAS schemes is analyzed and the effects of misalignment and detection technology on the secrecy outage performance of mixed systems are studied. We derive the closed-form expressions for probability density function (PDF) and cumulative distribution function (CDF) over M´alaga channel with imperfect CSI. Then the closed-form expressions for the CDF and PDF of the equivalent signal-to-noise ratio (SNR) at the legitimate receiver over Nakagami-m and M´alaga channels are derived. Furthermore, the bound of the effective secrecy throughput (EST) with different TAS schemes are derived. Besides, the asymptotic results for EST are investigated by exploiting the unfolding of Meijer’s G-function when the electrical SNR of FSO link approaches infinity. Finally, Monte-Carlo simulation results are presented to testify the correctness of the proposed analysis. The results illustrate that outdated CSI shows a strong effect on the secrecy performance of the mixed RF-FSO systems. In addition, increasing the number of antennas at the source cannot significantly enhance the secrecy performance of the considered systems

Medical implants are an important part of Wireless Body Area Networks (WBANs) and play an important role to monitor, diagnose, and control various medical conditions. These tiny sensors are injected inside human body to measure and communicate various vital signs of a human body. Since the information transmitted by implants is very sensitive and critical in nature, both availability and confidentiality of such information are of prime importance. A possible security threat in medical implants that can breach the availability of the medical implants is a Denial of Service (DoS) attack. In this work, we propose a solution to mitigate DoS attack in the Medical Implant Communication Service (MICS) network. We propose a three-level trust model for a MICS network based on its environment and couple a threshold of maximum allowed data rate to each environment. The simulation results show that DoS attacks can be seamlessly mitigated in many MICS settings.

Next generation satellite systems are required to perform robust frame synchronisation in the presence of large frequency offsets at low carrier‐to‐noise ratios. Differential correlation‐based frame acquisition is an appealing choice for these systems as it provides adequate performance with reasonable complexity. However, the theoretical characterisation of the multi‐span differential correlation metric is still an open problem due to the fact that the correlation outputs with multiple delays are correlated. In this study, the authors derived novel closed‐form approximations for the distribution of the multi‐span differential correlation metric as well as the probabilities of miss‐detection and false alarm. The close agreement between the simulated and theoretical receiver operating curves validates the analysis. This analysis can be used to characterise the performance of multi‐span differential correlation‐based frame synchroniser in terms of the number of delays without running computationally extensive Monte Carlo simulations.

This study focuses on the analysis of a decode‐and‐forward relay‐based asymmetric radio frequency‐free space optical (RF‐FSO) communication system. These types of communication systems are of very high speed, secure, and cost‐effective. Such systems can be used to provide the last‐mile access to many household users and can provide temporary network access during disasters and link failures. In the communication model analysed, the RF path is considered as Rayleigh fading, and the FSO path is considered as Málaga ( )‐distributed turbulence fading with the pointing error. Two types of detection schemes consisting of intensity modulation/direct detection and heterodyne detection are considered at the receiver for the analysis. For this cooperative communication system, novel mathematical expressions for the cumulative distribution function, probability density function, and moment generating function of the end‐to‐end signal‐to‐noise ratio are derived. With the aid of these statistical characteristics, new closed mathematical formulations are obtained for outage probability and the average bit error rate for different binary and M‐ary modulation approaches.

This paper considers the secrecy outage performance of a multiple-relay assisted non-orthogonal multiple access (NOMA) network over Nakagami-m fading channels. Two time slots are utilized to transmit signals from the base station to destination. At the first time slot, the base station broadcasts the superposition signal of the two users to all decode-and-forward relays by message mapping strategy. Subsequently, the selected relay transmits superposition signal to the two users via power-domain NOMA technology. Three relay selection schemes, i.e., optimal single relay selection (OSRS) scheme, two-step single relay selection (TSRS) scheme, and optimal dual relay selection (ODRS) scheme are proposed and the secrecy outage performance is analyzed. As a benchmark, we also examine the secrecy outage performance of the NOMA systems with traditional multiple relay forwarding (TMRF) scheme in which all the relay that successfully decode signals from the source forward signals to the NOMA users with equal power. Considering the correlation between the secrecy capacity of two users and different secrecy requirement for two NOMA users, the analytical expressions for the security outage probability (SOP) of the proposed OSRS, TSRS, and ODRS schemes along with the TMRF scheme are derived and validated via simulations. To get more insights, we also derive the analytical expressions for the asymptotic SOP for all the schemes with fixed and dynamic power allocations. Furthermore, the secrecy diversity order (SDO) and secrecy array gain of cooperative NOMA systems are obtained. The results demonstrate that our proposed schemes can significantly enhance the secrecy performance compared to the TMRF scheme and that all the schemes with fixed power allocation obtain zero SDO and the OSRS scheme with dynamic power allocation obtains the same SDO as TMRF.

WiFi direct is a variant of Infrastructure mode WiFi, which is designed to enable direct Device-to-Device (D2D) communications between proximity devices. This new technology enables various proximity-based services such as social networking, multimedia content distribution, cellular traffic offloading, Internet of Things (IoT), and mission critical communications. However, energy consumption of battery-constrained devices remains a major concern in all the aforementioned applications. In this paper, we model energy consumption of the WiFi direct protocol, starting from device discovery to actual data transmissions for intra group D2D communications. We simulate a content distribution scenario in Matlab and analyze our model for the energy consumption of the devices. We argue that the energy spent in device discovery becomes significant in the case of small data sizes. In particular, we find that smaller data sizes, such as 100KB, cause the equal amount of energy to spend in both device discovery and data transmission phases, even when the device discovery time is very small.

As the communication industry is progressing towards fifth generation (5G) of cellular networks, the traffic it carries is also shifting from high data rate traffic from cellular users to a mixture of high data rate and low data rate traffic from Internet of Things (IoT) applications. Moreover, the need to efficiently access Internet data is also increasing across 5G networks. Caching contents at the network edge is considered as a promising approach to reduce the delivery time. In this paper, we propose a marketplace for providing a number of caching options for a broad range of applications. In addition, we propose a security scheme to secure the caching contents with a simultaneous potential of reducing the duplicate contents from the caching server by dividing a file into smaller chunks. We model different caching scenarios in NS-3 and present the performance evaluation of our proposal in terms of latency and throughput gains for various chunk sizes.

The authors study the performance of an amplify‐and‐forward dual‐hop, switch‐and‐stay combining receiver, used in free space optical communications over non‐identical fading channels. One path is characterised by the generalised Málaga (or M distribution), whereas the other is influenced by the combined effects of Gamma–Gamma distributed atmospheric turbulence, pointing error and path loss. Novel closed‐form expressions for the end‐to‐end moment generating function, probability density function, and cumulative distribution function are derived in terms of Meijer's G function. Furthermore, the performance of the system is analysed, and closed‐form expressions are presented for the end‐to‐end outage probability and channel capacity.

https://doi.org/10.1155/2018/1907506

WiFi Direct is a new technology that enables direct Device-to Device (D2D) communication. This technology has a great potential to enable various proximity-based applications such as multimedia content distribution, social networking, cellular traffic offloading, mission critical communications, and Internet of Things (IoT). However, in such applications, energy consumption of battery-constrained devices is a major concern. In this paper, we propose a novel power saving protocol that aims at optimizing energy consumption and throughput of user devices by controlling the WiFi Direct group size and transmit power of the devices. We model a content distribution scenario in NS-3 and present the performance evaluation. Our simulation results demonstrate that even a small modification in the network configuration can provide a considerable energy gain with a minor effect on throughput. The observed energy saving can be as high as 1000% for a throughput loss of 12%.

Full duplex (FD) communication promises significant performance gains under ideal network settings. Generally, it has been shown that the throughput and delay gains of FD communication are somewhat limited in realistic conditions, leading researchers to study other possible applications where significantly higher gains over half duplex communication can be availed. The potential of FD nodes in improving the physical layer security of a communication link is investigated in this contribution. Specifically, we present a thorough analysis of the achievable secrecy rate for a transceiver pair in FD mode in the presence of a passive eavesdropper assuming a generic system model. The ergodic secrecy rate with FD communication is found to grow linearly with the log of the direct channel signal to noise ratio as opposed to the flattened out secrecy rate with conventional half duplex communication and irrespective of the eavesdropper channel strengths.

Device-to-Device (D2D) communication has emerged as a new technology, which minimizes data transmission in radio access networks by leveraging direct interaction between nearby mobile devices. D2D communication has a great potential in solving the capacity bottleneck problem of cellular networks by offloading cellular traffic of proximity-based applications to D2D links. This provides several benefits including, but are not limited to, lower transfer delays, higher data rates, and better energy efficiency. However, security in D2D communication, which is equally essential for the success of D2D communication in future networks, is a less investigated topic in literature. In this paper, we propose the combination of the PGP and reputation-based model to bootstrap trust in D2D environments. Our proposal aims at minimizing any suspicious connection with selfish users. Offloading cellular traffic to trusted D2D links provides significant throughput gain over the conventional cellular network. Our results show that the capacity gain can be as high as 133%.

In this paper, the secrecy outage performance of an underlay cognitive decode-and-forward (DF) relay network over independent and non-identical distributed (i.n.i.d) Nakagami-m fading channels is investigated, in which the secondary user transmitter communicates with the secondary destination via relays, and an eavesdropper attempts to overhear the information. We assume that the channel state information (CSI) of all links is available. The exact and asymptotic closed-form expressions for the secrecy outage probability with optimal relay selection are derived, and verified by Monte-Carlo simulations. Through asymptotic analysis, we find that the secrecy diversity order is determined by the number of relays and the fading parameters between relay and destination.

In this paper, we analyze the performance of decode-and-forward (DF) dual-hop relaying networks with wireless energy harvesting at the relay node over the generalized η-μ and κ-μ fading channels. In the analysis, the source and destination nodes are equipped with multiple antennas, whereas the relay node is equipped with a single antenna. Exact analytical expression for the system outage probability (OP) is derived and evaluated. The derived OP expression considers two practical energy harvesting techniques, namely, time switching-based relaying (TSR) and power splitting-based relaying (PSR). Some numerical examples are provided to study the overall system performance under different system parameters, such as fading parameters, energy harvesting time, power splitting factor, and signal-to-noise ratio (SNR). Our numerical results are supported with Monte-Carlo simulations to validate the accuracy of our analysis.

The satellite relaying system is a promising network architecture in next generation wireless communication systems, due to its large coverage and stability. In this paper, the performance of a dual-hop decode-and-forward based satellite relaying system over κ-μ shadowed fading channels is investigated, where a source earth station transmits information to a destination earth station via a satellite relay. We first obtain the exact closedform expressions of the outage probability of such a system in terms of bivariate confluent hypergeometric functions. By using a novel gamma approximation to the κ-μ shadowed distribution, the simple outage expression is derived. Moreover, the accurate expression of the average bit error rate (ABER) and the ergodic capacity are obtained in terms of Appell hypergeometric functions and hypergeometric functions, respectively. Again, with the help of the gamma approximation, we derive the approximate ABER and capacity expressions. In the high signal-to-noise ratio regime, the asymptotic ABER expression is obtained in terms of elementary functions. Finally, numerical and Monte-Carlo simulation results are provided to demonstrate the validity of the proposed unified expressions.

This study investigates the secrecy outage performance of a single‐input multiple‐output underlay cognitive radio network (CRN) with outdated channel state information (CSI). The confidential messages are transmitted from transmitter to the destination, while a multi‐antenna eavesdropper exists. The maximal ratio combining and selection combining schemes are utilised at the receivers to improve the quality of the received signal‐to‐noise ratio. The exact and asymptotic closed‐form expressions of secrecy outage probability are derived, and simulation results are provided to verify the authors' proposed analytical results. The results reveal that imperfect CSI of main channels deteriorates the secrecy outage performance while that of eavesdropping and interfering channels has contrary effect, and only a unity diversity order can be obtained in underlay CRNs with imperfect CSI.

Full-duplex communication enables simultaneous transmission from both ends of a communication link, thereby promising significant performance gains. Generally, it has been shown that the throughput and delay gains of full-duplex communication are somewhat limited in realistic network settings, leading researchers to study other possible applications that can accord higher gains. The potential of full-duplex communication in improving the physical-layer security of a communication link is investigated in this contribution. We specifically present a thorough analysis of the achievable ergodic secrecy rate and the secrecy degrees of freedom with full-duplex communication in the presence of a half-duplex eavesdropper node, with both single-user decoding and multi-user decoding capabilities. For the latter case, an eavesdropper with successive interference cancellation and joint decoding capabilities is assumed. Irrespective of the eavesdropper capabilities and channel strengths, the ergodic secrecy rate with full-duplex communication is found to grow linearly with the log of the direct channel signal-to-noise-ratio (SNR) as opposed to the flattened out secrecy rate with conventional half-duplex communication. Consequently, the secrecy degrees of freedom with full-duplex is shown to be two as opposed to that of zero in half-duplex mode.

A mixed free-space optical (FSO) communication scheme is considered with the help of a fixed gain relay. We assume that the links from the source to the relay are radio frequency links with multiuser diversity operating in η-μ fading channels, while the link between the relay and the destination is a FSO link with M-distribution. We first derive expressions for the cumulative distribution function of the end-to-end signal-tonoise ratio for the considered system with pointing errors, and then use them to derive some exact closed-form expressions for the outage probability, bit-error rate performance, and ergodic capacity. To investigate the diversity order and effects of different system and channel parameters on the system performance, we further present the asymptotic performance expressions. On the other hand, we also present the performance analysis for a mixed RF/FSO system with variable-gain relaying and multiuser diversity. Results show that the system diversity orders for both fixed and variable gains systems are min{2Kμ, g2/2, α/2, k/2}, where K is the number of users, g represents the pointing error, and α and k are the channel parameters. Finally, some selected numerical results are given to corroborate the derived analytical results.

In this work, the outage performance analysis of a dual-hop transmission system composed of asymmetric radio frequency (RF) channels cascaded with free-space optical (FSO) links is presented. The RF links are modeled by the Rayleigh fading distribution and the FSO links are modeled by Malaga (M) turbulence distribution. The FSO links account for pointing errors and both types of detection techniques (i.e. heterodyne detection as well as intensity modulation/direct detection (IM/DD)). Transmit diversity is applied at the source, selection combining is applied at the destination, and the relay is equipped with single RF receive antenna and single aperture for relaying the information over FSO links. With this model, a new exact closed-form expression is derived for the outage probability of the end-to- end signal-to-noise ratio of such communication systems in terms of the Meijer's G function under fixed amplify-and-forward relay scheme. All new analytical results are verified via computer-based Monte-Carlo simulations and are illustrated by some selected numerical results.

In this work, we consider the transmission of confidential message through independent and identically distributed generalized-K fading single-input multiple-output (SIMO) channels in the presence of an eavesdropper. The security performance of SIMO generalized-K systems are investigated using a mixture gamma (MG) distribution, and the analytical expressions for the average secrecy capacity (ASC) and the secure outage probability (SOP) of SIMO systems are derived. Numerical results are presented and verified via Monte-Carlo simulations.

Full duplex communication promises a theoretical 100% throughput gain by doubling the number of simultaneous transmissions. Such compelling gains are conditioned on perfect cancellation of the self interference power resulting from simultaneous transmission and reception. Generally, self interference power is modelled as a noise-like constant level interference floor. However, experimental validations have shown that the self interference power is in practice a random variable depending on a number of factors such as the surrounding wireless environment and the degree of interference cancellation. In this study, we derive an analytical model for the residual self interference power, and demonstrate various applications of the derived model in analysing the performance of a Full Duplex radio. In general, full duplex communication is found to provide only modest throughput gains over half duplex communication in a dense network scenario with practical self interference cancellation models.

In this study, the secrecy performance of the classic Wyner's wiretap model over generalised‐ K fading channels is studied. The closed‐form expressions for the average secrecy capacity, the lower bound of secure outage probability, and the probability of strictly positive secrecy capacity are derived. The new expressions provide a unified form, which can handle several of the well‐known composite fading environments as special or limiting cases. Moreover, all the derived expressions are given in terms of Meijer's G ‐function, which can be simply realised in MATLAB and MATHEMATICA. Monte‐Carlo simulations are performed to verify the proposed analysis models.

In this study, the channel capacity performance of a dual‐hop asymmetric radio‐frequency–free space optical (RF–FSO) communication system in the presence of pointing errors is presented. Here, both fixed‐gain amplify and forward (AF) and decode and forward (DF) relays are considered. The RF link experiences Rayleigh fading and the FSO link experiences Málaga distributed turbulence channel. For this mixed RF–FSO cooperative system, novel mathematical expressions for cumulative distributive function (CDF) and the channel capacity are derived and performance is analysed with both fixed‐gain AF and DF relays in the presence of pointing errors. In addition, the authors derive the asymptotic expressions for the CDF and the channel capacity derived earlier in terms of Meijer's G function in the high signal‐to‐noise ratio regime.

In this paper, the transmission of confidential messages through single-input multiple-output (SIMO) independent and identically generalized- K ( K G ) fading channels is considered, where the eavesdropper overhears the transmission from the transmitter to the receiver. Both the receiver and the eavesdropper are equipped with multiple antennas, and both active and passive eavesdroppings are considered where the channel state information of the eavesdropper’s channel is or is not available at the transmitter. The secrecy performance of SIMO K G systems is investigated. Analytical expressions for secrecy outage probability and average secrecy capacity of SIMO systems are derived via two different methods, in which K G distribution is approximated by the Gamma and mixture Gamma distributions, respectively. Numerical results are presented and verified via the Monte-Carlo simulation.

In this letter, we consider a single-input multiple-output cognitive wiretap system over generalized-K channels, where the eavesdropper overhears the transmission from the secondary transmitter (ST) to the legitimate receiver. Both the primary user and the ST are equipped with a single antenna, whereas the legitimate and the eavesdropper receivers are equipped with multiple antennas. The close-form expression for the secrecy outage probability is derived. Simulations are presented to validate the accuracy of our proposed analytical results.

In this work, we present a unified performance analysis of a free-space optical (FSO) link that accounts for pointing errors and both types of detection techniques [i.e., intensity modulation/direct detection (IM/DD) and heterodyne detection]. More specifically, we present unified exact closed-form expressions for the cumulative distribution function, the probability density function, the moment generating function, and the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system, all in terms of the Meijer's G function except for the moments that is in terms of simple elementary functions. We then capitalize on these unified results to offer unified exact closed-form expressions for various performance metrics of FSO link transmission systems, such as the outage probability, the scintillation index (SI), the average error rate for binary and $M$-ary modulation schemes, and the ergodic capacity (except for IM/DD technique, where we present closed-form lower bound results), all in terms of Meijer's G functions except for the SI that is in terms of simple elementary functions. Additionally, we derive the asymptotic results for all the expressions derived earlier in terms of Meijer's G function in the high SNR regime in terms of simple elementary functions via an asymptotic expansion of the Meijer's G function. We also derive new asymptotic expressions for the ergodic capacity in the low as well as high SNR regimes in terms of simple elementary functions via utilizing moments. All the presented results are verified via computer-based Monte-Carlo simulations.

Capacity analysis of composite lognormal (LN) shadowed links, such as Rician-LN, Gamma-LN, and Weibull-LN, is addressed in this work. More specifically, an exact closed-form expression for the moments of the end-to-end signal-to-noise ratio (SNR) of a single composite link transmission system is presented in terms of well- known elementary functions. Capitalizing on these new moments expressions, we present asymptotically tight lower bounds for the ergodic capacity at high SNR. All the presented results are verified via computer-based Monte-Carlo simulations.

In this work, the performance analysis of digital communications over a composite Weibull-Gamma (WG) multipath-fading and shadowing channel is presented wherein WG distribution is appropriate for modeling fading environments when multipath is superimposed on shadowing. More specifically, in this work, exact closed-form expressions are derived for the probability density function, the cumulative distribution function, the moment generating function, and the moments of a composite WG channel. Capitalizing on these results, new exact closed-form expressions are offered for the outage probability, the higher- order amount of fading, the average error rate for binary and M-ary modulation schemes, and the ergodic capacity under various types of transmission policies, mostly in terms of Meijer's G functions. These new analytical results were also verified via computer-based Monte-Carlo simulation results.

In this work, we present a unified performance analysis of a free-space optical (FSO) link that accounts for pointing errors and both types of detection techniques (i.e. intensity modulation/direct detection as well as heterodyne detection). We, then, present unified exact closed-form expressions for various statistical characteristics of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system. We capitalize on these unified results to offer unified exact closed-form expressions for various performance metrics. Additionally, we derive the asymptotic results for all the expressions derived earlier in the high SNR regime in terms of simple elementary functions. We also derive new asymptotic expressions for the ergodic capacity in the low as well as high SNR regimes in terms of simple elementary functions via utilizing moments. All the presented results are verified via computer-based Monte-Carlo simulations.

In this work, we carry out a unified performance analysis of a dual-hop amplify-and-forward fixed gain relay system over asymmetric links composed of both radio-frequency (RF) and unified free-space optics (FSO) under the effect of pointing errors. The RF link is modeled by the Nakagami-m fading channel and the FSO link by the Gamma-Gamma fading channel subject to both types of detection techniques (i.e. heterodyne detection and intensity modulation with direct detection (IM/DD)). In particular, we derive new unified closed-form expressions for the cumulative distribution function, the probability density function, the moment generating function, and the moments of the end-to-end signal-to-noise ratio of these systems in terms of the Meijer's G function. Based on these formulas, we offer exact closed-form expressions for the outage probability, the higher-order amount of fading, and the average bit-error rate of a variety of binary modulations in terms of the Meijer's G function. Further, an exact closed-form expression for the end-to-end ergodic capacity for the Nakagami-m-unified FSO relay links is derived in terms of the extended generalized bivariate Meijer's G function. All the given results are verified via computer-based Monte-Carlo simulations.

Starting with the double generalized Gamma (GG) model to describe turbulence-induced fading in free-space optical (FSO) systems, we propose a new unified model that accounts for the impact of pointing errors and type of receiver detector. More specifically, we present unified closed-form expressions for the cumulative distribution function, the probability density function, the moment generating function, and the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system in terms of the Meijer's G-function. We then use these unified expressions to evaluate performance measures such as the bit error rate, the outage probability, and the ergodic capacity of: 1) a single FSO link operating over double GG fading model; and 2) asymmetric RF-FSO dual-hop relay transmission system with fixed gain relay. Using an asymptotic expansion of the Meijer's G-function at high SNR, we express all the expressions, derived earlier, in terms of elementary functions. All our analytical results are verified using computer based-Monte Carlo simulations.

A unified capacity analysis of a free-space optical (FSO) link that accounts for nonzero boresight pointing errors and both types of detection techniques (i.e. intensity modulation/direct detection as well as heterodyne detection) is addressed in this work. More specifically, an exact closed-form expression for the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system is presented in terms of well-known elementary functions. Capitalizing on these new moments expressions, we present approximate and simple closed-form results for the ergodic capacity at high and low SNR regimes. All the presented results are verified via computer-based Monte-Carlo simulations.

In this work, we carry out a unified performance analysis of a dual-branch transmission system composed of a direct radio-frequency (RF) link and a dual-hop fixed gain relay over the asymmetric links composed of both RF and unified free-space optics (FSO) under the effect of pointing errors. RF links are modeled by the Nakagami-m fading channel and the FSO link by the Gamma-Gamma fading channel subject to both types of detection techniques (i.e. heterodyne detection and intensity modulation with direct detection (IM/DD)). Selection combining (SC) and maximum ratio combining (MRC) diversity schemes are investigated. More specifically, for the SC method, we derive new unified closed-form expressions for the cumulative distribution function (CDF), the probability density function (PDF), the moment generating function (MGF), the moments, the outage probability (OP), the average bit-error rate (BER) of a variety of binary modulations, and the ergodic capacity for end-to-end signal-to-noise ratio (SNR). Additionally, using the MGF-based approach, the evaluation of the OP, the average BER, and the ergodic capacity for the MRC diversity technique can be performed based entirely on the knowledge of the MGF of the output SNR without ever having to compute its statistics (i.e. PDF and CDF). By implementing SC or MRC diversity techniques, we demonstrate a better performance of our system relative to the traditional RF path only. Also, our analysis illustrates MRC as the optimum combing method. All the analytical results are verified via computer-based Monte-Carlo simulations.

A unified capacity analysis under weak and composite turbulences of a free-space optical (FSO) link that accounts for pointing errors and both types of detection techniques (i.e. intensity modulation/direct detection as well as heterodyne detection) is addressed in this work. More specifically, a unified exact closed-form expression for the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system is presented in terms of well-known elementary functions. Capitalizing on these new moments expressions, unified approximate and simple closed- form results are offered for the ergodic capacity at high SNR regime as well as at low SNR regime. All the presented results are verified via computer- based Monte-Carlo simulations.

In this work, we derive the statistical characteristics of the maximum and the minimum of two modified1Gamma-Gamma variates in closed-form in terms of Meijer's G-function and the extended generalized bivariate Meijer's G-function. Then, we rely on these new results to present the performance analysis of (i) a dual-branch free-space optical selection combining diversity undergoing independent but not necessarily identically distributed Gamma-Gamma fading under the impact of pointing errors and of (ii) a dual-hop free-space optical relay transmission system. Computer-based Monte-Carlo simulations verify our new analytical results.

In this work, we present the performance analysis of a dual-hop transmission system composed of asymmetric radio frequency (RF) and free-space optical (FSO) links in underlay cognitive networks. For the RF link, we consider an underlay cognitive network where the secondary users share the spectrum with licensed primary users, where indoor femtocells act as a practical example for such networks. More specifically, we assume that the RF link is subject to an interference constraint. The FSO link accounts for pointing errors and both types of detection techniques (i.e. intensity modulation/direct detection (IM/DD) as well as heterodyne detection). On the other hand, RF link is modeled by the Rayleigh fading distribution that applies power control to maintain the interference at the primary network below a specific threshold whereas the FSO link is modeled by a unified Gamma-Gamma fading distribution. With this model, we derive new exact closed-form expressions for the cumulative distribution function, the probability density function, the moment generating function, and the moments of the end-to-end signal-to-interference plus noise ratio of these systems in terms of the Meijer's G functions. We then capitalize on these results to offer new exact closed-form expressions for the outage probability, the higher-order amount of fading, and the average error rate for binary and Mary modulation schemes, all in terms of Meijer's G functions. All our new analytical results are verified via computer-based Monte-Carlo simulations and are illustrated by some selected numerical results.

The probability density function (PDF) and cumulative distribution function of the sum of L independent but not necessarily identically distributed squared η-μ variates, applicable to the output statistics of maximal ratio combining (MRC) receiver operating over η-μ fading channels that includes the Hoyt and the Nakagami-m models as special cases, is presented in closed-form in terms of the Fox's H-bar function. Further analysis, particularly on the bit error rate via PDF-based approach, is also represented in closed form in terms of the extended Fox's H-bar function (H-hat). The proposed new analytical results complement previous results and are illustrated by extensive numerical and Monte Carlo simulation results.

In this work, the performance analysis of a dual-hop relay transmission system composed of asymmetric radio-frequency (RF)/free-space optical (FSO) links is presented. This work is based on the fact that FSO links are cost-effective, license-free and can provide even higher bandwidths compared to the traditional RF links. More specifically, in this work, we build on the cumulative distribution function presented in [1] to derive new exact closed-form expressions for the probability density function, moment generating function, and moments of the end-to-end signal-to-noise ratio. We then capitalize on these results to offer new exact closed-form expressions for the higher-order amount of fading, average error rate for binary and M-ary modulation schemes, and ergodic capacity, all in terms of Meijer's G functions. Our new analytical results were also verified via computer-based Monte-Carlo simulation results.

In this work, the performance analysis of a dual-hop relay transmission system composed of asymmetric radio-frequency (RF) and unified free-space optical (FSO) links subject to pointing errors is presented. These unified FSO links account for both types of detection techniques (i.e. indirect modulation/direct detection (IM/DD) as well as heterodyne detection). More specifically, we derive new exact closed-form expressions for the cumulative distribution function, probability density function, moment generating function, and moments of the end- to-end signal-to-noise ratio of these systems in terms of the Meijer's G function. We then capitalize on these results to offer new exact closed-form expressions for the outage probability, higher-order amount of fading, average error rate for binary and M-ary modulation schemes, and ergodic capacity, all in terms of Meijer's G functions. All our new analytical results are verified via computer-based Monte-Carlo simulations.

Error performance is one of the main performance measures and the derivation of its closed-form expression has proved to be quite involved for certain systems. In this paper, a unified closed-form expression, applicable to different binary modulation schemes, for the bit error rate of dual-branch selection diversity based systems undergoing independent but not necessarily identically distributed generalized-K fading is derived in terms of the extended generalized bivariate Meijer G-function.

Error performance is one of the main performance measures and the derivation of its closed-form expression has proved to be quite involved for certain communication systems operating over composite fading channels. In this letter, a unified closed-form expression, applicable to different binary modulation schemes, for the bit error rate of dual-branch selection diversity based systems undergoing independent but not necessarily identically distributed generalized-K fading is derived in terms of the extended generalized bivariate Meijer G-function.