This paper explores the energy efficiency (EE) of integrated sensing and communication (ISAC) systems employing massive multiple-input multiple-output (mMIMO) techniques to leverage spatial beamforming gains for both communication and sensing. We focus on an mMIMO-ISAC system operating in an orthogonal frequency-division multiplexing setting with a uniform planar array, zero-forcing downlink transmission, and mono-static radar sensing to exploit multi-carrier channel diversity. By deriving closed-form expressions for the achievable communication rate and Cramér-Rao bounds (CRBs), we are able to determine the overall EE in closed-form. A power allocation problem is then formulated to maximize the system’s EE by balancing communication and sensing efficiency while satisfying communication rate requirements and CRB constraints. Through a detailed analysis of CRB properties, we reformulate the problem into a more manageable form and leverage Dinkelbach’s and successive convex approximation (SCA) techniques to develop an efficient iterative algorithm. A novel initialization strategy is also proposed to ensure high-quality feasible starting points for the iterative optimization process. Extensive simulations demonstrate the significant performance improvement of the proposed approach over baseline approaches. Results further reveal that as communication spectral efficiency rises, the influence of sensing EE on the overall system EE becomes more pronounced, even in sensing-dominated scenarios. Specifically, in the high ω regime of 2 × 10−3, we observe a 16.7% reduction in overall EE when spectral efficiency increases from 4 to 8 bps/Hz, despite the system being sensing-dominated.

Bushfires across remote areas can easily spread regionally due to extreme weather conditions. Unmanned aerial vehicles (UAVs) can play a significant role in postdisaster assessment as they have low-cost and flexible deployment characteristics. Detecting bushfires in their initial phase is important to save the inhabitants, infrastructure, and ecosystem. In the context of smart cities, we have applied state-of-the-art deep learning (DL) algorithms to detect and differentiate between fire and no-fire regions. However, certain factors like reachability to forest fires and timely detection of the region of interest (ROI) are quite challenging. Therefore, we incorporate UAVs for capturing the real-time images and process these images into our proposed YOLOv5-s (you only look once-small) model that helps achieve fast and accurate detection of the affected region. We have proposed a lightweight single-stage network with an improved bottleneck cross-stage partial (CSP) module and pyramid attention network (PAN) layers to enhance precise feature extraction and reduce computation time in fire detection. Notably, the HardSwish activation function outperformed ReLU in a specific fire detection scenario. Based on the provided dataset, simulation results demonstrate that the optimized model can effectively detect and differentiate between fire and nonfire regions, which may be challenging to discern with the naked eye. The results indicate that the proposed model surpasses existing models, achieving an accuracy of 97.4%, a low false-positive rate of 1.258%, and nonmaximum suppression (NMS) of 3 ms. Our model can provide real-time applications for fire and rescue relief teams.

A corrugated horn antenna is proposed for the unmanned aerial vehicle energy transmitter (UAV-ET) application. Firstly, the proposed antenna can be manufactured using polylactic acid (PLA) 3-dimensional (3-D) printing with copper conductive paint coating, which is lightweight and cost-effective compared to metal 3-D printing. Secondly, the results confirm that the sidelobe level of the antenna is below -30 dB, and radiation efficiency is above 99 % throughout the operating frequency band. Also, the proposed antenna increases the UAV-ET wireless power transfer (WPT) time by 47.5 % and 4.5 % compared to UAV-ETs equipped with a dipole array and a slotted waveguide array respectively. Furthermore, the mass production of the antenna is easy because of its design simplicity which is highly desirable for the large swarm of UAV-ETs to increase the wireless power transfer coverage for charging ground sensors.

Abstract This paper investigates intelligent reconfigurable surface‐assisted non‐orthogonal multiple access (NOMA) networks for short packet communications where the source with multiple antennas utilizes beamforming technology to serve two end users including a near user and a far user. The analysis system, closed‐form expressions of the average block error rates (BLERs), latency and reliability at all users are derived under assuming perfect channel state information over quasi‐static Rayleigh fading channels. For evaluating the improvement of the network system, a deep neural network (DNN) framework is designed to predict the performance parameters in two cases: (i) BLERs prediction of the users, (ii) transmit power allocation under the constraints of BLERs at each user which satisfy the extremely high reliability requirements of uRLLCs. The extensive results demonstrate that first, the DNN‐based estimation results are more accurate than Monte‐Carlo simulation results with low execution time. Second, the allocated power for each user can be accurately predicted at the high layers. Finally, two methods of evaluating the effectiveness of the DNN model, i.e. root mean square error and mean absolute percentage error, reach low error which verify the power of the designed DNN model for future analysis.

A ground base station (GBS) antenna array system (AAS) geometry and feed technique are proposed for 360° azimuth beam scan, elevation beam scan, azimuth beam-width control, elevation beam-width control, and in existing AASs these four capabilities do not coexist. First, the results confirm that the number of active radio-frequency (RF) switches in the proposed AAS feed network is reduced by more than 99%, and the AAS achieves a power consumption reduction of up to 50% without fully connected (FC) architecture and 35% with FC architecture compared to the existing AAS. Also, an independent GBS AAS azimuth and elevation plane beam-width control can be achieved from 65° to 0.01° which makes it suitable for GBS-assisted wireless back-hauling plus wireless charging of unmanned aerial vehicle base stations (UAV-BSs), dynamic GBS sectorisation order control, and millimeter wave beam tracking. Also, a parallel concurrent UAV-BS battery charging configuration with power source swap capability is proposed to charge UAV-BS using the GBS back-haul and onboard power amplifier (PA) system as the power sources. The results show that the proposed charging configuration improves hovering time by 180.7% compared to the existing onboard PA system configuration for battery charging. Furthermore, the proposed charging configuration can recharge the battery of the inactive state UAV-BS to increase the state of charge of two 16-Ah batteries to 80% in 180.13 min, and UAV-BS’s inactive state charging was not proposed in the existing onboard PA system configuration for UAV-BS’s battery charging.

This paper offers unified modelling for opportunistic-relay outdatedness using the joint distribution of bivariate exponential-correlated generalised-Rician fading. Line-of-sight power and larger-than-two degrees of freedom under independently-and-identically-distributed Rayleigh fading environments employing maximal ratio combining (MRC) are considered. Unavoidable infinite summations are employed, which are shown to fast-converge for a finite number of terms. Ergodic channel capacity is employed for performance assessment. Thorough comparisons between performance of selection combining and MRC are also given. Monte Carlo simulation is employed to validate this work.

Infrastructure-to-vehicle (I2V) and vehicle-to-vehicle (V2V) communications are often combined to extend the connectivity and coverage in the Intelligent Transportation System (ITS) and its applications, e.g., augmented reality, real-time parking management and online shopping. Through multi-hop I2V and V2V communications, requesting vehicles are always connected to road side units (RSUs) even when they do not reside within the RSUs’ coverage range. However, there may be not adequate network resource for several I2V and V2V links when multiple vehicles request services simultaneously. In this paper, we propose a joint frequency scheduling and power control scheme to enhance connectivity in multi-hop I2V/V2V networks. We associate I2V and V2V links with tuple-links, then formulate an NP-hard problem in which a frequency scheduler and a power controller are jointly designed for the tuple-links. The NP-hard problem is decomposed into two separate subproblems by employing the delayed column generation technique. Then, we employ a method for linear programming and a greedy algorithm to address these subproblems. Through numerical experiments with practical parameter settings, we demonstrate the proposed scheme outperforms several existing ones in terms of connectivity enhancement, measured by the service resumption number and average achieved throughput. Furthermore, the efficiency of our scheme is further enhanced when the number of available channels is high, and buffer size equipped to the requesting vehicles is large.

In this paper, we propose a downlink cognitive underlay relay networks with non-orthogonal multiple access (CR-NOMA), where a secondary source node communicates with two secondary destination nodes with the help of multi secondary relays. We derive exact expressions of the outage probability for two secondary destination nodes with fixed relaying and partial relay selection. The effect of imperfect channel state information on partial relay selection is also investigated. The provided numerical results confirm that the derived expressions for the outage probabilities are in excellent agreement with the Monte-Carlo simulations.

Using a well-known wiretap model, secrecy outage probability is computed under dual correlated Rician fading employing opportunistic relays. A signal-to-noise ratio distribution of dual correlated Rician fading is first obtained as a function of four nested infinite summations, which (i) converges for a finite number of terms, and (ii) is employed to compute secrecy outage probability for a passive wiretapper. Relationships among important parameters are elaborated and explained. Proof for infinite summation convergence is also given, which realises the practicality of this work. Simulation results are shown to match theoretical predictions.

In this paper, a random cognitive radio networks schemes combined with Non-orthogonal Multiple Access (NOMA) is investigated. In the proposed protocol, relying on the channel gains, a secondary source selects two best secondary destinations to transmit the data. For performance evaluation and comparison, we derive exact and asymptotic closed-form expressions of outage probability (OP) over Rayleigh fading channel. Finally, Monte-Carlo simulations are performed to verify the theoretical results.

In this paper, we evaluate the end-to-end outage probability of multi-hop cooperative transmission networks, where transmitters including source and relay nodes are powered by a power beacon. In multi-hop cooperative transmission networks, the active relay, which successfully decodes the data and is nearest to the destination, is selected to re-encode and forward the encoded data to the destination. For performance analysis, we employ the recursive method to obtain the exact closed form expression of the system outage probability over Rayleigh fading channels. Monte Carlo simulations is used to verify the analysis approach and is to confirm the advantage of the proposed networks over multi-hop direct transmission networks.

This paper studies the performance of multi-hop cognitive wireless powered communication networks (WPCNs), where secondary nodes can harvest energy from multiple dedicated power beacons and access spectrum of primary receivers (PRs) to support data transmission. Specifically, we consider a practical scenario of cognitive WPCNs, where the channel state information (CSI) of interference links is assumed to be imperfect. To improve the network performance, we propose dual-hop scheduling scheme (DHS) for multi-hop network, where two best relays in two consecutive clusters are selected for data transmission. We then analyze the performance of the proposed scheme in terms of outage probability and outage floor. Numerical results show that DHS scheme outperforms random scheduling scheme, arising as an efficient scheme for multi-hop transmission. Furthermore, the effects of the number of hops, number of power beacons, and time switching ratio on multi-hop cognitive WPCNs are evaluated and discussed.

This study investigates two‐way relaying where an energy harvesting capable relay exchanges information between two sources. Legitimate information is wire‐tapped by an eavesdropper. To intercept wire‐tapping, this study exploits a friendly jammer. Secrecy outage analysis of the energy harvesting two‐way relaying network with the friendly jammer over Rayleigh fading channels is first proposed in terms of individual secrecy outage probabilities and then validated by computer simulations. Various results demonstrate the efficacy of the jammer in preventing the eavesdropper from stealing the source information and significant impacts of relay location, jammer location, jammer's transmit power, energy conversion efficiency, time switching ratio on the security performance.

In this study, the authors study secure multiuser transmission in a massive multiple‐input multiple‐output (MIMO) relaying system, where a base station sends its messages to multiusers via an amplify‐and‐forward relay station. Beamforming matrices of maximum ratio combining/maximum ratio transmission (MRC/MRT) and zero‐forcing reception/zero‐forcing transmission (ZFR/ZFT) at relay are considered. The authors derive exact and asymptotic expressions for user rate and outage secrecy rate for a predetermined secure outage probability of eavesdropper links with channel state information imperfection. They have shown that ZFR/ZFT is a better choice than MRC/MRT from the perspectives of secrecy performance. Furthermore, the asymptotic analysis is proposed to show that almost the eavesdropper rates in all cases are degraded as a number of relay antennas goes to infinity, and simultaneously the transmit power at the base station and the relay can be scaled down significantly. Finally, numerical results provide more insightful validity of the proposed analysis.

In this study, the authors consider a two‐way amplify‐and‐forward communication system over Nakagami‐ m fading environments, where an intermediate relay node harvests energy from its surrounding radio frequency environment using an energy harvesting technique. They propose a novel derivation approach to obtain exact expressions for user outage probability, system outage probability, and upper bound on system ergodic capacity per unit bandwidth over Nakagami‐ m fading channels. Monte–Carlo simulation results under Matlab software packages match the proposed analytical analyses confirming the correctness of the proposed derivation approach and the advantage of the system under consideration.

This study is concerned with outage performance analysis of a cognitive two‐way relay system having a primary network of one transmitter and multiple receivers over Nakagami‐ m fading channels. In the considered cognitive radio system, the secondary network facilitates information exchange between source nodes with the aid of multiple decode‐and‐forward two‐way relays. In the presence of multiple relays, opportunistic relay selection is employed to obtain a relay with the best channel quality for reliable information recovery. To analyse the performance of the considered cognitive radio system, exact and asymptotic closed‐form expressions of outage probability (OP) are derived in this study. The derived theoretical OP expressions are in good agreement with related empirical values which show that using relays can enhance the performance of secondary networks without sacrificing that of the primary network.

In this paper, we analyze the downlink outage performance of opportunistic scheduling in dual-hop cooperative networks consisting of one source, multiple radio-frequency energy harvesting relays, and multiple destinations. To this end, two low-complexity, suboptimal, yet efficient, relay-destination selection schemes are proposed, namely direct links plus opportunistic channel state information (CSI)-based selection (DOS) scheme and direct links plus partial CSI-based selection (DPS) scheme. Considering three relaying strategies, i.e., decode-and-forward (DF), variable-gain amplify-and-forward (VG-AF), and fixed-gain amplify-and-forward (FG-AF), the performance analysis in terms of outage probability (OP) is carried out for each selection scheme. For the DF and VG-AF strategies, exact analytical expressions and tight closed-form approximate expressions for the OP are derived. For the FG-AF strategy, an exact closed-form expression for the OP is provided. Additionally, we propose a gradient-based search method to find the optimal values of the power-splitting ratio that minimizes the attained OPs. The developed analysis is corroborated through Monte Carlo simulation. Comparisons with the optimal joint selection scheme are performed and it is shown that the proposed schemes significantly reduce the amount of channel estimations while achieving comparable outage performance. In addition, regardless of relaying strategy used, numerical results show that the DOS scheme achieves full diversity gain, i.e., M + K, and the DPS scheme achieves the diversity gain of M+1, where M and K are the numbers of destinations and relays, respectively.

This is a Special Issue of IET Communications: ‘Green Computing and Telecommunications Systems,’ published in association with the 3rd International Conference on Computing, Management and Telecommunications (ComManTel 2015). There were 30 submissions to the issue, ranging across the subject of green computing and networks. These spanned emerging technologies and methods for green computing, to green wireless and multimedia telecommunications networks, resource allocation, and test-beds for green telecommunication networks. This Special Issue comprises 9 papers (3 of which were extended from papers presented at ComManTel 2015 and invited to submit to the special issue) which were chosen for publication after a rigorous peer review and selection process. The accepted papers cover the energy-efficiency aspects of telecommunications systems, address the requirement for minimising consumed resources whenever possible, propose approaches for green connected energy as well as presenting designs for components of a green wireless system. The paper entitled “Uplink training for multicell massive multiple-input–multiple-output systems: A combination of time-shifted and time-aligned pilot approaches” by H. V. Nguyen, V.-D. Nguyen and O.-S. Shin proposes two schemes to mitigate the effect of pilot contamination with the aim to improve the achievable uplink and downlink rates in a multicell massive multiple-input–multiple-output (MIMO) system. Their results show that the two proposed strategies significantly improve both the achievable uplink and downlink rates when compared with those of a conventional time-aligned pilot strategy and a previously proposed time-shifted pilot strategy. Considering cellular networks having multi-tier heterogeneous architectures in which the channel conditions change rapidly, D.-A. Le, H.V. Vu, M. Ranjbar, N.H. Tran, T. Karacolak and T.-M. Hoang in the paper “On the capacity and energy efficiency of non-coherent Rayleigh fading channels with additive Gaussian mixture noise” examine the capacity and energy efficiency of non-coherent Rayleigh fading channels with Gaussian mixture noise where neither the transmitter nor the receiver has the knowledge of channel state information. The energy efficiency, which is related to the capacity and optimal input in low-power regimes, is examined by calculating the minimum bit energy and wideband slope of the spectral-efficiency curve. Q.-T. Vien, T.A. Le, B. Barn and C.V. Phan adopt non-orthogonal multiple access (NOMA) and propose power allocation for the wireless downlink of a cloud-based central station to multiple base stations in a heterogeneous cloud radio access network (HCRAN) sharing the same time and frequency resources. The energy efficiency of the practical HCRAN utilising NOMA is analysed taking into account practical channel modelling with power consumptions at base stations of different cell types (e.g. macrocell, microcell etc.) and backhauling power. These results are presented in the paper “Optimising energy efficiency of non-orthogonal multiple access for wireless backhaul in heterogeneous cloud radio access network.” For the potential of fully cooperative OFDM in the design of emerging low power applications, such as a wireless body area network comprising wearable computing devices, L.C. Tran and A. Mertins present an analysis of decode-and-forward, space-time coded, fully cooperative OFDM systems from both error performance and energy efficiency perspectives, in identically/non-identically distributed frequency selective Rayleigh fading channels. Results from their paper “Error performance and energy efficiency analyses of fully cooperative OFDM communication in frequency selective fading” demonstrate that the fully cooperative OFDM outperforms direct OFDM transmission with respect to error performance and energy efficiency in many cases. In their paper entitled ‘’Energy efficient medium access scheme for visible light communication system based on IEEE 802.15.7 with unsaturated traffic’’ H. Liu, L. Zhang and M. Jiang propose a medium access scheme for reducing power consumption and improving the random channel access mechanism for multiuser visible light communication (VLC) networks under unsaturated traffic conditions. The proposed scheme is shown to outperform the IEEE 802.15.7 CSMA/CA scheme in terms of average power consumption, system throughput and packet dropping probability. N.-S. Vo, D.-B. Ha, B. Canberk and J. Zhang propose an energy, bandwidth, and quality (EBQ) optimisation framework for green two-tiered wireless multimedia sensor systems, where the first tier contains the camera sensors and the second includes cluster heads selected from the camera sensors with higher available energy and processing capacity. These results are presented in the paper “Green two-tiered wireless multimedia sensor systems: An energy, bandwidth, and quality optimisation framework.” The next two papers in the issue consider energy harvesting techniques in cooperative and cognitive networks. N.T. Do, D.B. da Costa and B. An consider the joint impact of energy harvesting technique and transceiver hardware impairment on the outage performance of multirelay decode-and-forward cooperative networks in their paper “Performance analysis of multirelay RF energy harvesting cooperative networks with hardware impairments”. It is shown that the “harvested energy-based relay selection” scheme achieves a diversity order of 1 and is independent of the relay numbers, while the “channel quality-base relay selection” scheme achieves full diversity. The paper “Impact of primary networks on the performance of energy harvesting cognitive radio networks” by Jinghua Zhang, N.-P. Nguyen, Junqing Zhang, E. Garcia-Palacios and N.P. Le examines the influence of the primary transmitter's transmit power on the energy harvesting secondary network in the presence of multiple power beacons and multiple secondary transmitters. Results reveal that the influence is negative in both the near/far scenarios of the primary transmitter's location to the secondary network. However, it can be alleviated by increasing the number of power beacons and primary transmitters. The paper “Design of compact frequency reconfigurable planar invert-F antenna for green wireless communications” proposes a single frequency reconfigurable planar invert-F antenna (FRPIFA) using PIN diodes based on the changes of shorting pin positions. H.T.P. Thao, V.T. Luan and V.V. Yem also present a frequency reconfigurable multiple-input multiple-output (MIMO) antenna consisting of two single reconfigurable ones with a distance of half-wavelength, which is shown to achieve a high isolation in all operating bands. The proposed compact single and MIMO antennas are demonstrated as suitable for green wireless communication systems. Trung Q. Duong (S′05, M′12, SM′13) received his Ph.D. degree in Telecommunications Systems from Blekinge Institute of Technology (BTH), Sweden in 2012. Since 2013, he has joined Queen's University Belfast, UK as a Lecturer (Assistant Professor). His current research interests include physical layer security, energy-harvesting communications, and cognitive relay networks. He is the author or co-author of more than 230 technical papers published in scientific journals (116 articles) and presented at international conferences (114 papers). Dr. Duong currently serves as an Editor for IEEE Transactions on Wireless Communications, IEEE Transactions on Communications, IEEE Communications Letters and IET Communications. He was an editor of Wiley Transactions on Emerging Telecommunications Technologies, Electronics Letters and has also served as the Guest Editor of Special Issues in some major journals including IEEE Journal in Selected Areas on Communications, IET Communications, IEEE Access, IEEE Wireless Communications Magazine, IEEE Communications Magazine, EURASIP Journal on Wireless Communications and Networking and EURASIP Journal on Advances Signal Processing. He was awarded the Best Paper Award at the IEEE Vehicular Technology Conference (VTC-Spring) in 2013, and the IEEE International Conference on Communications (ICC) 2014. He is the recipient of the prestigious Royal Academy of Engineering Research Fellowship (2016–2021). Vo Nguyen Quoc Bao (SMIEEE) is an associate professor of Wireless Communications at the Posts and Telecommunications Institute of Technology (PTIT), Vietnam. He also served as Dean of the Faculty of Telecommunications and as Director of the Wireless Communication Laboratory (WCOMM). His research interests include wireless communications and information theory with current emphasis on MIMO systems, cooperative and cognitive communications, physical layer security, and energy harvesting. He has published more than 140 journal and conference articles that have 1300+ citations and H-index of 20. He is an Editor of Transactions on Emerging Telecommunications Technologies (Wiley ETT), VNU Journal of Computer Science and Communication Engineering, and REV Journal on Electronics and Communications. He is also a Guest Editor of a EURASIP Journal on Wireless Communications and Networking “Special Issue:Cooperative Cognitive Networks” and an IET Communications “Special Issue: Secure Physical Layer Communications”. He served as a Technical Program co-chair for ATC (2013, 2014), NAFOSTED-NICS (2014, 2015, 2016), REV-ECIT 2015, ComManTel (2014, 2015), and SigComTel 2017. He is a Member of the Executive Board of the Radio-Electronics Association of Vietnam (REV) and the Electronics Information and Communications Association Ho Chi Minh City (EIC). He is currently serving as a scientific secretary of the Vietnam National Foundation for Science and Technology Development (NAFOSTED) scientific Committee in Information Technology and Computer Science. Mohsen Guizani (S′85–M′89–SM′99–F′09) received B.S. (with distinction) and M.S. degrees in electrical engineering, M.S. and Ph.D. degrees in computer engineering from Syracuse University, Syracuse, NY, USA, in 1984, 1986, 1987, and 1990, respectively. He is currently a professor and Electrical and Communications Engineering Department Chair at the University of Idaho. Previously, he was Professor and Associate Vice President of Graduate Studies at Qatar University, Doha, Qatar, served as Chair of the Computer Science Department, Western Michigan University, Kalamazoo, MI, USA, from 2002 to 2006, and Chair of the Computer Science Department, University of West Florida, Pensacola, FL, USA, from 1999 to 2002. He also served in academic positions at the University of Missouri- Kansas City, Kansas City, MO, USA, University of Colorado-Boulder, Boulder, CO, USA, Syracuse University, and Kuwait University, Kuwait City, Kuwait. His research interests include wireless communications and mobile computing, computer networks, mobile cloud computing, and smart grid. He currently serves on the Editorial Boards of many international technical journals and is the Founder and Editor-in-Chief of Wireless Communications and Mobile Computing journal (Wiley). He is the author of nine books and more than 400 publications in refereed journals and conferences. He has guest edited a number of Special Issues in IEEE journals and magazines. He has also served as member, Chair, and General Chair of a number of conferences. He was selected as the Best Teaching Assistant for two consecutive years at Syracuse University (1988 and 1989). He was the Chair of the IEEE Communications Society Wireless Technical Committee and the Chair of the TAOS Technical Committee. He served as the IEEE Computer Society Distinguished Speaker from 2003 to 2005.

In this paper, we propose a high-speed wireless signal transmission over a simple analog intensity modulation/direct detection (IM/DD) fiber-millimeter-wave (MMW) system at 92.5 GHz. The system employs a frequency and phase stabilized optical MMW signal generation at transmitter and a simple direct detection at receiver. We confirm a successful transmission of 10-Gb/s 16-QAM OFDM-based wireless signal over a seamless 8-km SMF and 27-cm 92.5-GHz wireless system. To further increase the fiber transmission range, we use a simple adaptive modulation approach. Successful transmission over 10-km single mode fiber (SMF) system is confirmed for a 8.1 Gb/s wireless signal using both 16-QAM and QPSK modulation. We also estimate the maximum transmission range for the MMW link, and it is proved that a transmission over a 1-km MMW link can be achieved. Both the confirmed fiber length and estimated MMW range are sufficiently long for future mobile front-haul systems in next-generation wireless networks. The system therefore can provide a high-speed, low-latency, and flexible solution for front-hauling in new emerging wireless systems such as 5G mobile networks.

In this study, the authors evaluate secrecy performance of cooperative protocols with relay selection methods under impact of co‐channel interference. In particular, the authors propose an optimal selection scheme to maximise the secrecy capacity obtained at the cooperative phase. In addition, the authors also consider suboptimal and random selection schemes which reduce the complexity of implementation, when compared with the optimal one. For performance evaluation, the authors derive exact and asymptotic closed‐form expressions of secrecy outage probability and probability of non‐zero secrecy capacity for the considered schemes over Rayleigh fading channels. Monte Carlo simulations are performed to validate the derivations.

In this paper, we investigate the end-to-end performance of dual-hop proactive decode-and-forward relaying networks with Nth best relay selection in the presence of two practical deleterious effects: i) hardware impairment and ii) co-channel interference. In particular, we derive new exact and asymptotic closed-form expressions for the outage probability and average channel capacity of Nth best partial and opportunistic relay selection schemes over Rayleigh fading channels. Insightful discussions are provided. It is shown that, when the system cannot select the best relay for cooperation, the partial relay selection scheme outperforms the opportunistic method under the impact of the same co-channel interference (CCI) . In addition, without CCI but under the effect of hardware impairment, it is shown that both selection strategies have the same asymptotic channel capacity. Monte Carlo simulations are presented to corroborate our analysis.

Cooperative spatial multiplexing (CSM) system has played an important role in wireless networks by offering a substantial improvement in multiplexing gain compared with its cooperative diversity counterpart. However, there is a limited number of research works that consider the performance of CSM systems. As such, in this paper, we have derived exact performance of CSM with amplify-and-forward and decode-and-forward relays in terms of outage capacity and ergodic capacity. We have shown that CSM systems yield a unity diversity order regardless of the number of antennas at the destination and the number of relays in the networks, which is the direct result of diversity and multiplexing gain trade-off. Our analytical expressions are corroborated by Monte-Carlo simulations

In this paper, we investigate the performance of Nth best relay selection networks with secrecy constraints where several eavesdroppers try to overhear the source message. In order to enhance the network security, a single jammer is introduced to jam the eavesdroppers. In addition, sub-optimal selection strategy is introduced to combat the malicious attempt of eavesdroppers. We derive the exact secrecy performance in terms of probability of the non-zero secrecy capacity and the secrecy outage probability of the proposed relay selection approach. Based on these expressions, the effect of several important network parameters, i.e., the number of relays and the number of eavesdroppers, as well as the quality of the relay links, jammer links, and eavesdroppers links, on the proposed network are analytically characterized.

Distributed switch-and-stay combining (DSSC) has been envisioned as an effective transmission technique to achieve spatial diversity in a distributed fashion, with low implementation complexity. In this paper, we take a step further to incorporate DSSC into spectrum-limited environment, where the operating nodes have to share the frequency radio spectrum with licensed users. In particular, by deploying DSSC scheme in cognitive radio networks, we have shown that the low transmit power at unlicensed users, inflicted by the peak interference power constraint at licensed users, can be alleviated. We present closed-form expressions for outage probability and spectral efficiency, enabling us to evaluate and optimize the considered network performance. Numerical and simulation results show that when the switching threshold is below the outage threshold the full diversity order can be guaranteed at the secondary networks.

Cognitive relay technology has been envisioned as a promising transmission scheme to enhance the reliability and coverage of secondary networks. However, the performance of cognitive relay networks (CRNs) is limited by the lack of accurate channel state information (CSI). As such, this paper adequately addresses the impact of imperfect CSI on the performance of cognitive multihop networks by proposing a simple yet effective backoff control power method. In addition, novel exact and asymptotic expressions for outage probability and ergodic capacity over Rayleigh fading channels are also derived. These tractable analytical results reveal new insight into the design, e.g., the number of hops for secondary network, and optimization of cognitive multihop networks.

Multihop network has been considered as a breakthrough frontier to enhance the coverage of wireless network. Spectrum-sharing is an efficient technique to enhance the utilization of the limited radio frequency bandwidth. In this paper, we therefore consider the extension of multihop network to cognitive radio networks with the spectrum sharing approach. In particular, we investigate the cognitive multihop networks in the presence of multiple licensed transmitters and receivers. Under the stringent power constraint imposed by the licensed users, we derive the closed-form and asymptotic expressions for the outage probability over Nakagami-m fading channels. The tractable closed-form expressions reveal the impact of important network parameters such as the fading severity parameters of the unlicensed network, the number of licensed users, the peak interference power imposed by the licensed receivers, the interference power from licensed transmitters. A significant observation corroborated by our study shows that the cognitive multihop networks benefit both cognitive radio and multihop networks for improving the coverage extension and frequency spectrum utilization.

This paper proposes and analyzes cognitive multihop decode-and-forward networks in the presence of interference due to channel estimation errors. To reduce interference on the primary network, a simple yet effective back-off control power method is applied for secondary multihop networks. For a given threshold of interference probability at the primary network, we derive the maximum back-off control power coefficient, which provides the best performance for secondary multihop networks. Moreover, it is shown that the number of hops for secondary network is upper-bounded under the fixed settings of the primary network. For secondary multihop networks, new exact and asymptotic expressions for outage probability (OP), bit error rate (BER) and ergodic capacity over Rayleigh fading channels are derived. Based on the asymptotic OP and BEP, a pivotal conclusion is reached that the secondary multihop network offers the same diversity order as compared with the network without back off. Finally, we verify the performance analysis through various numerical examples which confirm the correctness of our analysis for many channel and system settings and provide new insight into the design and optimization of cognitive multihop networks.

In this paper, we study opportunistic relay selection in cooperative networks with secrecy constraints, where a number of eavesdropper nodes may overhear the source message. To deal with this problem, we consider three opportunistic relay selection schemes. The first scheme tries to reduce the overheard information at the eavesdroppers by choosing the relay having the lowest instantaneous signal-to-noise ratio (SNR) to them. The second scheme is conventional selection relaying that seeks the relay having the highest SNR to the destination. In the third scheme, we consider the ratio between the SNR of a relay and the maximum among the corresponding SNRs to the eavesdroppers, and then select the optimal one to forward the signal to the destination. The system performance in terms of probability of non-zero achievable secrecy rate, secrecy outage probability and achievable secrecy rate of the three schemes are analyzed and confirmed by Monte Carlo simulations.

We examine the impact of multiple primary transmitters and receivers (PU-TxRx) on the outage performance of cognitive decode-and-forward relay networks. In such a joint relaying/spectrum-sharing arrangement, we address fundamental questions concerning three key power constraints: 1) maximum transmit power at the secondary transmitter (SU-Tx), 2) peak interference power at the primary receivers (PU-Rx), and 3) interference power at SU-Rx caused by the primary transmitter (PU-Tx). Our answers to these are given in new analytical expressions for the exact and asymptotic outage probability of the secondary relay network. Based on our asymptotic expressions, important design insights into the impact of primary transceivers on the performance of cognitive relay networks is reached. We have shown that zero diversity order is attained when the peak interference power at the PU-Rx is independent of the maximum transmit power at the SU-Tx.

Several diversity combining techniques have been proposed for multiple-input multiple-output (MIMO) systems, but only isolated performance comparisons have been reported. In this paper, we aim at comparing three MIMO schemes using selection combining (SC), maximal ratio combining (MRC) and switch-and-stay combining (SSC). It is analytically demonstrated that all the systems achieve full diversity gain with different coding gain. Besides, the performance gap between SC and MRC approaches to the limit and tends to increase linearly proportional to the number of transmit antennas. In case of SSC, the loss between SSC and SC, as well as between SSC and MRC, is not bounded as increasing signal-to-noise ratio (SNR).

In this paper, we analyze the performance of dual-hop channel state information (CSI)-assisted amplify-and-forward (AF) cooperative networks using orthogonal space-time block codes (OSTBCs) over independent but not identically distributed Nakagami-$m$ fading channels. Specifically, we present closed-form expressions of the outage probability (OP) and the symbol error probability (SEP). The analytical results are given in tractable forms which readily allow us to assess the performance of AF relay systems using OSTBCs. For sufficiently large signal-to-noise ratio, we obtain the asymptotic results for OP and SEP which reveal insights into the effect of fading factors on the diversity and coding gains. It has been shown that between the two hops the more severe link solely determines the diversity and coding gains. In particular, these two gains strictly depend on the fading severity parameters and the channel mean powers of the more rigorous hop, respectively. Numerical results are provided showing an excellent agreement between our analytical results and those of Monte-Carlo simulations for selected scenarios.

We analyze the performance of amplify-and-forward (AF) multiple-input multiple-output (MIMO) cooperative networks over independent but not identically distributed Nakagami-m fading channels. Specifically, we consider an AF MIMO relay network where the source deploys the transmit antenna selection scheme to communicate with the destination through the help of a relay. We derive analytical expressions for outage probability (OP) and symbol error probability (SEP). Moreover, asymptotically tight approximations for OP and SEP have been obtained to facilitate insights on how fading parameters affect the performance. Our analytical results are verified by Monte-Carlo simulations for respective scenarios.

In this paper, we investigate the average symbol error probability (SEP) of fixed decode-and-forward relay networks over independent but not identically distributed Nakagami-m fading channels. We have derived closed form expression of SEP for general rectangular quadrature amplitude modulation (QAM) under relay selection scheme where only the best relay forwards message from the source to the destination. The expressions are in terms of hypergeometric series which can be efficiently numerically evaluated. The numerical results are validated with Monte-Carlo simulations.

This paper offers a study on Rayleigh channel capacity of opportunistic cooperative networks in conjunction with adaptive transmission where the source adapts its rate and/or power level according to the changing channel conditions while the best relay simply amplifies and forwards the signals. To this end, the upper and lower bound of the end-to-end effective signal-to-noise ratio (SNR) for an arbitrary number of cooperative relays equipped amplify-and-forward protocol is derived and then used to derive the closed-form expressions of the system channel capacity under three different adaptive policies: optimal simultaneous power and rate adaptation (OPRA), constant power with optimal rate adaptation (OPA) and channel inversion with fixed rate (TIFR). Our results are verified through comparison with Monte Carlo simulations where we also illustrate that, among them, for an arbitrary number of relays, TIFR gives the worst channel capacity; OPRA gives the best channel capacity and ORA has a channel capacity quality in between the others.

A compact expression for pdf of SC combiner on independent but not necessarily identical distributed Rayleigh fading channels is derived. Using this expression, new exact-closed form expressions for average SER and average BER of M-PAM and M-QAM are studied. The proposed mathematical analysis is verified by various simulation results which demonstrate the accuracy of the theoretical approach.