This paper investigates an intelligent reflective surface (IRS) assisted secure multi-user two-way communication system. The aim of this paper is to enhance the physical layer security by optimizing the minimum secrecy-rate among all user-pairs in the presence of a malicious user. The optimization problem is converted into an alternating optimization problem consisting of two sub-problems. Transmit power optimization is handled using a fractional programming method, whereas IRS phase shift optimization is handled with semi-definite programming. The convergence of the proposed algorithm is investigated numerically. The performance gain in minimum secrecy-rate is quantified for four different user configurations in comparison to the baseline scheme. Results indicate a 3.6-fold gain in minimum secrecy rate over the baseline scheme when the IRS is positioned near a legitimate user, even when the malicious user is located close to the same legitimate user.

Unmanned aerial vehicles (UAVs)-assisted communication systems are considered as a promising technology in diverse verticals. This paper studies the deployment of UAVs in wireless sensor network (WSN) systems. Considering the energy-constrained nature of the wireless sensors , we have proposed a multi-UAV deployment algorithm that minimizes the maximum power transmitted among the sensor nodes (SN) for given minimum data collection rate, minimum data-transferring rate, maximum power and height constraints. The problem is divided into three subproblems in order to reduce the complexity involved in solving them as a single problem. The subproblems are UAV-SN association, 2D positioning of the UAVs and the altitude optimization of the UAVs. Each subproblem is optimized by fixing other parameters as constant. First, the UAV-SN association is addressed using a customized Gale–Shapley algorithm. Second, the 2D positions of the UAVs are optimized using a modified pattern search algorithm. Third, the altitudes of the UAVs are optimized through a customized inexact line search algorithm. Finally, we proposed a combined optimization algorithm that integrates the approaches of all three subproblems in the suitable hierarchy to provide an optimal or a near-optimal solution. In the combined optimization, the first and second subproblems are iteratively solved until the convergence. After that, the third subproblem is solved independently for each UAV. Moreover, the combined optimization gives the minimum number of UAVs required to serve all the SNs with the given rate and power constraints. The numerical simulation validates the efficacy of our proposed algorithms. The results indicate a significant performance gain compared to the benchmark methods in terms of the number of iterations for convergence, maximum transmission power requirement power and the minimum number of UAV requirements.

Cycling is a popular leisure and fitness activity, making it a prime candidate for emerging virtual and augmented reality applications. This paper details the design, development, and testing of a competitive virtual cycling platform that allows two players to compete regardless of their geographical location on customized stationary bicycles. They wear head-mounted Virtual Reality (VR) devices to immerse themselves in a 360° video experience. Video playback responds to their cycling speed and head orientation. Competitors' locations are displayed on a map within their VR dashboard. The platform's functionality is tested on 4G and 5G networks and an experimental 4G network implemented on software-defined radios. To evaluate the system's usability, the critical metric of end-to-end delay is measured for the different communication architectures. Delays of under 100ms, crucial for preventing motion sickness, are achievable for several scenarios. A novel approach is introduced to synchronize the start of the game to account for variable network latencies. A user experience survey is presented for feedback and improvement insights. Furthermore, improving the scalability of the platform to support multiple users is also discussed.

This paper proposes and analyzes a distance-based duplex mode switching scheme for maximizing the average throughput of a cellular network and its underlay device-to-device (D2D) network. For each duplex mode of the cellular network, a node distance based duplex mode selection scheme is proposed to maximize the throughput of the D2D network. The proposed duplex mode selection scheme provides average throughput improvements in the range of 10%-200% for the D2D network compared to the always half-duplex and always full-duplex communications for high D2D user scatter variances.

This paper presents an analytical framework to investigate the performance of full duplex (FD) device-to-device (D2D) networks where devices in a cluster are capable of caching popular content. Assuming spatially randomly distributed D2D users in the cluster where the users request for content according to the Zipf distribution, analytical expressions are derived for the device communication probability, coverage probability, cluster average spectral efficiency, and content average download latency of the system. The system performance metrics are derived for the three device operating modes of FD only mode, half duplex (HD) only mode, and mixed FD/HD mode. Numerical results show that the mixed FD/HD mode is the most appropriate communication mode for cache enabled FD D2D networks to achieve the highest cluster average spectral efficiency and low content average download latency.

A throughput analysis is conducted for a large scale peer-to-peer wireless network whose devices are capable of operating in both full- and half-duplex modes, using the tools of stochastic geometry. Each device selects its operating duplex mode based on the distance to its partner node. In both duplex modes, the energy consumption and the hardware configurations of the nodes are made equivalent for fair comparisons between full-duplex and half-duplex operations. Using the results of the analysis, an approach is proposed to determine a distance threshold value for duplex mode selection, and the proposed distance threshold can be computed offline. It is found that the throughput performance of the hybrid full-/half-duplex network generated with the proposed distance threshold based duplex mode selection technique outperforms both the pure half-duplex and pure full-duplex network settings for most practically common network parameter values.

The outage probability of a two-hop coordinated decode-and-forward relay network is investigated. Relay coordination is performed only with the dominant interferer. Different levels of network coordination are studied and their performances are compared. Exact expressions are derived for the outage probability of a particular mobile user for each coordination scheme. Asymptotic outage probability is derived to identify the diversity and coding gains for each coordination scheme.

The outage probability of a two-hop coordinated decode-and-forward relay network is investigated. The case of two interfering cells is considered. This is analogous to the case when network coordination is performed with the dominant cochannel interfering cell. Different levels of network coordination are studied and their performances are compared. Exact expressions are derived for of the system for each coordination method. The impact of user location randomness on the outage probability is investigated.

The downlink performance of a dual-cell relay enhanced wireless network is investigated. A single relay is shared by the two base stations in the system. The relay is assumed to be placed in a region covered by both base stations. The relay station is operating in the decode-and-forward mode. Closed-form approximations which follow the exact results extremely closely are derived for the outage probability and the ergodic rate of the system.

A theoretical framework is presented for the evaluation of sum ergodic rate of a full-duplex underlay device-to-device network, when it shares the uplink resources of a conventional cellular user. The sum-rate of the full-duplex network is compared with a half-duplex network with equivalent radio frequency hardware complexity. Closed-form approximations are derived for the sum ergodic rate of the systems. Furthermore, the sum-rate performances are investigated for the case when a transmit power constraint is imposed on the underlay network to minimize the interference on the cellular network. The analytical results presented can be used as a tool to identify when full-duplex transmissions are viable in underlay device-to-device networks.

The downlink performance of a two-cell relay enhanced wireless network is investigated. A single relay is shared by the two base stations in the system. The relay is assumed to be placed in a geographic region covered by both base stations. The relay station is operating in the decode-and-forward mode. Closed-form approximations which estimate the exact results extremely closely are derived for the outage probability and the ergodic rate of the system. The impact of finite rate channel state information feedback on the user ergodic rate is examined.

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

The outage probability of a multiuser amplify-and-forward relaying protocol is investigated. The practical case where there are co-channel interference signals present at the network is considered for the analysis. Exact expressions and closed-form lower bounds are derived for the outage probability. Three network configurations are analyzed based on the presence of co-channel interference in the system.

The outage probability of a recently proposed relay network with multiple antennas at the relay is analyzed. The relay uses maximal ratio combining to combine the received signals, while it uses maximal ratio transmission for the transmission. It is assumed that the reception at the relay and the destination are corrupted by multiple co-channel interfering signals. Closed-form outage probability expressions are derived when the relay is operated in the amplify-and-forward mode with fixed gain. Both cases of equal power and unequal power interferers are considered.

A novel single-integral representation for the bivariate Rician distribution was presented in a recent letter in this Transactions (ibid., vol. 59, no. 11. pp. 2951-2954, Nov. 2011). The expression given for the bivariate Rician probability density function (PDF) [1, eq. (12a)] contains a typographical error. The correct expression for the bivariate Rician PDF is presented here.

A novel approach is introduced for the analysis of energy detection of unknown deterministic signals, where the energy detector uses dual diversity reception. The energy detector is assumed to employ a low complexity diversity technique, namely square-law combining. A general case where the two diversity branches are correlated is treated by the analysis. Detection and false alarm probabilities for the energy detector are derived for correlated Rayleigh and Rician fading channels.

Novel representations for the multivariate probability density function (PDF) and cumulative distribution function (CDF) of the equi-correlated non-central chi-square (χ2) distribution are derived. The new representations are given as single integral solutions in terms of well known mathematical functions which are available in common mathematical software packages. The advantage of the new representations is that only a single integral computation is needed to evaluate the PDF and CDF for an arbitrary number of dimensions. The new representations are used to numerically evaluate the outage probability of a single user multiple input multiple output system with receiver antenna selection diversity, operating in correlated Rician fading channels. The well known constant (equal) correlation model, which is considered to be a useful model for a closely placed set of antennas, is used for the analysis in this paper. A novel single-integral representation for the joint characteristic function of the equi-correlated non-central χ2distribution is also given.

Novel single-integral representations for the bivariate probability density function and cumulative distribution function of two correlated Rician random variables are derived. The solutions are expressed in terms of well known functions which are available in common mathematical software. The two random variables are not necessarily identically distributed as required by some past solutions. The new form of the bivariate Rician cumulative distribution function is applied to give a new expression for the outage probability of dual selection combining diversity operating in correlated Rician fading.

Novel representations for the multivariate probability density function and cumulative distribution function of the non-central chi-square distribution are derived. The solutions are expressed in terms of well known functions which are available in common mathematical software. When the number of degrees of freedom, m, is even, the new representation has the advantage that only a single-integral computation is needed to compute a N-dimensional distribution. The new representations are used to numerically evaluate the outage probability of multiple input multiple output systems with receiver antenna selection, operating in correlated Rician fading. The well known equal correlation model, which is considered to be a useful model for a closely placed set of antennas, is used for the analysis.

Novel single-integral representations for the multivariate probability density functions (PDFs) and cumulative distribution functions (CDFs) of the Gaussian class Weibull distribution are derived. The solutions are expressed in terms of familiar mathematical functions which are available in common mathematical software. The well known equal (constant) correlation model is considered. A special linear transformation of independent Gaussian random variables is used to generate correlated Weibull random variables. The advantage of the new representation is that only a single integral computation is needed to compute a N-dimensional distribution. The new representation of the CDF is used for the performance evaluation of a selection diversity combiner operating in equally correlated Weibull fading channels. The new PDF representation is also used for an analysis of the moments of the output signal-to-noise ratio of an equal-gain diversity combiner operating in equally correlated Weibull fading channels.

Novel single-integral representations for the multivariate probability density functions and cumulative distribution functions of Gaussian class distributions (Rayleigh, Rician, Weibull, Nakagami-m, and generalized Rician) are derived. The solutions are expressed in terms of well-known functions which are available in common mathematical software. The marginal random variables are not necessarily identically distributed as is the case for some past solutions. A generalized correlation structure based on a special linear transformation of independent Gaussian random variables is used in this study. The advantage of the new representation is that only a single-integral computation is needed to compute anN-dimensional distribution.

Novel single integral representations for the multivariate probability density function and cumulative distribution function of Rayleigh and Rician distributions are derived. A generalized correlation structure is used in this analysis. The derived novel representations are used to evaluate the outage probability of N-branch selection diversity operating in correlated Rayleigh and Rician fading channels modeled by the generalized correlation model.

Novel single integral representations for the multivariate probability density function (PDF) and cumulative distribution function (CDF) of Gaussian class Weibull distributions are derived. A special linear transformation of independent Gaussian random variables is used to generate correlated Weibull random variables. The solutions are expressed in terms of familiar functions which are available in common mathematical software. The well known equal (constant) correlation model is used in this paper. The advantage of the new representation is that only a single integral computation is needed to compute a L-dimensional distribution. Some applications of the new distribution representations are also given.

Novel simple forms for the probability density function (PDF) and the cumulative distribution function (CDF) of two correlated Rician random variables (RVs) are derived. The new representations for the bivariate Rician PDF and CDF are given in the form of single integral solutions in terms of well known functions that are available in common mathematical software packages. The general case of non-identically distributed Rician RVs is considered in this analysis. The new form of the bivariate Rician cumulative distribution function is applied to give a new expression for the outage probability of dual selection combining diversity operating in correlated Rician fading.

Novel single integral representations for the multivariate probability density function (PDF) and cumulative distribution function (CDF) of the Nakagami-m distribution with integer and identical fading severity parameter m are derived. A generalized correlation structure is used in this model. The single integral solutions for the PDF and the CDF are given in terms of well known mathematical functions which are available in common mathematical software packages. The novel representation derived for multivariate CDF is used to evaluate the outage probability of N-branch selection diversity combining operating in correlated Nakagami-m fading modeled by the generalized correlation model.