This paper addresses multi-user multi-cluster massive multiple-input-multiple-output (MIMO) systems with non-orthogonal multiple access (NOMA). Assuming the downlink mode, and taking into consideration the impact of imperfect successive interference cancellation (SIC), an in-depth analytical analysis is carried out, in which closed-form expressions for the outage probability and ergodic rates are derived. Subsequently, the power allocation coefficients of users within each sub-group are optimized to maximize fairness. The considered power optimization is simplified to a convex problem, which makes it possible to obtain the optimal solution via Karush-Kuhn-Tucker (KKT) conditions. Based on the achieved solution, we propose an iterative algorithm to provide fairness also among different sub-groups. Simulation results alongside with insightful discussions are provided to investigate the impact of imperfect SIC and demonstrate the fairness superiority of the proposed dynamic power allocation policies. For example, our results show that if the residual error propagation levels are high, the employment of orthogonal multiple access (OMA) is always preferable than NOMA. It is also shown that the proposed power allocation outperforms conventional massive MIMO-NOMA setups operating with fixed power allocation strategies in terms of outage probability.

Satellite communication systems need to be integrated with emerging cooperative relaying techniques to provide seamless connectivity and high-speed broadband access for mobile users in future wireless networks. In this paper, we study a multi-antenna multiuser hybrid satellite-terrestrial relay network (HSTRN) employing opportunistic user scheduling with outdated channel state information (CSI) and amplify-and-forward relaying with co-channel interference (CCI). By adopting Shadowed-Rician fading for satellite links and Nakagami-m fading for terrestrial links, we derive novel and accurate expressions for outage probability and ergodic capacity of the proposed HSTRN and further examine its achievable diversity order. More importantly, we conduct the performance analysis by taking both uncorrelated and correlated Shadowed-Rician fading channels into account and show that the antenna correlation at the satellite does not affect the overall system diversity order. Our derived analytical expressions provide efficient tools to characterize the impact of CCI, outdated CSI, and antenna correlation on the system performance of HSTRN with arbitrary number of satellite antennas, number of interferers, number of users, and integer values of the per-hop fading severity parameters. Our results provide useful guidelines in the design of futuristic HSTRNs for satellite mobile communications.

Important statistical properties of the doublegeneralized Gamma (dGG) distribution are studied in this paper. The dGG distribution is suitable for modelling non-homogeneous double-scattering radio propagation fading conditions, which can be frequently observed in vehicle-to-vehicle (V2V) communications. In this context, important statistical metrics for the bivariate dGG distribution, such as the joint probability density function, cumulative distribution function, and the moments, are derived for the first time, while simplified expressions for the corresponding marginal statistical metrics are presented. Moreover, the second-order statistics of this distribution are also analytically studied. The derived analytical framework has been employed to analyze the performance of a transmit antenna selection system operating in V2V communication channels modeled by the dGG distribution. In this scenario, the impact of outdated channel state information (CSI) to the system’s performance is investigated in terms of various metrics including the level crossing rate and the average fade duration. Furthermore, simplified asymptotic closed-form expressions for the outage probability have been derived to examine the achievable diversity and coding gains. Based on our analysis, insightful discussions are provided. It is shown that the diversity gain is independent from the number of transmit antennas when the available CSI becomes outdated.

In this paper, the secrecy performance of a dual-hop mixed radio-frequency/underwater optical wireless communication (RF-UOWC) system is investigated. The considered system consists of one single antenna source node ( $S$ ) communicating with one destination node ( $D$ ), considered as the legitimate receiver, through an amplify-and-forward relay node equipped with multiple antennas for reception. Specifically, the relay receives the incoming signal from $S$ via an RF link, applies maximal-ratio combining technique, amplifies the output combined signal with either a fixed gain or variable gain, and then forwards it to the destination via an UOWC link. The transmission protocol is performed under the eavesdropper’s attempt to overhear the RF link (i.e., $S$ - $R$ ). We derive exact closed-form expressions for the system’s average secrecy capacity and the intercept probability in terms of Meijer’s $G$ -function as well as the univariate and bivariate Fox’s $H $ -functions. A complexity analysis is also performed to analyze the evaluation time of the derived analytical formulas as well as Monte Carlo simulation method complexity. Our derived analytical formulas present an efficient tool to depict the impact of some system and channel parameters on the secrecy performance, namely, the number of relay antennas, the number of eavesdropping nodes, relay gain, fading severity of RF links, and water turbulence severity of the UOWC link.

The present work investigates the secrecy performance of multiple-input multiple-output systems under generalized α-μ fading conditions. To this end, we focus on two distinct scenarios: i) the transmitter has knowledge of the channel state information (CSI) of the eavesdropper channel; ii) the transmitter is not aware of the CSI of the wiretap link. By considering transmit antenna selection in the underlying system, we develop closed-form analytical expressions for the lower bound of the secrecy outage probability (SOP) and the probability of the strictly positive secrecy capacity. Furthermore, two novel approaches are proposed to derive an analytical expression of the average secrecy capacity (ASC). Firstly, the ASC is expressed as a function of the average capacity of the desired link and an interaction term regarded as the ASC loss. Secondly, the ASC is expressed in terms of the average capacities of the desired and eavesdropper links, plus an interaction term that can be regarded as some sort of ASC gain due to the statistical independence between the desired and eavesdropper links. In addition, asymptotic studies of the SOP and ASC at high signal-to-noise ratio are carried out, which precisely reveal the secrecy diversity and array gains.