The impact of imperfect channel state information (CSI) on a reconfigurable intelligent surface (RIS)-aided wireless system is investigated in this letter. More specifically, considering the imperfect CSI from the RIS to the destination, we develop the cumulative distribution function (CDF) of the end-to-end signal-to-interference-plus-noise ratio (SINR). Then, using the CDF, we derive the closed-form expressions of the outage probability (OP), average bit error rate (BER), and average capacity. Furthermore, we also derive the asymptotic OP, average BER, and average capacity at high signal-to-noise ratio (SNR). Simulation results show that inaccurate CSI results in zero diversity order and a floor phenomenon. Also, numerical results demonstrate that the derived closed-form expressions match the simulated results.

To legitimately monitor suspicious wireless communications is an important issue. In this letter, we propose a proactive monitoring via jamming scheme over an amplify-and-forward relay network, which consists of a legitimate monitor, a suspicious source, a suspicious relay, and a suspicious destination. Our objective is to design the optimal jamming power to maximize average monitoring rate at the legitimate monitor. For the optimization problem, we propose to find the true optimal jamming power by a bisection search method. Furthermore, we propose an approximate optimal jamming scheme whose closed-form expression on average monitoring rate is theoretically derived. Simulation results demonstrate that our proposed true optimal jamming scheme outperforms passive monitoring and proactive monitoring via constant-power jamming. Furthermore, our proposed approximate optimal jamming scheme achieves almost the same average monitoring rate as true optimal one.

Cognitive relay networks employ cooperative relaying scheme in the cognitive secondary user transmission. In this letter, we theoretically derive a closed form expression and a lower bound of the outage performance for underlay cognitive relay networks considering the interference from the primary transmitter to the secondary receiver, the interference from the secondary transmitter to the primary receiver and the dependence introduced due to the interference power constraint. It is shown from simulation results that the derived closed form expression matches the simulated results.

In this letter, considering the reconfigurable intelligent surface’ (RIS’) service coverage limitation, we investigate the outage probability (OP) of an RIS-aided cognitive radio network where the RIS is used only to eliminate the interference from the secondary transmitter to the primary receiver. Specifically, a closed-form expression for the OP is derived and the asymptotic OP is obtained at high signal-to-noise ratio (SNR). We also present the asymptotic OP when the number of reflecting elements is large. Simulation results validate our analysis, and show that at low tolerable interference-to-noise ratio (INR), the considered scheme can achieve significant performance gains over the coverage-neglected scheme and the signal enhancement scheme.

In this letter, we investigate the outage probability of a dual-hop N^{th}-best decode-and-forward multicast relay network in which the relay and destination undergo multiple co-channel interferences (CCIs). It is shown that the signal-to-interference-plus-noise ratio (SINR) of the link from source to destination and that from relays to destination are correlated due to the common CCI at the destination. Considering the correlated SINRs, the exact closed-form expression for the outage probability is derived. It is shown that the analytical results perfectly match the simulation results.