Joint Antenna Selection and Transmit Power Optimization for UAV-Assisted Relaying in Cognitive Radio IoT Networks

In this paper, we study a cognitive relay Internet of Things (IoT) network aided by an unmanned aerial vehicle (UAV) equipped with multiple antennas. The UAV performs relaying for secondary communication under stringent interference constraints imposed by the primary network. To address the outage probability floor problem caused by strong interference channels, we propose a novel joint antenna selection and transmit power optimization scheme for Rician fading channels. By using the time-sharing condition and the Lagrangian dual method, the nonconvex mixed-integer optimization problem is efficiently solved to obtain the optimal solution. Additionally, a closed-form asymptotic lower bound on the outage probability is derived for Rayleigh fading channels, providing valuable performance insights. Numerical results demonstrate that the proposed joint optimization scheme significantly outperforms existing works.