Optimal Multiuser MISO Beamforming for Power-Splitting SWIPT Cognitive Radio Networks

This paper studies a simultaneous wireless information and power transfer multi-input single-output cognitive radio network in which a multi-antenna secondary transmitter sends data streams to multiple single-antenna secondary receivers (SRs) equipped with a power-splitting (PS) structure for information decoding and energy harvesting in the presence of multiple single-antenna primary users (PUs). First, the max-min fair SRs' harvested energy problem is formulated and solved by combining the tight semidefinite relaxation (SDR)-based solution of the transmit power minimization problem with the bisection search method. Second, the balancing problem examines the tradeoff between the worst-user harvested energy at the SR and the interference power at the PU. The proposed solution for this challenging non-convex problem includes two steps. First, the problem with fixed PS ratios is solved using the SDR technique and the tight solution is proved; then, the approximately optimal PS ratios are found using the particle swarm optimization method. Additionally, the closed-form solutions of transmit power minimization and harvested energy maximization problems are derived for the special case where only one SR and one PU are present. Finally, the numerical results demonstrate the effectiveness of the proposed approaches in comparison with two baseline schemes.