Energy Harvesting in Cognitive Networks with Cooperative Beamforming:Power Allocation and Stability Analysis

Energy harvesting(EH)is a promising technology to improve both energy efficiency and spectral efficiency in cognitive radio(CR)networks.However,due to the randomness of the harvested energy and the interference constraint at the primary users(PUs),the limited transmission power of secondary users(SUs)may reduce the service rate of SUs.To solve this problem,this paper investigates a cooperative transmission method where a zero-forcing beamforming method is used in the EH based secondary network.Considering the transmission power constraint and energy causality,we derive the closed-form solution of the optimal transmission power for the secondary source and relays,which achieves the maximal stable throughput of the secondary network.Numerical results show the impact of different system parameters to the maximal stable throughput.In addition,compared with the traditional decode-and-forward(DF)scheme,the cooperative beamforming method achieves higher stable throughput under an high quality source-to-relay channel.