Transmit Antenna Selection for Interference Aided Wireless Energy Harvesting in Cache-Assisted Cognitive Relay Networks

In this work, we consider a spectrum sharing scenario where secondary network exists with primary network comprising of multiple users. The secondary transmitter communicates with secondary destination using a decode and forward (DF) energy constrained relay. The secondary relay harvests energy from primary interference and secondary transmitted signal to decode, re-encode and transmit the information to secondary destination. Additionally, the secondary network exploits caching to enhance its maximum achievable rate. A times-witching (TS) policy is employed at relay to harvest energy and decode information which is followed by caching and retransmission. We propose a transmit antenna selection with maximal-ratio combining (TAS-MRC) based scheme to improve performance of secondary network in presence of multiple primary interferers. Further, an optimization problem is formulated to improve the energy efficiency of the system by maximizing energy stored at secondary relay while ensuring the quality of service requirements of primary and secondary networks are met. Using KKT conditions, we solve the formulated problem and present simulation results demonstrating the effectiveness of the proposed scheme. In particular, we study and demonstrate the impact of number of primary users, primary interference constraint, secondary quality of service constraint as well as secondary transmit power on the energy stored at secondary relay.