Cognitive Relaying With Wireless Energy Harvesting and Accumulation

In this article, we propose a cognitive relaying (CR) scheme with both the secondary source (SS) and the secondary relay (SR) capable of harvesting wireless energy. Along with the data transmission of primary system, a power beacon actively transfers wireless power to SS and SR. The interference from the primary data transmission can increase the amount of harvested energy at SS and SR. After harvesting and accumulating energy for a number of successive time blocks, the CR will be performed in two continuous time blocks. In CR-Block-One, SS will transmit the secondary data to SR by exhausting its available energy. In CR-Block-Two, SR will forward the secondary data to SD if it has correctly decoded the data from SS; otherwise, it will stay silent. We properly model the energy accumulation process of SS and SR by defining a group of discrete energy levels. We analyze the approximate throughputs of both systems by considering various transmit powers of SS and SR. The optimal number of time blocks used for the wireless power transfer is determined through maximizing the secondary throughput while slightly degrading the primary performance. Numerical results show that the secondary data transmission can be well accommodated.