Relay Selection for Energy Harvesting Relays With Energy Prioritization and Inter-Relay Charging

In Internet of Things (IoT) networks for carrying out environment monitoring tasks, maintaining low energy consumption of IoT devices can prolong the lifetime of IoT but the effective communication range may be restrictive. The two-hop transmission with relay selection has been shown to achieve a good trade-off between extended communication range and undesired bandwidth penalty due to information repetition using multiple relays. In this work, we propose a relay selection scheme for buffer-aided relays that store the received signal in a finite data buffer and accumulate the energy harvested from RF signals in a finite energy storage. In the proposed scheme, relays are prioritized according to their instantaneous energy and data buffer status as well as channel conditions reported by relays. To render practical implementation, the anticipated cost of status update for relay selection that has been commonly ignored is explicitly considered. Besides, the energy accumulation rate is increased by utilizing both the source-relay and inter-relay channels to harvest energy. The performance of the proposed relay selection scheme is theoretically analyzed using a discrete-time Markov chain. Numerical results show the superiority of the proposed relay selection scheme than the state-of-art and the key factors that dominate the outage performance.