Performance Analysis of Relay Selection for Cooperative Relays Based on Wireless Power Transfer With Finite Energy Storage

Cooperative relaying with relay selection (RS) is a promising technique in exploiting diversity gain using simple hardware. In this paper, the outage probability performance of a new RS scheme for energy harvesting (EH) relays based on wireless power transfer is investigated. First, a timing structure for enabling EH, RS, and information relaying is defined. Based on the timing structure defined, we propose an RS scheme considering both the channel state information (CSI) and battery status of EH relays, assuming that each relay has finite energy storage for accumulating the energy harvested from the source signal. To understand the impact of critical system parameters on outage probability, a finite-state Markov chain is developed to capture the evolution of relay batteries under the proposed RS scheme, and the resultant outage probability is derived. As the computational complexity of the Markovian-based analysis exponentially grows with the number of relays, an approximated analysis with reduced complexity is conducted based on certain simplified assumptions. We present simulation results to verify the accuracy of both exact and approximated analyses. We also discuss the performance of the proposed RS scheme, subject to various important parameters via numerical results, to shed light on future developments of cooperative networks utilizing EH relays.