Relay Selection in Wireless Powered Cooperative Networks With Energy Storage

Abstract

This paper deals with the problem of relay selection in wireless powered\ncooperative networks, where spatially random relays are equipped with energy\nstorage devices e.g., batteries. In contrast to conventional techniques and in\norder to reduce complexity, the relay nodes can either harvest energy from the\nsource signal (in case of uncharged battery) or attempt to decode and forward\nit (in case of charged battery). Several relay selection schemes that\ncorrespond to different state information requirements and implementation\ncomplexities are proposed. The charging/discharging behavior of the battery is\nmodeled as a two-state Markov chain and analytical expressions for the\nsteady-state distribution and the outage probability performance are derived\nfor each relay selection scheme. We prove that energy storage significantly\naffects the performance of the system and results in a zeroth diversity gain at\nhigh signal-to-noise ratios; the convergence floors depend on the steady-state\ndistribution of the battery and are derived in closed-form by using appropriate\napproximations. The proposed relay selection schemes are generalized to a\nlarge-scale network with multiple access points (APs), where relays assist the\nclosest AP and suffer from multi-user interference.\n