On the Adaptive Transmission Scheme in Buffer-aided Wireless Powered Relay Network

In this paper, we consider wireless-powered relay network consisting of one source, one wireless powered relay and one sink, where the relay is provisioned with both data buffer and energy storage. Firstly, a novel time-switching transmission scheme is proposed to divide the transmission from source to sink into three phases, namely, the relay energy harvesting phase, the relay receiving phase and the relay forwarding phase. And the achievable end to end (E2E) throughput and optimal timeswitching parameter are derived. Secondly, the transmission scheme is reformulated as a stochastic optimization problem to take into considerations of all the dynamic characteristics of the energy harvesting status, the data buffer status and the underlying time-varying channel conditions. By employing the Lyapunov optimization theory, an online buffer-energyaware adaptive transmission scheme is proposed to adjust the transmission at both source and relay according to the channel state information(CSI), the data buffer state information (BSI) and the energy state information (ESI). Moreover, the tradeoff between the average E2E throughput and the transmission delay is presented to show the great potential of the proposed adaptive transmission design to improve the achievable transmission throughput. Finally, simulations are presented to validate the efficiency of the proposed relaying protocols.