In this paper, we consider a wireless cooperative network with an energyharvesting relay which is powered by the energy harvested from ambient RFwaves, such as that of a data packet. At any given time, the relay operateseither in the energy harvesting (EH) mode or the data decoding (DD) mode, butnot both. Separate energy and data buffers are kept at the relay to store theharvested energy and decoded data packets, respectively. In this paper, weoptimize a time switching policy that switches between the EH mode and DD modeto maximize the system throughput or minimize the average transmission delay.Both static and dynamic time switching policies are derived. In particular,static policies are the ones where EH or DD mode is selected with apre-determined probability. In contrast, in a dynamic policy, the mode isselected dynamically according to the states of data and energy buffers. Weprove that the throughput-optimal static and dynamic policies keep the relaydata buffer at the boundary of stability. More specifically, we show that thethroughput-optimal dynamic policy has a threshold-based structure. Moreover, weprove that the delay-optimal dynamic policy also has a threshold-basedstructure and keeps at most one packet at the relay. We notice that thedelay-optimal and throughput-optimal dynamic policies coincide in most cases.However, it is not true for optimal static policies. Finally, through extensivenumerical results, we show the efficiency of optimal dynamic policies comparedwith the static ones in different conditions.
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