Time-Switching Energy Harvesting Relay Optimizing Considering Decoding Cost

Energy harvesting (EH) from natural and man-made sources is of prime importance for enabling the Internet of Things (IoT) networks. Although, energy harvesting relays in a relay network, which form building blocks of an IoT network, have been considered in the literature, most of the studies do not account for the processing costs, such as the decoding cost in a decode-and-forward (DF) relay. However, it is known that the decoding cost amounts to a significant fraction of the circuit power required for receiving a codeword. Hence, in this work, we are motivated to consider an EH-DF relay with the decoding cost and maximize the average number of bits relayed by it with a time-switching architecture. To achieve this, we first propose a time-switching frame structure consisting of three phases: (i) an energy harvesting phase, (ii) a reception phase and, (iii) a transmission phase. We obtain optimal length of each of the above phases and communication rates that maximize the average number of bits relayed. We consider two EH scenarios, (a) when the radio frequency (RF) energy, to be harvested by the relay, is transmitted from a dedicated transmitter, and (ii) when the energy is harvested at the rely from the ambient environment. By exploiting the convexity of the optimization problem, we derive analytical optimum solutions under the above two scenarios and provide numerical simulations for verifying our theoretical analysis.