The cooperative communication with simultaneous wireless information and power transfer can provide a potential solution to meet the demands of next-generation green transmission. In this paper, we consider a cooperative system where each user has the capability of energy harvesting (EH) from the radio frequency and relays the data of other users. Our target is to minimize the overall energy consumption while satisfying the quality of service constraints of each user in terms of minimum required data rate. The time division scheme is adopted for data transmission and relaying while power splitting protocol is used at each node to receive information and energy, concurrently. We optimize the transmit power for data and relay transmission at each node and find the optimal time sharing for user cooperation. Unfortunately, under the decode and forward relaying the complex primal problem is not convex. Thus, we first re-formulate the problem into standard optimization and then transform to a convex problem. We solve the problem through duality theory and derive the closed form solution of the primal variables. Further, we consider the cooperative communication without EH and non-cooperative transmission with EH, and then optimal solutions are obtained from similar techniques. Finally, simulation results are provided where the performance of the proposed solutions is compared with the non-optimized cooperation time and without EH models.
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