Optimal Power Control And Multi-users Energy Cooperation In Wireless Relay Networks With Energy Harvesting

Relaying technique is effective to combat fading channel, enhance the capacity and extend the coverage. Wireless Relaying network can overcome the bottleneck of energy-constrained and increase the running time of the network, since network nodes can collect the energy from surrounding environment. SWIPT(Simultaneous Wireless Information and Power Transfer,SWIPT) is a new technology which is to make use of RF(Radio Frequency) not only transferring information but also transferring power to deal with the wireless nodes without fix power supply. In this paper, we focused on SWIPT wireless relying network with energy harvesting,and investigated in this network how to optimal power control and energy cooperation in multi-user, the main works in described as follows:(1)This paper considers optimal power control solutions in one-way and two-way relay system with SWIPT. First, we develop SWIPT protocols for one-way and two-way relay systems. For one-way relay system, the closed-form solution for optimal power splitting ratio is derived to maximize the system throughput. For asymmetric two-way relay system, we propose a novel power splitting strategy to maximize system throughput. Considering the total transmit power constraints, we develop a semi-closed form solution for power allocation among all nodes by exploiting convex optimization technology. It is shown that the optimal power allocation in two-way relay system would degrade into one-way relay mode if the relay node is close to one of the terminals. For symmetric two-way relay system, a closed-form solution for power allocation and power split ratio is derived. The performances of the three systems are compared numerically. It is revealed that the proposed power allocation algorithm can improve the transmission rate without consuming additional resource compared with non-cooperation relaying scheme.(2)Energy cooperation schemes are considered in wireless cooperative networks. The paper is focused on the energy cooperation strategies for the relay to distribute the harvested energy between the multiple user pairs in Amplify-and-Forward(AF) and in Decode-and-Forward(DF) mode. Specifically, optimal solutions without energy cooperation at the relay node are firstly proposed and then we formulate the energy cooperation optimization problem. This optimization problem is non-convex. We propose an iterative energy cooperation solution to maximize the system throughput by assigning the proper harvested energy to each user pair for both types of forwarding models. We show that with the proposed method, the update in each iteration consists of a group of convex problems with a continuous parameter. Moreover, we derive the optimal solution to these convex problems in closed-form and it is shown that the solution can converge to a local optimum. Simulation results demonstrate that the proposed algorithm outperforms the traditional non-cooperation method.