Research On Resource Allocation Algorithms In Energy Harvesting Relay Networks

With the rapid development of mobile communication technology,the requirement of network quality and data rate is higher and higher.The emergence of cooperative relay technology could solve the problem of weak coverage of cell edge effectively,and can provide a good diversity gain to certain extent.As an advanced technology in recent years,energy harvesting could achieve the goal of green communication by collecting energy from renewable resources in the surrounding environment.Therefore,the combination of cooperative relay and energy harvesting is a hot research topic currently.From the two research directions of single carrier and multiple carriers,the resource allocation algorithms of energy harvesting relay networks are studied in this thesis.Taking the multi relays networks which have the function of energy harvesting as the research object,the resource allocation problems of power allocation,relay selection,time allocation and subcarrier pairing of the wireless nodes are analyzed and studied,and three resource allocation algorithms are proposed in this thesis.To sum up,the main contents are as follows:(1)A power allocation and single relay selection scheme is proposed to improve the outage performance for a wireless cooperative network with multiple energy-harvesting relay nodes.The optimization problem is formulated to minimize the system outage probability under the constraints of both relay joint maximum transmit power and individual energy limitation caused by energy-harvesting.By using Lagrange multiplier method and KKT(Karush-Kuhn-Tucker)conditions,the optimal transmit power of multi-relay can be solved.Taking into consideration that single relay is more feasible to implement in practical communication scenarios,a best relay can be selected by calculating the contribution factor of relay nodes.In addition,the lower bound of system outage probability is derived in this paper.Simulation results show that the proposed power allocation and single relay selection scheme can reduce system outage probability efficiently,and verify the conclusion of the lower bound of outage probability.(2)A time allocation scheme which is based on relay selection is proposed to improve the system average throughput performance for a wireless cooperative network with multiple relay nodes,which are employed energy harvesting with wireless energy transfer(WET).The optimization problem is formulated to maximize the system total end-to-end throughput under the constraint of energy and data causality.The branch and bound method is used to select the relay node for each time slot.According to the different usage of the relay node to the remaining energy,by using simplex method and independent solution method,the transmission time of the source node and the relay nodes in each time slot is optimized to increase the amount of data received by the destination node.Simulation results show that the proposed scheme can improve the system average throughput efficiently.(3)A joint optimization scheme for power allocation and subcarrier pairing is proposed to improve the average throughout capacity for an OFDM wireless cooperative network with multiple relay nodes,which are employed energy harvesting with simultaneous wireless information and power transfer(SWIPT).The optimization problem is formulated to maximize the total end-to-end throughput capacity under the constraint of source node maximum transmit power.By solving the power splitting(PS)factor of every relay node based on the two-hop Decode-and-forward(DF)relay system,the optimization problem is simplified by introducing the equivalent channel gain,and the power allocation and subcarrier pairs are joint optimized by using Lagrangian dual programming and Hungarian method.Simulation results show that the proposed scheme can improve the system average throughout capacity efficiently.