Radio Frequency Energy Harvesting Based Cooperative Relaying Technique

In recent years,radio frequency energy harvesting(RF-EH)technique is getting more and more matured and has gradually entered the application phase.Further research on this technique has been extended to various technical fields.Among them,RF-EH based cooperative relaying integrates the advantages of both cooperative relaying technique and RF-EH technique.Thus,it becomes one of the key techniques for realizing the future communication networks with high reliability,high coverage,and sustainability.RF-EH based cooperative relaying technique not only has the advantages of two original techniques,but also can cover up the shortage of each technique.On one hand,hybrid relay cooperation can provide more efficient wireless power transfer and more reliable information transmission for users far from the base station.Thereby,the doubly near-far problem can be solved when RF-EH technique is deployed in cellular networks.Since in hybrid relay networks,relays provide information and energy simultaneously,how to balance the energy acquisition and information transmission when selecting a relay node becomes a problem for multi-relay scenario.On the other hand,for RF-EH based cooperative relaying,cooperation behavior can be motivated by energy supply from the source node.This can solve the problem that mobile devices in self-organizing communication networks are unwilling to participate in cooperation due to the extra energy consumption.However,in RF-EH relay networks,the energy transmission process will inevitably occupy the network resources originally used for information transmission.Therefore,how to allocate limited network resources to improve the communication performance is another problem in RF-EH based cooperative relaying technique.To solve the above problems,this thesis develops the following research on RF-EH based cooperative relaying technique.1.Research on relay selection strategies under hybrid relay cooperationA two-step relay selection strategy is proposed in the hybrid relay network to maximize energy harvested by the source node under the condition that information transmission quality can be guaranteed.For the implementation of the proposed strategy,a low-overhead distributed implementation scheme is also presented in this thesis.Furthermore,in order to evaluate the performance of the proposed strategy,the transmission outage probability is derived in a closed form,and the diversity order is also obtained,which shows that the proposed strategy can achieve full network diversity gain.Finally,simulations show that,in hybrid relay networks,the proposed strategy can achieve higher network performance than the max-min SNR strategy,which is optimal in traditional relay networks.2.Research on time-switching based relaying protocols under RF-EH relay cooperationA time-switching based adaptive relaying protocol is proposed in the RF-EH relay network,which dynamically allocates relay power and time resources according to the channel state and the energy state of the network.Further,the optimal relay power and time-switching factor are obtained by modeling and solving an optimization problem which aims at maximizing the network long-term throughput.Results show that when three specific conditions are satisfied,an entire time slot of the network should be actively used for RF-EH.Finally,through simulations,the superiority of the proposed relaying protocol is demonstrated,and the impact of network parameters on performance is analyzed.