Energy Efficiency Optimization In Wireless Relay System

Wireless relaying has always been drawing extensive attentions in the past several decades.It still continues developing with the development of wireless communication network to the era of 5G(5th Generation).It is expected that there will be a massive number of users in the mobile communication network,including a large number of machine-type communication users which will pose a great challenge to the wireless network.Therefore,the users are most likely to be organized in a hierachical way where many clusters of users are connected to the base station through some head nodes.In this case,the cooperative relay must be thoroughly investigated.Moreover,as one of the key indicators of the 5G network,energy efficiency plays an important role in the relay communication technologies.The high energy efficiency in wireless relay must be achieved while satisfying the requirements of the rate and the quality of service(QoS).In this dissertation,we review the basic theory starting from Shannon formula.After surveying a variety of working modes of relay systematically,we introduce the relay communicaiton joint with the energy harvesting technology which helps improve energy efficiency.We study three problems in this dissertation.First,we consider a relay system with an energy harvesting relay while the source node is supplied with grid power which comes from fossile fules ultimately.In this part,based on the Shannon theorem,we use the optimization algorithm to find out the optimal sleep time and transmit power of all the nodes to achieve maximal energy efficiency of the source node.Second,a practical system are most likely to transmit data with a limited qual-ity of service(QoS)when coding and modulation are used.So though the analysis based on Shannon formula can provide some insight,there are still some gaps between a theory and a practical system.In this dissertation,we consider the energy efficiency optimization based on the packet transmission in an inremental relay system where the modulation are taken into account.Still we consider a relay being capable of energy harvesting.Because the inremental relay needs only to work when the initial transmis-sion from the source node fails,it can favor the transmission even with a low energy harvesting rate.Finally,an energy efficient power control scheme for the two-way relay is pro-posed.The key point of various working modes of relay is actually to coordinate the interference,usually the transmission-recieving interference,of the relay.The two-way relay deal with the transmission-receiving interference jointly with the two-way inter-ference so that it boosts the capacity.However,the interference leads to some tricky problem in energy efficiency optimization in the relay.In this work,we propose a two-step optimization method to solve the original non-convex problem to achieve the optimal energy efficiency.Simulation results show that the proposed algorithms may effectively impromve the energy efficiency.