Energy Efficiency Optimization Of Cooperative Relay System

With the rapid development of mobile Internet,explosive growth has emerged in the data traffic of wireless cellular network.Thus,the energy consumption of the network become larger and larger.Recently,how to reduce the energy consumption has become a hot issue in communication industry.Cooperative relaying is regarded as a promising technology to improve the network energy efficiency(EE),based on which the energy efficiency optimization of relay system is studied in this thesis,the detailed work is as follows:Firstly,the EE of practical two-way relay(TWR)systems with non-ideal power amplifiers(PA)and non-negligible circuit power consumption is maximized,an algorithm is proposed where both the transmit powers and durations are jointly optimized.The key idea is to convert the original non-convex optimization problem into a tractable problem only with time variables.Another important aspect is that we rigorously prove that the new problem has only one local optima under both non-ideal PA models,which is also the global optima.Based on these key findings,a simple local optimization algorithm is developed.Simulation results show that the proposed algorithm is able to support TWR with a variety of practical non-ideal PAs,and provides higher EE than the state of the art.The imbalance of traffic demand also has an impact on EE,and the most energy efficient transmission scheme depends on the traffic.Secondly,the EE of multi-relay system is optimized through relay selection and resource allocation.By theoretic analysis,it is proved that when the direct channel gain outperforms the channel between relay and user,the direct channel can achieve higher EE.While in other cases,the most energy efficient transmission lies in the EE optimization problem,and a simple algorithm is proposed to solve it.Simulation results verify the conclusion,and show that the EE of relay selection based on maximum minimum and maximum harmonic mean of channel gain are not optimal.The more energy efficient between the two schemes depends on the specific channel.Finally,the EE for amplify-and-forward protocol based TWR system with nonlinear PA models and real traffic model is evaluated.We define two parameters to describe PA characteristics,and another two parameters to describe the realistic data traffic behavior.Simulation results show that the EE of envelope tracking PA is not always higher than traditional PA.Furthermore,the EE of two PAs are compared with various traffic and PA parameters,based on which an EE-oriented PA selection is proposed.