Research On Energy-Efficient Resource Allocation Algorithms In OFDM Relay Systems

With the development of intelligent mobile phones, mobile network has become the basic guarantee for the communication, sharing, shopping, video entertainment, and so on in human life. Therefore, people demand more and more high quality of communication system. Orthogonal frequency division multiplexing(OFDM) technology and relay communication technology can satisfy the high speed wireless communication system and wide coverage requirements. In order to significantly reduce the network energy consumption and improve the efficiency of energy use wireless communication network, green communication technology has come into people’s horizons gradually. The combination of OFDM, relay and green communication is a practical research direction in the current communication network.This thesis focuses on the energy efficiency of OFDM relay systems. Adaptive resource allocation algorithms are given respectively for single relay single user, single relay multi-user and multi relay multi-user three different scenarios.Detailed research content are as follows:(1) In a single relay multiuser OFDM system, an energy efficient optimization algorithm is proposed on purpose of maximize the energy efficiency, combining the power optimization allocation and subcarrier pairing. The AF(amplify and forward) relay is adopted as the relay mode. The problem is divided into two steps. Firstly, the Dinkelbach algorithm is used to transform the fractional problem into an integral convex problem reducing the computational complexity. Secondly the optimal power allocation on subcarriers at source and relay is achieved by dual decomposition theorem, with respect to separate transmit power constraints. The performance of energy efficiency optimization algorithm and maximum system capacity algorithm is compared by simulation, results show that the algorithm in bit-rate guarantee under the premise of can obtain better efficiency, improve the whole performance of the system.(2) For the downlink multiuser OFDM cooperative network scenario, the sum of the logarithmic per user time-averaged bits-per-Joule is maximized with separate transmit power constraints at the base station and relays. The optimization problem is divided into two steps. First, the solution for the subcarrier allocation is obtained by considering the user’s channel condition of past scheduling time, which can enhance the proportional fairness in systems. Second, we allocate power at the base station uniformly to get the optimal power allocation at relays, the optimal power aloocation at base station is obtained for a given relays power allocation, iterating continuously to obtain the optimal power allocation.Numerical results present the algorithm can quickly converge, at the same time, the proposed scheme can achieve similar performance by reducing the complexity of the system to ensure the performance of the system.(3) For multi-user OFDM relaying systems in single cell, the problem of resource assignment with proportional fairness is considered. The optimal purpose is to maximize the sum of the logarithm per user rate per power. Meanwhile, minium rate are limited to ensure the fairness among users.The optimization problem is decomposed into some sub-problems. Firstly, to employ Dinkelbach’s method for transforming the fractional programming to integral expression. Then, convex programming will be used to solve the dual problem by bisection method, iterative gradient and power injection method. Figure simulation gives the system energy efficiency and the fair comparison chart between the users, results show that the proposed algorithm has a good trade-off between the throughput and fairness compared with other scheme, great improvement in system energy efficient has been got in the algorithm proposed.