Research On Several Optimization Technologies In Cooperative Communnication

Recently, the idea of cooperation is successfully applied and developed in the field of communication. Technology based on relay cooperation has become one of the key technologies of modern mobile communication and wireless access, and has emerged in several communication standards. By using cooperative communication theory,we can acquire more diversity gain, higher transmission rate, extended network coverage and less terminal power consumption. It could be predicted that cooperation is going to be widely applied in the field of communication along with the rise and development of the Internet of things, which has the characteristics of broadband, heterogeneity, slef-organization and individuality.Together with the typical cooperation and relay applications in the future mobile communication, this paper researches the following three key problems: how to enhance the utilization of energy, how to improve the capacity of system and how to decrease the outage probability of system. The paper's main contents and innovation are as follows:1 When the total power and own peak power of source and cooperative nodes are limited, equate the question of optimizing asymmetry decode-and-forward cooperative ergodic capacity with the max-min question, further the solution are given. Aiming at joint optimization of nodes'relative location, power allocation and slot allocation, an optimized algorithm of outage probability is designed, and a method of simplified power and slot parameters allocation is bought forward. The theoretical analysis and numerical simulation reveal that this simplified parameters optimization method approaches the performance of joint optimization method, and both methods have distinct diversity gain relativing to symmetry decode-and-forward cooperation.2 A method of cooperative nodes selection based on order statistics is come up, which solve the problem of selecting multiple cooperative partners when the power and processing capability of single node is limited. After analyzing the relation expression between node number and outage probability of system, a decided algorithm of optimal node number is put forward and the upper and lower bound analytic expression of outage probability is worked out using the distributing characteristic of order statistics.3 The concept of outage capacity ratio is put forward in low SNR, based on which the relation of energy utilization and outage capacity in cooperative communication is founded. A new joint relay scheme based on feedback is brought forward, which adjusts the cooperative strategy dynamically based on the feedback state of nodes, and this scheme overcomes the problem that decode-and-forward is prone to cause waste of energy because of the cooperative nodes'decoding errors. The theoretical analysis and numerical simulation reveal that the new method achieves the outage capacity ratio bound of multi-node cooperation and improves the performance of decode-and-forward's outage probability and throughput in low SNR.4 The application effect of different modes of cooperation are analyzed and compared in cellular network. The research shows that multi-relay cooperation has better performance than multi-user cooperation in aspects of network capacity, outage probability and energy efficiency. In the cellular communication of multi-relay cooperation, maximum utilization of the network is a cross-layer design problem, which contains relay selection, power allocation and quality of service configuration. Exhaustion search water-filling method and opportunistic equal power method are researched based on the non-convex characteristic of this problem, and the optimal solution and approximate solution are extracted. Aiming at the complexness of exhaustion search water-filling method and poor performance of opportunistic equal power method, a hierarchical decomposable convex optimization based on distributed execution method is proposed, which gets the suboptimal solution at the same time the algorithm complexness is reduced to linear relation of users'number.5 An enhanced amplify-and-forward relay scheme is researched, and eigenvalues'sequences of the forward channel matrix, reverse channel matrix and relay matrix are demonstrated when singular value decomposition is used, which gives the theoretical basis of maximizing the mutual information between base stations and users.