Research On Relay Selection Scheme In Wireless Communication System

Recently, cooperative relay technology is known as a new direction in wireless communication, which can solve the problem that MIMO can’t be implemented for mobile devices due to the limitation such as power and size. Cooperative relay technology allows single-antenna mobile users to share their antennas, which creates a virtual MIMO (Multiple-Input Multiple-Output) system. By applying cooperative relay technology, the impact from shading and instability in wireless channel could be reduced, and the spectral efficiency and transmission rate could be improved.In this thesis, two major research directions which are the cooperative partner selection method for wireless one-way relay system and the cooperative partner selection method for wireless two-way relay system are studied in this paper. The research contents and innovation points are as follows:1. In the study on cooperative relay selection scheme for one-way relay system, after the research on the related cooperative system models, a dynamic relay selection scheme for vehicle communications in the AF (Amplify-and-Forward) communication mode is proposed in highway environment, which is based on known channel information estimation and power allocation for every node. First, the total power of the relay cooperative system is assumed to be fixed, and channel state information can be previously acquired. Thereafter, the relay state value is set to remove the unwanted relay through theoretical derivation of bandwidth normalized capacity and system outage probability for a multiple relay scenario, which is used to be compared with the least state gate. Furthermore, the relationships among bandwidth normalized capacity, Signal-to-noise ratio and the source power ratio have been investigated. Simulation and analytical results illustrate that the proposed scheme is efficient enough to reduce outage probability and maintain system capacity in highway environment.2. In the study on cooperative relay selection scheme for two-way relay system, with summarizing the related works for two-way relay selection, an algorithm was improved to select the proper relay nodes. Aiming at the resource allocation problem, a power allocation scheme based on weighted sum-rate maximization was improved, which is under a constraint on the total transmit power consumption. Besides, the performance of system transmit reliability with different sum-rate weights was also discussed. After several simulations, the results show that the proposed relay selection scheme notably improves system performance compared to other existing two way relay selection schemes in certain cases, and the proposed power allocation scheme can also increase the system sum rate compared to other existing power allocation schemes in certain cases.