Research On Multi-Realay-Based Virtual Mimo In Cognitive Radio Networks

Currently, along with the development of wireless communication technologies and the popularity of smart mobile devices, the deployment scale of wireless communication networks is rising rapidly. The deployment of high-density heterogeneous wireless relaying networks in cognitive radio environment have become one of the key technologies which can improve wireless communication network coverage, data transfer rate, spectrum efficiency and quality of service (QoS) of users.This thesis focuses on the research on relay coordination transmission in cognitive radio network and pays more attention on the design of transmission plan and the simulation of the plan’s performance. The main contributions and innovations include the following aspects:(1) The multi-relay virtual MIMO transmission scheme in cognitive radio network for ideal feedback channel is investigated. By analyzing the multi-relay collaboration transmission in cognitive network, the main network interference model and optimizing the transfer vector of the collaborative signal of relay node cluster, two transmission schemes which can minimize the overall power consumption or maximize weighted sum of the transmission rate of business transmission are proposed based on the actual power consumption constraints of the relay nodes and the interference threshold constraint of the main user nodes. An evaluation method which combines positive semidefinite programming and random matrix theory is presented; Based on maximum weighted sum of the transmission rate model and the observations that there is duality between the problem of minimum sum-power and the maximize weighted sum of the transmission rate, a solution, based on the weighted sum of rate segmentation is put forward. Compared with the simple time division multiplexing scheme, the simulation results show that the scheme can greatly increase successful service transmission probability and reduce the whole energy consumption of relay nodes since the reference of virtual MIMO technique brings spatial multiplexing gain.(2)Taking into account the existing feedback error of node channel in the actual communication system, the robust multi-relay virtual MIMO transmission scheme in cognitive radio network for non-ideal feedback channel is analyzed. By modeling the feedback error of the given channel, the lowest available SINR at this time and maximum receiving interference of the main network node are analyzed. Through deviating the closed-form expression of the service SINR under the worst case and the receiving interference of the main user nodes and referencing the optimization ideas of ideal feedback channel, the problem solving method that combines positive semidefinite programming and random matrix theory is proposed and the design of the robust multi-relay virtual MIMO transmission scheme in cognitive radio network for non-ideal feedback channel is given. Compared with the non-robust scheme which disregards channel feedback error, the simulation results show that the proposed robust scheme can guarantee the requirement of lowest service SINR of cognitive network, the maximum interference threshold of the main network node, the legitimate use of unlicensed spectrum and improve the reliability of the service transmission alhough it increases the whole power consumption of relay nodes.