The Adaptive Transmission Technique For MIMO Cooperative Cognitive Radio Network

With the rapid growth of wireless communication services, the demands on data rate, network coverage and reliability are permanently growing. A new challenge has emerged in wireless spectrum resources utilization. Cognitive radio techniques achieve dynamic spectrum access via spectrum monitoring, and improve the spectral efficiency over conventional fixed radio spectrum allocation policy. By combining MIMO technique and cooperative relay theory with cognitive radio, secondary users are employed as relays to help the transmission of primary users. In return, they could get the opportunities to access the spectrum for their own traffic without affecting primary users. The MIMO-CCRN has becomes a promising technology because of the spectral efficiency enhancement. In this thesis, the spatial signal processing and related transmission techniques are discussed, the main contributions are:First, a scheme uses comprehensive utilization of interference cancellation and spatial signal processing techniques is designed for MIMO-CCRN. Primary users recruit some secondary users as the cooperative relays, to cooperatively forward primary users’ data in the TDMA mode. As a reward, secondary users obtain communication opportunity concurrently. The proposed strategy uses interference cancellation in phase two, using the known information to cancel the interference and realize concurrent transmission of primary and secondary communications. Utilizing zero forcing beam-forming theory in both two phases, can project the interference onto the subspace orthogonal to the one spanned by the desired signal, so as to achieve the effective use of spatial resources. Also, we use matched filtering algorithm to improve the transmission performance of primary users as much as possible. Furthermore, an adaptive algorithm is designed to eliminate bottleneck effect in both time domain and power control, and enhance the end-to-end performance of primary transmission. The simulation results show that the proposed method could increase the spectral efficiency, and create a “win-win” situation for both primary and secondary users.Second, we propose a joint adaptive beamforming and power allocation algorithm in MIMO-CCRN system. The object is to minimize the total transmit power, subject to the signal to interference plus noise ratio(SINR) at each user is above a certain threshold. The Lagrangian relaxation and semidefinite optimization are used to jointly design the optimal beamforming vectors of all users and power consumption of the transmitters. Also, we introduce the generalized eigenvalue problem to optimize the solution by an iterative method. The proposed strategy can eliminate the mutual interference in concurrent transmission effectively, and enhance spectral efficiency. By computer simulation, the feasibility of our approach is verified.At the end of this thesis, we conclude the research work and give directions for the future work.