Research On The Key Technology Of The Next Generation Wireless Communication System

With the development of mobile communication, Internet and multimedia message service, the demand for transmission rate in wireless communication is increasing rapidly overall the world. However, the available spectrum is limited; people's growing requirements for wireless communication cannot be satisfied if we cannot make a breakthrough in spectrum ultilization as soon as possible. To solve the scarcity problem for spectrum resource, various technologies have been explored to make full use of the spectrum. It can be saided that the development of wireless communication is a history of solving the effective ultilization for spectrum. In order to achieve the goals of high rate, wide band and high spectrum efficiency for next generation of wireless communication, OFDM technology, MIMO technology and cognitive radio are proposed and become the research focus in the future.By exploring the technology of OFDM, MIMO and cognitive radio,this thesis mainly studied some key technologies of the next generation of wireless communication: the channel estimation and power allocation for OFDM uplink transmission in fast time-varing channel; the pre-coder desin and interference alignment in cognitive network. In this master thesis, some new or optimal algorithms are proposed based on the existing literatures and a number of good results are also obtained.The main research contents in this master thesis are as follows:(1) A new channel estimation algorithm and optimal power allocation for OFDM uplink transmission in fast time-varing channel are proposed. Compared with the existing algorithms, the proposed algorithm has better estimation performance and lower complexity. What is more, the optimal power allocation can also achieve the desired goals in the simulation which demonstrating the correctness and effectiveness of the proposed algorithm. The overall research is very meaningful for the realization of the channel estimation.(2) For a two-tier MIMO cognitive network with a common receiver, an improved cognitive precoder for secondary transmitter and the corresponding space alignment algorithm are proposed in this master thesis. The simulations reveal that, on the premise of achieving Qo S for primary system, our proposed algorithm can get larger capacity in secondary system,which proves the effectiveness of the algorithm.(3) By exploiting multi-user MIMO-VFDM transmission, an optimal pre-coder design for secondary transmitter is proposed in two-tier cognitive networks. Compared with the unoptimized algorithm, the proposed pre-coder design can ultilize the optimal null space to construct the precoding matrix, which will lead to more channel capacity and high spectrum efficiency for secondary network.