Research On Key Technologic Applications Of MIMO In Wireless Communication System

With the development of modern wireless mobile applications, high speed and reliable communication has increasingly high requirements on bandwidth efficiency and transmission performance. Along with this rise of rate comes the even undesired wireless transmission environment and fast signal fading; meanwhile, the frequency spectrum resource is more and more limited. So searching new communication technologies to improve transmission performances and realize high speed, high efficiency digital transmission will be the main task of current mobile wireless communication.MIMO and OFDM will be the key technologies in the next generation of wireless communication systems. The MIMO-OFDM technology which is the combination of the two technologies, improves the system capacity and makes efficient use of frequency spectrum. It is also to be the focus research field in the future wireless mobile communication. On the basis of international current researeh works, this paper establishs correlated communication system medols, investigates some key technologies for MIMO-OFDM systems and carries on the MATLAB simulations in the following topics:diversity techniques, multi-carrier CDMA techniques, precoding techniques, multi-user scheduling techniques and cross-layer resource allocation.In this paper, firstly we establish the medol of the MIMO-OFDM system based on STBC. Sencondly, the medol of the STBC-MC-CDMA system is enstablished combined with CDMA technique. Then chaotic sequences instead of pseudo-random (PN) sequence are used as new spread sequences in the STBC-MC-CDMA system, and the performances of chaotic sequences are proved. Also, we introduce the precoding technologies in the multi-user MIMO system with perfect/imperfect channel state information (CSI), and the simulations are carried on. At last, in order to resist delay sensibility of real time services, this paper proposes an adaptive cross-layer resource allocation scheme employing Hopfield Neural Networks (HNN) algorithm in multi-user OFDM system. In setting of the user scheduling priority, we considere not only the CSI at the physical layer, but also users'queue state information and waiting time at media access control (MAC) layer. By the HNN algorithm, the proposed scheme aimes at decreasing the average delay and packet loss ratio, and maximizing the system capacity.