Research On Application Of Smart Antenna In The Uplink Of DS/CDMA System

During the past decade, wireless communication systems have made a great progress world-wide. The number of mobile subscribers has been increasing rapidly, at the same time, there is great demand of the mobile subscribers for a higher quality services, more sorts of wireless services and higher rate data services . Therefore, how to use the precious wireless resources more efficiently has come to be an urgent problem to be solved.The application of smart antenna technique in wireless communications allows the base station to transmit to and receive from mobiles by directional beams, which can improve the system performance by relieving the CCI, decreasing the transmission power, improving the spectrum efficiency, enlarging the system capacity, relieving the space electronmagnatic interference and so on. Smart antenna technique has wide applications in radar and sonar and other military communication areas. Due to the difference of the communication environments and the complexity of communication devices between mobile and military communications, the application of smart antenna in wireless communication systems is still a new research topic.Because the CDMA technique has a relatively better immunity to interference, a better concealment of information data and a larger system capacity, it has come to be the primary multiple access techniques for the third generation mobile communication systems. Consequently, this thesis focuses on the smart antenna technique and its applications in DS/CDMA mobile communication systems, which includes application algorithms, implementation structure, and itscombination with the MUD techniques and Rake receiver techniques.The main contributions of the thesis include:1. Summarizes the achieved fruit of international research on smart antenna technique, including the current research status, the implementing structures, and its effect on system performance etc.2. Aiming at the frame characteristics of time multiplexed pilot bits, a new algorithm named pilot bits assisted LMS-DRMTA is formed. This algorithm has a much lower computational complexity and a better performance than the LS-DRMTA used in DS/CDMA systems.3. A simple method of locating the initial DO A of the desired user is proposed for the DOA tracking array-processing method. This method can locate the initial DOA of the desired user into the 3dB width of the array main beam quickly and accurately. It solves the premise problem of the DOA tracking array processing method.4. An adaptive step adjustment method is put forward for the DOA tracking array-processing method. This adaptive method is simple, robust, and has low implement complexity, which on the one hand, avoids the danger in which the scan speed of the base station main beam can't keep up with the angle speed of mobile stations, on the other hand, decreases the deviation of DOA tracking, all of which making the DOA tracking method more accurately and more efficiently.5. Partial parallel interference cancellation (PPIC) technique .oriented for the space-temporal combination interference cancellation scheme, has such advantages as reducing the computational complexity and buffering space,further more, avoiding the losing of system performance due to the inaccurate estimation of the weak CCI. When the array processing scheme adopts DOA tracking method, the DOA information of all the receiving channels can be used directly to differentiate the strong and weak CCI.6. The combination scheme including 2D-Rake receiver and PPIC is proposed for the uplink of DS/CDMA system. In this receiving structure, smart antenna takes cancellation of the interference whose DOA is different from the desired user , while the Rake receiver, collecting the different time delay copies of the desired signals, gives its output to PPIC which cancels the interference whose DOA fall into the main beam of the array at the base station. The proper configuration of smart antenna, Rake receiver and PPIC will produce a self-contained CCI cancellation scheme for DS/CDMA mobile communication systems.