Research On Smart Antennas Technique For CDMA Systems

With the people's more and more demands on communication services, the global communication is currently undergoing very rapid development. As the dominating technique for the coming personal communications, the wireless communication is making a great attention and is becoming one of the hotspots of communications research. The direct-sequence code-division multiple-access (CDMA) technique is the most promising multiple access method in modern communication systems. However, the rapid increase in user amount and the shortage of communication resources cause a series of problems to be solved, such as the deficient capacity, dropping communication quality, and etc. How to combat the multiple access interferences (MAI) and the multi-path fading which limit the quality of CDMA systems is the main consideration in the attempt to improve the CDMA mobile communication systems. The smart antenna system is an antenna array system that is composed of several antenna units. By using digital signal processing technique, the smart antenna can produce multiple beams with the maximum aiming at the different users and the nulls pointing to the interferences automatically. Therefore, the smart antennas can combat the MAI and improve the mobile communication systems. Compared with other mature interference canceling method, the smart antenna technique is developing and the most prospective.This dissertation presents the new results of our researches on the control algorithm of the smart antennas in CDMA systems.One of the contributions of this dissertation is to give a de-spread re-spread adaptive smart antenna with time domain equalizer and referent signal equalizer. By using the time domain equalizer and referent signal equalizer, we assign the interference canceling to different parts of the smart antenna. The antenna array responds for combating the MAI and the time domain equalizer responds for eliminating the multi-path interferences. We simulated the performance of the proposed smart antennas. The results show that the hybrid of de-spread re-spread adaptive smart antennas with equalizer can give better performance.Another contribution of this dissertation is to present a multi-user detection re-spread adaptive smart antenna by substituting the multi-user detector for the match filter in the de-spread re-spread adaptive smart antenna. Compared with the tradition de-spread re-spread adaptive smart antenna, the new smart antenna can combat the MAI better and improve the system stability. The new smart antenna does the multi-user detection in the output of the antenna array. Therefore, compared with the space-time process of the multi-user detection + array scheme, our method can save calculation. We simulated the performance of the multi-user detection re-spread adaptive smart antenna in computer. The results show that the introduction of multi-user detector can improve the performance of the smart antenna.Based on the repeat adaptive algorithm given in this dissertation, which can converge better with short data length, we derive a LMS adaptive smart antenna that uses the spread-sequence as the reference signal directly for CDMA systems. Simulation shows that the proposed smart antenna is feasible. The repeat adaptive algorithm and the adaptive smart antenna using the spread-sequence as the reference signal directly is the third contribution of the dissertation.The smart antenna technique is one of the hotspot of the recent researches and its control algorithm is crucial. This dissertation demonstrates our benefic exploration and research in this area. The results given in the dissertation would be helpful to the smart antenna research.The research work in the thesis was supported by the Torch Project of Guangdong Province"The Research and Exploitation of Integrate Cross Platforms Wide Band Wireless Network Systems"(2002C1010106), Natural Science Fund of Guangdong Province (Project 31441 :"Research on the Software Integrate Antenna in TD-SCDMA Systems"), and the Constructing High Level University Project of South China University of Technology"The Research on the Smart Antennas in Wireless Access Systems".