The Research Of Smart Antenna Technology For DS/CDMA Mobile Communication Systems

Recently, smart antenna has become a very promising technology for wireless communication, which could enhance the system capacity. This thesis begins with the introduction of the modeling of array signal and wireless channel, as well as the explanation of the fundamentals of smart antenna. Vector channel model is analyzed, and the features of the array receiver under wireless multi-path propagation are illustrated.Second, both the beamforming methods for smart antenna and adaptive beamforming algorithms are explored. We deeply study the performance of adaptive array under wireless multi-path environment. In addition, the beamforming techniques for CDMA systems are discussed emphatically. The algorithm based on code filtering is deduced in detail theoretically, and the performances such as convergence and bit error rate (BER) are simulated. Meanwhile , we improve a decision-projected algorithm based on Least-Mean-Square(LMS) error. The improved algorithm is combined with Normalized Least-Mean-Square(NLMS) algorithm. Computer simulation results are presented detailedly showing that the algorithm exhibits excellent convergence, tracking capability, as well as lower BER.In the case of having interferences external to the system, this paper presents a new method able to estimate the spatial signatures of all active users projected onto the subspace orthogonal to the external interferences subspace. With these spatial signatures we can design a specific beamformer for each user in order to combat the external and multiple access interference.