The Performance Enhancement Of Smart Antenna On CDMA/SDMA Systems

CDMA, as a multiple access technology, has been widely used in wireless communication systems. Broadband CDMA is a core technique in 3G system, and it needs faster speed and more capacity. Smart antenna can satisfy this demand, and in fact smart antenna has been one of the hottest technologies.Smart antenna using digital signal process technique, produces space directional beam, and utilizes space filter ability for improving the performance of CDMA systems. On the other hand, utilizing the smart antenna and the users' spatial information, we can develop the Space Division Multiple Access (SDMA) technology. But for SDMA, it makes the traditional three-dimensional channel model to four-dimensional one. In order to realize SDMA, the four-dimension channels should be used effectively. This thesis deploys studies about the two application aspects of smart antenna, the performance improvement and the channel allocation schemes in SDMA systems.In chapter 1, we give the research background, the recent research results about smart antenna and SDMA, and give the signification of the study. Then, the channel models in antenna array system and the basic concepts of the smart antenna are introduced in chapter 2.Then, in the 3rd part of the thesis, the analysis of the bit error rate (BER) in CDMA system with smart antenna is presented. We develop a vector approach to the BER calculation formulas in multi-path condition, in which the signal is received through both of single path and multi-path, and we discuss the influence factors to the BER. The analysis shows that the CDMA systems with antenna array can get lower BER and can be of better performance than the present CDMA systems.In chapter 4, we get the ways realizing SDMA in the TDD CDMA systems equipped with smart antenna. We sum up the schemes of the dynamic time slot allocation in TDMA/SDMA, and the schemes of the dynamic spread spectrum codes allocation in CDMA/SDMA. Further more, we compare the schemes with each other.In the last chapter, we develop an approach that can easily realize SDMA in TDD CDMA system, which uses the phase-controlled- by-time-switching linear array to realize duplicated channel in spatial domain periodically. This antenna model can easily realize the SDMA.As a key technique in 3G, smart antenna must be more and more important in the wireless system in the future. This thesis would be a good guide and reference to theory study in the future.