The Study On The Technology Of Digital Beamforming In The Smart Antenna System

With the anticipation that communication to a mobile device anywhere on the globe at all times will be available in the near future, a demand for wireless mobile communications services is growing at an explosive rate, so frequency has become more and more valuable. In order to accommodate more users in a limited frequency, many kinds of technique are proposed, among which smart antenna is the research hotspot.The smart antenna combines the antenna array technology with the signal processing in space and time. The spatial processing lead to more degrees of freedom in the system, improves its overall performance, and enhances the system capacity and spectrum efficiency. Smart antenna adopts SDMA and in terms of the difference of transmission direction, it can distinguish signals of the same frequency, the same time and the same code. Smart antenna can enlarge capacity greatly. Digital Beam Forming is a important part of smart antenna, by using it antenna array could have Adaptive beam, lower Side-lobe beam and beam scanning, as well as multi-users beamformering, which could transmitted multiple co-channel signals to hold more users.First, the background & trends of the research on smart antenna technology are introduced; moreover, the base theory of smart antenna is presented. Second, the realization of smart antenna based on software radio architecture is discussed, and a kind of software radio architecture of smart antenna is given in the paper. Last, the paper pays attention to the two parts of problem about smart antenna beamforming. One is the technology of downlink multi-user digital beamforming. It utilizes the difference of directions among users to make the user receive the desired signal without co-channel interference. An optimum design is presented in the paper, simulation shows that compared with other methods: this method can realize Space Division Multiple Access with controllable co-channel interference. Another is adaptive beamforming with antenna arrays. It uses the digital signal processing technologies to produce spatial and directional beam, then let the antenna's major lobe point to the coming direction of reference user and the side lobe point to the coming direction of interference user, this can reduce the co-channel interferences (CCI), enhance the user capacity and spectrum efficiency. Specially, the author analyzes several beamforming algorithms for CDMA system, and simulates the adaptive beamforming of LS-DRMTCMA.