The Research On Implementations Of Transceivers Based On Beam-forming Technology Of Smart Antenna

Smart antenna is considered to be one of the key technologies that will be used to cope with the shortage of frequency resources and to enhance the capability of communication system. It has drawn more and more attention now, and became one of the research hotspots both at home and abroad. Smart antenna can help communication system utilize multi-path energy more efficiently, reduce interference, and then realize the optimal reception under a certain principle. Therefore, the introduction of smart antenna will greatly improve the system's performance.Based on the basic structure of array antenna and its signal expressions, this article introduces some key techniques in smart antenna system, such as beam-forming, DOA (Direction of Arrival) estimation, etc. The performance of each common used algorithm has been analyzed through simulation. Taking TD-SCDMA as an example, this article also gives out a new DOA searching method based on CDMA system. This method is simple and stable. More importantly, by using this method, the number of signals which can be estimated is not limited by the number of array elements, which solves the common problem of traditional DOA estimation methods. Multiple beam-forming should be the main application scenarios for smart antenna, so the effect of different beam-forming algorithms under multi-user environment are stimulated and analyzed in this article. The result shows when using the traditional phase-shifting-and-sum method, the received signal will be affected by the other users'signals. The impact of interference is decided by the level of side lobes. So it can not realize ideal spatial division multiple access (SDMA). And when used in practical system, it must be combined with other multi-access technologies in order to obtain the expected result. However, algorithms based on zero-point technique, such as LMS, can automatically adjust the beam to make sure that gains of interference signals are all zero. So even in multi-user environment, the reception of the expected signal will not be affected by other uses'signals. To some extent, this kind of algorithms can realize SDMA and thus have better performance. At last, based on the spatial-time model of CDMA signal, this article makes a brief introduction of 2D-RAKE receiver conception and then gives out an applicable structure of it, which combines smart antenna and RAKE receiver. At the same time, multi-path signal coherent demodulation RAKE receiver is also proposed to solve the problem of radio loss factors caused by non-coherent demodulation. The application of 2D-RAKE receiver can make full use of the spatial and time characteristic of multi-path signals and improve the system performance to the greatest degree.