Research Of Smart Antenna In CDMA Mobile Telecommunication Systems

According to the increasing maturity and the practical application of the third generation of mobile telecommunication technology at present, the practical application of CDMA smart antenna system is required urgently day by day. The article provides the research of CDMA mobile telecommunication smart antenna and the basis of intelligent antenna's further research and application. To cellular mobile telecommunication, because of complicated multi-path spread of wireless signal which brings time spread, Doppler spread and angle spread, frequency-optional fading and time-optional fading are produced when base stations receive signals, which results in Inter-Signal Interference(ISI), At the same time, to saving frequency resource, wireless cellular network adopt frequency-reuse technology, which produces Common Channel Interference(CCI), especially CDMA system, when base stations receive anticipates, the same time and the same frequency can be occupied by all the users of CDMA, the only difference is that every user has one's unique mutual orthogonal frequency-spread code, receivers de-spread only by each frequency-spread code. Because of much existence of Multiple-Access Interference(MAI), the receive of CDMA mobile telecommunication system is limited by interference. In order to restrict CCI , to eliminate ISI and to improve the system's capability ,much work was done by scholars from many countries, and many efficient methods were studied. Originally, divide integrated disposal technology is adopted such as space-integrated , each signal received by wireless separates from each other, whose beam-charts don't superpose, many peak values are sampled at the peak moment, and combined by proper ways; Afterwards, adaptive array disposal technology and time-space adaptive balanced technology are adopted, but ,now, people mainly study the time-space two-dimensional disposal technology of time-field and space-field combined. Because smart antenna system combines array antenna and advanced signal disposal technology, and makes use of space-field information to restrict MAI effectively, system capacity and communication quality are improved greatly. Smart antenna system is studied by referring to much literature in this article, whose main work by inheriting previous achievements are as follows: 1.Firstly, smart antenna technology and research actuality in CDMA system are expatiated concretely and smart antenna technology is presented comprehensively, including working way, fundamental, research content and actuality. Research content and experimentation system are expatiated in detail. Smart antenna includes two kinds: Switched Beam smart antenna and adaptive array smart antenna. Because of the volume and the complex degree and so on, the concept of smart antenna only applies to base stations. Switched beam and adaptive beam have their own merits and shortcomings, Switched beam's merits include simple structure , low-cost engineer, low-risk investment; Adaptive beam's merits include increasing anticipates'gain and reducing noise and interference by pointing beams. Because the maximum of beams can be aimed at anticipates better and adaptive interference can be returned to zero, the improvement of the Interference-to-Noise ratio of power is better than switched beam, furthermore, the capacity and the ratio of using frequency spectral will be increased greatly. But, because adaptive beam's shortcomings are that thedifficulty of realization and system's cost are more than switched beam, and the combination with existing base stations is more difficult than switched beam, adaptive beam smart antenna hasn't been used widely. 2.Presenting space spectral direction finding theory, then analyzing the classic space spectral direction finding algorithm -MUSIC basing on characteristic-decomposed,analyzing DOA estimative capability of MUSIC algorithm, providing estimate warp and distinguish ratio of MUSIC, and indicating the direction finding characteristic of MUSIC can be increased by increasing Signal-to-Noise ratio, numbers of array unit and figure of the fast beat. 3.Analyzing the effect to MUSIC space spectral by amplitude and phase error in theory, and providing the theoretical relation of space spectral and amplitude's dismatch. The result is: because eigenvalue and eigenvector result from amplitude of array unit channel and phase error, space spectral produces error. Emulational result proves the theory correct. Single amplitude error effects precision estimated by space spectral DOA weakly, but reduces space spectral peak value, and reduce estimative distinguish ratio. However, phase error not only reduces space spectral peak value, but also changes the position of space spectral peak value, lastly, effects the precision and distinguish ratio estimated by space spectral DOA. When amplitude and phase error exist in array unit channel, MUSIC space spectral error and interference variance are direct ratio, it's scale coefficient is related with eigenvalue and eigenvector in Utopian instance. Emulational result proves that amplitude and phase error reduce space spectral...