Application Research Of MUD In CDMA System

In recently about ten years , because CDMA communication rapidly is developing and the amount of user is increasing in striking speed, the capability of communication give prominence to fall. The capacity of channel is limited by interference, especially for the interference from the same channels and the adjacent channels . Moreover, since in the wireless communications, channel is generally Time-variation. The adaptation should be sufficiently fast to track the variation of channel. If the rate change is allowed, the application of the adaptive receiver to the CDMA system is somewhat cumbersome. The main difficulty to use the adaptive receiver is that the adaptation should resume after the rate change. As a result, the Performance will be degraded due to the transient.Multi-user detection (MUD) is one of the key techniques for CDMA systems. Through joint detection and interference canceling, multi-user detection can reduce multiple access interference(MAI) and inter-symbol interference(ISI) dramatically, relax "near-far" effect, evidently, improve the system performance and increase the capacity of CDMA systems.However, MUD does not work without using the array of training before coefficient is locked, what is more, constant sending of array of training will cause big waste of spectral resources. Therefore, people turn to the study of the blind self-adaptation that does not need training. In recent years, the study on blind multi-user detection has aroused great attention around the world.In this paper, the application of multi-user detection in the CDMA system is investigated. Two aspects of MUD are mainly discussed: One is the blind adaptive multi-user detection technology, and the other is the application of MUD in the mobile fading channel.Several representative multi-user detectors are recited before the main contents. Firstly, the concept of blind adaptive MUD is educed by the introduction of the MMSE detector requiring training sequences. Secondly, Make analysis andsimulations on Signal Interference Rate(SIR), Bite Error Rate(BER), minimal output energy and anti-interference Performance in different channel environment of LMS algorithm, RLS algorithm and Kalman algorithm of the blind multi-user measures. The computer simulation shows that RLS algorithm and Kalman algorithm are of great convergence performance, stable SIR and accurate tracking in timing channels. Finally, Autoregressive Modeling for Rayleigh Fading Channel for MUD which flat Rayleigh fading synchronous channel is introduced, and to enhance the system efficiency of MUD simulation.