Study On Spatial MAI Suppression Techniques In CDMA System

Code division multiple access (CDMA) technique which the three mainstream techniques (WCDMA, cdma2000, TD-SCDMA) of 3G stem from is grounded on the fundamental of spread spectrum communication. Owing to its broadband characteristic, the CDMA technique offers an outstanding potential to restrain interference and noise. The imperfect orthogonality of PN code causes certain dependence between subscribers, which is called the multiple access interference (MAI). MAI is a main interference in CDMA communication systems. To suppress MAI is of vital importance.The adaptive array which has been widely used in radar and sonar areas has recently been named "smart antenna" and aroused more attention in its applications of suppressing MAI in CDMA systems. The smart antenna is able to improve SINR significantly and reduce time delay spread and multipath fading at the same time.This paper begins with an introduction to the principles of array processing and a simple summarize of beam forming methods. Then the beam forming method grounds on minimum mean-square error criterion (MMSE) has been reviewed, and so does its anti-interference ability. Some simulation results with LMS are presented to prove the validity of previous analysis. And then, the MAI suppressing performance of an optimal LCMV array has been discussed when the location of the subscriber has already been known. Finally, a new scheme of the combination between optimal array base on the principle of maximum signal to noise ratio and multistage multiuser detection technique is discussed and bit error rate formula is given at the same time.