Abstract: A new mixed seria-l parallel mult-i user detection algorithm with decision feedback was proposed on the basis of RLS algorithm．Theoretical analyses of the new algorithm in fading channels were carried out‚where the system data transfer rates were divided into two cases： one is related to ISI‚the other is not．A theoretical formula for BER （Bit Error Rate） calculation was then presented and the simulation of the algorithm was performed．The results show that the algorithm proposed here is of high correctness and low BER with low cost‚thus making the algorithm practicable． 

Key words: DS-CDMA system, mult-i access interference, mult-i user detection