Removal of Multiple Access Interference in DS-CDMA System

Multiple access interference (MAI) is a factor which limits the capacity and performance of DS-CDMA systems. MAI refers to the interference between direct-sequence users. This interference is the result of the random time offsets between signals, which make it impossible to design the code waveforms to be completely orthogonal. While the MAI caused by any one user is generally small, as the number of interferers or their power increases, MAI becomes substantial. The conventional detector does not take into account the existence of MAI. It follows a single-user detection strategy in which each user is detected separately without regard for other users. Because of the interference among users, however, a better detection strategy is one of multi-user detection (also referred to as joint detection or Interference cancelation). Here, information about multiple users is used jointly to better detect each individual user.