Improvement of the DS-CDMA performance with parallel interference cancelation (PIC)

In CDMA systems a unique code is assigned to each user to make them distinguished from each other. For the perfect detection, these codes must be orthogonal. But the number of the orthogonal codes with a limited length is very little and this will restrict the number of users. One way for increasing the number of users is extending the length of codes which leads to complicating the system that is not suitable in telecommunication systems. Another way is using the non-orthogonal codes with proper auto-correlation and cross-correlation characteristics. The number of these codes is much more than the complete orthogonal codes, and therefore leading to increase the number of the users. But, because of the non-orthogonality of the codes, the signals wilt have some interference with each other, which is called Multiple Access Interference (MAI). In traditional receivers with Single User Detection (SUD), this MAI is added to desired signal and leads to greedily decrease in performance of system. For compensating the effect of MAI, Multi-User Detection (MUD) is used. In this method, MAI effect of other users on a specific user is detected and omitted from the signal of that user. MUD is done in various ways including Serial Interference Cancellation (SIC) and Parallel Interference Cancellation (PIC). In this Paper, the effect of various parameters of PIC on the value of performance improvement of CDMA system using PIC is studied. The results show that, every parameter increasing MAI will increase effect of PIC on performance improvement of CDMA system using it, compared with SUD.