In a limited network resource, techniques are needed to share the channel among different users as efficiently and as fairly as possible. Among multiple access techniques; Code Division Multiple Access (CDMA) has the exclusive advantage of allowing all active users share the same channel concurrently.  When CDMA technique is used, Multi User Detection (MUD) is needed to reject or reduce the Multiple Access Interference (MAI) affecting each active user. In this thesis, it is shown that multiuser detection using Parallel Interference Cancellation (PIC) technique provides a good compromise among the complexity, latency, and performance. This technique is suitable for Digital Video Broadcasting-Return Channel via Satellite (DVB-RSC) as well as Base Station (BS) in cellular communication systems. We offer a new scheme that is a combination of soft and hard PIC detectors whose performance is superior to that of the other famous sub-optimal detectors.  For most MUD schemes, a perfect knowledge of users' parameters is required. In this thesis, we apply a very simple method to estimate the parameters. PIC detectors are usually studied in equal-power case, i.e., a perfect power control scheme is assumed. We study PIC detector in near-far condition as well, where users arrive at receiver with different power levels. It is shown that our proposed scheme has some advantages over other schemes. First, it is much less complex than optimal and linear detectors. Second, it is much faster than sequential detector. Third, it has better performance than that of linear detectors