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Application of interference cancellation to third generation partnership project wireless systems Olawale, Kassim Olabode


Direct Sequence Code Division Multiple Access (DS-CDMA) is one of the technologies available for present day as well as future wireless systems. A major limitation on the use of CDMA is Multiple Access Interference (MAI). This is caused by imperfect separation of users communicating within the same physical frequency and time domain. Eliminating MAI enhances detection of the desired user's signal in a DS-CDMA system. Multiuser detection considers the interference caused by other users in the same communication system while detecting the* desired user. Our work involves critical study and evaluation of some of the many multiuser detection algorithms for Third Generation Partnership Project (3GPP) wireless systems. We selected and compared performance of the Parallel Interference Cancellation (PIC), Successive Interference Cancellation (SIC) and Group-wise Serial Interference Cancellation (GSIC) methods in the uplink of a 3 GPP system. To evaluate the expected performance improvement, computer simulations were carried out using MATLAB® software. A UMTS (Universal Mobile Telecommunications System) base station with a conventional receiver was compared to another one employing PIC, SIC and GSIC receivers. Test parameters were set to values provided in the 3 GPP Standard. Power control was not implemented in our study. Results of these simulations demonstrate lower bit error rates in those receivers employing interference cancellation in most cases. We observe that the three receivers are equally suitable at low SIR, low data rates and small number of users. None of the three schemes is suitable for systems using high data rates (raw bit rate of 480 kbps or higher) or high number of users (more than 25 users per sector). The PIC receiver is better than the SIC and GSIC at about 0 dB SIR. With these observations, we conclude that any of these three schemes can be deployed to a 3 GPP system. Channel conditions under the 3GPP test scenarios are harsh and may give worst-case performance results with interference cancellation, especially without use of power control. In some environments such as wireless LAN's, low number of users and moderate data rates would prevail, in which case interference cancellation would improve performance significantly.

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