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Title: Multiple access interference cancellation for CDMA
Author: Oon, Tik Bin
ISNI:       0000 0001 3459 3981
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1998
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The application of multiple access interference cancellation techniques to improve the performance of code division multiple access (CDMA) mobile radio systems is addressed. The discourse commences by describing the present mobile radio scene with emphasis on the evolutionary paths towards third generation cellular systems. This is followed by a brief review of the mobile radio channels. Next we examine the multi-stage parallel cancellation (MSPC) scheme, the zero forcing (ZF) scheme and the zero forcing with decision feedback (ZF-DF) scheme for overcoming the basic limitations of the conventional CDMA scheme that employs single user matched filter detection. From analysis and simulation, these enhanced CDMA detection schemes are found to have inherent limitations, particularly, when the number of active users approaches the processing gain N. We then determine analytically and by simulations the performance of a successive serial parallel cancellation (SSPC) CDMA scheme in the presence of flat Rayleigh fading up-link asynchronous channels. The scheme is shown to have the potential to reach the single user bound without the use of FEC coding and close-loop power control, with the proviso that sufficiently accurate channel estimates are available for both signal ranking and regeneration. Using the performance criterion of average bit error rate, the SSPC scheme is compared with the MSPC, ZF and ZF-DF detection schemes, and found to be superior for different numbers of active users. Similarly, the computational complexity requirement of the SSPC scheme is found to be lower than the ZF and ZF-DF schemes. An adaptive technique to reduce the processing delay in the serial stage is also proposed. We also investigate the performance of the SSPC scheme using RAKE receivers and having perfect channel estimation when operating in two-path frequency selective Rayleigh channels. The analytical and simulation results show that the SSPC scheme performs equally well when compared to operation in flat Rayleigh fading channels. At this junction our results mostly rely on the assumption of perfect channel estimation. To overcome this limitation we examined a robust channel estimation technique, namely the maximum likelihood channel estimation (MLCE) scheme, for coherent, up-link transmissions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Communication systems & telecommunications