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UBC Theses and Dissertations

Reverse link capacity of cellular CDMA systems employing group successive interference cancellation Silvester, Anna-Marie


Successive Interference Cancellation (SIC) is a much studied multi-user detection technique capable of increasing reverse link capacity significantly [1, 2, 3, 4]. Current issues blocking industry from adopting multi-user detection include complexity, cost, and detection delay [5, 6, 7, 8, 9, 10, 11]. In this thesis, we evaluate the benefits of a simplified SIC scheme, called group successive interference cancellation (GSIC), in which users are cancelled in groups rather than individually. Canceling users by group has a number of benefits, including reduced detection delay time, and decreased hardware complexity as compared with practical implementations of SIC [7]. We begin by extending a model of inter-cell interference first developed for SIC and presented in [12, 13, 14, 15]. Using the inter-cell interference factor developed in [12, 13, 14, 15] we derive expressions for the outage probability of GSIC. In order to improve system performance we consider four different diversity cases. These diversity cases include selection macro-diversity (SM), when a user is detected based on 1 copy of its signal received at its assigned base station, and combining macro-diversity (CM), when a user is detected based on 3 copies of its signal received at surrounding base stations. We also consider the case of multi-cell cancellation (MGSIC), when a user's detected signal is regenerated and cancelled not only from its assigned base station, but also from 2 other base stations in its vicinity. The group sizes for which we evaluate outage probability are 1, 10, and 20. Our numerical evaluation of the theoretical expressions indicates that higher values of capacity can be obtained from the SIC-SM, SIC-CM, MSIC-SM, and MSIC-CM techniques than was previously indicated by [12, 13, 14, 15]. Our research has shown that the work in [12, 13, 14, 15] applies a bound on the inter-cell interference factor. Numerical results show significant increases in capacity for CM as compared to SM, and for MGSIC as compared to GSIC. However, simulation results generated in an environment with good but imperfect power control, and with looser restrictions on the power distribution of users indicate that gains for MGSIC are not as significant as indicated by theory. Both simulation and numerical evaluation demonstrate that CM provides a significant capacity increase over SM. Increasing group size reduces the number of users a base station can support on the reverse link; however, these losses may be tolerable considering the reduction in detection delay and hardware complexity that accompany increasing group size. On average, group size can be increased to 10 with a 3.5% loss in capacity, while detection delay and hardware complexity are decreased by a factor of approximately 1/10. Similarly, group size can be increased to 20 with a 7% loss in capacity, for which detection delay and hardware complexity are decreased by a factor of approximately 1/20.

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