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UBC Theses and Dissertations

Capacity improvements using adaptive nullsteering antennas in IS-95 cellular CDMA systems Chiu, See-Ming David


In this thesis, the effect of adaptive nullsteering on the system capacity of an IS-95 system is investigated. Adaptive nullsteering is a Spatial Division Multiple Access (SDMA) technology which can be used to increase the system capacity by exploiting a new spatial dimension. By using this SDMA smart antenna with Code Division Multiple Access (CDMA), the system capacity can be increased significantly. In order to simulate and compare the performance of adaptive algorithms in the IS-95 receivers, both IS-95 uplink and downlink are simulated at chip level. Classical adaptive algorithms such as Direct Matrix Inversion (DMI), Least Mean Square (LMS) and Recursive Least Square (RLS) are modified accordingly to conform to this IS-95 receiver architecture. With this receiver structure, performances between different adaptive nullsteering algorithms and that without smart antenna are compared in terms of Signal-to- Interference Ratio (SIR) and their convergence rate to the steady-state SIR. Based on these performance results, a power method is proposed which can be used to estimate the IS-95 system capacity efficiently in a multiple-cell scenario without performing Monte-Carlo simulation. Realistic urban multipath models are used in the simulation to obtain accurate system capacity results. From these results, the advantages of adaptive nullsteering over that without smart antenna are presented. In addition, the performances of adaptive nullsteering and beamforming are also compared in terms of IS-95 system capacity. It is shown that both adaptive nullsteering and beamforming have their own advantages in different urban environments.

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