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UBC Theses and Dissertations

Interference cancellation and macrodiversity for wideband CDMA systems employing software radio base stations Nie, Hong

Abstract

This thesis focuses on the applications of Successive Interference Cancellation (SIC) and Combining Macrodiversity (CM) in software radio base station receivers to increase the reverse link capacity of wideband Code Division Multiple Access (CMDA) systems. In the software radio base station receiver, an Analog-to-Digital Converter (ADC) with very high resolution is required to digitize the wideband analog signals received by the receiver. In order to mitigate this stringent ADC resolution requirement, we have proposed a novel digitization method, Adaptive Prediction & Cancellation Digitization (APCD) method. By predicting and canceling the high power narrowband signals among the wideband analog signals, the APCD method in conjunction with Auto-Regressive (AR) or Periodic Auto- Regressive (PAR) predictor can significantly reduce the high dynamic range of the wideband analog signals, and hence, can effectively relax the steep ADC resolution requirement. Furthermore, since the high power narrowband signals can usually be modeled as cyclostationary signals, by theoretical analysis and by means of computer simulations, it is shown that the PAR predictor can achieve a much higher prediction gain than the AR predictor. Although CM and Multi-cell SIC (MSIC) have the potential to increase the reverse link capacity of cellular CDMA systems, they cannot be used in conventional base station receivers. For base station receivers employing software radio technology, we have proposed a new base station system architecture, software radio Distributed Base Station (DBS) system architecture. In this system architecture, base station receivers can simultaneously exploit the radio signals received by several DBSs to detect mobile users; hence, the applications of CM and MISC become possible. When either CM, Single-cell SIC (SSIC) or MSIC is employed, the receiving power of mobile users assigned to the same DBS have controlled disparity. Consequently, the existing inter-cell interference model, which is based upon the assumption of equal received power, cannot be used to evaluate the inter-cell interference of these mobiles. We have proposed a new inter-cell interference model, which can precisely evaluate the inter-cell interference of mobile users with controlled power disparity. Furthermore, it has been proven that the existing inter-cell interference model for mobile users with equal receiving power can be obtained from the inter-cell interference model for mobile users with controlled power disparity. In order to demonstrate the reverse link capacity improvement CM and MSIC offer, by applying the inter-cell interference model for mobile users with controlled power disparity, Signal-to-Interference-plus-Noise Ratio (SINR) expressions for mobile users employing the following detection techniques have been obtained by theoretical analysis: i) Single-User Detection (SUD) in conjunction with Selection Macrodiversity (SM), ii) SUD in conjunction with CM, iii) SSIC in conjunction with SM, iv) SSIC in conjunction with CM, v) MSIC in conjunction with SM, and vi) MSIC in conjunction with CM. From these SINR expressions, the corresponding reverse link capacities of cellular CDMA systems have been analyzed by evaluating the outage probability of the systems. Both the analysis results and the computer simulation results show that regardless being employed individually or jointly, CM and MSIC can significantly increase the reverse link capacity of cellular CDMA systems.

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