Communications Project

Document Type:Master's Thesis
Name:Pascal G. Renucci
Title:Optimization of Soft Interference Cancellation in DS-CDMA Receivers
Degree:Master of Science
Department:Electrical and Computer Engineering
Committee Chair: Brian D. Woerner
Committee Members:Theodore S. Rappaport
Charles W. Bostian
Keywords:code division multiple access, multiuser receivers, interference cancellation, spread spectrum communications, mobile radio
Date of defense:May 22, 1998
Availability:Release the entire work immediately worldwide.


Parallel interference cancellation for DS-CDMA has been shown to suffer from biased amplitude estimates if a matched-filter estimator is used. The bias magnitude is proportional to the number of interfering users. For heavy system loads, the bias has been shown to adversely effect the accuracy of the interference cancellation process, thereby impairing BER after cancellation. Empirical simulation work has demonstrated that weighting down interference estimates can improve BER performance. This thesis substantiates these BER improvements by modelling and analyzing a soft interference cancellation technique which mitigates the effects of the bias by minimizing BER after cancellation in a bit-synchronous parallel interference cancellation CDMA receiver. We analyze system decision metrics with down-scaled interference estimates and determine both the mean and variance of the biased decision statistics. From these two metric moments, system BER is evaluated, and the optimal interference scaling function which minimizes BER is derived. We demonstrate BER performance enhancements by simulating this soft interference cancellation technique in systems under perfect power control and in the near-far situation. We further discuss the applicability of the results to asynchronous systems.

List of Attached Files

etd.tar.gz renucci.pdf

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