Date of Award

Fall 1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering - (Ph.D.)

Department

Electrical and Computer Engineering

First Advisor

Yeheskel Bar-Ness

Second Advisor

Alexander Haimovich

Third Advisor

Zoran Siveski

Fourth Advisor

Eliza Zoi-Heleni Michalopoulou

Fifth Advisor

Branimir Vojcic

Abstract

The classical multiple access techniques such as Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA) schemes are band limited in terms of their capacity to be used for mobile radio communication. Recent developments in the area of digital signal processing, makes Code Division Multiple Access (CDMA) as a possible solution to the demand of capacity for the mobile radio communication. The capacity of CDMA is limited by multiuser interference, that is the interference from the other users.

The goal of this dissertation is to improve the multiuser CDMA detector with high Bit Error Rate (BER) performance, low complexity, near-fax resistance as well as flexibility to be applied to a wide range of communication channels. We developed an adaptive multi-stage CDMA detector to cancel the multiuser interference. The first-stage of the detector, called decorrelating detector, decorrelates the correlated signals obtained at the match filter bank. The second-stage, called canceller, cancels the multiuser interference exist in the desired signals, using the decorrelated user signals obtained at the decorrelating detector output. The key future of this multi-stage detector is being purely adaptive. The combination of adaptive decorrelating detector and adaptive canceller allows the multi-stage detector achieve near-optimum BER performance and at the same time remain computationally effective. To increse achievable BElT performance an adaptive soft limiter is used at the canceller stage. The underlying structure of this multi-stage detector (i.e. being purely adaptive) allows it to be applied to different channel characteristics. However, throughout this dissertation we use Additive White Gaussian Noise (AWG N) channel for simplicity. To address some of the potential problems that may arise in practice, the adaptive decorrelating detector is tested using computer simulation and in-depth analysis of the problem. If necessary, an alternative solution that do not change the main characteristics of the detector (such as adaptivity and simplicity) is provided. Overall, we conclude that our adaptive detector with its high BER performance and adaptation ability to different channel characteristics, can be considered as an alternative solution to the problem of multiuser interference cancellation in CDMA communication.

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