Scholarly Communications Project



Yash M. Vasavada

Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of



Dr. Jeffrey H. Reed, Chair
Dr. Brian D. Woerner
Dr. Dennis G. Sweeney

May 1996
Blacksburg, Virginia


Analog frequency modulated (FM) systems offer advantages of reliable speech quality and simplicity, whereas code division multiple access (CDMA) systems promise high capacity, resistance to multipath fading, and simplified frequency planning. In this thesis, we investigate the performance of a wireless local loop (WLL) system that uses the frequency modulation with the CDMA technique.

The performance of the FM CDMA system is affected by the choice of the frequency demodulation method. Performance of different state-of-art DSP based FM demodulators is evaluated. Design improvements with threshold extension, pre-deemphasis, and voice companding techniques are explored, and the limitations of the DSP based FM demodulation methods are identifed.

The transmitter, the channel, and the receiver of the FM CDMA system are simulated for particular values of FM bandwidth and spread-spectrum processing gain. The capacity supported by the FM CDMA sysem is estimated with different levels of orthogonal as well as non-orthognal multiple access interference. The performance of the FM CDMA system in AWGN, multipath fading, Doppler spread, and nonlinear signal processing effects is predicted. A power control algorithm for the FM CDMA system is proposed, and its effect on the system performance is studied.

The capacity of the FM based wireless system may saturate as the system evolves. An adaptive FM CDMA interference cancelation technique and a digital modulation with CDMA are two approaches investigated as ways to improve system capacity.

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The author grants to Virginia Polytechnic Institute and State University or its agents the right to archive and display their thesis or dissertation in whole or in part in the University Libraries in all forms of media, now or hereafter known. The author retains all proprietary rights, such as patent rights. The author also retains the right to use in future works (such as articles or books) all or part of this thesis or dissertation.
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