Effects of Cross-Correlation Interference on an Optical Code Division Multiple Access Communication System
Peterson, George Dennis
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https://hdl.handle.net/2142/66242
Description
Title
Effects of Cross-Correlation Interference on an Optical Code Division Multiple Access Communication System
Author(s)
Peterson, George Dennis
Issue Date
1980
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
The effects of cross-correlation interference and intensity fading on the error rate performance of an optical code division multiple access communication system are investigated. The system model is a multiaccess satellite repeater in which user separation is accomplished by direct sequence modulation. The analysis is for direct detection, optical polarization modulation systems. Generalized expressions for the conditional probability of error for the uplink and downlink channels are derived in terms of the number of active users, signal strength and the normalized cross-correlation between user codes. Numerical results are obtained for systems of two users, for both length 31 and 127 Gold codes. Analysis of a random sampling of the length 31 codes has shown that performance is significantly dependent on the magnitude of the normalized second moment of the cross-correlation between user codes. Further analysis showed that the error probability decreases with increasing code length. The multiuser capabilities of the uplink and downlink channels were shown to differ significantly. It was shown that for K users at a given error rate in the uplink, K('2) users can be supported at the same error rate in the downlink. Fading effects were analyzed using the Nakagami m-distribution as a generalized statistical model of fluctuations in the received optical intensity. The average probability of error was derived for both correlated and uncorrelated fading in terms of the number of interfering users, the Nakagami fading parameter and the average number of photons counted in a bit interval. The results are valid for negligible background noise and cross-correlation interference. Numerical results are given for both severe and moderate lognormal fading, using the Nakagami m-distribution to approximate the lognormal distribution. It was shown that the downlink performs consistently better than the uplink under all of the fading conditions evaluated. Under lognormal fading, with intensity variances comparable to measured data, it was shown that reasonable error rates for multiple users can be obtained by boosting the signal power in the uplink channel.
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