A Study of Spread-Spectrum Multiple-Access Communications Over Fading Channels
Geraniotis, Evaggelos A.
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https://hdl.handle.net/2142/69256
Description
Title
A Study of Spread-Spectrum Multiple-Access Communications Over Fading Channels
Author(s)
Geraniotis, Evaggelos A.
Issue Date
1983
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
Abstract
The performance of asynchronous direct-sequence (DS) and slow-frequency-hopped (SFH) spread-spectrum multiple-access (SSMA) communications over fading channels is investigated. Nonselective, wide-sense-stationary uncorrelated-scattering time- or frequency-selective, and specular multipath fading channels are considered. Thermal noise modeled as additive white Gaussian noise (AWGN) is also assumed to be present at the receiver.
For DS/SSMA systems with coherent demodulation, we develop a method for approximating the average probability of error, which has very satisfactory accuracy and required computational effort, growing linearly with the number of simultaneous transmitters and the length of the signature sequences. For the performance of DS/SSMA systems over AWGN and fading channels, we establish for all cases in which a strong stable path for the desired signal exists, that DS modulation discriminates against other signals or other paths and achieves a satisfactory performance at the expense of possibly increasing the length of the signature sequences. If there is no strong stable path then we find that the performance of DS/SSMA systems with conventional matched filter receivers is not satisfactory. Post-detection processing at the receiver or adaptive equalization look more promising but they lie beyond the scope of this thesis.
We first introduce a suitable model for SFH/SSMA systems. Then we develop several bounds and approximations on the average probability of error. These are easy to evaluate, and they apply to a variety of cases. Our study of the performance of SFH/SSMA communications via fading channels reveals that slow-frequency-hopping alone (with hopping rates no larger than the data rate) is not sufficient to provide multiple-access capability and combat nonselective or selective fading. Fortunately, the natural mechanism that frequency-hopping provides facilitates the use of error-control coding. Although coding is not treated in this thesis, the results can be utilized to determine the performance of error-control coding in SFH/SSMA systems. This is partly due to the fact that one of the techniques that we developed for the performance evaluation of uncoded SFH/SSMA systems is applicable to coded systems as well.
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