Date of Award

2009

Degree Type

Thesis

Department

Electrical and Computer Engineering

First Advisor

Hizlan, Murad

Subject Headings

Spread spectrum communications, Digital communications, Code division multiple access, Coding theory, Generalized spread spectrum, GDSSS, Orthogonal codes, Multiple access

Abstract

In this thesis we investigate and compare the average performances of ordinary and generalized direct sequence spread spectrum (DSSS) systems under multi-path fading and multiple-access interference. As part of multiple access performance, we also consider generation of orthogonal and semi-orthogonal codes using various algorithms, and compare cross correlation properties of codes formed by 2-level and 3-level signature sequences. In order to simulate ordinary and generalized DSSS performance under various scenarios, we develop a complete Java library with classes that are well encapsulated with regard to communication modules and loosely coupled so that we can reuse them to create any type of DSSS communication model. We verify the library under Gaussian noise before performing simulations under multi-path fading and multiple-access interference. We find with regards to multi-path fading that generalized DSSS does not perform any better than ordinary DSSS, regardless of how the signature sequences are generated. For multiple access, when using perfectly orthogonal signature sequences, we observe that ordinary and generalized DSSS perform exactly the same. We investigate semi-orthogonal sequences in great detail, and observe that generalized DSSS can accommodate more users than ordinary DSSS for the same performance

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