Date of Award

Spring 1-1-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical, Computer & Energy Engineering

First Advisor

Timothy X Brown

Second Advisor

Youjian (Eujene) Liu

Third Advisor

Juan Restrepo

Abstract

This thesis considers a model consisting of a cognitive radio (CR) on an unmanned aircraft (UA) and a network of licensed primary users on the ground. The cognitive radio uses the same frequency spectrum as the primary users for its operation and hence acts as an interferer. This work analyzes the duration of interference in such a model. It defines two important metrics -- the interference radius and the detection radius. The interference radius determines the boundary of the area within which a primary user might be subjected to harmful interference due to the operation of the CR. The detection radius determines the boundary of the area within which the presence of a primary user might be detected by the CR. The interference and detection radii might vary due to the dynamic nature of the radio environment. This thesis derives the dependence of these metrics on the radio propagation parameters like antenna gain, antenna height, path-loss exponents, etc. It uses these metrics and characterizes the model using an M/G/infinity queue to determine the statistics of the interference time for the entire excursion of the unmanned aircraft. The key statistics determined are the distribution of the duration of interference periods, the mean and the total interference time. Firstly, this work analyzes a 1D system model where the primary users are distributed randomly along a straight line. The results are then extended to a 2D system where the primary users are distributed randomly over an area. The analysis is carried out for both sparsely-dense and highly-dense primary user ground network. This work gives a new dimension to analyze the effects of interference in terms of duration of interference. It also shows how these interference effects can be minimized on enhancing the detection capability of the cognitive radio. The results from this work can be used to determine the optimum setting for the cognitive radio system such that it restrains the duration of interference below tolerable limits.

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