Date of Award

3-14-2014

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Electrical and Computer Engineering

First Advisor

Robert J. McTasney, PhD.

Abstract

In 2010, the Shared Spectrum Company showed in a survey of Radio Frequency (RF) bands that underutilization of spectrum has resulted from current frequency management practices. Traditional frequency allocation allows large bands of licensed spectrum to remain vacant even under current high demands. Cognitive radio's (CR) use of Dynamic Spectrum Access (DSA) enables better spectrum management by allowing usage in times of spectrum inactivity. This research presents the CR problem of rendezvous for fast Frequency Hopping Spread Spectrum (FHSS) networks, and examines protocols for disseminating RF environment information to coordinate spectrum usage. First, Gold's algorithm is investigated as a rendezvous protocol for networks utilizing fast frequency hopping. A hardware implementation of Gold's algorithm on a Virtex-5 Field Programmable Gate Array (FPGA) is constructed to determine the resource requirements and timing limitations for use in a CR. The resulting design proves functionality of the algorithm, and demonstrates a decrease in time-to-rendezvous over current methods. Once a CR network is formed, it must understand the changing environment in order to better utilize the available spectrum. This research addresses the costs a network incurs to coordinate such environment data. Three exchange protocols are introduced and evaluated via simulation to determine the best technique based on network size. The resulting comparison found that smaller networks function best with polled or timedivision based protocols where radios always share their environment information. Larger networks, on the other hand, function best when a dispute-based exchange protocol was utilized. These studies together conclude that the selection of a rendezvous algorithm or a protocol for the exchange of environment data in a CR network are determined by the characteristics of the network, and therefore their selection requires a cognitive decision.

AFIT Designator

AFIT-ENG-14-M-52

DTIC Accession Number

ADA599048

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