Date of Award


Document Type


Degree Name

Master of Science


Department of Electrical and Computer Engineering

First Advisor

Richard A. Raines, PhD


This thesis provides a performance evaluation of the IRIDIUM Low Earth Orbit Satellite system. It examines the system's ability to meet real time communications constraints with a degraded satellite constellation. The analysis is conducted via computer simulation. The simulation is run at low, medium, and high loading levels with both uniform and non-uniform traffic distributions. An algorithmic approach is used to select critical satellites to remove from the constellation. Each combination of loading level and traffic distribution is analyzed with zero, three, five and seven non-operational satellites. The measured outputs are end-to-end packet delay and packet rejection rate. In addition to the delay analysis, a user's ability to access the network with a degraded satellite constellation is evaluated. The average number of visible satellites, cumulative outage time, and maximum continuous outage time are analyzed for both an Equatorial city and a North American city. The results demonstrate that the IRIDIUM network is capable of meeting real-time communication requirements with several non-operational satellites. Both the high loading level and the non-uniform traffic distribution have a significant effect on the network's performance. The analysis of both network delay performance and network access provides a good measure of the overall network performance with a degraded satellite constellation.

AFIT Designator


DTIC Accession Number