Modeling the transformational communications system Urban Land Mobile Satellite Channel
Gillespie, Timothy T. A.
Robertson, R. Clark
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The success of the Transformational Communications System depends on providing high quality communications to the mobile user in any environment. A hurdle to this success is the urban Land Mobile Satellite Channel which experiences frequent and extended deep signal fades due to shadowing by man-made structures. The problem is exacerbated for the Communications-on-the-Move channel due to use of a directional antenna. This dissertation evaluates available empirical test data, develops an improved channel model and investigates mitigation strategies focused on improving channel throughput and latency. The improved channel model is developed using continuous transmission mixed-Gaussian hidden Markov models and Expectation-Maximization parameter estimation. The improved model provides a better match to empirical data than previous efforts. Two fade mitigation strategies are examined. The first strategy involves modification of packet routing protocols. A detailed, time-based network simulation is developed for performance assessment. Results show substantial reductions in packet latency under a broad range of conditions. The second mitigation strategy is based on fade prediction using real-time adaptive linear filters. Signal inputs from directional and non-directional antennas are investigated. Initial results indicate a requirement for a high temporal resolution input signal.
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