Software Package for Predicting the Performance of VLF-Navigation Systems

Frederick H. Raab, C. Chip Brewster

Abstract:	This paper describes a software package that has been developed to predict the performance of very low frequency (VLF) navigation systems. The package consists of modules for predicting signal strength, noise level, SNR, modal interference, position accuracy, and coverage. The software package is divided into separate programs for maximum flexibility, and to allow its use on small computers. It is written in FORTRAN and currently runs on personal computers with CP/M® and MS-DOS® operating systems. Signal-strength prediction is accomplished by a combination of the full-wave, spherical-earth model and a force-fit empirical model. Noise levels are based upon CCIR tables. Short- and long-path modal-interference flags are set according to distance from the transmitter, while trans-equatorial modal-interference flags are set by a rule based upon launch angle and nighttime propagation across the magnetic equator. Position accuracy is based upon three-station pseudoranging, and incorporates the effects of both SNR and phase-prediction accuracy. The coverage-prediction program checks each point in a latitude-longitude grid to find whether at least one triad yields a position fix with the specified accuracy.
Published in:	Proceedings of the 42nd Annual Meeting of The Institute of Navigation (1986) June 24 - 26, 1986 Seattle, Washington
Pages:	32 - 40
Cite this article:	Raab, Frederick H., Brewster, C. Chip, "Software Package for Predicting the Performance of VLF-Navigation Systems," Proceedings of the 42nd Annual Meeting of The Institute of Navigation (1986), Seattle, Washington, June 1986, pp. 32-40.
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