Wide Area Reference Station Placement for an Indian WAAS

P. Laxminarayana, K.V.S. Saiprasad and D.C. Reddy

Abstract:	Wide Area Reference Stations (WRS™s) are the ihsystem componentsly that collect range measurements from the GPS satellites to calculate differential corrections. These corrections are basically of two types: satellite ephemeris/clock and ionospheric-delay. Validity and accuracy of the these generated corrections for the region of interest of service area depends on the number and location of the WRSs. Geographical boundaries of the service area impose additional constraints for meeting the requirements of availability, continuity and integrity. Therefore determination of the optimal number and location of WRSs varies from country to country and no ‚straight-jacket™ approach can be adopted for the purpose. This paper reports the findings of a preliminary study carried-out for an Indian WAAS that meets the RNP of different phases of flight up to CAT-I. The study envisages a WAAS that monitors integrity, generates ephemeris/clock corrections as well as the ionosphere corrections for broadcast by a geo-stationary satellite. For generation of ephemeris/clock corrections it uses the dynamic model approach. For generation of ionospheric corrections a reference grid of (North-South 800km and 1200km for East-west) ionospheric measurement stations is suggested. For integrity monitoring whereas literature suggests the use of a square with WRSs located at its corners, we propose a hexagonal structure with WRSs located at its vertices. This has the effect of not only reducing the BOWING EFFECT but also increasing the service area for a larger coverage. The paper concludes by proposing 14 WRSs for the entire Indian sub-continent.
Published in:	Proceedings of the 2001 National Technical Meeting of The Institute of Navigation January 22 - 24, 2001 Westin Long Beach Hotel Long Beach, CA
Pages:	559 - 564
Cite this article:	Laxminarayana, P., Saiprasad, K.V.S., Reddy, D.C., "Wide Area Reference Station Placement for an Indian WAAS," Proceedings of the 2001 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 2001, pp. 559-564.
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