Test Results of Geostationary Satellite (GEO) Uplink Sub-System (GUS) Using GEO Navigation Payloads

M.S. Grewal, W. Brown, R. Lucy, P. Hsu

Abstract:	The WAAS system uses geosynchronous (GEO) satellites to relay correction/integrity messages to users from ground-based sensors and processors. A secondary, but equally important, use of the GEO signal is to provide users with a GPS-like ranging source. The ranging signal is generated on the ground and is provided via a C-Band uplink to the GEO, whose navigation payload translates the uplinked signal to an L1 downlink frequency. The GEO incorporates an additional C-Band downlink to provide ionospheric delay observability to the GEO uplink ground station. An important requirement of the ground station is to provide closed-loop control of the code chipping rate, carrier phase, carrier frequency and epoch timing of the GEO’s broadcast signal-in-space. A control loop algorithm was developed to ensure that the GEO signal-in- space meets similar performance specifications as GPS. The uplink station’s closed-loop control algorithm estimates and compensates for various sources of divergence between the code and carrier phase, including the uplink inonospheric delay, uplink Doppler, and divergence due to carrier frequency translation errors induced by the GEO’s transponder (C-Band to GPS L1). This paper presents in-orbit test (IOT) analysis results which show that the prototype WAAS signal-in-space control algorithm, in conjunction with WAAS ground based hardware and Inmarsat-3 (I-3) GEO navigation payloads, meet the long and short term code carrier coherency, and short term frequency stability requirements of the WAAS System Signal Specification [Ref. 1].
Published in:	Proceedings of the 54th Annual Meeting of The Institute of Navigation (1998) June 1 - 3, 1998 The Adams Mark Hotel Denver, CO
Pages:	549 - 557
Cite this article:	Grewal, M.S., Brown, W., Lucy, R., Hsu, P., "Test Results of Geostationary Satellite (GEO) Uplink Sub-System (GUS) Using GEO Navigation Payloads," Proceedings of the 54th Annual Meeting of The Institute of Navigation (1998), Denver, CO, June 1998, pp. 549-557.
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