Field Test Results of Clock Stability and Code-Carrier Coherency of Dual-Frequency Navigation Transponders*

Abstract

: The various satellite-based augmentation systems currently under development utilize geostationary earth orbit (GEO) satellites to provide the user with ranging signals that also contain integrity data on GPS, GLONASS, and Galileo satellites. These signals are generated on the ground and provided via C-band (or K-band) uplink to the GEO. The GEO's navigation transponder frequency translates the signals to L1 and C-band (or K-band) downlink frequencies, and then broadcasts the signals throughout the GEO's coverage footprint. An important aspect of the navigation transponder is its frequency stability. To maintain code-carrier coherency, the code phase, carrier phase, and carrier frequency are controlled via the uplink signal. This is accomplished using closed-loop algorithms that are capable of maintaining the code chipping rate and carrier frequency of the received signal in a constant ratio of 1:1540, as well as maintaining the correct Doppler and ionospheric divergence as observed by the user. This paper describes and presents the field results for code-carrier coherency and clock stability obtained at Wide Area Augmentation System (WAAS) GEO uplink subsystems (GUSs) for the AOR-W and POR satellites. In these tests, the GUS is integrated with the remainder of WAAS in a closed system via the Type 9 navigation message from the correction and verification function of the wide-area master station (WMS), as compared with earlier prototype stand-alone tests. The results meet the specifications for short- and long-term code-carrier coherency and for clock stability over 1–10 s, just as with GPS signals [1, 2].