FREQUENCY SYNTONIZATION USING GPS CARRIER-PHASE MEASUREMENTS BASED ON ANFIS

K.-Y. Tu∗ and C.-S. Liao∗∗

Keywords

Frequency syntonization, frequency stability, GPS carrier phase, GPSDO, ANFIS, fuzzy control

Abstract

This study designs a GPS carrier-phase disciplined oscillator (GP- SCDO), which uses pure carrier-phase measurements to steer a low-cost oven-controlled crystal oscillator (OCXO). The proposed GPSCDO is demonstrated to be with high short-term frequency sta- bility. But similar to traditional GPSDO, the long-term performance of the GPSCDO is limited due to the atmospheric effect. There- fore, a new scheme for frequency syntonization based on the GPS carrier-phase measurements using an adaptive neural-fuzzy inference system (ANFIS) is presented to improve the long-term frequency stability of the GPSCDO. By applying the off-line data predicted by the ANFIS, the remote GPSCDO can correct the estimation of the frequency offsets which are used as the input of a fuzzy controller. Thus, the remote GPSCDO clock can be steered to synchronize with the primary clock via a D/A converter. Experimental results show that for an average time of one day, the frequency stability of the GPSCDO can be significantly improved from a few parts in 1012–1014.

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