Tightly Coupled Oscillator and GPS Receiver

Legacy GPS receivers do not make use of the disciplined atomic oscillator flywheel output in GPS Disciplined Oscillator systems. The attached proposal shows how the disciplined oscillator signal can be used to improve GPS carrier and code tracking, mitigate multipath, jamming and spoofing, and to detect GPS receiver and satellite system anomalies. Using the disciplined oscillator as the frequency reference inside the GPS receiver itself results in better jamming and spoofing immunity, faster re-acquisition, direct-Y code acquisition after a cold-start, and complete removal of the 1PPS sawtooth. Multi-sensor fusion using a built-in Inertial Navigation Subsystem (INS) and the Chip Scale Atomic Clock (CSAC) is used to detect physical motion allowing detecting and mitigation of spoofing and multipath signals and the reduction of clock errors. The built-in INS also allows detecting if the unit is operating in a stationary position mode, which the proposed algorithm can then use to discipline the internal CSAC with as little as a single satellite in view, allowing operation under foliage and in urban canyons. A 3-cornered-hat approach is used in the proposed algorithm to detect and remove errors and abnormalities on any one of the three input signals (GPS, INS, CSAC).