LEO	Low Earth Orbit
GNSS	Global Navigation Satellite System
OCXO	Oven-Controlled Crystal Oscillator
RT	Real Time
PPS	Pulse Per Second
LQR	Linear Quadratic Regulator
KF	Kalman Filter
LS	Least Squares
LQG	Linear Quadratic Gaussian
FDCI	Four Dimension Constraint Integrated
STS	Short-Term Stability
LTS	Long-Term Stability