Satellite navigation

A receiver compares the time a signal was sent with the time it arrived. Multiplying travel time by the speed of light gives a distance-like measurement. Because the receiver’s clock is not perfectly synchronized, the result includes an error that must be solved along with position.^[1][4]

A code pseudorange contains geometric range, receiver and satellite clock terms, propagation delays, and measurement errors. Broadcast orbit and clock information allow the receiver to model satellite state. The observable is called a pseudorange because it is not simply the true geometric distance between two known points.^[1][4]

Three coordinates describe where a receiver is, but its clock adds another unknown. Signals from at least four suitably placed Satellites allow a basic solution for all four. More signals can improve resilience and geometry, though buildings and reflections can still cause trouble.^[1][4]

An unconstrained single-epoch solution estimates three position components and receiver clock bias. At least four independent pseudoranges with adequate geometry are required. Additional measurements support redundancy and estimation, but accuracy also depends on dilution of precision, multipath, atmospheric models, and signal quality. Satellite count is not itself an accuracy guarantee.^[1][4]

GPS and Galileo provide global navigation services. ISRO’s NavIC is designed for regional service over India and its surrounding region. A device can only use signals it supports. The constellation, ground control, and receiver all contribute to the service a person experiences.^[2][3]

Global and regional navigation systems use different constellation geometries and service definitions. Multi-constellation receivers can combine compatible observations, while inter-system time offsets and signal models require treatment. The space segment alone does not define service availability: control-segment monitoring, receiver capability, and local reception conditions also matter.^[2][3]

Radio signals move about 300 metres in one microsecond. That makes precise timing essential. The atmosphere, reflections, and clock differences must be accounted for. Navigation is therefore a measurement and estimation problem, not a satellite simply “seeing” your phone.^[4]

Pseudorange modelling includes ionospheric and tropospheric delays, satellite clock corrections, and receiver noise. Carrier-phase observations can support much finer precision but introduce integer ambiguity resolution and other processing requirements. Corrections and differential methods improve particular error terms; they do not remove every limitation of the local observing environment.^[4]