GPS & Satellite Navigation
How 31 atomic clocks orbiting 20,180 kilometers above Earth in Medium Earth Orbit broadcast relativistic radio signals to calculate your exact position on the planet down to the meter.
Pieces in this series
How GPS Actually Knows Where You Are
Orbital atomic clocks, pseudorange trilateration, relativistic time dilation, and the four-satellite geometry equation
GPS does not track your phone from orbit or receive signals from your device. Your phone is a purely passive radio listener, capturing microscopic time-stamped radio pulses from at least four atomic-clock satellites in orbit. By…
Why GPS Sometimes Shows the Wrong Location
Ionospheric plasma delay, urban canyon multipath reflections, Dilution of Precision, and Assisted GPS
GPS accuracy falters because satellite radio waves must travel through solar-charged ionospheric plasma, refract through humid tropospheric air, and bounce off skyscraper glass. When reflected multipath signals travel longer paths or…
How Differential GPS and Real-Time Kinematics Achieve Centimeter Precision
From code pseudoranges to carrier phase tracking (L1/L2), double differencing, integer ambiguity resolution, and NTRIP networked corrections
Standard GPS tracks the coarse C/A code, where each binary chip is 300 meters long. Real-Time Kinematic (RTK) positioning switches from measuring code chips to counting individual cycles of the raw 19-centimeter microwave carrier wave…
How Satellite Navigation Constellations Operate
From Keplerian orbital mechanics and Walker Delta constellations to space-hardened atomic clocks, L-band CDMA modulation, and multi-GNSS interoperability
Global satellite navigation requires more than solitary spacecraft; it demands an interconnected space, control, and user segment. By deploying 24 to 36 satellites in precisely inclined Walker Delta constellations in Medium Earth Orbit…
How Direct-Sequence Spread Spectrum (DSSS) and CDMA Work
From pseudo-random Gold codes and processing gain to sub-noise-floor reception and code division
How spreading signals with pseudo-random Gold codes allows GPS satellites to transmit below the thermal noise floor and enables dozens of transmitters to share the exact same frequency.