GNSS

Each GNSS satellite continuously broadcasts its own precise orbital position (ephemeris) and a precisely timed signal. A receiver measures the arrival time of signals from several satellites simultaneously, and because it knows exactly when each signal was transmitted and each satellite's position, it can calculate the distance to each satellite and, from multiple such distances, triangulate its own position — a receiver typically needs at least four satellites in view to solve for its three-dimensional position and correct its own clock error simultaneously.

The dependency chain that makes GNSS foundational to so many other systems in this corpus runs through both position and time: applications that need to know where something is (AIS vessel position, ADS-B aircraft position) and applications that need precise, synchronized time (network timing, NTN Doppler and timing pre-compensation) both draw on the same underlying GNSS signal, even though the two use cases look quite different on the surface. This dual utility is precisely why GNSS receivers have become nearly ubiquitous well beyond dedicated navigation devices — any system needing either accurate position or a reliable, globally synchronized time reference can obtain both from the same GNSS chipset rather than requiring separate infrastructure for each. For CE verticals, GNSS availability is a hard prerequisite rather than a convenience for several corpus-documented systems — NTN user equipment cannot compute the pre-compensation values needed for satellite access without a GNSS fix, and both AIS and ADS-B fundamentally depend on GNSS-derived position as the data they broadcast — making GNSS-denied environments (deep underground, certain contested or jammed environments) a real operational constraint on which systems remain functional at all.