Modern armed forces have become deeply dependent on GNSS — Global Navigation Satellite System. Not only for determining their own position, but also for guiding precision weapons (JDAM, cruise missiles), synchronising data links and networks, and stamping an accurate time on practically every digital system. That dependence makes GNSS a first-order target — and therefore a core subject for the EW specialist.
GNSS is the collective name; the best-known systems are:
| System | Owner | Special feature |
|---|---|---|
| GPS (NAVSTAR) | United States | oldest, most widely used; military and civil signals |
| GLONASS | Russia | uses FDMA (a separate frequency per satellite) instead of CDMA |
| Galileo | European Union | under civil control; offers signal authentication (OSNMA) |
| BeiDou | China | global coverage since 2020 |
The principles in this chapter apply to all four; we use GPS as the running example because its signal design is public and well documented. The common thread: GNSS is wonderfully accurate but relies on an extremely weak signal, and that very weakness determines everything — how you jam it, how you falsify it, and how you protect against both.
The overarching military term is Navigation Warfare (NAVWAR): protecting your own use of PNT (Position, Navigation & Timing), denying it to the opponent, and keeping civil use outside the area of operations undisturbed. NAVWAR is in effect EW (What is Electronic Warfare?) applied to the navigation spectrum.