EW Academy · Contents · Chapter 14 · Nederlandse versie
Chapter 14: GNSS and navigation warfare
Satellite navigation as an EW target: operating principle, frequencies and codes (C/A, P(Y), M), processing gain, jamming and spoofing, and protection with CRPA, FRPA, M-code and INS coupling.
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14.1Introduction
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…
Read §14.1 →14.2Operating principle: trilateration and time
Each GPS satellite keeps transmitting "here I am and this is the time". From how late each signal arrives, the receiver works out its distance to at least four satellites — and from that its position and a very accurate time.
Read §14.2 →14.3Frequencies and bands
GNSS works in the L band (1–2 GHz). That choice is a compromise: low enough to pass relatively well through the atmosphere and light vegetation, high enough for usable antenna dimensions. All GPS frequencies are derived from a single base…
Read §14.3 →14.4Codes and signals
All GPS satellites transmit on the same frequencies. So how does the receiver tell them apart? With CDMA (Code Division Multiple Access): each satellite modulates its signal with a unique, pseudo-random PRN code (Pseudo-Random Noise). The…
Read §14.4 →14.5Processing gain: the key to everything
Whispering in a crowded canteen and still being understood: that works if the listener knows exactly which words to expect. In the same way, a GPS receiver uses its known code to pick out a signal that is weaker than the noise.
Read §14.5 →14.6The fundamental vulnerability
Put the numbers side by side and the vulnerability speaks for itself. The satellite signal travels ~20,200 km and arrives at about −160 dBW . A jammer is much closer and only has to transmit one way — the inverse-square law ( Inverse…
Read §14.6 →14.7GNSS jamming
GPS jamming drowns the weak satellite signal in noise. The receiver notices that it no longer has a position — inconvenient, but at least you know something is wrong.
Read §14.7 →14.8Spoofing and meaconing
Spoofing feeds in a fake GPS signal that looks genuine. The receiver notices nothing and believes it is somewhere else — and that makes spoofing more dangerous than jamming.
Read §14.8 →14.9Protection and anti-jam
Protecting GNSS (the EPM side, Electronic Protective Measures , applied to navigation) works in layers. No single measure is enough on its own; together they raise the J/S threshold and close the spoofing back doors. The antenna is the…
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