Does OSNMA stop meaconing?

What OSNMA does

OSNMA (Navigation Message Authentication) is Galileo's digital signature for its open signal. It stops forged messages: a spoofer who builds fake signals cannot produce valid signatures, so a receiver that checks them can reject the fake.

Why it does not stop meaconing

Authentication answers one question: "Did this message come from a satellite?" In meaconing the honest answer is yes. The attacker never forges anything. They copy a real message, signature included, and play it somewhere else or later.

The signature cannot tell the receiver where or when it was captured. That is the only false part of the attack, and nothing in the message checks it.

Why integrity monitoring does not help either

RAIM (Receiver Autonomous Integrity Monitoring) looks for one satellite that disagrees with the others. In meaconing every satellite signal arrives through the same relay, so they all agree perfectly. The check passes.

What about several constellations and frequencies?

Comparing GPS, Galileo, BeiDou and several frequency bands helps only partly. A wideband relay copies every band at once, so the copies agree with each other.

What does work

The reliable approach is to compare GNSS with something the attacker cannot copy. Independent absolute navigation, such as terrain referencing and scene matching combined with inertial motion, asks whether the reported position matches the world below. A replayed signal can fool a receiver, but it can't move the hills, roads and coastlines under the aircraft.

Summary: what each defence checks