Drone Link Defense: FHSS Anti-Jamming & GPS Spoofing Detection

Command-Link Hopping

Hop rate 6 hops/s

Jammer band coverage 30%

Link Telemetry

Packet delivery

100%

Active channel

1 / 32

GPS Integrity

GPS↔INS divergence

0.0 m

Nav status

Nominal

How it works

Anti-jamming — keyed frequency hopping. The link splits its bandwidth into N discrete channels and both radios retune every hop interval T = 1/rate, following a sequence known only to them:

c(n) = PRNG(key, n) mod N   — keyed, unpredictable
c(n) = n mod N               — sequential, predictable

A jammer that cannot recover the key can only cover a fixed fraction ρ of the band at once ("partial-band jamming"). Since the drone's next channel is uniformly unpredictable, a hop is lost with probability ≈ ρ — the Jammer band coverage slider is exactly this ρ, and delivery settles near 1 − ρ. If the sequence is instead a plain counter, an adaptive "follower" jammer learns the pattern after a few hops and retunes onto the drone's next channel every time, driving delivery toward zero regardless of how narrow its band is. The security comes from the secrecy of the key, not from hopping itself.

GPS spoofing detection — sensor cross-check. The drone keeps a second, independent position estimate from its IMU by dead reckoning:

x_ins(t) = x_ins(t-dt) + v(t)·dt      (accelerometer + gyro integration)
d(t) = |x_gps(t) − x_ins(t)|

Under normal operation both estimates track the same truth and stay within sensor noise. A spoofer that broadcasts a stronger, fabricated GPS signal can drag the GPS fix away — but it cannot touch the IMU. Once the divergence d(t) exceeds a threshold and stays there, the autopilot flags a spoofing alarm and falls back to INS-only navigation until GPS is trustworthy again. This is the same cross-check principle used in real GNSS-denial-resilient autopilots.

Active channel Jammed channel GPS satellite Spoofed apparent fix

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