GPS Simulator (Concept & Defence)
How GPS works — and how spoofing is detected
What it does
SimpleGPS is how phones and cars know where they are: they listen to faint signals from satellites far out in space and use the tiny timing differences to work out their position. This page explains how that works, and how experts detect 'spoofing' — when someone tries to fool a receiver with fake satellite-like signals.
Why only explain and not do it? Because broadcasting fake GPS in the open air could confuse cars, phones, ships, and planes, so it's illegal and dangerous. The valuable part for learning is understanding *how* GPS is trusted and *how* fakery is caught, which is exactly what engineers who protect these systems study.
How it works
SimpleEach satellite sends a special repeating code stamped with the exact time. Your receiver hears several satellites, sees how long each code took to arrive, and from those tiny delays works out where it must be. A spoofer would try to send louder fake codes — so defences watch for signals that are suspiciously strong, don't agree with the phone's motion sensors, or arrive from the wrong direction.
How to use it, step by step
Simple- This is for understanding only — never transmit fake GPS in the open air.
- Learn how satellites' timing signals let a receiver find its position.
- See why civilian GPS has no 'signature' to prove it's genuine.
- Learn the tricks that catch spoofing: odd signal strength, disagreeing sensors, wrong direction.
Examples
Walk through how four satellite pseudoranges solve for 3D position plus clock error.
Understand the signatures defenders watch for: sudden C/N0 jumps, position that fights the IMU, single-direction arrival.
See how cross-checking GPS against Galileo/GLONASS makes a consistent fake far harder to produce.
Tips & things to try
- The receiver-side defences are the real lesson — that's how anti-spoofing is engineered.
- Civilian L1 is unauthenticated by design; understanding that motivates every mitigation.
- Never transmit near GPS frequencies; the value here is comprehension and defence.