10) Satellite Navigation — GNSS

I. GNSS Fundamentals
• Position from timing of signals received from multiple satellites.
• Trilateration — measure distance to at least four satellites.
• Atomic clocks for extreme accuracy.

II. The Four Systems
• GPS (USA) — 31 satellites.
• Galileo (EU) — 30 satellites.
• GLONASS (Russia) — 24 satellites.
• BeiDou (China) — 45+ satellites.

III. Signal Structure
• L1, L2, L5 frequencies.
• C/A code · P(Y) code.
• Navigation message — ephemeris, clock corrections.

IV. Accuracy and Augmentation
• Standard positioning ~ 3–5 m.
• SBAS (WAAS, EGNOS) — 1–3 m.
• RTK — centimetre accuracy.
• PPP — precise point positioning.

V. Applications
• Vehicle navigation, aviation, maritime.
• Surveying, precision agriculture, construction.
• Timing for financial networks, telecoms.

VI. Vulnerabilities
• Jamming — overpowering the weak signal.
• Spoofing — fake signal to mislead.
• Ionospheric and tropospheric delays.
• Urban canyons and multipath.