Introduction
You're standing on a city street surrounded by glass skyscrapers. Your navigation app shows you in the middle of the block, but you're at the intersection. You've just met the multipath effect.
What Is Multipath?
Multipath occurs when a GNSS signal reaches your receiver via multiple paths: a direct signal followed by reflected signals arriving later.
The problem: Your receiver sees a composite signal, distorting the measurement and making the satellite appear farther than it really is.
Types of Multipath Environments
Urban Canyons (Worst)
- Tall buildings on both sides
- Often no direct signal, only reflections
- Errors: 10–50+ meters
Suburban Areas
- Houses and trees
- Mostly ground reflections
- Errors: 2–10 meters
Near Water
- Calm water acts as perfect mirror
- Strong reflections interfere with direct signal
- Errors: 1–5 meters
Mountainous Terrain
- Signal bounces off rock faces
- Multiple paths possible
- Errors: 5–20 meters
How Receivers Fight Multipath
Antenna Design
- Patch (smartphone): Poor rejection
- Ground plane: Good rejection
- Choke ring: Excellent rejection (survey-grade)
Signal Processing
- Narrow correlator techniques
- Multipath estimating algorithms
- Signal-to-noise monitoring
Practical Tips
- Move 10–20 meters, often solves the problem
- Avoid reflective surfaces (glass buildings, calm water)
- Hold phone properly (don't cover antenna)
- Be patient, accuracy improves as satellites move
Vital Points
- Multipath is signal reflection causing delayed copies
- Worst in urban areas with glass/metal buildings
- Errors can reach 50+ meters in extreme cases
- Moving is often the best solution for consumer devices
- Professional antennas and processing can reduce it significantly