Why GPS Signal Can Be Weak and How to Mitigate It

For every user of a mobile navigation app, the most dreaded warning is "weak satellite navigation signal" because it means inaccurate positioning and potentially no guidance. This article explains why the signal can be weak even without obvious obstructions and how to avoid the problem.

Gaode (Amap) reports a weak‑signal warning when the phone fails to upload satellite positioning results during navigation. Our analysis shows that in most cases (about 80%) the satellite signal is indeed too weak for positioning. In the remaining cases the satellite count and signal strength appear sufficient, but the device cannot decode the satellite messages due to anomalies or contradictory data.

Two main reasons cause a device to miss satellites or receive only a weak signal:

1. Electromagnetic interference around the phone. The GPS signal travels 20,000 km from the satellite and is attenuated to a fraction of the strength of 4G/5G signals (about one ten‑trillionth). Ordinary users cannot carry large satellite‑tracking antennas; mobile devices use very small antennas, which further reduces reception.

Because the antenna size is limited, the design compensates by lowering the data transmission rate (according to Shannon’s theorem). GPS transmits at about 50 bit/s, requiring roughly 6 seconds to receive a full positioning message, whereas 5G can reach gigabits per second. Even with this compensation, strong electromagnetic environments can still prevent successful message decoding.

The most problematic frequency band is 1.1 GHz–1.6 GHz, where many other devices (including car electronics) emit harmonics that interfere with GPS.

To mitigate interference, users can move the phone away from the central console in a car, place it near the windshield, or go outdoors to eliminate in‑vehicle sources. Since a full GPS message takes about 6 seconds to read, a few seconds of waiting after repositioning is required to see any improvement.

2. Device‑related issues. In completely open areas, if the phone still cannot locate satellites, the problem is likely the phone itself. Different manufacturers use different GNSS chips and antenna designs; high‑end models usually have better tracking and calculation capabilities, while older or low‑cost phones are more prone to weak‑signal failures.

Gaode has implemented several techniques to improve positioning under weak‑signal conditions since 2019:

Sensor fusion: Using the phone’s accelerometer, gyroscope, and magnetometer together with map matching to estimate speed, direction, and road position, allowing continuous tracking for up to about 30 seconds even without satellite data.

Network‑based positioning: Leveraging nearby cellular base stations and Wi‑Fi signals to estimate location when satellite signals are unavailable. Accuracy ranges from 30 m to 200 m depending on signal density.

Weak‑signal satellite decoding: Algorithmic optimizations that enable the device to produce a positioning result even when satellite data is sparse or noisy.

Additional notes: While Starlink satellites are much closer to Earth than traditional GPS satellites, their signals still suffer severe attenuation, making direct satellite phone calls impractical. Future solutions might involve external antennas that can be attached to the phone.

For more details, see the related articles linked in the original source.