Understanding the 3 States of GPS/GNSS Signals

To understand the quality of the signals received by a GPS or GNSS receiver, we need to understand the three states of GPS/GNSS signal: Single, Float, and Fix.

Global Positioning System (GPS) and Global Navigation Satellite System (GNSS) are satellite-based navigation systems that allow users to determine their precise location and track their movements. These systems rely on signals sent from satellites in orbit to ground-based receivers, and the quality of these signals can vary depending on the number of satellites in view, the strength of the signals, and other factors.

One way to understand the quality of the signals received by a GPS or GNSS receiver is to consider the three states of GPS/GNSS signal: Single, Float, and Fix.

Single

When a GPS or GNSS receiver can only pick up signals from one satellite, it is said to be in the "Single" state. In this state, the receiver can determine the user's location to within a wide range, but the accuracy is low, and the location can change rapidly. The receiver cannot provide any information about the user's movement or velocity. This state is common in places with poor satellite visibility, such as urban canyons or heavy tree cover.

Float

When a GPS or GNSS receiver can pick up signals from at least three satellites, it is said to be in the "Float" state. In this state, the receiver can determine the user's location within a moderate range and provide information about the user's movement and velocity. However, the accuracy is still low, and the location can change rapidly. This state is common in places with moderate satellite visibility, such as suburban areas or the countryside.

Fix

When a GPS or GNSS receiver can pick up signals from at least four satellites, it is said to be in the "Fix" state. In this state, the receiver can determine the user's location within a high range and can provide accurate information about the user's movement and velocity. The location is stable and does not change rapidly. This state is common in places with good satellite visibility, such as in open countryside or clear skies.

The states of GPS/GNSS signals indicate the quality of the signals received by the receiver and the accuracy of the location information provided by the receiver. Understanding these states can help users to make better use of GPS and GNSS systems and to avoid potential errors caused by poor signal quality.