Starting with GPS basics

Understanding GPS: The Precision Behind Positioning, Navigation and Timing

The Global Positioning System (GPS) is a satellite-based technology that determines location using trilateration—measuring distances, not angles. Despite common misconceptions, GPS does not rely on triangulation.

Imagine you're trying to find your position and all you know is your distance from two known locations, such as a tower and a mountain. You could draw a circle around each point, with the radius equal to your distance from them. The point where the circles intersect represents your location. In real-world scenarios, it’s usually easy to eliminate one of the possible points—say, if it falls in a lake and you're on land.

Now take this concept into three dimensions. Instead of circles, GPS uses spheres, each centered on a satellite. Knowing your distance from three satellites narrows your position to two points—only one of which makes physical sense. However, to account for minor inaccuracies in a GPS receiver's clock (unlike the atomic clocks on satellites), a fourth satellite is required to correct timing errors and accurately resolve your position in 3D space.

The GPS System Structure

The complete GPS system consists of three main components:

• Space Segment – A constellation of at least 24 satellites (currently 31) in six orbital planes, approximately 20,200 km above Earth.

• Control Segment – Ground-based monitoring stations that track satellites and upload updated positional data (ephemeris).

• User Segment – GPS receivers, including OEM modules, used across various industries.

To determine location, a GPS receiver needs to calculate its distance from at least four satellites and know the satellites' positions at that moment. This data is continually broadcast as part of each satellite’s navigation message.

Accuracy and Correction: Reducing GPS Errors

Various factors can introduce errors into GPS signals, such as signal delays in the atmosphere or clock discrepancies—collectively forming the “GPS error budget.” To mitigate this, Differential GPS (DGPS) and other augmentation systems provide corrections that significantly improve accuracy.

Correction services include:

• U.S. Nationwide DGPS (NDGPS) by the Coast Guard

• WAAS (Wide Area Augmentation System) by the FAA

• CORS (Continuously Operating Reference Stations) by the NGS

• International and commercial networks like Trimble RTX, which provide high-precision corrections via satellites or mobile networks.

GPS: Beyond Positioning

Due to the precision of atomic clocks on GPS satellites, the system is not only essential for positioning and navigation but also forms the backbone of timing infrastructure used in communications, financial transactions, broadcasting, and the internet. GPS is, therefore, more broadly known as a Positioning, Navigation, and Timing (PNT) service.

Looking for High-Precision GNSS Solutions?

Alrad Instruments offers a complete range of Trimble OEM GNSS receiver modules, antennas, and smart antennas designed for demanding applications. Whether you're integrating GPS into advanced systems or building new positioning technology, our team is here to help.

📩 Contact us today to find the right solution for your application.

For more information on Starting with GPS basics talk to Alrad Instruments Ltd