How GNSS Receivers Work

GNSS receivers are electronic devices designed to capture and interpret signals from one or more global navigation satellite systems to deliver highly accurate positioning, velocity, and timing information. Through a method called trilateration, GNSS receivers calculate their exact position by measuring the time it takes for satellite signals to reach them, converting these times into distances, and determining the intersection point of these distances from multiple satellites. Serving as the vital interface between users and the GNSS infrastructure, these devices are essential for a wide range of applications, from everyday navigation and logistics to scientific research and high-precision surveying.

A typical GNSS receiver consists of several key components:

• Antenna: Receives satellite signals and transfers them to the receiver

• Radiofrequency (RF) Front-End: Amplifies and filters the received signals

• Baseband Processor: Converts the analog signals into digital form for processing

• Navigation Processor: Performs the calculations necessary for determining position, velocity, and time information

• User Interface: Allows users to interact with the receiver and access its functionalities

These components work in harmony to provide accurate and reliable positioning information.

GNSS receiversdetermine their position using a process called trilateration. Here’s a step-by-step explanation:

GNSS satellites continuously transmit signals that include:

Pseudo-random code: A unique identifier for each satellite.

Ephemeris data: Information about the satellite’s position and health.

Almanac data: General information about the satellite constellation and system time.

The receiver’s antenna captures these signals and forwards them to the RF front-end.

The receiver calculates the time it took for the satellite signals to reach it. Since the signals travel at the speed of light, the travel time can be converted into a distance, known as the pseudo-range.

This is done for at least four satellites to determine the receiver's position in three-dimensional space and correct the clock error in the receiver.

Using the pseudo-ranges from multiple satellites, the receiver performs trilateration. This involves solving a set of equations to find the point where the spheres (representing the distances from the receiver to each satellite) intersect. This intersection point is the receiver’s position on Earth.

Once the receiver's position is determined, the microprocessor calculates the precise PVT information. This data can then be used for navigation, mapping, and other applications.

• Satellite geometry: The relative positions of the satellites affect the precision of the trilateration.

• Signal blockage: Obstacles like buildings, trees, and mountains can block or reflect signals.

• Atmospheric conditions: Ionospheric and tropospheric delays can alter the speed of the signals.

• Multipath effects: Signals reflecting off surfaces before reaching the receiver can cause errors.

• Differential GNSS (DGNSS): Uses reference stations with known positions to correct errors.

• Satellite-Based Augmentation Systems (SBAS): Provide additional correction signals from geostationary satellites.

• Real-Time Kinematic (RTK) and Precise Point Positioning (PPP): Advanced techniques for high-precision applications.