What Is a GNSS Module?
A GNSS (Global Navigation Satellite System) module is a module that uses signals from satellites to obtain positional information and other data.
It refers to the GPS of the United States, GLONASS of Russia, Galileo of the EU, BeiDou satellite positioning system of China, and QZSS of Japan, which are representative systems for determining positional information.
By using signals sent from various satellite systems, it is possible to measure position information with higher precision.
Uses of GNSS Modules
GNSS modules are used to measure a vehicle’s position, speed, and direction of travel information, as well as to acquire location information for mapping functions on smartphones. Other applications include tablets, smart watches, laptops, medical applications, smart agriculture, precision location, smart trains, robotics, autonomous vehicles, industrial automation, logistics and asset tracking, drones, agricultural machinery, and construction heavy equipment.
When selecting a GNSS module, considerations should include the size and cost of the module and the size of the signal received from the antenna and processed. Other considerations include shock strength against dropping for smartphones and tablet PCs, and heat and vibration strength for GNSS modules for automotive applications.
Principle of GNSS Modules
The position and time information sent from multiple satellites is received by the signal receiver. The distance between the satellite and GNSS is determined from the received time, the time the signal was transmitted, and the speed at which the signal is traveling.
On the other hand, signals transmitted by satellites are often weak, and various obstacles, environmental noise, and interference in the reception environment can hinder signal reception, making it challenging to determine accurate location information. Therefore, there are products that implement advanced signal processing to determine accurate position information.
Structure of GNSS Modules
The components of a GNSS module include a receiver, a low-noise amplifier, and a GNSS receiver. Weak signals emitted from satellites are received by the signal receiver and amplified by a low-noise amplifier.
The amplified signals are processed by the GNSS receiver to calculate position information. The position information is then sent to the device connected to the GNSS module for use in position-based applications.
Other Information About the GNSS Module
1. Main Error Sources of GNSS Modules
Although GNSS modules can provide high-quality position measurements by catching signals from satellites, errors can occur due to factors such as satellite orbit, satellite clock, ionospheric delay, tropospheric delay, receiver (antenna), multipath, etc. The reasons for errors caused by each factor are described below:
Satellite Orbit Factor
Positioning calculations are performed by receiving ephemeris data (satellite orbit data) and almanac data (satellite orbit history) from satellites. Ephemeris data is updated every two hours and Almanac data every six days. Therefore, during the periods when both data are not updated, the position must be estimated based on the most recent data, which may lead to errors.
Satellite Clock Factor
Data from satellites contains satellite clock information. There is a lag time between when the satellite clock information is transmitted from the satellite and when it is caught by the receiver.
Ionospheric Delay Factor
The ionosphere is a region between 50km and 1,000km above the Earth’s surface where solar activity causes variations in the type and density of gases. When radio waves from satellites pass through the ionosphere, the refraction of light causes a delay in the transmission speed.
Tropospheric Delay Factor
The troposphere is the area between the ground and 11km above the ground. When radio waves from satellites pass through the troposphere, as in the ionosphere, the refraction of light causes a delay in the transmission speed.
Receiver (Antenna) Factor
After the satellite information is received by the antenna, various factors such as cable, circuit, and radio delays, as well as the speed of positioning calculation operations and memory access speed, can affect the error.
Multipath Factor
Multipath refers to radio waves that bounce off reflective objects and thus are delayed behind directly incident radio waves. In the case of radio waves from satellites, there are cases where the output of multipath radio waves is larger than that of directly incident radio waves. In this case, the positioning calculation may be performed using the multipath data with higher output.
2. Positioning Method of GNSS Module
GNSS module positioning methods can be broadly classified into two types: single positioning and relative positioning.
Independent Positioning
In stand-alone positioning, signals from four or more satellites are received by a single receiver to perform positioning. The accuracy of single-satellite positioning is limited to 10 to 20 meters due to satellite clock factor errors.
Relative Positioning
Relative positioning performs simultaneous, independent positioning at the reference point for which precise coordinates are required and at the point to be measured. In this case, information from multiple receivers is used, enabling higher quality positioning than with stand-alone positioning.