Global Navigation Satellite Systems (GNSS)

Learn more about GNSS Technology and How it Works

Global Navigation Satellite Systems (GNSS) are an integral part of modern navigation and positioning technology, providing users across the globe with precise location data. These systems are composed of three primary segments: satellite constellations in orbit, ground-based control stations, and end-users equipped with receivers. Several independent GNSS are in operation today, each offering unique features and capabilities.

Key GNSS Systems

GPS – Operated by the United States The Global Positioning System (GPS), initially developed by the United States Department of Defense, features a constellation of 24 satellites orbiting approximately 22,000 km above Earth. These satellites transmit signals on multiple frequencies, including L1, L2, and L5, to deliver precise location data to both civilian and military users. The GPS offers two main services: Precise Positioning Service (PPS): Reserved for military and authorized users. Standard Positioning Service (SPS): Available to civilian users worldwide.

GLONASS – Operated by Russia GLONASS, managed by the Russian Aerospace Defense Forces, mirrors GPS in many respects but offers enhanced coverage at higher latitudes. It currently operates approximately 24 satellites and plans to expand its frequency offerings with future launches. The system includes: Precise Positioning Service (PPS): Restricted to military and authorized users. Standard Positioning Service (SPS): Accessible to civilian users globally.

BeiDou – Operated by China The BeiDou Navigation Satellite System is managed by the China National Space Administration. Often referred to as COMPASS or BeiDou-2, this system comprises both regional and global satellites. The regional satellites cover the eastern hemisphere, while the global satellites orbit the Earth like other Global Navigation Satellite Systems (GNSS). Although BeiDou is still in the deployment phase, it currently offers operational coverage in regions such as Asia, Australia, New Zealand, India, Russia, Africa, and Europe. Once fully established, the system will consist of 5 geostationary satellites (GSO) and 30 non-GSO satellites. Among the non-GSO satellites, 27 will be positioned in Medium Earth Orbit and 3 in Inclined Geosynchronous Orbit, all contributing to comprehensive global coverage. 

Galileo – Operated by the European Union Galileo, a civilian-operated GNSS managed by the European Space Agency, aims to provide increased accuracy and reliability. Once fully operational, it will consist of 30 satellites and offer several services, including: Open Service (OS): Available for mass-market applications like vehicle navigation. Commercial Service (CS): Provides centimeter-level accuracy for professional use. Public Regulated Service (PRS): For government-authorized users.

IRNSS (NavIC) – Operated by India The Indian Regional Navigation Satellite System (IRNSS), also known as NavIC, is designed to serve the Indian region and surrounding areas. IRNSS offers two services: Standard Positioning Service (SPS): Available to all users. Precision Service (PS): Reserved for authorized users.

QZSS – Operated by Japan Japan's Quasi-Zenith Satellite System (QZSS) enhances GNSS performance in the Asia-Oceania region. It includes multiple signals designed to increase the availability of Position, Navigation, and Timing (PNT) services, with notable features like: L1-SAIF: Provides sub-meter augmentation, interoperable with GPS and SBAS. LEX: An experimental signal for high-precision services compatible with Galileo's E6 signal.

Conclusion
Each GNSS offers distinct advantages based on its design and operational goals. By utilizing a combination of these systems, users can achieve superior accuracy and reliability in navigation and positioning, supporting a wide range of applications from everyday navigation to specialized industrial operations.


About GNSS Technology

How It Functions

A GNSS receiver identifies the position of each satellite in orbit and measures the time it takes to receive their signals. By using these measurements, the receiver calculates its precise location on Earth.

A GNSS receiver can only detect satellites that are visible above the horizon. Generally, between 6 to 12 satellites can be seen at any given moment. The receiver strives to track all visible satellites. If some satellites are obstructed or "shaded" by tall buildings or other significant barriers, the receiver automatically attempts to regain those blocked signals. While at least four satellites are necessary for a three-dimensional solution (latitude, longitude, and altitude), a receiver can maintain a two-dimensional position (latitude and longitude) with just three satellites.

GNSS constellations are designed to offer global positioning services with accuracy levels ranging from 5 to 15 meters. Achieving higher precision with standard GNSS is challenging due to minor timing discrepancies, satellite orbit inaccuracies, and atmospheric conditions that can impact signal transmission and arrival times on Earth. However, there are methods to enhance GNSS accuracy through additional services. Four primary services are available, each capable of improving positioning accuracy to less than one meter:

DGPS
Radiobeacon Differential GPS (DGPS) Corrections The U.S. Coast Guard and Army Corps of Engineers have set up a network of radiobeacons that continuously broadcast differential GPS (DGPS) corrections to compatible receivers. This extensive network spans the United States from coast to coast. Similarly, the Canadian Coast Guard offers beacon coverage along its coastlines, the Great Lakes, and the St. Lawrence River. Many other regions around the globe also have comparable beacon networks. A significant advantage of radiobeacon DGPS is that the corrections are available free of charge to anyone with the necessary equipment, which is relatively affordable. The long-range signals are capable of penetrating valleys and urban canyons, navigating around obstacles to provide service where other options may fall short. Additionally, these corrections are consistently monitored to maintain their integrity. At present, most radiobeacon stations only transmit corrections for GPS satellites, although some stations in Russia also provide GLONASS corrections.

Space-Based Augmentation Systems
While radiobeacon stations transmit DGPS correction signals from the ground, Space-Based Augmentation Systems (SBAS) deliver correction signals from geostationary satellites. SBAS corrections depend on a network of base stations on the ground that monitor GPS satellites. Instead of sending corrections directly to users, these networks transmit signals to geostationary satellites, which then relay the signals back to individual SBAS-compatible receivers on Earth. Similar to radiobeacon differential signals, SBAS differential signals are available free of charge to anyone with the necessary equipment. Instead of calculating localized corrections at each base station, systems like WAAS, EGNOS, MSAS, and GAGAN aggregate data from all base stations to determine corrections for extensive regions. This approach allows for more consistent corrections across larger areas, often spanning entire continents. For instance, the WAAS network comprises 38 reference stations, which includes base stations in both Canada and Mexico. It offers relatively uniform accuracy and coverage from the Arctic Ocean to Hawaii, the mid-Caribbean, the mid-Atlantic, and the coasts of Greenland. In contrast, roughly 100 radiobeacon DGPS stations operated by the U.S. Coast Guard, the Army Corps of Engineers, and the Canadian Coast Guard cover the U.S. coast to coast and parts of Canada’s coastal waters, but do not extend into Mexico. At present, SBAS corrections exclusively provide complete correction information for GPS satellites.

L-Band
Satellite systems offer differential correction signals to subscribers of their services. The term ‘L-band’ refers to the operational frequency range of 1000 – 2000 MHz within the radio spectrum utilized by these private satellites. Their signals are accessible nearly worldwide. Since the content of the messages is managed by the private companies, they have the discretion to provide corrections for more than just GPS satellites. GNSS global correction service is an L-band-based solution that delivers scalable corrections for GPS, GLONASS, Galileo and BeiDou.

Real-Time Kinematic Positioning
Real-Time Kinematic (RTK) positioning represents the pinnacle of accuracy in GNSS navigation and positioning. It operates through a method that utilizes a nearby stationary GNSS reference receiver, known as the ‘base’, along with a radio link. The base supplies more detailed data to the user’s receiver, referred to as the ‘rover’, compared to other correction techniques like SBAS or beacon corrections. This added information, known as ‘carrier-phase information’, serves as the foundation for achieving high-precision positioning. For RTK positioning to function, GNSS base data must be transmitted to the rover at one-second intervals. Generally, a digital radio link facilitates this transmission from the base to the rover, which then calculates a carrier-phase solution. This solution typically boasts an accuracy of approximately one centimeter in most cases. To ensure effective RTK operation, the base usually needs to be situated within 30 to 50 km of the rover. RTK data can incorporate corrections for any or all GNSS constellations.



Space Weather Status

Overview of Conditions, Maps, & Weather Status

Space weather encompasses the dynamic environmental changes occurring in near-Earth space and the area between the Sun and the Earth’s atmosphere. It is affected by phenomena such as solar flares, ionospheric fluctuations, and energetic particle events. The energy our sun emits varies over time, with scientists referring to this pattern as the solar cycle. During phases of heightened solar activity within the cycle, increased ionospheric activity is noted, which includes episodes of scintillation that can distort GNSS signals. This distortion impacts the performance of GNSS receivers, with ionospheric scintillation being most significant near the Earth’s magnetic equator, particularly in Brazil.

Here are some resources to help you monitor space weather conditions:

Current TEC (Total Electron Content) Maps:
- NASA Jet Propulsion Laboratory – Vertical TEC Map

Space Weather Services
– TEC Global Map Space Weather Conditions: Space Weather Prediction Center

Current Scintillation Maps:
- Space Weather Services – Australia