What are Global Navigation Satellite Systems (GNSS) and how are they used? (2024)

Determining a precise location is necessary in several industries for several reasons, including navigation, direction, timing, tracing, and safety. Global Navigation Satellite Systems (GNSS) let users pinpoint exact locations via satellites.

GNSS supports critical infrastructure, emergency response, and navigation. GPS, GLONASS, Galileo, and Beidou are the only navigation systems offering global coverage. Regional satellite systems like NAVIC and QZSS are similar but provide area-specific coverage.

In this article, we’ll cover these navigation systems and review the different GNSS options.

What is GNSS?
Global Navigation Satellite Systems are satellite-based navigation systems that enable users to determine exact, real-time position, velocity, and timing data from any location on Earth. GNSS receivers use satellite signals to triangulate a user’s position. By comparing the signals from different satellites, a GNSS receiver can accurately calculate a specific location and precise time.

The first operational GNSS, the Global Positioning System (GPS), was developed by the United States Department of Defense in the 1970s and became fully operational in the ’90s. This system was ground-breaking for the time, offering previously unattainable location and navigation accuracy.

Soon after, several countries developed their own GNSS systems.

For example:

• Russia developed GLONASS
• Europe developed Galileo
• China developed Beidou
• Japan developed
• QZSS and India developed NAVIC

GNSS systems enable various applications, such as navigation, positioning, timing, and communication, by utilizing a network of satellites in orbit, ground control stations, and user receivers.

How GNSS works
Global Navigation Satellite Systems has three key segments:

1. The space segmentconsists of a constellation of multiple satellites orbiting the Earth in precise and predictable paths. Each satellite transmits its precise position and time at the moment of transmission and a navigation message containing data about the satellite’s health and orbital parameters.

2. The control segmentconsists of a network of ground stations that monitor the satellites, update their orbital information, and ensure system health.

3. The user segmentis formed by GNSS devices, which receive and process signals from the satellites to determine their location and time.

An antenna on the receiving device (such as a smartphone or GPS receiver) picks up satellite signals and decodes the navigation message to determine the position and time data. It measures the time delay between when the satellite transmitted the signal and the moment it was received. It also uses the distance-time relation (distance = speed of light x time delay) to determine its distance from the satellite as the speed of light is already known.

A receiver requires signals from at least four satellites (three for altitude information) to establish an accurate position. It carries out a mathematical procedure known as trilateration (also known as multilateration or hyperbolic positioning) using the estimated distances from each satellite.

Essentially, this process centers spheres with a radius equal to the computed distance around each satellite. The spot where these spheres connect is the correct position.

To improve accuracy, Global Navigation Satellite Systems factor in other considerations, such as atmospheric effects and clock discrepancies. Some GNSS receivers also use additional information like terrain data or signals from ground-based stations to refine location estimates.

GNSS applications
The most common GNSS applications are as follows.

1. Navigation: GNSS enable navigation services in various modes of transportation, including aviation, maritime, and land-based navigation. The navigation system provides turn-by-turn directions for drivers, pedestrians, and cyclists.

2. Surveying and mapping: GNSS permit precise mapping and surveying of geographic areas. This is used in various industries, such as construction, agriculture, and resource management.

3. Timing and synchronization: GNSS synchronize clocks around the world. This is useful in maintaining accurate timekeeping for critical systems such as financial transactions, telecommunications, and power grids.

4. Military and defense: GNSS are commonly used for navigation, target tracking, and synchronization in defense applications.

5. Emergency response: GNSS help locate individuals or objects in distress during emergencies.

6. Location services: All location-based services in smartphones and automobiles are possible only with GNSS.

GNSS systems

The global navigation systems available around the world are as follows.

1. GPS
2. GLONASS
3. Galileo
4. Beidou
5. NAVIC
6. QZSS

GPS
Global Positioning System, commonly known as GPS, is a GNSS system owned and operated by the United States Space Force. It’s the most widely used GNSS globally, offering users free positioning, navigation, and timing (PNT) services. The system was developed as a concept called Navstar, and its first operational satellite was launched in 1978. By the ’90s, it was fully operational as GPS, offering civilian use alongside its military applications.

It comprises a constellation of 24 to 32 operational satellites in medium Earth orbit (MEO). Each satellite transmits two primary navigation signals, L1 C/A-code signal and L2C signal. The frequency of L1 signal is 1575.42 MHz and L2C signal is 1227.6 MHz. Each satellite has an average lifetime of around 12 years.

• The L1 C/A-code signal is for civilian use and offers positioning accuracy of approximately 15 meters horizontally and 30 meters vertically (95% confidence level).
• The L2C signal is more powerful and reserved for military applications. However, it’s authorized for civilian use with differential GPS (DGPS) techniques.

A network of global monitoring and control stations managed by the US Space Force forms the control segment. The receiver devices are generally standalone GPS receivers or integrated into smartphones, vehicles, and other navigation devices. GPS signals are always available and can be used anywhere on Earth.

GLONASS
GLobal’naya Navigatsionnaya Sputnikovaya Sistema, or GLONASS, is a global navigation satellite system. It’s Russia’s GNSS and is an alternative to the more widely used GPS.

GLONASS was developed by the Soviet Union in the ’70s, primarily for military purposes, and became globally operational in 1993. It provides real-time positioning and velocity determination for military and civilian users.

The GLONASS constellation consists of 24 satellites orbiting Earth in a medium circular orbit at an altitude of approximately 19,100 km, with an inclination of 64.8 degrees. Each satellite transmits two primary signals, L1 and L2.

• The L1 signal has a frequency of 1602-1615 MHz and is mainly used by civilians.
• The L2 signal has a frequency of 1246-1256 MHz and is mainly used for military applications. However, it’s accessible for authorized civilian use as differential GPS.
• L3 is a third signal with a 1200-1215 MHz frequency and is reserved for future use.

The satellites have a lifetime of seven to ten years. GLONASS ground stations are located throughout Russia and monitor and control the satellites.

GLONASS offers a civilian accuracy of five to 10 meters horizontal and 10 to 20 meters vertical, with a 95% confidence level. It’s compatible with SDGPS, which is similar to differential GPS. Although GLONASS offers global coverage, its signal strength might be weaker than GPS in some regions, particularly outside Russia.

Galileo
Galileo is a GNSS system developed and operated by the European Union (EU) in collaboration with the European Space Agency (ESA). It’s a highly accurate and independent navigation system developed for civilian use worldwide. The program was officially launched in 1999 in response to concerns about European dependence on the US-operated GPS. The first operational satellites were launched in 2011, and initial operational capability was achieved in December 2016.

As of February 2024, Galileo comprises a constellation of 26 operational satellites in medium earth orbit (MEO) at an altitude of about 23,222 km, with an inclination of 56 degrees. Galileo operates with 30 satellites, each transmitting three frequencies: E1, E5a, and E5b.

• The E1 signal has a frequency of 1575.42 MHz and is mainly used for civilian purposes, offering basic positioning, navigation, and timing (PNT) capabilities.
• The E5a signal has a frequency of 1191.795 MHz, serving as an open-service signal with improved accuracy and integrity. Specific sectors, like aviation, use it.
• The E5b signal has a frequency of 1207.14 MHz and is mainly used for commercial services. The signal offers high accuracy and integrity for demanding user authorization applications.

Galileo’s ground stations are located worldwide. It currently offers slightly better civilian accuracy of four to six meters horizontal and six to eight meters vertical, with a 95% confidence level.

BeiDou
BeiDou is a Chinese GNSS system offering an alternative to the widely used GPS. In Mandarin, BeiDou means “Great Bear.” It was developed between 2000 and 2012 to provide regional coverage for China and surrounding areas. Between 2012 and 2020, it expanded coverage to the Asia-Pacific region and offered basic navigation services. In 2020, it achieved full global coverage. BeiDou is an independent navigation system that is interoperable with other Chinese positioning systems like BeiDou-2.

BeiDou comprises a constellation of 35 operational satellites, including medium-earth orbit (MEO) satellites at about 20,000 km altitude and Inclined Geosynchronous Orbit (IGSO) satellites at about 35,786 km altitude. Each satellite transmits three signals: B1, B2, and B3.

• The B1 signal has a frequency of 1561.098 MHz and is used for civilian purposes like navigation and positioning.
• The B2 signal has a frequency of 1191.795 MHz and 1207.14 MHz. It provides public and private service signals for authorized users with enhanced accuracy and functionalities.
• The B3 signal has a frequency of 1268.520 MHz and provides public service signals with improved accuracy and integrity for specific user groups.

BeiDou offers a civilian accuracy of 5.7 meters horizontal and 5.9 meters vertical, with a 95% confidence level. Its ground stations are located worldwide.

NAVIC
NAVIC stands for Navigation with Indian Constellation but is also known by its operational name Indian Regional Navigation Satellite System (IRNSS). It’s India’s regional navigation satellite system developed by the Indian Space Research Organization (ISRO). It was launched in 2013 to meet India’s growing need for precise positioning services. It achieved initial operational capability in 2016.

NAVIC comprises seven operational satellites, which include MEO and IGSO satellites. Eleven satellites are targeted to be operational within the NAVIC system. Each satellite transmits two signals, L5 and S-band.

• The L5 signal has a frequency of 1176.45 MHz and enables Standard Positioning Service (SPS) for civilian use, such as navigation and timing data.
• The S-band has a frequency of 2492.028 MHz and is used for the encrypted Restricted Service (RS) for authorized users, which offers higher accuracy and additional functionalities.

NAVIC offers a civilian accuracy of approximately three and two meters horizontally, with a 95% confidence level. The Restricted Service (RS) offers even higher accuracy. It primarily covers India and extends up to 1,500 km beyond its borders, reaching parts of neighboring countries. NAVIC’s ground stations are located across India.

As of 2022, all 5G smartphones must have an integrated NAVIC sensor. Smartphones can use NAVIC maps using apps like MapmyIndia Mappls and NaviMaps (for 3D GPS navigation).

QZSS
QZSS stands for Quasi-Zenith Satellite System. Its operational name is “Michibiki,” which means guiding. QZSS is a regional satellite navigation system developed and operated by the Japanese government. It was launched in 2018 and got operational in the same year. While it’s not a full-fledged GNSS like GPS or Galileo, it’s useful in enhancing the performance of existing GNSS systems in the Asia-Pacific region. It was designed to improve the availability and reliability of GPS signals in urban areas and mountainous regions of Japan, where buildings and landscapes can obstruct satellite signals.

QZSS comprises four satellites, three of which are in highly elliptical orbits (HEO), ensuring they are nearly directly overhead (quasi-zenith) from locations in Japan. One of these satellites is in geostationary orbit (GEO).

The HEO satellites of the constellation are inclined at approximately 40 degrees and have an orbital period of approximately 24 hours providing continuous and strong signal reception even in challenging environments. The satellite in geostationary orbit (GEO) is positioned at approximately 140 degrees east longitude and offers additional coverage. Each satellite transmits three signals: L1c/A, L1C, and L2C.

• The L1C/A is similar to the GPS C/A code
• L1C is similar to GPS’ L1C signal
• L2C is similar to GPS’ L2C signal

GNSS receiver devices are compatible with the GPS L1C/A signals. Some newer receivers use additional QZSS signals (L1C and L2C) for improved accuracy and performance. QZSS is not a standalone GNSS. It functions as an augmentation system, enhancing GPS.

Conclusion
GNSS systems are the backbone of location, positioning, and mapping services. GPS, GLONASS, Galileo, and Beidou are the only GNSS providing global coverage. GPS is the most widely used GNSS, with decent accuracy and well-established infrastructure. However, it could be more accurate in some regions. Galileo is a relatively new system but offers better accuracy and features. The drawback is that Galileo is still under development and not be as readily available as GPS in all regions.

GLONASS offers an alternative to GPS but has slightly lower civilian accuracy than others. Its accuracy might not be as consistent as GPS in some regions. BeiDou offers improved accuracy in Asia compared to other GNSS systems.

Despite Galileo and BeiDou offering slightly better civilian accuracy than GPS, their global availability and interoperability are limited compared to GPS. NAVIC is more accurate, but its coverage is restricted to India. QZSS serves only as an augmentation system to GPS in Japan and its surrounding regions.

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