Global National Navigational System (GNSS) is a generic term for constellation of satellites or satellite navigation (SatNav) systems which provides positioning, navigation and timing (PNT) services on global basis.
Smartphones and in-vehicle systems have greatly increased the use of GNSS devices. GNSS have application in several other areas such as agriculture, aviation, drones, maritime, rail, surveying, and timing & synchronizing.
The GNSS technology was originally developed by the United States for an independent military navigation capability which dates back to the Sputnik era when the US Navy experimented satellite navigation to track its nuclear submarines.
Department of Defense launched its first navigation system with a network of satellites in 1978. This space-based radionavigation system was named ‘Navstar GPS’ which was later retitled as ‘Global Positioning System (GPS)’.
Initially, GPS comprised 24 satellites and it became fully operational in 1993. The system was declared operational in 1995 and has never been deactivated since then. US Air Force is responsible for the operation and maintenance of the system.
GPS is the most prevalent GNSS in the world. It provides two levels of services, civilian and military. Civilian service is freely available to all users around the world however its military service is limited to the US and allied armed forces as well as to the approved government agencies.
As of 12-May-2018, a total of 31 operational satellites were in the GPS constellation. GPS-enables smartphones are typically accurate to with 4.9 meters however high-end GPS users have real-time positioning within a few centimeters and long-term measurements at the millimeter level.
But GPS is only one of the four global satellite navigational systems. The other three GNSS are: GLONASS (Russia), Galileo (Europe), and BeiDou (China), in addition to two regional systems including QZSS (Japan) and IRNSS or NavIC (India).
GLONASS – GLObal NAvigation Satellite System – is the oldest GPS rival. ISS-Reshetnev is responsible for the space complex of the GLONASS. It is a world-wide navigation system that ensures global coverage and 24/7 signal availability.
Like GPS, GLONASS was also designed in 1970s for Russian military and is only the second system around the world to provide global coverage in October 2011. As of 18-July-2018, GLONASS has a cluster of 26 satellites in orbit.
BeiDou Navigation Satellite System (BDS) – is a Chinese space infrastructure which is developed by China independently. Previously known as COMPASS, It is being used by China for as a standardized system for national security and enormous other areas.
The technics of BeiDou chips has been increased from 0.35 microns to 28 nanometers whereas the lowest price of a single chip is only 6 yuan. As of now, a total of 65 million chips have been sold in China – generating revenue of 250 billion last year.
Besides providing domestic services in various sectors such as public security, transportation, electric power, fishery, forestry, disaster management, smart city construction, and social governance – BeiDou is quickly going global.
In latest developments, BeiDou is providing an accuracy of with 1 to 2 meters from prior up to 10 meters. Sources say that BeiDou accuracy could be even close to centimeters or millimeters in its encrypted service.
With an estimated of 18 satellites to be launched by 2018, the global network will be more or less built-up. By 2020, more than 30 satellites would have been launched and BeiDou Navigational Satellite System will cover the world.
Galileo is a joint effort of the European Union which is developed by European Space Agency. It provides highly accurate and guaranteed service under civilian control and is interoperable with GPS and GLONASS.
By offering dual frequencies a standard, Galileo is set to deliver real-time positioning accuracy to the meter range. The fully deployed Galileo will consist of operational 30 satellites including 6 in-orbit spares.
QZSS (Quasi-Zenith Satellite System) is a Japanese regional navigation system, operated by Japan Aerospace Exploration Agency (JAXA). The first generation of QZSS was launched in 2010 and it is planned to expand it constellation to 7 satellites in future.
The service of QZSS is available in Asia-Oceania regions with longitudes close to Japan. It will start to develop its GPS-compatible satellite positioning system in 2018 which will expand its usage to other countries in these regions as well.
NavIC (Navigation for India Constellation) is an Indian Regional Navigation Satellite System (IRNSS) which provides positioning system for critical national applications. Indian Space Research Organization (ISRO) is the overseer of the program.
Cloned from US GPS, it provides two types of services: Standard Positioning Service (SPS) and Restricted Service (RS) and consists of three segments: Ground Segment, Space Segment, and User Segment.
ISRO claims that NavIC is much more accurate than the systems developed by foreign countries. But earlier this month, Indian native SatNav system confronted threats before its commercial rollout in the next few months.
According to ISRO, seven-satellite constellation is sending signals in S-band frequency which is utilized for NavIC systems and also shared by other communication technologies such as Bluetooth, Wi-Fi, and long-term evolution (LTE).