GNSS vs GPS: Understanding the Key Differences

This page compares GNSS vs GPS and mentions the difference between GNSS and GPS terminologies.

Introduction: Both GPS and GNSS terms are associated with satellite navigation systems used to determine the location and elevation of devices. These technologies are employed in many consumer electronics, automotive applications, marine guidance, surveying, cellular handsets, etc. GPS is one of the many GNSS systems used across the globe. GNSS is an umbrella term that includes GPS, GLONASS, GALILEO, COMPASS, etc.

There are three main components in GNSS architecture, as shown in the figure: space segment, control segment, and user segment.

• Space Segment: It consists of satellites orbiting the Earth. They continuously transmit radio signals towards the Earth.
• Ground Control Systems: They are used to assure the accuracy of the system. There are about 5 control stations. They enable information on the Earth to be transmitted to the satellites, such as updates and fine-tuning. Control stations continuously track the satellites and update the positions of each of the satellites.
• GPS or GNSS receivers: The radio signals are picked up by these receivers to determine location. This is possible as the GPS receiver knows about the time required by the signal to travel from the satellite to the receiver. At least four satellites are required to determine the exact location and elevation by GPS receivers.

Distance = time x velocity

Using the above formula, the GPS receiver calculates the exact distance from the satellite.

GPS

• GPS refers to the constellation of navigation satellites associated with the American system.
• GPS was developed by the US Department of Defense at a cost of greater than $12 billion.
• Initially, only GPS was available for a long time. Hence, all the components such as satellites, receivers, etc., were referred to as GPS.
• After a few years, other GNSS systems have been developed.
• GPS consists of 24 to 32 MEO (Medium Earth Orbit) satellites orbiting in six planes at an altitude of approximately 11,000 nautical miles.
• The total number of satellites varies due to replacement and newly introduced satellites.
• GPS is the most utilized satellite navigation system across the world.

There are two types of GPS signals:

• P-code (Precise code): Only available to the military and some public officials, very precise and not degraded.
• C-code (Civilian code): Less precise, the signal can be degraded in times of conflict. GARMIN receivers and all public receivers work with this.

GNSS

GNSS includes all of the following satellite-based navigation systems:

• GPS: US, operational since 1994.
• GLONASS: Russian, re-operational since 2010.
• GALILEO: European Union, 2011
• BeiDOU: CHINA, operational in Asia/Pacific since 2000

Other regional GNSS systems include IRNSS (Indian Regional Navigation Satellite System) used in INDIA and QZSS (Quasi-Zenith Satellite System) used in Japan.

The figure above depicts the difference between GNSS and GPS systems.

There are three different grades of GNSS receivers based on their accuracy, usage, and cost:

• Recreational Grade GNSS:
  • Accurate within 5 meters
  • Lowest cost
  • Suitable for hunting, recreational use, some businesses, etc.
• Mapping Grade GNSS:
  • Accurate within 1 meter
  • Medium cost
  • Suitable for natural resources, city planning, etc.
• Survey Grade GNSS:
  • Accurate within 1 cm
  • Higher cost
  • Suitable for building bridges, etc.

Tabular comparison between GNSS and GPS

The following table mentions the comparison between GNSS and GPS terms.