• GPS and GLONASS are operated by defence agencies of the respective nations. It is possible that the civilian service can be degraded or denied.
• NavIC is an independent regional system over the Indian region and does not depend on other systems for providing position service within the service region.
• It is fully under the control of Government of India.

NavIC, like any other navigation satellite system, consists of three segments:

• Space segment: Consists of the constellation of satellites.
• Ground segment: Consists of a network of ground stations that generate navigation data to be uplinked to the satellites, and subsequently to be used by the user receiver for aiding in position computation.
• User segment: Consists of the users utilizing the navigation signals for the purpose of position, navigation, and timing.

• International Telecommunication Union (ITU)
• United Nations Office for Outer Space Affairs (UNOOSA)
• International Committee on GNSS (ICG)
• Other navigation service providers (like GPS, GLONASS, Galileo, BeiDou, QZSS)

• NavIC is conceived and built mainly with the aim of having an independent navigation satellite system for India to remove the dependence on foreign satellite systems for navigation service requirements, especially for the strategic sector.
• It is not built for the purpose of revenue generation.
• However, many civilian applications are possible using free-to-air navigation signals broadcast from the satellites.
• The industry can produce receivers capable of receiving NavIC signal and use for various applications in several areas.
• Thus, economic benefit will accrue to the Indian economy by usage of position and navigation technologies.

• GNSS is an acronym for global navigation satellite systems.
• GNSS allows users worldwide to pinpoint their locations or the locations of objects, other people and goods at any given moment.

Global navigation system caters to the users in the entire world, whereas regional navigation system caters to the users in the limited service area.

• Satellite navigation is based on the use of range measurements between navigational satellite and the user.
• Information about the satellite’s coordinates is given to the user through navigation signal.
• Range measurements are based on the calculation of the receiving signal time delay compared with the signals generated by the user equipment.

• For determining position and time, a minimum of four satellites are required.
• In ideal case, when the measurements are precise and satellite time is identical with the user’s equipment time, the user position can be computed with 3 satellites.
• In reality, satellite time differs from the time on user’s equipment.
• So,difference between user equipment time and satellite time also needs to be determined. That is the reason four satellites are needed.

• There is no limit on the number of users.
• The satellite based navigation system sends signals in broadcast mode, and any number of users within the coverage area can receive the signals.

• Atomic clocks are highly accurate and stable clocks, with errors of less than 10 nanoseconds.
• The low errors results in providing accurate ranging for position determination.

• GAGAN stands for GPS Aided Geo Augmented Navigation.
• It is a satellite based augmentation system developed primarily for safety-of-life civil aviation applications catering to the Indian airspace.
• It provides correction and integrity messages for GPS.
• GAGAN has been established jointly by ISRO and AAI. It is being operated and maintained by AAI.

• Following are the major differences between GAGAN and NavIC systems: