engleski

Overview of PNT Alternatives for GNSS

Many technical systems and technologies today are dependent on accurate time synchronization and precise positioning. These requirements are usually provided by Global Navigation Satellite Systems (GNSS). Most of our critical infrastructure would cease to function without GNSS. However, GNSS signals are very vulnerable to intentional and non-intentional disturbances and interferences, so there is no guarantee for continuous availability of those signals. This paper will list some of the systems that would be affected in case when GNSS signals would be unavailable or severely degraded, and explain potential alternatives that could provide positioning, navigation and timing (PNT) functionality for these systems. The timing function of PNT is engaged in mobile and fixed telecommunication systems, digital terrestrial television, digital audio broadcast, Terrestrial Trunked Radio (TETRA), financial institutions, internet datacentres, electrical power grids, etc. PNT functions are necessary in transportation sector, especially in modern applications such as autonomous vehicles, unmanned aerial systems, railway networks, air traffic control systems. Because of diversity of technologies dependent on PNT, categorising them into characteristic usage scenarios enables viable evaluation. The fundamental division of scenarios is based on usage domain, dividing scenarios to those requiring timing and those requiring positioning. The position of the user equipment divides scenarios into outdoor and indoor applicable. The movement of user equipment indicates static and dynamic scenarios, both in 2D and 3D. As there is no straightforward alternative for GNSS that would comprise all scenarios, and even GNSS is not applicable in some of them, such as deep indoor PNT, a variety of technologies will be considered as candidates for GNSS PNT alternative. Their applicability differs by their geographical coverage and the number of scenarios they support. Some of the technologies are also based on satellites, but situated in Low Earth Orbit (LEO), with received power much higher than from traditional GNSS in Medium Earth Orbit (MEO), and with signals in different frequency bands, protected by encryption. Some rely on terrestrial transmitters, whether in low frequency, as eLoran, with low number of high-power transmitters, or in UHF, with higher number of transmitters. Different approach includes map-matching supported by Inertial Measurement Unit (IMU) and ultra-wideband (UWB) technologies. Other technologies aim at specific scenarios, providing transfer of time by Precision Time Protocol (PTP) or indoor positioning using signals-of-opportunity. Technologies are compared and evaluated for usage in different scenarios, depending on domain-specific criteria.

Positioning ; Navigation ; Timing ; Alternatives ; GNSS

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