Deployment of Global Positioning System (GPS) satellites by the US in 1960s has provided (almost) ubiquitous opportunity to determine the position of a GPS Receiver with a relatively good accuracy. This unique feature is the main reason why GPS (or as a more broad term GNSS (Global Navigation Satellite System) is integrated with the Inertial Navigation System (INS) to reduce errors. INS uses sensors and mathematical models in order to produce position information with respect to a starting point and is always at the heart of a navigation system. However, due to mathematical model mismatch and sensor limitations, INS errors build up in time requiring a positional fix is for better accuracy and the GPS is usually the most reliable source to provide that positional fix information.
While INS/GPS integration is mostly used to accommodate military needs in terms of navigation, with the current technology and ever so cheap GPS Receivers, GPS is increasingly being employed in many non-military equipment, such as mobile phones, to help with the needs of the general public. Recently, the GPS technology has been used in a large number of civilian applications as well ranging from intelligent transportation systems to precision farming. The functionality provided by the GPS/GNSS has gone beyond positioning and now has a more general term, namely, Position, Navigation and Timing (PNT) . While GNSS is, without a doubt, at the heart of almost all military and safety and mission-critical PNT applications, it has vulnerabilities that can impair its performance significantly. The vulnerabilities stem from the efforts to make it widely available, namely using satellite constellations, and can be listed as follows;
- GNSS signals have a very well-known frequency/modulation and structure and travel a long way before they reach the receiver rendering the signal become rather weak. This makes GNSS vulnerable to jamming and spoofing. In fact while spoofing a GPS signal requires a bit more elaborate effort, a GPS Jammer can easily be purchased cheaply online .
- Since GNSS works on the time of arrival of signals from each satellite in the constellation, line of sight (LOS) becomes an issue. High mountains and especially high rise buildings in urban areas prevent LOS and reduce GNSS availability especially when satellites are at low elevation angles.
Such vulnerabilities cause a phenomenon called “GNSS degradation” which is not to be taken lightly as GNSS degradation seriously hinders PNT capabilities. This is probably why “PNT in GPS-denied environments” was identified as one of the top 12 (in terms of priority) research areas that should be emphasized in the near future by the Chief Scientist of the US Air Force [1]. The concept of Assured PNT or All Source PNT dwells around the assumption that the GNSS is not available and or not reliable because it is being spoofed and/or jammed. The solution is to look for sources other than the GNSS that can provide position information. However, no other source can beat the GNSS accuracy.
Then, perhaps, the solution to the problem is incerasing the resilience of the GNSS rather than looking for more elaborate and complicated systems that will never perform as good/accuarate as the GNSS itself. Tualcom Anti Jam Family has been developed to provide exactly that, resilience for your most trusted source posiotion information whether it is a legacy system or a system being developed for spesific purposes both military and civilian.
REFERENCES
[1] United States Air Force Chief Scientist (AF/ST), Report on Technology Horizons: A Vision for Air Force Science and Technology during 2010–2030, vol. 1, AF/ST-TR-10-01-PR (Washington, DC: Headquarters US Air Force, Office of the USAF Chief Scientist, 15 May 2010).
