GPS World, February 2017

AVIATION A CONTROLLED RADIATION PATTERN ANTENNA can preserve GNSS positioning while providing at least an azimuth angle towards an interference source If integrated with an attitude and heading reference system only a few lines of position pointing towards the RFI source could provide a fast indication of the probable ground location 48 GPS WORLD WWW GPSWORLD COM FEBRUARY 2017 Interference Localization Using a CRPA G NSS is an essential enabler for many aviation applications that rely on either accurate position or time synchronization While the idea of sole means GNSS is disappearing it remains challenging to match the performance and coverage of GNSS with terrestrial systems This is why aviation is working on Alternate Positioning Navigation and Time APNT to cope with the potential for a wide area GNSS outage Current navigation aids are clearly part of this approach in the short term We will continue to need a terrestrial capability for some time but we dont expect that it will support the same level of performance as GNSS Even if we have back up we must be able to resolve GNSS outages efficiently Amon g p r i n c i p a l G N S S vulnerabilities constellation performance issues space solar weather and radio frequency interference RFI RFI is the one where observability on the ground is often limited While the protection of radio services from interference is a state responsibility typically assigned to a telecommunications or other government agency it is in the interest of an air navigation service provider ANSP to be able to request help and enforcement action from the telecommunications regulator in an efficient manner As a part of its contribution to Single European Sky ATM Research SESAR a collaborative project to improve European airspace and its air traffic management EUROCONTROL has developed an RFI Mitigation Plan as a guidance framework with the objective to maintain risks to GNSS and the associated operations at tolerable levels The document will be published by ICAO in its GNSS Manual in the new 2017 edition MITIGATION PLAN RFI can be a security issue Consequently a commonly used philosophy in the security domain was used in the mitigation plan there are many potential threats but not necessarily all of them translate into operationally relevant risks Threats are thus sort of dormant risks which if left to develop unmitigated could develop into risks to aviation The mitigation process monitors threats assesses risks and then implements suitable mitigation to stop threats from developing into risks Three successive stages have been identified where such barriers can be applied Prevent transmission of RFI mostly through radio regulatory actions and coordination Prevent interruption of positioning and navigation capabilities in the presence of RFI This is achieved at the avionics level by making sure receivers can tolerate some RFI as well as redundant capabilities If interruption cannot be avoided ensure that other communication navigation and surveil lance capabilities provide continued safety while being able to detect locate and eliminate an RFI source efficiently This third barrier is where flight inspection or other aerial work platforms can play a significant role However this role is not limited to risk mitigation Aerial measurement capabilities can also play a role in threat monitoring by getting data on RFI emissions that are too weak to pose operational risks and facilitate risk assessment by providing a reliable reference of the impact of such signals on an aircraft in flight FLIGHT INSPECTION Similar to the subject of flight validation airborne GNSS signal in space testing must not necessarily rely on traditional flight inspection capabilities Other aerial work capabilities can be used and it is hoped that over time data from regular aircraft operations and event recording systems can be used at least for threat monitoring purposes However as soon as a significant RFI occurs purpose built aerial detection and localization capabilities are hard to beat Given that aviation is carrying the risks related to RFI and telecom regulators are unlikely to have such capabilities this naturally points to the experience and resources of flight inspection aircraft and their crews Even if a significant amount of TRACKING RFI BY Gerhard E Berz Pascal Barret Brent Disselkoen Michael Richard Vincent Rocchia Florence Jacolot Todd Bigham and Okko F Bleeker