GPS World, August 2015

DESIGN TEST Algorithms Methods Sentry Stands on Jammer Alert Jeffrey Coffed and Joseph Rolli Harris T he first and best step to combat the growing worldwide problem of GPS jamming is to pursue technologies that can detect and locate the jammers Signal Sentry 1000 uses arrayed sensors to do just that look out for jamming and track down its source once sensed An array of sensors can be deployed for sensitive and high value entities such as infrastructure installations including airports railroads chemical plants electric power plants and grids cargo ports wireless communication systems and financial transfer centers The sensors will connect to servers that assimilate the sensor data and provide operator interfaces Signal Sentry 1000 is based on a server client model The user accesses Signal Sentry using a URL and secure log in specific to the users system The users particular home screen displays a map with each installed sensor displayed with an icon reflecting status Interferers are displayed as red stars or as error ellipses The Signal Sentry web page lists all the interferers stored in the database with their start and end times The user can manipulate the list by changing the minimum duration of the event to be displayed as well as if the interferer had been geolocated or not or both If an interference event was less than a minute long it may not have a geolocation entry Geolocation Methodology Geolocation of jammers is accomplished through proprietary algorithms running at the network server that utilize digitized timestamped I and Q samples of received interference waveforms GPS observables and other parameters captured by each sensor This data is processed in a Kalman filter based location algorithm to determine an initial jammer position and track the position of the jammer throughout the jamming event This improves performance with moving jammers that is vehicle based and enables continued jammer location with a limited sensor set potentially due to signal blockage erroneous data due to multipath or out of range conditions Upon detection of an interference event by any sensor the server polls the entire sensor network for data and determines if the information is sufficient to perform geolocation The user receives near real time status of event detections and geo location of the interferer if possible Sensor data polling geolocation processing and GUI updates continue until the interference stops or the emitter goes out of sensor range Sensor data from each event is stored for later replay and processing using Signal Sentry event analysis tools An interference event frequency chart FIGURE 1 provides a tool for forensically evaluating the occurrence of interferers It displays interference events as circles the size of the circle FIGURE 1 Interference event frequency chart FIGURE 2 Interferer details GPS World August 2015 www gpsworld com 18