Determining GPS anti-jamming performance on tactical missiles

The use of the Global Positioning System (GPS) for aiding the navigation of missiles in a tactical environment is growing. Two missile systems which have fielded GPS are the Tomahawk Cruise Missile and the Standoff Land Attack Missile (SLAM). Other systems such as the Army Tactical Missile System (ATACMS) are incorporating GPS into their navigation solution. When integrating GPS into a vehicle, the designer has to determine the specifications of the receiver that will meet the system objectives. One of these specifications will be the amount of jammer-to-signal (J/S) power the receiver and antenna system can withstand without losing track of the satellites. To aid in determining this requirement two simulation tools, VISJAM and VISCON, were developed to measure the performance of the GPS user equipment in a jamming environment. Both of the tools use an externally generated vehicle trajectory and a user supplied almanac to calculate the vehicle to satellite geometry. VISJAM determines the number of visible satellites, the optimum set of satellites to track, the corresponding geometric dilution of precision (GDOP), the J/S for each satellite, and the acquisition state for each satellite (State 3 or State 5) at each time step for multiple jammers. VISCON calculates a contour map showing the minimum required jamming power at each point on the map that will deny the GPS function to the missile. The resolution of the contour map is user definable