Results of validation of SSR mode S interrogator identifier code coordination

Secondary surveillance radar (SSR) mode S is an air traffic control radar system with improved surveillance and datalink capability. In SSR mode S system, each mode S ground station (GS) has interrogator identifier (II) code. II code is set in interrogation and signals. It makes possible transponders identify the source site of interrogation and GS distinguish the destination of reply. International Civil Aviation Organization (ICAO) standard prepares 4 bits space in interrogation and reply for II code. Fifteen II codes are available for GS. As the number of SSR mode S GS increases, SSR operator is not able to assign II codes without conflicts between neighboring GS. This problem is called II code shortage problem. If the same II code is assigned to neighboring GS that have overlapping coverage, GS is not able to achieve continuous aircraft surveillance in overlapping area. To overcome the problem, GS is required to have II code coordination function. To prepare for the II code shortage problem in Japan, Electronic Navigation Research Institute (ENRI) developed SSR mode S with II code coordination function and conducted validation of fundamental functions in 2008. In this paper, we mention II coordination technique, experimental system and experiments. Then we show the results of validation.