Spectrum planning for the transition to a digital air/ground radio system for air traffic control

The Federal Aviation Administration (FAA) plans to upgrade the air/ground (A/G) radio system that it uses for air traffic control (ATC). The Next-Generation A/G Radio Communications System (NEXCOM) will use the VKF Digital Link Mode 3 (VDL3) to provide a voice and data capability. The nationwide transition from today's analog voice system to NEXCOM will take several years. Since VDL3 interference characteristics differ from those of analog radios, nearly every A/G circuit at the time of its conversion to NEXCOM will need to change its operating frequency to avoid interference with neighboring circuits. A step-by-step frequency plan is needed. The MITRE Corporation's Center for Advanced Aviation System Development (CAASD) has developed an automated simulation model that facilitates spectrum planning for the transition. The model incorporates all applicable frequency assignment rules. It has the crucial ability to simulate "neighbor-repacking"-selective changes to the frequency assignments of neighboring circuits when necessary to create spectral room for circuits being converted to NEXCOM. Using this model, CAASD has developed strawman frequency plans for a wide variety of transition scenarios. This paper describes the model and presents our key simulation results. We demonstrate that a nondisruptive incremental transition is feasible but will require widespread neighbor-repacking. We also show that starting the transition as soon as possible, and giving NEXCOM circuits access to as many frequencies as possible in the "new" 136136.475 MHz subband as well as the previously available frequencies below 136 MHz, will reduce the complexity of the transition and thus tend to minimize its overall cost.