A collisi on avoidance concept for VDL mode 2

The FAA is currently investigating the migration path to data-enabled digital air traffic services using VDL mode 2. Under certain loading conditions, simulations have shown that VDL mode 2 cannot meet future delay requirements with more than a few dozen aircraft per channel. Since the VDL radios must share limited spectrum with the current analog voice radios, this poses a problem during the transition period. Analysis has show that collisions of the transmitted data frames lead to retransmissions and increased delays. This paper investigates a method to reduce theses collisions through modification of the MAC protocol in the hope of increasing the capacity of a VDL mode 2 channel. Several possible future traffic profiles are used to compare the performance of the modified VDL mode 2 protocol against the standard. A discussion on the modifications necessary to implement these changes, along with interoperability issues with standard VDL mode 2 radios, is presented.