Analysis of temporal impairments on airborne VDL Mode 2 packet reception

The FAA planned Data Communications Network Service (DCNS) will enable digital air/ground (A/G) communication between Air Traffic Control (ATC) facilities and VHF Digital Link (VDL) Mode 2 (VDL-2) equipped aircraft. In successive program segments, ATC services will evolve to include both \´essential\´ and \´safety critical\´ applications. Appropriate requirements will be imposed on the DCNS to transport these applications. These requirements will place challenging demands on the performance of the VDL-2 A/G links. Predicting and accommodating the impairments to the air-ground radio channel are necessary for the DCNS provider to deploy a design that assures endto-end performance requirements are satisfied. Good engineering practice requires the characterization of the air-ground radio channel and development of detailed link budgets. Certain significant VDL-2 channel impairments are intermittent (temporal) and add complexity to the analysis. A significant intermittent impairment to VDL-2 uplink messaging can occur while airborne VHF radio systems, such as those used for ATC and Airline Operational Control (AOC) voice communications, are transmitting on their respective downlinks. Another intermittent VDL-2 impairment may occur with VDL-2 transmissions from "hidden terminal" aircraft within radio line of sight of each other, but not communicating with the same ground station. This may happen when aircraft in different service volume \´cells\´ share the same channel frequency. The impairment occurs when a hidden terminal transmission is received at the victim aircraft with sufficient signal strength. A DCNS A/G subnetwork design analysis and its associated radio channel models should take into consideration any significant intermittent impairment. The interference impairments just described add to the noise calculations in a link budget model. For the uplink VDL-2 channel on the aircraft, the link noise plus interference can cause significant impairment of the channel.- - This paper develops a framework to predict the coincidence of intermittent impairments with VDL-2 packet reception. The framework is then applied, as example, to the airborne VHF radio cosite problem.