Connectivity of ad hoc networks for advanced air traffic management

This paper presents the concept and studies connectivities of wireless ad hoc networks among aircraft for enhanced situational awareness. Under this multi-hop broadcast concept, an aircraft would periodically broadcast not only its own state information, but also relay state information received from neighboring aircraft. In this paper, a basic architecture of such an airborne ad hoc network is established. The relationship between network connectivity and information reachability, which accounts for information latency and depends on transmission protocols, is discussed. Two general performance criteria are introduced that measure the connectivity performance of an airborne network subject to a specified maximum number of hops in the network. The first metric is the ratio of the total coverage area of a network cluster over that of a single aircraft. The second metric is the number of aircraft each individual aircraft can connect to within the network cluster. Three representative types of traffic scenarios are considered: a one-dimensional flight stream, two streams merging into one, and randomly distributed traffic over a horizontal region. In all cases, aircraft positions are checked against their conflict-free requirements. For the one-dimensional traffic and merging traffic scenarios, the best, the worst, and the average values of the connectivity performance criteria are obtained via numerical simulations. For the two-dimensional random traffic scenario, random simulations are repeated, and both average connectivity performances and their standard deviations are calculated. Simulation results indicate that the connectivity of the proposed airborne ad hoc network is always better than that of the non-relay scheme. Overall, the proposed concept offers great flexibilities through the use of different transmission protocols and maximizes the benefits of a given digital data link.