Configuration selection for fusion of range and Doppler measurements from multistatic radars for air collision warning

A requisite for unmanned aircraft systems (UAS) to operate within a controlled airspace is a capability to sense and avoid collisions with non-cooperative aircraft. Ground-based transmitters and UAS-mounted receivers are preferred due to the limitations on the size, weight and power of UAS. This paper assumes a constant velocity motion of an intruder (target) aircraft and presents a method to estimate the state (motion parameters - position and velocity) of the target so as to predict the closest point of approach. Bistatic range and Doppler are assumed the only measurements available, with the employment of low-cost omni-directional antennas. Several configurations are investigated from a parameter observability point of view. It turns out that one needs three transmitters in a general three-dimensional (3-D) scenario to achieve very good observability of the target motion parameter. With the assumption that the target is at the same altitude as the ownship, one has a two-dimensional (2-D) scenario in which two transmitters are required to have good observability. Simulation results show that the maximum likelihood (ML) estimate of the target parameter using iterated least squares (ILS) search is statistically efficient in both multistatic configurations with good observability. The collision warning is formulated as a hypothesis testing problem using a generalized likelihood function. The warning algorithm has no missed detection of a collision event in either configuration. It has a lower false alarm rate in a 3-D scenario than in a 2-D scenario at the expense of one more ground-based transmitter.