Radionavigation Kalman filtering: case studies in two dimensions
Michael S. Braasch · 2022
So far we have spent a good deal of time estimating scalars and even the radar example involved a vehicle traveling in essentially a straight line. It is time to move into two dimensions and see where that takes us. We will investigate horizontal positioning and, as an example, will consider the distance measuring equipment (DME) system. DME comprises ground stations (known as transponders) that respond to RF interrogations transmitted from a unit in an aircraft (known as an interrogator). The two-way transmissions enable the airborne unit to determine the distance (range) to the ground station. The measured ranges are an approximation to the horizontal distance from the ground station to the aircraft. Range measurements made to at least two ground stations may be used (along with the known ground station locations) to compute the horizontal position of the aircraft. Since there is no need for receiver clock bias estimation, the use of DME for horizontal positioning provides us with a simpler solution that is possible with GPS and allows us to ease into the topic. Throughout this chapter (and the next), we will consider positioning via radionavigation only.