Cyclic routing of unmanned aerial vehicles

Various missions carried out by Unmanned Aerial Vehicles (UAVs) are concerned with permanent monitoring of a predefined set of ground targets under relative deadline constraints, which means that there is an upper bound on the time between two consecutive scans of that target. The targets have to be revisited ‘indefinitely’ while satisfying these constraints. Our goal is to minimize the number of UAVs required for satisfying the timing constraints. The solution to this problem is given in the form of cyclic (synchronized) routes that jointly satisfy the timing constraints. We develop lower- and upper-bounds on the number of required UAVs, show a reduction of the problem to a Boolean combination of ‘difference constraints’ (constraints of the form x - y ≥ c where x, y ∈ R and c is a constant), and present numerical results based on our experiments with several hundred randomly generated problems.