Distributed Reactive Collision Avoidance - University of Washington

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paths dynamically for the vehicles. While most of the computations are distributed, a central
server is still required to make the trades. Additionally, no guarantee has been made
that a collision-free set of paths will be found.
The authors of [27] also use a negotiation process to optimize collision avoidance maneuvers,
but another algorithm must be present to give collision-free paths for the vehicles
to start from for the guarantees to work. The idea is that this other algorithm need not be
optimal, but merely feasible. Then the second stage enables the vehicles to negotiate a more
optimal solution derived from the first. The algorithm for finding a set of feasible paths is
not given, assuming instead that one of the other approaches discussed here will suffice.
A major improvement in the computation time of optimization methods is shown in
[28], which uses satisficing game theory to make a truly decentralized optimization scheme.
This algorithm is efficient enough to make real-time computation reasonably scalable to
large numbers of vehicles. The price paid for efficient computation is a loss of the safety
guarantees, as simulation results show that collisions are rare, but that they do occur.
In [29], a distributed collision avoidance algorithm with guaranteed safety is presented
for a homogeneous group of n aircraft. This prescribed maneuver approach involves two
discrete heading and speed changes for each aircraft, where each aircraft turns the same
way. The method is based upon perturbations from an exact conflict, where all vehicles
are headed toward a single collision point. This algorithm was extended in [30] to work in
3D and to account for bounded acceleration. Since the algorithm is computed only once,
it is unclear how it could account for a dynamically changing environment where vehicles
are not necessarily capable of performing the exact maneuver prescribed. Additionally, the
algorithm may run into trouble with extremely inexact conflicts, since it is based upon a
transformation to an exact conflict.
Probably the safest collision avoidance algorithm to date is that of [31], which considers
a homogeneous group of constant-speed unicycles. This method uses a completely decentralized,
prescribed maneuver algorithm for n vehicles which has an absolute guarantee of
safety in the presence of constrained control authority. While this solution might appear