A trajectory-based approach for the lateral control of car following systems

A crucial task for steering an autonomous vehicle along a safe path in a car following scenario is the lateral control. The sensory input of such a lateral control are the position coordinates of the leader vehicle. The following problem occurs: due to the distance between the leader vehicle and the autonomous ego-vehicle, the lateral control has to interpolate a trajectory between the two vehicles. Using as a trajectory either a straight line or a curve of constant curvature causes the ego-vehicle to deviate from the leader vehicle's trajectory. Given a system delivering 3D points of the leader vehicle with time lags, one has a handle to reconstruct the leader vehicle's trajectory. In addition, one has to compensate the motion of the ego-vehicle by using its motion parameters. Once this transformation is performed, the position coordinates of the leader vehicle are available in a coordinate system at rest. Knowing the position of the ego-vehicle in that coordinate system, one can select the trajectory point of the leader vehicle that is closest to the ego-vehicle as input to the lateral controller. This simple approach increases significantly the precision of car following systems. The algorithm is applied successfully to an autonomous car for platooning at small velocities.