Traffic flow monitoring systems in smart cities: Coverage and distinguishability among vehicles.

Traffic flow monitoring systems aim to measure and monitor vehicle trajectories in smart cities. Their critical applications include vehicle theft prevention, vehicle localization, and traffic congestion solution. This paper studies an RoadSide Unit (RSU) placement problem in traffic flow monitoring systems, in order to secure vehicles through location proofs. Given some traffic flows on streets, the objective is to place a minimum number of RSUs to cover and distinguish all traffic flows. A traffic flow is covered and distinguishable, if the set of its passing RSUs is non-empty and unique among all traffic flows. The RSU placement problem is NP-hard, monotonic, and non-submodular. It is a non-trivial extension of the traditional set cover problem that is submodular. Three bounded RSU placement algorithms are proposed with respect to the number of given traffic flows. To further reduce the number of deployed RSUs, this paper extends a credential propagation mechanism via vehicle-to-vehicle communications, which essentially enlarges the coverage of an RSU. Extensive real data-driven experiments demonstrate the efficiency and effectiveness of the proposed algorithms.