Protecting Ports using Range-Free Triangulated Sensor Networks: A Case Study

Range-free wireless sensor networks rely on sensors that detect only the bearing of an incoming signal, so that localizing a transmitter requires simultaneous detection by at least three sensors, a condition known as triangulated coverage. This paper extends a previously developed geospatial computational framework with a formal treatment of sensor activation and applies it to the protection of the port of Thessaloniki, Greece. Eleven sensors, in the presence of seven known transmitters that induce angular blind zones, monitor four areas of interest that form successive protection layers: the dock, the gulf, the maritime passage, and the adjacent airport zone. We formulate the protection of several areas as a constrained combinatorial optimization problem over sensor activations and orientations, and present a group-based activation strategy, stated as an explicit algorithm, which restricts the problem to a feasible subset, determined by the geography of the deployment. Each group of sensors is oriented towards its nearest area, and neighboring sensors reinforce it only when coverage is insufficient. We further prove that the blind zones induced by the transmitters are invariant under rotation of a sensor’s field of view, so that the reachable set of the sensors yields a computable upper bound on the coverage that is attainable by any configuration of the network. We also show that the triangulated coverage ratio of an area is exactly the probability of detecting and localizing a new transmitter that is equally likely to appear anywhere in it. All four areas of interest achieve high triangulated coverage. The proposed group-based activation strategy is a practical, transparent, and computationally cost-effective approach to the protection of critical infrastructures.