This article addresses the coverage problem of non,convex environments by a mobile multi-robot system characterized by omnidirectional 'field of view' sensing capabilities. The mobile robotic network is heterogeneous in terms of robots' sensing ranges. Moreover, each robot is capable of communicating with all robots located within a predefined distance from its position. A distributed gradient-based coordination scheme is proposed, based on a novel partitioning of the environment, leading the network to a local optimum of an area-wise criterion. Simulation studies are carried out verifying the efficiency of the proposed distributed control law. (C) 2014 Elsevier Ltd. All rights reserved.