A Testbed for Coverage Control using Mixed Wireless Sensor Networks Theofanis P. Lambrou ∗∗ , Christos G. Panayiotou KIOS Research Center for Intelligent Systems and Networks, Dept. of Electrical and Computer Engineering, University of Cyprus, Nicosia, Cyprus. Abstract Wireless Sensor Networks (WSNs) is a relatively new technology that has been proposed for several applications including wide area monitoring. Such applications may include stationary or mobile sensor platforms or they may include several stationary and some mobile-robotic sensor nodes that can move in the area in order to achieve certain objectives, e.g., monitor areas that are not adequately covered or assist in the transfer of data to prevent the energy depletion of certain critical nodes. Such networks that consist of both stationary and mobile nodes are referred to as mixed WSNs. This paper presents the development of an experimental testbed for mixed WSNs consisting of stationary and mobile sensor nodes that collaborate to improve the sensing coverage and event detection of the network in a given deployment area. The paper describes the hardware and infrastructure of the testbed as well as a case study for coverage control that was investigated using the testbed. We point out that the developed testbed can be used for the evaluation and validation of different algorithms for coverage control that involve collaboration between stationary and mobile sensors to improve the WSN’s monitoring capabilities. In addition, it can also be used to investigate other objectives as well as other concepts (e.g., network control). Keywords: Mixed WSN testbed, distributed path-planning, coverage. 1. Introduction Recent advancements in wireless communication and microelectronics have enabled the development of simple nodes that can communicate wirelessly to form a Wire- less Sensor Network (WSN). Such networks have great potential in many applications such as area monitoring, smart buildings, precision agriculture and traffic control. Their unique feature is that they can capture the spatial and temporal dynamics of the environment or process they monitor. Depending on the applications, a WSN may consists of either stationary sensor nodes or mobile sensors, e.g., sen- sors installed on robots or aerial vehicles. Another possi- bility are the mixed WSNs which consist of several station- ary nodes together with some mobile nodes that collabo- rate in order to achieve objectives like improved coverage, improved network connectivity, or prolonged network life. This paper provides an overview of a mixed WSN exper- imental testbed. The testbed includes several stationary ✩✩ This work is partly supported by the European Structural Funds, the Cyprus Government, the Cyprus Research Promotion Founda- tion and the European Project CONtrol for COORDination of dis- tributed systems (CON4COORD). ** Corresponding author Email addresses: faniseng@ucy.ac.cy (Theofanis P. Lambrou), christosp@ucy.ac.cy (Christos G. Panayiotou) URL: http://www2.ucy.ac.cy/~faniseng/index.html (Theofanis P. Lambrou) nodes as well as some nodes mounted on mobile robots. A main objective of the testbed is to demonstrate and vali- date algorithms that allow the mobile nodes to move au- tonomously in the area in order to achieve their objectives. For the purposes of this paper, the objective is to improve the network’s sensing coverage. Furthermore, the testbed can be used to demonstrate the collaboration between the sensor nodes. Moreover, we emphasize that the testbed can also be used to demonstrate other objectives (e.g., network connectivity) as well as other concepts such as networked control or control over wireless networks, how- ever, these objectives are out of the scope of this paper. In monitoring applications that involve a large area, coverage holes (areas not sufficiently monitored, where, if an event occurs it may not be detected) are inevitable; ei- ther due to an effort to reduce the overall cost, or due to random failures of some nodes. An approach to address the problem of coverage holes is to employ mobile sen- sor nodes that collaborate with stationary nodes in order to improve the area coverage and/or to detect an event as fast as possible. We are particularly interested in ap- proaches where the mobile nodes (agents) autonomously decide their own path based only on “local” information in order to sample areas that have not been sampled by other nodes, stationary or mobile. To achieve this, mo- bile nodes collaborate by exchanging some information so that they do not sample the same areas. The node collab- oration approaches investigated in this paper have been Preprint submitted to Elsevier Tuesday 25 th January, 2011