A. Jiménez · J.R. Martínez-de Dios · J.M. Sánchez-Matamoros · A. Ollero
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TOWARDS AN OPEN TESTBED FOR THE COOPERATION OF ROBOTS AND WIRELESS SENSOR NETWORKS ABSTRACT This paper describes a testbed for general experimentation in cooperative algorithms, techniques and applications involving robots and wireless sensor networks (WSN). The objective is to establish a common framework for evaluation and comparison of different methods and interoperations of robots and WSNs. The proposed testbed uses an open and modular architecture based on Player. Currently, integrated by 5 Pioneer 3AT and 40 Xbow nodes, the testbed is easily extensible and has good scalability properties. The main experiments already carried out focused on trajectory following, robot localization, data muling and WSN network formation and recovery. The testbed is operative since September 2009.
I. INTRODUCTION A Wireless Sensor Network (WSN) comprises of a large number of distributed low-cost devices with computing, sensing and communication resources. Wireless communication and battery operation facilitate their deployment with low invasion and low installation and maintenance costs. WSNs use mechanisms that provide ﬂexibility, fault tolerance and reconﬁgurability. In the last years they have been used in a wide range of applications . Cooperation between WSNs and mobile robots provides a wide variety of complementarities that have attracted significant research efforts in the recent years, . Networks with distributed nodes can enhance the perception capabilities of robots endowed with local sensors. Also, WSNs provide robust communication coverage that can be used for robots interaction. Besides, robots mobility and their capability to carry equipment are useful to enlarge the communication ranges of static WSN nodes. Note that low communication range and power capacity are two main constraints of static WSN. Robots equipped with mobile nodes can be used for network deployment, , and repairing, . Moreover, nodes mounted on mobile robots have been proposed for data collection, : they move close to the nodes to collect WSN data ensuring error-free data transmission and minimizing the WSN radio’s transmission power, . Also, robots have been proposed for WSN deployment  and repairing , retrieving of WSN data  and WSN localization  among others. Despite their rich synergies, some of the main difﬁculties of research on robot-WSN cooperation are high costs and low repeatability of experiments, which disables or hinders evaluation and comparison of techniques. Also, while a number of testbeds for mobile robots, see for instance  and  and for WSNs, see  and  have been developed, the number of testbeds for robot-WSN collaboration is scarce. Furthermore, there are important differences among them in terms of approach, intended applications, levels of software abstractions, capabilities, etc. Some are focused on speciﬁc aspects: Mobile Emulab,  is mainly focused on WSN experiments providing a testing platform for WSN mobile nodes whereas Explorebots  concentrates on the robotics approach. ISROBOTNET  was designed as a
response to the necessities of a concrete application within the framework of a project. The Clarity UbiRobot testbed  has a balanced approach. In fact, the lack of a common testbed is considered of a major drawback for the development of the topic, . This paper describes an open testbed for cooperation of static and mobile wireless sensor nodes and robots. One of its main objectives is to facilitate and speed up the development, validation and comparison of techniques involving cooperation of robots and WSNs. The testbed proposed in this paper is being developed in the EU-funded Cooperating Object Network of Excellence CONET (INFSO-ICT-224053). It uses an open architecture, which can be easily extended to other hardware elements and have good scalability and extensibility features. The testbed allows the abstraction of each hardware element regardless of its sensing and computing capacities and treats them as entities. All these entities have the capability of communicating with each other. This approach allows the tested experiments to be focused on either WSN or robotics techniques, as well as to involve both at the same level. The structure of this paper is as follows. Section II describes the main requirements and some intended experiments of the testbed. The software architecture is provided in Section III. Section IV presents the hardware elements currently involved in the testbed. Section V brieﬂy depicts some experimental results. The ﬁnal sections are conclusions and acknowledgments.
II. REQUIREMENTS AND INTENDED EXPERIMENTS The requirements of the proposed testbed are driven to service both scientiﬁc community and future industrial applications. Many of these envisioned techniques, applications and experiments can be found in the Cooperating Objects prospective analyses in  and . According to them the following set of basic properties should be complied by the proposed testbed: - Generality and openness, - Scalability, - Timeliness (use of real-time systems),
readings. The objective is the optimization of the movement of each robot in order to achieve the best images, laser readings and WSN sensors readings of the scenario and at the same time be energy and time efﬁcient, using techniques such as POMDPs, .
VII. ACKNOWLEDGMENTS The authors thank the CONET partners and associated members. We express our gratitude to Mr. Victor Vega and other members of the GRVC, for their contribution in the hardware and technical support.
Figure 7 · Picture of the Pioneer robots in a MRTA experiment in the laboratory building of the School of Engineering of Seville.
Figure 8 · Left) RSSI-Distance relationship in an open scenario. Right) Basic scheme of the experiment.
VI. CONCLUSIONS AND FUTURE WORKS This paper describes an open testbed for the cooperation of robots and WSNs. Its objective is to accelerate the development and validation of techniques involving cooperation of robots and WSNs as well as to facilitate their comparison. The testbed has been developed in the EUfunded Cooperating Object Network of Excellence CONET (INFSO-ICT-224053). The testbed uses a modular and ﬂexible software architecture based on Player that considers a number of heterogeneous elements at the same level. Currently integrated by 5 Pioneer 3-AT and tenths of Xbow WSN nodes, the testbed is easily extensible and has good scalability properties. The testbed is operative since September 2009. The main experiments already carried out focused on trajectory following, robot localization, data muling and WSN network formation and recovery. A video of the ﬁrst demo of the testbed with some of these experiments can be observed from . The testbed experiments can be performed in indoor and outdoor scenarios. Thus, incorporation of Unmanned Aerial Vehicles (UAVs) and the combination with outdoor testbeds will be the subject of future research and development. The improvement of human-robot interaction including remote operation is object of current work.
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