upgrades, these systems are reliable and companies trust them. ... vironments, such as refineries, are truly challenges for wireless communications. Besides, in ...
GINSENG - Performance Control in Wireless Sensor Networks FP7-ICT-2007-2 GINSENG University of Coimbra, University College Cork, University of Cyprus, Lancaster University, TUBS, SAP, SICS, GALP
Abstract. Real deployments of wireless sensor networks (WSN) are rare, and virtually all have considerable limitations when the application in critical scenarios is concerned. On one side, research in WSNs tends to favour complex and non-realistic mechanisms and protocols and, on the other side, the responsible for the critical scenarios, such as the industry, still prefer well-known but expensive analog solutions. However, the aim of the GINSENG Project is to achieve the same reliability of WSNs that the conventional analog systems provide, by controlling the network performance. In this paper we present the GINSENG architecture and the platform that have been implemented in a real scenario, considered one of the most critical in the world: an Oil Refinery.
1
Introduction
Traditionally, monitoring and control systems are analog and wired. Constituted by basic hardware and requiring complex and expensive deployments and upgrades, these systems are reliable and companies trust them. Nevertheless, wireless solutions have evolved and their low cost are making them more attractive. The idea of avoiding the deployment of thousands of cables, most of them located underground in long and inaccessible ditches, together with the amount of money that could be saved, have attracted large companies to these technologies. However, in critical scenarios, present in most industries, the only the use of reliable systems is permitted and therefore it is necessary to assure performance control of the deployed wireless systems, making them as reliable and trustworthy as the wired solutions. In the scope of the European Project GINSENG (http://www.ict-ginseng.eu/), the consortium has been developing a tightly controlled WSN to operate in critical and unstable environments. Currently, the consortium has successfully deployed a WSN in an oil refinery in Portugal , which is used as an indicator system (sensing, no actuation) in a critical zone. The Ginseng project focuses on controlling wireless system performance, and
R. Silva, J. Sa Silva, A. Cardoso, P. Gil, J. Cecilio, P. Furtado, A. Gomes, C. Sreenan, T. O Donovan, M. Noonan, A. Klein, Z. Jerzak, U. Roedig, J. Brown, R. Eiras, J. O, L. Silva, T. Voigt, A. Dunkels, Z. He, L. Wolf, F. Bsching, W. Poettner, J. Li, V. Vassiliou, A. Pitsillides, Z. Zinonos, M. Koutroullos, C. Ioannou
has targeted a set of different monitoring scenarios within the oil refinery. When monitoring tank levels, pipes pressure, product flows or employees health , the project aims to provide a trustworthy wireless system. To deploy a performance controlled WSN the consortium defined and implemented the architecture shown in Fig. 1.
Fig. 1. GINSENG software modules
The GINSENG architecture is based on the GINSENG MAC 1 , which main function is to provide addressing and channel access control mechanisms to allow GINSENG nodes that are within radio range to communicate. It is a multi-hop system that uses an exclusive TDMA for channel access with a pre-dimensioned virtual tree topology and hierarchal addresses. The Overload Control module operates over GINSENG MAC and is responsible to drop packets that have expired or cannot be sent due to low capacity. It may also increase the priority of low priority packets, and reorder packet queues. The Topology Control is responsible for managing the tree topology, implemented by the GINSENG MAC. Performance Debugging 2 is a cross-layer module and is main function is to determine whether performance requirements are being met by the wireless sensor network. The GINSENG middleware connects the wireless sensor nodes to the high-level business applications in the backend such as ERP systems, data warehouses and advanced visualization tools. The GINSENG WSN is supported by the Contiki Operating System.
1
2
T. ODonovan, J. Brown, U. Roedig, C. J. Sreenan, J. doO, A. Dunkels, A. Klein, J. Sa Silva, V. Vassiliou and L. Wolf, ”GINSENG: Performance Control in Wireless Sensor Networks”. Proceedings of SECON 2010: 7th annual IEEE SECON conference. V. Pejovic, C. Sreenan. PerDB: Performance Debugging for Wireless Sensor Networks, Proc. Of European Conference on Wireless Sensor Networks (EWSN), Poster/Demo session, 2009
2
Real Deployment
At this stage, we have deployed a 15 nodes Wireless Sensor Network, in the refinery, in order to monitor pipe pressure and products flow in a specific critical area. From the first deployment, many lessons have been learnt. Industrial environments, such as refineries, are truly challenges for wireless communications. Besides, in critical areas, hardware components that might behave as ignition must be compliance with the ATEX directive. Therefore, each deployed mote was inserted in an ATEX compliance box and external antennas were included as inside the ATEX box standard antennas become inoperable. Fig. 2 shows the mote inside the box with the external antenna. The hardware chosen to deploy in the refinery was the TelosB mote, using the
Fig. 2. TelosB motes in ATEX Boxes and 9dB Antennas.
available ADC and DAC connectors to make the interface with the local pressure and flow sensors. As previously mentioned, we used external 9dB antennas. Other models were evaluated, such as 1dB and 5dB external antennas. Scanning all available channels in different locations of the refinery, we concluded that the 9dB was the best option to assure the desired reliability. In the same study, we also concluded that channel 15 would be, in general, the best option for the location of the current network. However, any industrial environment has different patterns regarding radio communication. Reflections, refractions, absorptions, diffractions or scattering may occur in different levels, not only from place to place, but also from time to time. From our first deployment we have learnt that radio spectrum analysis is fundamental to assure a good and stable wireless communication. In Fig. 3 we can see the scenario aspect and part of the deployed network. The deployed network is being controlled from a portable office, located near the network, in which the sink is installed. All data is received through the sink and processed locally. To analyze the system accuracy, we have compared the data received via the WSN with the data received in the Petrogal control room,
Fig. 3. Photos taken from our WSN deployed in the Petrogal oil refinery.
via the conventional wired solution. Despite the signal noise, we realized that the sensors are quite accurate and our solution is operating as desired (Fig. 4).
Fig. 4. Comparison of data received via the two different systems, wired (PT5170) and wireless (ADC0), from the same sensor at the same time.
As mentioned before, the GINSENG middleware is responsible to provide data from the sensor network to the applications. At this stage, the middleware supports a local application responsible for locally present the real time information through an interface based on the local synoptic. The same synoptic is also provided through a web-service and therefore, remotely accessible. Future work comprises the extension of the GINSENG network to cover other scenarios and areas in the refinery. Furthermore, all the software modules running in the motes are still under development, aiming to provide motes with more intelligence while keeping the requirements as low as possible.
