M. Brischetto

A Hybrid Wired/Wireless Networking Infrastructure for Greenhouse Management

In this paper, the problems related to the management of a farm made up of several greenhouses are discussed. The management of this kind of farms requires data acquisition in each greenhouse and their transfer to a control unit which is usually located in a control room, separated from the production area. At present, the data transfer between the greenhouses and the control system is mainly provided by a suitable wired communication system, such as a fieldbus. In such contexts, even though the replacement of the wired system with a fully wireless one can appear very attractive, a fully wireless system can introduce some disadvantages. A solution based on a hybrid wired/wireless network, where Controller Area Network and ZigBee protocols are used, is presented along with all the related problems that this integration involves. In particular, in order to integrate at the Data Link Layer the wireless section with the wired one, a suitable multiprotocol bridge has been implemented. Moreover, at the Application Layer, porting of Smart Distributed System services on ZigBee, called ZSDS, allows one to access the network resources independently from the network segment they are connected to.

Dynamic Continuous clock Synchronization for IEEE 802.15.4 based sensor networks

Clock synchronization is an important service in wireless sensor networks (WSN) since it can be used for data integration, for the implementation of TDMA based approaches or for synchronous data acquisition. One main issue in WSN concerns the power consumption since the batteries have a limited capacity an often they cannot be replaced. In this paper we present a dynamic continuous clock synchronization algorithm which provides a virtual common clock among a master and a group of slaves. The main feature of the approach proposed is the ability to allow nodes to sleep for long times and exchange only rare synchronization packets however providing a good quality common clock. The synchronization algorithm has been implemented inside embedded devices as a middleware over the MAC, without any modification to the original communication protocol.

Home control system over an MHP based architecture

The interactions between controls units and users in Domotics applications constitute a critical aspect which has greatly limited the diffusion of home automation systems. Usually, ordinary people have not familiarity with automation systems and find difficult to use their control interface. In this paper the authors exploit the interactive and representative potentialities provided in synergy by both the MHP decoder and TV, in order to develop an innovative way to simplify this interaction. As an example the control of a home alarm system is presented.

Evaluation of clock synchronization protocols for Wireless Sensor Networks

In this paper we compare three clock synchronization protocols for Wireless Sensor Networks and evaluate their performances under different operating conditions. The “Dynamic Continuous Clock Synchronization” (DCCS), here is compared with the “Reference Broadcast Synchronization” (RBS) and the “Continuous Clock Synchronization” (CCS). The performance evaluation of the three protocols has been carried out via simulation using the OMNeT++ discrete event simulation system. Synchronization is a key aspect in WSNs but some features such as the limited bandwidth, hardware and energy available, as well as the nature of the wireless medium, make a good synchronization a challenging objective. We performed a set of simulations to evaluate how the protocols behave by varying some influent factors, and compared the results obtained in order to achieve information useful to select the most suitable protocol for a specific application.

Performance evaluation by petri nets of a full duplex wireless link for an industrial backbone

This paper addresses the performance evaluation of a full duplex wireless protocol for an industrial backbone making a comparison with the traditional IEEE802.11 half duplex protocol. A Petri net model is used as the basis for the evaluation. The paper first examines the features of a wireless backbone and some issues they impose. Then, the paper describes the limits of the 802.11 and the solution here proposed which is based on the use of full duplex wireless links and discusses the PN models. At last the results of the performance evaluation are presented and the advantages offered by the full duplex solution are discussed.

Fast handoff for mobile wireless process control

Handoff is defined as the phase during which a mobile node has a temporary connection loss during the transfer from one wireless communication cell to another one. As in industrial applications wireless networks are often used to connect mobile devices such as, robot, trolleys, conveyors, to a control station, handoff introduces a temporary interruption of monitoring and control of the mobile device that can be disruptive. This paper proposes the Mobile Association Handoff Protocol (MAHP), which, if compared with the standard protocol, provides a notable reduction of the handoff latency.

Hybrid networking infrastructure for greenhouse management system

In this paper we focus on the problems related to the management of a farm made up of several greenhouses. Management of this kind of farms requires data acquisition in each greenhouse and their transfer to a control unit which is usually located in a control room, separated from the production area. At present, data transfer between the greenhouses and the control system is mainly provided by a suitable wired communication system, such as a Fieldbus. In such contexts, even though the replacement of the wired system with a fully wireless one can appear very attractive, a fully wireless system can introduce some disadvantages. A solution based on a hybrid wired/wireless network, where CAN and ZigBee protocols are used, is presented along with all the related problems that this integration involves. In particular, in order to integrate the wireless section with the wired one at the Data Link Layer, a suitable multi-protocol bridge has been implemented, while, at the application layer, a porting of SDS services on ZigBee, which we called ZSDS, allows us to access the network resources independently from the network segment they are connected to.

A network based virtual lab for motion control applications

In this paper we describe the architecture and implementation of a virtual lab designed to show the effect of the network delay on a distributed network-based control system. In particular, we focus on electric motor actuators which represent one of the most time-critical devices in the process control area. The virtual lab allows the user to send commands to the motors through several communication networks with different features and to evaluate the performance degradation produced by the network delay.

Simulation and measurements integration for the evaluation of wireless communication networks

Performance evaluation via simulation requires to create models that are often difficult and are not able to faithfully reflect the operating conditions. This paper discusses an approach based on the integration of trace files into an OMNeT + + model. This approach allows to represent and evaluate complex systems by simple models. Moreover, in the case a simulation model of the communication system is not available, a trace file can efficiently substitute it. The results obtained with reference to a specific case study confirm the validity of the proposed approach and the advantages it offers over using just simulators.

Improving the Dynamic Continuous Clock Synchronization for WSNs

Clock synchronization is an important feature in Wireless Sensor Networks, as a common vision of time can be required in order to perform synchronous operations. In this paper we present a new version of the Dynamic Continuous Clock Synchronization protocol which offers a greater robustness and requires less power than the original protocol. The role of the Reference Node which sends periodic snapshots necessary for the synchronization is in turn assigned to different slaves under the control of the time Master. The discussion in the paper explains the features and the advantages of this approach. The measurements performed on a testbed point out the effectiveness of the new protocol and its suitability for real applications.