The recent advancement in information technology and the continuously increasing complexity of digital systems has led to the need for a new generation of intelligent solutions – Cyber-Physical Systems (CPS).
They integrate computing, communication and storage capabilities with monitoring and control of the entities in the physical world, actions that have to be performed dependably, safely, securely, efficiently and in real-time.
CPSs consist of interconnected objects, embedded with sensors, collecting information from the physical world, and actuators, acting upon the environment, and integrated under an intelligent decision system, representing the cyber world.
In this context, the present paper proposes a CPS architecture for the real-time monitoring of environmental status, based on the Wireless Sensors Network (WSN) technology for data acquisition and on the cloud computing technology for storing, managing and analysing the data in a large context.
Cyber-physical systems exploit the physical information collected by WSNs to bridge real and cyber spaces. A WSN is composed of multiple low-power small embedded devices, called nodes, deployed in a physical environmental and having communication, sensing and data storage, and processing capabilities.
Depending on the application, the nodes, consisting of a sensor unit, a processor and storage unit, a transceiver and a power supply, have resource constraints regarding energy usage, communication range, processing power, and storage capabilities.
Due to the recent progress of the technology in micro- electromechanical systems, integrated circuits and radio frequency, WSNs are used in a wide range of applications, with emphasis on environmental monitoring.
Theproposed CPS architecture gathers temperature and humidity information from portable low cost nodes. Thanks to the development of new generations of sensors, other physical units, such as different gas concentrations in the air, can be measured.
Data sensed by the sensor are sent using the User Datagram Protocol (UDP) to a measurements database, where they are collected. An intelligent cloud-based decision system transforms these sensing data into knowledge, reported to the end-users under various modalities.
The sensor nodes in environmental monitoring applications have to satisfy requirements in terms of cost, reliability, maintenance-free operation times and size.
Hence, a battery-powered embedded system, with the core represented by a programmable system on chip microcontroller, an 8051-based PSoC 3 produced by Cypress Semiconductor, was developed for implementing the bottom layer of the proposed CPS architecture.
Using the JADE add-on, the Web Service Integration Gateway (WSIG) and its specific elements, the WSIG Agent and WSIG Servlet, the CPS multi-agent society interacts with web services invoked by end-users through the client applications.
By integrating discrete analog and programmable logic along with memory and a microcontroller, these devices are becoming increasingly attractive for the design of embedded systems. The use of such a device provides the system with enhanced flexibility and reduces the part count on the printed circuit board because they include a wide range of components into the chip.
This has a direct impact on the node production costs and power consumption. The sensing component of the node consists in a DHT22 digital temperature and humidity sensor. Due to the flexibility provided by the core microcontroller, a wide range of analog and digital sensors can be attached to the device.
The environmental monitoring and data analyses web services use the Simple Object Access Protocol (SOAP) and Web Service Definition Language (WSDL) to access the measurement data. The most straightforward solution for the web services methods requests is a web portal, which links the measurement data to client applications.
Client applications with monitoring and management features, dedicated to different categories of end-users, have to be developed for efficient and customized data exchange and also for testing the web services.
Different categories of end-users involve the definition of diverse levels of access. Depending on the data access method used, access restrictions have to be put in place, together with solutions for data protection: a password management system and/or a challenge-response encrypted mechanism for the web portal and WS-Security (on SOAP) for web services.
To read this external content in full, download the complete paper from the author's open online archives at the Technical University of Torino, Italy.