Supporting Real-Time Communication in Large-Scale Wireless Sensor Networks

Automation activities are essential for the competitiveness increase in all industrial sectors. According to Chen, German, & Dressler (2010), an increasing number of industrial applications are focusing on wireless networks as a core technology. Wireless technologies have also been identified as a very attractive option for industrial and factory automation, distributed control systems, automotive systems and other kinds of networked embedded systems (Willig, 2008). Within this context, wireless sensor systems can revolutionize industrial processing and help industry meet the demands of increased competitiveness. Wireless sensor technology offers reliable, autonomous process control to improve product quality, increase yield and reduce costs. Thus, the use of Wireless Sensor Networks (WSN) in the industry is an attractive topic of research. Multiple research works have been addressing routing and energy-efficiency problems. However, little attention has been given to the support of real-time communication in large-scale WSNs. The WSN literature proposes two work contexts: standards and routing protocols. In the standard context, one of the more frequently used wireless Sensor Network technologies is the IEEE 802.15. 4 standard. The IEEE 802.15. 4-2011 (IEEE Std 802.15.4-2011, 2011) is a standard designed for Low-Rate Wireless Personal Area Networks (LR-WPANs), which focus on short-range operation, low-data rate, energy-efficiency, and low-cost implementations. However, the standard has a number of limitations that hinder the construction of large-scale wireless sensor networks with temporal constraints. Thus, the IEEE 802.15. 4e and 802.15. 5 standards were released to enhance the real-time properties of the 802.15. 4 MAC protocol (e.g. lower latency and higher robustness and determinism), and to increase the network scalability through the support of mesh topologies. The IEEE 802.15. 4e standard (IEEE Std 802.15.4e-2012, 2012) introduces additional medium access control (MAC) mechanism and frame formats that allow devices to support a wide range of industrial and commercial applications. However, this standard also has a limitation set, as the lack of performance evaluation works in large-scale networks (Rodenas-Herraiz, Garcia-Sanchez, Garcia-Sanchez, & Garcia-Haro, 2013). The IEEE 802.15. 5 standard (IEEE Std 802.15.5-2009, 2009) proposes a mesh topology through to implementation of a logical tree and mesh links, increasing the network scalability. In the routing protocol context, the literature proposes several challenges and special considerations in the design of routing protocols for wireless sensor networks (Li, Zhang, Hao, & Li, 2011; Akkaya, & Younis, 2005; Liu, 2012; Radi, Dezfouli, Bakar, & Chung, 2012). Multiple research works have been addressing routing and energy-efficiency problems. However, little attention has been given to the support of real-time communication in large-scale WSNs. This article discusses the state-of-the-art of standards and routing protocols for WSN, focusing on their adaptation to large-scale WSNs and on the impact that WSN topologies have upon their real-time properties. It first includes a background and discussion about the standards for WSN and their main features, involving the real-time and large-scale aspects. Then, within this Erico Meneses Leão University of Porto, Portugal & DC Federal University of Piauí, Brazil