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Supporting Different QoS Levels in Multiple-Cluster Wireless Sensor Networks
Ref: HURRAY-TR-100603       Publication Date: Jan 2010

Abstract:
Recent advancement in technology and rapid reduction in costs have led to the uses of Wireless Sensor Networks (WSNs) for applications with requirements significantly differing form traditional monitoring applications. Sensor nodes are now being increasingly used for real-time embedded applications having stringent QoS requirements in terms of timeliness and reliability. However, most of the current set of communication protocols use best effort service and do not provide any real-time guarantees on data delivery. Real-time communication and QoS support in WSN remains an open issue and are the focus of this work. Towards this end, IEEE 802.15.4/Zigbee protocols are considered among the most promising candidates and have been under recent investigations. However, the attempts to evaluate the protocols by implementing them over TinyOS, the most popular operating system for sensor nodes, encountered several problems, mainly because of the limitations of the OS, namely lack of task pre-emption and prioritization. To provide a more reliable platform for a better evaluation of the protocol, we first implement the stack over ERIKA, a real-time operating system with support for task prioritization and priority based preemption. In order to support cluster-tree formation in synchronized mode, we additionally implemented a Time Division Beacon Scheduling mechanism. While IEEE 802.15.4 does provide options for guaranteed bandwidth by providing contention free time slots, its usefulness is severely restricted for large scale distributed applications with even distribution of critical message. For the rest of the period the protocol uses CSMA/CA algorithm for channel access, without any provisions of QoS support. In this dissertation we extend the QoS to Contention Access Period by introducing priority based service differentiation in CSMA/CA.

Manish Batsa

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