MAC Protocols for Wireless Sensor Networks

MAC Protocols for Wireless Sensor Networks

Torsten Braun (University of Bern, Switzerland), Markus Anwander (University of Bern, Switzerland), Philipp Hurni (University of Bern, Switzerland) and Markus Wälchli (University of Bern, Switzerland)
Copyright: © 2011 |Pages: 10
DOI: 10.4018/978-1-60566-250-3.ch016
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The chapter describes related work on medium access control protocols for wireless sensor nodes. We focus on scheduled and contention-based protocols that have been proposed by the research community during the last few years. In particular, we evaluate the potential to save energy of several representative protocols, namely LMAC, TEEM, and WiseMAC. This has been done by measurements of implementations in real sensor networks. The measurement results show that by sophisticated MAC protocol design we can significantly improve the energy-efficiency and increase the lifetime of a sensor node. Real-world measurements are important to determine power consumption parameters of sensor nodes.
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There are two basic classes of MAC protocols for WSNs: scheduled protocols and contention-based protocols . By combining the basic concepts, hybrid protocols can be designed .

Scheduled protocols are either based on polling or multiplexing. With polling a central controller polls other sensor nodes to detect whether they have pending transmissions. This avoids energy waste caused by collisions but introduces polling overhead and delays. In case of multiplexing, channels are pre-allocated based on time, frequency, or code multiplexing. Scheduling based approaches often form clusters with cluster controllers responsible for the channel allocation. Since only a certain number of channels can be allocated the scalability might be limited then.

Contention-based protocols allow sharing channels and allocating channels on-demand. The main problem is that contention can happen in case of dense networks and highly active sensor nodes. Moreover, collision avoidance is rather difficult to achieve in WSNs due to potentially hidden nodes.

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