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1XMAC Protocol
X-MAC: A Short Preamble MAC Protocol for Duty-Cycled WirelessSensor Networks
Presented by : Ankur Sharma
Michael Buettner, Gary V. Yee, Eric Anderson, Richard Han,
Department of Computer Science University Of Colorado, Boulder, USA
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Agenda
• LPL->BMAC->XMAC - The Evolution of MAC protocols
• X-Mac - A little Insight • Conclusion / The Critic in me• Q n A (if we still have any )
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Catch me if you CAN !
X MAC provides an optimum solution to most of the problems faced by a typical wireless sensor network.
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Evolution Of MAC Protocols
2000
2001
2002
2003
2004
2005
2006
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Reasons For Evolution ?
• Slow transmission of Bytes to faster packet communication.
• Synchronous protocols were not always adaptive to various applications and networks.
• ENERGY
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LPL
“On-Demand” transmission and reception
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BMAC : Clear Channel Assessment
Noise has significant variance in channel energy.Packet reception has fairly constant energy
NOISE
SIGNAL
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How BMAC is better ?
• On the fly reconfiguration.• Provides bi-directional interfaces for system services to
optimize performance.• Varying Preamble size and check-interval.
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B-MAC achieves 4.5 times the throughput of the standard S-MAC unicast protocol
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BMAC consumes less power
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Do We Need Another MAC ?
Some Improvements ?
Something ?
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XMAC – The new MAC on the block!
XMAC builds upon the foundation provided by asynchronous duty-cycled MAC protocols.
• To improve problems of low power listening.• Overhearing.
• Excessive preambling.
• To use network-traffic-load-adaptive algorithm for efficiency.
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X-MAC Solving: Excessive Preambling
Randomized backing-off for transmitters.
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XMAC Strobing
Solving: Excessive Preambling
EACKs save energy !!
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XMAC
• Embedding the Target ID in the Preamble
Solving : Overhearing
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XMAC : Adaptation to Traffic Load
The Problem• Different nodes in a multi-hop network may experience different
average traffic loads• For applications with time varying traffic loads, any pre-
determined fixed schedule will be sub-optimal.
XMAC’s Solution: Adaptive Algorithm: The Basic Idea:• The performance of a duty-cycling MAC is largely determined by
the choice of radio sleep and wake periods for both the senders and receivers.
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If an estimate of probability of receiving a packet in any given interval and a suitable “objective function*” is known, then the optimal protocol parameters for sleep and listen periods of receiver can be determined.
*Objective Function: Any linear combination of sender energy consumption, receiver energy consumption and latency.
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So Isn’t X MAC the best of all ?
Let the facts speak for themselves
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32.5% increase in energy lifetime of the receiver for X-MAC
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Energy consumption remains relatively constant as network density increases
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X-MAC uses 10% less energy under Contention
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X-MAC’s adaptive optimization has a lower duty cycle
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The Critic in Me
• The process of “avoiding overhearing” by embedding the target receiver-node ID will make multicasting/broadcasting difficult.
• to be continued…
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Conclusion• Energy Efficiency drove the birth and evolution of different
MAC protocols in the last few years.• Each MAC has certain strong points over the other but also
suffers in some areas under some circumstances.
“The “perfect” sensor network software must have a stable base along with a flexible enhancement interface that could be dynamically tailored for any wireless sensor network “
(Ankur Sharma)
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References
• X –MAC: A Short Preamble MAC Protocol for Duty Cycled Wireless Sensor Networks http://www.cs.colorado.edu/~rhan/Papers/xmac_sensys06.pdf
• Comparision of XMAC and BMAC protocols www.cse.iitb.ac.in/~vijaygabale/projects
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Questions ?
