Outline Paper presentation Ultra-Portable Devices Introduction - - PowerPoint PPT Presentation

Paper presentation – Ultra-Portable Devices

Paper: Presented by:

Xiaolei Shi, Thomas Sturm, et al. Wake-Up-Frame Scheme for Ultra Low Power Transceivers. Globecom (vol. 6), pp. 3619-3623, Nov 2004.

Carl Bryant

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Outline

• Introduction
• Related work
• Wake-Up-Frame
• Comparison
• Discussion
• Simulation
• Summary

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Introduction

• Wireless sensor networks (WSN) etc.
• Networking with small cheap devices
• Sparse communication (mostly)
• Battery time important
• WUP = Wake-Up-Preamble
• WUF = Wake-Up-Frame

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Introduction

• Transceiver power hungry – keep on as little as possible
• Receiver off – node deaf
• Strategy required to make/receive connection with minimum

waste of power

• Passive receiver would allow immediate wake up, but

implementation and use problematic

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Wake up! Zzzz...

Related work

• WiseMAC*
• Transmission is preceeded by a long preamble

(Wake-Up-Preamble, WUP)

• Receiver periodically wakes up to check for transmission
• Transmission detected from signal strength
• Sampling schedule piggybacked on last received packet to

allow shorter WUP in subsequent communication

09-08-21 Paper Presentation - Ultra Portable Devices 5 *El-Hoiydi, A.; Decotignie, J.-D., "WiseMAC: an ultra low power MAC protocol for the downlink of infrastructure wireless sensor networks," Computers and Communications, 2004. Proceedings. ISCC 2004. Ninth International Symposium on , vol.1, no., pp. 244-251 Vol.1, 28 June-1 July 2004 (among Nafiseh’s presentation papers)

Related work

• Limitations:
• Broadcasts must still use full length WUP
• Clock instability will degrade sync. over time
• Listening nodes must stay awake the full duration of the

WUP, even those not addressed

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Wake-Up-Frame

• Idea: Replace preamble with smarter transmission containing

more information

• Pretransmission is divided into many short frames each

containing a MAC frame and remaining duration of WUF

• Allows listening nodes to make early wake/sleep desicion
• Allows recipient to sleep until data is transmitted
• Additional idea: Use different data rate for pretransmission
• Data rate detection supposedly fast and easy
• Complements signal strength detection to minimize

unneccesary wakeups

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Comparison, WUP/WUF

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• Hardware example for comparison

Comparison, WUP

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’Worst’ case – receiver sleeps just before start of WUP Determines shortest WUP required for certain detection

Comparison, WUP

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Receiver wakes up early – long wait Receiver fully on while waiting – wasted power

Comparison, WUF

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Receiver waking up early can go back to sleep Receiving node saves power

Discussion

• Succeeds in making listening nodes work less, but transmitting

node still needs to work the full WUF duration (long pretransmission also limits channel capacity).

• Introducing duplex would allow receiver to send ACK as suggested

in XMAC*

• Does WUF still have any use?
• Broadcasting
• For a node with good power supply a long transmission matters less
• Different pretransmission data rate useful?

09-08-21 Paper Presentation - Ultra Portable Devices 12 *Michael Buettner, Gary V. Yee et. al. “X-MAC: a short preamble MAC protocol for duty-cycled wireless sensor networks”, SenSys '06: Proceedings of the 4th international conference on Embedded networked sensor systems (2006), pp. 307-320 (among Nafiseh’s papers)

Discussion

• Paper argues that power savings increase with increased

traffic.

• For frequent traffic a WiseMAC based WUP scheme would

have up to date sampling schemes, reducing wasted power

• Incidentally the authors later got another paper adding this

feature to the WUF scheme*

09-08-21 Paper Presentation - Ultra Portable Devices 13 *Xiaolei Shi; Stromberg, G., "SyncWUF: An Ultra Low-Power MAC Protocol for Wireless Sensor Networks," Mobile Computing, IEEE Transactions on , vol.6, no.1, pp.115-125, Jan. 2007

Simulation

• Simulations of different scenarios to judge if WUF has

noticable advantage over WUP

• Data packets generated by a Poisson process with arrival

rate λ (packets/s)

• Data frames @ 100kbit/s, WUF @ 70kbit/s
• Caution: Unknow if WUP scheme includes sampling schedule

information

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Simulation

• 3V, 1000mAh battery assumed

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Simulation

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Power consumption without traffic

Simulation

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Master-Slave, unicast

Simulation

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Master-Slave, broadcast

Simulation

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Peer-To-Peer communication in a flat topology

Simulation

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Peer-To-Peer, unicast

Simulation

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Peer-To-Peer, broadcast

Summary

• Paper builds on Wake-Up-Signal type network with duty-

cycled reception, like WiseMAC

• Unnecessary listening is avoided by including additional

information and by making the pretransmission distinct

• Simulations seem to indicate significant potential savings
• There may be solutions that improve on this, but this scheme

may still have merit for broadcasting and transmission from ’high power’ nodes

• Using different data rate for pretransmission might have

general use

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