mmsn: multi-frequency media access control for wireless sensor networks
DESCRIPTION
MMSN: Multi-Frequency Media Access Control for Wireless Sensor Networks. Gang Zhou, Chengdu Huang, Ting Yan, Tian He John. A. Stankovic, Tarek F. Abdelzaher Department of Computer Science University of Virginia. Outline. Motivation State of the Art Overhead Analysis - PowerPoint PPT PresentationTRANSCRIPT
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MMSN: Multi-Frequency Media Access Control for Wireless Sensor Networks
Gang Zhou, Chengdu Huang, Ting Yan, Tian HeJohn. A. Stankovic, Tarek F. Abdelzaher
Department of Computer ScienceUniversity of Virginia
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Outline
Motivation State of the Art Overhead Analysis Contribution – New Protocol Framework
Frequency Assignment Media Access Design
Performance Evaluation Conclusions
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Ad Hoc Wireless Sensor Networks• Sensors• Actuators• CPUs/Memory• Radio• Minimal capacity
Self-organize
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Motivation Limited single-channel bandwidth in WSN
19.2kbps in MICA2, 250kbps in MICAz/Telos The bandwidth requirement is increasing
Support audio/video streams (assisted living, …)
Multi-channel design needed
Hardware appearing Multi-channel support in MICAz/Telos More frequencies available in the future
Collision-based: B-MAC Scheduling-based: TRAMA Hybrid: Z-MAC
Software still lags behind
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State of the Art: Multi-Channel MAC in MANET
① Require more powerful hardware/multiple transceivers Listen to multiple channels simultaneously
[Nasipuri 1999], [Wu 2000], [Nasipuri 2000], [Caccaco 2002]
② Frequent Use of RTS/CTS Controls For frequency negotiation Due to using 802.11
Examples: [Jain 2001], [Tzamaloukas 2001], [Fitzek 2003], [Li 2003], [Bahl 2004], [So 2004], [Adya 2004], [Raniwala 2005]
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Basic Problems for WSN
Don’t use multiple transceivers Cost Form factor
Packet Size 30 bytes versus 512 bytes (or larger) in
MANET RTS/CTS
Costly overhead
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RTS/CTS Overhead Analysis
MMAC: RTS/CTS frequency
negotiation 802.11 for data
communication
RTS/CTS are too heavyweight for WSN: Mainly due to small packet size: 30~50 bytes in WSN vs.
512+ bytes in MANET From 802.11: RTS-CTS-DATA-ACK From frequency negotiation: case study with MMAC
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Contributions A new multi-frequency MAC, specially
designed for WSN; Single half-duplex radio transceiver; Small packets sizes;
Developed four frequency assignment schemes
Supports various tradeoffs Toggle transmission and toggle snooping
techniques for media access control; An optimal non-uniform backoff algorithm,
and a lightweight approximation;
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Frequency Assignment
F1
F2
F3
F4
F5F6
F7
F8 Reception Frequency
Complications• Not enough frequencies• Broadcast
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Frequency Assignment
When #frequencies >= #nodes within two
hops
When #frequencies < #nodes within two
hopsExclusive Frequency
AssignmentImplicit-Consensus Even Selection Eavesdropping
Both guarantee that nodes within two hops get different frequencies
The left scheme needs smaller #frequencies
The right one has less communication overhead
Balance available frequencies within two hops
The left scheme has fewer potential conflicts
The right one has less communication overhead
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Media Access Design
F1
F2
F3
F4
F5F6
F7
F8Issues:• Packet to Broadcast• Receive Broadcast• Send Unicast• Receive Unicast• No sending/no receiving
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Media Access Design Different frequencies for unicast reception The same frequency for broadcast reception Time is divided into slots, each of which consists
of a broadcast contention period and a transmission period.
Tbc Ttran Tbc Ttran… ...
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Media Access Design
Case 1: When a node has no packet to transmit
Receive BC (f0)
Snoop (f0) Snoop (fself)
Snoop (f0) Snoop (fself)
Receive UNI (fself)
Signal(f0)Snoop (f0)
Signal(fself)
Tbc Ttran
(a)
(b)
(c)
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Media Access Design
Back off (f0) Receive BC (f0)
Back off (f0) Send broadcast packet (f0)
Signal(f0)
Tbc Ttran
(a)
(b)
Case 2: When a node has a broadcast packet to transmit
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Media Access Design
Receive BC (f0)
Tbc Ttran
(a) Snoop (f0) Signal(f0)
Snoop (f0) Back off (fself,fdest) Receive UNI (fself) Signal(fself)
Snoop (f0) Back off (fself,fdest) Snoop(fself) Receive UNI (fself) Signal(fdest) Signal(fself)
Snoop (f0) Back off (fself,fdest) Toggle send unicast packet(fdest)
Snoop (f0) Back off (fself,fdest) Snoop(fself)Signal(fdest)
(b)
(c)
(d)
(e)
Case 3: When a node has a unicast packet to transmit
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Toggle Snooping During “ “, toggle snooping is usedback off (fself,fdest)
fself
fdest
TTS
fself
fdest
fself
fdest
fself
fdest
fself
fdest
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Toggle Transmission
…….
PHY Protocol Data UnitPreamble
Use fselfUse fdest
TTT
When a node has unicast packet to send Transmits a preamble
so that no node sends to me so that no node sends to destinationdestf
selff
TTS=2TTT We let
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Simulation ConfigurationComponents SettingSimulator GloMoSimTerrain (200m X 200m) SquareNode Number 289 (17x17)Node Placement Uniform Payload Size 32 BytesApplication Many-to-Many/Gossip CBR StreamsRouting Layer GFMAC Layer CSMA/MMSNRadio Layer RADIO-ACCNOISERadio Bandwidth 250KbpsRadio Range 20m~45mConfidence Intervals The 90% confidence intervals are shown in each figure
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Performance with Different #Physical Frequencies- With Light Load
① Performance when delivery ratio > 93%② Scalable performance improvement③ Overhead observed when #frequency is small④ More scalable performance with Gossip than many-to-
many traffic
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Performance with Different #Physical Frequencies– With Higher Load
① When load is heavy, CSMA has 77% delivery ratio, while MMSN performs much better
② MMSN needs less channels to beat CSMA, when the load is heavier
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Performance with Different System Load
Observation:CSMA has a sharp decrease of packet delivery ratio, while MMSN does not.
Reason:The non-uniform backoff in time-slotted MMSN is tolerant to system load variation, while the uniform backoff in CSMA is not.
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Conclusions First multi-frequency MAC, specially designed
for WSN, where single-transceiver devices are used
Explore tradeoffs in frequency assignment Design toggle transmission and toggle snooping Theoretical analysis of an non-uniform back-off
algorithm MMSN demonstrated scalable performance in
simulation
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The End!
Thanks to anonymous reviewers for their valuable comments!
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Performance with Different Node Densities
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Backup Slides: Optimal Non-Uniform Backoff
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Even Selection Frequency Assignment Beacon (multiple times) to collect nodes’ IDs within
two hops
Frequency decision is made sequentially in the increasing order of nodes’ IDs
When making a decision, randomly choose one of the least chosen frequencies (once no unique ones left)
Notify neighbors of decision
NOTE: Frequency assignment happens once (or a few times)
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Back Off Period - Slotted
Backoff into a slot
Transmit at end of a slot
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Non-Uniform Backoff: Motivation & an Optimal Solution
Uniform backoff
Non-uniform backoff
Let 34 slices of length TTS;68 nodes compete for the channel --- a timer fires
An optimal distribution is presented in the paper Uses recursive computation Distribution depends on node density
A simple approximation is needed
TPacketTransmissionTTS …...
BackoffTtran
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Non-uniform Backoff: A Simple Approximation
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