MMSN: Multi-Frequency Media Access Control for Wireless Sensor Networks

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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

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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, )

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State of the Art Multi-Channel MAC in MANET

• Require more powerful hardware/multiple
  transceivers
• Listen to multiple channels simultaneously
• Nasipuri 1999, Wu 2000, Nasipuri 2000,
  Caccaco 2002
• 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

• Dont 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

• RTS/CTS are too heavyweight for WSN
• Mainly due to small packet size 3050 bytes in
  WSN vs. 512 bytes in MANET
• From 802.11 RTS-CTS-DATA-ACK
• From frequency negotiation case study with MMAC

• MMAC
• RTS/CTS frequency negotiation
• 802.11 for data communication

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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
Reception Frequency
F8
F7

• Complications
• Not enough frequencies
• Broadcast

F6
F5
F1
F4
F2
F3
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Frequency Assignment
When frequencies gt nodes within two hops When frequencies lt nodes within two hops
Exclusive Frequency Assignment Implicit-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

• Issues
• Packet to Broadcast
• Receive Broadcast
• Send Unicast
• Receive Unicast
• No sending/no receiving

F8
F7
F6
F5
F1
F4
F2
F3
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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.

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Media Access Design
Case 1 When a node has no packet to transmit
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Media Access Design
Case 2 When a node has a broadcast packet to
transmit
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Media Access Design
Case 3 When a node has a unicast packet to
transmit
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Toggle Snooping

• During , toggle
  snooping is used

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Toggle Transmission

• When a node has unicast packet to send
• Transmits a preamble
• so that no node sends to me
• so that no node sends to destination

• We let

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Simulation Configuration
Components Setting
Simulator GloMoSim
Terrain (200m X 200m) Square
Node Number 289 (17x17)
Node Placement Uniform
Payload Size 32 Bytes
Application Many-to-Many/Gossip CBR Streams
Routing Layer GF
MAC Layer CSMA/MMSN
Radio Layer RADIO-ACCNOISE
Radio Bandwidth 250Kbps
Radio Range 20m45m
Confidence 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 gt 93
2. Scalable performance improvement
3. Overhead observed when frequency is small
4. 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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Thanks to anonymous reviewers for their valuable
comments!
The End!
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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

• An optimal distribution is presented in the paper
• Uses recursive computation
• Distribution depends on node density
• A simple approximation is needed

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Non-uniform Backoff A Simple Approximation