Mmsn multi frequency media access control for wireless sensor networks
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MMSN: Multi-Frequency Media Access Control for Wireless Sensor Networks. Cheoleun Moon Computer Science Div. at KAIST. Contents. Motivation Overhead Analysis New Protocol Framework Frequency Assignment Media Access Design Performance Evaluation Conclusions. Self-organize.

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

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

Cheoleun Moon

Computer Science Div. at KAIST


Contents

  • Motivation

  • Overhead Analysis

  • New Protocol Framework

    • Frequency Assignment

    • Media Access Design

  • Performance Evaluation

  • Conclusions


Self-organize

Ad-hoc Wireless Sensor Networks

  • Sensors & Actuators

  • Limited CPU and memorys

  • Limited radio bandwidth


Multi-channel design needed

Hardware appearing

Software still lags behind

  • Multi-channel support in MICAz/Telos

  • More frequencies available in the future

  • Collision-based: B-MAC

  • Scheduling-based: TRAMA

  • Hybrid: Z-MAC

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 MAC in MANET

  • Require more powerful hardware/multiple transceivers

    • Listen to multiple channels simultaneously

  • Frequent Use of RTS/CTS Controls

    • For frequency negotiation

    • Due to using 802.11


Basic Problems for WSN

  • Don’t use multiple transceivers

    • Energy

    • Cost

  • Packet Size

    • 30 bytes versus 512 bytes in MANET

  • RTS/CTS

    • Costly overhead


RTS/CTS Overhead Analysis

  • 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

  • MMAC

    • RTS/CTS frequency negotiation

    • 802.11 for data communication


Contributions

  • First multi-frequency MAC, specially designed for WSN

  • Developed four frequency assignment schemes

    • Supports various tradeoffs

  • New toggle transmission and toggle snooping for media access control


F8

F7

F6

F5

F1

F4

F2

F3

Frequency Assignment

Complications

- Not enough frequencies

- Broadcast

Reception Frequency


Frequency Assignment Schemes


...

T

T

T

T

c

b

tran

b

c

tran

Media Access Design (1/4)

  • 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


Media Access Design (2/4)

  • Case 1

    • When a node has no packet to transmit


Media Access Design (3/4)

  • Case 2

    • When a node has a broadcast packet to transmit


Media Access Design (4/4)

  • Case 3

    • When a node has a unicast packet to transmit


Toggle Snooping

  • During “back off (fself, fdest)”, toggle snooping is used


Toggle Transmission

  • When a node has unicast packet to send transmits a preamble

    • fself so that no node sends to me

    • fdestso that no node sends to destination


Simulation Configuration


Performance Metrics

  • Aggregate MAC throughput

    • Total amount of data successfully delivered in MAC per unit time

  • Packet delivery ratio

    • (Total # of data packets delivered by MAC layer)

      (Total # of data packet the network layer requests MAC)

  • Channel access delay

    • Delay data packet from the network layer waits for the channel

  • Energy consumption


Performance with Different #Physical Frequencies – With Light Load

  • Performance when delivery ratio > 93%

  • Scalable performance improvement

  • Overhead observed when #frequency is small

  • More scalable performance with Gossip than many-to-many traffic


Performance with Different # Physical Frequencies – With Higher Load

  • When load is heavy, CSMA has 77% delivery ratio, while MMSN performs much better

  • MMSN needs less channels to beat CSMA, when the load is heavier


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.


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

    • MMSN demonstrated scalable performance in simulation


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