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

Cheoleun MoonComputer Science Div. at KAIST

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Contents Motivation Overhead Analysis New Protocol Framework

Frequency Assignment Media Access Design

Performance Evaluation Conclusions

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Ad-hoc Wireless Sensor Networks

Sensors & Actuators Limited CPU and mem

orys Limited radio bandwidt

h

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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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

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Basic Problems for WSN Don’t use multiple transceivers

Energy Cost

Packet Size 30 bytes versus 512 bytes 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: 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

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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

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Frequency Assignment

Complications - Not enough frequencies - BroadcastF1

F2F3

F4

F5F6

F7

F8Reception Frequency

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Frequency Assignment Schemes

When #frequencies >= #nodes within two

hops

When #frequencies < #nodes within two

hopsExclusive 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 (1/4) Different frequencies for unicast reception The same frequency for broadcast reception Time is divided into slots, each of which consis

ts of a broadcast contention period and a transmission period

Tbc Ttran Tbc Ttran… ...

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Media Access Design (2/4) 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 (3/4) Case 2

When a node has a broadcast packet to transmit

Back off (f0) Receive BC (f0)

Back off (f0) Send broadcast packet (f0)

Signal(f0)

Tbc Ttran

(a)

(b)

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Media Access Design (4/4) Case 3

When a node has a unicast packet to transmit

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)

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

fself

fdest

TTS

fself

fdest

fself

fdest

fself

fdest

fself

fdest

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Toggle Transmission When a node has unicast packet to send transmits a

preamble fself so that no node sends to me fdest so that no node sends to destination

…….

PHY Protocol Data UnitPreamble

Use fselfUse fdest

TTT

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Simulation ConfigurationComponents 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 20m~45m

Confidence Intervals The 90% confidence intervals are shown in each figure

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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

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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 MMSN demonstrated scalable performance in

simulation