1 Crowded Spectrum in Wireless Sensor Networks Gang Zhou, John A. Stankovic, Sang H. Son Department...

1

Crowded Spectrum in Wireless Sensor

NetworksGang Zhou, John A. Stankovic, Sang H. Son

Department of Computer Science

University of Virginia

May, 2006

2/16University of Virginia

Spectrum Crisis – Single Network

AA…

Find objects;The position is (x,y);Persons with guns;

What are they talking about? (Audio)What are they doing? (Video)

Need Higher Throughput!


Spectrum Crisis – Co-existing

Health Care WSN

Security WSN

Other Devices

Co-existing WSNs & Electric Appliances

Need Frequency Management


Outline

The Spectrum Crisis Initial solutions in three dimensions

Single Network Throughput Cooperative Networks Non-cooperative Networks and Electric Appliances

Open Challenges Summary


Single Network Throughput

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


State of the Art: Multi-Channel MAC in MANET① 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]


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


RTS/CTS Overhead Analysis [Zhou INFOCOM’06]

MMAC: RTS/CTS frequency

negotiation 802.11 for data

communication

RTS/CTS Controls 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


Design Consideration - Frequency Assignment

F1

F2

F3

F4

F5

F6

F7

F8 Reception Frequency

Complications• Not enough frequencies• Broadcast


Design Consideration - Media Access

F1

F2

F3

F4

F5

F6

F7

F8Issues:• Packet to Broadcast• Receive Broadcast• Send Unicast• Receive Unicast• No sending/no receiving

See [Zhou,INFOCOM’06] for our solution


Co-existing & Cooperative Networks The Challenges:

QoS Control Different priorities for different networks, different

bandwidths Map to frequency decision

Space-Dimension Flexibility Frequency decision depends on node density & network

density Time-Dimension Flexibility

Dynamic frequency adjustment

See [Zhou, EmNets’06] for our solution


Non-cooperative Networks and Devices IEEE Standards in 2.4GHz ISM Band

2.4 GHz Electronic Devices & Electric Appliances

802.11 (1997)

78 channels (1 MHz Distance)

802.11 b


802.15.4


802.15.1 (Bluetooth)79 channels

(1 MHz Distance)


When MICAz operates on 2.45 GHz, 46%~81% PRR When MICAz operates on 2.42 GHz, PRR not impacted by presenter

Measurement with Spectrum Analyzer


Deal With the Crowded Spectrum New challenges:

Interference from a different radio Measurement & metrics

Interference from electric appliances Measurement & metrics

Incorporate these into: Static frequency assignment Dynamic frequency adjustment Media access


More Open Challenges

What is/are the best place/places to provide spectrum management in WSN communication stack?

More unlicensed frequencies from the FCC? Tradeoff between #channels and bandwidth:

static/dynamic? More sophisticated radio hardware? Take advantage of partially-overlapping channels? A service between MAC and PHY, supporting

existing single-channel minded MACs?


Summary

Present a vision of crowded WSNs & the spectrum crisis

Initial efforts in three complementary dimensions Single WSN Cooperative WSNs Non-cooperative WSNs


Backup Slides


Frequency Assignment

When #frequencies >= #nodes within two hops

When #frequencies < #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

19University of Virginia

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… ...


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)


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


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


Toggle Snooping

During “ “, toggle snooping is usedback off (fself,fdest)

fself

fdest

TTS

fself

fdest

fself

fdest

fself

fdest

fself

fdest


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 compete for the same channeldestfselff

TTS=2TTT We let


Co-existing & Cooperative Networks The Challenges:

QoS Control

Space-Dimension Flexibility Node density & network density

Time-Dimension Flexibility More dynamics

spectrumfrequency available ofpercent gets Enforce1

ii

Ki

inet


Co-existing & Cooperative Networks The Solutions:

Static frequency assignment Collect (ID, gID, ) from (two-hop) neighbors Chained frequency decision: (increasing gID & ID)

The candidate frequency range

Randomly choose one of the least chosen frequencies from the range

Dynamic frequency adjustment Reassign nodes from crowded frequencies to light ones Avoid pushing around “hot potatoes”

iKi

i N

1

i where

],[ range The ii EfreSfre

1 Crowded Spectrum in Wireless Sensor Networks Gang Zhou, John A. Stankovic, Sang H. Son Department...

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