1 crowded spectrum in wireless sensor networks gang zhou, john a. stankovic, sang h. son department...
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1
Crowded Spectrum in Wireless Sensor
NetworksGang Zhou, John A. Stankovic, Sang H. Son
Department of Computer Science
University of Virginia
May, 2006
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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!
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Spectrum Crisis – Co-existing
Health Care WSN
Security WSN
Other Devices
Co-existing WSNs & Electric Appliances
Need Frequency Management
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Outline
The Spectrum Crisis Initial solutions in three dimensions
Single Network Throughput Cooperative Networks Non-cooperative Networks and Electric Appliances
Open Challenges Summary
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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
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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]
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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 [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
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Design Consideration - Frequency Assignment
F1
F2
F3
F4
F5
F6
F7
F8 Reception Frequency
Complications• Not enough frequencies• Broadcast
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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
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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
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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
14 channels (5 MHz Distance)
802.15.4
16 channels (5 MHz Distance)
802.15.1 (Bluetooth)79 channels
(1 MHz Distance)
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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
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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
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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?
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Summary
Present a vision of crowded WSNs & the spectrum crisis
Initial efforts in three complementary dimensions Single WSN Cooperative WSNs Non-cooperative WSNs
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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
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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 compete for the same channeldestfselff
TTS=2TTT We let
25University of Virginia
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
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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”
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