Wireless Ad Hoc/Sensor Networks
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Transcript of Wireless Ad Hoc/Sensor Networks
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Wireless Ad Hoc/Sensor Networks
Ten-Hwang Lai
Ohio State University
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Outline
Wireless LANs Ad Hoc Networks IEEE 802.11 Bluetooth Berkeley Motes Smart Dust
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Wireless LANs
IEEE 802.11 Bluetooth HiperLan (Europe)
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History of IEEE 802.11
802.11 standard first ratified in 1997– 802.3 LAN emulation– 1 & 2 Mbps in the 2.4 GHz band
Two high rate PHY’s ratified in 1999– 802.11a: 6 to 54 Mbps in the 5 GHz band– 802.11b: 5.5 and 11 Mbps in the 2.4 GHz band
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The Beat Goes On
802.11c: support for 802.11 frames 802.11d: new support for 802.11 frames 802.11e: QoS enhancement in MAC 802.11f: Inter Access Point Protocol 802.11g: 2.4 GHz extension to 22 Mbps 802.11h: channel selection and power control 802.11i: security enhancement in MAC 802.11j: 5 GHz globalization
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802.11 BSS
Basic Service Set (BSS) --- a basic LAN Infrastructure BSS Independent BSS (Ad Hoc LAN)
Access point
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802.11 ESS
Extended Service Set (ESS)
Distributed System
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Bluetooth Piconet & Scatternet
Master
Slaves
Master
Slaves
Master
Slaves
M
S
Piconet
Scatternet
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Comparison of Bluetooth to 802.11b
Bluetooth 802.11b
Bandwidth 1 Mbps 11 Mbps
Range 10 meters 100 meters
Profiles Almost unlimited AP, STA
Current consumption 60mA 300mA
Cable replacement Serial, USB, Audio 802.3
Circuit cost (9/2001) $11.00 $46.00
Ad hoc networking multi-hop single-hop
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Why do we need MAC?
Bluetooth or 802.11?
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Can Bluetooth Compete with 802.11?
IEEE 802.11 already has been widely accepted.
What are Bluetooth’s chances of success stacking against 802.11?
Answer: ? 802.11 --- WLANBluetooth-- WPAN
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Ad Hoc Networking
BT Scatternet --- multihop? 802.11 --- single hop? Master
Slaves
Master
Slaves
M
S
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BT Scatternet Formation
Problem: design a protocol that given a set of bluetooth nodes organizes the nodes into a scatternet.
Still an interesting research problem.
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A Sensor Node
Processor
Sensor Actuator NetworkInterface
Memory(Application)
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Berkeley Mote: a sensor device prototype
Atmel ATMEGA103 – 4 Mhz 8-bit CPU– 128KB Instruction
Memory– 4KB RAM
RFM TR1000 radio– 50 kb/s
Network programming
51-pin connector
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Berkeley DOT Mote
Atmel AVR 8535– 4MHz– 8KB of Memory– 0.5KB of RAM
Low power radio Power consumption
– Active 5mA– Standby 5μA
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Tightly-Coupled Sensor Array
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Artificial Retina
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Smart Clothing & Wearable Computing
Smart Underwear Smart Eyeglasses Smart Shoes …
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Berkeley Smart Dust
bi-directional communications
sensor: acceleration and ambient light
11.7 mm3 total circumscribed volume
4.8 mm3 total displaced volume
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Speckled Computing
愛丁堡大學( University of Edinburgh)科學家即將研發出大小跟灰塵差不多的超微型晶片 , 這些晶片可以分散或
噴灑到物體上彼此溝通、傳遞資訊。這種名為斑點運算( speckled computing)的技術可望在三年內成為事實。
將晶片噴到患者的衣物上 , 可監控其心跳、呼吸與體溫。
Source: Silicon Glen R&D Update, April, 2003
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What need to be done?
Interdisciplinary
A few sample problems
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Sensor Deployment
How to deploy sensors over a field?– Planned deployment– Random deployment + improvement
What are desired properties of a “good” deployment?
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Coverage, Connectivity, Density
Every point is covered by a sensor The network is connected No area is too dense
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Unreliable Sensor Grid: Coverage and Connectivity
INFOCOM 2003 Active Dead Be dead with a prob p transmission and sense
range r A necessary and sufficient
condition for the network to remain covered and connected
N nodes
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Connected Sensor Coverage
Mobihoc’03 Given a sensor network Given a query Find a smallest connected subset of sensors
that can serve the query.
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Localization from Mere Connectivity
Mobihoc’03 Find geographic positions of sensors Not using GPS But using only connectivity information of the
net + a few nodes with known positions.
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Reliable Transport
Mobihoc’03 What is reliable transport in sensor
networks?
Data center
event
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Energy Efficiency
Done at every level from physical to application.
Energy-efficient routing. Energy-efficient MAC. Energy-efficient everything.
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S-MAC: an energy-efficient MAC
In IEEE INFOCOM 2002, By Ye, Heidemann, Estrin
IEEE 802.11-like RTS/CTS/Data/Ack Go to sleep on hearing a RTS or CTS