Wireless Ad Hoc/Sensor Networks
Ten-Hwang Lai
Ohio State University
Outline
Wireless LANs Ad Hoc Networks IEEE 802.11 Bluetooth Berkeley Motes Smart Dust
Wireless LANs
IEEE 802.11 Bluetooth HiperLan (Europe)
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
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
802.11 BSS
Basic Service Set (BSS) --- a basic LAN Infrastructure BSS Independent BSS (Ad Hoc LAN)
Access point
802.11 ESS
Extended Service Set (ESS)
Distributed System
Bluetooth Piconet & Scatternet
Master
Slaves
Master
Slaves
Master
Slaves
M
S
Piconet
Scatternet
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
Why do we need MAC?
Bluetooth or 802.11?
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
Ad Hoc Networking
BT Scatternet --- multihop? 802.11 --- single hop? Master
Slaves
Master
Slaves
M
S
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.
A Sensor Node
Processor
Sensor Actuator NetworkInterface
Memory(Application)
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
Berkeley DOT Mote
Atmel AVR 8535– 4MHz– 8KB of Memory– 0.5KB of RAM
Low power radio Power consumption
– Active 5mA– Standby 5μA
Tightly-Coupled Sensor Array
Artificial Retina
Smart Clothing & Wearable Computing
Smart Underwear Smart Eyeglasses Smart Shoes …
Berkeley Smart Dust
bi-directional communications
sensor: acceleration and ambient light
11.7 mm3 total circumscribed volume
4.8 mm3 total displaced volume
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
What need to be done?
Interdisciplinary
A few sample problems
Sensor Deployment
How to deploy sensors over a field?– Planned deployment– Random deployment + improvement
What are desired properties of a “good” deployment?
Coverage, Connectivity, Density
Every point is covered by a sensor The network is connected No area is too dense
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
Connected Sensor Coverage
Mobihoc’03 Given a sensor network Given a query Find a smallest connected subset of sensors
that can serve the query.
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.
Reliable Transport
Mobihoc’03 What is reliable transport in sensor
networks?
Data center
event
Energy Efficiency
Done at every level from physical to application.
Energy-efficient routing. Energy-efficient MAC. Energy-efficient everything.
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
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