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