Location Estimation Media, Location Estimation Media, Algorithms - - PowerPoint PPT Presentation

06/04/2005 1

Location Estimation Media, Location Estimation Media, Algorithms and Systems, Algorithms and Systems, Location Technologies Location Technologies

Gábor Nyíri

06/04/2005 2

Agenda Agenda

Introduction Taxonomy of Location Location Estimation Media Location Estimation Algorithms Location Estimation Systems Summary

06/04/2005 3

Introduction Introduction

Wired – wireless – Location is constantly changing – „A key distinguishing feature of mobile computing is the ability to detect, react to and make use of changing environmental conditions to provide users with a better seamless and intuitive experience” Revenue: 2000: $1 billion

2006: over $40 billion

Location-based application (LBA) – Applications capable of finding the geographical location of an

• bject and providing services based on this location information

– NOT only in mobile communication systems – Examples:

• E-911
• Road assistance
• Geotargeting adverisement
• Fleet tracking …

06/04/2005 4

LBA LBA -

• Examples

Examples

06/04/2005 5

General framework to support LBA’s General framework to support LBA’s

Location Sensor Infrastructure Location- Based Applications Location Format Transformation Location Estimation Algorithm

Measurement Estimation Presentation

Location Estimation System

Requirements, Preferences

06/04/2005 6

Taxonomy of Location Taxonomy of Location

Physical and Symbolic Location – Physical location:

• uniquely identifies a point on a 2D map
• f the Earth eg.:degree/min/sec(DMS)
• (in 3D also altitude is required)
• Helsinki, Latitude: 60°10´N Longitude 25°0´E

– Symbolic location:

• In the way of natural-language
• Like: at home, in the bed, on the train…
• Not always needed the precise physical location eg.:home

security sys.

• Coarse

– Can be mapped to each other with help from a location information database

• Resolution: in a room ~ 10m

06/04/2005 7

Taxonomy of Location Taxonomy of Location

Absolute and Relative Location

– Absolute location

• uses a shared reference grid like DMS

– Relative Location

• Depends on its own frame of reference

– With the help of relative location absolute location can be computed

06/04/2005 8

Location Estimation Location Estimation Media Media

Radiofrequency: – widely used: cellular phone systems, satellite communication systems, WLAN systems – Most estimation algorithms depends on the existence of a line of sight – Accuracy:

• Dominant source of error:

Multipath propagation: line of sight (LOS) + NLOS – Reflection & Diffraction & Scattering

• Multipath fading

– Rapid variation in signal strength – Received signal strenght (RSS)

• Delay spread

– Signal on NLOS paths are delayed – act as noise – Mainly outdoors

06/04/2005 9

Location Estimation Location Estimation Media Media

• Infrared (IR)

– Interference with ambient light source (incandescent sources, fluorescent lighting, sunlight) – Mainly used for object detection, sensing and tracking – Every object emit unique IR radiation -> fingerprint database

• Advantage: no transmitter required
• Disadvantage: very sensitive IR receivers are required

(expensive) distinguishing same type of objects?

• Not suitable for general-purpose location estimation

services

– With limited transmission range it is cheap and can be integrated to large-scale sensor networks

06/04/2005 10

Location Estimation Location Estimation Media Media

Ultrasound

– 20-100kHz – Speed of sound in air: v=331+0.6*T (at 20C 343m/s) – More accurate than systems based on RF and IR – Measurement errors: like with RF + speed changes (humidity & temp) – Sensitive to in-band noise – Inexpensive – piezoelectric ceramic

06/04/2005 11

Location Estimation Location Estimation Algorithms Algorithms

• Triangulation

– Location is estimated relative to some known framework – Lateration & angulation – Time of Arrival (TOA):

• At least 3 base station measures the time of arrival
• Distance can be computed, target at the intersection of

circles

– Time Difference of Arrival (TDOA):

• The same but with hyperbolas
• Two pair of measurement
• Eliminates the clock offset of

the estimated object – Angle of Arrival (AOA):

• Directional antennas or antenna arrays are required

06/04/2005 12

Location Estimation Algorithms Location Estimation Algorithms

• Scene analysis

– First collects features/fingerprints not directly related to geometric information – Than matching with the closest a priori location fingerprints – Eg:

• smart floor: pressure sensors in the floor (Georgia IT)
• 3D cameras (Easy Living by Microsoft)

– RF-based scene analysis?!

• No need for special infrastructure, wireless infrastructure is

already deployed indoors (WLAN, bluetooth)

• Two main characteristics:

– Signal strength (SS), Signal-to-noise ratio (SNR) – Cannot be used to derive accurate location information – Rather match SS entries in a database

06/04/2005 13

Location Estimation Algorithms Location Estimation Algorithms

Scene analysis – 2

– General Framework of scene analysis:

• Profiling

– Off line: The area is devided into small pieces, containing multiple observation points – Sampling of RF parameters are collected -> stored in a database after postprocessing – This procedure has to be repeated:

• After the building layout is changed
• Samples has to be collected at different times of the day

– Increasing the number of observation points leads to larger database, and after a threshold no much influence

• Matching

– Real- time measaurement is obtained – Comparing the measurements with the entries of the database

• Estimation

– Location estimation based on the match(es) – Kind of averaging

06/04/2005 14

Location Estimation Systems Location Estimation Systems

Indoor Location Estimation Systems

– RADAR (Microsoft Research)

• WLAN based scene analysis
• 3APs, floor with 50rooms
• SS & SNR measured by APs
• SS is orientation dependent (multiple measurements are collected)

– BAT (AT&T)

• Central RF basestation + matrix of receivers
• Measured objects equipped with RF receiver and ultrasonic

transmitter + unique ID

• Base station broadcasts ID, in respose an immediate ultrasonic

pulse from the owner of the ID

• Also the neighbours can measure their distance from the measured
• bject

06/04/2005 15

Location Estimation Systems Location Estimation Systems

Indoor Location Estimation Systems – 2

– Cricket (MIT)

• Privacy! = Location estimation on user side
• RF + ultasonic transmitters

– Active Badge

• Infrared based
• One IR sensor per room
• Employees are equipped with a badge that sends out IR

beacons with a unique ID every 15 secs

Positioning System Positioning Method Accuracy Precision Deployment / Scale Limitations E911 (Cellular Networks: GSM, etc.) Base station triangulation 50-300m Density of cellular infrastructure Only where cell coverage exists GPS RF time-of-flight lateration 1-5m 24 satellites worldwide Not indoors Cricket (MIT) ultrasound; proximity lateration RF and ultrasound 4ft 1 beacon per 16 grid required; receiver computation Ceiling beacon ultrasound; proximity lateration RADAR (Microsoft Research) Cell-id (802.11 RF triangulation) & scene analysis 3-4m 3+ bases per floor RADAR (Microsoft Research) SmartLOCUS (HP Labs) synchronized RF and ultrasound differential time

• f

flight 2-15**cm** Nodes placed every 2-15 m Active Bats (AT&T Cambridge) Cell-id (Ultrasound time-of-flight lateration) 9cm 1 base per 10 sq m Ceiling sensor grid required UbiTags (UbiSense) Time-of-flight + angle-of-arrival 15cm 2-4 sensors per cell (100-1000m); 1 UbiTag per

• bject

06/04/2005 17

Location Estimation Systems Location Estimation Systems

Outdoor Location Estimation Systems

– GPS:

• 24 satellites, 5 monitor stations, 3 ground antennas, master

control station

• 2 levels: precise positioning service(PPS) and standard

positioning service (SPS)

• PPS is originally for military purposes from 1st May 2000 it is

available for civil use

• Satellites are broadcasting their positions
• 4 satellites are required at the same time for 3D positioning
• Differential GPS accuracy can be higher ~1m
• 20mm is also achievable ~ $15.000
• Assisted GPS: reduces search time from minutes to seconds

special HW/SW

06/04/2005 18

Location Estimation Systems Location Estimation Systems

Outdoor Location Estimation Systems

– Cellular-based systems:

• Since 1996 in the US operators must provide E-911 services
• This information can be used for a lot more purposes
• Cell location is known during a call – Cell ID
• Between calls location information is updated in the network
• If the cell is known, location can be measured (TOA,TDOA)

– This can require add-ons, more expensive than cell id determination

• Time synchronization nedded among basestations

06/04/2005 19

Location Estimation Systems Location Estimation Systems

Outdoor Location Estimation Systems

– Cellular-based systems – accuracy / errors:

• CDMA: near-far effect = strong signals from nearby mobile

stations vs. weak signals from remote mobile hosts solution:power control, but during localization communication with at least 3 basestations AFLT (Advanced Forward Link Trilateration) 50-200m EFLT (Enchanced FLT) 250-350m

• CDMA/TDMA: dilution of precision (DOP)

relative geometry of basestations eg: along a highway

• TDMA:

location accuracy is >500m EOTD (Enhanced Observed TDOA): 50-300m

06/04/2005 20

Location Estimation Systems Location Estimation Systems

Outdoor Location Estimation Systems

– Cellular-based systems – Hybrid systems:

• AFLT/AGPS

CDMA

• EOTD/AGPS

TDMA

• Cell ID/AGPS

All

06/04/2005 21

Location Format Transformation Location Format Transformation

OpenGIS(geographic information system) Consortium(OGC)

– Goal:

• Provide open interface specifications

– Consists of:

• GIS software vendors
• Databese vendors
• Integrators
• Application providers

06/04/2005 22

Summary Summary

Technology Networks Computation Handset impact Accuracy Cell ID All central none Depends on the size of the cell 100m-3km TDOA All central none 300-500m AOA All central none 300-500m EFLT CDMA central none 250-350m AFLT CDMA central yes 50-200m EOTD GSM central yes 50-200m GPS/AGPS All in user device yes 5-30m