Location and Position MeasurementsPresentation forLicentiate course in measurement science and technology

Marion Hermersdorf

28.03.2007

2 2007

Motivation (1/2)

Smart Environments

Internet of Things

Logistics

Person Tracking

Asset Tracking

Animal/Pet Tracking

Context Awareness

Sensor Networks

Photo Meta Data

Safety

Surveillance & Security

Games

Location Based Services

Location

E911

3 2007

Motivation (2/2)

4 2007

Table of Content

Introduction

Positioning Methods

Positioning Technologies

Special focus onRepresentation of positionGPSWLAN based positioning

5 2007

Overview

IntroductionPosition verses Location

Mobile Positioning

Description of Position

Position Accuracy

Challenges

Positioning Methods

Positioning Technologies

6 2007

Position verses Location

The term position is used to express the capability of locating the physical position of an object in a pre-determined space

e.g. indoor positionGPS location

7 2007

Mobile Positioning

Determining the position of a person or object that is changing position.

Use of devices that are positioned at know locations.

8 2007

Description of PositionAbsolute locations share a common, global, coordinate system, e.g. longitude/latitude.

Relative locations may have a different frame of reference, e.g. in buildings.

Symbolic locations are names. They are more significant to a human than a pair of numbers, e.g. “home”, “work”.

9 2007

Absolute Position (1/3)

How to describe a certain location on earth?

The earth is not round !

Use of geoid to describe Earth.

Ellipsoid = approximation to geoid.

10 2007

Absolute Position (2/3)

How convert an ellipsoid into a map?

Geodetic datum (=map system) defines how a coordinate system is seated over the ellipsoid.

Australian National

International 1924

International 1924

WGS84

Ellipsoid

-120-96-87Western Europe

EUR-A

149-48-134AustraliaAUG

-120-95-87Finland, Norway

EUR-C (KKJ)

000AllWGS84

dZ [m]dY [m]dX [m]Used byDatum

11 2007

Absolute Position (3/3)

How to describe a location on the map?

Coordinate system.

Coordinate systems:

Longitude/latitude/heightUniversal Transverse Mercator (UTM)ECEF X, Y, ZWorld Geographic Reference System

(GEOREF)Military Grid Reference System (MGRS)

Position data formats (mostly WGS84 based):

Geo (simple, long./lat.)GPX (GPS Exchange Format)KML (Google Earth, long./lat.)

12 2007

Position AccuracyEuclidean distance between the estimated location and true location

Circular error probability or circular error

probable (CEP) is the radius of a

circle centered at the true position.

Cumulative distribution function (CDF) is often used in visualizing the positioning error.

Radius of the 50% (R50), 67% (R67) and 95% (R95) are commonly used.

Root mean square error

13 2007

Challenges

It has to work everywhere and anytime

E.g. in buildings, in dense cities, underground, outsides

People spend 80-90% of their time indoors

70% of cellular calls and 80% of data connections originate from

indoors. (Source Strategy Analytics)

It has to provide appropriate accuracy

E.g. “ Where are my keys?” => about 10cm, indoors“ Where is the digital oscilloscope?” => a few meters, indoors“ Where is the nearest pizza place?” => about 10 meters, outdoors

Privacy and usability

14 2007

Overview

Introduction

Positioning MethodsMobile verses Network Base Positioning

Radio Signal Propagation

Signal Strength Measurement

Signal Signature

Time Measurement

Angle of Arrival Measurement

Proximity

Positioning Technologies

15 2007

Mobile verses Network Base Positioning

Mobile Based Positioning

The mobile device is measuring and calculating the position.Advantages: - privacy

- availability (no connection to network/service) required.Disadvantage: - measurements consume power

Mobile Assisted Positioning

The mobile device is measuring and send the data to the location server, which calculates the position.

Network Based Positioning

The network device is measuring and calculating the position.Advantages: - low power consumption on mobile device.Disadvantage: - Privacy control lost.

- Connection to location server needed.

16 2007

Radio Signal Propagation

17 2007

Signal Strength Measurement

Signal strength is proportional to the distance

RSS: received signal strengthPt: transmitted powerα: distance-power gradient (constant in open spaces)d: distanceX: shadow fading

Line-of-sight required !

Triangulation and the knowledge of the

signal sources provides location.

18 2007

Signal Signature

Methods:

Least mean square (LMS) method

K-nearest neighbor

Fuzzy logic

Neural systems

Applied:

GSM positioning

WLAN positioning

Reference fingerprint (training) data collection

19 2007

Time Measurement

Time of arrival - ToA

The time needed for the signal to travel from the source to the receiver. The time is proportional to the distance.Triangulation of three signals provide the location.

Round-trip time or time reference.

Time difference of arrival - TDoA

The time difference of a signal received at a know location (base station) and at a unknown

location (mobile device) is measured.

20 2007

Angle of Arrival Measurement

Direction/angle of arrival – DoA or AoA

This method uses multiple antennas at a base station to determine the incident angle of an arriving signal.

21 2007

Proximity

Detection of proximity to a devices at a certain know location.

E.g.: RF radio (CellID, Bluetooth, RFID)light barriercomputer login

22 2007

Overview

Introduction

Positioning Methods

Positioning TechnologiesGPSCellular NetworkWireless LANUltra Wide BandWiMaxDigital TVShort Range RadiosUltrasonicInfraredCamera AssistedSensor AssistedHybrid Solution

23 2007

Global Positioning System – GPS (1/4)

Position calculation is based on time measurements.

24 satellites ensure a visibility of at least 4 satellites.

Fully operational in 1994.

Line of sight required (only outdoors).

Position accuracy of up to 3 meters (commonly 5-20m).

Differential GPS (D-GPS) is an enhancement that uses a network of fixed ground based reference stations.

Assisted GPS (A-GPS) uses cellular networks (like GSM/UTMS) to provide position information indoors and in urban canyons and give a fast position fix.

GLONASS (Russian system)Galileo (test phase 2008)Beidou (Chinese system)

24 2007

Global Positioning System – GPS (2/4)

Pseudorandom code (C/A)

Satellite unique code.1,023 bit long pseudo-random code. Repeated every millisecond.Is used to calculate the time of flight on

the GPS receiver.

Navigation message

Contains ephemeris and almanac data.Almanac data provides coarse information

about location and health of all satellites and current time.

Ephemeris data provides detailed (actual/corrected) location information of satellite for next 6h.

Takes several minutes to receive data (cold start).

time of flight + satellite location = position

25 2007

Global Positioning System – GPS (3/4)

Distance information of two satellites => position on the edge of a circle

Distance information of three satellites => position at two points

=> Distance information of four satellites => distinct position available

26 2007

Global Positioning System – GPS (4/4)

Solutions for indoors

Pseudolites (centimeter accuracy)

Increased sensitivity of receiver.

A-GPS

27 2007

Cellular Based Positioning

Cell ID

Signal strength or proximity.Cell size 100m to 20km.Radio maps for indoors => accuracy of up to 5m reported.Advantage: cheap and existing.

GSM Network

ToA or TDoA.Location measurement unit (LMU) required in base station.

CDMA Network

Advanced Forward Link Trilateration (A-FLT) similar to TDoA.Location measurement unit (LMU) required in base station.

E-OTD: Enhanced observed time difference (similar to TDoA)A-FLT: Advanced Forward Link Trilateration

28 2007

Wireless LAN Positioning (1/4)

Principle

Measurement of distance to WLAN access points.

Triangulation.Information of location of WLAN access

points required.

Advantages

Works also indoors.No additional infrastructure/technologies

required.

Disadvantages

Knowledge of location of WLAN access points required (work effort).

Accuracy normally lower than GPS.Only works in dense urban areas.

29 2007

Wireless LAN Positioning (2/4)

Real-time indoor positioning

Asset and people tracking inclosed and defined environment(1-3m accuracy)

Training data needed -> no largescale implementation possible

Offered by Ekahau, Cisco,AeroScout and others.

Lacks coverage

Large scale indoor positioning

WiFi database

Limited positioningresolution and accuracy

Large scale implementation possible

Lacks accuracy

30 2007

Skyhook map

Wireless LAN Positioning (2/3)

31 2007

Wireless LANPositioning (4/4)

WLAN access points in Helsinki area gathered by

“war-drivers”

32 2007

Ultra Wide Band Positioning

Wide bandwidth (typically > 1 GHz) enables very fine time measurements

ToA/TDoA measurements and trilateration

30 cm accuracy

Line-of-sight (LOS) required.

Discrimination between multipath components.

Proprietary art solutions (e.g. GeoDan)

33 2007

Short Range Radios

Bluetooth

Limited range (5-10m).Highly distributed.Complex and long scan procedure.Very power hungry.

RFID

Very short range (1-3m).Low cost.Low power.

Others

WibreeZigbee

34 2007

Ultrasonic

Cricket System

MIT project (2001-2005).

Beacons on ceiling.

5cm accuracy.

35 2007

Infrared

36 2007

Camera Assisted

Mapping of base stations or sensor nodes

Scene analysis

37 2007

Sensor Assisted

Use of magnetometer, accelerometer, barometer and gyroscope.

Calibration frequently needed (drifting over time).

38 2007

Conclusion

Different use cases require different technologies.

Hybrid solutions are the key.

39 2007

Thank you

for your

attention.