Ubiquity & Virtuality

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Nov 30, 2013 (3 years and 10 months ago)

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Agents, Mobility,
Ubiquity & Virtuality

Gregory O’Hare

Department of Computer Science,

University College Dublin











Locating the User



COMP40300 Context
-
Sensitive Service Delivery




Lecture 2











Professor Gregory O’Hare

School of Computer Science & Informatics,

University College Dublin (UCD)

Objectives


Introduce some principles of electronic navigation


Describe state
-
of
-
the
-
art in satellite navigation


Introduce techniques based on cellular telephony


Outlined current developments in Satellite Based
Augmentation Systems



Why the sudden interest?


Location
-
aware services



also called proximity services



Examples include:


personal locator services


asset tracking


Emergency services provision



E
-
911



E112

Exercise
:

Find
some research reports and see what they say regarding market
projections and types
of services required

HIPS & Gulliver’s Genie Objectives


Provide an infrastructure which
supports simultaneous user navigation
of a physical space and it’s
corresponding information space


Deliver contextualised information to
roaming tourists


Provide seamless movement between
the physical & virtual spaces

Localisation Technologies

Satelite based Systems

Global Positioning System (GPS);

Differential GPS (DGPS);

Galilleo
-

European

GLONASS


Russian;

Radio Based Systems

Base Cell Identification;

Base Cell Triangulation based on either Angle of Arrival
(AOA) or Time of Arrival (TOA);

Location Fingerprinting


each location has a unique signal
pattern create database to record these and match;

Hybrid Systems;

Enhanced/Assisted GPS (EGPS)


Ericsson Mobile
Positioning System (MPS).


HIPS : A Handheld Tourist Aid

Tourist Content Delivered
in a Proactive (Push)
Tailored fashion.

The key personalisation &
Contextualisation
parameters are:

Location (Longitude,
Latitude, Orientation)
acquired from a Global
Positioning System (GPS)
device & electronic
compass;

User Preferences
extracted from a user
profile;

Administration Toolkit

Gulliver’s Genie

Gulliver’s Genie

Gulliver’s Genie

WAY GUI

Zoomed In

Zoomed Out

EasiShop

Mobile Agent based

U
-
Commerce

System

Agent Factory

Thinlets

Midp

Bluetooth

EasiShop

Client

Side

EasiShop

Server

Side

Some References


O’Grady, M.J., & O’Hare G.M.P.,
Gullivers’s Genie: Agency,
mobility, Adaptivity,
Computers &
Graphics Journal
, Special Issue on
Pervasive Computing and Ambient
Intelligence


Mobility, Ubiquity
and Wearables Get Together, Vol.
28, No. 5, pp 677
-
689, Elsevier
Science, 2005.
(ISI Impact Factor
0.787), Journal Rank 67th of 93
Computer Science, Software
Engineering.


O’Grady, M.J. & O’Hare, G.M.P.,
Mobile Devices & Intelligent
Agents
-
Towards a New Generation
of Applications and Services,
Special Issue on Intelligent
Embedded Agents,
Journal of
Information Sciences
, Vol 171,
No. 4, pp 335
-
353, Elsevier Press,
2005,
(ISI Impact Factor 3.291),
Journal Rank 6th of 116
Computer Science, Information
Systems,

Some References


O’Grady, M.J., O’Hare, G.M.P. &
Sas, C., Mobile Agents for Mobile
Tourists: A User Evaluation of
Gulliver’s Genie,
Interacting with
Computers Journal
, Vol. 17, No. 4,
May, pp 343
-
366, Elsevier Press,
2005.

(ISI Impact Factor 1.698),
Journal Rank, 7th of 19
Computer Science, Cybernetics.


Keegan, S. O'Hare, G.M.P. &
O'Grady, M.J., EasiShop: Ambient
Intelligence Assists Everyday
Shopping,
Journal of Information
Sciences

, Elsevier Press, 2007,
(ISI Impact Factor 3.291),
Journal Rank 6th of 116
Computer Science, Information
Systems,

Classification


Terrestrial Radio


Satellite


Cellular Network


Hybrid

Terrestrial Radio
-

Techniques


Radio Direction Finding



directional antenna


Tune into radio station with known coordinates


Determine bearing


Repeat with a second station


Construct two lines using appropriate bearing


Intersection indicates position


Hyperbolic Technique


Tune into two stations at known positions


Calculate time difference between signals


Repeat with a second station


Construct hyperbola


Intersection indicates position



Terrestrial Radio
-

Examples


DECCA


1937 in USA


Problems


short range signal


large number of transmitters


expensive to implement and maintain


LORAN
-
C (LOng
-
RAnge Navigation
-
C)


Successor to DECCA


1950 in USA


Deployed worldwide


Civilian use since early 1990


Now operated by North West Europe LORAN
-
C System (NELS)



Satellite
-

History


1950s


Russian space program



Doppler Shift


Measurements of the Doppler Shift in the signals broadcast by a
satellite following a known and well defined orbit could be used to
estimate position


Example: Transit


Navy Navigational Satellite System


5 satellites following low altitude (1100km) polar obits


Decommissioned in 1996 ( due to GPS!)

Satellite
-

GPS


Global Positioning System (GPS)


Navstar GPS


US Department of Defense (DoD)


Military ownership and control


History


Initial tests in 1973 using ground transmitters


First satellites launched in 1978


10 satellites launched by 1989


24 satellites in operation


1995
-

Full operational capacity


Services


Navigation (accuracy variable but 20m is realistic)


Time


GPS
-

Architecture


GPS comprises of three segments



Space Segment



Control Segment



User Segment

GPS
-

Space Segment (I)


GPS Satellites


Space Vehicles (SVs)


24 SVs in constellation


3 spares


Orbit every 12 hours


Altitude of 20,200 km


Space Vehicle Characteristics


2 solar panels


I small rocket


4 types (Block I, II etc)


4 atomic clocks (2 caesium & 2 rubidium)

GPS
-

Space Segment (II)


Constellation structure


6 equally spaced (60 degrees) orbital planes


4 SVs per plane


Each plane inclined at 55 degrees with respect to the equatorial
plane


Objective


Ensure that between 5 and 8 SVs are visible from any point on earth
at any given time

GPS
-

Space Segment (III)

GPS
-

Control Segment (I)


Structure



Originally, 5 monitoring stations


2005


6 additional stations added



Function


Track SVs


relay satellite time and ranging information to master control station
in Colorado



At the master control station


orbit and timing parameters calculated for each SV


information then uploaded to the appropriate SVs


Every satellite can be seen by at least three monitor stations


GPS
-

Control Segment (I)

GPS
-

User Segment


Two groups of users



Military


standard military applications



Civilian


Commercial


Surveying


Vehicle monitoring


Precision agriculture


Recreational


Geocaching

GPS
-

Theory (I)

Trilateration:
a basic geometric principle that allows the
position of an object be determined if its distance from three
objects is known

if distance to one object is known
---

I am on a sphere with
that object is centre.

if distance to a second object is known
----
I am on a circle
that denotes the intersection of the two spheres.

if distance to a third object is known
---
I am on either of two
points where the three spheres intersect.


GPS
-

Theory (II)

But clock on receiver NOT synchronised with those on
the satellites!


So fourth satellite required to eliminate clock bias


4 equation
-

4 unknowns


3D fix (longitude, latitude, altitude), time bias eliminated


Extra satellites can be used to improve calculation


World geodetic System 1984 (WGS84)


If altitude assumed fixed
-

three satellites adequate for a reading
(2D fix)

Note: distance to satellite referred to technically as a pseudorange

GPS
-

Signals


Each satellite broadcasts at 2 frequencies



L1


1575.42 MHz


Civilian users



L2


1227.6 MHz


Military users


Encrypted


GPS
-

Sources of Error


clock and ephemeris errors


ionospheric & tropospheric delays


multipath & shading


satellite geometry or Geometric Dilution of
Precision (GDOP)


receiver noise & delay


Note: Selective availability has been removed since May 2000

Note
:

One

nanosecond

of

inaccuracy

results

in

30



centimeters

error

approximately

GPS
-

DOP


Dilution of Precision (DOP)


Measurement of the geometry of the visible satellite constellation


satellites spread across sky gives good (small) DOP values


clustered satellites give poor DOP values (


Geometric Dilution of Precision (GDOP)
-
position, time


Horizontal Dilution of Precision (HDOP)
-

Latitude, longitude


Vertical Dilution of Precision (VDOP)
-

altitude


Positional Dilution of Precision (PDOP)
-

position


Time Dilution of Precision (TDOP)
-

time


Examples:


1 indicates perfection


if HDOP greater than 5, reading is rejected!


PDOP of 8 is acceptable provided HDOP less than 5

Differential GPS (DGPS)

1.

if the position of a GPS receiver is



known, the error in the pseudoranges can be calculated

2.

These “corrections” may be broadcast to nearby users

thus improving their position readings accordingly


DGPS demands


network of reference stations


Allocated FM frequency


specialist receiver


Readings of up to 5 meters may be obtained easily


sub
-
meter accuracy may also be obtained subject to
cost and quality of the equipment



DGPS

DGPS Signal
GPS Receiver Station
DGPS Transmitter
Shipboard GPS &
DGPS Receivers
Satellite
-

GLONASS


Soviet equivalent of GPS


Initial satellite launched in 1992


Last satellite deployed in 1996


Working constellation of 24 satellites


Architecturally similar to GPS


Control segment within borders of former Soviet Union



Satellite
-

Galileo


Conceived in 1999


Initial satellites scheduled for launch in 2004


Initial services scheduled for 2006


Full operational capacity by 2008


Objectives


state
-
of
-
the
-
art positioning and timing services


guarantees regarding accuracy & availability


designed for civilian requirements


Galileo
-

Architecture


30 satellites in circular orbits


Orbit planes inclined at 55
-
60 degrees to equatorial
plane


increase coverage in Northern Europe


Ground segment consists of 14 ground stations
spread around the globe


Interoperable with GPS and GLONASS

Cellular Techniques


Recall E
-
911 directive








Solution
67% of Calls
95% of Calls
Handset Based
50 meters
150 meters
Network Based
100 meters
300 meters
E
-
911 focused attention on how a cellular network’s features and
topology might be used to ascertain a subscriber’s position

Cell
-
ID


Also called Cell of Origin (COO)


Networks knows position of subscriber to cell level


Map geographic coordinates to Base Station


Advantages include:


speed & cost


Minimum modifications to network infrastructure


Disadvantages include


variable accuracy (as cell sizes vary)


Propagation effects may mean serving cell is not actually the nearest cell





Timing Advance (TA)


GSM Timing Advance parameter


used for synchronising time slots


may be defined as the time delay (distance!) between handset and Base
Station


6 bits in length


precision of about 550 meters


Requires augmentation


other positioning mechanism


directional antenna

Angle of Arrival (AOA)


Triangulation


Measure angles of signal at Base Station using sophisticated
antenna


Repeat for second Base Station


Intersection of lines projecting outwards will indicate
subscriber’s position


Disadvantages


Susceptible to interference and fading


Line
-
of
-
Sight (LOS) conditions essential


Will not work well in city


Advantage


may work very well in rural area


Time of Arrival (TOA)


Similar to GPS


Measure distance between handset and Base Station


Repeat for two more Base Stations


if time is synchronized this is adequate


if not, a further reading is required


Advantages


easy to implement


Disadvantages


Accurate clocks required at each station


Susceptible to errors in urban environments


May not access enough base stations in rural areas


Time Difference of Arrival (TDOA)


Uses Time Difference as distinct from absolute time


Hyperbolic curves must be constructed for at least two Base
Stations


Intersection indicates position


Enhanced Observed Time Difference (E
-
OTD)


Also called


Observed Time Difference (OTD)


Observed Time Difference of Arrival (O
-
TDOA)


Identical to TDOA except


Calculations are performed on the handset


Disadvantages


Significant modifications required on the handset

Advanced Forward Link Trilateration (A
-
FLT)


In principle, identical to TDOA or E
-
OTD


Can be implemented on handset or network


Implemented only on CDMA networks


Recall: CDMA is time synchronized so time differences are easier
to measure



Location Fingerprinting


Combines signal features such that a unique signature (fingerprint)
for a given location is created


Database is assembled by driving a vehicle through the area which
transmits signals to the Base Station


Signature is generated by analyzing the incoming signal


By comparing the subscriber’s signal with the signatures in the
database, a location estimate can be obtained




Assisted GPS (A
-
GPS)


Utilizes GPS and topology of cellular network


GPS receivers are placed throughout the PLMN


These “advise” the handset on which satellites to observe


Information is then sent back to the server for position calculation


Advantages


quick & accurate


easy to incorporate DGPS


can track weak signals


Disadvantages


expensive


Assisted GPS
-

Schematic

MSC
Fixed GPS Receiver
AGPS Server
Assistance Information
Pseudo-ranges
Pseudo-ranges
Position
Base Station
Hybrid Positioning Systems


No technique capable of delivering accurate positions
under all circumstances


But


Pragmatic combination may lead to better results sometimes


Example


A
-
GPS


TDOA


Each system has complementary strengths and weakness

Standardization
-

Satellite Navigation


Recall: GPS and GLONASS remain under the control of
their respective militaries


International Civil Aviation Organization (ICAO)


active but limited in its effectiveness


Galileo


SAGA (Standardization Activities for Galileo)


work is currently ongoing


Standardization
-

2G Cellular Networks

Access
Technology
Analogue Mode – TIA (TR45.1)
A-GPS
CDMA – TIA (TR45.5)
A-GPS
A-FLT
GSM – 3GPP (3G TS 23.271)
A-GPS
TOA
E-OTD
TDMA – TIA (TR 45.3)
A-GPS
Standardization
-

3G Cellular
Networks

Radio Access Network
Positioning Mechanism
GPRS/EDGE
TA
E-OTD
GPS
UMTS
Cell-ID
OTDOA
A-GPS
UTDOA

(Uplink TDOA)

Product: Garmin NavTalk GSM

Note: New version of this planned for 2009

Recent Products

Nokia N95

SE C905

References


E
-
911


http://www.fcc.gov/911/enhanced/


GPS


http://tycho.usno.navy.mil/gpsinfo.html


http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.ht
ml


GLONASS


http://www.glonass
-
center.ru/


Galileo


http://www.esa.int/export/esaSA/GGGMX650NDC_navigation
_0.html


EGNOS


http://www.esa.int/export/esaSA/GGG63950NDC_navigation
_0.htm


SISNet


http://esamultimedia.esa.int/docs/egnos/estb/sisnet/sisnet.htm
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