10 Location-Based Services
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Transcript of 10 Location-Based Services
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Department of Computer Science Institute for System Architecture, Chair for Computer Networks
Location-based Services
Mobile Communication and Mobile Computing
. .
http://www.rn.inf.tu-dresden.de
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Positionin and Trackin S stems
both outdoor and indoor s stems can be classified into
stand-alone infrastructure
dedicated infrastructure for positioning/tracking
e.g. satellite systems, infrared-based systems
integrated infrastructure ex s ng commun ca on n ras ruc ure a so use or
positioning/tracking
e. . cellular s stems WLAN-based s stems
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Positionin vs. Trackin
positioning (client-based
positioning)
device actively determines/calculates
+ location information under control oflocated device
device required
tracking (infrastructure-basedpositioning)
position determined by infrastructure,i.e. device is passively located
location information not under controlof located object
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Global Positionin S stem GPS
(1) Satellites 24 satellites on 6 orbits,
i.e. 4 satellites per orbit
additional satellites for
robustness height = 20.200 km
(medium earth orbit)
min. 5, max. 11 satellitesvisible from each point on
earth
hours, i.e. satellites are at thesame position each 24 hours
(3) User Devices GPS receiver
min. 12 channels, i.e.12 satellite signals can bereceived in parallel
[Roth, Ortsbezogene Anwendungen und Dienste]
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Satellite S stems
+ advantages
few environmental influences (e.g. weather)
high accuracy (in the range of meters)
disadvantages
high costs, since for global availability many satellites are required
enough signals have to be available for positioning
at least 4 signals (3 for positioning, 1 for time synchronization)
example: GPS
originally named NAVSTAR (Navigation System with Timing andRanging)
toda known as GPS Global Positionin S stem
consists of
(1) satellites
(3) user devices
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Cellular S stems - GSM
positioning based on GSMcell ID
available from Home
cell size 1 35 km
Mobile Positioning System
(MPS) by Ericsson to
few changes ofinfrastructure;
no c anges o user ev ces
Cell Global Identity (CGI)for identification of the cell
uses GSM cell ID
if sector-antennas used[Roth, Ortsbezogene Anwendungen und Dienste]
segment of circle6
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Cellular S stems - GSM
GSM based on FDMA and TDMA
certain time slot used forcommunication
exact timing required for signalsynchronization
time shift depends on
base station
device calculates distance
based on signal propagationtime
n orma on s use orpositioning in combination
with CGI Roth, Ortsbezo ene Anwendun en und Dienste7
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Cellular S stems - GSM
U link Time Of Arrival UL-TOA
can be used, if device is inrange of four base stations
measurement of signalpropagation time at
calculation of position
accuracy 50 150m
osition information
stored in MobilePositioning Center (MPC)
rac ng [Roth, Ortsbezogene Anwendungen und Dienste]
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Cellular S stems
inte rated a roach based on existin infrastructure
advantages
+ low costs
high availability
works indoor and outdoor
sa van ages
lower accuracy
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Indoor Positionin Trackin
satellite or cell s stems often not available in buildin s ornot accurate enough
therefore other approaches required:
(1) stand-alone infrastructure approaches infrared
radio
(2) integrated infrastructure approach WLAN
,
installation effort yields high costs
usuall users have to carr additional e ui ment bad e
most of the systems are scientific prototypes
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Active Bad e
stand-alone infrastructure based trackin s stem
based on infrared (IR)
users carry badge sending specific user ID
IR-receivers in the rooms receive those signals
position of user is tracked by central server
energy-efficient badges (sending short signals of
0,1 s each 15 s)
problems:
users position is positionof IR-beacon which
location
system
received the signal
user does not get positionactive badge
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infrared receiver infrared
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Wireless Indoor Positionin S stem WIPS
stand-alone infrastructure based ositionin s stem
based on infrared (IR)
beacons installed in the rooms sending unique ID
users badges receiving signals of local beacons
received beacon ID is sent to location server via WLAN
server maps received beacon ID to semantic location
which is sent back to the user
+ advantage:
users nows s own pos onlocation
system
integration of two wireless
techniques
IR receiver
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infrared beacons infrared WLAN
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Further S stems
Active Bat stand-alone infrastructure based tracking system
based on ultrasonic
which is sent to the location server for processing
accuracy up to 10 cm
SpotOn-
based on radio signals
radio signals are able to pervade walls compared to infrareds gna s
strength of radio signal depends not only on distance (thinkof walls, ) accuracy of 3 m for WIPS
compensation of errors if more beacons available
variant: using RFID-tags (user carries tag, reader in rooms)13
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WLAN-based Positionin
based on alread installed WLAN infrastructure(that was installed for communication purposes primarily) integrated infrastructure based positioning
measurement of signal strength of various access points
positioning by means of lateration
at least three access points have to be available
measurements are influenced by obstacles like walls,
idea: tagging the environment with radio tags
+ improved accuracy
startup phase required for reference measurements
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Radio Ma
measurement of si nal stren th at reference oints
positioning based on current measurement
accuracy depends on amount of reference points
environmental changes require new referencemeasurements
15cross points of measurement circle access points
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Ma ic Ma
developed by Humboldt University Berlin
based on WLAN, but could also use ZigBee, Bluetooth orRFID
hybrid approach based on measured signal strength andradio ma s
calculation algorithm called probabilistic graph mapping
accuracy: access points only 10m
more reference points 1m
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Ma ic Ma
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Com arison of S stems
Name Category Positioning/Tracking Mechanism Medium Accuracy
GPS Satellite Positioning TOA Radio 25 m
DGPS Satellite Positioning TOA Radio 3 m
ActiveBadge
Indoor Tracking COO IR Cell
n oor os on ng e
SpotOn Indoor Tracking Signal
strength
Radio 3 m
ActiveBat
Indoor Tracking TOA Ultrasonic 0.1 m
GSM Network Both Radio Cell, ,TOA
MPS Network Both COO, AOA,TOA
Radio 150 m
MagicMap
Network Positioning Signalstrength
Radio 3 m
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Wh Location Models?
think of Alice and Bob:
Where is Alice?
What is the distance between Alice and Bob?
n w c room s o How many bus stops are between Alice and the faculty of computer
science?
for answering those questions we need a model of ourenvironment location models
geometric coordinates geometric models (51.0298N 13.72896E)
symbolic coordinates symbolic models (HSZ TU-DD, Bergstr.64)
location models should model the following:
object position
topological relation connected to and contains
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Geometric Location Models
define places in form of coordinate tuples relative to referencecoordinate system e.g. World Geodetic System 1984 (WGS-84)
mapping between coordinates of different reference
North Pole coordinates usually do not have
a meanin for humans
calculation of distances,
overlappings and inclusions of
Equator
90 West 90 EastOrigin
geometric operations possible
topological relationPmcontains implicit available
topological relation connected
World geocentric coordinate system
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S mbolic Location Models
define laces in form of abstract s mbols
e.g. Cell ID in GSM, sensor identifiers in active badge
system, room and street names
no distance and other topological relations implicitlydefined
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S mbolic Models: Set-based Models
usage of symbolic names
e.g. a building with several floors and rooms can be modelled like this
L ={L , L , }
LFloor2={2.002, 2.003, , 2.067}
contains relation defined by intersection of sets ( {xyz} L = {xyz} ? )
overlappings can be identified ( L1 L2 ? )
nearest nei hbour and navi ation
connected to relation can be defined by modelling pairs of connected locations
also simple (only qualitative) notion of distance possible
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S mbolic Models: Gra h-based Models
symbolic coordinates define vertices V of graph G=(V, E)
connected to relation modelled by edges between vertices
simple distance by calculation of hops
weights for edges to model advanced distance notion
no ex licit contains definition
other: hybride models as a combination of geometric andsymbolic models
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Back to the Exam le uestions
How can the different model t es be used for answerinthe introduced questions?
absolute question relative question
model
coordinates?
Alice and Bob?
symbolic
model
In what room isBob
located at?
How many bus stops arebetween Alice and the facultyof com uter science?
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A lication Areas
rovision location-based information
museum, city guide, shopping guide, tourist guide
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buddy-finder
service search ost office, restaurant nearb
navigation systems
tracking systems
mediation of incoming calls
a arm sys ems or c ren or e er y peop e
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Mobilis - Solution
Scenario: touristapplication
roup o our s sexploring a cityindividually
see each other on the,
reusable frameworkwith services formobile real-time
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Mobilis: Im lementation technolo ies
Client: Android and Java, further implementations with Java ME and Java SE
Communication: Extensible Messaging and Presence Protocol (XMPP)OpenStandard for real-time collaboration
Numerous extension protocols for presence, pub/sub, location, etc.
Server: OpenFireXMPP Server imp ementation ase on JavaBro erservices implemented as XMPP clients based on Java 27
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Summar
lar e set of ositionin s stems
satellite based, cellular, local/indoor
different types of location models hybrid approach is preferable
suppor s a ypes o quer es
enables mapping between geometric and symbolic coordinates
disadvantage: higher modelling effort, more data
location-based services widely adopted
e.g. navigation systems or tourist guides
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f h d
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Some further readin s 1
Becker, C. & Duerr, F.: On location models for ubiquitous computing.Personal Ubiquitous Comput., Springer-Verlag, 2005, 9, 20-31
Dedes, George; Dempster, Andrew G.: Indoor GPS Positioning Challenges and Opportunities, 2005
Hightower, J.; Borriello, G. & Want, R.: SpotON: An Indoor 3D LocationSensing Technology Based on RF Signal Strength 2000
P.; Abowd, Gregory D.: TrackSense: Infrastructure Free Precise IndoorPositioning Using Projected Patterns, ETH Zrich, 2007
-, . , .,ISBN 978-0470-09231-6, 2005
MagicMap: http://www2.informatik.hu-berlin.de/rok/MagicMap/
c er, . o sar , . oca on- ase serv ces
Morgan Kaufmann, 2004 Want, R.; Hopper, A.; Falcao, V. & Gibbons, J. The active badge
oca on sys em rans. n . ys ., , , , -
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S f h di 2
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Some further readin s 2
WIPS Technical Documentation, Royal Institute of Technology,Schweden, www.online.kth.se/csd/projects/0012/
Yeh, Shun-yuan; Chang, Keng-hao; Wu, Chon-in; Okuda, Kenji; Chu,Hao-hua: GETA Sandals: Walk Away with Localization, National Taiwan
University, 2005
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