Data Collection 13 th April, 2005 Software System Laboratory Korea University Yongsik, Kong.

Data Collection

13th April, 2005

Software System LaboratoryKorea UniversityYongsik, Kong

Contents

Introduction Satellite Positioning Systems Indoor Positioning Systems Network-Based Positioning Conclusion and Open Issues

Introduction- Properties of Location Data

Coordination System Latitude, Longitude, and Altitude (LLA) systems use 2 angles and a

height Earth Centered, Earth Fixed (ECEF) systems use Cartesian coordinates

with the zero point in the earth’s center of gravity Scope : A positioning system has a certain scope and defines an

area of potential coordinates Coverage : The actual coverage of a location system may be

smaller than the area of potential locations specified by the scope Precision : a positioning system produces certain measurement

errors Geographic vs. semantic locations : Users are often interested

in the meaning of a location rather than in the geographic coordinates.

University of Hagen, building IZ, back door > N51 ˚ 22.579/E007˚29.615/169m

Additional spatial data : Besides the location, more spatial information sometimes is required

Introduction Systems that determine the location of a mobile

user can be divided into two categories : tracking & positioning

Tracking : if a sensor network determines the location

The location information is first available in the sensor network

Positioning : if the mobile system determines the location itself

The location information is directly available at the mobile system and does not have to be transferred wirelessly. Location information is not readable for others.

Introduction- Basic Location Techniques

Cell of Origin (COO) : used if the positioning system has a cellular structure

Time of Arrival (TOA), Time Difference of Arrival (TDOA) : use the time difference between sending and receiving a signal to compute the spatial distance of transmitter and receiver

Angle of Arrival (AOA) : 지향성 안테나를 사용 , 어느 각도에서 전파가 수신되는 지 식별

Measuring the signal strength : Given a specific signal strength, we can compute the distance to the sender

Processing video data : 특수 레이블이 장착된 비디오 스트림을 인식하여 위치 파악 가능 . 특정 이미지가 카메라의 상대적인 각도를 의미 . AOA 와 유사 .

Introduction-Triangulation, Trilateration, and Traversing

Computing methods for the coordinates of a location u Triangulation ( 삼각측량 ) : from 2 poin

ts, we measure the angle to the location u

Trilateration ( 삼변측량 ): get the location u if we intersect 2 circles.

Traversing : uses several distance-angle pairs.

Satellite Positioning Systems Idea started from the 1960s Important advantages

Positioning can be carried out everywhere on earth Environmental conditions have only minimal

influence on the positioning process A high precision is obtained

Disadvantages Considerable costs arise for launching and

supervising the satellites The positioning only works if the user receives a

sufficient number of satellites

Satellite Positioning Systems Basic Principles

위치 파악을 위해서는 위성의 위치 (si) 와 거리 (ri)를 알아야 함 .

사용자의 위치는 각 위성의 구면 교차점으로 제한 We need at least three satellites to determine the

user’s location u in three dimensions

Satellite Positioning Systems-Global Positioning System (GPS)

The GPS system is divided into 3 segments : user, space, control

User Segment Contains the devices of the mobile users


Space Segment Includes the satellites and the Delta

rockets that launch the satellites GPS satellites fly in circular orbits at an

altitude of 20,200km and with a period of 12hours.

Orbits are tilted to the earth’s equator by 55˚ to ensure coverage of polar regions

Each of the 24 satellites, positioned in 6 orbital planes, circles the earth twice a day


Control Segment Administrating of satellites Correct internal data (system time and orbits) of the

satellite Master Control Station : responsible for overall

management of the remote monitoring and transmission sites

Monitor Stations : check the exact altitude, position, speed, and overall health of the orbiting satellites

Ground Antennas : monitor and track the satellites from horizon to horizon, transmit correction information to individual satellites

Satellite Positioning Systems-Global Positioning System (GPS) Control Segment


2 GPS services Mechanism is based on one-way

communication of the satellites to the user Precise Positioning Service (PPS) : allows

positioning with a precision of 22m in the horizontal and 27.7m in the vertical. PPS is encrypted and can only be decoded by the armed forces of the USA and NATO

Standard Positioning Service (SPS) : is available for civilian users. 2000 년까지 수평100m, 수직 156m 정밀도


The entire GPS system is subject to the following distorting effects, which influence the precision

Clock errors : clocks cause an error of 1.5m in the position calculation

Fluctuations of the orbits : the satellites do not move as exactly as calculated in their orbits

Disturbances of the atmosphere : Atmospheric pressure and weather conditions affect the signal spreading

Disturbances of the ionosphere ( 전리층 ) : loaded particles disrupt the signal spreading

Multipath error : reflected signals in the environment of the receiver

Satellite Positioning Systems-DGPS and WAAS With Differential GPS (DGPS), the precision can be

improved significantly with the help of base stations on the earth’s surface

DGPS : GPS with an additional correction (differential) signal added

This correction signal improves the accuracy of the GPS and can be broadcast over any authorized communication channel

How does DGPS work? : The GPS determined position of a reference station is computed and compared to its surveyed geodetic position. The differential information is transmitted to user receivers by radio or other means.

Satellite Positioning Systems-DGPS and WAAS Wide Area Augmentation System (WAAS)

Follows a principle similar to that of DGPS With the help of base receivers, correction data are

computed Unlike DGPS, the transmitting is not executed with

the help of terrestrial transmitters, but rather with help of geostationary satellites

Satellite Positioning Systems Other Satellite Systems

GLONASS the Russian counterpart to GPS 초기 24 대 , 현재 9 대 위성 서비스중

EGNOS : 유럽의 GPS, 2004 부터 서비스 GALLILEO :

second step of a European navigation system like GPS or GLONASS

By 2006, 30 개 위성 발사 , 2008 서비스 시작

Indoor Positioning Systems-Infrared Beacons (Active Badge)

Infrared devices are highly available and cheap

A very early project based on infrared beacons, called the Active Badge (AB), started in 1992

Every 15seconds, AB sends an infrared signal of approximately 0.1s. This signal transports a code that specifies the user’s identity.

2 advantages AB has long lifetime (only infrared light pulse

consumes the energy) Rarely produce colliding infrared light pulses


several Active Badges(http://www.uk.research.att.com/thebadge.html)

Figure 7.7a Active Badges

First project stage : Serial 4-wire connectionSecond stage : Ethernet network


2-way communication request arose 비인가사용자 인증문제 , 위치의 정확성 문제 (

위치 기반 근무평가 등 ) Location server collects the information of the sen

sors Name server manages a DB of all system users wit

h the corresponding badge addresses Message server coordinates the passing of messa

ges directed to the AB Exchange servers can combine different systems h

ierarchically to a larger system

Indoor Positioning Systems-Wireless Indoor Positioning System (WIPS)

exchanges the roles of beacons and sensors from the Active Badges system

Characteristics of WIPS The infrared transmitters are no longer mobile, but

form the fixed installation The badges receive the signal of the beacons and

pass the corresponding location information to the location server via a wireless LAN network

The location data are then processed by the location server and replied to the mobile device via wireless LAN

The concepts of WIPS allows the creation of more complex location-based applications

Indoor Positioning Systems-Wireless Indoor Positioning System (WIPS)

Mobile devices (WIPS badge) are full computers and are connected to the location servers, thus demanding services can be executed

The beacons can be built up very simply because they only need to periodically send out a fixed signal, and they do not require any network connection

Figure 7.7b WIPS

Indoor Positioning Systems-Radio Beacons (SpotON)

적외선은 투과성이 없어서 각 방마다 설치 필요 전파의 투과성 , 전파 신호 세기를 이용하여 위치

측정 가능 . Positioning systems can use signal

strengths as well as Time Of Arrival (TOA) to compute a location

Figure 7.7c SpotON

Indoor Positioning Systems-Radio Beacons The signal strength depends on several factors

(e.g., obstacles, disturbances, or variations in the transmitting power). As a result, it is not possible to get a precise measurement (effective precision : 3m)

Radio Frequency Identification (RFID) transponders are a variant of radio beacons

Passive RFID tags are small systems with a processor, memory, and antenna but without a power supply

RFID tags are frequently used to track objects

Indoor Positioning Systems-Ultrasound systems

음파 속도 (330m/s) 가 전파보다 낮아서 고정밀 위치 측정 가능 (10cm)

A user carries a device, the so-called Bat, which sends a short ultrasound impulse upon a request to the server

The server transmits the send request by radio The server always selects one specific Bat for positi

oning; therefore, ultrasound signals from different Bats cannot collide

The server has all of the necessary information about the positioning of the corresponding user

Indoor Positioning Systems-Ultrasound systems

The server calculates the position of user with ultrasound signals

The calculation simplifies because the radio signals have very short runtimes compared to the ultrasound signals

For positioning in 3D, the input of at least three sensors is required

Figure 7.7d Active Bat

Indoor Positioning Systems-Ultrasound systems (Cricket)

The Cricket system switches the roles of transmitter and receiver

Fixed installed beacons send ultrasound signals received by mobile badges

With the Cricket system, mobile users can determine their locations without a server

Figure 7.7e Cricket

Indoor Positioning Systems-Video-Based Systems

The position of the squares in relation to each other can carry, similar to bar codes, simple information such as the user’s identity

Because the size of the badges is fixed, the distance to the camera and the orientation in the room can be roughly detected 2D barcode –

Ultracode

Visual-tags

Indoor Positioning Systems-Video-Based Systems

Detecting a user’s location can be done in two ways

The building can be equipped with cameras, which look for the visual tags in their image data stream. Because the positions of the cameras are known, they can compute the user’s location by triangulation

The mobile user is equipped with a small camera. Visual tags are attached on walls inside the building. In this case, the visual tags have fixed positions. If the mobile camera detects two or more tags, it can find out its own position

Figure 7.8c Detecting a location with camera

Network-Based Positioning-Global System for Mobile comm. (GSM)

Cellular phone infrastructures are often viewed as the most promising platforms for LBS

Any participant who enters a specific area is recorded by Visitor Location Register (VLR) within GSM network

This information is passed to the central DB, Home Location Register (HLR)

Mobile participant can access location-related data via Cell Broadcast Channels (CBCHs)


Resolution of the position is too inaccurate for some services (especially rural side)

Mobile Positioning System (MPS) developed by Ericsson makes exact positioning possible in large cells

Cooperates with standard GSM systems and minima modifications of comm. Infrastructures

Conceivable applications with MPS Mobile user can query for location-dependent data Users can supervise the location of other mobile users Route planning applications can calculate an optimal

route to a target


Several mechanisms used by MPS Cell of Global Identity (CGI) : uses the id

entification of a cell to roughly determine the position

Segment Antennas : segment antennas can limit the location

Timing Advance (TA) : using a time slot, more exactly determine the location

Uplink Time of Arrival (UL-TOA) : 4 기지국에 접속가능시 , similar computation case as in the case of satellite navigation

Network-Based Positioning-Wireless LAN

Inside a building equipped with wireless LAN AP, a mobile user can find out one’s location by measuring the signal strengths of all AP

Must be trained For every location, the user makes

measurements and stores coordinates (x, y) and orientation (d) in a table

The system measures the signal strengths of all available wireless LAN AP, which can be identified by their network address

Network-Based Positioning-Wireless LAN

Disadvantages sparsely equipped wireless LAN AP

causes frequent jumps of the location output, even if the user moves only slightly

Time-consuming training phase To avoid training phase : use physical

simulation model of the building

Conclusion and Open Issues The basic mechanisms, techniques, and

systems to capture location data of mobile users

GPS receivers are inexpensive, and the corresponding location output is accurate. But GPS only works outdoors

Indoor positioning systems : cost-intensive, require extensive installations, small coverage, provide moderate precision

Table Summary of some location systems

Data Collection 13 th April, 2005 Software System Laboratory Korea University Yongsik, Kong.

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Transcript of Data Collection 13 th April, 2005 Software System Laboratory Korea University Yongsik, Kong.