Lecture08 Mobile Positioning and LBS 第 8 讲 移动定位与服务

Lecture08 Mobile Positioning and LBS

第 8 讲 移动定位与服务§8.1 LBS Basics

§8.2 LBS Technologies

§8.3 Mobile Positioning

§8.4 Geographic Information System

Location Based Services (LBS)

What is it? Allow you to report real time current location to a given platform

Information service accessible using mobile devices through mobile network

Ability to make use of geographical position of mobile device

Why need it ？Location is important

Evolution of LBS

First generationManually input location info.

E.g. zip code, a city name or street address.

Customized contentE.g. driving directions, nearby restaurant or store locations, or weather information.

Second generationAutomatically determine location info.

Usually accurate to within a few kilometers (1 to 2 miles), similar accuracy as in first-generation applications.

Similar services to those in first-generation applications.

Evolution of LBS

Third generationCan obtain more accurate location info.

Can initiate services based on location.

Can provide timely updatesnearby brick-and-mortar services,

asset tracking information, and

street-level mapping and routing.

Feature-rich and user-friendly

LBS Applications

What are the top uses? Emergency servicesGPS Navigation Weather alerts Traffic updates Find-it servicesWireless advertisingAccess controlSocial networking

Notable players Google Maps Foursquare Facebook Places 街旁

§8.2 LBS Technologies

LBS App.

Location Management

Localization Module

Geographic Information

System

LBS Technologies

Localizing or Positioning MethodsGlobal Positioning System (GPS)

Cellular, WiFi, NFC, RFID, Bluetooth � Geographic Information Systems (GIS)

Provide tools to provision and administer base map data

Manage point-of-interest data Location Management

Process positioning and GIS data

Acts as gateway between positioning equipment and LBS infrastructure

LBS System based on GSM

Mobile Positioning System of GSM

Specified by ANSI and ETSI Extend classical GSM system Hardware and Software

LMU: Location Measurement UnitTo measure the time difference between BSs

MLC: Mobile Location CenterSMLC: Service MLC

Measurement and calculation

GMLC: Gateway MLCInterface to others

Mobile Positioning System of GSM

图 9-10 ， p262

Mobile Positioning System of GSM

MTGMLC GMLCauth.HLR GMLCloc. req.MT/VLR MT/VLRloc. rep.GMLC

WebSphere LBS

Location Component

To collect and process client location records

§8.3 Mobile Positioning

PositioningTo capture the location of a mobile device

Considerations: Accuracy vs. Cost Categories: based on where the calculation is done

Network-basedFor both new and legacy handsets.Quite cost-effectiveLow accuracy: from hundred meters to several kilometers

Terminal-based High accuracy: several metersHigh cost, for both the terminal and network.

Cell Identity

A naive solution Location of BS Location of MT Accuracy

Depending on the density and coverage of BS

~100m to ~10km

Timing Advance (TA)

TA: The time of a round trip between base station and mobile terminal.Usually between 0 and 63 bit period (~ 3.69 microseconds).

TA distance1 bit 550m63 × 550m 35km

Pros and consLow accuracy: 0.2~10km

Multipath fading

Simple: no change at MT, minor change at BS

CGI + TA

Cell Global Identity, CGIA standard identifier for mobile phones cells

TA: within a cell CGI+TA: global

Time of Arrival (TOA)

d = v * t Distance values to >3 base stations High accuracy

100~150m High complexity

Synchronization among BSs

Special LMU

Computation Work flow

MT sends to BSs

Each BS measures time

Time Difference of Arrival (TDOA)

TDOA = TOA1 – TOA2

Angle Of Arrival (AOA)

Input data: Angle with two BSs,

Distance between the two BSs Two BSs for 2D location Three BSs for 3D location Need special antenna

Multipath Fingerprinting

RF pattern match Based on the characteristics of multipath signal Collecting fingerprinting

Dedicated learning phase

Store the fingerprint in a database Locating mobile device

collect the current signal pattern

Match it with those in database

Mobile Terminal based Positioning

More accuracy than network-based technologies Terminal participant in the location calculation Suitable for 3rd generation of LBS Popular technologies

E-OTD: uses BSs

GPS: uses satellites.

Enhanced Observed Time Difference (E-OTD)

TOA at mobile terminal But the MT makes the time measurements instead of BS

Enhanced Observed Time Difference (E-OTD)

Values to measureOTD: observed time difference

RTD: real time difference

GTD: geographic time difference

Global Positioning System (GPS)

HistoryFeasibility studies begun in 1960’s.

First satellite launched in 1978.

System declared fully operational in April, 1995. Consists of 24 MEO satellites that transmit precise

microwave signalsAbout 20,200km above the Earth’s surface.

Control Segment

Space Segment

User Segment

Monitor Stations

GroundAntennas

Master Station

Three Segments of GPS

Four Basic Functions of GPS

Position and coordinates.

The distance and direction between any two waypoints, or a position and a waypoint.

Travel progress reports.

Accurate time measurement.

Position Is based on Time

T + 3

Distance between satellite and receiver = “3 times the speed of light”

TSignal leaves satellite at time “T”

Signal is picked up by the receiver at time “T + 3”

The satellites constantly broadcast signals that can be read by GPS-enabled devices.Line of sight : suitable for outdoor only

Three Satellites (2D Positioning)

Three Dimensional (3D) Positioning

GPS

Accuracy5m-40m

Highly relying on the accuracy of clockAtomic clock at each satellite

1ms300km

LimitationsLine of sight to the satellites outdoor only

Solution: Backup method: cell based ones

Long delay of positioning: 20s-40s

A-GPS

Network-assisted GPS GPS + assistance from Additionally uses network resources to locate and use

the satellites in poor signal conditions. To alleviate both restrictions of GPS

Assistance of Location Server in A-GPS

Information used to more quickly acquire satellitesIt can supply information of GPS satellites, enabling the GPS receiver to lock to the satellites more rapidly.

The network can provide precise time.

Calculation of position by the server using information from the GPS receiver

The assistance server has a good satellite signal, and plentiful computation power, so it can compare fragmentary signals relayed to it.

Accurate, surveyed coordinates for the cell site towers allow better knowledge of conditions affecting the GPS, enabling more precise calculation of position.

Comparisons

CGI+TA AOA TOA/TDOA E-OTD A-GPS

定位精度 100m~1.1km <125m 50~200m 50~125m 5~50m

使用区域 无限制 无限制 乡村以上 乡村以上 城市

响应时间 3s 10s 10s 5s 1s

设备升级 无 网络、天线

网络 网络、终端 网络、终端

建设成本 低 高 高 高 高

建设周期 短 短 长 长 短

§8.4 Geographic Information System

GIS, mapping software that Relates the location information with other pertinent information to give it meaning and value.

Such as building locations, street layouts, population densities, and a plethora of other information.

A GIS can provide information and insight to both mobile users and people at fixed locations.

GIS

Common Uses of GIS

Uses the location coordinates provided by positioning technologies to give details that are relevant to the user at that specific moment.

Finding what is nearby Routing information Information alerts Mapping densities Mapping quantities

A Summary

ConceptsLBSMobile device positioning

Mobile positioning system Positioning technologies

Network-basedCGI, TA, CGI+TATOA, TDOAAOAFingerprint

Terminal-basedE-OTDGPS, A-GPS