GPS AND MOBILES.pdf

7/29/2019 GPS AND MOBILES.pdf

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Combining GPS & Cellular NetworkCombining GPS & Cellular Network

Measurements for Positioning.Measurements for Positioning.

Presented by:Presented by:

ShekShek Leung, CHAN (3046678)Leung, CHAN (3046678)

HuiHui Qin, TEOH (3049234)Qin, TEOH (3049234)

Supervisor: Andrew Dempster

Assessor : Robert Malaney

Outline

System Overview

Positioning Systems Global Positioning System

(GPS)

DGPS

WAAS

Sources of Error

Simulation

Cellular Network UMTS

GSM

Errors in Cellular Network

Method of Measurement Time of Arrival (TOA)

Time Difference of Arrival

Signal Strength

Angle of Arrival (AOA)

Thesis Overview Thesis Part A

Future Development

Plans for Thesis Part B

What is Positioning system?

To allocate the position of one location

Using the signal send from one end system to another end system.

GNSS (Global Navigation Satellite System)A global navigation satellite system is a network of satellites that transmitranging signals used for positioning and navigation anywhere around theglobe; on land, in the air or at sea. The US Global Positioning System (GPS),the Russian GLObal NAvigation Satellite System (GLONASS) and theupcoming European GALILEO system are examples of GNSS.

Variety of applications

Resource investigation

Surveying

Military defence system

Navigation car navigation systems

Map-making

Mission ambulance, police, etc

Aviation - fundamental to Australias present and future AirTraffic Management System (ATM)

Mountain-climbing

What is GPS ?

_ Global Positioning Systems (GPS)

_A network of satellites that continuously transmit codedinformation, which makes it possible to precisely identify locationson earth by measuring distance from the satellites.

_ space-based radio positioning systems.

_ developed in the 1980s by the U.S. Department of Defence.

_ 24 satellites approximately 20200 km above the earth.

_To be able to track a 3D coordinate

- minimum 4 satellites.

Three segments of GPS

Space segment At least 24 satellites around

the earth

Control segment

Five control stationslocated around the world

User segment

GPS receiver


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Space segment

Consists of at least 24 satellites (21 activeplus 3 operating spares) is the heart of thesystem. The satellites are in whats called ahigh orbit about 12,000 miles above theEarths surface. Operating at such a highaltitude allows the signals to cover a greater

area.

The satellites are arranged in their orbits soa GPS receiver on earth can always receivefrom at least four of them at any given

time.

Control segment

Controls the GPS satellites by tracking them and providing them withcorrected orbital and clock information.

Including 4 monitor stations and 1 master control station

Monitor stations constantlyreceive data from the satellites and

then send that information tomaster control station.

Master control station corrects

the satellite data and, together withtwo other antenna sites, sends the

information to the GPS satellites(uplinks)

User segment

You and your GPS receiver

Consists of boaters, pilots, hikers, hunters, the militaryand anyone else who wants to know their location.

Satellite Signal

Use L-band which is a nominal portion of the microwaveelectromagnetic spectrum ranging from 1 to 2 GHz

Two Types of L-Band in satellite: L1 and L2

L1 and L2 are designations of the two basic carrier frequenciestransmitted by GPS satellites that contain the navigation signals.The L1 frequency is 1,575.42 MHz, while the L2 frequency is

1,227.60 MHz Low power signal, 20-50 watts (FM signal is around 100,000

watts), it is the reason of why important to have clear view of thesky

Digital code in signal

Protected (P) Code The P-code is bi-phase shift modulated on both the L1 and L2 carrier

frequencies.

10.23MHz bit rate.

High bit rate, not easy interfere.

Restricted by U.S. Military

Clear Acquisition (C/A) Code The C/A-Code modulates only the L1 carrier frequency on GPS

satellites.

1.023MHz bit rate

allows a receiver to quickly lock-on to a satellite.

For civil use

Sources of GPS signal errors

_ Ionosphere and troposphere delays_ Signal multipath

_ Receiver clock errors

_ Orbital errors

_ Number of satellites visible

_ Satellite geometry (GDOP)/shading

_ Intentional degradation of the satellite signal


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Ionosphere and troposphere delays

The satellite signal slows as it passes through theatmosphere. The GPS system uses a built- in model that

calculates an average amount of delay to partially correctfor this type of error.

Notes: IonosphereThe ionosphere consists of the layers of ionized air in the atmosphere extending from 70

kilometers to 700 kilometers and higher. Depending on frequency, the ionosphere caneither block radio signals completely or change the propagation speed. Global navigationsatellite signals are delayed as they penetrate the ionosphere. This ionospheric delay can beeither predicted using models, though with relatively poor accuracy, or corrected using two

frequency receivers.

Signal multipath

This occurs when the GPS signal is reflected off objectssuch as tall buildings or large rock surfaces before it

reaches the receiver. This increases the travel time of thesignal, thereby causing errors.

Receiver clock errors

A receiver's built-in clock is not as accurate as the atomicclocks onboard the GPS satellites. Therefore, it may have

very slight timing errors

Note: Atomic ClockAn atomic clock is an extremely accurate timekeeping device regulated by the naturalregular oscillations of an atom or molecule. An atomic clock powered by a hydrogenatom (maser) is accurate to 1 part in 2 quadrillion. A cesium atom powered clock has anerror of about one second in one million years. GPS satellites carry multiple atomic

clocks, regulated by these precise atomic vibrations, to ensure accuracy. The GPS MasterControl Station uses cesium clocks and a hydrogen maser clock.

Orbital errors

Also known as ephemeris errors, these are inaccuracies ofthe satellite's reported location.

Notes: EphemerisEphemeris is a set of parameters used by a global navigation satellite receiver to predictthe location of a satellite and its clock behavior. Each satellite contains and transmits

ephemeris data about its own orbit and clock. Ephemeris data is more accurate than thealmanac data but is applicable over a short time frame from four to six hours. Ephemerisdata is transmitted by the satellite every 30 seconds

Number of satellites visible

The more satellites a GPS receiver can see (Line-Of-Sight) , the better the accuracy. Buildings, terrain,

electronic interference, or sometimes even dense foliagecan block signal reception, causing position errors orpossibly no position reading at all. GPS units typically will

not work indoors, underwater or underground

Notes: Line-Of-Sight means signal can pass throughclouds, glass, and plastic, but will not go through mostsolid objects such as buildings and mountains

Satellite geometry/shading

Also called Geometric Dilution of Precision (GDOP) This refers to the relative position of the satellites at any

given time. Ideal satellite geometry exists when the

satellites are located at wide angles relative to each other.Poor geometry results when the satellites are located in aline or in a tight grouping

Notes: Dilution Of Precision (DOP)DOP relates the statistical accuracy of the global navigation satellite measurements to thestatistical accuracy of the solution. Geometric Dilution of Precision (GDOP) is composedof Time Dilution of Precision (TDOP) and Position Dilution of Precision (PDOP), whichare composed of Horizontal Dilution of Precision (HDOP) and Vertical Dilution of

Precision (VDOP).


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Intentional degradation of the

satellite signal

Selective Availability (SA) is an intentional degradation ofthe signal once imposed by the U.S. Department of

Defense. SA was intended to prevent military adversariesfrom using the highly accurate GPS signals. Thegovernment turned off SA in 2 May 2000, which

significantly improved the accuracy of civilian GPSreceivers

Notes: Selective Availability (SA)Selective Availability is a process whereby the U.S. Department of Defensedithers the satellite clock and/or broadcasts erroneous orbital ephemeris data to

create a pseudorange error to prevent adversaries from using the extremelyaccurate GPS positioning data.

GPS Error Sources

3.961.288.544.25User ranging error (RMS)

02.62

C/A codeC/A code

Predicted Error (m)

DGPSGPS

P code

2.45

0.6

0.15

3.48

0

2.45

0.4

6.4

3.48

3.48

0

0

1.22

0.15

0.15

0.240.24Receiver error

0.4Tropospheric delay

0.4Ionospheric delay

1.22Multipath error

3.48Satellite clock error

2.62Satellite ephemeris error (Orbital)

P code

Error Sources

What else?

Standard Positioning System (SPS)SPS is the less accurate GPS capability which is freely

available to anyone using a GPS receiver. Under selectiveavailability.

Precise Positioning System (PPS)The more accurate GPS capability that is restricted to

authorized, typically military, users.

Differential GPS (DGPS)

By placing additional GPS receiver (called referencestation)

A technique whereby data from a receiver at a known

location is used to correct the data from a receiver at anunknown location. Differential corrections can be appliedin either real time or by post processing. Since most of

the errors in GPS are common to users in a wide area, theDGPS-corrected solution is significantly more accurate,typical DGPS accuracy is 1-5 meters.

DGPS (continue) DGPS (continue)

Since the reference station knows its exact location, it candetermine the errors in the satellite signals.

By measuring the ranges to the actual ranges calculated

from its known position.

Differential corrections are applied to the GPS receivers

calculations, removing many of the common errors andimproving accuracy


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Wide Area Augmentation Signal (WAAS)

A satellite navigation system designed by the U.S. Federal AviationAdministration (FAA) to boost the accuracy of GPS satellite navigation.Improvements in accuracy are approximated to be within 5 metershorizontally and 7 meters in altitude.

Note: Currently, WAAS is not fully implemented. It

was created for aviation applications. It uses

geostationary satellites over the equator, whichmakes WAAS signals easily blocked in North

America by terrain obstructions. Users may

experience temporary loss of WAAS support,especially in wooded areas.

WAAS (continue)

Wide Area refers to a network of 25 ground reference stationscover the entire U.S. and some of Canada and Mexico. Eachreference station is linked to a master station, which puts togethera correction message and broadcasts it via satellite.

Accuracy of Positioning System

WAAS< 3 m

DGPS3-5 m

GPS

without SA

15 m

GPS

with SA

100 m

Pos i t ioningos i t ioningSy s t emy s t emRangeange

SimulationProgram Design

Using Matlab & Constell GNSS Toolkit

It can simulates various environments basedon Sydney city areas

Basic design idea

Compare the accuracy between GPS andDGPS

Acceptable for applications

Input:

Alamanc file which includes Satellitesinformation start at Thursday, May 26,2005 (http://www.navcen.uscg.gov/)

User position [lat, long, height] in Sydney

Note: Almanac

The almanac is a set of parameters used by a Global Positioning System (GPS)

receiver to predict the approximate location of a navigation satellite and the

expected offset of the satellite's clock. Each GPS satellite contains and transmits

the almanac data for the entire satellite network.

SimulationResult

GPS DGPS

Limitation of GPS

Line-Of-Sight essential signal cannot pass through building, ithappens in urban area, i.e. Sydney city circle

Long position time around 15 minutes, depends on howaccuracy

Battery - run out of the battery in GPS receiver, since longcalculation time, 4 AA battery can last for 4 hours only

Need improvement? Cellular Network!


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Outline

System Overview


(GPS)

DGPS

WAAS

Sources of Error

Simulation


GSM




Signal Strength



Future Development


Cellular network

_Widely use in wirelesssystem

_Ability of signal passthrough building

_ Positioning with 3satellite & 1 cellularnetwork base station

_ Protocols:_UMTS

_GSM

SS = -70

SS = -56

SS = -62

TA = 2 SS = -60

SS = -82

What is UMTS (CDMA)?

Universal Mobile Telephone Service.

Third Generation (3G) Mobile System.

Developed by

CDMA system.

Similar to the structure in satellite navigation systems.

What is GSM?

_ Global System for MobileCommunication.

_ Developed in the 1980s by theEuropean TelecommunicationStandard Institute (ETSI).

_ FDMA/TDMA

_ 2 frequencies band_ Uplink

_ Downlink

UPLINK

DOWN

LINK


20 27m270-380 mTotal error (1 sigma)Total error (1 sigma)

7.5 m7.5 mOscillator errorOscillator error

3 6 m3 6 mSynchronization ofSynchronization ofnetwork/handsetnetwork/handset

0.3 3m0.3 3 mTroposphereTroposphere

0 17m0 250 mMultipathMultipath

18m270 mMeasurement noiseMeasurement noise

UMTS (CDMA)UMTS (CDMA)GSMGSMError sourceError source

Pocket PC

New Tri-Band, Bluetooth and WiFi Pocket PC!

The Qtek Pocket PC is very similar to the O2 XDA IIi. The unit is a fullyintegrated voice enabled GSM/GPRS portable personal computing devicethat runs the phone edition of Windows Mobile 2003 Second Edition andfeatures a built-in XVGA-resolution (1.3 megapixel) digital camera. Alsofeatures an SDIO slot,

so you can use memorycards as well as other

devices like GPS cards

it can be used with any

GSM network worldwide.


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Outline

System Overview


(GPS)

DGPS

WAAS

Sources of Error

Simulation


GSM




Signal Strength




Future Development

Methods for measurement

_Signal strength _Angle of Arrival (AOA)

_Time Different of Arrival (TDOA)_Time of Arrival (TOA)

Time of Arrival (TOA)

Time of arrival

Estimate by distancebetween transmitter andreceiver.

Transmitted by theMobile Station (MS) andreceived at multiple BaseStations (BSs)

Circle centered at theBSs.

Requirement: position of satellite

timestamp

Time Of Arrival (TOA)

Mobile(xm, ym)

Anchor 2 (xA2,

yA2)

Anchor 3(xA3, yA3)

Anchor 1(xA1, yA1)

3 anchors with known positions (at least) are

required to retrieve a 2D- position from 3 TOAs

( ) ( )

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Measurements Estimated P osition

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Time Different Of Arrival (TDOA)

Hyperbolic system.

Converted to a constant distance difference to two basestations.

Intersection of two hyperbolas.

Requirement: Geographical coordinates

Precisely synchronized clocks

Time Different Of Arrival (TDOA)

Mobile(xm, ym)

Anchor 1(xA1, yA1)

Anchor 2(xA2, yA2)

Anchor 3(xA3, yA3)

3 anchors with known positions (at

least) are required to find a 2D-position from a couple of TDOAs

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Measurements Estimated Position

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Specific PositioningAlgorithms

Geometric Interpretation

Pair wise subtracting


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Signal Strength

_ Distributed ReceivingSystem (Monitoring Post).

_ Distributed TransmissionSystem (Sign Post).

_ similar to TOA.

_ measures signalattenuation.

_P(dB) = 10. log(f/g) _ 10._.log(4d)


Measuring the direction angles

Least two antenna array systems

Require: Two dimensional positioning

Antennas installation

Interconnection of antennas

Comparison for 4 methods

specialized antennae

low accuracy in large cells

simple computationsAngle of Arrival (AOA)

low accuracy in large cells low cost measurements

simple computations

Signal Strength

synchronized network required

expensive measurement

complex calculations

time measurement required for

TDMA/CDMA network operation

receiver does not need time of

transmission

Time Difference of

Arrival (TDOA)

synchronized network required

receiver must know time of

transmission

expensive measurement

time measurement required for

TDMA/CDMA network operation

simple computations

Time of Arrival (TOA)

Disadvantagesdvantageseasurement Type

Outline

System Overview


(GPS)

DGPS

WAAS

Sources of Error

Simulation Cellular Network

UMTS

GSM




Signal Strength


Thesis Overview Thesis Part A Future Development


Task Interface Diagram

Thesis Part A

Documentation MethodAnalysis Simulation

Seminar

LiteratureReviewGPS CellularNetwork

Thesis Part B

Future Developmentuture DevelopmentGSM PDA

Dopod565s


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Continue on the research

Focus on UMTS

Simulations

Improve the accuracyQuestions?

Documents

GPS AND MOBILES.pdf