Upload
webster-vaz
View
221
Download
0
Embed Size (px)
Citation preview
7/29/2019 GPS AND MOBILES.pdf
1/9
1
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
7/29/2019 GPS AND MOBILES.pdf
2/9
2
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
7/29/2019 GPS AND MOBILES.pdf
3/9
3
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).
7/29/2019 GPS AND MOBILES.pdf
4/9
4
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
7/29/2019 GPS AND MOBILES.pdf
5/9
5
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!
7/29/2019 GPS AND MOBILES.pdf
6/9
6
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
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
Errors in Cellular Network
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.
7/29/2019 GPS AND MOBILES.pdf
7/9
7
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
Plans for Thesis Part B
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
( ) ( )
( ) ( )
( ) ( )223
22
2
22
1
33
22
11
MAMA
MAMA
MAMA
yyxxd
yyxxd
yyxxd
+=
+=
+=
321
~,
~,
~ddd
Measurements Estimated P osition
MMyx ~,~
Specific Positioning
Algorithms
)(~
12 ttcda
=here,
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
( ) ( ) ( ) ( )
( ) ( ) ( ) ( )222231
2222
32
1133
2233
MAMAMAMA
MAMAMAMA
yyxxyyxxd
yyxxyyxxd
++=
++=
3132
~,
~dd
Measurements Estimated Position
MM yx~
,~
Specific PositioningAlgorithms
Geometric Interpretation
Pair wise subtracting
7/29/2019 GPS AND MOBILES.pdf
8/9
8
Signal Strength
_ Distributed ReceivingSystem (Monitoring Post).
_ Distributed TransmissionSystem (Sign Post).
_ similar to TOA.
_ measures signalattenuation.
_P(dB) = 10. log(f/g) _ 10._.log(4d)
Angle of Arrival (AOA)
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
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
Task Interface Diagram
Thesis Part A
Documentation MethodAnalysis Simulation
Seminar
LiteratureReviewGPS CellularNetwork
Thesis Part B
Future Developmentuture DevelopmentGSM PDA
Dopod565s
7/29/2019 GPS AND MOBILES.pdf
9/9
9
Plans for Thesis Part B
Continue on the research
Focus on UMTS
Simulations
Improve the accuracyQuestions?