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Location Based Services – LocationProviderProvider

Thomas Mundtthm@informatik.uni-rostock.de

Übersicht

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Example An example – cell phone with GPS

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Example GMDSS Global Maritime Distress and Safety System (GMDSS)

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Basics How to determine a position with compass and

landmarks?

Triangulation Determine a position by measuring two angles Cross bearing

Trilateration Determine a position by measuring two distances

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Determine a position by measuring two distances

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Triangulation

150 degrees

250 degreesFix point

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150 degrees

Bearing point

Bearing point

Triangulation Fix point is situated at the crossing of two lines with

known direction G t f li ( l b t li ) ff t ibl Geometry of lines (angle between lines) affects possible

precission (90 degrees would be best)

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TrilaterationBearing point

2000

1000m

1000m

Fix point

2000m

1000m

Bearing point

Bearing point

Trilateration Signal strength or derived indicators Known signal attenuation per distance

Signal travelling time Known speed of signal (speed of light in most cases)

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Signal attenuation Calculating the expected signal strength (vacuum, free

field, Friis)

Signal travelling times Need to know time difference (latency) between sender

and receiver Cl k i t itt d i Clocks in transmitter and receiver Signal travels about 1.7E-7s for 50 metres 2m precission requires approx. 150MHz clock (or 75MHz if

round trip time is measured)

How to synchronize those clocks?

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Problem: two way propagation

Fast and Slow Fading

Green: Fast Fading Red: Slow Fading 40 dB means a factor of 10000

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GPS System

GPS Space vehicles More than 20 satellites in orbit Weight 1000 – 2000 kg S d 10200k h Speed 10200km per hour TX power 20 – 50W

Input Correction data

Output Output L1 channel: C/A Code (Coarse Acquisition) – civil use L2 channel: P-Code (Precise) – military / special licensees only

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Satellite constellation At least 24 satellites permanently in orbit (typically at

least one spare per plane) Fli ht ltit d 20000k Flight altitude approx. 20000km 2 orbits per day 6 orbital planes 55° Inclination 60° between planes 4 satellites per plane 4 satellites per plane

At least 4 satellites are above the horizon Satellite constellation has to be distributed to the

receiver

Almanac and ephemeris Almanac data Almanac contains parameters describing the general system

health and rough orbits of the entire satellite fleethealth and rough orbits of the entire satellite fleet

Ephemeris data Precise orbital information about position of particular space

vehicle

Download speed is about 75 bits per second (approx. 30s for ephemeris and 12min for almanac)

Parameter description can be found athttp://www.navcen.uscg.gov/gps/almanacs.htmhttp://www.ngs.noaa.gov/orbits/

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Example********Week 272 almanac for PRN-01********ID: 01Health: 000Eccentricity: 0.5485057831E-002Time of Applicability(s): 61440.0000Orbital Inclination(rad): 0.9817560932Rate of Right Ascen(r/s): -0.7783181344E-008SQRT(A) (m 1/2): 5152.596191Right Ascen at Week(rad): 0.1478141790E-001Argument of Perigee(rad): -1.698520076g g ( )Mean Anom(rad): -0.8001380110E+000Af0(s): 0.3719329834E-003Af1(s/s): 0.3637978807E-011week: 272

Example********Week 272 almanac for PRN-01********ID: 01Health: 000

ID of satellite

Eccentricity: 0.5485057831E-002Time of Applicability(s): 61440.0000Orbital Inclination(rad): 0.9817560932Rate of Right Ascen(r/s): -0.7783181344E-008SQRT(A) (m 1/2): 5152.596191Right Ascen at Week(rad): 0.1478141790E-001

„health“ status

Diverse BahnparameterDiverse BahnparameterOrbit parameters

Argument of Perigee(rad): -1.698520076Mean Anom(rad): -0.8001380110E+000Af0(s): 0.3719329834E-003Af1(s/s): 0.3637978807E-011week: 272

Clock error and drift

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Ephemeris13200.54850578308105E-0002 0.12502670288086E-0001 -0.24774635676295E-00080 51525961914063E+0004 0 47050714492798E 0002 0 54065573215485E+00000.51525961914063E+0004 0.47050714492798E-0002 -0.54065573215485E+0000-0.25469183921814E+0000 0.37193298339844E-0003 0.36379788070917E-001109

RPNSVNURAEccentricity Inclination Offset Rate of Right AscensionSquare Root of Semi- Longitude of Orbital Argument of PerigeeSquare Root of Semi Longitude of Orbital Argument of PerigeeMajor Axis PlaneMean Anomaly Zeroth Order Clock First Order Clock

Correction CorrectionSatellite HealthSatellite Configuration

SV

Air Force Ground Control

ControlStation

User

Corrections

(x,y,z,t)i(x,y,z,t)i

+ Corrections

SVi

Master Control Station at Schriever AFB, Colorade Springs

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Ground control Flight paths of the satellites are tracked by US Air Force

monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs, Colorado, along with monitor stations operated by the National Geospatial-monitor stations operated by the National Geospatial-Intelligence Agency (NGA).

The tracking information is sent to the Air Force Space Command's master control station (MCS) at Schriever Air Force Base in Colorado Springs

Then MCS contacts each GPS satellite regularly with a navigational update.

These updates synchronize the atomic clocks on board the

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These updates synchronize the atomic clocks on board the satellites to within a few nanoseconds of each other, and adjust the ephemeris of each satellite's internal orbital model.

During space maneuvers the space vehicle is marked unhealthy.

SV Data Structure

Data frame:1500 bits, 30 sec

1 2 3 4 5

1

2

Subframe:300 bits, 6 sec

Clock corrections

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.

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Precise (ephemeris)orbital position data SV system data

Completenavigationmessage:25 frames,12.5 min

50Hz binary data sent in 300-bit packets (subframes) 5 subframes per frame, 25 frames per message Message restarts every 12.5 min Data is encrypted and modulated before transmission Each subframe contains parity bits for data corrections

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SV Data Transmission

SPS Carrier freq.(uniform)

Pseudo-Random Noise (PRN)

Data @ 50Hz

PPS Carrier freq.(uniform)

SV data (position, time, system info, etc.) logical OR’d with PRN code, then used to modulate high-freq. carrier

PRN codes are unique signatures for each SV, one C/A and one P-code for each L1 = SPS signal (civil use), repeats every 1023 cycles L2 = PPS signal (military and special use only), repeats every seven days

Calculation of time difference Correlation along time axis

Actual PRN received from SV

Replica of SV PRN from receiver almanac

Quelle: Joe Frankel

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Doppler shift

Correlationoutput(normalized)

Frequency Offset (kHz) Code Delay (chips)

Distance measuring

TX: 0 00 s

RX: 0,06 s

TX: 0.00 s

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Calculating Position The receiver position is calculated

by solving a set of four Pythagorean equations:

(x1 - X)² + (y1 -Y)² + (z1 - Z)² = c²(t1 - T-d1)² (x2 - X)² + (y2 -Y)² + (z2 - Z)² = c²(t2 - T-d2)² (x3 - X)² + (y3 -Y)² + (z3 - Z)² = c²(t3 - T-d3)² (x3 - X)² + (y3 -Y)² + (z4 - Z)² = c²(t4 - T-d4)²

Where: X,Y,Z and T are unknown position and

time at receiver (x,y,z)i are the four known satellite

positions di are the known differences in data

arrival time, from correction dataReceiver determines best solution

Satellite Position One satellite

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Satellite Position Two satellites

Satellite Position 3 satellites

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Satellite Position• 4 satellites

Satellite Position Plausibility Near the surface O i t One point

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Satellite Position

Error SourcesSOURCE ERROR CONTRIBUTION

Ionospheric delays 10 m

Tropospheric delays 1 m

PRN Code Noise 1 m

SV Clock 1 m

SV Ephemeris Data 1 m

Pseudo-Range Noise 1 m

Receiver Noise 1 m

Multi-Path 0.5 m

TYPICAL ERROR WITH BASIC GPS 15 m

Note: Selective Availabilty (SA) limited accuracy of SPS service to 100m until May 2000

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Dilution of precision (DOP) Geometry of satellites Small angles cause higher DOP

HDOP h l DOP HDOP: horizontal DOP VDOP: vertical DOP PDOP: positional DOP (combination of HDOP & VDOP) TDOP: time DOP GDOP: geometric DOP (combination of PDOP & TDOP)

Dilution of precision (DOP)

Das Bildelement mit der Beziehungs-ID rId4 wurde in der Datei nicht gefunden.

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Signal strength Outdoor only Not under water Morphologic obstacles (Caves, narrow valleys) Human body

Precise timing Very good clocks needed 1/1000s delay 300,000m distance Space vehicles contain atomic clocks (Cs or Rb) Receiver contains cheap clocks

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Atomic clocks within the space vehiclesA. BLOCK I : NONE B. BLOCK II: PRNS 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16

PLANE : SLOT F6, C2, D4, B4, C1, C4, A3, A1, E3, D2, F3, F1, D5, B1CLOCK : CS, CS, RB, CS, RB, RB, CS, CS, CS, RB, RB, RB, CS, RBBLOCK II PRNS 17 18 19 20 21 22 23 24 25 26 27 28 29 30BLOCK II: PRNS 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30PLANE : SLOT D6, E4, C3, E1, D3, E2, F4, D1, A2, F2, A4, B3, F5, B2CLOCK : RB, RB, RB, RB, RB, RB, RB, CS, CS, RB, RB, RB, RB, RBBLOCK II: PRNS 31PLANE : SLOT C5CLOCK : RB

Af0(s): 0 3719329834E-003Af0(s): 0.3719329834E 003Af1(s/s): 0.3637978807E-011

Af0 – Clock ErrorAf1 - Drift

Timing – example First estimation of receiver time

Clock is ahead of time

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Timing Clock is behind time

Timing Calibration to generate minimum time difference

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Indoor GPS Attenuated reception Approx. 10 – 20dB per floor level

Correlation (lock) very hard Correlation (lock) very hard Doppler-Shift and Code Delay „Integration“ of energy needs more time

Correlation

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Assisted GPS Almanac will be distributed by other means such as the

Internet N l ti ti d d t 10% (h i Necessary correlation time reduced to 10% (hence, gain

by A-GPS is 10dB)

A-GPS

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Chips Correlator GL16000 from GlobalLocate 8x8mm B fit f tl f ARM7 Bus fits perfectly for ARM7

GPS RF Tuner GL-HSRF 3,5x4,5mm Fits to the GL16000

Pseudolites

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Selected Availability

Principle of D-GPS Reference station receives GPS signals and calculates

position Di t diff b t k d l l t d Distance or difference between known and calculated

position (pseudorange) PRM(t) is being determined Difference will be distributed as Pseudorange correction

PRC(t) and Rate Correction RRC(t) GPS receiver calculates position as

PR(t) = PRM(t) + PRC(t)PR(t) PRM(t) PRC(t)

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LAAS Local Area Augmentation System (LAAS) Information is locally collected an transmitted locally

A Airports Ports Shores

LAAS

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LAAS examples

Perry

CCV3

MCD1

MOB1

Tallahassee Jacksonville

TampaMelbourne

ProposedCCAFS/KSC Micro-Net

KYW1

MAI1Miami

Key West

EXISTING USCG DGPS SITE

POTENTIAL FDOT DGPS SITE

FDOT DGPS SITE at NOAA/NWS WFO

0 50 100 km

LAAS

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D-GPS via satellites Wide Area Augmentation System (WAAS) distributes

correction signal via geostationary satellites (Inmarsat) on same frequencies as GPS SV (free PRNs)same frequencies as GPS SV (free PRNs)

EGNOS European Geostationary Navigation Overlay System (compatible to WAAS)

Cellular location providers Usually LBS need a mobile network anyway GSM

HSCSD GPRS EDGE

UMTS HSDPA HSDPU

WLAN / Bluetooth / UWB

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Utilization of those networks for position determination is obvious

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GSM (HSCSD, EDGE, GPRS) Cell structure

GSM (HSCSD, EDGE, GPRS) Sectors

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GSM (HSCSD, EDGE, GPRS) Umbrella Cells

GSM (HSCSD, EDGE, GPRS)

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GSM (HSCSD, EDGE, GPRS)

GSM (HSCSD, EDGE, GPRS) Cell Global Identity Uses Measurement Reports

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GSM (HSCSD, EDGE, GPRS) Observed Time Difference of Arrival

GSM Spectrum GSM900 (Europa, Asien) 880 - 915 MHz (uplink) und 925 - 960 MHz (downlink)

GSM1800 (E A i ) GSM1800 (Europa, Asien) 1710 - 1785 MHz und 1805 - 1880 MHz

GSM1900 (USA) 1850 - 1910 MHz und 1930 - 1990 MHz

GSM400 und GSM 850 are also possible

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GSM (HSCSD, EDGE, GPRS) LBS in GSM

Positioning in WLANs Without additional hardware Signal strength / signal precense Si l l t Signal latency Plausibility

Structure of the building

Position of APs could be known

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Triangulation Latency Speed of light / sound is known

Si l h Signal strength Attenuation is known

Latency Precise clocks needed in AP or mobile client 150 MHz are needed for 2m accuracy (or 75 MHz when RTT

is being considered)is being considered)

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Signal strength (geometric approach) Friis Formula

Two Ray model

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Fast and Slow Fading

Signal strength (Bayesian approach) Calculation of position with maximum likelihood

according to earlier test measurements

Radio map / propagation modelS l h f f Signal strength is a function of position

Position determination is an inverse problem

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Principle Calculation of propagation model, test measurements

within a raster, additional calculations of obstaclespossiblepossible

Ausbreitungsmodell

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Commercial system

Location providersWLAN RFID A-GPS GSM

Accuracy 1 m 50 cm-2 meters 1)

15-50 m 50 m

Continuous tracking Yes No Yes YesContinuous tracking Yes No Yes Yes

Proprietary hardware No Reader/tag New mobile phones No

Resource requirements Low Low High Low

Availability WLAN Readers required Indoor & urban Everywhere

Calibration Yes No No No

Penetration All WLAN Low, requires readers

Mobile users Mobile users

Cost Low Low (USD 10- High Low(1000)

g

Roll out time Fast Fast Slow Fast

Frequencies 2,4 GHz 50 kHz-2.5 GHz

800, 1900, 1575 MHz

800, 1900 MHz

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Proximity sensors Position determination according to which transmitters

are in range For instance Bluetooth WLAN RFID radio stations For instance Bluetooth, WLAN, RFID, radio stations Database contains position of transmitters

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Loran-C (Long Range Navigation) Developed shortly after WWII Position determined by measuring phase shifts between at

l t th t tileast three stations

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Chain configurations in NELS

GRI 6731, Lessay Chain

Designator Station name Latitude Longitude ED Power Blanking Nominal ECD

M Lessay, France 49º 08' 55.224'' N 01º 30' 17.029'' W 0 250 Priority 6731 0

X Soustons, France 43º 44' 23.099'' N 01º 22' 49.584'' W 13000 250 Not dual rated 0

Y Loophead, Ireland 52º 35' 01.576'' N¹ 09º 49' 07.969'' W¹ 27300 250 Priority 9007 +0,5

Z Sylt, Germany 54º 48' 29.975'' N 08º 17' 36.856'' E 42100 250 Priority 7499 +0,5

GRI 7001, Bø Chain

Designator Station name Latitude Longitude ED Power Blanking Nominal ECD

M Bø, Norway 68º 38' 06.216'' N 14º 27' 47.350'' E 0 400 Priority 9007 0

X Jan Mayen, Norway 70º 54' 51.478'' N 08º 43' 56.525'' W 14100 250 Priority 9007 0

Y Berlevåg, Norway 70º 50' 43.014'' N 29º 12' 15.980'' E 29100 250 Not dual rated 0

GRI 7499, Sylt Chain

Designator Station name Latitude Longitude ED Power Blanking Nominal ECD

M Sylt, Germany 54º 48' 29.975'' N 08º 17' 36.856'' E 0 250 Priority 7499 +0,5

X Lessay France 49º 08' 55 224'' N 01º 30' 17 029'' W 14100 250 Priority 6731 0X Lessay, France 49 08 55.224 N 01 30 17.029 W 14100 250 Priority 6731 0

Y Værlandet, Norway 61º 17' 49.435'' N 04º 41' 46.618'' E 29500 250 Priority 7499 0

GRI 9007, Ejde Chain

Designator Station name Latitude Longitude ED Power Blanking Nominal ECD

M Ejde, Faroe Islands 62º 17' 59.837' N 07º 04' 26.079'' W 0 400 Not dual rated 0

W Jan Mayen, Norway 70º 54' 51.478'' N 08º 43' 56.525'' W 14200 250 Priority 9007 0

X Bø, Norway 68º 38' 06.216'' N 14º 27' 47.350'' E 28000 400 Priority 9007 0

Y Værlandet, Norway 61º 17' 49.435'' N 04º 41' 46.618'' E 41100 250 Priority 7499 0

Z Loophead, Ireland 52º 35' 01.576'' N¹ 09º 49' 07.969'' W¹ 55700 250 Priority 9007 +0,5

Loran

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Loran

Eine Loran-C Chain

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Coverage

Landmarks Recognition of landmarks Artifical marks

Strips on the street Strips on the street Skyline

Light houses

RFID tags

Natural Valleys

Rivers Rivers

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Where are we?

Examples

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VOR (VHF Omni Range)

Tire sensors

Quelle: Renate Czommer

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Tire sensors

Quelle: Renate Czommer

DOP DOP over time

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Sensor fusion

RFID

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RFID Passive Tags

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RFID Active Tag (Backscatter)

RFID Miniatures

American banknotes bear the motto "In God we trust".

The National Security Agency added:"All Others, we monitor".

Quelle:The EconomistQuelle:The Economist