Precision for all: GNSS Global High Precision and Integrity
Transcript of Precision for all: GNSS Global High Precision and Integrity
Sogei S.p.A. - Sede Legale Via M. Carucci n. 99 - 00143 Roma
Precision for all: GNSS Global High Precision and
Integrity IGAW 2017
DO-11-DO-03 - Pubblic 1
20 June 2017 R. Capua
Sogei S.p.A. - Sede Legale Via M. Carucci n. 99 - 00143 Roma
Agenda
• State of the Art of High Precision GNSS Systems
• Local Augmentation: Network-RTK
• Regional and Global High Precision Systems: PPP
• High Precision and Integrity
• Standardization Status
• A Vision of the future
• Conclusions and Recommendations
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High Precision and Integrity: the needs
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Accuracy Availability Integrity Continuity
Aviation ++
(depending on flight
phases en-
route/approach)
+++ +++/++++
(depending on
flight phases, e.g.
CATI-CAT III)
+++
Rail ++
(depending on the
operation phase)
++
(integration with
odometers)
++++
(at system level)
++++
(at system level)
Automotive +++
(aided by INS)
+++ ++++
(Keep attention
to Driverless
cars)
++++
Geodesy/Surveying
+++++ ++++ ++
(costs for lost
surveying)
++
Maritime ++
(depending on
navigation mode
en-route/approach)
+++ +++ +++
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Hype Cycle for the Automotive Sector
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Electrification: hybrid-electric, electric, and fuel-cell technologies as they mature and become cheaper Autonomous driving: from advanced driver-assistance systems to fully autonomous driving Mobility: autonomous vehicles rentals and car sharing Connectivity: new traffic services, new business models and services for connected vehicles (V2V, V2I)
Source: Gartner Hype Cycle for Smart Machines 2016
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Connected Vehicles and Autonomous Driving
• Challenging environments and Local Effects
• High Availability and Safety
• High Precision
• Multisensor fusion
• Push for istantaneous accuracy and integrity
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Single to
Multi-
frequency
PPP Multisensor
fusion
V2V
High
Precision
Mapping
High
Precision/
High
Integrity
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Notes on High Precision Augmentation Infrastructures
• “The biggest question mark today is not cost-related, but instead how
to achieve reliable, worldwide satellite navigation coverage to
support correction techniques, such as real time kinematic, or
RTK, and precise point positioning, or PPP. This is an extremely
expensive undertaking, with currently no guarantee of a return on
investment”
• “Google recently announced it will make GPS pseudoranges
available to developers, which, although extremely nascent, could
open up the door for a lot of innovation. And in China, Alibaba is a
major partner in the roll-out of Continuous Operating Reference
Stations, or CORS, networks in the region”
[Source ABI Research]
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Basic Model
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Ptropionorb ddddTdtcP )(
Pseudorange
NddddTdtc tropionorb)(
Phase
300Km
19 cm
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Frequency Combinations Selection
• Widelane: Easier fixing, but noisier
• Iono-free: free from ionospheric error, remaining real numbers ambiguities
(float): to be chosen for high ionospheric conditions and long baselines
• For RTK/NRTK positioning, the following frequency selection are preferred:
Close Reference Station: use Narrowlane
Medium baselines: use L1
Medium/Long baseline: use WL
Long baselines: use IF
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Frequency
Combination
m n Wavelength
(m)
Mutipath Noise
(wrt L1)
Widelane (WL) 1 -1 0.8619 6.405
Narrowlane (NL) 1 1 0.107 0.795
Ionofree (IF) 0.0063 2.97
21, LLnm nm
)/( 2
2
2
1
2
1 fff )/( 2
2
2
1
2
2 fff
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Network-RTK
• Differenced Measurements (Rover Receiver-Reference Receiver)
• VRS, FKP, MAC, SSR modes
• Reduced Local Reference Stations Networks (70 Km interdistance)
• Single Error Interpolation (e.g. Ionosphere)
• Network Ambiguity Resolution
• Observation Space Representation, State Space Representation
• Time To Fix Ambiguities: 30s-3 min (@baseline)
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Wide-Lane Ambiguities
Iono-Free Ambiguities
Network Ambiguities
Network Processing
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Network-RTK estimation Approach (VRS or State Space Representation)
• Area Corrections Parameters (e.g. FKP)
• State Space Representation: estimation of single errors
• Atmospheric Error Interpolation (e.g. Collocation, Kriging, etc..)
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VRS
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Ionospheric delay Estimation
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Precise Point Positioning (PPP)
• Precise Positioning using a Single Receiver (undifferenced)
• Real-Time Precise Orbits and Clocks from Augmentation Service Providers
and sparse Regional/Global Networks
• First-Order Ionospheric Error Estimation (e.g. Dual-Frequency receivers)
• ZTD to be estimated
• Other errors to be modelled in undifferenced mode: Phase-windup, Ocean
loading and Earth tides, relativistic effects, Sagnac effect
• Convergence to 10 cm in 10-40 min (no Ambiguity Fix)
• The challenge: Real-Time Ambiguity Fix and cm level positioning
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CPF
Precise Orbits and Clocks
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Precise Point Positioning (PPP): basic formulation and Ambiguity Fixing
• Undifferenced High Precision System
• Based on Ionofree observables
• Ambiguity Fixing Methods;
Fractional Cycle Biases (FCB)
Decoupled Clock Model (DCM)
Integer Phase Clock
12
'
2
2
2
1
2
2
21
2
1
2
2
2
1
2
2
21
2
1
)(
)(
IFIFtropLL
IF
PtropLL
IF
NdddTdtcff
ff
dddTdtcff
PfPfP
)()( 00
' ttNN s
IF
r
IFIFIF
Receiver and Satellite Uncalibrated Fractional Biases Real Numbers!
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Network-RTK to PPP comparison
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Network-RTK PPP
Convergence Time Short TTFA
Ambiguity Fixing
Long TTFA
Ambiguity Fixing
Number of RSs Quite Dense
Networks: High
Development Costs
(<70 Km baseline)
Sparse Networks
(500-1000 Km
baseline)
Maintenance and
Operational Costs
High Medium/Low
Geographic
Distribution
Local Effects taken
into account (Local
Modelling)
Local Effects not
taken into account
(Global Modelling)
Coordinate
Reference
Framework
Datum differences
among overlapping
networks and
handover
National/Local
Datum not fixed
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High Precision Systems Classification
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Network-RTK
Observation Space Representation
(OSR)
State Space Representation
(SSR)
Observation Corrections
FKP VRS MAC
User Interpolation
User Interpolation
Single Station Nearest
PPP
Single Errors Estimation
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The IGS-RTS Service
Type Accuracy Latency
Broadcast
orbits ~100 cm
real-time Sat. clocks
~5 ns RMS
~2.5 ns SDev
Ultra-Rapid
(predicted half)
orbits ~5 cm
real-time Sat. clocks
~3 ns RMS
~1.5 ns SDev
Ultra-Rapid
(observed half)
orbits ~3 cm
3 - 9
hours Sat. clocks ~150 ps RMS
~50 ps SDev
Rapid
orbits ~2.5 cm
17 - 41
hours Sat. & Stn.
clocks
~75 ps RMS
~25 ps SDev
Final
orbits ~2.5 cm 12 - 18
days Sat. & Stn.
clocks
~75 ps RMS
~20 ps SDev
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Worldwide
Reference Station
Network
• More than 200 GNSS Reference Stations Worldwide
• 5 Regional and 3 Global Data Centers • Standard NTRIP/RTCM Data Broadcasting
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GNSS Augmentation Systems
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And then..? 20 June 2017 DO-11-DO-03 - Pubblic
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Augmentation Networks Implementation Constraints
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Reference Stations Costs
Maintenance and Operations
Costs
Integrity
Monitoring
RSN
Replenishement Obsolescence Firmware Upgrade
Coverage Area
Remote RS Failures recovery CPF Software Licencing
Certification costs (RSs and CPF)
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PPP Triple Frequency and Multicontellation Solution
Frequency GPS Galileo Beidou
GA L1 E1 B1
GB L2 E5a B3
GC L5 E5b B2
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Frequency GPS
wavelength (m)
Galileo
wavelength (m)
Beidou
wavelength (m)
MW Extra-
widelane
(GB,GC)
5.86 9.76 4.88
MW Extra-
widelane
(GA,GB)
0.86 0.75 1.02
MW Extra-
widelane
(GA,GC)
0.75 0.71 0.85
Widelane only
Iono-Free
3.40 3.21 4.52
TCAR istantaneous fixing PPP convergence time reduction
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Accurate Ionospheric Estimation for PPP
• Very Accurate Ionospheric Estimation needed (<1 TECU) for PPP Real-Time
positioning and long time for decorrelating pseudoranges from biases
• Estimation based on:
Carrier-Levelling (estimation of Code-to-Carrier biases through averaging)
Global Ionospheric Tomography
Local Models
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STEC in presence of a Geomagnetic storm
Multi-Layer Model
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Impact of Ionosphere on PPP Performances
• Global Ionospheric Map (GIM) TEC Estimation applied to PPP solution
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Causes of GNSS Faults
• GNSS System Faults
Ephemeris
Clock
• Propagation Environment
Ionosphere anomaly and storms
Troposphere errors
• Local Effects
Multipath
Receiver Hardware Faults
Unintentional Interferences
Intentional Interferences (Jamming/Spoofing)
• Augmentation System Faults
Single and Multiple Reference Receivers Faults
Control Centre Software Faults
Interferences close to RR
Communication losses
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Integrity States
• Misleading Information (MI): the true navigation error exceeds a
Protection Level (PE>PL)
• Hazardous Misleading Information (HMI): the true navigation error exceed
an Alert Limit, no timely warning provided (PE>AL & PL<AL)
• Integrity Risk: probability of HMIs during a predefined operational time
int.: e.g. 10-7/150 s for the Aviation Precision Approach
• RTK Ambiguity Resolution Risk: Probability that uncorrect Ambiguities are
fixed while validated as correct by the receiver
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x
y
PE
AL PL Error overbounding
Misleading Information (PL<PE)
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Stanford Plot
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Fault without Alert!
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PPP Integrity
• CRAIM (Carrier Phase Receiver Autonomous Integrity Monitoring)
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PPP corrections
(precise eph, clock,
iono corrections)
Iono-Free
Combination
PPP
KF algorithm
AR
PL1
Innovation
vector
Test
statistics
Failure
Detection
PL>AL
LIF, PIF,
LW-PN,L1
Integrity
Position PL2
P L
Source: Integrity Monitoring for Carrier Phase Ambiguities, Feng, Ochieng, Samson, Tossaint, Hernandez-Pajares, Miguel Juan, Sanz, Aragon-Angel, Ramos-Bosch, Jofre, The Journal of Navigation (2012)
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Single-Frequency COTS Low Cost RTK Receivers
• Hardware Receivers:
Low-Cost, Single-Frequency RTK needed for existing and
emerging applications: Surveying, Robotics, UAV
Multiconstellation, single frequency receivers, RTCM input,
Time To Fix Ambiguities in the order of a few minutes with:
- Short baselines (Physical or VRS Stations)
- Medium-High number of visible satellites (7-9)
Clear Roadmap toward dual-frequency
• SDR (Software Dedined Radio) Receivers:
Full SDR: able to perform RTK through generation and processing of Raw
measurement on a PC or a Tablet (e.g. «A Totally SDR Single-Frequency
Augmentation Infrastructure for RTK Land Surveying: Development and Test»,
Sogei ION GNSS 2016 paper)
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High Precision for all
• Google announced raw GNSS measurements output from
smartphones and tablets running Android N
• Smartphones Processing problems:
Nonzero and drifting bias in the carrier-phase measurements
High Pseudorange noise (tens of meters)
Carrier Phase affected by frequent outliers
• 1 meter-level positioning
• GNSS antenna uses linear polarization: susceptible to
multipath (10 dB-Hz lower than geodetic receivers)
• PCV not available for smartphones antennas
• Duty cycle to be disabled for allowing continuous Phase
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High Precision on Smarthphones: where are we?
• PPP experiment in literature:
Carrier-Phase processing
Precise satellite clock and orbits
Global Ionospheric Maps
Relativistic effects, Earth tides modelling
Ionospheric Delay estimation from nearby
Reference Stations
• Current Limitations:
Battery life: duty cycling to be disabled or snapshot solutions developed
Pseudoranges measurement noise affects Ambiguity Fixing time
Smarthphone Antenna quality, polarization and low multipath rejection lead to high
measurement noise
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Source GPS World Banville, Diggelen, 2016
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The Local-Global Dilemma for PPP Ambiguity Fix
• PPP Solution based on sparse Reference Station Networks
• but …
• PPP-Ambiguity Resolution needs tigth Local Effects estimation (e.g.
ionospheric delay)
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PPP-Float
Sparse Network
PPP-Ambiguity
Resolution
Local Effects not
properly modelled
Close RS constraint
Leading to Network-
RTK
Global Local
? 20 June 2017 DO-11-DO-03 - Pubblic
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Regional Augmentation Network and PPP
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• A Unique Regional Federated Augmentation Network for all High Precision
applications is needed with Cost Sharing advantages
• Augmentation messages broadcasting through Galileo Commercial Services
• A possible Architecture for future HP services can be based on:
PPP Regional Services: Backbone of Hardware Receivers (including EDAS RIMS)
Local Services: densification through low cost SDR and Moving platforms
SBAS (EGNOS) and Local Augmentation Integration: 2-tiers (ERSAT, RHINOS)
Spoofing Monitoring
CPF
Densification HW RS
RTCM SSR
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Galileo CS
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A vision of the future
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Local Augmentation
Global Systems High Costs CP/Dual-Frequency
Moore’s Law Economy of Scale Automotive appl.
Single Frequency Low Cost
Low cost Multiple-Frequency
RTK NRTK
Real-Time PPP-AR
High Precision/ Integrity merge SDR
Dual Frequency
PPP
Receiver Costs Augmentation Coverage
time
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The role of Standardization and Regulation
• Regulation on transport can foster the implementation of technologies, e.g.
eCall Regulation 2007/46/EC: «The provision of accurate and reliable
positioning information is an essential element of the effective operation of
the 112-based eCall in-vehicle system. Therefore, it is appropriate to require
its compatibility with the services provided by the Galileo and European
Geostationary Navigation Overlay Service (EGNOS) programmes as set out
in Regulation (EU) No 1285/2013 of the European Parliament and of the
Council»
• High Precision Systems and PPP requires standardization: RTCM SSR
Working Group
• High Precision and High Integrity Standardization and Certification:
Aviation: RTCA Do-229 and Do-245
Rail: similar path for ERTMS
RTCM: WG «Integrity Monitoring for High Precision Applicarions»
Cross Standardization Working Group (RTCM, RTCA, SAE, etc..) for defining a
common High Precision and High Integrity standard among all applications
31 20 June 2017 DO-11-DO-03 - Pubblic
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Conclusions and Recommendations
• Current Dense Local Augmentation Network are expensive (Receiver costs
and obsolescence, firmware updates, maintenance, certification costs)
• Transport applications will boost High Precision and High Integrity
positioning at low cost (e.g. self-driving cars and taxing)
• Economy of Scale reducing Multi-frequency receivers costs
• High Precision Positioning Systems are moving toward Regional Scale
Augmentation Sparse Networks – PPP (Precise Point Positioning)
• High Integrity of positioning needed for Rail, Aviation and Automotive
• Unique Federated Network with cost sharing among applications and
integration with EGNOS/EDAS (ERSAT-EAV and RHINOS)
• Software Receivers and loe cost receivers to be used for densification
• Local Augmentation Networks can be used for Spoofing Monitoring
• Cross Standardization Working Group for High Precision and High Integrity
applications
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Thanks for the attention
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