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


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

20 June 2017 2 DO-11-DO-03 - Pubblic


High Precision and Integrity: the needs

3

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)

+++ +++ +++

20 June 2017 DO-11-DO-03 - Pubblic


Hype Cycle for the Automotive Sector

4 20 June 2017 DO-11-DO-03 - Pubblic

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


Connected Vehicles and Autonomous Driving

• Challenging environments and Local Effects

• High Availability and Safety

• High Precision

• Multisensor fusion

• Push for istantaneous accuracy and integrity

5

Single to

Multi-

frequency

PPP Multisensor

fusion

V2V

High

Precision

Mapping

High

Precision/

High

Integrity



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]



Basic Model

7

Ptropionorb ddddTdtcP )(

Pseudorange

NddddTdtc tropionorb)(

Phase

300Km

19 cm



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

8

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



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)

9

Wide-Lane Ambiguities

Iono-Free Ambiguities

Network Ambiguities

Network Processing



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..)

10

VRS


Ionospheric delay Estimation


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

11

CPF

Precise Orbits and Clocks



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!



Network-RTK to PPP comparison

13

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



High Precision Systems Classification

14

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



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

15

Worldwide

Reference Station

Network

• More than 200 GNSS Reference Stations Worldwide

• 5 Regional and 3 Global Data Centers • Standard NTRIP/RTCM Data Broadcasting



GNSS Augmentation Systems

16

And then..? 20 June 2017 DO-11-DO-03 - Pubblic


Augmentation Networks Implementation Constraints

17

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)



PPP Triple Frequency and Multicontellation Solution

Frequency GPS Galileo Beidou

GA L1 E1 B1

GB L2 E5a B3

GC L5 E5b B2

18

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



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

19

STEC in presence of a Geomagnetic storm

Multi-Layer Model



Impact of Ionosphere on PPP Performances

• Global Ionospheric Map (GIM) TEC Estimation applied to PPP solution



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



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

22

x

y

PE

AL PL Error overbounding

Misleading Information (PL<PE)



Stanford Plot

23

Fault without Alert!



PPP Integrity

• CRAIM (Carrier Phase Receiver Autonomous Integrity Monitoring)

24

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)



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)

25



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



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

27

Source GPS World Banville, Diggelen, 2016



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)

28

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


Regional Augmentation Network and PPP

29

• 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


Galileo CS


A vision of the future

30

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



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



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



Thanks for the attention


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Precision for all: GNSS Global High Precision and Integrity

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