Real-Time PPP using open CORS Networks and RTCM · PDF fileReal-Time PPP using open CORS Networks and RTCM Standards Andrea Stu¨rze 1 Leos Mervart 2 Wolfgang Sohne 1 Georg Weber 1

Real-Time PPP using open CORS Networks andRTCM Standards

Andrea Sturze 1 Leos Mervart 2 Wolfgang Sohne 1

Georg Weber 1 Gerhard Wubbena 3

1Federal Agency for Cartography and Geodesy, Frankfurt, Germany

2Geodetic Institute Czech Technical University, Prague

3Geo++ GmbH Garbsen, Germany

March 27, 2012

Outline

1 IntroductionObservation Space Representation (OSR)State Space Representation (SSR)

2 StandardizationRTCM in generalStatus and plans regarding RTCM-SSR messages

3 RealizationIGS Real-Time InfrastructureBKG example

4 Summary

MCG 2012 (Stuttgart) Real-Time PPP March 2012 2 / 23

Introduction: GNSS Error Components

Precise GNSS positioning requires the knowledge of all error componentswith corresponding accuracy

How this information can be provided in real-time?


Introduction: Observation Space Representation (I)

Sum of GNSS errors per station, GNSS,frequency and signal

Distance dependent errors are derived from and combined withreference station observations

Technique used with current RTCM standards (VRS, MAC, FKP)RTK networking:

- RTK service uses network of reference stations- RTK rover uses reference station observations and RTK corrections


Introduction: Observation Space Representation (II)

Disadvantages:

only satellites and signals tracked within the RTK network are usable

no reduction of reference station dependent errors

update rate of the corrections depends on component with highestdynamics (satellite clock, ionosphere)

limited spatial validity of corrections


Introduction: State Space Representation (I)

Transmission of individual GNSS error components

functional and optional stochastic state description

Precise Point Positioning (PPP):- observations of single GNSS receiver- global or regional real-time network- rover uses state space information (e.g. IGS products)


Introduction: State Space Representation (II)

Advantages:

high reduction of reference station dependent errors through highredundancy within the network

independent from single reference stations

more realistic physical models for individual errors enables bettermodelling and interpolation

update rate can be optimized for different state parameters

Scalability of accuracy and hence of the derived services

Broadcasting of parameters possible

Disadvantages:

higher standardization effort

higher implementation effort


Standardization: RTCM

Radio Technical Commission for Maritime Services

Development of international open standards

RTCM SC-104: DGNSS Standards- Working Groups examples regarding

o communication and data transfer: WG Internet Protocol (NTRIP)o modelling: WG RTK network MSG, WG State Spaceo GNSS: WG Galileo, WG GLONASSo multi constellation concepts: WG Version 3

WG State Space

- since 2007- RTCM-SSR messages


Standardization: RTCM-SSR messages

1 precise orbits, satellite clocks and code biases, quality indicator- Real-Time PPP for dual frequency users- compatible to basic PPP mode using IGS products- RTCM recommended Standard since May 2011, included in RTCM 3

2 vertical Total Electron Content (VTEC) and satellite phase biases- Real-Time PPP for single frequency users

3 Slant Total Electron Content (STEC) and troposphere- enable PPP-RTK


Standardization: RTCM-SSR - messages Step 1

1057 SSR GPS orbit correction

1058 SSR GPS clock correction

1059 SSR GPS code bias

1060 SSR GPS combined orbit and clock correction

1061 SSR GPS User Range Accuracy (URA),

1062 SSR GPS high rate clock correction

1063 SSR GLONASS orbit correction

1064 SSR GLONASS clock correction

1065 SSR GLONASS code bias

1066 SSR GLONASS combined orbit and clock correction

1067 SSR GLONASS User Range Accuracy (URA)

1068 SSR GLONASS high rate clock correction


Standardization: RTCM-SSR - Satellite Orbit (I)

Orbit corrections refer to broadcast orbits

reduces bandwidth

XOrbit = XBroadcast − δX

XBroadcast .. satellite position corrected by SSR orbit correction messageXOrbit .. satellite position computed according GNSS ICD

from broadcast parameter set identified by IOD/IODEin SSR correction message

δX .. satellite position correction


Standardization: RTCM-SSR - Satellite Orbit (II)

Orbit corrections defined radial, along-track and cross-track

ealong =r∣∣r∣∣ ecross =

r × r∣∣r × r∣∣ eradial = ealong × ecross

δX =[eradial ealong ecross

]δO

r = X .. satellite broadcast position vector

r = X .. satellite broadcast velocity vectorei .. direction unit vector, i = {radial , along , cross}δO .. orbit correction vector

Orbit corrections consists of correction and velocity correction term

δO =

δOradial

δOalong

δOcross

+

δOradial

δOalong

δOcross

(t − t0)

δOi , δOi .. orbit correction terms from SSR orbit message,i = {radial , along , cross}

t, t0 .. time, reference time obtained from SSR orbit messageMCG 2012 (Stuttgart) Real-Time PPP March 2012 12 / 23

Standardization: RTCM-SSR - Satellite Clock (I)

Clock corrections refer to broadcast clocks

clock correction terms: C0,C1,C2 polynomial coefficientsreduces bandwidth

tSatellite = tBroadcast −δC

c0

tBroadcast .. satellite time computed according to GNSS ICDfrom broadcast clock parameters, identified by IOD/IODEof corresponding SSR orbit correction message

tSatellite .. satellite time corrected by SSR clock correction messageδC .. clock correction obtained from SSR clock correction message

δC = C0 + C1(t − t0) + C2(t − t0)2

Ci .. polynomial coefficients from SSR clock correction message,i = {0, 1, 2}

t .. timet0 .. reference time obtained from SSR clock correction message


Standardization: RTCM-SSR - Satellite Clock (II)

High rate clock

additional and optional message type

both, polynomial and high rate clock describes the complete clockstate

enables higher resolution and update rates

Satellite code bias

absolute correction term

for every signal and tracking mode

enables higher resolution update rates


Standardization - RTCM-SSR: Consistency

Basic concept:

SSR messages support different update rates, accuracy requirementsadditional SSR message types adds additional resolution and thereforeposition accuracy

SSR update interval and GNSS epoch time:

define changes of parameters and ensure consistency of dataprocessingMCG 2012 (Stuttgart) Real-Time PPP March 2012 15 / 23

Realization: RTCM-SSR - IGS Real-Time Infrastructure

IGS (International GNSS Service)

voluntary federation of more than 200 worldwide agencies

pool of resources and permanent GPS and GLONASS station data

generate precise GPS and GLONASS products

IGS real-time infrastructure

IGS Real-Time Pilot Project (IGS RT PP) from 2007-2011

- development (RTCM member) and investigation of standards andformats for real-time data and product dissemination

- maintaining a global GNSS real-time tracking network- generation of real-time products

10 participating Analysis Centres (ACs)

AC Coordinator: ESOC (European Space Operations Centre)

Ambiguity fixing working group

- studying techniques and formats for PPP ambiguity fixing

Formats and processes are now ready to allow an initial operationalservice



IGS real-time tracking network

station operators provide more than 100 observation data streams

using NTRIP technique



Real-Time PPP performance (North, East, Up displacements)

24h time series of PPP applying RTCM-SSR of different AC’sPPP monitor at http://igs.bkg.bund.de/ntrip/ppp

2D RMS of 4-5 cm after convergenceMCG 2012 (Stuttgart) Real-Time PPP March 2012 18 / 23

Realization: RTCM-SSR - BKG

Support of IGS real-time pilot project and infrastructure

hosting several NTRIP broadcaster for data and productdissemination

- http://igs-ip.net/home (observations)- http://products.igs-ip.net/home (products)

RTCM member: format (SSR) and protocol (NTRIP) development

RT-IGS AC

- providing several RTCM-SSR product data streams- generation of clock combination product based on Kalman Filter

approach

development of RTCM, NTRIP and PPP supporting software

websites regarding NTRIP and PPP monitoring

- http://igs.bkg.bund.de/ntrip- http://igs.bkg.bund.de/ntrip/ppp


Realization: RTCM-SSR - BKG NTRIP Client

BNC Contributors

Concept and coding: CTU, Leos MervartTest, validation, documentation: BKG, Georg Weber and colleaguesRTCM stream encoding and decoding: Alberding GmbH, Dirk Stocker

BNC purposes

multi stream NTRIP clientfeed real-time GNSS enginessynchronization of decoded observations via IP portRTCM steam decoding and encodingsaves RINEX observation and navigation fileshandles and saves RTCM-SSR message content..Precise Point Positioning (PPP)combination of clock correction

Open Source

source code at http://software.rtcm-ntrip.orgintention: push development of open standards for PPP


Realization: RTCM-SSR - BKG NTRIP Client

Real-Time Precise Point Positioning with BNC


Summary and Outlook

SSR status

RTCM-SSR products have been available since 2008

interested users who may want to test these products are able to startwith

- BKG NTRIP client available fromhttp://igs.bkg.bund.de/ntrip/download

- RTCM-SSR data available from http://products.igs-ip.net/home

SSR can replace OSR techniques for all types of GNSS processing

SSR future steps

further standardization effort required

next steps are more complex

next steps add accuracy and therefore applications

Final goal

Open Standard for PPP up to PPP-RTK


Thank you for your attention

[email protected]

http://products.igs-ip.net/home

http://igs.bkg.bund.de/ntrip

http://igs.bkg.bund.de/ntrip/ppp


Documents

Real-Time PPP using open CORS Networks and RTCM · PDF fileReal-Time PPP using open CORS Networks and RTCM Standards Andrea Stu¨rze 1 Leos Mervart 2 Wolfgang Sohne 1 Georg Weber 1