real-time precise point positioning utilising the japanese quasi-zenith satellite system (qzss) lex...

Real-Time Precise Point Positioning Utilising the Japanese Quasi-Zenith Satellite System (QZSS) LEX Corrections

Suelynn Choy1, Ken Harima1, Shaocheng Zhang1, Yong Li2,

Yaka Wakabayashi3, Hiroaki Teteshita3, Satoshi Kogure3, and

Chris Rizos2

1School of Mathematical and Geospatial Sciences, RMIT University, Australia2School of Civil and Environmental Engineering, University of New South Wales, Australia3Satellite Navigation Office, Space Applications Mission Directorate I, Japan Aerospace Exploration Agency, Japan

Outline

• Overview of the Japanese Quasi-Zenith Satellite System (QZSS)

• Introduction to the QZSS LEX signal

• CRCSI-JAXA Project

–Utilisation of LEX signal for Precise Point Positioning (PPP)

–Post-processed LEX-PPP experiment

–Real-time LEX-PPP experiment

• Future work

RMIT University PPP Workshop 2013, Ottawa 2

Note: LEX – L-band EXperimental

CRCSI – Cooperative Research Centre for Spatial Information

JAXA – Japan Aerospace Exploration Agency

Introduction to QZSS


Quasi-Zenith Satellite System (QZSS)

The Quasi-Zenith Satellite System (QZSS) developed by Japan Aerospace Exploration Agency (JAXA) is a regional navigation satellite system, which uses a constellation of satellites placed in highly-inclined elliptical orbits. This is to ensure that one of the satellites is always visible near zenith over Japan, including in urban and mountainous areas whereby it is difficult to receive GNSS signals.

Multiple satellites on the quasi-zenith orbits ©JAXA Asymmetry orbit in the shape of a ‘figure 8’ ©JAXA

4RMIT University PPP Workshop 2013, Ottawa

Overview of QZSS

• Functional Capability:– GNSS complementary

– Improve availability

– Improve accuracy

• Coverage: – East Asia and Oceania

• Signals:– L1C/A, L1C, L2C and L5 positioning

– L1-SAIF on 1575.42 MHz

– LEX on 1278.75MHz

• First QZSS Satellite ‘Michibiki’:– Launched in September 2010

• Future QZSS Satellites:– 2 HEO and 1 GEO

– End of March 2018

The first QZSS satellite ‘Michibiki’ ©JAXA

QZSS improves positioning accuracy ©JAXA

augmentation


Coverage Area (1 QZSS Satellite)


(JAXA, 2012)

Coverage Area (3 QZSS Satellites)


(JAXA, 2012)

Introduction to LEX Signal


QZSS LEX Signal

• QZSS Signals:– GPS compatible signal for positioning : L1C/A, L1C, L2C and L5

– GPS augmentation: L1-SAIF and LEX

• LEX (L-band EXperimental) Signal:– For experimental purposes

– Frequency: 1278.75 MHz (similar to Galileo E6)

– Message rate: 2 Kbps

– For high accuracy (cm-level) positioning applications experiment, e.g. Precise Point Positioning (PPP)

9

Note: SAIF – Submetre-class Augmentation with Integrity Function

RMIT University PPP Workshop 2013, Ottawa

QZSS LEX Signal Specifications


Item Specification

Frequency 1278.75MHz (Galileo E6)

Bandwidth 42.0MHz

Signal Power -155.7dBW (Min)

Modulation Kasami-sequences, BPSK(5), short-code/long-code

Spreading Code

Short Period: 4ms, Length: 10,230 chips

Long Period: 410ms, Length: 1,048,575 chips

Navigation DataShort-code: 2000 bits/frame, 1 frame/sLong-code: data-less

LEX Message Structure


Message Type Definition


Message Type Content Notes

0-9 Spare (System use)

10-19 10 Signal health (35 satellites)Ephemeris & SV clock (3 satellites)

For JAXA experiment

11 Signal health (35 satellites)Ephemeris & SV clock (2 satellites)Ionospheric correction

12~19 Spare

20 For experiment by GSI

21~155 For experiment For experimental users except JAXA and GSI and users of application demonstration in private sector

156-255 For application demonstration in private sector

For experimental users of application demonstration in private sector by means of performance enhancement signal

Note: JAXA – Japan Aerospace Exploration Agency GSI – Geographical Survey Institute of Japan

JAXA-LEX Message Interval (Nominal)

Message Data Broadcast Update Effective Period

Signal health 1 second 1 second -

Ephemeris 12 seconds 3 minutes 6 minutes

SV clock 12 seconds 3 minutes 6 minutes

Ionospheric correction 12 seconds 30 minutes -


Joint CRCSI-JAXA LEX Project


Note: CRCSI – Cooperative Research Centre for Spatial Information

JAXA – Japan Aerospace Exploration Agency

Australian Government Positioning Policy

• In 2012, the Australian Government developed a National Satellite Utilisation Policy (Australia’s first ever space policy)

– National Earth Observation from Space Strategic Infrastructure Plan

– National Positioning Infrastructure (NPI) Plan

• In April 2013, the policy was launched and released

– providing certainty and strategic direction for Australian users of satellite technology

• Australian NPI Vision

Instantaneous, reliable and fit-for-purpose positioning and timing services anywhere, anytime across the Australian landscape and its maritime jurisdictions


Australian GNSS CORS Infrastructure


(Hausler, 2013)

Motivation: CRCSI – JAXA LEX Project

• Aim:– Evaluate the feasibility of using the QZSS LEX signal

– to provide a high accuracy real-time positioning service to GNSS users in Australia

– in support of the Australian National Positioning Infrastructure (NPI) plan

• Uniqueness:– Opportunity to experiment with QZSS LEX signal

– Better acquisition and coverage of the augmentation information– nationwide high accuracy positioning

– Robust and effective data transmission capacity– e.g. lower bandwidth than the current NRTK

– Reduced reliance on local CORS infrastructure – not constrained by baseline length and CORS coverage

– An alternative data communication infrastructure– not restricted by land-based communication technologies e.g. 3G mobile coverage


Evaluation of LEX Messages


Quality of JAXA-LEX GPS Orbits and Clocks (Regional)


One week: 1 to 7 January 2013

Site: Alice Spring (IGS – ALIC)


23 Australian GNSS Stations; 1 January 2013; 30s

Distribution of Test Sites in Australia

Longitude


Po

sit

ion

Err

or

(m)

JAXA-LEX PPP Position Errors (Post-processed)

Real-time LEX PPP Experiment

• First LEX field experiment in Australia

– RMIT, Melbourne

• 8 – 10 March 2013

• LEX Message Type 10 and 11

– GPS-only

• Series of static and kinematic PPP tests



Availability of LEX Message

Quality of the JAXA-LEX Orbits and Clocks (Bundoora)


RMS X/Y/Z/CLK: 37.4, 33.3, 35.0 cm / 2.3 ns

Kinematic LEX-PPP Real-Time


JAVAD Delta, 08/03/2013 – 09/03/2013, 1 Hz, LEX MT 10 and 11

East

North

Up

RMS E/N/U: 44.1, 35.1, 71.7 cm

Static LEX-PPP Real-Time


JAVAD Delta, 09/03/2013 –10/03/2013, 1 Hz, LEX MT 10 and 11

East

North

Up

RMS E/N/U: 23.9, 7.4, 11.1 cm

Static IGS-PPP Real-Time


JAVAD Delta, 09/03/2013 – 10/03/2013, 1 Hz, products.igs-ip.net:2101(mountpoint:CLK11)

East

North

Up

RMS E/N/U: 3.5, 2.4, 5.4 cm

On-going Work

• Evaluation of the “new” Message Type 12

– Since April 2013, JAXA has started to transmit MADOCA products

– RTCM SSR format

• Evaluation of the IGS real-time service products and the Australian regional products

• Development of an “Australian LEX”

– Correction messages and “packaging”

– Processing algorithm and software

– LEX receivers

Note: MADOCA – Multi-GNSS Advanced Demonstration tool for Orbit-and-Clock Analysis


Acknowledgements

• RMIT University, Australia

• University of New South Wales, Australia

• Department of Sustainability and Environment, Victoria, Australia

• Land and Property Information, New South Wales, Australia

• Geoscience Australia, Australia

• Japan Aerospace Exploration Agency, Japan

• Cooperative Research Centre for Spatial Information, Australia


Thank you!

real-time precise point positioning utilising the japanese quasi-zenith satellite system (qzss) lex...

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