1. 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, Australia
2School of Civil and Environmental Engineering, University of New South Wales, Australia
3Satellite Navigation Office, Space Applications Mission Directorate I, Japan Aerospace Exploration Agency, Japan

2. 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
Note: LEX – L-band EXperimental
CRCSI – Cooperative Research Centre for Spatial Information
JAXA – Japan Aerospace Exploration Agency
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3. Introduction to QZSS
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4. 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.
MICHIBIKI means “Guiding” or “Showing the way”
Multiple satellites on the quasi-zenith orbits ©JAXA
Asymmetry orbit in the shape of a ‘figure 8’ ©JAXA
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5. Overview of QZSS Functional Capability: Coverage: Signals:
GNSS complementary
Improve availability
Improve accuracy
Coverage:
East Asia and Oceania
Signals:
L1C/A, L1C, L2C and L positioning
L1-SAIF on MHz
LEX on MHz
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
augmentation
– First phase JAXA-LEX PPP accuracy < 30 cm (H-RMS)
- Note: SAIF – Submetre-class Augmentation with Integrity Function
QZSS improves positioning accuracy ©JAXA
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6. Coverage Area (1 QZSS Satellite)
Percentage of Time during which a Single QZS can be seen at an Elevation Angle of 10° or more
(JAXA, 2012)
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7. Coverage Area (3 QZSS Satellites)
Percentage of Time during which at least One QZS in the 3-satellite QZSS constellation can be seen at an Elevation Angle of 10° or more
(JAXA, 2012)
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8. Introduction to LEX Signal
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9. QZSS LEX Signal QZSS Signals: LEX (L-band EXperimental) Signal:
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: MHz (similar to Galileo E6)
Message rate: 2 Kbps
For high accuracy (cm-level) positioning applications experiment, e.g. Precise Point Positioning (PPP)
LEX (L-band experiment) is a unique signal from "MICHIBIKI". The objectives of LEX signal are to enhance the performance of GPS(realizing improved precision) and to establish the next generation's positioning based technology.
Note: SAIF – Submetre-class Augmentation with Integrity Function
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PPP Workshop 2013, Ottawa

10. QZSS LEX Signal Specifications
Item
Specification
Frequency
MHz (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 Data
Short-code: 2000 bits/frame, 1 frame/s
Long-code: data-less
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11. LEX Message Structure
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12. Message Type Definition
Content
Notes
0-9
Spare (System use)
10-19 10
Signal health (35 satellites)
Ephemeris & SV clock (3 satellites)
For JAXA experiment 11
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
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
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13. JAXA-LEX Message Interval (Nominal)
Message Data
Broadcast
Update
Effective Period
Signal health
1 second -
Ephemeris
12 seconds
3 minutes
6 minutes
SV clock
Ionospheric correction
30 minutes
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14. Joint CRCSI-JAXA LEX Project
Note: CRCSI – Cooperative Research Centre for Spatial Information
JAXA – Japan Aerospace Exploration Agency
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15. 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
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16. Australian GNSS CORS Infrastructure
(Hausler, 2013)
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17. 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
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18. Evaluation of LEX Messages
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19. Quality of JAXA-LEX GPS Orbits and Clocks (Regional)
One week: 1 to 7 January 2013 Site: Alice Spring (IGS – ALIC)
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20. Distribution of Test Sites in Australia
23 Australian GNSS Stations; 1 January 2013; 30s
Longitude
23 Australian Continuously Operating Reference Stations (CORS) on 1 January 2013 were post-processed and analysed.
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21. JAXA-LEX PPP Position Errors (Post-processed)
Position Error (m)
The PPP accuracy in the horizontal and up directions is about ~0.3 m and ~0.6 m, respectively. The 3D precision of the estimated LEX-PPP solutions are sub-metre level.
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22. 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
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23. Availability of LEX Message
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24. Quality of the JAXA-LEX Orbits and Clocks (Bundoora)
RMS X/Y/Z/CLK: 37.4, 33.3, 35.0 cm / 2.3 ns
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25. Kinematic LEX-PPP Real-Time
JAVAD Delta, 08/03/2013 – 09/03/2013, 1 Hz, LEX MT 10 and 11
East
North
Statistical computation, ignoring the first hour, using data collected from the experiment. Plot only shows daily 24 hour time series. Up
RMS E/N/U: 44.1, 35.1, 71.7 cm
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26. Static LEX-PPP Real-Time
JAVAD Delta, 09/03/2013 –10/03/2013, 1 Hz, LEX MT 10 and 11
East
North
Statistical computation, ignoring the first hour, but using data collected from the experiment. Plot only shows daily 24 hour time series.
STD E/N/U: 16.7, 4.8, 5.1 cm Up
RMS E/N/U: 23.9, 7.4, 11.1 cm
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27. Static IGS-PPP Real-Time
JAVAD Delta, 09/03/2013 – 10/03/2013, 1 Hz, products.igs-ip.net:2101(mountpoint:CLK11)
East
North
Ignoring the first one hour of solutions.
CLK11: APC; GPS GLO; 1059,1060,1065,1066; CODE Ultra Rapid; ITRF2008; BKG RTNet + BNC Up
RMS E/N/U: 3.5, 2.4, 5.4 cm
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28. 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
RMIT University
PPP Workshop 2013, Ottawa

29. Thank you! 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!
RMIT University
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