0. GPS/GLONASS/QZSS Multi-GNSS Augmentation Trial by L1-SAIF Signal
5th AOR W/S on GNSS
Hanoi, Vietnam
Dec. 1-3, 2013
GPS/GLONASS/QZSS Multi-GNSS
Augmentation Trial by L1-SAIF Signal
Takeyasu Sakai
Electronic Navigation Research Institute

1. Introduction QZSS (Quasi-Zenith Satellite System) program:
AOR W/S Dec Slide 1
Introduction
QZSS (Quasi-Zenith Satellite System) program:
Regional navigation service broadcast from high-elevation angle by a combination of three satellites on the inclined geosynchronous (quasi-zenith) orbit;
Broadcast GPS-like supplemental signals on three frequencies and two augmentation signals, L1-SAIF and LEX.
L1-SAIF (Submeter-class Augmentation with Integrity Function) signal offers:
Submeter accuracy wide-area differential correction service;
Integrity function for safety of mobile users; and
Ranging function for improving position availability; all on L1 single frequency.
ENRI has been developing L1-SAIF signal and experimental facility:
Signal design: SBAS-like message stream on L1 C/A code (PRN 183);
Possibility of Multi-GNSS augmentation: combined use of GPS and other constellations would improve the availability of position solutions.
Especially where visibility is limited.
Upgraded L1-SAIF experimental facility and conducted a Multi-GNSS trial.

2. QZSS Concept Broadcast signal from high elevation angle;
AOR W/S Dec Slide 2
QZSS Concept
QZS
GPS/GEO
Broadcast signal from high elevation angle;
Applicable to navigation services for mountain area and urban canyon;
Augmentation signal from the zenith could help users to acquire other GPS satellites at any time.
Footprint of QZSS orbit;
Centered at 135E;
Eccentricity 0.075, Inclination 43deg.

3. QZSS L1-SAIF Signal QZSS broadcasts wide-area augmentation signal:
AOR W/S Dec Slide 3
QZSS L1-SAIF Signal
QZSS broadcasts wide-area augmentation signal:
Called L1-SAIF (Submeter-class Augmentation with Integrity Function);
Augmentation signal for mobile users designed and developed by ENRI.
L1-SAIF signal offers:
Wide-area differential correction service for improving position accuracy; Target accuracy: 1 meter for horizontal;
Integrity function for safety of mobile users; and
Ranging function for improving position availability.
Augmentation to GPS L1C/A based on the SBAS specifications:
Broadcast on L1 freq. with RHCP; Common antenna and RF front-end;
Modulated by BPSK with C/A code (PRN 183);
250 bps data rate with 1/2 FEC; Message structure is identical with SBAS;
Differences from SBAS: PRN, large Doppler, and some additional messages.
Developed easily if one has the experience to develop SBAS-capable receiver;
Specification of L1-SAIF: See IS-QZSS document (Available at JAXA HP).

4. L1-SAIF Signal Functions
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L1-SAIF Signal Functions
Ranging
Function
Error
Correction
Integrity
QZS satellites
GPS Constellation
Ranging Signal
3 Functions by L1-SAIF
Three functions by a single signal: ranging, error correction (Target accuracy: 1m), and integrity;
User receivers can receive both GPS and L1-SAIF signals with a single antenna and RF front-end;
Message-oriented information transmission: Flexible contents.
User GPS/L1-SAIF
Receivers
SAIF： Submeter-class Augmentation with Integrity Function

5. ENRI L1-SAIF Master Station
AOR W/S Dec Slide 5
ENRI L1-SAIF Master Station
L1-SAIF Master Station (L1SMS):
Generates L1-SAIF message stream in realtime and transmits it to QZSS MCS developed by and installed at JAXA;
Installed at ENRI, Tokyo; 90km from JAXA Tsukuba Space Center;
Dual frequency GPS measurements at some locations in Japan necessary to generate L1-SAIF messages are sent from GEONET in realtime.
L1SMS
GEONET
QZS
QZSS MCS
GPS
Satellites
Measure-
ments
L1-SAIF
Message
GSI Server
(Tokyo)
ENRI
JAXA TKSC
(Tsukuba)
L1-SAIF Signal
Ranging Signal
K-band Uplink

6. L1-SAIF Correction: GPS only
AOR W/S Dec Slide 6
L1-SAIF Correction: GPS only
Standalone GPS
L1-SAIF Augmentation
GPS Only Result
6 reference
stations
User location for this test
L1-SAIF expe- rimental area
Horizontal
Error
Vertical
1.45 m
2.92 m
6.02 m
8.45 m
System
Standalone
GPS
0.29 m
0.39 m
1.56 m
2.57 m
w/ L1-SAIF
RMS
Max
Example of user position error at Site (Takayama);
Realtime operation with MSAS-like 6 reference stations in Japan;
Period: Jan (5 days).
Note: Results shown here were obtained with geodetic-grade antenna and receivers at open sky condition.

7. Adding GLONASS: Motivation
AOR W/S Dec Slide 7
Adding GLONASS: Motivation
QZS
GPS constellation
Additional Constellation
= GLONASS
Augmentation
Users
Increase of augmented satellites improves availability of position solution;
Also possibly reduce protection levels; Improve availability of navigation;
Chance of robust position information at mountainous areas and urban canyons.

8. GLONASS: Differences from GPS
AOR W/S Dec Slide 8
GLONASS: Differences from GPS
FDMA signals:
Change carrier frequency settings with regard to ranging sources.
Reference time and coordinates:
Time: broadcast time offset information by an L1-SAIF message; Avoids increase of unknowns in user receivers;
Coordinates: convert PZ to WGS-84.
PRN numbers and insufficient capacity of mask pattern:
Assign PRN numbers of 38 to 61 as GLONASS slot numbers of 1 to 24;
Introduce dynamic PRN mask solution to broadcast augmentation information supporting more than 51 ranging sources, reflecting the actual visibility.
Missing IOD (Issue of Data):
IOD is used to identify ephemeris information in order to match ephemerides between L1-SAIF Master Station and users; Currently using IODE for GPS;
Identify ephemeris information based on the time of broadcast.
Satellite position computation: based on PVA as described in GLONASS ICD.

9. Upgrade of L1SMS L1-SAIF Master Station (L1SMS):
AOR W/S Dec Slide 9
Upgrade of L1SMS
L1-SAIF Master Station (L1SMS):
Generates the L1-SAIF message stream and transmits it to JAXA MCS.
Upgrade for supporting GLONASS and QZSS:
Input module: Supports BINEX observables and navigation message records;
Implemented GLONASS extension based on SBAS standards;
User-domain receiver software (MCRX) is also upgraded to be GLONASS-capable;
QZSS is also supported as it is taken into account like GPS.
L1SMS
GEONET
QZS
QZSS MCS
GPS
Measure-
ments
L1-SAIF
Message
GSI
ENRI
JAXA
L1-SAIF Signal
L1C/A
L2P
K-band
GLONASS
L1SA
Upgrade

10. Configuration of Experiment
AOR W/S Dec Slide 10
Configuration of Experiment
Japanese GEONET is already providing GLONASS and QZSS observables in addition to GPS;
Currently about 1,200 stations are GLONASS/QZSS-capable;
Data format: BINEX
L1SMS generates L1-SAIF message in realtime and broadcast it via QZS-1.
For our experiment:
6 sites for reference stations;
Reference Station (a) to (f)
11 sites for evaluation.
User Station (1) to (11)
Period: 2013/1/6 01:00
to 2013/1/9 23:00 (94 hours).

11. PRN Mask Transition QZSS GLONASS GPS
AOR W/S Dec Slide 11
PRN Mask Transition
GPS
GLONASS
QZSS
PRN Mask indicates which satellites are currently augmented;
Semi-dynamic PRN mask: GPS and QZSS satellites are always ON in the masks;
PRN masks for GLONASS satellites are set ON if the satellite are visible and augmented;
Reflecting our implementation, PRN mask is updated periodically at every 30 minutes.
IODP (issue of Data, PRN Mask) indicates change of PRN mask.

12. Elevation Angle GPS GLONASS QZSS PRN Mask Transition 5 deg @ User (7)
AOR W/S Dec Slide 12
Elevation Angle
GPS
GLONASS
QZSS
PRN Mask
Transition
5 deg
@ User (7)
Rising satellites appear at 5-12 deg above the horizon; Latency due to periodical update of PRN mask;
However, GPS satellites also have similar latency; Not a major problem because low elevation satellites contribute a little to improve position accuracy.

13. # of Satellites vs. Mask Angle
AOR W/S Dec Slide 13
# of Satellites vs. Mask Angle
16 SVs
9.8 SVs
7.3 SVs
@ User (7)
Introducing GLONASS satellites increases the number of satellites in roughly 75%;
QZSS increases a satellite almost all day by only a satellite on the orbit, QZS-1 "Michibiki"
Multi-constellation with QZSS offers 16 satellites at 5 deg and 7.3 satellites even at 40 deg.

14. User Position Error: Mask 5deg
AOR W/S Dec Slide 14
User Position Error: Mask 5deg
GPS+GLO+QZS: 0.310m RMS of horizontal error at user location (7);
Looks some limited improvement by using multi-constellation.

15. User Position Error: Mask 30deg
AOR W/S Dec Slide 15
User Position Error: Mask 30deg
GPS+GLO+QZS: 0.335m RMS of horizontal error at user location (7);
Multi-constellation offers a good availability even for 30 deg mask.

16. Error vs. User Location: 5 deg
AOR W/S Dec Slide 16
Error vs. User Location: 5 deg
North
South
0.421m
0.283m
Expect horizontal accuracy of 0.3 to 0.5m with L1-SAIF augmentation, regardless GLONASS is used or not;
There is a little dependency upon the latitude of user location possibly due to an effect of ionosphere activities.

17. Error vs. User Location: 30 deg
AOR W/S Dec Slide 17
Error vs. User Location: 30 deg
North
South
0.425m
The horizontal accuracy is still within a range between 0.3 and 0.5m for the multi-constellation configuration;
The accuracy degrades to 1 or 2.5m for GPS-only single-constellation configuration.

18. Conclusion ENRI has been developing L1-SAIF signal:
AOR W/S Dec Slide 18
Conclusion
ENRI has been developing L1-SAIF signal:
Signal design: GPS/SBAS-like L1 C/A code (PRN 183);
Planned as an augmentation to mobile users.
GPS/GLONASS/QZSS multi-constellation support:
L1-SAIF Master Station was upgraded to support GLONASS and QZSS in addition to GPS based on the existing SBAS specifications;
Conducted an experiment with broadcast of L1-SAIF signal containing augmentation information of GPS, GLONASS, and QZSS;
Using multi-constellation it can be expected to maintain a good position accuracy even in higher mask angle conditions representing limited visibility conditions.
Further Investigations will include:
Dynamic PRN mask driven by almanac information;
Use of GLONASS observables in generation of ionospheric corrections;
Considerations of different types of receiver for reference/user stations; and
Extension to Galileo.
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