ION ITM 2012
Newport Beach, CA
Jan.30 - Feb.1, 2012
Ranging Quality of
QZSS L1-SAIF Signal
T. Sakai, H. Yamada, and K. Ito
Electronic Navigation Research Institute, Japan
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
Introduction
SLIDE 1
• 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;
– The first QZS satellite was successfully launched on Sept. 11, 2010.
• 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);
– Ranging function is now available: Ephemeris information has been broadcast
during the experiments conducted by ENRI since Nov. 2011;
– Investigated ranging quality of L1-SAIF signal.
 Expect comparable to GPS thanks to signal bandwidth of 24 MHz.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 2
QZSS Concept
GPS/GEO
• Footprint of QZSS orbit;
• Centered at 135E;
• Eccentricity 0.075, Inclination 43deg.
QZS
• 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.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
Inclined Geosynchronous Orbit
SLIDE 3
Apogee
40000km
8:40
15:20
Perigee
32000km
Orbital Planes of QZSS (3 SVs)
Ground Track
• Semi-major axis (42164km) is equal to GEO orbit: synchronous with rotation of
the earth;
• Inclined obit makes ground track ‘8’-figure; Called IGSO or Quasi-Zenith Orbit;
• With three or more satellites on the same ground track, navigation service can
be provided from the zenith to regional users at any time.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 4
Space Segment: QZS-1
Mass
4,020kg (wet) 1,802kg (dry)
(NAV Payload：320kg)
Power
Approx. 5.3 kW (EOL)
(NAV Payload: Approx. 1.9kW)
Design Life
10 years
Radiation Cooled TWT
TWSTFT Antenna
Successfully launched on Sept.
11, 2010 and settled on QuasiZenith Orbit (IGSO).
C-band TTC Antenna
Nickname: “Michibiki”
Laser Reflector
L1-SAIF Antenna
L-band Helical Array
Antenna
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
QZSS Frequency Plan
Signal
Channel
Frequency
L1CD
Bandwidth Min. Rx Power
24 MHz
–163.0 dBW
24 MHz
– 158.25 dBW
24 MHz
– 158.5 dBW
24 MHz
– 160.0 dBW
25 MHz
– 157.9 dBW
25 MHz
– 157.9 dBW
QZS-L1C
L1CP
1575.42 MHz
QZS-L1-C/A
QZS-L2C
1227.6 MHz
L5I
QZS-L5
SLIDE 5
Interoperability
GPS-like supplemental
signals with minimum
modifications from GPS
signals
1176.45 MHz
L5Q
QZS-L1-SAIF
1575.42 MHz
24 MHz
– 161.0 dBW
QZS-LEX
1278.75 MHz
42 MHz
– 155.7 dBW
SBAS-like augmentation
signal (250bps)
QZSS-specific augmentation signal (2kbps)
Find detail in IS-QZSS document.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
QZSS L1-SAIF Signal
SLIDE 6
• QZSS broadcasts wide-area augmentation signal:
– Called L1-SAIF (Submeter-class Augmentation with Integrity Function);
– 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 SBAS techniques:
– 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: Large Doppler and additional messages.
– Specification of L1-SAIF: See IS-QZSS document (Available at JAXA HP).
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
L1-SAIF Signal
QZS satellites
SLIDE 7
Ranging
Function
GPS Constellation
Error
Correction
Integrity
Function
• 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.
SAIF： Submeter-class Augmentation with Integrity Function
Ranging Signal
User GPS
Receivers
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 8
L1-SAIF Corrections
• Example of user position error at Site
940058 (Takayama: near center of
monitor station network);
• Realtime operation with MSAS-like 6
monitor stations;
• Period: 19-23 Jan. 2008 (5 days);
• L1-SAIF provides corrections only;
No L1-SAIF ranging.
Horizontal
Error
Vertical
Error
Standalone RMS
GPS
Max
1.45 m
2.92 m
6.02 m
8.45 m
RMS
0.29 m
0.39 m
Max
1.56 m
2.57 m
System
Standalone GPS
Augmented by L1-SAIF
L1-SAIF
No L1-SAIF Ranging
Note: Results shown here were obtained with surveygrade antenna and receiver in open sky condition.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
Usage of L1-SAIF Ranging
SLIDE 9
• Ranging function of L1-SAIF signal:
– RF signal design: Identical with GPS L1 C/A modulated by PRN 183 code;
– Necessary to broadcast ephemeris information in order to make ranging
function available to users.
 L1-SAIF extended message of Type 58 Ephemeris Information is designed
for this purpose.
• Completed L1-SAIF Master Station (L1SMS) upgrade:
– To be capable of broadcasting MT58 Ephemeris Information during the
experiments conducted by ENRI;
– Using JAXA monitor stations for generation of MT58.
• Investigation of ranging quality including effects of Ephemeris Information:
– RF quality: Expect comparable to GPS thanks to signal bandwidth of 24MHz;
– How about quality of ephemeris information on L1-SAIF ?
– User receiver setup:
 JAVAD ALPHA-G3T with QZSS extension;
 Output pseudorange measurements are processed by ENRI;
 5 deg Elevation Mask, 100 seconds Carrier Smoothing.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 10
L1-SAIF Message Structure
Preamble
8 bits
Message Type
6 bits
Data Field
212 bits
1 message = 250 bits broadcast every second
Transmitted First
MT
CRC parity
24 bits
Contents
Interval
[s]
MT
Contents
Interval
[s]
0
Test mode
6
17
GEO almanac
300
1
PRN mask
120
18
IGP mask
300
Fast correction & UDRE
60
24
FC & LTC
6
6
UDRE
6
25
Long-term correction
7
Degradation factor for FC
120
26
Ionospheric delay & GIVE 300
9
GEO ephemeris
120
27
SBAS service message
300
10
Degradation parameter
120
28
Clock-ephemeris covariance
120
12
SBAS time information
300
63
Null message
2 to 5
120
—
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 11
L1-SAIF Message (1)
Message Type
Contents
Used by
Status
0
Test mode
SBAS and L1-SAIF
Fixed
1
PRN mask
SBAS and L1-SAIF
Fixed
Fast correction & UDRE
SBAS and L1-SAIF
Fixed
6
UDRE
SBAS and L1-SAIF
Fixed
7
Degradation factor for FC
SBAS and L1-SAIF
Fixed
8
Reserved
SBAS
Fixed
9
GEO ephemeris
SBAS
Fixed
10
Degradation parameter
SBAS and L1-SAIF
Fixed
12
SBAS network time
SBAS
Fixed
17
GEO almanac
SBAS
Fixed
18
IGP mask
SBAS and L1-SAIF
Fixed
24
Mixed fast/long-term correction
SBAS and L1-SAIF
Fixed
25
Long-term correction
SBAS and L1-SAIF
Fixed
26
Ionospheric delay & GIVE
SBAS and L1-SAIF
Fixed
2 to 5
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 12
L1-SAIF Message (2)
Message Type
Contents
27
SBAS service message
28
Clock-ephemeris covariance
Used by
Status
SBAS
Fixed
SBAS and L1-SAIF
Fixed
29 to 51
Undefined
—
—
52
TGP mask
L1-SAIF
Tentative
53
Tropospheric delay
L1-SAIF
Tentative
Advanced Ionospheric delay
L1-SAIF
TBD
56
Intersignal biases
L1-SAIF
Tentative
57
Ephemeris-related parameter
L1-SAIF
TBD
58
QZS ephemeris
L1-SAIF
Tentative
59
QZS almanac
L1-SAIF
TBD
60
Regional information
L1-SAIF
TBD
61
Reserved
L1-SAIF
Tentative
62
Reserved
SBAS and L1-SAIF
Fixed
63
Null message
SBAS and L1-SAIF
Fixed
54 to 55
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
L1-SAIF Ephemeris (MT58)
SLIDE 13
Item
Bits
Range
Resolution
Contents
t0,Q
8
0-10740 s
60 s
Epoch time/IODN
URA
4
0-15
1
Accuracy indicator
x
26
42950 km
1.28 m
Position X in ECEF
y
26
42950 km
1.28 m
Position Y in ECEF
z
26
42950 km
1.28 m
Position Z in ECEF
vx
24
4.194 km/s
0.5 mm/s
Velocity X in ECEF
vy
24
4.194 km/s
0.5 mm/s
Velocity Y in ECEF
vz
..
x
..
y
..
z
24
4.194 km/s
0.5 mm/s
Velocity Z in ECEF
5
32 mm/s2
2 mm/s2
Acceleration X in ECEF (only perturbation)
5
32 mm/s2
2 mm/s2
Acceleration Y in ECEF (only perturbation)
5
32 mm/s2
2 mm/s2
Acceleration Z in ECEF (only perturbation)
aGf0
22
1.953 ms
2-30 s
aGf1
13
3.725 ns/s
2-40 s/s
Total
212
Clock correction, offset
Clock correction, drift
Stored in 1 message (1sec)
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 14
Generation of Ephemeris
QZS-1
JAXA MCS
Decode
ephemeris
Format
into MT58
Compute
PVA
L1-C/A Users
Ephemeris Reconstruction
L1-SAIF Users
No need to receive
QZS-L1-C/A (PRN 193)
L1-SAIF Master Station (L1SMS) at ENRI
• Ephemeris information is generated based on reconstruction from MCS products
broadcast on QZS-L1-C/A (PRN 193):
 L1SMS receives L1 C/A Nav message and extract QZS-1 PVA for generation of MT58.
• Users do not need to receive any signals other than L1-SAIF (PRN 183).
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 15
SV Position Error of MT58
QZS-1
Reconstructed from
broadcast Nav Msg
on L1C/A PRN 193
2011-08-18
00:00 to 24:00 GPST
Processing by ENRI
Assumed user location:
@ENRI, Tokyo
• Integration error in user receiver with regard to time after broadcast of
MT58 with LTC (long-term correction) in MT24/25 messages;
• Range error is within 0.3m for 300 seconds integration.
 Note that ephemeris message of SBAS has timeout interval of 240-360s.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
User Receiver Setup
JAVAD ALPHA-G3T with QZSS extension
SLIDE 16
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 17
HPE w/L1-SAIF Ranging
2011-08-18
02:18:45 to 21:16:20
L1-SAIF (PRN183) Ranging ON
L1SMS Configuration:
6 DF GPS GMS (GEONET)
4 SF GPS/QZS GMS (JAXA)
User location:
@ENRI, Tokyo
Receiver:
JAVAD ALPHA-G3T
Processing by ENRI
Mask 5deg, Smoothing 100s
L1-SAIF Correction
OFF
ON
L1-SAIF Ranging
Hor RMS
Hor Max
Ver RMS
Ver Max
OFF
1.809 m
6.241 m
2.673 m
7.187 m
ON
1.403 m
8.982 m
3.714 m
15.196 m
OFF
0.680 m
8.686 m
0.988 m
13.308 m
ON
0.658 m
2.494 m
0.937 m
4.682 m
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
HPE w/o L1-SAIF Ranging
SLIDE 18
2011-08-18
02:18:45 to 21:16:20
L1-SAIF (PRN183) Ranging OFF
L1SMS Configuration:
6 DF GPS GMS (GEONET)
4 SF GPS/QZS GMS (JAXA)
User location:
@ENRI, Tokyo
Receiver:
JAVAD ALPHA-G3T
Processing by ENRI
Mask 5deg, Smoothing 100s
L1-SAIF Correction
OFF
ON
L1-SAIF Ranging
Hor RMS
Hor Max
Ver RMS
Ver Max
OFF
1.809 m
6.241 m
2.673 m
7.187 m
ON
1.403 m
8.982 m
3.714 m
15.196 m
OFF
0.680 m
8.686 m
0.988 m
13.308 m
ON
0.658 m
2.494 m
0.937 m
4.682 m
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 19
Observed Residuals
2011-08-18
02:18:45 to 21:16:20
L1-SAIF Correction ON
L1SMS Configuration:
6 DF GPS GMS (GEONET)
4 SF GPS/QZS GMS (JAXA)
User location:
@ENRI, Tokyo
Receiver:
JAVAD ALPHA-G3T
Processing by ENRI
Mask 5deg, Smoothing 100s
• Residual error dependents upon elevation angle for GPS satellites;
• L1-SAIF: Looks small dependency.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 20
Observed Residuals
2011-08-18
02:18:45 to 21:16:20
L1-SAIF Correction ON
L1SMS Configuration:
6 DF GPS GMS (GEONET)
4 SF GPS/QZS GMS (JAXA)
User location:
@ENRI, Tokyo
Receiver:
JAVAD ALPHA-G3T
Processing by ENRI
Mask 5deg, Smoothing 100s
• PRN 3 operates with Cs AFS; PRN 6 with Rb AFS;
• L1-SAIF is comparable to GPS signal; A bit noisy at high elevation.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 21
Residuals on L1-SAIF
2011-08-18
02:18:45 to 21:16:20
L1-SAIF Correction ON
L1SMS Configuration:
6 DF GPS GMS (GEONET)
4 SF GPS/QZS GMS (JAXA)
User location:
@ENRI, Tokyo
Receiver:
JAVAD ALPHA-G3T
Processing by ENRI
Mask 5deg, Smoothing 100s
• Residual error within 1.8m from low to high elevation angle; 0.44m RMS;
• Observed a small uncorrected bias.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
SLIDE 22
Residuals on GPS
PRN 3 with Cs AFS
PRN 6 with Rb AFS
• RMS of residual error: 0.4 to 0.5m for GPS satellites;
• Largely biased.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
Continuous Observation
SLIDE 23
• ENRI has been conducting continuous observation of L1-SAIF signal for technical
verification since October 2011; Also observes other supplement signals;
• Observation is available on the web: URL http://www.enri.go.jp/sat/qzss_e.htm
• Range measurements are converted into RINEX format and navigation message is
formatted in EMS file; Both are slightly extended for QZSS;
 Identifier: ‘J01’ for L1C/A and ‘S83’ for L1-SAIF.
• Data files are stored on daily basis.
Receiver
JAVAD ALPHA-G3T
Antenna
Location
ENRI, Tokyo - Top of the tower of No. 6 Building
35.679518936N 139.560964491E 109.1971m from ellipsoid
X=-3947737.9910 Y=3364428.7640 Z=3699428.9764
Antenna
Trimble Zephyr Geodetic 2 (L1/L2/L5)
Target SV
Measurements
GPS, GLONASS, SBAS, QZSS (incl. L1-SAIF)
Code Range, Carrier Range, Doppler, C/N0 (L1, L2, L5)
Note - Sometimes there is missing data due to some reason such as power outage.
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
QZSS L1-SAIF Data Source
SLIDE 24
QZSS L1-SAIF General Information
List of RINEX Files
http://www.enri.go.jp/sat/qzss_e.htm
http://www.enri.go.jp/cnspub/sat/data/rinex/
• URL http://www.enri.go.jp/sat/qzss_e.htm
• General Information, RINEX observation, EMS message archive, and schedule of
L1-SAIF experiments by ENRI
ION ITM 30 Jan.-1 Feb. 2012 - ENRI
Conclusion
SLIDE 25
• 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.
• Ranging Function of L1-SAIF:
– Available as an additional ranging source with self-contained Ephemeris Information;
– L1-SAIF Master Station (L1SMS) has been upgraded to broadcast Ephemeris
Information and Corrections for L1-SAIF signal itself;
– Tested successfully; Confirmed that residual error was comparable to GPS;
– Ranging function reduces the maximum position error for both horizontal and vertical.
• Ongoing work:
– Experiments on mobile conditions;
– Broadcasting corrections for MSAS and GLONASS satellites.
• L1-SAIF observation is available at http://www.enri.go.jp/sat/qzss_e.htm
RINEX
EMS
http://www.enri.go.jp/cnspub/sat/data/rinex/
http://www.enri.go.jp/cnspub/sat/data/ems/