Transcript Implementation of the QZSS L1

ION NTM 2008
San Diego, CA
Jan. 28-30, 2008
Implementation of the QZSS
L1-SAIF Message Generator
T. Sakai, S. Fukushima, N. Takeichi, and K. Ito
Electronic Navigation Research Institute, Japan
ION NTM 28-30 Jan. 2008 - ENRI
Introduction
SLIDE 1
• QZSS will provide augmentation signals:
– In addition to supplement signals;
– L1-SAIF (Submeter-class Augmentation with Integrity Function) on
GPS/SBAS L1 frequency and LEX on Galileo E6;
– L1-SAIF augmentation signal offers: wide-area differential correction,
integrity function, and ranging function.
• ENRI is responsible for developing L1-SAIF:
– Signal design: identical with SBAS;
– Message design is in progress: upper compatible with SBAS.
• L1-SAIF Message Generator (L1SMG):
– Subsystem of L1-SAIF Master Station (L1SMS);
– Generates message stream in realtime and transmit it to QZSS MCS.
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 2
Part 1
Overview of QZSS Program
and L1-SAIF Signal
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 3
QZSS Concept
GPS/GEO
• Footprint of QZS orbit
• Centered 137E
• Eccentricity 0.1, Inclination 45deg
QZS
• Signal from high elevation angle
• Applicable to navigation services for
mountain area and urban canyon
ION NTM 28-30 Jan. 2008 - ENRI
QZSS Signals
SLIDE 4
• Supplement signals:
– GPS-compatible L1C/A, L2C, L5, and L1C signals working with GPS;
For improving availability of navigation;
– With minimum modifications from GPS signal specifications;
– Coordination with GPS JPO on broadcasting L1C signal;
– JAXA is responsible for all supplement signals.
• Augmentation signals:
– Augmentation to GPS; Possibly plus Galileo;
– L1-SAIF (Submeter-class Augmentation with Integrity Function):
compatible with SBAS; reasonable performance for mobile users;
– LEX: for experimental purposes; member organizations may use as
2kbps experimental data channel;
– ENRI is working for L1-SAIF and JAXA is developing LEX.
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 5
Frequency Plan
Signal
Channel
Frequency
Bandwidth
Min. Rx Power
L1CD
24 MHz
–163.0 dBW
L1CP
24 MHz
– 158.25 dBW
QZS-L1-C/A
24 MHz
– 158.5 dBW
QZS-L1-SAIF
24 MHz
– 161.0 dBW
24 MHz
– 160.0 dBW
25 MHz
– 157.9 dBW
25 MHz
– 157.9 dBW
42 MHz
– 155.7 dBW
QZS-L1C
1575.42 MHz
QZS-L2C
1227.6 MHz
L5I
QZS-L5
1176.45 MHz
L5Q
QZS-LEX
1278.75 MHz
Find detail in IS-QZSS document.
ION NTM 28-30 Jan. 2008 - ENRI
L1-SAIF Signal
SLIDE 6
• QZSS will transmit wide-area augmentation signal:
– Called L1-SAIF (Submeter-class Augmentation with Integrity Function);
– Developed by ENRI (Electronic Navigation Research Institute), Japan.
• L1-SAIF signal offers:
– Wide-area differential corrections for improving position accuracy;
Target accuracy: 1 meter for horizontal;
– Integrity function for safety of mobile users; and
– Ranging function to improve signal availability.
• Interoperable with GPS L1C/A and fully compatible with SBAS:
– Broadcast on L1 freq. with RHCP; Common antenna and RF front-end;
– Modulated by BPSK with C/A code;
– 250 bps data rate with 1/2 FEC; message structure is same as SBAS.
ION NTM 28-30 Jan. 2008 - ENRI
L1-SAIF Augmentation Concept
GPS
Satellites
QZS
Clock Error
Orbit
Error
SLIDE 7
• Error Corrections
• Integrity
Augmentation
Ionosphere
Ranging
Troposphere
High
Elevation
User (Single Frequency)
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 8
L1 PRN Assignment
PRN
Signal
Satellite
183
QZS-L1-SAIF
QZS #1
184
QZS-L1-SAIF
QZS #2
185
QZS-L1-SAIF
QZS #3
186
QZS-L1-SAIF
QZS #4
187
QZS-L1-SAIF
QZS #5
188 to 192
QZS-L1-SAIF
(Reserved)
193 to 197
QZS-L1-C/A
QZS #1-5
198 to 202
QZS-L1-C/A
(Reserved)
Find detail in IS-QZSS document.
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 9
SBAS Message Structure
Preamble
8 bits
Message Type
6 bits
Data Field
212 bits
CRC parity
24 bits
250 bits
MT
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
2～5
120
—
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 10
L1-SAIF Message (1)
Message Type
Contents
Compatibility
Status
0
Test mode
SBAS
Fixed
1
PRN mask
SBAS
Fixed
Fast correction & UDRE
SBAS
Fixed
6
UDRE
SBAS
Fixed
7
Degradation factor for FC
SBAS
Fixed
8
Reserved
Unused
Fixed
9
GEO ephemeris
Unused
Fixed
10
Degradation parameter
SBAS
Fixed
12
SBAS network time
Unused
Fixed
17
GEO almanac
Unused
Fixed
18
IGP mask
SBAS
Fixed
24
Mixed fast/long-term correction
SBAS
Fixed
25
Long-term correction
SBAS
Fixed
26
Ionospheric delay & GIVE
SBAS
Fixed
2 to 5
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 11
L1-SAIF Message (2)
Message Type
Contents
27
SBAS service message
28
Clock-ephemeris covariance
Compatibility
Status
Unused
Fixed
SBAS
Fixed
29 to 51
(Undefined)
—
—
52
TGP mask
New
Tentative
5３
Tropospheric delay
New
Tentative
(Advanced Ionospheric delay)
New
TBD
56
Intersignal biases
New
Tentative
57
(Ephemeris-related parameter)
New
TBD
58
QZS ephemeris
New
Tentative
59
(QZS almanac)
New
TBD
60
(Regional information)
New
TBD
61
Reserved
New
Tentative
62
Reserved
SBAS
Fixed
63
Null message
SBAS
Fixed
54 to 55
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 12
Messaging Capacity
Message
Type
Messages Required
for Constellation
Interval
Messages
per min
Fast Correction
2 to 5
3
10 s
18
Long-Term Correction
25
4
60 s
4
Ionosphere
26
2
60 s
2
Troposphere
54 and 55
3
60 s
3
QZS Ephemeris
58
1
30 s
2
FC Degradation
7
1
60 s
1
Degradation Parameter
10
1
60 s
1
PRN Mask
1
1
60 s
1
IGP Mask
18
2
60 s
2
C-E Covariance
28
10
60 s
10
Total
44
Margin for Other Messages
16
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 13
Part 2
L1-SAIF
Message Generator
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 14
ENRI L1SMS
• L1-SAIF Master Station (L1SMS):
– Generates L1-SAIF message stream in realtime and transmits them to
QZSS MCS developed by JAXA;
– Installed at ENRI, Tokyo;
– Subsystems: GEONET Server, Primary Receiver, Interface Processor,
Message Generator, Ionosphere Processor, Troposphere Processor, and
QZS
Batch Processor.
GPS
Closed
Loop
Measured
Data
L1-SAIF
Message
GEONET
L1SMS
QZSS MCS
GSI
ENRI
JAXA
ION NTM 28-30 Jan. 2008 - ENRI
L1SMS Subsystems (1)
SLIDE 15
• GEONET Server:
– Receives dual frequency measurement from GEONET operated by
Geographical Survey Institute (GSI), Japan;
– Output rate: 1 sample per second (1 Hz); In native binary format of
receivers; Latency is less than 2 seconds;
– 5 servers for 1,000 GEONET stations distributed all over Japan.
• Primary Receiver:
– Installed inside L1SMS with connection via Ethernet LAN;
– Provides measurements for immediate response to satellite failure to
ensure integrity function;
– Collects navigation message every subframe;
– Provides the actual time to the message generator;
– Currently NovAtel OEM-3 MiLLennium-STD.
ION NTM 28-30 Jan. 2008 - ENRI
L1SMS Subsystems (2)
SLIDE 16
• Interface Processor:
– Distributes GPS measurement data stream to other processors;
– Other subsystem processors access to this processor to obtain
measurement to avoid generating lots of direct connections to GEONET
Server and Primary Receiver;
– Also relays L1-SAIF message packets from Message Generator to QZSS
MCS at JAXA.
• Message Generator:
–
–
–
–
–
Generates L1-SAIF message and sends packets to Interface Processor;
Variable configuration of monitor stations;
Capable several types of receiver: RINEX, NovAtel, Trimble, JAVAD;
Standard planar fit algorithm for ionospheric correction;
Standard correction model for troposphere.
ION NTM 28-30 Jan. 2008 - ENRI
L1SMS Subsystems (3)
SLIDE 17
• Ionosphere Processor (under development):
– Generates ionospheric correction and integrity information based on
vast number of monitor stations (tested up to 200 stations);
– Implements ‘residual bounding’ algorithm (See ION GNSS 2007);
– This processor is optional; If not exist, L1SMG employs its own
standard algorithm.
• Troposphere Processor (under development):
– Estimates atmospheric condition and generates tropospheric delay
information;
– Semi-realtime estimation: latency is less than 1 hour;
– Formats delay information into vertical delay at TGP (tropospheric grid
point) like IGP for ionosphere;
– Also optional; If not exist, standard troposphere model is used.
ION NTM 28-30 Jan. 2008 - ENRI
L1SMS Subsystems (4)
SLIDE 18
• Batch Processor:
– Estimates satellite and receiver hardware biases so-called Interfrequency bias or L1/L2 bias;
– Runs on daily basis; Constructs model of ionosphere based on
measurements for at least two days and performs estimation;
– Provides stable and accurate estimation in comparison with a realtime
sequential processing.
• Data Storage Server:
– Very large capacity storage with RAID configuration;
– Holds input measurements and resulted message stream for several
months (depending on the number of monitor stations).
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 19
L1SMS Installed at ENRI
I/F
Message
Generator
Ionosphere
Processor
Storage
Storage
Router to
GEONET
GEONET
Server
Storage
UPS
UPS
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 20
Configuration of L1SMS
GEONET
TCP/IP
Observation
File (RINEX)
via FTP
Batch Processor
(IFB Estimation)
Dual Freq. Ant.
GEONET Server
Primary Receiver
Message
Output
via TCP/IP
Interface Processor
IFB
Estimates
L1SMS Batch Subsystem
Message Generator
(L1SMG)
Ionosphere Processor
Troposphere Processor
L1SMS Realtime Subsystems
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 21
Message Generator (L1SMG)
Dual Freq. Ant.
GEONET Server
Primary Receiver
Time and
NAV Message
Monitor Stations
Measurement
Input Module
Clock and Orbit
Corrections
Correction Module
Ionosphere Module
(Planar Fit)
Messaging Module
Message
Log
Standard Ionospheric
Correction
Input from
Iono Processor
Message
Output
via TCP/IP
L1-SAIF Message
Generator (L1SMG)
ION NTM 28-30 Jan. 2008 - ENRI
SLIDE 22
Transmission Latency
• QZS is not a Bent-Pipe transponder:
– QZS synthesizes RF signals onboard;
ENRI
– Onboard computer has a message queue
for synchronization to Z-count epoch;
– MCS waits for available time slot of TTC JAXA
channel to uplink L1-SAIF message; Again
a queue;
– Latency up to 10 seconds from departure
at L1SMS to reception by user receivers.
Worst Case
Latency [s]
L1SMS
ISDN
QZSS MCS
3.70
Uplink Station
K-band
– 10-15 seconds in advance;
– Possible unless SA turned on;
– Affects on integrity performance, TTA.
0.20
Onboard Computer
4.60
QZS
• L1SMG generates message earlier:
0.20
Modulator
L-band
User
User Receiver
1.20
0.10
Total 10.00
ION NTM 28-30 Jan. 2008 - ENRI
Realtime Operation Test
SLIDE 23
#1 JAXA Monitor Stations (4)
#2 MSAS Domestic Stations (6)
#3 ENRI Realtime Sites (9)
Evaluation Locations (14)
#4
(11)
L1-SAIF Experimental Area
• Tested L1SMG with 4 configurations of
monitor stations;
• Analyzed user position error at 14
evaluation locations; Numbered from
North to South;
• Used GEONET stations as all monitor
stations and evaluation sites.
ION NTM 28-30 Jan. 2008 - ENRI
Initial Results – Error Sample
SLIDE 24
Standalone GPS
L1-SAIF Augmentation
• Example of user positioning error at Site
940058 (Takayama; near center of
monitor station network);
• MSAS-like 6 monitor stations;
• Period: 19-23 Jan. 2008 (5 days).
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
L1-SAIF
ION NTM 28-30 Jan. 2008 - ENRI
Clock and Orbit Corrections
SLIDE 25
• Clock and orbit corrections for PRN 09 satellite;
• IODE is changed by MT24 long-term correction message at 15:56:45;
• Even discontinuities on corrections, pseudorange residual is continuous.
ION NTM 28-30 Jan. 2008 - ENRI
User Position Accuracy
HOR VER
• Needs at least 6 monitor stations;
• 11 stations configuration offers better accuracy in Southern region.
SLIDE 26
ION NTM 28-30 Jan. 2008 - ENRI
Maximum User Position Error
HOR VER
• Unstable with 4 monitor stations configuration;
• 11 stations configuration prevent large errors in Southern region.
SLIDE 27
ION NTM 28-30 Jan. 2008 - ENRI
Conclusion
SLIDE 28
• ENRI has been developing QZSS L1-SAIF signal:
– L1-SAIF augmentation signal on GPS/SBAS L1 frequency;
– Signal design: compatible with SBAS;
– Message design is in progress: upper compatible with SBAS.
• Development of L1SMS:
– Most subsystems including L1SMG successfully implemented;
– Ionosphere and Troposphere Processors under development;
– Realtime operation test successfully conducted.
• Future works will include:
– Ionosphere and Troposphere Processors handling lots of monitor stations;
– Implementation of integrity function and necessary monitors;
– Contact: [email protected]