Transcript The Ionospheric Correction Processor for SBAS and QZSS L1 …

ION ITM 2009
Anaheim, CA
Jan. 26-28, 2009
The Ionospheric Correction Processor
for SBAS and QZSS L1-SAIF
T. Sakai, T. Yoshihara, S. Fukushima, and K. Ito
Electronic Navigation Research Institute, Japan
ION ITM 26-28 Jan. 2009 - ENRI
Introduction
SLIDE 1
• MSAS has been operational since 2007:
– SBAS augmentation signal offers: wide-area differential correction,
integrity function, and ranging function.
• QZSS will broadcast another augmentation signal in 2010:
– ENRI is developing L1-SAIF (Submeter-class Augmentation with
Integrity Function) on GPS/SBAS L1 frequency;
– Upper compatible with SBAS signal; Also offers WADGPS, integrity,
and ranging.
• Ionosphere is a major problem for both systems:
– Developed the Ionospheric Correction Processor (ICP) independent
from WADGPS correction processor;
– Implemented and integrated with QZSS L1-SAIF Message Generator
(L1SMG); Tested successfully.
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 2
Part 1
Overview of MSAS
and
QZSS L1-SAIF Programs
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 3
WADGPS Concept
Clock Correction
Ionospheric Correction
• Function of user location;
• Up to 100 meters;
• Vertical structure may be
described as a thin shell.
Ionosphere
• Same contribution to any user
location;
• Not a function of location;
• Needs fast correction.
Orbit Correction
• Different contribution to different
user location;
• Not a function of user location; but
a function of line-of-sight direction;
• Long-term correction.
Tropospheric Correction
Troposphere
• Function of user location, especially height of user;
• Up to 20 meters;
• Can be corrected enough by a fixed model.
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 4
MSAS Status
• Satellite navigation for civil aviation use:
– SBAS international standard;
– Compatible with US WAAS and
European EGNOS.
• MSAS facilities:
– 2 GEOs: MTSAT-1R (PRN 129) and
MTSAT-2 (PRN 137) on orbit;
– 6 domestic GMSs and 2 RMSs
(Hawaii and Australia) connected with
2 MCSs;
– IOC WAAS software with localization.
• IOC service since Sept. 27, 2007:
– Certified for Enroute to NPA
operations as a sole mean navigation;
– Stable operation.
MTSAT-1R
MTSAT-2
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 5
MSAS Performance
GPS
@Kawagoe (93011)
08/1/17-19 PRN129
MSAS
GPS
MSAS
@Kawagoe (93011)
08/1/17-19 PRN129
Horizontal Position Accuracy
RMS 0.42m MAX 1.64m
Vertical Position Accuracy
RMS 0.57m MAX 2.34m
ION ITM 26-28 Jan. 2009 - ENRI
Concerns for MSAS
SLIDE 6
• The current MSAS is built on the IOC WAAS:
– As the first satellite navigation system developed by Japan, the design
tends to be conservative;
– The primary purpose is providing horizontal navigation means to aviation
users; Ionopsheric corrections may not be used;
– Achieves 100% availability of Enroute to NPA flight modes.
• The major concern for vertical
guidance is ionosphere:
– The ionospheric term is dominant factor
of position solution uncertainty;
– Necessary to reduce ionospheric
uncertainty to provide vertical guidance
with reasonable availability.
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 7
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 ITM 26-28 Jan. 2009 - ENRI
QZSS Signals
SLIDE 8
• 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 Wing 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 ITM 26-28 Jan. 2009 - ENRI
QZSS Frequency Plan
Signal
Channel
Frequency
SLIDE 9
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 ITM 26-28 Jan. 2009 - ENRI
QZSS L1-SAIF Signal
SLIDE 10
• QZSS will broadcast wide-area augmentation signal:
– Called L1-SAIF (Submeter-class Augmentation with Integrity Function);
– Developed by ENRI.
• 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 ITM 26-28 Jan. 2009 - ENRI
SLIDE 11
SBAS/L1-SAIF Message Structure
Preamble
8 bits
Message Type
6 bits
Data Field
212 bits
250 bits per 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
2～5
120
—
ION ITM 26-28 Jan. 2009 - ENRI
SBAS/L1-SAIF Message (1)
Message Type
Contents
SLIDE 12
Compatibility
Status
0
Test mode
Both
Fixed
1
PRN mask
Both
Fixed
Fast correction & UDRE
Both
Fixed
6
UDRE
Both
Fixed
7
Degradation factor for FC
Both
Fixed
8
Reserved
SBAS
Fixed
9
GEO ephemeris
SBAS
Fixed
10
Degradation parameter
Both
Fixed
12
SBAS network time
SBAS
Fixed
17
GEO almanac
SBAS
Fixed
18
IGP mask
Both
Fixed
24
Mixed fast/long-term correction
Both
Fixed
25
Long-term correction
Both
Fixed
26
Ionospheric delay & GIVE
Both
Fixed
2 to 5
ION ITM 26-28 Jan. 2009 - ENRI
SBAS/L1-SAIF Message (2)
Message Type
Contents
27
SBAS service message
28
Clock-ephemeris covariance
SLIDE 13
Compatibility
Status
SBAS
Fixed
Both
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
Both
Fixed
63
Null message
Both
Fixed
54 to 55
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 14
Part 2
Ionospheric Correction Processor (ICP)
and L1-SAIF Message Generator
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 15
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 ITM 26-28 Jan. 2009 - ENRI
L1SMS Subsystems (1)
SLIDE 16
• 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 ITM 26-28 Jan. 2009 - ENRI
L1SMS Subsystems (2)
SLIDE 17
• Interface Processor:
– Distributes GPS measurement data stream to other processors;
– Other subsystem processors access to this processor for measurements
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 (L1SMG):
–
–
–
–
Generates L1-SAIF message with clock and orbit corrections;
Variable configuration of monitor stations;
Accepts several types of receiver: RINEX, NovAtel, Trimble, JAVAD;
Standard planar fit algorithm for ionospheric correction; Identical with
WAAS/MSAS ionospheric corrections;
– Standard correction model for troposphere.
ION ITM 26-28 Jan. 2009 - ENRI
L1SMS Subsystems (3)
SLIDE 18
• Ionospheric Correction Processor (ICP):
– Generates ionospheric correction and integrity information based on vast
number of monitor stations;
– Tested with realtime measurements from up to 200 monitor stations;
– IGP location is not fixed and identified by QUERY command;
– This processor is optional; If not exist, L1SMG employs its own standard
algorithm.
• Tropospheric Correction Processor (under development):
– Estimates atmospheric condition and generates tropospheric delay;
– Semi-realtime estimation: latency is less than 5 min;
– 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 ITM 26-28 Jan. 2009 - ENRI
L1SMS Subsystems (4)
SLIDE 19
• 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 ITM 26-28 Jan. 2009 - ENRI
SLIDE 20
L1SMS Installed at ENRI
I/F
Message
Generator
Ionosphere
Processor
Storage
Storage
Router to
GEONET
GEONET
Server
Storage
UPS
UPS
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 21
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 ITM 26-28 Jan. 2009 - ENRI
SLIDE 22
Message Generator (L1SMG)
Dual Freq. Ant.
Primary Receiver
Time and
NAV Message
GEONET Server
GMS measurement
(6 stations)
IMS measurement
(200 stations)
Input Module
Clock and Orbit
Correction
Ionospheric Correction QUERY
(Standard Planar Fit)
Messaging Module
Message
Log
Input Module
Ionospheric
Correction Module
RESPONSEInput from
Iono Processor
Message
Output
L1-SAIF Message
Generator (L1SMG)
Ionospheric Correction
Processor (ICP)
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 23
Command and Response
QUERY Command
RESPONSE Message
Variable
Bytes
Unit
Variable
Bytes
Unit
Command Time
8
(double)
Response Time
8
(double)
Number of IGPs
2
—
Number of IGPs
2
—
Latitude
2
0.1 deg
Vertical Delay
8
(double)
Longitude
2
0.1 deg
GIVE
8
(double)
Vertical Delay
8
(double)
GIVE
8
(double)
IGP 1
IGP 1
:
IGP n
:
Latitude
2
0.1 deg
Longitude
2
0.1 deg
IGP n
• Each command and message is packed with Header and CRC;
• QUERY command identifies location of each IGP; ICP computes vertical delay
for each IGP location separately;
• If Message Generator could not receive any response from ICP for 150
seconds, the command shall be timed out.
ION ITM 26-28 Jan. 2009 - ENRI
Realtime Operation Test
SLIDE 24
GMS Stations (6) for L1SMG
IMS Station (200) for ICP
Evaluation Locations (14)
L1-SAIF Experimental Area
• Tested performance of the ICP
Implemented as a subsystem of
L1SMS; running with L1SMG;
• Analyzed user position error at 14
evaluation locations; Numbered from
North to South;
• Used GEONET stations as all
monitor stations and evaluation sites.
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 25
Results – Position Error Sample
L1-SAIF Augmentation
MSAS Augmentation
Standalone GPS
• Example of user positioning error at Site
#5 93022 Choshi (East of Tokyo);
• ICP: 200 IMS, 5-deg IGP, 0th Order Fit;
• Period: 16-21 Jan. 2009 (5 days).
Horizontal
Error
Vertical
Error
RMS
0.23 m
0.36 m
MAX
1.67 m
3.35 m
RMS
0.46 m
0.59 m
MAX
1.73 m
2.43 m
Standalone RMS
GPS
MAX
1.25 m
2.99 m
4.30 m
8.11 m
System
L1-SAIF
MSAS
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 26
Computation Time
L1SMG
ICP
Connection
Computation Time
0.16 s / IGP
ACK
QUERY
Command
Request 42 IGPs (5 deg)
Delay and GIVE
RESPONSE
Message
7 seconds
for 42 IGPs
Cache for 42 IGPs
QUERY
Command
Request 143 IGPs (2.5 deg)
Delay and GIVE
RESPONSE
Message
16 seconds
for 101 IGPs
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 27
Test Cases
Case
A
B
C
D
E
MSAS
Ionospheric
Correction Made by
L1SMG
ICP
ICP
ICP
ICP
MSAS
Used Stations
6 GMS
200 IMS
200 IMS
200 IMS
200 IMS
6 GMS
IGP grid
5 deg
5 deg
5 deg
2.5 deg
2.5 deg
5 deg
Estimation Order
1
1
0
1
0
1
Rmax (km)
2100
1000
1000
1000
1000
2100
Nmax
30
30
30
30
30
30
Nmin
10
10
10
10
10
10
• Rmax, Nmax, and Nmin are parameters to select ionospheric pierce point (IPP)
measurements to be used for estimate the IGP delay;
• The ICP collects IPPs within smaller radius because 200 IMS stations provide
vast number of measurements.
ION ITM 26-28 Jan. 2009 - ENRI
SLIDE 28
Location vs. Horizontal Accuracy
• ICP improves position accuracy in the Southern Region;
• First order estimation is better to ensure accuracy.
ION ITM 26-28 Jan. 2009 - ENRI
Location vs. Vertical Accuracy
• 1 meter accuracy is achievable even for vertical direction;
• Note that these results associate with solar minimum phase.
SLIDE 29
ION ITM 26-28 Jan. 2009 - ENRI
Conclusion
SLIDE 30
• ENRI has been developing QZSS L1-SAIF signal:
– L1-SAIF augmentation signal on GPS/SBAS L1 frequency;
– Signal design: upper compatible with SBAS.
• Development of Ionospheric Correction Processor (ICP):
– Improves accuracy of WADGPS such as SBAS and L1-SAIF;
– Implemented as a subsystem of L1-SAIF Master Station; Respond to
QUERY command issued from L1-SAIF Message Generator;
– Achievable accuracy: 0.2-0.3m horizontal at center of Japan; 0.5-0.7m at
the edge of service area; Note: nominal condition of solar minimum phase.
• Future works will include:
– Verify the performance during ionospheric storm condition;
– Consider other L1-SAIF message formats for ionospheric correction.
– Contact: [email protected]