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T. Sakai, S. Fukushima, N. Takeichi, and K. Ito Electronic Navigation Research Institute, Japan

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. Introduction. QZSS will provide augmentation signals: In addition to supplement signals;

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T. Sakai, S. Fukushima, N. Takeichi, and K. Ito Electronic Navigation Research Institute, Japan

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  1. 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

  2. Introduction • 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.

  3. Part 1 Overview of QZSS Program and L1-SAIF Signal

  4. QZSS Concept QZS GPS/GEO • Signal from high elevation angle • Applicable to navigation services for mountain area and urban canyon • Footprint of QZS orbit • Centered 137E • Eccentricity 0.1, Inclination 45deg

  5. QZSS Signals • 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.

  6. Frequency Plan Signal Channel Frequency Bandwidth Min. Rx Power QZS-L1C L1CD 1575.42 MHz 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 QZS-L2C 1227.6 MHz 24 MHz – 160.0 dBW QZS-L5 L5I 1176.45 MHz 25 MHz – 157.9 dBW L5Q 25 MHz – 157.9 dBW QZS-LEX 1278.75 MHz 42 MHz – 155.7 dBW Find detail in IS-QZSS document.

  7. L1-SAIF Signal • 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.

  8. GPS Satellites QZS • Error Corrections • Integrity Clock Error Augmentation Orbit Error 0100101001…… Ionosphere Ranging Troposphere High Elevation User (Single Frequency) L1-SAIF Augmentation Concept

  9. 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.

  10. 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 2～5 Fast correction & UDRE 60 24 FC & LTC 6 6 UDRE 6 25 Long-term correction 120 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 —

  11. L1-SAIF Message (1) Message Type Contents Compatibility Status 0 Test mode SBAS Fixed 1 PRN mask SBAS Fixed 2 to 5 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

  12. L1-SAIF Message (2) Message Type Contents Compatibility Status 27 SBAS service message Unused Fixed 28 Clock-ephemeris covariance SBAS Fixed 29 to 51 (Undefined) — — 52 TGP mask New Tentative 5３ Tropospheric delay New Tentative 54 to 55 (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

  13. 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

  14. Part 2 L1-SAIF Message Generator

  15. QZS GPS L1C/A, L2P L1-SAIF Signal K-band L1C/A, L2P Closed Loop Measured Data L1-SAIF Message GEONET L1SMS QZSS MCS GSI ENRI JAXA 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 Batch Processor.

  16. L1SMS Subsystems (1) • 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.

  17. L1SMS Subsystems (2) • 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.

  18. L1SMS Subsystems (3) • 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.

  19. L1SMS Subsystems (4) • Batch Processor: • Estimates satellite and receiver hardware biases so-called Inter-frequency 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).

  20. Message Generator Ionosphere Processor I/F Storage Storage Storage Router to GEONET GEONET Server UPS UPS L1SMS Installed at ENRI

  21. GEONET TCP/IP Dual Freq. Ant. Observation File (RINEX) via FTP Message Output via TCP/IP GEONET Server Primary Receiver Batch Processor (IFB Estimation) Interface Processor IFB Estimates Ionosphere Processor Troposphere Processor Message Generator (L1SMG) L1SMS Batch Subsystem L1SMS Realtime Subsystems Configuration of L1SMS

  22. Dual Freq. Ant. GEONET Server Primary Receiver Time and NAV Message Monitor Stations Measurement Input Module Ionosphere Module (Planar Fit) Clock and Orbit Corrections Correction Module Standard Ionospheric Correction Messaging Module Input from Iono Processor L1-SAIF Message Generator (L1SMG) Message Output via TCP/IP Message Log Message Generator (L1SMG)

  23. Worst Case Latency [s] L1SMS ENRI ISDN 0.20 QZSS MCS JAXA 3.70 Uplink Station K-band 0.20 Onboard Computer QZS 4.60 Modulator L-band 1.20 User Receiver 0.10 User Total 10.00 Transmission Latency • QZS is not a Bent-Pipe transponder: • QZS synthesizes RF signals onboard; • Onboard computer has a message queue for synchronization to Z-count epoch; • MCS waits for available time slot of TTC channel to uplink L1-SAIF message; Again a queue; • Latency up to 10 seconds from departure at L1SMS to reception by user receivers. • L1SMG generates message earlier: • 10-15 seconds in advance; • Possible unless SA turned on; • Affects on integrity performance, TTA.

  24. Realtime Operation Test #1 JAXA Monitor Stations (4) #2 MSAS Domestic Stations (6) #3 ENRI Realtime Sites (9) #4 (11) Evaluation Locations (14) 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.

  25. Initial Results – Error Sample Standalone GPS L1-SAIF Augmentation System Horizontal Error Vertical Error Standalone GPS RMS 1.45 m 2.92 m Max 6.02 m 8.45 m L1-SAIF RMS 0.29 m 0.39 m Max 1.56 m 2.57 m • 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).

  26. Clock and Orbit Corrections • 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.

  27. HOR VER • Needs at least 6 monitor stations; • 11 stations configuration offers better accuracy in Southern region. User Position Accuracy

  28. HOR VER • Unstable with 4 monitor stations configuration; • 11 stations configuration prevent large errors in Southern region. Maximum User Position Error

  29. Conclusion • 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: sakai@enri.go.jp

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