1. T. Sakai, H. Yamada, S. Fukushima, and K. Ito Electronic Navigation Research Institute, Japan T. Sakai, H. Yamada, S. Fukushima, and K. Ito Electronic Navigation Research Institute, Japan Generation and Evaluation of QZSS L1-SAIF Ephemeris Information Generation and Evaluation of QZSS L1-SAIF Ephemeris Information ION GNSS 2011 Portland, OR Sept. 20-23, 2011

2. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 1Introduction QZSS (Quasi-Zenith Satellite System) program: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 :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 position availability; all on L1 single frequency. ENRI has been developing L1-SAIF signal and experimental facility:ENRI has been developing L1-SAIF signal and experimental facility: –Signal design: SBAS-like message stream on L1 C/A (PRN 183); –Implemented L1-SAIF Master Station (L1SMS); –Need to broadcast ephemeris message to make ranging function available.  What is the best way to generate ephemeris information for L1-SAIF?

3. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 2 QZSS Concept Broadcast signal from high elevation angle;Broadcast signal from high elevation angle; Applicable to navigation services for mountain area and urban canyon;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.Augmentation signal from the zenith could help users to acquire other GPS satellites at any time. Footprint of QZSS orbit;Footprint of QZSS orbit; Centered 135E;Centered 135E; Eccentricity 0.075, Inclination 43deg.Eccentricity 0.075, Inclination 43deg. QZS GPS/GEO

4. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 3 Inclined Geosynchronous Orbit Orbital Planes of QZSS (3 SVs) Ground Track Perigee 32000km Apogee40000km Semi-major axis (42164km) is equal to GEO orbit: synchronous with rotation of the earth;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;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 zenith to regional users at any time.With three or more satellites on the same ground track, navigation service can be provided from zenith to regional users at any time. 8:40 15:20

5. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 4 L-band Helical Array Antenna L1-SAIF Antenna Laser Reflector C-band TTC Antenna Radiation Cooled TWT TWSTFT Antenna 25.3m Successfully launched on Sept. 11, 2010 and settled on Quasi- Zenith Orbit (IGSO). 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 Life10 years

6. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 5 QZSS Frequency Plan Find detail in IS-QZSS document. SignalChannelFrequencyBandwidth Min. Rx Power QZS-L1CL1CD 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-L5L5I 1176.45 MHz 25 MHz – 157.9 dBW L5Q 25 MHz – 157.9 dBW QZS-LEX 1278.75 MHz 42 MHz – 155.7 dBW Interoperability GPS-like supplemental signals with minimum modifications from GPS signals SBAS-like augmentation signal (250bps) QZSS-specific augmenta- tion signal (2kbps) 1575.42 MHz

7. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 6 QZSS broadcasts wide-area augmentation signal:QZSS broadcasts wide-area augmentation signal: –Called L1-SAIF (Submeter-class Augmentation with Integrity Function); –Designed and developed by ENRI. L1-SAIF signal offers: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 position availability. Augmentation to GPS L1C/A based on SBAS:Augmentation to GPS L1C/A based on SBAS: –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). QZSS L1-SAIF Signal

8. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 7 L1-SAIF Signal User GPS Receivers Three functions by a single signal: ranging, error correction (Target accuracy: 1m), and integrity;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;User receivers can receive both GPS and L1-SAIF signals with a single antenna and RF front-end; Message-oriented information transmission: flexible contents.Message-oriented information transmission: flexible contents. SAIF ： Submeter-class Augmentation with Integrity Function RangingFunction ErrorCorrection IntegrityFunction QZS satellite GPS Constellation Ranging Signal

9. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 8 L1-SAIF Message Structure Preamble 8 bits Message Type 6 bits Data Field 212 bits CRC parity 24 bits 1 message = 250 bits broadcast every second MT 0 1 2 - 5 6 7 9 10 12 17 18 Contents Test mode PRN mask Fast correction & UDRE UDRE Degradation factor for FC GEO ephemeris Degradation parameter SBAS time information GEO almanac IGP mask Interval[s] 6 120 60 6 120 120 120 300 300 300 24 25 26 27 28 63 FC & LTC Long-term correction Ionospheric delay & GIVE SBAS service message Clock-ephemeris covariance Null message 6 120 300 300 120 — MTContentsInterval[s] Transmitted First

10. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 9 L1-SAIF Message (1) Message Type Contents Used by Status 0 Test mode SBAS and L1-SAIF Fixed 1 PRN mask Fixed 2 to 5 Fast correction & UDRE Fixed 6UDREFixed 7 Degradation factor for FC Fixed 10 Degradation parameter Fixed 18 IGP mask Fixed 24 Mixed fast/long-term correction Fixed 25 Long-term correction Fixed 26 Ionospheric delay & GIVE Fixed 9 GEO ephemeris SBASFixed 17 GEO almanac SBASFixed 12 SBAS network time SBASFixed 8ReservedSBASFixed SBAS and L1-SAIF

11. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 10 L1-SAIF Message (2) Message Type Contents Used by Status 27 SBAS service message SBASFixed 29 to 51 Undefined—— 28 Clock-ephemeris covariance SBAS and L1-SAIF Fixed 62Reserved Fixed 63 Null message SBAS and L1-SAIF Fixed 52 TGP mask L1-SAIFTentative 56 Intersignal biases L1-SAIFTentative 57 Ephemeris-related parameter L1-SAIFTBD 58 QZS ephemeris L1-SAIFTentative 59 QZS almanac L1-SAIFTBD 60 Regional information L1-SAIFTBD 61ReservedL1-SAIFTentative 53 Tropospheric delay L1-SAIFTentative 54 to 55 Advanced Ionospheric delay L1-SAIFTBD

12. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 11 Example Position Error Example of user position error at Site 940058 (Takayama: near center of monitor station network);Example of user position error at Site 940058 (Takayama: near center of monitor station network); Realtime operation with MSAS-like 6 monitor stations;Realtime operation with MSAS-like 6 monitor stations; Period: 19-23 Jan. 2008 (5 days).Period: 19-23 Jan. 2008 (5 days). HorizontalErrorVerticalError 1.45 m 2.92 m 6.02 m 8.45 m System StandaloneGPS 0.29 m 0.39 m 1.56 m 2.57 m L1-SAIF RMS Max RMS Max Note: Results shown here were obtained with survey- grade antenna and receivers in open sky condition. Standalone GPS Augmented by L1-SAIF

13. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 12 Broadcast Ephemeris for Ranging Orbit Information for ranging function:Orbit Information for ranging function: –Need to broadcast ephemeris information (navigation-grade orbit information) on QZS signal in order to use it for ranging; –QZS L1C/A, L2C, L5, and L1C broadcast ephemeris information on their navigation message similar with GPS; Available since June 2011; –How about L1-SAIF and LEX signals? Option A: Do not broadcast on L1-SAIF, but on other signals:Option A: Do not broadcast on L1-SAIF, but on other signals: –L1-SAIF users receive and utilize ephemeris information broadcast on L1C/A, L2C, L5, or L1C signals;  Antenna offset may be cancelled by differential correction. –Users must receive al least two signals (eg. L1-SAIF + L1C/A) to use ranging function of L1-SAIF signal. Option B: Broadcast ephemeris information on L1-SAIF:Option B: Broadcast ephemeris information on L1-SAIF: –Users can use QZS for ranging by receiving only L1-SAIF signal; –Require to design some new message because SBAS GEO ephemeris message is not applicable; MT58 needs to be designed. We employ this option

14. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 13 Ephemeris Message Design Requirements for ephemeris information:Requirements for ephemeris information: –Contained by a single message (212 bits);  GPS legacy-Nav message consumes 420 bits for a set of ephemeris information of a single GPS SV;  SBAS GEO ephemeris message consists of only 204 bits; But this is for GEO. –Available for 600-900 seconds from broadcast; –SV position error should be within 0.3-0.5m;  Will be cancelled by applying differential corrections;  The minimum resolution of corrections is 0.125m. –Clock correction term should cover a range of  1ms.  Required by payload developer during discussion of specification. Representations in other systems:Representations in other systems: –GPS legacy-Nav: Representation by Keplerian 6-element parameters; –GLONASS: Represented by position, velocity, and acceleration in ECEF;  Users need numerical integration to obtain the position of the intended moment. –SBAS: Transmit position, velocity, and acceleration in ECEF.  No need for numerical integration.

15. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 14 GPS Ephemeris for MEO ItemBitsContents t oc 16Epoch time t oe 16Epoch time af0af0 22Clock corr. (const) af1af1 16Clock corr. (1 st order) af2af2 8Clock corr. (2 nd order) M0M0 32Mean anomaly 00 32Longitude of ascension  32Argument of perigee i0i0 32Inclination nn 16Mean motion ItemBitsContents e 32Eccentricity 32Semi-major axis 24 Rate of  14Rate of i C rc 16Harmonic correction C rs 16Harmonic correction C uc 16Harmonic correction C us 16Harmonic correction C ic 16Harmonic correction C is 16Harmonic correction Total 420 Stored in 3 SFs (18s)  A A A A i. .

16. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 15 GLONASS Ephemeris for MEO ItemBitsRangeResolutionContents tbtb 715-1425 min15 minEpoch time nn 22  2 - 9 s 2 - 30 sClock correction (const) nn 11  2 - 30 s/s 2 - 40 s/sClock correction (1 st order) x 27  27000 km 2 - 11 kmPosition X in ECEF y 27  27000 km 2 - 11 kmPosition Y in ECEF z 27  27000 km 2 - 11 kmPosition Z in ECEF vx 24  4.3 km/s 2 - 20 km/sVelocity X in ECEF vy 24  4.3 km/s 2 - 20 km/sVelocity Y in ECEF vz 24  4.3 km/s 2 - 20 km/sVelocity Z in ECEF 5  6.2  m/s 2 2 - 30 km/s 2 Acceleration X in ECEF (only perturbation) 5  6.2  m/s 2 2 - 30 km/s 2 Acceleration Y in ECEF (only perturbation) 5  6.2  m/s 2 2 - 30 km/s 2 Acceleration Z in ECEF (only perturbation) Total 208 Stored in 4 strings (8s) x y z......

17. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 16 SBAS Ephemeris for GEO ItemBitsRangeResolutionContents t 0,GEO 130-86384 s16 sEpoch time URA 40-151Accuracy indicator x 30  42950 km 0.08 mPosition X in ECEF y 30  42950 km 0.08 mPosition Y in ECEF z 25  6710 km 0.4 mPosition Z in ECEF dx/dt 17  40.96 m/s 0.625 mm/sVelocity X in ECEF dy/dt 17  40.96 m/s 0.625 mm/sVelocity Y in ECEF dz/dt 18  524.288 m/s 4 mm/sVelocity Z in ECEF d 2 x/dt 2 10  6.4 mm/s 2 12.5  m/s 2 Acceleration X in ECEF d 2 y/dt 2 10  6.4 mm/s 2 12.5  m/s 2 Acceleration Y in ECEF d 2 z/dt 2 10  32 mm/s 2 62.5  m/s 2 Acceleration Z in ECEF a Gf0 12  0.9537  s 2 - 31 sClock correction (const) a Gf1 8  0.11642 ns/s 2 - 40 s/sClock correction (1 st order) Total 204 Stored in 1 msg (1s)

18. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 17 QZSS SV Position in ECEF Computed based on broadcast ephemeris on QZSS L1C/A for day of 2011-08-18;Computed based on broadcast ephemeris on QZSS L1C/A for day of 2011-08-18; QZS-1 was operating normally and healthy except LEX signal.QZS-1 was operating normally and healthy except LEX signal. QZS-1 Broadcast Nav Msg on L1C/A PRN 193 2011-08-18 00:00 to 24:00 GPST GPS/QZSS Rx @Koganei, Tokyo @Koganei, Tokyo Processing by ENRI 24 different IODEs in 2846 frames

19. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 18 QZSS SV Velocity in ECEF QZS-1 Broadcast Nav Msg on L1C/A PRN 193 2011-08-18 00:00 to 24:00 GPST GPS/QZSS Rx @Koganei, Tokyo @Koganei, Tokyo Processing by ENRI 24 different IODEs in 2846 frames Velocity of QZS-1 computed from broadcast ephemeris.Velocity of QZS-1 computed from broadcast ephemeris.

20. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 19 QZSS SV Acceleration in ECEF Acceleration of QZS-1 computed from broadcast ephemeris.Acceleration of QZS-1 computed from broadcast ephemeris. QZS-1 Broadcast Nav Msg on L1C/A PRN 193 2011-08-18 00:00 to 24:00 GPST GPS/QZSS Rx @Koganei, Tokyo @Koganei, Tokyo Processing by ENRI 24 different IODEs in 2846 frames

21. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 20 Representation of Acceleration Reduction of information:Reduction of information: –GLONASS transmits ephemeris information as position, velocity, and acceleration in ECEF;  Navigation-grade ephemeris is provided in 208 bits for a single GLONASS SV;  Broadcast information is valid for 15 minutes; Enough for L1-SAIF; –Centripental acceleration is removed from transmitted information;  These terms can be computed for the specific position and velocity of SV;  GLONASS ICD A.3.1.2 gives the equations below (with some corrections). –This technique is applicable to L1-SAIF ephemeris representation. Transmit these perturbation terms

22. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 21 Perturbation Term Acceleration of QZS-1 computed from broadcast ephemeris;Acceleration of QZS-1 computed from broadcast ephemeris; Perturbation only: Centripetal acceleration term is removed.Perturbation only: Centripetal acceleration term is removed. QZS-1 Broadcast Nav Msg on L1C/A PRN 193 2011-08-18 00:00 to 24:00 GPST GPS/QZSS Rx @Koganei, Tokyo @Koganei, Tokyo Processing by ENRI 24 different IODEs in 2846 frames

23. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 22 Proposed Message (MT58) ItemBitsRangeResolutionContents t 0,Q 80-10740 s60 sEpoch time/IODN URA 40-151Accuracy indicator x 26  42950 km 1.28 mPosition X in ECEF y 26  42950 km 1.28 mPosition Y in ECEF z 26  42950 km 1.28 mPosition Z in ECEF vx 24  4.194 km/s 0.5 mm/sVelocity X in ECEF vy 24  4.194 km/s 0.5 mm/sVelocity Y in ECEF vz 24  4.194 km/s 0.5 mm/sVelocity Z in ECEF 5  32  m/s 2 2  m/s 2 Acceleration X in ECEF (only perturbation) 5  32  m/s 2 2  m/s 2 Acceleration Y in ECEF (only perturbation) 5  32  m/s 2 2  m/s 2 Acceleration Z in ECEF (only perturbation) a Gf0 22  1.953 ms 2 - 30 sClock correction (const) a Gf1 13  3.725 ns/s 2 - 40 s/sClock correction (1 st order) Total 212 Stored in 1 msg (1s) x y z......

24. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 23 Generation of Ephemeris Option A: Generation independent of other systems:Option A: Generation independent of other systems: –Need realtime monitor station network:  Monitor stations also necessary for generation of wide-area differential corrections;  JAXA’s monitor network covering Japan and Southeast Asia Region is available for experimental purpose. –Need some orbit determination software; –Independent of other systems.  However, observations from monitor network are provided by JAXA MCS. Option B: Reconstruction from MCS products:Option B: Reconstruction from MCS products: –L1-SAIF is broadcast from QZS-1 SV.  QZS-1 itself broadcasts ephemeris information on L1C/A signal; –Ephemeris information can be generated based on L1C/A ephemeris;  Reconstruction from Keplerian representation in L1C/A legacy Nav message into ECEF PVA representation for MT58;  L1C/A and L1-SAIF are broadcast from different antennas; Antenna offset may be cancelled by differential corrections. –Users still do not need to receive any signals other than L1-SAIF. We employ this option

25. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 24 Ephemeris Reconstruction Decodeephemeris ComputePVA Format into MT58 QZS-L1C/A (PRN 193) Ephemeris in Legacy Nav L1-SAIF (PRN 183) Ephemeris in MT58 L1-SAIF Master Station at ENRI JAXA MCS QZS-L1C/A Uplink Ephemeris Reconstruction L1-C/A Users L1-SAIF Users QZS-1

26. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 25 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 @ENRI, Tokyo SV Position Error for PVA Integration error in user receiver with regard to time after broadcast of PVA;Integration error in user receiver with regard to time after broadcast of PVA; LOS component including satellite clock offset;LOS component including satellite clock offset; SV PVA is computed from broadcast ephemeris on QZSS L1C/A.SV PVA is computed from broadcast ephemeris on QZSS L1C/A. Quantization of corrections

27. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 26 SV Position Error for MT58 PVA is formatted into proposed MT58 format and integrated;PVA is formatted into proposed MT58 format and integrated; Initial position error is dominant component because of its resolution of 1.28m; Need some correction.Initial position error is dominant component because of its resolution of 1.28m; Need some correction. 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 @ENRI, Tokyo

28. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 27 Correction by LTC Message MeasuredPseudorangeCorrectedPseudorange OrbitClock MeasuredPseudorangeCorrectedPseudorange OrbitClock ClockCorr. ClockCorr. Clock & Orbit Corr. SBAS GEO QZSS L1-SAIF MT2-5 Fast Correction (FC) MT2-5 (FC) MT9 GEO Ephemeris MT58 QZS Ephemeris MT24/25Long-Term Correction (LTC) (0.125m)(0.125m) (1.28m)(0.125m) (0.125m) Apply MT24/25 LTC orbit and clock correction like GPS SVs;Apply MT24/25 LTC orbit and clock correction like GPS SVs; LTC has 0.125m resolution.LTC has 0.125m resolution. PRN 183 PRN 120-138 Resolution

29. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 28 Applying LTC Correction Assumed that initial position error is corrected by LTC (long-term correction) in MT24/25 messages;Assumed that initial position error is corrected by LTC (long-term correction) in MT24/25 messages; Range error is within 0.3m for 300s integration.Range error is within 0.3m for 300s integration.  Note that ephemeris message of SBAS has timeout interval of 240-360s. 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 @ENRI, Tokyo

30. ION GNSS 20-23 Sept. 2011 - ENRI S LIDE 29Conclusion ENRI has been developing L1-SAIF signal: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; –Implemented L1-SAIF Master Station (L1SMS) which generates augmentation message stream in realtime and transmit it to QZSS MCS. QZSS ephemeris message:QZSS ephemeris message: –Need to broadcast ephemeris information to make ranging function available; –For L1-SAIF signal, MT 58 is designed to broadcast ephemeris information; –MT 58 provides SV position, velocity, and acceleration in ECEF; –Integration error is within 0.3m when combined with LTC correction. Ongoing work:Ongoing work: –Upgrade L1SMS to generate corrections for L1-SAIF signal itself; –User side consideration of combined use of QZSS and MSAS.