ION ITM 26 28 ION Jan ITM 2009

ION ITM 26 -28 ION Jan. ITM 2009 - ENRI Anaheim, CA Jan. 26 -28, 2009 The Ionospheric Correction Processor for SBAS and QZSS L 1 -SAIF T. Sakai, T. Yoshihara, S. Fukushima, and K. Ito Electronic Navigation Research Institute, Japan

ION ITM 26 -28 Jan. 2009 - ENRI Introduction 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 L 1 -SAIF (Submeter-class Augmentation with Integrity Function) on GPS/SBAS L 1 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 L 1 -SAIF Message Generator (L 1 SMG); Tested successfully.

ION ITM 26 -28 Jan. 2009 - ENRI 2 Part 1 Overview of MSAS and QZSS L 1 -SAIF Programs

ION ITM 26 -28 Jan. 2009 - ENRI 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 4 MSAS Status • Satellite navigation for civil aviation use: – SBAS international standard; – Compatible with US WAAS and European EGNOS. • MSAS facilities: – 2 GEOs: MTSAT-1 R (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-1 R MTSAT-2

ION ITM 26 -28 Jan. 2009 - ENRI 5 MSAS Performance GPS @Kawagoe (93011) 08/1/17 -19 PRN 129 MSAS GPS MSAS @Kawagoe (93011) 08/1/17 -19 PRN 129 Horizontal Position Accuracy RMS 0. 42 m MAX 1. 64 m Vertical Position Accuracy RMS 0. 57 m MAX 2. 34 m

ION ITM 26 -28 Jan. 2009 - ENRI Concerns for MSAS 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 7 QZSS Concept GPS/GEO • • • Footprint of QZS orbit Centered 137 E Eccentricity 0. 1, Inclination 45 deg 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 8 • Supplement signals: – GPS-compatible L 1 C/A, L 2 C, L 5, and L 1 C signals working with GPS; For improving availability of navigation; – With minimum modifications from GPS signal specifications; – Coordination with GPS Wing on broadcasting L 1 C signal; – JAXA is responsible for all supplement signals. • Augmentation signals: – Augmentation to GPS; Possibly plus Galileo; – L 1 -SAIF (Submeter-class Augmentation with Integrity Function): compatible with SBAS; reasonable performance for mobile users; – LEX: for experimental purposes; member organizations may use as 2 kbps experimental data channel; – ENRI is working for L 1 -SAIF and JAXA is developing LEX.

ION ITM 26 -28 Jan. 2009 - ENRI 9 QZSS Frequency Plan Signal QZS-L 1 C Channel Bandwidth Min. Rx Power L 1 CD 24 MHz – 163. 0 d. BW L 1 CP 24 MHz – 158. 25 d. BW 24 MHz – 158. 5 d. BW 24 MHz – 161. 0 d. BW 24 MHz – 160. 0 d. BW 25 MHz – 157. 9 d. BW 42 MHz – 155. 7 d. BW QZS-L 1 -C/A Frequency 1575. 42 MHz QZS-L 1 -SAIF QZS-L 2 C QZS-L 5 QZS-LEX 1227. 6 MHz L 5 I L 5 Q 1176. 45 MHz 1278. 75 MHz Find detail in IS-QZSS document.

ION ITM 26 -28 Jan. 2009 - ENRI QZSS L 1 -SAIF Signal 10 • QZSS will broadcast wide-area augmentation signal: – Called L 1 -SAIF (Submeter-class Augmentation with Integrity Function); – Developed by ENRI. • L 1 -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 L 1 C/A and fully compatible with SBAS: – Broadcast on L 1 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 11 SBAS/L 1 -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 12 SBAS/L 1 -SAIF Message (1) Message Type Contents 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 13 SBAS/L 1 -SAIF Message (2) Message Type Contents 27 SBAS service message 28 Clock-ephemeris covariance Compatibility Status SBAS Fixed Both Fixed 29 to 51 (Undefined) — — 52 TGP mask L 1 -SAIF Tentative 5３ Tropospheric delay L 1 -SAIF Tentative (Advanced Ionospheric delay) L 1 -SAIF TBD 56 Intersignal biases L 1 -SAIF Tentative 57 (Ephemeris-related parameter) L 1 -SAIF TBD 58 QZS ephemeris L 1 -SAIF Tentative 59 (QZS almanac) L 1 -SAIF TBD 60 (Regional information) L 1 -SAIF TBD 61 Reserved L 1 -SAIF Tentative 62 Reserved Both Fixed 63 Null message Both Fixed 54 to 55

ION ITM 26 -28 Jan. 2009 - ENRI 14 Part 2 Ionospheric Correction Processor (ICP) and L 1 -SAIF Message Generator

ION ITM 26 -28 Jan. 2009 - ENRI 15 ENRI L 1 SMS • L 1 -SAIF Master Station (L 1 SMS): – Generates L 1 -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 GEONET GSI Measured Data L 2 P al n g Si IF A Closed S Loop L 1 SMS ENRI L 1 -SAIF Message nd ba K- 2 P L A, / C L 1 C/ A, QZSS MCS JAXA

ION ITM 26 -28 Jan. 2009 - ENRI L 1 SMS Subsystems (1) 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 L 1 SMS 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 Nov. Atel OEM-3 Mi. LLennium-STD.

ION ITM 26 -28 Jan. 2009 - ENRI L 1 SMS Subsystems (2) 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 L 1 -SAIF message packets from Message Generator to QZSS MCS at JAXA. • Message Generator (L 1 SMG): – – Generates L 1 -SAIF message with clock and orbit corrections; Variable configuration of monitor stations; Accepts several types of receiver: RINEX, Nov. Atel, 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 L 1 SMS Subsystems (3) 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, L 1 SMG 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 L 1 SMS Subsystems (4) 19 • Batch Processor: – Estimates satellite and receiver hardware biases so-called Interfrequency bias or L 1/L 2 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 20 L 1 SMS Installed at ENRI I/F Message Generator Ionosphere Processor Storage Router to GEONET Server Storage UPS

ION ITM 26 -28 Jan. 2009 - ENRI 21 Configuration of L 1 SMS 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 L 1 SMS Batch Subsystem Message Generator (L 1 SMG) Ionosphere Processor Troposphere Processor L 1 SMS Realtime Subsystems

ION ITM 26 -28 Jan. 2009 - ENRI 22 Message Generator (L 1 SMG) 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 L 1 -SAIF Message Generator (L 1 SMG) Ionospheric Correction Processor (ICP)

ION ITM 26 -28 Jan. 2009 - ENRI 23 Command Response QUERY Command RESPONSE Message Variable Bytes Unit Command Time 8 (double) Response Time 8 (double) 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 n : Latitude 2 0. 1 deg Longitude 2 0. 1 deg IGP n • Each command 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 24 GMS Stations (6) for L 1 SMG IMS Station (200) for ICP Evaluation Locations (14) L 1 -SAIF Experimental Area • Tested performance of the ICP Implemented as a subsystem of L 1 SMS; running with L 1 SMG; • 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 Results – Position Error Sample 25 L 1 -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, 0 th 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 L 1 -SAIF MSAS

ION ITM 26 -28 Jan. 2009 - ENRI 26 Computation Time L 1 SMG ICP Connection Computation Time 0. 16 s / IGP ACK QUERY Command Request 42 IGPs (5 deg) Delay and GIVE QUERY Command Request 143 IGPs (2. 5 deg) Delay and GIVE RESPONSE Message 7 seconds for 42 IGPs Cache for 42 IGPs RESPONSE Message 16 seconds for 101 IGPs

ION ITM 26 -28 Jan. 2009 - ENRI 27 Test Cases Case A B C D E MSAS Ionospheric Correction Made by L 1 SMG ICP ICP MSAS Used Stations 6 GMS 200 IMS 6 GMS IGP grid 5 deg 2. 5 deg Estimation Order 1 1 0 1 Rmax (km) 2100 1000 2100 Nmax 30 30 30 Nmin 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 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. 29

ION ITM 26 -28 Jan. 2009 - ENRI Conclusion 30 • ENRI has been developing QZSS L 1 -SAIF signal: – L 1 -SAIF augmentation signal on GPS/SBAS L 1 frequency; – Signal design: upper compatible with SBAS. • Development of Ionospheric Correction Processor (ICP): – Improves accuracy of WADGPS such as SBAS and L 1 -SAIF; – Implemented as a subsystem of L 1 -SAIF Master Station; Respond to QUERY command issued from L 1 -SAIF Message Generator; – Achievable accuracy: 0. 2 -0. 3 m horizontal at center of Japan; 0. 5 -0. 7 m 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 L 1 -SAIF message formats for ionospheric correction. Contact: sakai@enri. go. jp