Dual Frequency SBAS Trial and Preliminary Results SBAS IWG/26 New Delhi, India Feb. 5-7, 2014 Dual Frequency SBAS Trial and Preliminary Results (Work Plan: Identify Benefits) Takeyasu Sakai Electronic Navigation Research Institute, Japan

Introduction Dual Frequency SBAS = The solution for Ionosphere: SBAS IWG/26 - Slide 1 Introduction Dual Frequency SBAS = The solution for Ionosphere: The dominant factor which lowers the performance of single frequency SBAS is the uncertainty of ionosphere, especially at the low magnetic latitude region; Employing dual frequency system is an essential solution against ionosphere; It becomes no longer necessary to have a large margin for ionosphere threat; The signal specification of dual frequency SBAS is now being discussed at SBAS IWG (interoperability working group) meeting as a preparation for standardization at the ICAO. Simulation of Dual Frequency (DF) SBAS: It is necessary to characterize the performance of dual frequency SBAS to assist making the standard properly; We have implemented DF-SBAS simulator and evaluated the performance; It is confirmed that employing DF system eliminates ionosphere threat and improves availability of the system especially for the ionospheric storm condition.

Motivation: Situation of MSAS SBAS IWG/26 - Slide 2 Motivation: Situation of MSAS MSAS = Japanese SBAS: Has been operational since Sept. 2007; Configuration: 2 GEO (MTSAT-1R and MTSAT-2) + 2 MCS; Single Frequency and Single Constellation (GPS only); Achieves 100% availability for Enroute (RNP 0.3) to NPA flight modes within Fukuoka FIR. Currently Horizontal Navigation Only: MSAS is built on the IOC WAAS; The major concern for vertical guidance is ionosphere; Users must be protected during ionospheric storm as well as normal condition; Need to reduce ionospheric uncertainty to provide vertical guidance. MTSAT-1R GEO

APV-I Availability of MSAS SBAS IWG/26 - Slide 3 APV-I Availability of MSAS MSAS Broadcast 06/10/17 00:00-24:00 PRN129 (MTSAT-1R) Test Signal Contour plot for: APV-I Availability HAL = 40m VAL = 50m Note: 100% availability of Enroute through NPA flight modes.

VPL Component VPL Ionosphere (5.33 sUIRE) Clock & Orbit (5.33 sflt) SBAS IWG/26 - Slide 4 VPL Component VPL Ionosphere (5.33 sUIRE) Clock & Orbit (5.33 sflt) MSAS Broadcast 06/10/17 00:00-12:00 @93011 Tokyo PRN129 (MTSAT-1R) Test Signal The ionospheric term is dominant component of Vertical Protection Level.

Solution: Dual Frequency SBAS IWG/26 - Slide 5 Solution: Dual Frequency Problem of MSAS: The distribution of monitor stations is almost linear; Difficult to observe ionosphere enough; The service area of MSAS contains a low magnetic latitude region where ionospheric disturbance is severe. Dual Frequency Operation: An essential solution against ionosphere; No longer necessary to have a large margin against ionosphere threat; We need L5 signal for aviation use; Now we have 4 Block IIF satellites transmitting L5 signal; 24 satellites by 2020? Japanese QZSS will also broadcast L5 signal; Planned 4 satellites by 2018. MSAS GMS

Concerns Amplified Measurement Noise: SBAS IWG/26 - Slide 6 Concerns Amplified Measurement Noise: Measurement for DF receivers, so-called Ionosphere-Free combination, is noisy due to differential computation between two frequencies; 2.6 times of SF mode (L1 and L5); 3.0 times of SF mode (L1 and L2). This noise cannot be corrected by DGPS correction information. No correlation between DGPS station and users. Compatibility with Single Frequency (SF) Users: Could two sets of SBAS messages generated for SF users and for DF users, respectively, be same? In other words, is it possible to apply a set of SBAS messages to both DF users and SF users? Investigate These Concerns using DF SBAS Simulator. Ionosphere-Free Combination

SBAS IWG/26 - Slide 7 DF SBAS Experiment L1 Data L2 Data Ionosphere Correction Clock/Orbit Position Computation SBAS MCS (Simulator) User Receiver SBAS Message MT 2 to 6, 24, and 25 MT 26 New SF DF The software SBAS simulator is upgraded to be able to generate DF mode corrections; Internal Ionosphere Correction is: Based on broadcast MT26 (SF mode); Linear combination of L1 and L2 pseudoranges (DF mode). Message is based on the current standard. The user receiver software is also upgraded for DF mode processing; Ionosphere Correction is: Based on received MT26 (SF mode); Linear combination of L1 and L2 pseudoranges (DF mode).

Monitor and User Locations SBAS IWG/26 - Slide 8 Monitor and User Locations Observation Data from GEONET: Operated by Geospatial Information Authority of Japan; Survey-grade receivers over 1,200 stations within Japanese territory; RINEX archive open to public: Dual frequency (L1C/A and L2P/Y) measurement of 30s interval. Monitor Stations: Selected MSAS-like 6 stations from GEONET: (a) to (f). User Stations: Selected 15 stations from North to South: (1) to (15).

Result: Quiet Ionosphere SBAS IWG/26 - Slide 9 Result: Quiet Ionosphere GPS SF DF 12/7/22 to 12/7/25 96 Hours Max Kp=3 @GEONET 940058 (Takayama) # GMS: 6 Mask Angle: 5 deg SF augmentation achieves the best accuracy (0.49m HRMS); DF users suffer noisy measurement; Will be reduced using L5.

Result: Stormy Ionosphere SBAS IWG/26 - Slide 10 Result: Stormy Ionosphere GPS SF DF 11/10/23 to 11/10/26 96 Hours Max Kp=7 @GEONET 940058 (Takayama) # GMS: 6 Mask Angle: 5 deg SF and GPS are largely affected by the ionospheric activity; DF accuracy is not degraded.

Accuracy vs. Location: Quiet SBAS IWG/26 - Slide 11 Accuracy vs. Location: Quiet Max Error RMS Accuracy 12/7/22 to 12/7/25 96 Hours Max Kp=3 # GMS: 6 Mask Angle: 5 deg Large error at the south SF augmentation achieves the best accuracy; RMS accuracy has no relationship with the latitude of user; The maximum error becomes large at the south for SF and standalone GPS.

Accuracy vs. Location: Quiet SBAS IWG/26 - Slide 12 Accuracy vs. Location: Quiet 12/7/22 to 12/7/25 96 Hours Max Kp=3 # GMS: 6 Mask Angle: 5 deg Using DF, the maximum error tends to be large at the north.

Accuracy vs. Location: Storm SBAS IWG/26 - Slide 13 Accuracy vs. Location: Storm 11/10/23 to 11/10/26 96 Hours Max Kp=7 # GMS: 6 Mask Angle: 5 deg SF and DF augmentations expect similar accuracy at the mid-latitude region; The accuracy of SF mode degrades at the southwestern islands; DF augmentation maintains a constant accuracy regardless of the user location.

Accuracy vs. Location: Storm SBAS IWG/26 - Slide 14 Accuracy vs. Location: Storm 11/10/23 to 11/10/26 96 Hours Max Kp=7 # GMS: 6 Mask Angle: 5 deg The maximum error of SF mode becomes large at the southwestern islands; In case of DF, the maximum error is not affected by the user location.

Integrity: Single Frequency SBAS IWG/26 - Slide 15 Integrity: Single Frequency User (1): Northenmost Station User (13): Near Naha (Southwestern Island) Vertical Protection Level with regard to the actual error during ionospheric storm; Unsafe condition does not exist at both user location; The system is available if PL is less than AL; The availability of APV-I flight mode (VAL=50m) is 98% at User (1) and 50% at User (13) for SF mode.

Integrity: Dual Frequency SBAS IWG/26 - Slide 16 Integrity: Dual Frequency User (1): Northenmost Station User (13): Near Naha (Southwestern Island) Using DF, the availability of APV-I flight mode is 100% at both user location; LPV-200 mode (CAT-I equivalent, VAL=35m) is also supported with 100% availability.

SBAS IWG/26 - Slide 17 Compatibility: Quiet 12/7/22 to 12/7/25 96 Hours Max Kp=3 # GMS: 6 Mask Angle: 5 deg Compatibility issue: Is it possible that DF users apply the set of messages generated by SF MCS? The combination of SF MCS and DF users works not so bad.

SBAS IWG/26 - Slide 18 Compatibility: Storm 11/10/23 to 11/10/26 96 Hours Max Kp=7 # GMS: 6 Mask Angle: 5 deg DF users at the south reduce error regardless of MCS mode; The set of messages generated by SF MCS could be applied to both SF and DF users; Further consideration needed in terms of integrity assurance.

Conclusion Dual Frequency SBAS: Ongoing and future works: SBAS IWG/26 - Slide 19 Conclusion Dual Frequency SBAS: Dual Frequency SBAS simulator is implemented and tested successfully; Generated message is based on the current standard for Single Frequency; This trial intends to characterize the performance of dual frequency SBAS to assist making the standard properly; It is confirmed that employing DF system eliminates ionosphere threat and improves availability of the system especially for the ionospheric storm condition; It might be possible that the set of messages generated by SF MCS could be applied to both SF and DF users; Need further study for this issue. Ongoing and future works: Improvement of DF mode accuracy; Consideration of the message structure for DF operation; Further investigation on the compatibility issue in terms of integrity assurance.