sbas iwg/26 new delhi, india feb. 5-7, 2014

SBAS IWG/26SBAS IWG/26New Delhi, IndiaNew Delhi, IndiaFeb. 5-7, 2014Feb. 5-7, 2014

Dual Frequency SBAS Trialand Preliminary Results

(Work Plan: Identify Benefits)

Dual Frequency SBAS Trialand Preliminary Results

(Work Plan: Identify Benefits)

Takeyasu SakaiElectronic Navigation Research Institute, Japan

Takeyasu SakaiElectronic Navigation Research Institute, Japan

SBAS IWG/26SBAS IWG/26 - Slide - Slide 22

IntroductionIntroduction• Dual Frequency SBAS = The solution for Ionosphere:Dual Frequency SBAS = The solution for Ionosphere:

– The dominant factor which lowers the performance of single frequency SBAS is The dominant factor which lowers the performance of single frequency SBAS is the uncertainty of ionosphere, especially at the low magnetic latitude region;the uncertainty of ionosphere, especially at the low magnetic latitude region;

– Employing dual frequency system is an essential solution against ionosphere; It Employing dual frequency system is an essential solution against ionosphere; It becomes no longer necessary to have a large margin for ionosphere threat;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 The signal specification of dual frequency SBAS is now being discussed at SBAS IWG (interoperability working group) meeting as a preparation for standardization IWG (interoperability working group) meeting as a preparation for standardization at the ICAO.at the ICAO.

• Simulation of Dual Frequency (DF) SBAS:Simulation of Dual Frequency (DF) SBAS:– It is necessary to characterize the performance of dual frequency SBAS to assist It is necessary to characterize the performance of dual frequency SBAS to assist

making the standard properly;making the standard properly;

– We have implemented DF-SBAS simulator and evaluated the performance;We have implemented DF-SBAS simulator and evaluated the performance;

– It is confirmed that employing DF system eliminates ionosphere threat and It is confirmed that employing DF system eliminates ionosphere threat and improves availability of the system especially for the ionospheric storm condition.improves availability of the system especially for the ionospheric storm condition.


Motivation: Situation of MSASMotivation: Situation of MSAS• MSAS = Japanese SBASMSAS = Japanese SBAS::

– Has been operational since Sept. 2007;Has been operational since Sept. 2007;

– Configuration: 2 GEO (MTSAT-1R and MTSAT-2) + 2 MCS;Configuration: 2 GEO (MTSAT-1R and MTSAT-2) + 2 MCS;

– Single Frequency and Single Constellation (GPS only);Single Frequency and Single Constellation (GPS only);

– Achieves 100% availability for Enroute (RNP 0.3) to NPA flight modes within Achieves 100% availability for Enroute (RNP 0.3) to NPA flight modes within Fukuoka FIR.Fukuoka FIR.

• Currently Horizontal Navigation OnlyCurrently Horizontal Navigation Only::– MSAS is built on the IOC WAAS;MSAS is built on the IOC WAAS;

– The major concern for vertical guidanceThe major concern for vertical guidance

is ionosphere; Users must be protectedis ionosphere; Users must be protected

during ionospheric storm as well as normalduring ionospheric storm as well as normal

condition;condition;

– Need to reduce ionospheric uncertaintyNeed to reduce ionospheric uncertainty

to provide vertical guidance.to provide vertical guidance.MTSAT-1R GEOMTSAT-1R GEO


APV-I Availability of MSASAPV-I Availability of MSAS

MSAS Broadcast06/10/17 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 ComponentVPL Component

• The ionospheric term is dominant component of Vertical Protection Level.The ionospheric term is dominant component of Vertical Protection Level.

VPLVPL

Clock & OrbitClock & Orbit(5.33 (5.33 fltflt))

IonosphereIonosphere(5.33 (5.33 UIREUIRE))

MSAS Broadcast06/10/17 00:00-12:00@93011 Tokyo

PRN129 (MTSAT-1R)Test Signal


Solution: Dual FrequencySolution: Dual Frequency• Problem of MSASProblem of MSAS::

– The distribution of monitor stationsThe distribution of monitor stations

is almost linear; Difficult to observeis almost linear; Difficult to observe

ionosphere enough;ionosphere enough;

– The service area of MSAS containsThe service area of MSAS contains

a low magnetic latitude region wherea low magnetic latitude region where

ionospheric disturbance is severe.ionospheric disturbance is severe.

• Dual Frequency OperationDual Frequency Operation::– An essential solution against ionosphere;An essential solution against ionosphere;

No longer necessary to have a large margin against ionosphere threat;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 We need L5 signal for aviation use; Now we have 4 Block IIF satellites transmitting L5 signal; 24 satellites by 2020?transmitting L5 signal; 24 satellites by 2020?

– Japanese QZSS will also broadcast L5 signal; Planned 4 satellites by 2018.Japanese QZSS will also broadcast L5 signal; Planned 4 satellites by 2018.

MSAS GMSMSAS GMS


ConcernsConcerns• Amplified Measurement NoiseAmplified Measurement Noise::

– Measurement for DF receivers, so-called Ionosphere-Free combination, is noisy Measurement for DF receivers, so-called Ionosphere-Free combination, is noisy due to differential computation between two frequencies;due to differential computation between two frequencies;

2.6 times of SF mode (L1 and L5);2.6 times of SF mode (L1 and L5); 3.0 times of SF mode (L1 and L2).3.0 times of SF mode (L1 and L2).

– This noise cannot be corrected by DGPSThis noise cannot be corrected by DGPScorrection information.correction information.

No correlation between DGPS stationNo correlation between DGPS stationand users.and users.

• Compatibility with Single Frequency (SF) UsersCompatibility with Single Frequency (SF) Users::– Could two sets of SBAS messages generated for SF users and for DF users, Could two sets of SBAS messages generated for SF users and for DF users,

respectively, be same?respectively, be same?– In other words, is it possible to apply a set of SBAS messages to both DF users In other words, is it possible to apply a set of SBAS messages to both DF users

and SF users?and SF users?

• Investigate These Concerns using DF SBAS Simulator.Investigate These Concerns using DF SBAS Simulator.

Ionosphere-Free CombinationIonosphere-Free Combination


DF SBAS ExperimentDF SBAS Experiment

• The software SBAS simulator is upgraded to be able to generate DF The software SBAS simulator is upgraded to be able to generate DF mode corrections;mode corrections;

• Internal Ionosphere Correction is:Internal Ionosphere Correction is: Based on broadcast MT26 (SF mode);Based on broadcast MT26 (SF mode); Linear combination of L1 and L2 pseudoranges (DF mode).Linear combination of L1 and L2 pseudoranges (DF mode).

• Message is based on the current standard.Message is based on the current standard.

• The user receiver software is also upgraded for DF The user receiver software is also upgraded for DF mode processing;mode processing;

• Ionosphere Correction is:Ionosphere Correction is: Based on received MT26 (SF mode);Based on received MT26 (SF mode); Linear combination of L1 and L2 pseudoranges (DF mode).Linear combination of L1 and L2 pseudoranges (DF mode).

L1 DataL1 Data

L2 DataL2 DataIonosphereIonosphereCorrectionCorrection

Clock/OrbitClock/OrbitCorrectionCorrection

PositionPositionComputationComputation

L1 DataL1 Data L2 DataL2 Data

SBAS MCS (Simulator) User Receiver

SBAS Message

MT 2 to 6,24, and 25

MT 26NewNew

NewNew

SFDF

SF DF


Monitor and User LocationsMonitor and User Locations• Observation Data from GEONETObservation Data from GEONET::

– Operated by Geospatial Operated by Geospatial Information Authority of Japan; Information Authority of Japan;

– Survey-grade receivers over 1,200 Survey-grade receivers over 1,200 stations within Japanese territory;stations within Japanese territory;

– RINEX archive open to public:RINEX archive open to public:

Dual frequency (L1C/A and L2P/Y) Dual frequency (L1C/A and L2P/Y) measurement of 30s interval.measurement of 30s interval.

• Monitor StationsMonitor Stations::

– Selected MSAS-like 6 stations from Selected MSAS-like 6 stations from GEONET: (a) to (f).GEONET: (a) to (f).

• User StationsUser Stations::

– Selected 15 stations from North to Selected 15 stations from North to South: (1) to (15).South: (1) to (15).


Result: Quiet IonosphereResult: Quiet Ionosphere

• SF augmentation achieves the best accuracy (0.49m HRMS);SF augmentation achieves the best accuracy (0.49m HRMS);• DF users suffer noisy measurement; Will be reduced using L5. DF users suffer noisy measurement; Will be reduced using L5.

12/7/22 to 12/7/2512/7/22 to 12/7/2596 Hours Max Kp=396 Hours Max Kp=3@GEONET 940058@GEONET 940058 (Takayama)(Takayama)# GMS: 6# GMS: 6Mask Angle: 5 degMask Angle: 5 deg

GPSGPS

SFSF

DFDF


Result: Stormy IonosphereResult: Stormy Ionosphere

11/10/23 to 11/10/2611/10/23 to 11/10/2696 Hours Max Kp=796 Hours Max Kp=7@GEONET 940058@GEONET 940058 (Takayama)(Takayama)# GMS: 6# GMS: 6Mask Angle: 5 degMask Angle: 5 deg

• SF and GPS are largely affected by the ionospheric activity;SF and GPS are largely affected by the ionospheric activity;• DF accuracy is not degraded.DF accuracy is not degraded.

GPSGPS

SFSF

DFDF


Accuracy vs. Location: QuietAccuracy vs. Location: Quiet

• SF augmentation achieves the best accuracy;SF augmentation achieves the best accuracy;• RMS accuracy has no relationship with the latitude of user;RMS accuracy has no relationship with the latitude of user;• The maximum error becomes large at the south for SF and standalone GPS.The maximum error becomes large at the south for SF and standalone GPS.

12/7/22 to 12/7/2512/7/22 to 12/7/2596 Hours Max Kp=396 Hours Max Kp=3# GMS: 6# GMS: 6Mask Angle: 5 degMask Angle: 5 deg

MaxMaxErrorErrorRMSRMS

AccuracyAccuracy

Large error at Large error at the souththe south


Accuracy vs. Location: QuietAccuracy vs. Location: Quiet12/7/22 to 12/7/2512/7/22 to 12/7/2596 Hours Max Kp=396 Hours Max Kp=3# GMS: 6# GMS: 6Mask Angle: 5 degMask Angle: 5 deg

• Using DF, the maximum error tends to be large at the north.Using DF, the maximum error tends to be large at the north.


Accuracy vs. Location: StormAccuracy vs. Location: Storm11/10/23 to 11/10/2611/10/23 to 11/10/2696 Hours Max Kp=796 Hours Max Kp=7# GMS: 6# GMS: 6Mask Angle: 5 degMask Angle: 5 deg

• SF and DF augmentations expect similar accuracy at the mid-latitude region;SF and DF augmentations expect similar accuracy at the mid-latitude region;• The accuracy of SF mode degrades at the southwestern islands;The accuracy of SF mode degrades at the southwestern islands;

DF augmentation maintains a constant accuracy regardless of the user location.DF augmentation maintains a constant accuracy regardless of the user location.


Accuracy vs. Location: StormAccuracy vs. Location: Storm11/10/23 to 11/10/2611/10/23 to 11/10/2696 Hours Max Kp=796 Hours Max Kp=7# GMS: 6# GMS: 6Mask Angle: 5 degMask Angle: 5 deg

• The maximum error of SF mode becomes large at the southwestern islands;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.In case of DF, the maximum error is not affected by the user location.


Integrity: Single FrequencyIntegrity: Single Frequency

User (1): Northenmost StationUser (1): Northenmost Station User (13): Near Naha (Southwestern Island)User (13): Near Naha (Southwestern Island)

• Vertical Protection Level with regard to the actual error during ionospheric storm;Vertical Protection Level with regard to the actual error during ionospheric storm;• Unsafe condition does not exist at both user location;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.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 FrequencyIntegrity: Dual Frequency

User (1): Northenmost StationUser (1): Northenmost Station User (13): Near Naha (Southwestern Island)User (13): Near Naha (Southwestern Island)

• Using DF, the availability of APV-I flight mode is 100% at both user location;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.LPV-200 mode (CAT-I equivalent, VAL=35m) is also supported with 100% availability.


Compatibility: QuietCompatibility: Quiet12/7/22 to 12/7/2512/7/22 to 12/7/2596 Hours Max Kp=396 Hours Max Kp=3# GMS: 6# GMS: 6Mask Angle: 5 degMask Angle: 5 deg

• Compatibility issue: Is it possible that DF users apply the set of messages generated by SF Compatibility issue: Is it possible that DF users apply the set of messages generated by SF MCS?MCS?

• The combination of SF MCS and DF users works not so bad.The combination of SF MCS and DF users works not so bad.


Compatibility: StormCompatibility: Storm11/10/23 to 11/10/2611/10/23 to 11/10/2696 Hours Max Kp=796 Hours Max Kp=7# GMS: 6# GMS: 6Mask Angle: 5 degMask Angle: 5 deg

• DF users at the south reduce error regardless of MCS mode;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 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.consideration needed in terms of integrity assurance.


ConclusionConclusion• Dual Frequency SBAS:Dual Frequency SBAS:

– Dual Frequency SBAS simulator is implemented and tested successfully;Dual Frequency SBAS simulator is implemented and tested successfully;– Generated message is based on the current standard for Single Frequency;Generated message is based on the current standard for Single Frequency;

This trial intends to characterize the performance of dual frequency SBAS to This trial intends to characterize the performance of dual frequency SBAS to assist making the standard properly;assist making the standard properly;

– It is confirmed that employing DF system eliminates ionosphere threat and It is confirmed that employing DF system eliminates ionosphere threat and improves availability of the system especially for the ionospheric storm condition;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 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.applied to both SF and DF users; Need further study for this issue.

• Ongoing and future works:Ongoing and future works:– Improvement of DF mode accuracy;Improvement of DF mode accuracy;– Consideration of the message structure for DF operation;Consideration of the message structure for DF operation;– Further investigation on the compatibility issue in terms of integrity assurance.Further investigation on the compatibility issue in terms of integrity assurance.

sbas iwg/26 new delhi, india feb. 5-7, 2014

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