t. sakai, h. yamada, k. hoshinoo, and k. ito electronic navigation research institute, japan t....

T. Sakai, H. Yamada, K. Hoshinoo, and K. ItoElectronic Navigation Research Institute, Japan

T. Sakai, H. Yamada, K. Hoshinoo, and K. ItoElectronic Navigation Research Institute, Japan

ION ITM 2013ION ITM 2013San Diego, CASan Diego, CA

Jan. 28-30, 2013Jan. 28-30, 2013

QZSS L1-SAIF SupportingGPS/GLONASS Multi-Constellation

Augmentation

QZSS L1-SAIF SupportingGPS/GLONASS Multi-Constellation

Augmentation

ION ITM Jan. 2013ION ITM Jan. 2013 - Slide - Slide 22

IntroductionIntroduction• QZSS (Quasi-Zenith Satellite System) programQZSS (Quasi-Zenith Satellite System) program::

– Regional navigation service broadcast from high-elevation angle by a combination Regional navigation service broadcast from high-elevation angle by a combination of three satellites on the inclined geosynchronous (quasi-zenith) orbit;of three satellites on the inclined geosynchronous (quasi-zenith) orbit;

– Broadcast GPS-like supplemental signals on three frequencies and two augmentatiBroadcast GPS-like supplemental signals on three frequencies and two augmentation signals, L1-SAIF and LEX;on signals, L1-SAIF and LEX;

– The first QZS satellite was successfully launched on Sept. 11, 2010.The first QZS satellite was successfully launched on Sept. 11, 2010.

• L1-SAIF L1-SAIF (Submeter-class Augmentation with Integrity Function) (Submeter-class Augmentation with Integrity Function) signal offers:signal offers:– Submeter accuracy wide-area differential correction service;Submeter accuracy wide-area differential correction service;– Integrity function for safety of mobile users; andIntegrity function for safety of mobile users; and– Ranging function for improving position availability; all on L1 single frequency.Ranging function for improving position availability; all on L1 single frequency.

• ENRI has been developing L1-SAIF signal and experimental facilityENRI has been developing L1-SAIF signal and experimental facility::– Possible to extend to augment GLONASS satellites;Possible to extend to augment GLONASS satellites;– Upgraded to support multi-constellation environment including GPS, GLONASS, anUpgraded to support multi-constellation environment including GPS, GLONASS, an

d QZSS satellites;d QZSS satellites;– Conducted experiment with broadcast of multi-constellation augmentation.Conducted experiment with broadcast of multi-constellation augmentation.


QZSS ConceptQZSS Concept

• Broadcast signal from high elevation angle;Broadcast signal from high elevation angle;

• Applicable to navigation services for Applicable to navigation services for mountain area and urban canyon;mountain area and urban canyon;

• Augmentation signal from the zenith could Augmentation signal from the zenith could help users to acquire other GPS satellites at help users to acquire other GPS satellites at any time.any time.

• Footprint of QZSS orbit;Footprint of QZSS orbit;• Centered at 135E;Centered at 135E;• Eccentricity 0.075, Inclination 43deg.Eccentricity 0.075, Inclination 43deg.

QZSQZSGPS/GEOGPS/GEO


L1-SAIF SignalL1-SAIF Signal

User GPSUser GPSReceiversReceivers

• Three functions by a single signal: ranging, error Three functions by a single signal: ranging, error correction (Target accuracy: 1m), and integrity;correction (Target accuracy: 1m), and integrity;

• User receivers can receive both GPS and L1-SAIF User receivers can receive both GPS and L1-SAIF signals with a single antenna and RF front-end;signals with a single antenna and RF front-end;

• Message-oriented information transmission: flexible Message-oriented information transmission: flexible contents.contents.

SAIFSAIF ：： Submeter-class Augmentation with Integrity FunctionSubmeter-class Augmentation with Integrity Function

RangingRangingFunctionFunction

ErrorErrorCorrectionCorrection

IntegrityIntegrityFunctionFunction

QZS satellitesQZS satellites

GPS ConstellationGPS Constellation

Ranging SignalRanging Signal


L1-SAIF SignalL1-SAIF Signal• QZSS broadcasts wide-area augmentation signalQZSS broadcasts wide-area augmentation signal::

– Called L1-SAIF (Submeter-class Augmentation with Integrity Function);Called L1-SAIF (Submeter-class Augmentation with Integrity Function);

– Designed and developed by ENRI.Designed and developed by ENRI.

• L1-SAIF signal offersL1-SAIF signal offers::– Wide-area differential correction service for improving position accuracy; TargeWide-area differential correction service for improving position accuracy; Targe

t accuracy: 1 meter for horizontal;t accuracy: 1 meter for horizontal;

– Integrity function for safety of mobile users; andIntegrity function for safety of mobile users; and

– Ranging function for improving position availability.Ranging function for improving position availability.

• Augmentation to GPS L1C/A based on SBAS techniquesAugmentation to GPS L1C/A based on SBAS techniques::– Broadcast on L1 freq. with RHCP; Common antenna and RF front-end;Broadcast on L1 freq. with RHCP; Common antenna and RF front-end;

Modulated by BPSK with C/A code (PRN 183);Modulated by BPSK with C/A code (PRN 183); 250 bps data rate with 1/2 FEC; Message structure is identical with SBAS;250 bps data rate with 1/2 FEC; Message structure is identical with SBAS; Differences: Large Doppler and additional messages.Differences: Large Doppler and additional messages.

– Specification of L1-SAIF: See IS-QZSS document (Available at JAXA HP).Specification of L1-SAIF: See IS-QZSS document (Available at JAXA HP).


L1-SAIF CorrectionsL1-SAIF Corrections• Example of user position error at Site 94Example of user position error at Site 94

0058 (Takayama: near center of monitor 0058 (Takayama: near center of monitor station network);station network);

• Realtime operation with MSAS-like 6 moRealtime operation with MSAS-like 6 monitor stations;nitor stations;

• Period: 19-23 Jan. 2008 (5 days);Period: 19-23 Jan. 2008 (5 days);• L1-SAIF provides corrections only;L1-SAIF provides corrections only;

No L1-SAIF ranging.No L1-SAIF ranging.

HorizontalHorizontalErrorError

VerticalVerticalErrorError

1.45 m1.45 m 2.92 m2.92 m

6.02 m6.02 m 8.45 m8.45 m

SystemSystem

StandaloneStandaloneGPSGPS

0.29 m0.29 m 0.39 m0.39 m

1.56 m1.56 m 2.57 m2.57 mL1-SAIFL1-SAIF

RMSRMS

MaxMax

RMSRMS

MaxMax

Note: Results shown here were obtained with survey-Note: Results shown here were obtained with survey-grade antenna and receiver in open sky condition.grade antenna and receiver in open sky condition.

Standalone GPSStandalone GPSAugmented by L1-SAIFAugmented by L1-SAIF

Augmentation to GPS OnlyAugmentation to GPS Only


GLONASS Support: MotivationGLONASS Support: MotivationQZSSQZSS

L1-SAIFL1-SAIF

• Increase of augmented satellites improves availability of position solution;Increase of augmented satellites improves availability of position solution;• Chance of robust position information at mountainous areas and urban Chance of robust position information at mountainous areas and urban

canyons.canyons.

• The current SBAS specification already has definition of GLONASS; Easy The current SBAS specification already has definition of GLONASS; Easy to support by L1-SAIF.to support by L1-SAIF.

GPS constellationGPS constellation Additional ConstellationAdditional Constellation= GLONASS= GLONASS

AugmentationAugmentation


Time and Coordinate SystemsTime and Coordinate Systems• GLONASS Time:GLONASS Time:

– GLONASS is operating based on its own time system: GLONASS Time;GLONASS is operating based on its own time system: GLONASS Time;

– The difference between GPS Time and GLONASS Time must be taken into accoThe difference between GPS Time and GLONASS Time must be taken into account for combined use of GPS and GLONASS;unt for combined use of GPS and GLONASS;

– The difference is not fixed and slowly changing: about 400ns in July 2012;The difference is not fixed and slowly changing: about 400ns in July 2012;

– SBAS broadcasts the difference by Message Type 12SBAS broadcasts the difference by Message Type 12;;

GLONASS-M satellites are transmitting the difference as parameter GLONASS-M satellites are transmitting the difference as parameter GPSGPS in al in al

manac (non-immediate) data: manac (non-immediate) data: GPSGPS = = ttGPSGPS − − ttGLONASSGLONASS..

• PZ-90 Coordinate System:PZ-90 Coordinate System:– GLONASS ephemeris is derived based on Russian coordinate system PZ-90;GLONASS ephemeris is derived based on Russian coordinate system PZ-90;

– The relationship between WGS-84The relationship between WGS-84

and the current version of PZ-90and the current version of PZ-90

(PZ-90.02) is defined in the SBAS(PZ-90.02) is defined in the SBAS

standard as: standard as:


PRN MasksPRN Masks

PRN Contents

1 to 37 GPS

38 to 61GLONASS slot number plus 37

62 to 119 Spare

120 to 138 SBAS

139 to 210 Spare

• PRN Mask:PRN Mask:– SBAS/L1-SAIF transmits PRN maskSBAS/L1-SAIF transmits PRN mask

information indicating satellites which areinformation indicating satellites which are

currently augmented;currently augmented;

– PRN number has range of 1 to 210;PRN number has range of 1 to 210;

– Up to 51 satellites out of 210 can beUp to 51 satellites out of 210 can be

augmented simultaneously by the singleaugmented simultaneously by the single

SBAS/L1-SAIF signal;SBAS/L1-SAIF signal;

But, 32 GPS + 24 GLONASS = 56 !!!But, 32 GPS + 24 GLONASS = 56 !!!

• Solution: Dynamic PRN MaskSolution: Dynamic PRN Mask– Actually, PRN mask can change; Controlled by IODP (Issue of Data, PRN Mask); Actually, PRN mask can change; Controlled by IODP (Issue of Data, PRN Mask);

– Change PRN mask dynamically to reflect the actual visibility of satellites from the Change PRN mask dynamically to reflect the actual visibility of satellites from the intended service area.intended service area.

PRN definition for SBASPRN definition for SBAS


IOD (Issue of Data)IOD (Issue of Data)• IOD indicator along with corrections:IOD indicator along with corrections:

– LTC (Long-Term Correction) in SBAS Message Type 24/25 contains orbit and LTC (Long-Term Correction) in SBAS Message Type 24/25 contains orbit and clock corrections;clock corrections;

– Such corrections depend upon ephemeris data used for position computation;Such corrections depend upon ephemeris data used for position computation;– IOD indicates which ephemeris data should be used in receivers.IOD indicates which ephemeris data should be used in receivers.

• IOD for GPS satellites:IOD for GPS satellites:– For GPS, IOD is just identical with IODE of ephemeris data.For GPS, IOD is just identical with IODE of ephemeris data.

Previous EphemerisPrevious EphemerisIODE=aIODE=a

Next EphemerisNext EphemerisIODE=bIODE=b

LTCLTCIOD=aIOD=a

LTCLTCIOD=bIOD=b

TimeTime

LTCLTCIOD=aIOD=a

LTCLTCIOD=bIOD=b

LTCLTCIOD=aIOD=a


IOD for GLONASSIOD for GLONASS• IOD for GLONASS satellites:IOD for GLONASS satellites:

– GLONASS ephemeris has no indicator like IODE of GPS ephemeris;GLONASS ephemeris has no indicator like IODE of GPS ephemeris;– IOD for GLONASS satellites consists of Validity interval (IOD for GLONASS satellites consists of Validity interval (VV) and Latency time () and Latency time (LL) )

to identify ephemeris data to be used:to identify ephemeris data to be used: 5 MSB of IOD is validity interval, 5 MSB of IOD is validity interval, VV;; 3 LSB of IOD is latency time, 3 LSB of IOD is latency time, LL..

– User receivers use ephemeris data transmitted at a time within the validity interval User receivers use ephemeris data transmitted at a time within the validity interval specified by specified by LL and and VV..

Ephemeris ValidityEphemeris ValidityIntervalInterval

LL11VV11

Previous EphemerisPrevious Ephemeris Next EphemerisNext Ephemeris

LTCLTCIOD=VIOD=V11|L|L11

Ephemeris ValidityEphemeris ValidityIntervalInterval

VV22

LTCLTCIOD=VIOD=V22|L|L22

LL22

TimeTime


Satellite PositionSatellite Position• GLONASS ephemeris data:GLONASS ephemeris data:

– GLONASS transmits ephemeris information as position, velocity, and acceleratiGLONASS transmits ephemeris information as position, velocity, and acceleration in ECEF;on in ECEF;

Navigation-grade ephemeris is provided in 208 bits for a single GLONASS SV;Navigation-grade ephemeris is provided in 208 bits for a single GLONASS SV; Broadcast information is valid for 15 minutes or more.Broadcast information is valid for 15 minutes or more.

– Numerical integration is necessary to compute position of GLONASS satellites;Numerical integration is necessary to compute position of GLONASS satellites;– Note: centripental acceleration is removed from transmitted information.Note: centripental acceleration is removed from transmitted information.

These terms can be computed for the specific position and velocity of SV;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).GLONASS ICD A.3.1.2 gives the equations below (with some corrections).

Perturbation Perturbation terms in terms in

ephemerisephemeris


Upgrade of L1SMSUpgrade of L1SMS• L1-SAIF Master Station (L1SMS):L1-SAIF Master Station (L1SMS):

– Generates the L1-SAIF message stream and transmits it to JAXA MCS.Generates the L1-SAIF message stream and transmits it to JAXA MCS.

• Upgrade for supporting GLONASS and QZSS:Upgrade for supporting GLONASS and QZSS:– Input module: Supports BINEX observables and navigation message records;Input module: Supports BINEX observables and navigation message records;– Implemented GLONASS extension based on SBAS standards;Implemented GLONASS extension based on SBAS standards;– User-domain receiver software (MCRX) is also upgraded to be GLONASS-capable;User-domain receiver software (MCRX) is also upgraded to be GLONASS-capable;– QZSS is also supported as it is taken into account like GPS.QZSS is also supported as it is taken into account like GPS.

L1SMSL1SMSGEONETGEONET

QZSQZS

QZSS MCSQZSS MCS

GPSGPS

MeasuredMeasuredDataData

L1-SAIFL1-SAIFMessageMessage

GSIGSI ENRIENRI JAXAJAXA

L1-S

AIF S

ignal

L1-S

AIF S

ignalL1C/A, L2P

L1C/A, L2P

L1C

/A, L

2PL1

C/A

, L2P

K-band

K-bandClosedClosedLoopLoop

GLONASSGLONASS

L1SAL1SAL2SAL2SA


Dynamic PRN MaskDynamic PRN Mask• Dynamic PRN mask:Dynamic PRN mask:

– Changes PRN mask dynamically to reflect the actual visibility of satellites;Changes PRN mask dynamically to reflect the actual visibility of satellites;– Set PRN masks ON for satellites whose pseudorange observations are available; Set PRN masks ON for satellites whose pseudorange observations are available;

Not based on prediction by almanac information not provided by RINEX;Not based on prediction by almanac information not provided by RINEX;– Semi-dynamic PRN mask: Fix masks ON for GPS and QZSS, and change dynamSemi-dynamic PRN mask: Fix masks ON for GPS and QZSS, and change dynam

ically only for GLONASS to reduce receiver complexity.ically only for GLONASS to reduce receiver complexity.

• Transition of PRN mask:Transition of PRN mask:– Periodical update of PRN mask: updates every 30 minutes;Periodical update of PRN mask: updates every 30 minutes;– Transition time 180s is given to users to securely catch the new PRN mask.Transition time 180s is given to users to securely catch the new PRN mask.

FCFC

PRN Mask (IODP=PRN Mask (IODP=ii)) PRN Mask (IODP=PRN Mask (IODP=ii+1+1))

ttcutovercutover180s180s

FCFC LTCLTC FCFC FCFC LTCLTC FCFC FCFC LTCLTC FCFC FCFC

Corrections before cutoverCorrections before cutover Corrections after cutoverCorrections after cutover

Transition timeTransition time CutoverCutover


GLONASS Time OffsetGLONASS Time Offset• Realtime computation:Realtime computation:

– Computes as the difference between receiver clocks for a group of GPS satellites Computes as the difference between receiver clocks for a group of GPS satellites (and QZSS) and the other group of GLONASS satellites;(and QZSS) and the other group of GLONASS satellites;

– Enough accuracy with a filter of long time constant;Enough accuracy with a filter of long time constant;– Need no almanac information broadcast by GLONASS satellites;Need no almanac information broadcast by GLONASS satellites;– Transmitted to users via Message Type 12 of SBAS.Transmitted to users via Message Type 12 of SBAS.

tt ttGPSGPSttGLONASSGLONASS ttRR

ttGPSGPS

ttGLONASSGLONASS BBGLONASSGLONASS^̂

BBGPSGPS^̂

TrueTrueTimeTime

GLONASSGLONASSSystem TimeSystem Time

GPSGPSSystem TimeSystem Time

ReceiverReceiverTimeTime

aaGLONASSGLONASS

Receiver clock forReceiver clock forGPS satellitesGPS satellites

Receiver clock forReceiver clock forGPS satellitesGPS satellites

Time offset Time offset broadcast to usersbroadcast to users


Experiment: Monitor StationsExperiment: Monitor Stations

• Recently Japanese GEONET Recently Japanese GEONET began to provide GLONASS and began to provide GLONASS and QZSS observables in addition to QZSS observables in addition to GPS;GPS;

• Currently more than 150 stations Currently more than 150 stations are GLONASS/QZSS-capable;are GLONASS/QZSS-capable;

• Data format: BINEXData format: BINEX

• For our experiment:For our experiment: 6 sites for reference stations;6 sites for reference stations;

Reference Station (a) to (f)Reference Station (a) to (f) 11 sites for evaluation.11 sites for evaluation.

User Station (1) to (11)User Station (1) to (11)• Period: 2013/1/6 01:00 Period: 2013/1/6 01:00

to 2013/1/9 23:00 (94 hours).to 2013/1/9 23:00 (94 hours).


PRN Mask TransitionPRN Mask Transition• Reflecting our implementation, PRN Reflecting our implementation, PRN

mask is updated periodically at every mask is updated periodically at every 30 minutes;30 minutes;

• Semi-dynamic PRN mask: GPS and Semi-dynamic PRN mask: GPS and QZSS satellites are always ON in the QZSS satellites are always ON in the masks;masks;

• PRN masks for GLONASS satellites PRN masks for GLONASS satellites are set ON if the satellite are visible are set ON if the satellite are visible and augmented;and augmented;

• Stair-like shape: because the slot Stair-like shape: because the slot number of GLONASS satellites are number of GLONASS satellites are assigned increasingly along with the assigned increasingly along with the orbit.orbit.

• IODP (issue of Data, PRN Mask) IODP (issue of Data, PRN Mask) indicates change of PRN mask.indicates change of PRN mask.

GPSGPS

GLONASSGLONASS

QZSSQZSS


Elevation AngleElevation Angle

• Rising satellites appear at 5-12 deg above the horizon; Latency due to periodical Rising satellites appear at 5-12 deg above the horizon; Latency due to periodical update of PRN mask;update of PRN mask;

• However, GPS satellites also have similar latency; Not a major problem because However, GPS satellites also have similar latency; Not a major problem because low elevation satellites contribute a little to improve position accuracy.low elevation satellites contribute a little to improve position accuracy.

GPSGPS

GLONASSGLONASS

QZSSQZSS

PRN MaskPRN MaskTransitionTransition

5 deg5 deg

@ User (7)@ User (7)


# of Satellites vs. Mask Angle# of Satellites vs. Mask Angle

• Introducing GLONASS satellites increases the number of satellites in roughly 75%;Introducing GLONASS satellites increases the number of satellites in roughly 75%;• QZSS increases a satellite almost all day by only a satellite on the orbit, QZS-1 "Michibiki" QZSS increases a satellite almost all day by only a satellite on the orbit, QZS-1 "Michibiki" • Multi-constellation with QZSS offers 16 satellites at 5 deg and 7.3 satellites even at 40 deg.Multi-constellation with QZSS offers 16 satellites at 5 deg and 7.3 satellites even at 40 deg.

9.8 SVs9.8 SVs

16 SVs16 SVs

7.3 SVs7.3 SVs

@ User (7)@ User (7)


User Position Error: Mask 5degUser Position Error: Mask 5deg

• GPS+GLO+QZS: 0.310m RMS of horizontal error at user location (7);GPS+GLO+QZS: 0.310m RMS of horizontal error at user location (7);• Looks some limited improvement by using multi-constellation.Looks some limited improvement by using multi-constellation.


User Position Error: Mask 30degUser Position Error: Mask 30deg

• GPS+GLO+QZS: 0.335m RMS of horizontal error at user location (7);GPS+GLO+QZS: 0.335m RMS of horizontal error at user location (7);• Multi-constellation offers a good availability even for 30 deg mask.Multi-constellation offers a good availability even for 30 deg mask.


Error vs. User Location: 5 degError vs. User Location: 5 deg

• Expect horizontal accuracy of 0.3 to 0.5m with L1-SAIF augmentation, Expect horizontal accuracy of 0.3 to 0.5m with L1-SAIF augmentation, regardless GLONASS is used or not;regardless GLONASS is used or not;

• There is a little dependency upon the latitude of user location possibly due There is a little dependency upon the latitude of user location possibly due to an effect of ionosphere activities.to an effect of ionosphere activities.

North South

0.421m0.421m0.283m0.283m


Error vs. User Location: 30 degError vs. User Location: 30 deg

• The horizontal accuracy is still within a range between 0.3 and 0.5m for The horizontal accuracy is still within a range between 0.3 and 0.5m for the multi-constellation configuration;the multi-constellation configuration;

• The accuracy degrades to 1 or 2.5m for GPS-only single-constellation The accuracy degrades to 1 or 2.5m for GPS-only single-constellation configuration.configuration.

North South

0.425m0.425m


ConclusionConclusion• ENRI has been developing L1-SAIF signalENRI has been developing L1-SAIF signal::

– Signal design: GPS/SBAS-like L1 C/A code (PRN 183);Signal design: GPS/SBAS-like L1 C/A code (PRN 183);

– Planned as an augmentation to mobile users.Planned as an augmentation to mobile users.

• GPS/GLONASS/QZSS multi-constellation supportGPS/GLONASS/QZSS multi-constellation support::– L1-SAIF Master Station was upgraded to support GLONASS and QZSS in addition tL1-SAIF Master Station was upgraded to support GLONASS and QZSS in addition t

o GPS based on the existing SBAS specifications;o GPS based on the existing SBAS specifications;

– Conducted an experiment with broadcast of L1-SAIF signal containing augmentation Conducted an experiment with broadcast of L1-SAIF signal containing augmentation information of GPS, GLONASS, and QZSS;information of GPS, GLONASS, and QZSS;

– Using multi-constellation it can be expected to maintain a good position accuracy evUsing multi-constellation it can be expected to maintain a good position accuracy even in higher mask angle conditions representing limited visibility conditions.en in higher mask angle conditions representing limited visibility conditions.

• Further Investigations will include:Further Investigations will include:– Dynamic PRN mask driven by almanac information;Dynamic PRN mask driven by almanac information;

– Use of GLONASS observables in generation of ionospheric corrections;Use of GLONASS observables in generation of ionospheric corrections;

– Considerations of different types of receiver for reference/user stations; andConsiderations of different types of receiver for reference/user stations; and

– Extension to Galileo.Extension to Galileo.

t. sakai, h. yamada, k. hoshinoo, and k. ito electronic navigation research institute, japan t....

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