sbas iwg/25 st. petersburg, russia june 25-27, 2013 gps/glonass multi-constellation sbas trial...

SBAS IWG/25SBAS IWG/25St. Petersburg, RussiaSt. Petersburg, Russia

June 25-27, 2013June 25-27, 2013

GPS/GLONASSMulti-Constellation SBAS Trial

GPS/GLONASSMulti-Constellation SBAS Trial

Takeyasu SakaiElectronic Navigation Research Institute

Takeyasu SakaiElectronic Navigation Research Institute

IWG/25 June 2013IWG/25 June 2013 - Slide - Slide 22

IntroductionIntroduction• Combined use of GPS and GLONASS with SBAS augmentation:Combined use of GPS and GLONASS with SBAS augmentation:

– GPS/GLONASS-capable receivers are now widely available;GPS/GLONASS-capable receivers are now widely available;

– SBAS (satellite-based augmentation system) is an international standard of the SBAS (satellite-based augmentation system) is an international standard of the augmentation system; US WAAS, Japanese MSAS, and European EGNOS are augmentation system; US WAAS, Japanese MSAS, and European EGNOS are already operational;already operational;

– All operational SBAS are augmenting only GPS;All operational SBAS are augmenting only GPS;

– To improve availability of SBAS-augmented position information, a possible way To improve availability of SBAS-augmented position information, a possible way is extending SBAS to support an additional constellation, e.g., GLONASS.is extending SBAS to support an additional constellation, e.g., GLONASS.

• Possibility of Multi-Constellation SBAS (MC SBAS):Possibility of Multi-Constellation SBAS (MC SBAS):– SBAS specification already has definitions necessary to augment GLONASS;SBAS specification already has definitions necessary to augment GLONASS;

– Investigating advantages of using GLONASS, we have implemented SBAS Investigating advantages of using GLONASS, we have implemented SBAS simulator capable of augmenting both GPS and GLONASS simultaneously;simulator capable of augmenting both GPS and GLONASS simultaneously;

– It is confirmed that introducing GLONASS improves availability and robustness It is confirmed that introducing GLONASS improves availability and robustness of position information especially where visibility is limited.of position information especially where visibility is limited.


MotivationMotivationSBASSBASGEOGEO

• Increase of augmented satellites improves availability of position solution;Increase of augmented satellites improves availability of position solution;• Also possibly reduce protection levels; Improve availability of navigation;Also possibly reduce protection levels; Improve availability of navigation;• Chance of robust position information at mountainous areas and urban Chance of robust position information at mountainous areas and urban

canyons.canyons.

GPS ConstellationGPS Constellation Additional ConstellationAdditional Constellation= GLONASS= GLONASS

AugmentationAugmentation


Current SBAS StandardCurrent SBAS Standard• Already has definition of GLONASS:Already has definition of GLONASS:

– The SBAS standard is documented as the The SBAS standard is documented as the ICAO SARPS;ICAO SARPS;

– GLONASS L1 CSA (channel of standard GLONASS L1 CSA (channel of standard accuracy) signal has already been described in accuracy) signal has already been described in the SBAS standard based on GLONASS ICD;the SBAS standard based on GLONASS ICD;

– SBAS signal is also able to contain information SBAS signal is also able to contain information on GLONASS satellites.on GLONASS satellites.

• Differences from GPS in terms of SBAS Differences from GPS in terms of SBAS augmentation:augmentation:

(1) FDMA signals;(1) FDMA signals;

(2) Reference time and coordination system;(2) Reference time and coordination system;

(3) PRN mask numbers;(3) PRN mask numbers;

(4) Missing IOD for ephemeris; and(4) Missing IOD for ephemeris; and

(5) Satellite position computation.(5) Satellite position computation.

The SBAS standard in the Annex The SBAS standard in the Annex to the Civil Aviation Conventionto the Civil Aviation Convention


(1) FDMA Signals(1) FDMA Signals• FCN (Frequency Channel Number):FCN (Frequency Channel Number):

– GLONASS ICD defines FCN of GLONASS ICD defines FCN of ––7 to +13;7 to +13;

– Historically 0 to +13 were used; After 200Historically 0 to +13 were used; After 2005 the range of FCN shifts to –7 to +6;5 the range of FCN shifts to –7 to +6;

– FCN cannot be used for identification of sFCN cannot be used for identification of satellites; two satellites share the same FCatellites; two satellites share the same FCN.N.

• Difference of carrier frequency affects:Difference of carrier frequency affects:– Carrier smoothing: Carrier smoothing:

Wave length per phase cycle is depenWave length per phase cycle is dependent upon carrier frequency.dent upon carrier frequency.

– Ionospheric corrections:Ionospheric corrections: Ionospheric propagation delay is inverIonospheric propagation delay is inver

sely proportional to square of carrier frsely proportional to square of carrier frequencyequency..

(GLONASS ICD v5.0)(GLONASS ICD v5.0)


(2) Time and Coordinate Systems(2) Time 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 the equation:standard as the equation:

– No need for PZ-90.11 ?No need for PZ-90.11 ?


(3) PRN Mask(3) PRN Mask

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 transmits PRN mask informationSBAS transmits PRN mask information

indicating satellites which are augmentedindicating satellites which are augmented

by the SBAS;by the SBAS;

– 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 signal;SBAS signal;

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

• A solution: Dynamic PRN MaskA solution: 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);

RTCA MOPS states this occurs “infrequently” while ICAO SARPS does not.RTCA MOPS states this occurs “infrequently” while ICAO SARPS does not.

– Change PRN mask dynamically (for GLONASS satellites only; semi-dynamic Change PRN mask dynamically (for GLONASS satellites only; semi-dynamic PRN masking) to reflect the actual visibility from the intended service area;PRN masking) to reflect the actual visibility from the intended service area;

– This is a tentative implementation for this MC-SBAS trial by ENRI.This is a tentative implementation for this MC-SBAS trial by ENRI.

PRN definition for SBASPRN definition for SBAS


(4) IOD (Issue of Data)(4) 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


(5) Satellite Position(5) Satellite 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


MC-SBAS ExperimentMC-SBAS Experiment• ENRI’s software SBAS simulator is upgraENRI’s software SBAS simulator is upgra

ded to support GLONASS and Japan’s Qded to support GLONASS and Japan’s QZSS constellations.ZSS constellations.

QZSS currently contains only 1 IGSO broaQZSS currently contains only 1 IGSO broadcasting PRN 193 on L1C/A;dcasting PRN 193 on L1C/A;

The software generates the complete SBAThe software generates the complete SBAS message stream based on input measurS message stream based on input measurements given as RINEX files.ements given as RINEX files.

• GNSS receiver network: GEONETGNSS receiver network: GEONET More than 1,200 stations are GLONASS/ More than 1,200 stations are GLONASS/

QZSS-capable;QZSS-capable; Data format: RINEX 2.12 observation and Data format: RINEX 2.12 observation and

navigation files.navigation files.

• Monitor stations for this experiment:Monitor stations for this experiment: 8 Reference Stations: (1) to (8).8 Reference Stations: (1) to (8). 3 User Stations: (a) to (c); In this presentati3 User Stations: (a) to (c); In this presentati

on, discussion for user (b) only.on, discussion for user (b) only.

• Period: 2012/7/18 to 2012/7/20 (3 days).Period: 2012/7/18 to 2012/7/20 (3 days).

User User LocationLocation


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 are set ON for GLONASS PRN masks are set ON for GLONASS satellites visible from 1 or more satellites visible from 1 or more stations; Set OFF if not visible.stations; Set OFF if not visible.

• IODP (issue of Data, PRN Mask) IODP (issue of Data, PRN Mask) indicates change of PRN mask at indicates change of PRN mask at every 30 minutes.every 30 minutes.

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 without prediction by almanac;update of PRN mask without prediction by almanac;

• However, GPS satellites also have similar latency; The latency of GLONASS However, GPS satellites also have similar latency; The latency of GLONASS satellites would not be a major problem.satellites would not be a major problem.

GPSGPS

GLONASSGLONASS

QZSSQZSS

PRN MaskPRN MaskTransitionTransition

5 deg5 deg

@ User (b)@ User (b)


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

• Introducing GLONASS satellites increases the number of satellites roughly 75%;Introducing GLONASS satellites increases the number of satellites roughly 75%;• QZSS increases a satellite almost all day by only a satellite on the orbit, QZS-1; QZSS increases a satellite almost all day by only a satellite on the orbit, QZS-1; • Multi-constellation with QZSS offers 17 satellites for 5 deg mask angle and 9.8 Multi-constellation with QZSS offers 17 satellites for 5 deg mask angle and 9.8

satellites even for 30 deg.satellites even for 30 deg.

9.8 SVs9.8 SVs

17 SVs17 SVs

7.4 SVs7.4 SVs



Availability vs. Mask AngleAvailability vs. Mask Angle

• The number of epochs with position solution decreases with regard to increase The number of epochs with position solution decreases with regard to increase of mask angle;of mask angle;

• Multi-constellation with QZSS achieves 100% availability even for 40 deg mask.Multi-constellation with QZSS achieves 100% availability even for 40 deg mask.

100% 100% AvailabilityAvailability



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

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


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

• GPS+GLO+QZS: 0.372m RMS of horizontal error at user location (b);GPS+GLO+QZS: 0.372m RMS of horizontal error at user location (b);• Multi-constellation offers good accuracy even for 30 deg mask.Multi-constellation offers good accuracy even for 30 deg mask.


RMS Error vs. Mask AngleRMS Error vs. Mask Angle

• User location near the centroid of reference station network;User location near the centroid of reference station network;• The accuracy degrades but is maintained to 0.6m for horizontal even for 40dThe accuracy degrades but is maintained to 0.6m for horizontal even for 40d

eg mask angle by using GLONASS and QZSS as well as GPS.eg mask angle by using GLONASS and QZSS as well as GPS.


0.602m0.602m


Vertical Protection LevelVertical Protection Level

GPS+GLO+QZSGPS+GLO+QZSGPS onlyGPS only

• Protection levels mean the confidence limit at 99.99999% confidential level;Protection levels mean the confidence limit at 99.99999% confidential level;• In these chart, unsafe condition exists if there are plots at the right of the diagonal line;In these chart, unsafe condition exists if there are plots at the right of the diagonal line;• GLONASS reduces VPL; This means improvement of availability of navigation.GLONASS reduces VPL; This means improvement of availability of navigation.

Reduce



ConclusionConclusion• Combined use of GPS and GLONASS with SBAS:Combined use of GPS and GLONASS with SBAS:

– Multi-constellation SBAS, capable of augmenting both GPS and GLONASS, anMulti-constellation SBAS, capable of augmenting both GPS and GLONASS, and additionally QZSS, is implemented and tested successfully;d additionally QZSS, is implemented and tested successfully;

– Potential problems and solutions on realizing a multi-constellation SBAS based Potential problems and solutions on realizing a multi-constellation SBAS based on the current standard were investigated;on the current standard were investigated;

– It is confirmed that the performance of SBAS-aided navigation is certainly improIt is confirmed that the performance of SBAS-aided navigation is certainly improved by adding GLONASS, especially when satellite visibility is limited;ved by adding GLONASS, especially when satellite visibility is limited;

– Adding GLONASS also reduces protection levels and thus improves availability Adding GLONASS also reduces protection levels and thus improves availability of navigation.of navigation.

• Ongoing and future works:Ongoing and future works:– Realtime operation test to broadcast multi-constellation augmentation informatioRealtime operation test to broadcast multi-constellation augmentation informatio

n via QZSS L1-SAIF augmentation channel; Preliminary tests have been condun via QZSS L1-SAIF augmentation channel; Preliminary tests have been conducted often in this year successfully;cted often in this year successfully;

– Using GLONASS observables in generation of ionospheric correction;Using GLONASS observables in generation of ionospheric correction;– Mixed use of different types of receiver for reference/user stations;Mixed use of different types of receiver for reference/user stations;– Further extension to support Galileo.Further extension to support Galileo.

sbas iwg/25 st. petersburg, russia june 25-27, 2013 gps/glonass multi-constellation sbas trial...

Documents