GNSS and Satellite-Based Augmentation Systemsproceedings.kaconf.org/papers/2019/bsw_2.pdf · 2019. 9. 21. · GNSS and Satellite-Based Augmentation Systems Takeyasu Sakai ... Not

17th BroadSky WorkshopSorrento, ItalySept. 30, 2019

GNSS and Satellite-BasedAugmentation Systems

Takeyasu SakaiElectronic Navigation Research Institute

National Institute of Maritime, Port and Aviation Technology, Japan

BroadSky Workshop, Sept. 2019

SLIDE 1Introduction• Satellite Navigation: Navigation from the Space

– Global and seamless navigation primarily for air and sea.– Available Anywhere and Anytime.– Typically using L-band navigation signals.

• GNSS and Augmentation System– GNSS: Basic navigation function giving the position fixes.

Available with user’s own risk: No guarantee if the position fixes are correct.– Augmentation systems: Guarantee of the correctness.

Some applications require ‘Integrity’ of position fixes: GNSS Integrity Channel. As well as integrity, improves the accuracy of position fixes.

• SBAS: Satellite-Based Augmentation System– International standard GNSS augmentation system.

US WAAS, Japanese MSAS, European EGNOS, and Indian GAGAN.– Current situation and future perspectives.


SLIDE 2

Part 1Satellite Navigation and GNSS


SLIDE 3Satellite Navigation• Nationwide navigation system

– A satellites could transmit navigation signals to the half of the globe, while the coverage of ground-based navigation facilities is limited within 200 to 400 km.

– The first artificial satellite ‘Sputnik’ launched in 1957. The first two applications in the context:

Communication and Navigation.– NNSS (Navy Navigation Satellite System) in 1964.

The first satellite navigation system served for marine.

• GNSS: Global Navigation Satellite System– The system of 20-30 navigation satellites: Most MEO satellites, some

optional GEO satellites.Regional system possible with 5-10 satellites.

– A user could have position fixes using 4 or more navigation satellites, anywhere and anytime.


SLIDE 4Example: GPS• GPS (Global Positioning System) by US military

– The first satellite in 1973, IOC (Initial Operational Capability) declaration in 1993, FOC (Full Operational Capability) declaration in 1995.

– Primarily for military, but dual use system from the origin.– Configuration: Nominal 24 satellites; Actually 30 or more on the orbit.– Real time positioning using L-band navigation signals.

Real time: Can be used for airplane, missiles, and space vehicles.

GPS Block IIF Satellite Nominal 24-satellite Configuration


SLIDE 5GNSS (RNSS) Systems

Courtesy: http://www8.cao.go.jp/space/comittee/dai4/siryou3-5.pdf

QZSS (Japan) GPS (US) GLONASS (Russia)

Galileo (EU) BeiDou (China) IRNSS (India)


SLIDE 6Use of Satellite NavigationAltitude 20,200km

for GPS

Need radiosignalsfrom 4 or more satellites

User Display

Navigation Satellites(GPS Satellites)

GPS satellite

Measures range by radiosignals

Global Positioning System(GPS)

Users(GPS Receivers)


SLIDE 7GPS Constellation• GPS Satellites:

– Orbiting altitude of 20,200km– 2 rounds per day; Not geostationary orbit– Operating about 30 satellites

• Minimum is 21 and 24 nominal constellation

– Typically 6 to 10 satellites are visiblesimultaneously from the ground

– Transmitted signals: (Legacy signals)• L1 C/A signal (1575.42MHz) for civil• L1 P/Y and L2 (1227.6MHz) P/Y signals for military• All satellites are transmitting at the same frequency

(CDMA: code division multiple access)

• Usage of GPS Signals:– Receivers measure the range (distance) from GPS satellites– Computes the current location based on measured ranges from multiple satellites– Satellite positions are computed based on orbit information broadcast by satellites

themselves

(Courtesy of FAA)


SLIDE 8Navigation Signals

Transmission Power~ 100W

Measures range(20,000-24,000km)

• GPS L1 C/A signal (Primary signal for civil use)– 1575.42MHz carrier frequency– BPSK modulation by

1.023 Mchip-per-second spectrum spreading sequence 50 bit-per-second navigation message (satellite orbit and clock)

– Bandwidth: 20.46 MHz 2 MHz for mainlobe, but 8 MHz or more for better ranging performance

– No encryption. Signal Specification IS-GPS-200 is open for public.


SLIDE 9Computing Position• Each GPS satellite has precise atomic clocks.

– Transmits ranging signals with very precisetiming known a priori;

– Ranging signals propagate at the speed of light;We can measure the distance from thetraveling time.

• GPS satellite position is also known.– Receivers can compute satellite positions at the

intended instance based on orbit informationbroadcast by GPS satellites themselves;

– Receivers also can compute its position with position of and distance from all satellites used;

– In order to compute 3-dimentional position, receivers need measurements of 4 or more satellites (4 unknowns: 3-D coordinates and receiver clock offset).

• Contents of GPS signal: Published as IS-GPS-200 document.

GPS satellite 2GPS satellite 1

User


SLIDE 10Data Flow inside a ReceiverGPS

satellite

User receiver

Ranging signal

Result: Time and Position(Latitude, Longitude, and Height)

NavigationMessage

ComputingSatellite Position

SatelliteClock Offset

ComputingPosition

PositionInformation

• Measures the distance between satellite and receiver• Transmits navigation message (clock and orbit information)

Contains clock offset of

satellite and receiver

Pseudorange

Atomic clock

Computes receiver clock

offset

Given inNavigation message

Orbit information


SLIDE 11Performance

(T. Marie, 52nd CGSIC)


SLIDE 12

Part 2Augmentation System and SBAS


SLIDE 13Augmentation System• Augmentation System

– Augments GNSS core system(s) in terms of reliability and/or accuracy.– Used in case that the performance of core system(s) does not meet the

requirements. Accuracy: 95% position accuracy for horizontal and vertical Integrity: 99.99999% containment level (protection level)Continuity: The probability of continuous operation

– Augmentation information needs to be transmitted to users in addition to navigation signals of GNSS core system(s).Works as GNSS Integrity Channel: Guarantee of the correctness.

• GNSS Integrity Channel– A communication channel transmitting integrity information from the

navigation service provider to users.– Real time transmission: TTA (Time to Alert) requirements (∼ 6 sec for

aviation).

GPS cannot support by itself


SLIDE 14Why Integrity ?

• PRN23 GPS satellite transmitted anomalous signal due to failure beginning at the morning of 2 Jan., 2004 JST. Caused user position error of over 100 km.

• Flagged to turn off the satellite 3.5 hours after the event. The event was not observable from GPS control stations at the beginning.

100 km3.5 hours

Flagging Anomaly

Latit

ude

Out

put,

deg

Time in 2004-01-02 (JST)


SLIDE 15Requirements for AviationOperation

Accuracy (95%)Integrity Time-

to-Alert Continuity Availa-bilityHorizontal Vertical

Enroute 3.7 km[7.4 km] N/A

1-1×10-7/h

5 min1-1×10-4/h

to1-1×10-8/h

0.99 to0.99999

Enroute, Terminal 0.74 km[1.85 km] N/A 15 s

Initial Approach,Non-precision

Approach (NPA)

220 m[556 m] N/A 10 s

Approach withVertical Guidance

(APV)

16 m[40 m]

20 m[50 m]

1-2×10-7

/approach

10 s1-8×10-6

/15 sCategory I

Precision Approach16 m

[40 m]

4 to 6 m[10 to 35 m]

6 s

Ranges of values for continuity and availability depend upon several factors including traffic density, complexity of the airspace, and availability of alternative navigation facilities, and so on.

Values in brackets are Alert Limit; Containment limits for given integrity level.


SLIDE 16SBAS Architecture

SBAS Satellite GNSSSatellites

Ground Monitor Network

UsersUplinkStation

GNSS SignalsSBAS Signal

• Monitors consistency of GNSS signals on the ground.• Transmits differential correction and integrity information via SBAS satellite.

SBAS Function (1)BroadSky Workshop, Sept. 2019

SLIDE 17

• Monitor and provide quality of GNSS navigation signals. Protect user receivers from using anomalous GNSS signals to ensure safety of

navigation.• TTA (time to alert): Time to be provided integrity information

Enroute and terminal: 5 min to 15 sec Non-precision approach: ≤ 10 sec Precision approach: ≤ 6 sec

• Implementation mechanism: Monitors GNSS signals at the

ground monitor station (GMS). Generate and transmit information

on GNSS signal quality. Transmit alert message when

detection of anomaly. GMS Detection AlertMessage

Users

Uplink Downlink

GNSS satellites SBAS satellite

Anomalous signal

Ensure Integrity


SLIDE 18

• Provide differential corrections to measured range for each GNSS satellite. Improve user position accuracy by differential corrections.

• Wide-area differential corrections: Corrections for: Satellite clock, Satellite orbit, Ionosphere propagation delay, and

Troposphere propagation delay. Applicable in continental-wide service

area seamlessly.• Expect 1m accuracy.

• Implementation mechanism: Monitors GNSS signals at the

ground monitor station (GMS). Separate ranging error into each error

source component. Generate corrections and transmit

messages.

Improve Accuracy

Troposphere

Ionosphere

GPSsatellite

Users

Orbit Error

Clock Error


SLIDE 19

• Works as ranging signal compatible with GPS C/A signal. User receivers could use SBAS signal as an additional ranging source. This means increase of GNSS satellite.

• Provide clock and orbit information of SBAS satellite via its own SBAS message.• Ranging accuracy depends upon

the bandwidth of SBAS signal.

• Implementation mechanism: Generate SBAS signal with highly

stable timing: Usage of the atomicfrequency standard.

Generate clock and orbit informationof SBAS satellite based on rangeinformation measured by someground station (at least 4).

Increase Ranging Source

Measurestime difference

SBASsatellite

Users

International StandardBroadSky Workshop, Sept. 2019

SLIDE 20

• The ICAO Augmentation System– ICAO (International Civil Aviation Organization) requires augmentation

system to be used with the core constellation used for civil aviation. In order to augment integrity and accuracy. Standardized as the SARPS (Standards and Recommended Practices)

appended to the Convention on International Civil Aviation.– SBAS (Satellite-Based Augmentation System):

L1 C/A signal (PRN 120 to 158) compatible with GPS. Augmentation for L1 single-frequency users.

• RTCA SC-159– Defines MOPS (Minimum Operational Performance Standards) for

GPS/SBAS receivers.

• IMO (International Maritime Organization)– Adopt ICAO SBAS as the standard augmentation system for marine.

US WAASBroadSky Workshop, Sept. 2019

SLIDE 21

38 Reference Stations

3 Master Stations

4 Ground Earth Stations

3 Geostationary Satellite Links

2 Operational Control CentersGalaxy XV

Anik F1R

Since 10 July, 2003

European EGNOSBroadSky Workshop, Sept. 2019

SLIDE 22

RIMS MCCs NLES ASQFPACF

- 48 sites connectedin real time

- 4 Control centers- Compliant to

ICAO SARPS- Interoperable with

other SBAS- Ready to be certified

Since 2 March, 2011

Japanese MSASBroadSky Workshop, Sept. 2019

SLIDE 23

• MSAS: SBAS Program by Japan– JCAB (Japan Civil Aviation Bureau) decided the development of its own

SBAS in 1993.– The system named MSAS, or MTSAT Satellite-based Augmentation System,

was originally planned to be operational in 2000. • Launch of the MTSAT-1 was unfortunately failed in 1999.

• MSAS GEO Satellites– MTSAT (Multi-functional Transport Satellite): Aviation and weather missions.

• MTSAT works for AMSS and SBAS services for aviation.– MTSAT-1R and MTSAT-2 were launched in 2005 and 2006, respectively.

• Beginning of Operation– Broadcast test signal since summer 2005. Certification activities for 2 years.– Finally, MSAS began its operation in September 27, 2007.

• Available for Enroute to NPA (non precision approach) flight modes.

MSAS GEO (MTSAT)BroadSky Workshop, Sept. 2019

SLIDE 24

• 3-axis stabilized spacecraft with the standard bus system.• Solar panel at the single side.

– Due to installation of equipment for the weather mission.• L-band transponder with the bandwidth of 2.2 MHz.

– Uplink: Ku-band (13 GHz) due to results of frequency coordination.• Also has downlink channel in Ku-band.

– For power control of uplink signal because of rain attenuation in Ku-band.

MTSAT-1R Spacecraft

MTSAT CoverageBroadSky Workshop, Sept. 2019

SLIDE 25

(Fukuoka FIR)

FIR: Flight Information Region

MTSAT-1R @140EMTSAT-2 @145E

Decommissionedin 2015

Current ConfigurationBroadSky Workshop, Sept. 2019

SLIDE 26

• 1 GEO, 2 MCS (Master Control Station) and 4 GMS (Ground Monitor Station);• MCS also has GMS function; MSAS has 6 domestic monitor stations.• MTSAT-2 is broadcasting 2 signals from 2 MCS (PRN129 and PRN137).

Ranging Signals

GPS Satellites

GroundNetwork

Naha GMS

Fukuoka GMSTokyoGMS

SapporoGMS

Hitachi-Ota MCS(and GMS)

Kobe MCS(and GMS)

Users

MTSAT-2

Augmentation Signals 6 GMSin Japan

MSAS Monitor Stations

PerformanceBroadSky Workshop, Sept. 2019

SLIDE 27

GEONET 940058 (Takayama) 16/8/8-12 (5 days)PRN129 and PRN137 Broadcast Signal

GPS onlyMSAS PRN129

Horizontal0.722m RMS

GPS onlyMSAS PRN137

Horizontal0.717m RMS


SLIDE 28

Part 3Future SBAS

DFMC SBASBroadSky Workshop, Sept. 2019

SLIDE 29

• The current SBAS (L1 SBAS)– Single frequency operation (L1 only).

Affected by ionosphere activities especially at the low latitude regions. Vertical guidance cannot be supported in such regions.

– Single constellation configuration. Supports GPS only. Emerging Galileo and BeiDou cannot be supported.

– Transmitted from GEO only.

• Dual-Frequency Multi-Constellation SBAS (L5 SBAS)– Eliminates ionospheric effects dramatically thanks to dual frequency operation.

Vertical guidance service everywhere in the coverage.– Supporting Multi-Constellation configuration.

Incorporating Galileo and BeiDou.– Allows transmission from non-GEO satellites.– Transmitted on L5 frequency (1176.45 ±12MHz): L5 SBAS.– The ICAO is now finalizing standardization of L5 SBAS.

Status of StandardizationBroadSky Workshop, Sept. 2019

SLIDE 30

• ICAO (International Civil Aviation Organization) has been discussing DFMC SBAS standards.– NSP (Navigation Systems Panel) issued the technical baseline standards.– Defined as L5 SBAS using L5 frequency.

L5 SBAS will be added to the current standards defining L1 SBAS.– RF specification and message contents are almost fixed.

Validation activities are ongoing.– Target: Adoption by End of 2020.

• EUROCAE has discussed receiver specifications.– WG-62 has been preparing MOPS (Minimum Operational Performance

Standards) for DFMC SBAS receivers.GPS/Galileo-capable L1/L5 dual-frequency processing. Initial version has been issued.

– In the US, RTCA SC-159 is responsible of GNSS receiver standards.Will synchronize with EUROCAE MOPS activities.

Prototype DFMC SBASBroadSky Workshop, Sept. 2019

SLIDE 31

• Prototype DFMC SBAS Developed by Japan– The second generation SBAS following L1 SBAS.

Eliminates ionospheric effects thanks to dual-frequency operation.Vertical guidance service everywhere in the coverage.

– Electronic Navigation Research Institute, National Institute of Maritime, Port and Aviation Technology has developed the prototype.GPS/GLONASS/Galileo/QZSS-capable dual-frequency SBAS.Compliant with the draft standards of L5 SBAS being discussed at ICAO.

Helps validation activities ongoing at ICAO.

• DFMC SBAS Experiment has been Conducted with QZSS– The First L5 SBAS experiment with live L5 signal from the space.

Using QZSS L5S augmentation signal transmitted from QZS-2, -3, and -4.– Prototype DFMC SBAS is used for the experiment.– Began the experiment on 23 Aug. 2017 via L5S signal of QZS-2 IGSO.

Now transmitting from QZS-2/4 IGSO and QZS-3 GEO.

Experimental ConfigurationBroadSky Workshop, Sept. 2019

SLIDE 32

• Supports DFMC• Provides observation in

real time

• Operates in real time• Dual-Frequency• Supports GPS, GLONASS,

Galileo, and QZSS

• Uplink L5 SBAS message stream for transmission

ENRI L5 SBASPrototypeGEONET QZSS C&C

MeasuredOBS

L5 SBASMessage

GSI(Shinjuku, Tokyo)

ENRI, MPAT(Chofu, Tokyo)

QZSS MCS(Hitachi-Ota, Ibaraki)

QZSS#2, #3, and #4GLONASS

GPSGalileo

BeiDou

GEO (QZS-3)+

IGSO (QZS-2/4)

Real Time ExperimentBroadSky Workshop, Sept. 2019

SLIDE 33

Output Message Stream

Clock/Orbit Correction

Position Solution

Satellites in Sky

MonitoredSatellites

5 GPS

No GLONASS

7 Galileo

2 QZSS

Galileo SV-8

Without SBAS With SBAS

ConclusionBroadSky Workshop, Sept. 2019

SLIDE 34

• Satellite Navigation: Global and Seamless Navigation– Available Anywhere and Anytime, but no guarantee of the correctness.– Augmentation systems: Guarantee of the correctness.

Some applications require ‘Integrity’ of position fixes: e.g. Aviation.

• SBAS: Satellite-Based Augmentation System– International standard GNSS augmentation system.

US WAAS, Japanese MSAS, European EGNOS, and Indian GAGAN. Existing standards: L1 single frequency system.

– New standards: Dual-Frequency Multi-Constellation SBAS (L5 SBAS) The standardization is ongoing by the ICAO. Target: end of 2020. The First L5 SBAS experiment by ENRI/MPAT, Japan, using QZSS

constellation.

• Contact: Dr. Takeyasu Sakai <[email protected]>Electronic Navigation Research InstituteNational Institute of Maritime, Port and Aviation Technology, Japan

Documents

GNSS and Satellite-Based Augmentation Systemsproceedings.kaconf.org/papers/2019/bsw_2.pdf · 2019. 9. 21. · GNSS and Satellite-Based Augmentation Systems Takeyasu Sakai ... Not