TOWARDS MULTI-FREQUENCY MULTI-CONSTELLATION GNSS AND SBAS

TOWARDSMULTI-FREQUENCY

MULTI-CONSTELLATION GNSS AND SBAS

Guenter W. Hein

Head of Galileo Operations and Evolution DepartmentEuropean Space Agency

2nd China Satellite Navigation Conference (CSNC), 2011Shanghai, 18-20 May 2011

2nd China Satellite Navigation Conference (CSNC), 2011Shanghai, 18-20 May 2011

CSNC 2011 | Guenter W. Hein | Shanghai, China | 18/05/2011 | Slide 2

OVERVIEW

• The World of GNSS International GNSS Trends

Compatibility and Interoperability

New Signals and Frequency Bands

The More Satellites The Better…?

• The Evolution of SBAS

• Conclusions


CURRENT AND PLANNED SATELLITE NAVIGATION SYSTEMS

GlobalGPS

Galileo

GLONASS

COMPASS

RegionalQZSS

IRNSS

AugmentationWAAS EGNOS

MSAS GAGAN

SDCM MASS

GINS (?)


International GNSS Systems Trends 1 1. Flexibility, higher power, coverage, ...

a. Signal flexibility and general increase of power level.High increase of power level (>20 dBs) regionally

2. Alternative frequency bands

a. S-Band Satellite Navigation allocated in ITU Region 2 and 3, used and planned by IRNSS and perhaps others

3. Inter-Satellite Links (ISL) and better system autonomy

a. GPS includes ISL for autonomy and NAVWAR purposes.GPS III will use ISL to improve performance via faster navigation message updates to whole constellation

b. Glonass and Compass may include ISL in the future. Main interest is up-linking all satellites from national territory


International GNSS Systems Trends 2

4. System on-board integrity capabilities

a. GPS III plans on-board integrity monitoring in few seconds

5. Worldwide positioning performance improvement

a. GPS provides new signals L1C, L2C, L5 and faster refresh of navigation message for world-wide meter-level point positioning

b. Similar plans apply with different time scales to all the other systems: Glonass, Compass, IRNSS and QZSS

6. Alternative orbits

a. QZSS introducing HEOs for better visibility over urban areas

b. Compass and IRNSS are introducing GEOs and IGSOs to establish their own regional service


• Compatibility refers to the ability of space-based positioning, navigation, and timing services to be used separately or together without interfering with each individual service or signal, and without adversely affecting national security

• Interoperability refers to the ability of civil space-based positioning, navigation, and timing services to be used together to provide better capabilities at the user level than would be achieved by relying solely on one service or signal

COMPATIBILITY & INTEROPERABILITY

*NSPD-39: U.S. Space-Based Position, Navigation, and Timing Policy, December 15, 2004


• Modernization of existing systems

• Deployment of new systems

• Intersystem interference is becoming an issue

Particularly for authorized services

Spectral separation plays a fundamental role

But also for open services

Galileo, GPS, Compass, QZSS, GLONASS (potentially) will provide interoperable signals increasing the noise floor and the consequent degradation of performance

• L-Band may not serve all users in an ideal way (indoor/single/frequency/ iono)

Spectral resources get scarce

NEW SIGNALS & FREQUENCY BANDSMOTIVATION


• ITU Allocation C-Band (5010-5030) for RNSS since WRC 2000

• Technical difficulties and limitations in performance for that allocation

• Advantages

– Higher resolution

– Smaller ionospheric impact

– Smaller antennas at satellite

• Drawbacks

– Higher attenuation in atmosphere

– Higher power at satellite or user array antennas needed

• Studies indicate that C-band for mass market is not (yet) mature

• C-band preferable for high-power signals and smaller antennas

• Search for more bandwidth on C-band necessary

C-BAND DOWN-LINK FREQUENCY


• S-Band (2483.5 – 2500 MHz) is RNSS regionally (Asia/America)

• S-Band already used today for telecommunication + WLAN + Bluetooth

• Advantage: Synergies between navigation & communication (front-end)

• Disadvantage: Harsh interference environment expected

Clarity needs to be gained on the added value of combining navigation and communication in S-Band for mass market

S-BAND DOWN-LINK FREQUENCY

• ITU divides world into three regions for radio spectrum management

• Region 1 • Europe, Africa, Middle East, west of the Persian

Gulf, Russia• Region 2

• American continent, some eastern Pacific Islands• Region 3

• China, Japan, East Asia and most of Oceania


INTEROPERABILITY TODAY

Interoperability achievedInteroperability still to be achieved

CSNC 2011 | Guenter W. Hein | Shanghai, China | 18/05/2011 | Slide 11ESA UNCLASSIFIED – Releasable to the Public

THE MORE SATELLITES THE BETTER?Galileo

GPS GLONASS

GalileoGPS

Galileo

COMPASSGLONASS

GPSGalileo

COMPASSGLONASS

GPSGalileo

GINS

?

GDOP decreases as the inverse square root of the number of satellites

satNGDOP

1

Once GNSS interference is dominant, noise floor increases linearly proportional to the number of satellites

satNI intra


THE FUTURE

• Large number of GNSS satellites in visibility in future

• The users will pick up the best GNSS signals based on:

Power level

Easy acquisition

Adherence to multi-constellation standards


IS THE BATTLE REALLY LOST?

• Not really…fortunately!

• Conventional GPS receivers consist of several parallel scalar DLLs, which individually

estimate the individual pseudoranges These measured pseudoranged are further fed to the

Kalman Filter Estimator Conventional receivers assume thus truly

independence of measurements

• As more satellites add to the noise floor, the lower will be the C/N0

of each individual acquisition/tracking channel At a certain number of satellites, the acquisition/tracking

channel C/N0 will be below the required threshold

Conventional GPS receivers could stop functioning Selection algorithms and Interference Cancellation

help in mitigating higher interference

CSNC 2011 | Guenter W. Hein | Shanghai, China | 18/05/2011 | Slide 14ESA UNCLASSIFIED – Releasable to the Public

SOME SOLUTIONS FOR CONVENTIONAL RECEIVERS

• At a certain number of satellites, some channels will have a too low

individual C/N0 to perform acquisition or tracking. This requires:

Selection of individual channels to compute the navigation solution:

Selection of channels with best C/N0

Selection of channels with best geometry

Selection of channels with best error budget

Additional constraints result from the fact that conventional receivers have a limited number of channels to process, resulting in

Reduction of satellites to process using convex geometry theory *

Maximization of polytope: Chan’s algorithm, Graham’s Scan algorithm, etc…

Convex geometry selection is based

on the approximate equivalence

between minimizing the geometric

dilution of precision (GDOP) and

maximizing the size of the polytope

(polyhedron in 3D or polygon in 2D)

contained in the convex hull of all

vector’s endpoints for the set of

satellites in view *

* Blanco Delgado, N. and Nunes, F. (2010), A Satellite Selection Method for Multi-Constellation GNSS Using Convex Geometry, IEEE Transactions on Vehicular Technology

• Since conventional receivers might not be able to process all satellites in view, the assumption that the GDOP decreases as the inverse square root of the number of satellites is not any more valid

• On the other hand the aggregate GNSS interference will still grow linearly as the number of satellites increases regardless of how many are actually used for computing the navigation solution

• As a result, at a certain number of satellites the number of channels with C/N0 above the acquisition or tracking threshold will be lower than 4, and conventional receivers that estimate individually the pseudoranges could unavoidably fail


VECTOR PROCESSING IS THE ANSWER

• Vector tracking (VDLL) estimates the signal delays of all satellites in view in a single processing loop

Generalization of Extended Kalman Filter (EKF) Total noise is reduced by considering all channels together VDLL accounts for the actual correlation amongst channels Shannon-Theorem on GNSS channel capacity

It is the total power received from all GNSS satellites what defines the capacity of a GNSS channel (!!)

VDLL explodes the capacity increase from additional satellites

“The use of signals from different satellites may provide enough total signal power to track successfully and to obtain position

estimates under the same conditions where the signal strength from each individual satellite is so low that

none of the individual scalar DLL can remain in lock” ** James J. Spilker Jr. Global Positioning System: Theory and Applications Vol. I, chapter 7


SHANNON-THEOREM ON GNSS CHANNEL CAPACITY

• Total multiple access channel capacity C increases with number of signals N

• where B is the bandwidth of the GNSS channel

Pi is the power of each received signal

N0 is the one-sided noise density

N is the number of GNSS signals received

• For PiB/N0>>1 the channel capacity increases in proportion to log2N

• The total information rate sought from the channel (x,y,z – navigation position) is a constant independent of N (!!!)

where the desired information rate (rate distortion function) for three coordinates is

being the rate at which measurements are sought 2W

)1(log)1(log1

022

N

ii BNPBSNRBC

2,, ˆ,ˆ,ˆ,, zyxzyxED zyx

3

,, ,,

2,,

2logzyx zyx

zyx

DWDR

• As far as C>R(D), the more satellites the better *• With N satellites in sight with good geometry, it

should be possible to operate with a signal power/satellite ratio that can decrease as N increases *

• High-speed and low-cost computer chips make this task more feasible now for tracking, whereas in the past it would have been too complex

BUT

• VDLL requires relatively high speed since the computation delay must be small

• In particular for acquisition, vector processing is still an issue today

* James J. Spilker Jr. Global Positioning System: Theory and Applications Vol. I, chapter 7


OVERVIEW

• The World of GNSS International GNSS Trends

Compatibility and Interoperability

New Signals and Frequency Bands

The More Satellites The Better…?


• Conclusions


OVERVIEW

• The World of GNSS

• The Evolution of SBAS International SBAS Developments

EGNOS and SBAS Evolution

Arctic and Antarctic Coverage

Integrity

• Conclusions


Overview existing SBAS

– EGNOS v2.3 being certified for APV-I, 2 GEO*, 38 RIMS, 4 MCC, 4 NLES.

– WAAS operational LPV (250 ft),

2 GEO**, 38 RIMS, 2 MCC, 4 NLES.

– MSAS operational RNAV,

2 GEO, 4 RIMS, 2 MCC, 4 NLES.

– Combined GEO footprints cover most of world land areas.

– SBAS looking ahead to LPV-200.

SBAS Systems LPV-200 coverage analysis

* One GEO used for test purpose.** Recent GEO failure CRW, planned to be replaced

soon.


International SBAS developments

– WAAS delivers full LPV-200 service in 2013 by enhancing the current system.

– WAAS will deliver a dual frequency L1/L5 service by 2018; first upgrades ongoing.

– FAA studies ARAIM dual frequency & constellation for the 2025-2030 timeframe.

– MSAS faces obsolesce issues now, but plans to deliver LPV-200 in 2014.

– GAGAN to be operational in 2012. Failed GEO launch in 2010 delayed the introduction.

– Russia develops SDCM with 3 Luch GEO satellites (2011-13). High precision services will be included.

– China develops MASS system; transmission by GEO and/or Compass. Augments GPS, Compass and Galileo. High precision services will be included.

CSNC 2011 | Guenter W. Hein | Shanghai, China | 18/05/2011 | Slide 21ESA UNCLASSIFIED – For Official Use

Upgrade Ground Segment to GPS/Galileo improves current EGNOS L1 service

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> 90%

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> 99%

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> 99.9%

Longitude (deg)

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-40 -30 -20 -10 0 10 20 30 40 50

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Longitude (deg)

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Current Performance Future Performance: GPS+Galileo G/S

APV-I Coverage Performance for EGNOS GPS L1 users


LPV-200 L1/L5 GPS Only

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Longitude (deg)

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L1/L5 Service / 24GPS Satellites / GEOs set to monitored / RIMS Elevation Mask 15deg / MT28 ImplementedTimestep 300s / Duration 1 day / Gridsize 2.5x2.5deg

-180 -120 -60 0 60 120 180-90

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LPV-200 L1/L5 GPS+ Galileo - Complete Coverage of Africa

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Longitude (deg)

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L1/L5 Service / 24GPS+27GAL Satellites / GEOs set to monitored / RIMS Elevation Mask 15deg / MT28 ImplementedTimestep 300s / Duration 1 day / Gridsize 2.5x2.5deg

-180 -120 -60 0 60 120 180-90

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LPV-200 L1/L5 GPS+Galileo Multi-Regional

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Longitude (deg)

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(deg

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L1/L5 Service / 24 GPS + 27 GAL Satellites / GEOs set to monitored / RIMS Elevation Mask 15deg / MT28 ImplementedTimestep 300s / Duration 1 Day / Grid 2.5 x 2.5 deg

-180 -120 -60 0 60 120 180-90

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CAT-I L1/L5 GPS + GAL

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Longitude (deg)

Latit

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(deg

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L1/L5 Service / 24GPS+27GAL Satellites / GEOs set to monitored / RIMS Elevation Mask 15deg / MT28 ImplementedTimestep 300s / Duration 1 day / Gridsize 2.5x2.5deg

-180 -120 -60 0 60 120 180-90

-60

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With only a few more RIMS in polar region LPV-200 service could be provided, but region outside of GEO coverage. Alternative orbits needed:

– Polar Communication & Weather (PCW) HEO Molniya type satellite(s)

– Alternative orbits like IGSO are also an option. Artemis could be test candidate.

EGNOS /PCW LPV-200 L1/L5 Availability

with +10 RIMS in Arctic

ARCTIC COVERAGE STUDIED BY ESA


INTEGRITY – From where? For whom?

GNSS ?

SBAS ?RAIM ?


OVERVIEW

• The World of GNSS


• Conclusions


CONCLUSIONS 1

• After 2020: More than 40 MEO navigation satellites in view

Higher accuracy and availability (urban areas), redundancy allows more sophisticated methods If signals RF compatible and interoperable

The more the better … right or wrong, questionable ? Increase of noise floor Conventional receivers and vector processing

• Integrity: Global versus SBAS versus User Level Multi-frequency/system regional SBAS can cover almost

whole world and ARAIM may be a new concept Just sophisticated RAIM for non-aviation integrity?


• Radio Frequency spectrum is full Intentional versus unintentional interference Degradation of navigation performance Security aspects for protected signals

No spectral overlap

• New frequency bands, S-band, C-band ?

• RF Interference might be the biggest GNSS problem in future

CONCLUSIONS 2

TOWARDS MULTI-FREQUENCY MULTI-CONSTELLATION GNSS AND SBAS

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