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{{Article Infobox2 | {{Article Infobox2 | ||
|Category=EGNOS | |Category=EGNOS | ||
| | |Editors=GMV | ||
|Level=Basic | |Level=Basic | ||
|YearOfPublication=2011 | |YearOfPublication=2011 | ||
|Logo=GMV | |Logo=GMV | ||
|Title={{PAGENAME}} | |||
}} | }} | ||
[[EGNOS General Introduction|EGNOS]] (European Geostationary Navigation Overlay Service) is the European satellite-based augmentation service (SBAS) that complements the existing satellite navigation services provided by the US Global Positioning System (GPS). The EGNOS signal-in-space is broadcast by Geostationary Earth Orbit (GEO) satellites in the L1 frequency, centred at 1575.42 MHz, meeting stringent standards established by organizations like ICAO and RTCA. | |||
The | The next evolution of EGNOS; namely EGNOS V3, will provide dual-frequency signals on both bands L1 and L5 augmenting both GPS and Galileo constellation data.<ref name="EGNOS V3">[https://www.gsa.europa.eu/newsroom/news/airbus-awarded-egnos-v3-contract EGNOS V3 contract awarded]</ref> | ||
==EGNOS SIS Interface Characteristics== | ==EGNOS SIS Interface Characteristics== | ||
[[File:EGNOS_Coverage.png|Source: EGNOS Service Notice #22 <ref name= SN 22">[https://egnos-user-support.essp-sas.eu/new_egnos_ops/sites/default/files/documents/service_notice_22_0.pdf EGNOS Service Notice #22] </ref> |340px|thumb|right]] | |||
The EGNOS Signal In Space format is compliant with the ICAO SARPs for SBAS<ref>SARPS Amendment 77, Annex 10 to the Convention on International Civil Aviation, Aeronautical Telecommunications: International Standards and Recommended Practices, Volume 1, Radio Navigation Aids, November 2002.</ref> as stated in the [[EGNOS Open Service | EGNOS Open Service]] Definition Document and the [[EGNOS Safety of Life Service|EGNOS Safety of Life]] Service Definition Document.<ref name=" EGNOS OS SDD">[http://www.essp-sas.eu/service_definition_documents EGNOS Open Service Definition Document]</ref><ref name=" EGNOS SOL SDD">[http://www.essp-sas.eu/service_definition_documents EGNOS Safety of Life Service Definition Document]</ref> The EGNOS SIS interface characteristics comprise carrier and modulation radio frequency, message structure, protocol and content of the EGNOS message (detailed in the [[EGNOS Messages | EGNOS Message Format ]] definition). | |||
The EGNOS Signal In Space format is compliant with the ICAO SARPs for SBAS<ref>SARPS Amendment 77, Annex 10 to the Convention on International Civil Aviation, Aeronautical Telecommunications: International Standards and Recommended Practices, Volume 1, Radio Navigation Aids, November 2002.</ref> as stated in the [[EGNOS Open Service | EGNOS Open Service]] | |||
EGNOS uses three GEO satellites at different longitude to broadcast its signals across the whole EGNOS service area. See details in the [[EGNOS Space Segment | EGNOS Space Segment]] article. The figure shows the most updated EGNOS GEO satellites coverage with a 5 degrees masking angle. | |||
Contrary to the case of core navigation space vehicles with active navigation payloads, the EGNOS GEO satellites carry transponders relaying the signal transmitted from the [[EGNOS Ground Segment|ground segment]] uplink stations.<ref name=" EGNOS OS SDD"/> | |||
EGNOS V3 will ensure a full continuity of service for the next decade and will be implement the dual frequency and multi constellation world standard, replacing EGNOS V2 which has been in operation since 2011. For this, a new generation of user terminals will be needed according with the new standards for Dual Frequency Multi Constellation (DFMC).<ref name="EGNOS V3">[https://www.gsa.europa.eu/newsroom/news/airbus-awarded-egnos-v3-contract EGNOS V3 contract awarded]</ref> | |||
==EGNOS SIS RF Characteristics== | ==EGNOS SIS RF Characteristics== | ||
As any other SBAS, EGNOS broadcasts its augmentation information in L1 band, at 1575.42 MHz, using right-hand circular polarization (RHCP). Each individual second, EGNOS transmit a navigation message containing 250 bits of information. | |||
This raw navigation message is ½ convolutional encoded with Forward Error Correcting (FEC) Code resulting in a 500 symbol/second EGNOS data stream. | This raw navigation message is ½ convolutional encoded with Forward Error Correcting (FEC) Code resulting in a 500 symbol/second EGNOS data stream. | ||
This data stream is added modulo-2 to a 1023-bit PRN code, which will then be biphase shift-keyed (BPSK) modulated onto the L1 carrier frequency at a rate of 1.023 Mega-chips/second (Mcps). <ref name=" RTCA MOPS DO 229">Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airborne Equipment (RTCA MOPS 229)</ref> | |||
For unobstructed view-lines with elevation angles greater than 5 degrees on the Earth surface, the EGNOS signal is received by 3dBi linearly polarised antennae with a power in the –161 dBW to –153 dBW range, assuming an orientation of the antenna orthogonal to the propagation direction. In addition, spurious transmissions are bounded at least 40dB below unmodulated carrier power.<ref name=" EGNOS OS SDD"/> It is planned to enhance the signal-to-noise ratio in future replenishments of the EGNOS space segment, with the intention to improve the tracking performance at user level. | |||
It is | |||
tracking performance | |||
As stated in MOPS DO 229, the most relevant EGNOS signal characteristics are detailed hereafter:<ref name=" RTCA MOPS DO 229"/> | |||
* '''Carrier Phase Noise''': The phase noise spectral density of the unmodulated carrier is such that a phase locked loop of 10Hz one-sided noise bandwidth is able to track the carrier to an accuracy of 0.1 radians rms. | * '''Carrier Phase Noise''': The phase noise spectral density of the unmodulated carrier is such that a phase locked loop of 10Hz one-sided noise bandwidth is able to track the carrier to an accuracy of 0.1 radians rms. | ||
* '''Signal Spectrum''': The broadcast signal is at GPS L1 frequency of 1575.42 MHz. At least 95% of the broadcast power is contained within a +/- 12MHz band | * '''Signal Spectrum''': The broadcast signal is at GPS L1 frequency of 1575.42 MHz. At least 95% of the broadcast power is contained within a +/- 12MHz band centred at the L1 frequency. The bandwidth of the signal transmitted by an EGNOS satellite is at least 2.2MHz. | ||
* '''Doppler Shift''': The Doppler shift, as perceived by a stationary user, on the signal broadcast by EGNOS GEOs is less than 40 meters per second (≈210 Hz at L1) in the worst case (at the end of life of the GEOs). The Doppler shift is due to the relative motion of the GEO. | * '''Doppler Shift''': The Doppler shift, as perceived by a stationary user, on the signal broadcast by EGNOS GEOs is less than 40 meters per second (≈210 Hz at L1) in the worst case (at the end of life of the GEOs). The Doppler shift is due to the relative motion of the GEO. | ||
* '''Carrier Frequency Stability''': The short term stability of the carrier frequency (square root of the Allan Variance) at the input of the user´s receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding the effects of the ionosphere and Doppler. | * '''Carrier Frequency Stability''': The short term stability of the carrier frequency (square root of the Allan Variance) at the input of the user´s receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding the effects of the ionosphere and Doppler. | ||
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* '''Correlation Loss''': Correlation loss is defined as the ratio of output powers from a perfect correlator for two cases: 1) the actual receiver EGNOS signal correlated against a perfect unfiltered PN reference, or 2) a perfect unfiltered PN signal normalized to the same total power as the EGNOS signal in case 1, correlated against a perfect unfiltered PN reference. The correlation loss resulting from modulation imperfections and filtering inside the EGNOS satellite payload is less than 1 dB. | * '''Correlation Loss''': Correlation loss is defined as the ratio of output powers from a perfect correlator for two cases: 1) the actual receiver EGNOS signal correlated against a perfect unfiltered PN reference, or 2) a perfect unfiltered PN signal normalized to the same total power as the EGNOS signal in case 1, correlated against a perfect unfiltered PN reference. The correlation loss resulting from modulation imperfections and filtering inside the EGNOS satellite payload is less than 1 dB. | ||
== | ==SBAS Signal Generators== | ||
Nowadays, there exists operational commercial off-the-shelf equipment to generate the SBAS signal to be uplinked to the GEO for relay.<ref name=" Novatel GUS-Type 1 Signal Generation Product Sheet ">[http://www.novatel.com/products/gnss-receivers/ground-reference-and-uplink-receivers/gus-signal-generator/ Novatel GUS-Type 1 Signal Generation Product Sheet]</ref> | |||
In addition, there are other flexible platforms useful to generate test signals for development and evaluation of user SBAS receivers.<ref name=" Spirent GSS4100 Signal Generator Product Reference Sheet">[http://www.testequipmentconnection.com/specs/Spirent_GSS4100.PDF Spirent GSS4100 Signal Generator Product Reference Sheet]</ref> These products allow to select specific navigation satellite systems, to define influencing error sources, to choose signal frequency and modulations schemes as well as the RF Front end and filter characteristics. | |||
<references group="footnotes"/> | <references group="footnotes"/> | ||
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<references/> | <references/> | ||
[[Category:EGNOS|Signal]] | |||
[[Category:EGNOS]] | [[Category:EGNOS Signal Structure|Signal]] | ||
[[Category:EGNOS Signal Structure]] | |||
Latest revision as of 13:58, 18 March 2020
| EGNOS | |
|---|---|
| Title | EGNOS Signal Structure |
| Edited by | GMV |
| Level | Basic |
| Year of Publication | 2011 |
EGNOS (European Geostationary Navigation Overlay Service) is the European satellite-based augmentation service (SBAS) that complements the existing satellite navigation services provided by the US Global Positioning System (GPS). The EGNOS signal-in-space is broadcast by Geostationary Earth Orbit (GEO) satellites in the L1 frequency, centred at 1575.42 MHz, meeting stringent standards established by organizations like ICAO and RTCA.
The next evolution of EGNOS; namely EGNOS V3, will provide dual-frequency signals on both bands L1 and L5 augmenting both GPS and Galileo constellation data.[1]
EGNOS SIS Interface Characteristics
Source: EGNOS Service Notice #22 [2]
The EGNOS Signal In Space format is compliant with the ICAO SARPs for SBAS[3] as stated in the EGNOS Open Service Definition Document and the EGNOS Safety of Life Service Definition Document.[4][5] The EGNOS SIS interface characteristics comprise carrier and modulation radio frequency, message structure, protocol and content of the EGNOS message (detailed in the EGNOS Message Format definition).
EGNOS uses three GEO satellites at different longitude to broadcast its signals across the whole EGNOS service area. See details in the EGNOS Space Segment article. The figure shows the most updated EGNOS GEO satellites coverage with a 5 degrees masking angle.
Contrary to the case of core navigation space vehicles with active navigation payloads, the EGNOS GEO satellites carry transponders relaying the signal transmitted from the ground segment uplink stations.[4]
EGNOS V3 will ensure a full continuity of service for the next decade and will be implement the dual frequency and multi constellation world standard, replacing EGNOS V2 which has been in operation since 2011. For this, a new generation of user terminals will be needed according with the new standards for Dual Frequency Multi Constellation (DFMC).[1]
EGNOS SIS RF Characteristics
As any other SBAS, EGNOS broadcasts its augmentation information in L1 band, at 1575.42 MHz, using right-hand circular polarization (RHCP). Each individual second, EGNOS transmit a navigation message containing 250 bits of information. This raw navigation message is ½ convolutional encoded with Forward Error Correcting (FEC) Code resulting in a 500 symbol/second EGNOS data stream. This data stream is added modulo-2 to a 1023-bit PRN code, which will then be biphase shift-keyed (BPSK) modulated onto the L1 carrier frequency at a rate of 1.023 Mega-chips/second (Mcps). [6]
For unobstructed view-lines with elevation angles greater than 5 degrees on the Earth surface, the EGNOS signal is received by 3dBi linearly polarised antennae with a power in the –161 dBW to –153 dBW range, assuming an orientation of the antenna orthogonal to the propagation direction. In addition, spurious transmissions are bounded at least 40dB below unmodulated carrier power.[4] It is planned to enhance the signal-to-noise ratio in future replenishments of the EGNOS space segment, with the intention to improve the tracking performance at user level.
As stated in MOPS DO 229, the most relevant EGNOS signal characteristics are detailed hereafter:[6]
- Carrier Phase Noise: The phase noise spectral density of the unmodulated carrier is such that a phase locked loop of 10Hz one-sided noise bandwidth is able to track the carrier to an accuracy of 0.1 radians rms.
- Signal Spectrum: The broadcast signal is at GPS L1 frequency of 1575.42 MHz. At least 95% of the broadcast power is contained within a +/- 12MHz band centred at the L1 frequency. The bandwidth of the signal transmitted by an EGNOS satellite is at least 2.2MHz.
- Doppler Shift: The Doppler shift, as perceived by a stationary user, on the signal broadcast by EGNOS GEOs is less than 40 meters per second (≈210 Hz at L1) in the worst case (at the end of life of the GEOs). The Doppler shift is due to the relative motion of the GEO.
- Carrier Frequency Stability: The short term stability of the carrier frequency (square root of the Allan Variance) at the input of the user´s receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding the effects of the ionosphere and Doppler.
- Polarization: The broadcast signal is right-handed circularly polarized. The ellipticity will be no worse than 2 dB for the angular range of ±9.1o from boresight.
- Correlation Loss: Correlation loss is defined as the ratio of output powers from a perfect correlator for two cases: 1) the actual receiver EGNOS signal correlated against a perfect unfiltered PN reference, or 2) a perfect unfiltered PN signal normalized to the same total power as the EGNOS signal in case 1, correlated against a perfect unfiltered PN reference. The correlation loss resulting from modulation imperfections and filtering inside the EGNOS satellite payload is less than 1 dB.
SBAS Signal Generators
Nowadays, there exists operational commercial off-the-shelf equipment to generate the SBAS signal to be uplinked to the GEO for relay.[7]
In addition, there are other flexible platforms useful to generate test signals for development and evaluation of user SBAS receivers.[8] These products allow to select specific navigation satellite systems, to define influencing error sources, to choose signal frequency and modulations schemes as well as the RF Front end and filter characteristics.
References
- ^ a b EGNOS V3 contract awarded
- ^ EGNOS Service Notice #22
- ^ SARPS Amendment 77, Annex 10 to the Convention on International Civil Aviation, Aeronautical Telecommunications: International Standards and Recommended Practices, Volume 1, Radio Navigation Aids, November 2002.
- ^ a b c EGNOS Open Service Definition Document
- ^ EGNOS Safety of Life Service Definition Document
- ^ a b Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airborne Equipment (RTCA MOPS 229)
- ^ Novatel GUS-Type 1 Signal Generation Product Sheet
- ^ Spirent GSS4100 Signal Generator Product Reference Sheet