SIST EN 16603-50-02:2014
(Main)Space engineering - Ranging and Doppler tracking
Space engineering - Ranging and Doppler tracking
EN 16603-50-02 is applicable to spacecraft that are supported for ranging or Dop-pler tracking by direct links to Earth stations and to all related Earth stations (therefore, this Standard is not applicable for spacecraft supported by data relay satellites) operating within the Space Operation, Space Research and Earth Exploration Satellite services (therefore, this Standard is not applicable to the Meteorological Satellite service) as defined in ECSS-E-ST-50-05 clause 1. Other space telecommunication services are not covered in this issue. This Standard applies to projects with unprocessed ranging accuracies of 2,5ns to 30 ns (for conventional projects with tracking accuracies less stringent than these, CCSDS 401.0-B recommendations may be sufficient) and Doppler tracking accuracies of 0,1 mm/s to 1 mm/s. The analysis of compatibility between systems compliant with this standard and with the CCSDS recommendations is given in Annexes A.2 and A.3. This document: • Defines the requirements concerning spacecraft transponder and Earth station equipment for the purposes of ranging and Doppler tracking. • Provides criteria by which the extent to which the accuracy of the measurements is influenced by equipment effects can be determined. This accuracy is different to the accuracy of the overall orbit determination process, which is also influenced by effects outside the scope of the standards, i.e. modelling of gravitational and non-gravitational forces, modelling of propagation effects, pre-processing and screening of data. This standard may be tailored for the specific characteristics and constraints of a space project in conformance with ECSS-S-ST-00.
Raumfahrttechnik - Entfernungsbestimmung und Dopplerverfolgung
Ingénierie spatiale - Mesure de distance et suivi Doppler
Vesoljska tehnika - Ugotavljanje oddaljenosti in doplersko sledenje
Standard EN 16603-50-02 velja za vesoljska plovila, ki omogočajo ugotavljanje oddaljenosti in doplersko sledenje z neposrednimi povezavami do zemeljskih postaj in vseh povezanih zemeljskih postaj (zato se ta standard ne uporablja za vesoljska plovila, podprta s sateliti za prenos podatkov), ki delujejo v okviru storitev za vesoljsko obratovanje, vesoljskih raziskav in satelitskega raziskovanja Zemlje (zato se ta standard ne uporablja za meteorološke satelitske storitve), kot je določeno v točki 1 standarda ECSS-E-ST-50-05. Druge vesoljske telekomunikacijske storitve niso zajete v tej izdaji. Ta standard velja za projekte z neobdelano natančnostjo razdalje od 2,5 ns do 30 ns (za običajne projekte s sledilnimi natančnostmi, manj strogimi od teh, so lahko dovolj priporočila CCSDS 401.0-B) in natančnostjo doplerskega sledenja od 0,1 mm/s do 1 mm/s. Analiza združljivosti med sistemi, ki so skladni s tem standardom, in priporočili CCSDS je podana v Dodatkih A.2 in A.3. Ta dokument: • določa zahteve glede transponderjev vesoljskih plovil in opreme zemeljskih postaj za ugotavljanje oddaljenosti in doplersko sledenje, • zajema merila, s katerimi je mogoče določiti, v kolikšni meri so na natančnost meritev vplivali učinki opreme. Ta natančnost se razlikuje od natančnosti celotnega postopka določanja orbite, na katerega vplivajo tudi učinki zunaj področja uporabe standardov, tj. modeliranje gravitacijskih in negravitacijskih sil, modeliranje učinkov širjenja, predobdelava in pregledovanje podatkov. Ta standard se lahko prilagodi posameznim lastnostim in omejitvam vesoljskega projekta v skladu s standardom ECSS-S-ST-00.
General Information
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Vesoljska tehnika - Ugotavljanje oddaljenosti in doplersko sledenjeRaumfahrttechnik - Entfernungsbestimmung und DopplerverfolgungIngénierie spatiale - Mesure de distance et suivi DopplerSpace engineering - Ranging and Doppler tracking49.140Vesoljski sistemi in operacijeSpace systems and operationsICS:Ta slovenski standard je istoveten z:EN 16603-50-02:2014SIST EN 16603-50-02:2014en,fr,de01-november-2014SIST EN 16603-50-02:2014SLOVENSKI
STANDARD
SIST EN 16603-50-02:2014
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 16603-50-02
September 2014 ICS 49.140
English version
Space engineering - Ranging and Doppler tracking
Ingénierie spatiale - Mesure de distance et suivi Doppler
Raumfahrttechnik - Entfernungsbestimmung und Dopplerverfolgung This European Standard was approved by CEN on 1 March 2014.
CEN and CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN and CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN and CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.
CEN and CENELEC members are the national standards bodies and national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels © 2014 CEN/CENELEC All rights of exploitation in any form and by any means reserved worldwide for CEN national Members and for CENELEC Members. Ref. No. EN 16603-50-02:2014 E SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 2 Table of contents Foreword . 4 Introduction . 5 1 Scope . 6 2 Normative references . 7 3 Terms, definitions and abbreviated terms . 8 3.1 Terms from other standards . 8 3.2 Terms specific to the present standard . 8 3.3 Abbreviated terms. 8 4 Requirements . 10 4.1 Functional . 10 4.1.1 Functional breakdown . 10 4.1.2 Earth-to-Space link function . 12 4.1.3 Transponder function . 12 4.1.4 Space-to-Earth link function . 13 4.1.5 Link control function . 14 4.1.6 Data acquisition function . 14 4.2 Frequency assignment, modulation and spectral sharing. 15 4.2.1 Frequency assignment . 15 4.2.2 Modulation . 16 4.2.3 Spectral sharing . 18 4.3 Carrier frequency stability . 22 4.4 Earth station . 24 4.4.1 Earth-to-Space link. 24 4.4.2 Space-to-Earth link. 25 4.5 Spacecraft transponder . 27 4.5.1 General . 27 4.5.2 Range and range rate operations . 27 4.5.3 Range only operations . 28 4.5.4 Group delay . 28 SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 3 4.5.5 Telemetered monitoring . 29 4.5.6 Amplitude response . 29 4.5.7 Phase modulation . 30 4.5.8 Baseband automatic gain control (AGC) . 30 4.5.9 Modulation index . 30 4.5.10 Ranging technological loss . 30 4.6 Performance . 31 4.6.1 Overview . 31 4.6.2 Integrated Doppler performance. 31 4.6.3 Ranging performance . 32 4.6.4 Ancillary measurements . 33 5 Compatibility testing . 35 5.1 General . 35 5.2 Tests. 35 Annex A (informative) Compatibility with other ground stations networks . 37 Annex B (informative) Transponder ranging technological loss . 39 Annex C (informative) Integrated Doppler measurement . 40 Bibliography . 42
Figures Figure 4-1: Ranging and Doppler tracking: functional block diagram . 11 Figure 4-2: Ranging signal spectrum for code length = 20 . 18 Figure 4-3: Ranging signal spectrum for code length = 22 . 19 Figure 4-4: Ranging signal spectrum for code length = 24 . 19 Figure 4-5: Ranging signal spectrum for code length = 212 . 20 Figure 4-6: Carrier frequency stability requirements . 23 Figure C-1 :Integrated Doppler measurement . 41
SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 4 Foreword This document (EN 16603-50-02:2014) has been prepared by Technical Committee CEN/CLC/TC 5 “Space”, the secretariat of which is held by DIN. This standard (EN 16603-50-02:2014) originates from ECSS-E-ST-50-02C. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by March 2015, and conflicting national standards shall be withdrawn at the latest by March 2015. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association. This document has been developed to cover specifically space systems and has therefore precedence over any EN covering the same scope but with a wider domain of applicability (e.g. : aerospace). According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 5 Introduction The purpose of this Standard is to: • Ensure compatibility between space agencies' spacecraft transponders and the ranging and Doppler tracking facilities of the Earth stations for the Space Operation, Space Research and Earth Exploration Satellite services. • Ensure, as far as possible, compatibility between space agencies' spacecraft transponders and other networks from which they request support. • Ensure an adequate level of ranging and Doppler tracking accuracy for missions conforming to this standard. Facilitate the early design of flight hardware and ensure that the resulting interfaces and system performances are compatible with given ranging and Doppler tracking configurations and specifications. SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 6 1 Scope This Standard is applicable to spacecraft that are supported for ranging or Dop-pler tracking by direct links to Earth stations and to all related Earth stations (therefore, this Standard is not applicable for spacecraft supported by data relay satellites) operating within the Space Operation, Space Research and Earth Exploration Satellite services (therefore, this Standard is not applicable to the Meteorological Satellite service) as defined in ECSS-E-ST-50-05 clause 1. Other space telecommunication services are not covered in this issue. This Standard applies to projects with unprocessed ranging accuracies of 2,5ns to 30 ns (for conventional projects with tracking accuracies less stringent than these, CCSDS 401.0-B recommendations may be sufficient) and Doppler tracking accuracies of 0,1 mm/s to 1 mm/s. The analysis of compatibility between systems compliant with this standard and with the CCSDS recommendations is given in Annexes A.2 and A.3. This document: • Defines the requirements concerning spacecraft transponder and Earth station equipment for the purposes of ranging and Doppler tracking. • Provides criteria by which the extent to which the accuracy of the measurements is influenced by equipment effects can be determined.
This accuracy is different to the accuracy of the overall orbit determination process, which is also influenced by effects outside the scope of the standards, i.e. modelling of gravitational and non-gravitational forces, modelling of propagation effects, pre-processing and screening of data. This standard may be tailored for the specific characteristics and constraints of a space project in conformance with ECSS-S-ST-00. SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 7 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this ECSS Standard. For dated references, subsequent amendments to, or revisions of any of these publications, do not apply. However, parties to agreements based on this ECSS Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references the latest edition of the publication referred to applies.
EN reference Reference in text Title EN 16601-00-01 ECSS-S-ST-00-01 ECSS system – Glossary of terms EN 16603-50 ECSS-E-ST-50 Space engineering – Communications EN 16603-50-05 ECSS-E-ST-50-05 Space engineering – Radio frequency and modulation
SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 8 3 Terms, definitions and abbreviated terms 3.1 Terms from other standards For the purpose of this Standard, the terms and definitions from ECSS-S-ST-00-01 and ECSS-E-ST-50 apply. 3.2 Terms specific to the present standard 3.2.1 category A category of those spacecraft having an altitude above the Earth's surface of less than 2 × 106 km 3.2.2 category B category of those spacecraft having an altitude above the Earth's surface equal to, or greater than, 2 × 106 km 3.3 Abbreviated terms For the purpose of this Standard, the abbreviated terms from ECSS-S-ST-00-01 apply:
Abbreviation Meaning AGC automatic gain control AU astronomical unit 2BL double-sided phase locked loop noise bandwidth BPSK binary phase shift keying (see PSK) CCSDS Consultative Committee for Space Data Systems CLCW command link control word C/N carrier to noise ratio dB decibel dBc dB with respect to the unmodulated carrier DRVID differenced range versus integrated Doppler SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 9 IF intermediate frequency LO local oscillator NRZ non-return to zero NRZ-L NRZ-level PCM pulse code modulation PLL phase-locked loop PM phase modulation PSK phase shift keying Pp peak to peak RF radio frequency r.m.s. root-mean-square SNR signal-to-noise ratio SPE static phase error SP-L split phase-level TC telecommand TM telemetry TR tracking UTC universal time (coordinated)
SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 10 4 Requirements 4.1 Functional 4.1.1 Functional breakdown The ranging and Doppler tracking system is a spacecraft tracking system capable of providing information on the range and range rate between a spacecraft and an Earth station. It uses an active transponder on-board the spacecraft for the retransmission to the ground of an Earth-to-Space link signal: ranging signal generation and measurement are performed in the Earth station. As a baseline, it is assumed that the spacecraft transponder is used not only for ranging purposes, but also for receiving telecommand signals from Earth and for transmitting telemetry signals to Earth modulated on the same RF carriers. When a transponder is used exclusively for ranging, the requirements in this standard concerning sharing with telecommand and telemetry have no relevance. A functional breakdown of the ranging and Doppler tracking system is presented in Figure 4-1. It depicts the five major functions of the system, broken down into functional blocks, as follows: • The Earth-to-Space link function, employing ground communication, process control, ranging signal generation and Earth-to-Space communication. NOTE
Ground communication between the Earth station and the Control Centre is not part of the present Standard. • The transponder function, either spacecraft transponder or ground-calibration transponder depending on the application. • The Space-to-Earth link function, employing Space-to-Earth communica-tion, Doppler measurement, ranging replica generation, ranging correla-tion, process control and ground communication. • The link-control function, resident partly in the Space-to-Earth and Earth-to-Space communication and partly in the process control. • The data-acquisition function, concerned with collection, measurement, processing and transfer of data to the control centre, employing the process-control and the ground communication functions. The requirements relevant to these five major functions are listed in clauses 4.1.2 to 4.1.6. SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 11
GROUND STATIONPROCESSCONTROLDOPPLERMEASUREMENTREPLICACORRELATIONGENERATIONSIGNALGENERATIONCOMMUNICATIONGROUNDEARTH-SPACECOMMUNICATIONSPACECRAFTRECEIVERSPACECRAFTTRANSMITTERTRANSPONDERSPACE-EARTHCOMMUNICATIONSPACECRAFTCoherentCarrierTransfer(Coherent Mode only)RangingTelecommandReference FrequencyReference TimingRANGINGRANGINGRANGINGCALIBRATIONGROUNDDOPPLER&RANGINGTelemetry
Figure 4-1: Ranging and Doppler tracking: functional block diagram SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 12 4.1.2 Earth-to-Space link function a. The Earth-to-Space link function shall consist of the following: 1. Reception of control signals for ranging signal composition (tone frequency, ambiguity resolution code, and modulation index). 2. Generation of the ambiguity resolution code. 3. Generation of the composite ranging signal, consisting of tone and code. 4. Selection of the modulating source, between. (a) ranging, (b) telecommand, and (c) ranging and telecommand. 5. Generation and phase modulation of the first Earth-to-Space link intermediate frequency (IF) carrier. 6. Local oscillator (LO) frequency selection and up-conversion of the modulated IF carrier to the assigned Earth-to-Space link radio frequency (RF). 7. Power amplification of the RF signal. 8. Transmission to spacecraft. 4.1.3 Transponder function 4.1.3.1 Spacecraft transponder a. The spacecraft transponder function shall consist of the following:
1. Reception of the RF signal. 2. Coherent down-conversion and phase tracking of the residual carrier. 3. Demodulation of ranging and telecommand signals. 4. Independent automatic gain control (AGC) of the residual carrier and baseband signal chains. 5. In the case of coherent transponders, selection of the Space-to-Earth link frequency source between a local reference (non-coherent mode) and a reference phase locked to the Earth-to-Space carrier (coherent mode). 6. Selection of the modulating source. NOTE
Modulating source can be selected between: • ranging (i.e. the demodulated video signal); • telemetry; • ranging and telemetry; • none of the above (for specific missions requiring Doppler measurement of high accuracy, whereby an unmodulated carrier is used). SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 13 7. Modulation of the carrier. 8. Up-conversion of the modulated carrier to the assigned Space-to-Earth link frequency. 9. Transmission to Earth. 4.1.3.2 Ground calibration transponder a. The ground calibration transponder function shall consist of the following:
1. Frequency conversion of the RF signal from the Earth-to-Space link carrier frequency to the Space-to-Earth link carrier frequency for the purpose of calibrating the ground equipment delay. NOTE
The ranging calibration measurement is usually performed before and after ranging operations with the spacecraft. 2. Frequency conversion of the RF signal from the Earth-to-Space link carrier frequency to the Space-to-Earth link carrier frequency for verification of Earth station phase stability. 4.1.4 Space-to-Earth link function a. The Space-to-Earth link function shall consist of the following:
1. Reception and amplification of the spacecraft signal. 2. Down conversion to an IF band, by means of local oscillators coherent with the station reference frequency or with the Earth receiver phase-locked reference. 3. Phase tracking of the IF signal. 4. Automatic gain control. 5. Reception of telemetry for transponder delay correction, if used
NOTE
The following housekeeping information which is embedded in the telemetry data stream, is transmitted for spacecraft control purposes to the Control Centre: • Information that enables delay correction
of the spacecraft transponder if used for orbit determination; • Transponder status for confirmation of relevant control commands and to initiate operational activities (e.g. start of ranging or Doppler operations). 6. Measurement of integrated Doppler shift on the Space-to-Earth link received or regenerated carrier. 7. Generation of ranging signal replica, taking into account: (a) the frequency and phase information from the integrated Doppler function; SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 14 (b) the transmitted ambiguity resolution code and the estimated two-way propagation delay towards the spacecraft. 8. Correlation of the generated replica with the received ranging signal. 9. Feedback of filtered correlation signal to the replica generation function for phase alignment of the replica signal with the received signal. 10. Maintenance of ranging signal replica during interruptions of ranging modulation on the Earth-to-Space link (e.g. due to telecommand transmission), by using information from the Doppler function.
NOTE
This serves as a time-sharing operation between telecommand and ranging. 4.1.5 Link control function a. The link control function used exclusively for the ranging function shall consist of the code acquisition for ranging, sequentially:
1. transmission of tone alone; 2. transmission of the tone modulated with the sequence of codes; 3. transmission of the tone modulated with the final code . NOTE 1 The control function concerned with reception and acknowledgment of link parameters, link frequency selection and antenna pointing angles is also used by telemetry and telecommand functions. This is beyond the scope of the present standard. NOTE 2 For certain deep space mission applications, the sequence of codes can be continuously re-started after the final code has been transmitted. The advantage of this scheme is a faster re-acquisition of the ranging signal in case of loss of link at the expense of a reduced accuracy. 4.1.6 Data acquisition function 4.1.6.1 Integrated Doppler function a. The integrated Doppler function shall consist of the following:
1. Reception and corresponding acknowledgment of Doppler measurement requests. 2. Pre-processing of Doppler data, in support of the ranging function; 3. Extraction of integrated Doppler data and storage thereof. SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 15 4. Integrated Doppler data transfer. NOTE
For information on integrated Doppler measurements, see Annex C. 4.1.6.2 Ranging function a. The ranging function shall consist of the following:
1. Reception and acknowledgment of ranging initialisation requests; 2. Control for generation of ranging signals and selection between different modes (i.e. deep space, coherent near Earth, non-coherent near Earth). 3. Execution of ambiguity resolution sequence. 4. Execution of ranging measurements by determination of the time interval between the transmitted ranging signal and the replica of the received ranging signal. 5. Storage of ranging data. 6. Ranging data transfer. 4.1.6.3 Meteo function a. The meteo function used for correction of tropospheric delay errors when the local meteo model does not meet the project specific accuracy requirements shall consist of the following:
1. Reception and acknowledgement of meteo data collection requests. 2. Measurement of atmospheric pressure, temperature and relative humidity at the Earth station. 3. Storage of meteo data. 4. Meteo data transfer. 4.2 Frequency assignment, modulation and spectral sharing
4.2.1 Frequency assignment
a. The ranging and Doppler tracking system shall operate in the frequency bands identified in ECSS-E-ST-50-05, clause 4.1.2. b. The maximum occupied bandwidth of the ranging signal shall meet ECSS-E-ST-50-05, clause 5.4.
c. In order to minimize the occupied bandwidth, the lowest tone frequency compatible with the spacecraft requirements (telecommand, telemetry and ranging) shall be selected. SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 16 4.2.2 Modulation 4.2.2.1 Modulation schemes
a. The ranging modulation on both Earth-to-Space and Space-to-Earth links shall be phase modulation (PM). NOTE
Requirements concerning modulation indexes are stated in clauses 4.4 and 4.5. b. The following two effects shall be considered: 1. power sharing between two or more additive signals, all phase modulated on the same link; 2. interference of the resulting overlying spectra. 4.2.2.2 Ranging signal composition The ranging baseband signal shall be as follows: a. it consists of a sine wave (tone), which is phase modulated by a series of codes, used for ambiguity resolution;
b. each code is synchronised to the tone such that phase transitions due to the code occur when the unmodulated tone phase is 90°;
c. the series of codes is described by means of the following expression: Cn = Q1
⊕
Q2
⊕
Q3
⊕ … Qn where Cn is the n-th code; ⊕ stands for exclusive or; Qi are square waves at frequencies 2-i x ft . d. Each code is transmitted for a fixed period of time to perform correlation and phase alignment at the receiving site. e. The RF carrier is phase modulated with this baseband signal. NOTE
The square waves Qi can be generated as the outputs of a divide-by-two flip-flop chain driven by the tone.
A simple way to generate the code Cn is to transmit the previous code Cn – 1 followed by its logical complement.
4.2.2.3 Incompatible modulation schemes a. Suppressed carrier modulation schemes as defined in ECSS-E-ST-50-05 clause 6.2 may be selected for the telemetry. NOTE
Such schemes are not compatible with simultaneous ranging modulation.
b. If suppressed carrier modulation is selected for telemetry, then the orbit determination shall be supported by one of the following: SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 17 integrated Doppler tracking on the carrier regenerated by the telemetry demodulator; time sharing between suppressed carrier telemetry and ranging; use of a separate ranging transponder.
c. If the orbit determination is supported by time sharing between suppressed carrier telemetry and ranging (see 4.2.2.3b), the transponder shall be capable of performing the ranging function. 4.2.2.4 Telemetry and ranging a. When an optimum choice of tone frequency is established, on the basis of the criteria set out in clause 4.2.3.2, modulation indexes shall be selected for both signals taking the following into account:
1. power sharing; 2. mutual interference; 3. reduction of the downlink ranging-signal power due to the uplink noise. 4.2.2.5 Telecommand and ranging
a. Simultaneous ranging and telecommanding should be adopted to avoid scheduling conflicts. b. For cases where the link budget constraints are not met for simultaneous ranging and telecommand, ranging and telecommand shall be performed in time sharing. c. The following constraints shall be taken into account for simultaneous ranging and telecommanding: 1. The telecommand signal can appear in the modulated Space-to-Earth link and can create undesirable effects on the transmitted spectrum, owing to power sharing and spectral overlap. 2. Transient overmodulation of the Space-to-Earth link and telemetry signal loss can occur owing to the slow response of the on-board baseband AGC due to the start of telecommand or ranging transmission; this effect can be reduced by the following: (a) ramping the uplink modulation at the start of transmission; (b) ensuring the presence of the telecommand signal in the ranging channel before switching the ranging mode on, in case the AGC is active on the telecommand signal. SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 18 4.2.3 Spectral sharing
4.2.3.1 Ranging spectra The ranging signal spectrum changes during the ambiguity resolution process, owing to different transmitted codes. The spectrum produced when the tone alone modulates the carrier has discrete lines at the carrier frequency plus or minus integral multiples of the tone frequency (see Figure 4-2). During the acquisition process, the code number increases and the code power is spread over an increasing number of lines (see Figure 4-3 and Figure 4-4). When the last step of the ambiguity resolution is completed, the code has created a quasi-continuous baseband spectrum, which extends (between first nulls) from 2-N ft to (2-2-N) ft where ft is the tone frequency, and N is the longest code length (see Figure 4-5). NOTE
The spectra plotted in Figure 4-2 to Figure 4-5 have been obtained with a carrier modulation index of 1,0 rad and with a tone modulation index of 45°. In these figures, the 0-dB reference level corresponds to the modulated carrier power, and f0 is the carrier frequency. 0123456-60-50-40-30-20-100Normalized frequency (F-F0)/FTPower spectrum in dB Power Spectral Density
Figure 4-2: Ranging signal spectrum for code length = 20 SIST EN 16603-50-02:2014
EN 16603-50-02:2014 (E) 19 0123456-60-50-40-30-20-100Normalized frequency (F-F0)/FTPower spectrum in dB Power Spectral Density
Figure 4-3: Ranging signal spectrum for code length = 22 0123456-60-50-40-30-20-100Normalized frequency (F-F0)/FTPower spectrum in dB Power Spectral Density
Figure 4-4: Ranging signal spectrum for code length = 24 SIST EN 16603-50-02:2
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