Workshop on Optical Clocks Düsseldorf, 08 / 09 Mar 2007 Microwave Transponders and Links ACES MWL and beyond W. SCHÄFER 1, M.P. HESS 2, 1 TimeTech GmbH, Stuttgart, Germany Wolfgang.Schaefer@timetech.de 2 ASTRIUM Space Transportation GmbH, Friedrichshafen, Germany Marc-Peter.Hess@space.eads.net This work is performed under ESA contract 16242/02/NL/JS
ACES: Clocks Involved PHARAO Frequency Comparison & Distribution Space Active H-Maser On-Board Ensemble Space-Ground Ground-Ground MicroWave Link MWL Ground Terminals Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 2
FCDP EM: Final Performance Verification Test set-up with external 100 MHz Phase Comparator FCDP Engineering Model Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 3
FCDP EM Performance: Phase Comparison Frequency Stability: samples filtered to 1 Hz BW Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 4
MWL Applications: Time & Frequency Transfer Inter-continental Relies on on-board clocks Regional: common view On-board clock cancelled Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 5
Reception of Pseudo-Noise (PN) coded signals using early-late Correlation Receiver search Allows negative S/N ratio within the signal bandwidth positive S/N for data Shannon criterium 'Early' AKF time shift S-Curve will be sampled sequentially: Typical 10 to 15 bins 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 'Late' Early - Late Operating Point 1 Chip, 10ns 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Parallel processing of two rows of bins, which are offset by 1/2 bin width Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 6
Noise properties of code & carrier tracking Jitter of DLL (PN code tracking): σ DLL = BW 2 C / N 0 1-chip delay between early and late arms = Chiplength BW = Loop Bandwidth (nom: 1Hz) Jitter of PLL (tone and carrier tracking): σ PLL λ = π BW 2 C / N 0 λ BW = Wavelength = Loop Bandwidth (nom: 1Hz) Phase-time jitter improves proportional to Code-Rate (PN code Tracking, modulation, group delay) Range-Tone Frequency (Tone-Ranging, modulation, group delay) Carrier Frequency (Carrier Phase, phase delay) but to SQRT(Signal Power)! Use Usehigh Chip-Rate Chip-Rate // Tone Tone // Carrier! Carrier! Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 7
Range Residuals at S/N of 30 db to GEO 0,25 Range-residuals from polynomial of 5th degree 08 Jan 1996 0,2 0,15 0,1 Residuals [m] 0,05 0-0,05-0,1-0,15-0,2 75000 77000 79000 81000 83000 85000 Time UTC [s] Typical Range Residuals from 5 th order orbit approximation, GEO satellite 20 MChip/s, C/No = 43 dbhz, tau = 1s, transponder loaded with analogue TV signal Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 8
Systematic Errors of End-to-End System Empirical formula based on Experience (conservative) PN Flicker: Chip-duration / 1000 Tone Flicker: Tone-Wavelength / 1000 Carrier Flicker: Wavelength / 1000 PN & Tone highly affected by multi-path and thermal variations Carrier less effected by multipath, but roughly similar by thermal Use Carrier to obtain best (short term) stability Use PN & Tone & datamodulation to fully remove ambiguity Careful pre-flight calibration & Delay Monitoring by calibration loop: improvement by 5-20 feasible (20% - 5% cal. Error) Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 9
MWL Performance Requirements: TDEV Short Term: 230 fs / pass Driven by Maser: one pass (300s) σ x (10 s τ 300 s) MWL 4,1 10-12 τ 1/2 Long Term: 5.5 ps / orbit, 16 ps / 10 d Driven by Pharao: > 1 orbit σ x (1orbit < τ < 15 days) MWL 1,7 10-14 τ +1/2 Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 10
MWL Performance Requirements: TDEV Comparison to operational systems Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 11
MWL System Aspects Microwave Link Mechanical Reference Point ML System Aspects Orbit, Relativistics, Attitude, ISS Specifics, etc 100 MHz +1E-9 S/C Ionosphere 'LINK' Troposhere G/S 100 MHz 1 pps Date & Time Electrical Reference Point MULTIPATH Space Ground Location, Relativistics Clocks as is Orbit Distance Velocity Acceleration Signal Link Ionosphere Troposphere Multipath Environment Temperature Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 12
Architecture & Signal Links Ku-Band, Up-link Power Tx: 2 W Carrier: 13.475 GHz PN-Code: 100 MChip/s 1pps: 1 time marker /s S/C: 4 Receiver Channels Ku-Band, Down-link S-Band, Down-link Power Tx: 0.5 W Carrier: 2248 MHz PN-Code: 1 MChip/s 1pps: 1 time marker /s Data: 2.5 kbit/s Power Tx: 0.5 W Carrier: 14.70333 GHz PN-Code: 100 MChip/s 1pps: 1 time marker /s Data: 2.5 kbit/s Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 13
Design Drivers by orbit & carrier (ISS) Coverage ISS orbit and attitude drives flight antenna design Signal dynamics drives RF, IF and 100-MHz electronics design drives signal acquisition and tracking requirements Multipath drives both Flight and Ground antenna designs, signal design and processing Thermal environment drives antennas, RF and electronics circuits stabilities and sensitivity to thermal slopes calibration requirements throughout the MWL Mass & Power consumption (8 Kg, 30 W) Instrumental noise noiseisiswithin within1-2 1-2 db db of of theoretical theoreticalvalue Most Most errors errorsdue dueto to thermal thermal // link link // operational operational aspects aspects Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 14
Continuous Delay Monitoring on-board and on ground TX Signal Generator Transmit Path 100 MHz Amplitude + Frequency Variation Calibration Mixer (CDMA) BP Ku-Antenna Conversion Reference BP Delay-Lock Loop-4 (Reference) 3x Receive Path Ku-band Diplexer Delay-Lock Loop Delay-Lock Loop Delay-Lock Loops 1..3 Continuously receive own signal via built-in Calibration Loop: Sum of Tx Path and Rx Path Delay (Range Calibration) Tx-Delay vs Temperature is known from Ground Calibration Calculate Rx Path Delay Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 15
Matched Up/Down Link Paths: λ-configuration Orbit MWL MWL FS FS internal internal delays delays applied applied Distance D 1 D 2 D 1 = D 2 Tx Delay Rx Delay Orbit: 10 15 m Time: 10 15 ns Time transmit time time of reception Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 16
Detection of Multi-path & Ionosphere using DRVID Data obtained from PRARE / ERS-2 Difference between phase-time measured simultaneously in X-Band on carrier phase phase delay code phase group delay, code-noise dominates! 0,40 0,30 g g pp [ ] 0,20 0,10 0,00-0,10 300 ps -0,20 10s -0,30-0,40 76560 76610 76660 76710 76760 76810 76860 76910 76960 77010 77060 77110 77160 77210 77260 77310 77360 File: H:\gz\PRO_PRA$.xls UTC time past 00:00, s DRVID DRVID detects detectsmultipath & even evenfast fast variations variationsdue dueto to ionosphere ionosphereor or plasma plasmaon on a a single singlefrequency frequencysignal Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 17
MWL Performance Requirements: TDEV Comparison to operational systems 100,000 C/No = 61 dbhz Corrections / calibrations not yet applied! Long-term is driven by PHARAO performance. 10,000 Short-term is driven by SHM performance. 1,000 0,100 Short-Term Specification Long-Term Specification Code-Phase Measurement Carrier-Phase Measurement 0,010 Performance limited for DM by thermal environment. Will be better for EM and PFM. 300 seconds = 1 orbit = pass-to- 0,001 1 10 100 1000 10000 100000 1000000 averaging time, τ, seconds Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 18
Summary & Conclusions Bi-directional Microwave Links perform simultaneous Time Transfer (difference between up-down link delays) Ranging (sum of up-downlink delay) Correlation technique allow low signal power Flicker highly independet from signal power! Select highest possible carrier frequency (watch for scintillations) with highest possible modulation rate Use dual-band to measure TEC, DRVID for TEC variation Instrumental delays are monitored continuously MWL TDEV is bounded to <= 10 ns / 1000.. 10000, 10 ps pessimistic, 1 ps optimistic! All-weather capability due to microwave Use Laser for absolute calibration in clear sky conditions Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 19
Outlook 500 MChips are allready feasible (Flying Laptop) Use full carrier cycle identification pass to pass Advanced conding scheme availble: Combined Tone- and PN code signals allow very wide bandwidth (~ 1 GHz) together with full ambiguity resolution at NO expense of additional signal power PRAREE proposal (~1990): Add one additional optical link to resolve wet component Add two additional optical links to resolve wet & dry component Link budget for a fully coherent communication system (Space and Ground) As long as we can communicate, we can perform time-transfer PN coding (spreading) by 10000 (40 db) easily achievable Chiprate can be 10 3 up to 10 5 higher than data rate, Tone arbitrary high Operations: Ranging & Time Transfer independent and simultaneous to TT&C Workshop on Optical Clocks Microwave Transponders and -Links: ACES MWL and beyond 20