ESA/DLR Blue Book Proposal
High-Flux Scenario
ESA Presentation to CCSDS Optical
Communications Working Group
11 November 2014
Books Under Development by
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Real-Time Weather
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ESA/DLR Input
• Most material was provided by European industry,
specifically TESAT Spacecom at the Spring 2014 CCSDS
meeting.
• Existing terminal implementation LCT is a commercially
available product, with heritage extending back to
1997 (LEO-LEO) and a 2nd generation for LEO-GEO links
developed since 2006.
• LCT was flown on NFIRE and the German TerraSAR-X
satellites, and has been selected for EDRS, with first
terminals already launched on Sentinel 1a and
AlphaSat. Operational validation is successfully
underway.
Evolution of Existing Implementation
• Current user bandwidth is 1.8 Gbps (2.8125 Gbps
raw)
• Doubling the clock rate (already in space since
2007 on NFIRE and TerraSAR-X) results in 3.6
Gbps user data rate.
• Switching from BPSK to QPSK provides a user
data rate of 7.2 Gbps. Benefit: Detector
bandwidth remains within validated performance
regime.
• Further scaling by WDM around 1064 nm. Yb
amplifier bandwidth is ≥60 nm.
1. Proposal Draft Blue Book Optical
Communications Physical Layer
Green Book Material
Optical Communications
Physical Layer
Blue Book
Optical Communications
Physical Layer
Blue Book
Green Book Material
Optical Communications Optical Communications
Coding &
Coding &
Synchronization
Synchronization
Green Book
Optical
Communications
Concepts and
Technologies
Green Book
Real-Time Weather
and Atmospheric
Characterization Data
Blue Book Optical Communications
Physical Layer – Proposed Contents
1.1 Signal Acquisition
1. Terminal A
• The center frequency shall be 281594.0 GHz ± 0.14%
• The transmit beam shall have a Left-hand Circular Polarization (LCP:
where the E-vector rotates counter-clockwise as viewed from the
transmitter in the direction of propagation)
• During spatial acquisition, the transmit signal shall be amplitude
modulated with a frequency of 1.0045 MHz +/- 200 ppm and a
modulation index higher than 95%.
2. Terminal B
• The center frequency shall be 281566.0 ± 0.14%
• The transmit beam shall have a Right-hand Circular Polarization
(RCP: where the E-vector rotates clockwise as viewed from the
transmitter in the direction of propagation)
• During spatial acquisition, the transmit signal shall be amplitude
modulated with a frequency of 1.7578 MHz +/- 200 ppm and a
modulation index higher than 95%.
1.2 Communication Signal (1/6)
1. Terminal A
• The center frequency shall be 281594.0 GHz
• The transmit beam shall have a Left-hand Circular Polarization
(LCP: where the E-vector rotates counter-clockwise as viewed
from the transmitter in the direction of propagation)
2. Terminal B
• The center frequency shall be 281566.0 GHz
• The transmit beam shall have a Right-hand Circular
Polarization (RCP: where the E-vector rotates clockwise as
viewed from the transmitter in the direction of propagation)
1.2 Communication Signal (2/6)
1. Both Terminals
• The TX laser shall be tunable within a range of +-10 GHz
• The maximum laser tuning rate shall be 120 MHz/s in
communication mode
• The un-modulated TX laser shall have a line width of less than
100 kHz over a time scale of 100 msec
• The TX laser Relative Intensity Noise (RIN) shall be less than 30 dB in the frequency range between 0.01 Hz and 1 MHz.
1.2 Communication Signal (3/6)
1. Both Terminals
• The spectral density of the RIN shall be better than given in
the Figure below
Frequency
10 Hz
-74 dB/Hz
10 kHz
10 MHz
1.4 GHz
-20 dB/decade
RIN/Δf
-134 dB/Hz
-20 dB/decade
quantum noise
5 dB
1.2 Communication Signal (4/6)
1. Both Terminals
• The frequency noise of the free running TX laser shall be less
than the limit in Figure below:
• The change rate of the laser phase noise shall be below 6400
rad/s (Δφ/ Δt).
1.2 Communication Signal (5/6)
1. Both Terminals
• Modulation scheme: Binary Phase-Shift Keying (BPSK) with Non-Return to
Zero (NRZ).
• Nominal symbol rate: 2812.5 Megasymbols/sec (Msps).
• The modulating base-band spectrum of the transmit signal shall fulfill the
spectral mask defined in the Figure below. This spectrum shall be
generated by the Line Product Code (LPC) as defined in Ref. CCSDS 000.0W-0 (Optical Communication Modulation and Coding Proposed Draft
Recommended Standard White Book)
1.2 Communication Signal (6/6)
1. Both Terminals
• The base-band eye-pattern shall fulfill the requirements listed in the Table
and as defined by the Figure below.
Symbol
Definition
UI (Unit Interval)
1 / 2812.5 Mbps (≈355.55 ps)
x1
0.1*UI
x2
0.15*UI
x3
0.85*UI
X4
0.9*UI
y1
0.10*mean level of logical 1
y2
0.90*mean level of logical 1
2. Material Collection for Future
Green Book Optical Communications
Physical Layer
Blue Book
Optical Communications
Physical Layer
Green Book Material
Optical Communications
Physical Layer
Blue Book
Green Book Material
Optical Communications Optical Communications
Coding &
Coding &
Synchronization
Synchronization
Green Book
Optical
Communications
Concepts and
Technologies
Green Book
Real-Time Weather
and Atmospheric
Characterization Data
Contents - Green Book Material Optical
Communications Physical Layer
2.1 Spatial Acquisition
PAT
•
•
•
•
•
Mutual spatial tracking and, in the case of homodyne communications, locking and tracking
of the opposing terminals carrier frequency must be achieved.
Depending on the relative size of the open-loop pointing Uncertainty Cone (UC) and the
aperture dependent Tx beam divergence, acquisition sequences either assisted by a higherdivergence Beacon or “Beaconless” acquisition schemes may be appropriate.
Detection and centering of a beacon requires utilization of a 2-D sensor (e.g. CCD or
Quadrant Photodiode).
High divergence beacon requires high optical transmit power.
Size of UC determines necessary acquisition strategy and speed. Contributing factors are:
1. Timing accuracy
2. Position knowledge
3. Attitude knowledge
4. (Micro)-vibration
5. Planning cycle and Telecommand opportunities
2.1 Spatial Acquisition
Beaconless PAT
• A beaconless PAT scheme is implemented in the European Data Relay
System (EDRS) and has been verified in-orbit with the TerraSar-X NFire
optical LEO intersatellite links.
• It uses the comms beam (i.e. same wavelength and beam divergence as
the comms signal) and scans the UC to achieve spatial acquisition.
• The scanning methodology mandates a time tagged sequence of steps.
• The transmitted beam is modulated to facilitate terminal identification
and to improve the PAT link budget.
• Establishment of a link with the EDRS optical terminals requires
knowledge of only the normative characteristics of the optical signal
(wavelength, modulation, etc.).
• The knowledge of the time tagged acquisition sequence is beneficial and
recommended to be agreed upon in a mission-specific ICD.
2.2 Acquisition Sequence
Beaconless PAT
Beacon-less acquisition sequence in a master-slave approach. M: master terminal, S: slave terminal
2.2 Acquisition Sequence
Beaconless Spatial Acquisition
Simplified flow chart of the beaconless spatial acquisition algorithm
2.2 Acquisition Sequence
Frequency Acquisition
• After successful spatial acquisition, the next step in the
acquisition sequence is to achieve homodyne tracking by
performing frequency acquisition. The laser frequencies
of the respective local oscillators must be adjusted such
that they are phase-locked to the received signal.
• On completion, each terminal is coherently phase locked
to the counter terminal. Homodyne tracking is thus
achieved and the terminals are ready to initiate
communication.
2.3 Acquisition Time
• Length of the acquisition time is determined mainly
the size of the total UC of the link.
• Based on the size of the UC, a trade-off between
reliability and speed of link acquisition is required.
• In a highly dynamic LEO-LEO intersatellite link
configuration acquisition times of 8 s (and in specific
cases 2 s) have been demonstrated in-orbit.
• For uncertainty cones of 1 mrad, acquisition times of
55 s are guaranteed for the EDRS intersatellite and
ground link (including a safety margin).
• Shorter acquisition times are expected after in-orbit
verification.
2.4 Optical Signal Characteristics
• Optical signal characteristics are valid for
coarse and fine spatial acquisition. For
tracking, communications signal
characteristics apply (direct detection on
acquisition sensors, but coherent detection on
tracking detector).
3. Material for Blue Book Optical
Communications Coding &
Synchronization
Blue Book
Green Book Material
Optical Communications Optical Communications
Physical Layer
Physical Layer
Blue Book
Optical Communications
Coding & Synchronization
Green Book Material
Optical Communications
Coding &
Synchronization
Green Book
Optical
Communications
Concepts and
Technologies
Green Book
Real-Time Weather
and Atmospheric
Characterization Data
Contents - Blue Book Material Optical
Communications Coding & Synchronization
4. Material Collection for Future
Green Book Optical Communications
Coding & Synchronization
Green Book
Material
Blue Book
Optical Communications
Optical
Physical Layer
Communications
Green Book Material
Physical Layer
Optical Communications
Coding & Synchronization
Blue Book
Optical Communications
Coding &
Synchronization
Green Book
Optical
Communications
Concepts and
Technologies
Green Book
Real-Time Weather
and Atmospheric
Characterization Data
Contents - Green Book Material Optical
Communications Coding & Synchronization