CCSDS 141.11-O-1.pdf

Research and Development for Space Data System Standards

OPTICAL HIGH DATA

RATE (HDR)

COMMUNICATION—

1064 NM

EXPERIMENTAL SPECIFICATION

CCSDS 141.11-O-1

ORANGE BOOK

December 2018

Research and Development for Space Data System Standards

OPTICAL HIGH DATA

RATE (HDR)

COMMUNICATION—

1064 NM

EXPERIMENTAL SPECIFICATION

CCSDS 141.11-O-1

ORANGE BOOK

December 2018

EXPERIMENTAL SPECIFICATION FOR OPTICAL HIGH DATA RATE COMMUNICATION

AUTHORITY

Issue: Orange Book, Issue 1

Date: December 2018

Location: Washington, DC, USA

This document has been approved for publication by the Consultative Committee for Space Data Systems (CCSDS). The procedure for review and authorization of CCSDS documents is detailed in Organization and Processes for the Consultative Committee for Space Data Systems (CCSDS A02.1-Y-4).

This document is published and maintained by:

CCSDS Secretariat National Aeronautics and Space Administration Washington, DC, USA E-mail: secretariat@mailman.ccsds.org

CCSDS 141.11-O-1 Page i December 2018

FOREWORD

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CCSDS has processes for identifying patent issues and for securing from the patent holder agreement that all licensing policies are reasonable and non-discriminatory. However, CCSDS does not have a patent law staff, and CCSDS shall not be held responsible for identifying any or all such patent rights.

Through the process of normal evolution, it is expected that expansion, deletion, or modification of this document may occur. This Experimental Specification is therefore subject to CCSDS document management and change control procedures, which are defined in Organization and Processes for the Consultative Committee for Space Data Systems (CCSDS A02.1-Y-4). Current versions of CCSDS documents are maintained at the CCSDS Web site:

http://www.ccsds.org/

Questions relating to the contents or status of this document should be sent to the CCSDS Secretariat at the e-mail address indicated on page i.

CCSDS 141.11-O-1 Page ii December 2018

At time of publication, the active Member and Observer Agencies of the CCSDS were:

Member Agencies

– Agenzia Spaziale Italiana (ASI)/Italy.

– Canadian Space Agency (CSA)/Canada.

– Centre National d’Etudes Spatiales (CNES)/France.

– China National Space Administration (CNSA)/People’s Republic of China.

– Deutsches Zentrum für Luft- und Raumfahrt (DLR)/Germany.

– European Space Agency (ESA)/Europe.

– Federal Space Agency (FSA)/Russian Federation.

– Instituto Nacional de Pesquisas Espaciais (INPE)/Brazil.

– Japan Aerospace Exploration Agency (JAXA)/Japan.

– National Aeronautics and Space Administration (NASA)/USA.

– UK Space Agency/United Kingdom.

Observer Agencies

– Austrian Space Agency (ASA)/Austria.

– Belgian Federal Science Policy Office (BFSPO)/Belgium.

– Central Research Institute of Machine Building (TsNIIMash)/Russian Federation.

– China Satellite Launch and Tracking Control General, Beijing Institute of Tracking and

Telecommunications Technology (CLTC/BITTT)/China.

– Chinese Academy of Sciences (CAS)/China.

– China Academy of Space Technology (CAST)/China.

– Commonwealth Scientific and Industrial Research Organization (CSIRO)/Australia.

– Danish National Space Center (DNSC)/Denmark.

– Departamento de Ciência e Tecnologia Aeroespacial (DCTA)/Brazil.

– Electronics and Telecommunications Research Institute (ETRI)/Korea.

– European Organization for the Exploitation of Meteorological Satellites (EUMETSAT)/Europe.

– European Telecommunications Satellite Organization (EUTELSAT)/Europe.

– Geo-Informatics and Space Technology Development Agency (GISTDA)/Thailand.

– Hellenic National Space Committee (HNSC)/Greece.

– Hellenic Space Agency (HSA)/Greece.

– Indian Space Research Organization (ISRO)/India.

– Institute of Space Research (IKI)/Russian Federation.

– Korea Aerospace Research Institute (KARI)/Korea.

– Ministry of Communications (MOC)/Israel.

– Mohammed Bin Rashid Space Centre (MBRSC)/United Arab Emirates.

– National Institute of Information and Communications Technology (NICT)/Japan.

– National Oceanic and Atmospheric Administration (NOAA)/USA.

– National Space Agency of the Republic of Kazakhstan (NSARK)/Kazakhstan.

– National Space Organization (NSPO)/Chinese Taipei.

– Naval Center for Space Technology (NCST)/USA.

– Research Institute for Particle & Nuclear Physics (KFKI)/Hungary.

– Scientific and Technological Research Council of Turkey (TUBITAK)/Turkey.

– South African National Space Agency (SANSA)/Republic of South Africa.

– Space and Upper Atmosphere Research Commission (SUPARCO)/Pakistan.

– Swedish Space Corporation (SSC)/Sweden.

– Swiss Space Office (SSO)/Switzerland.

– United States Geological Survey (USGS)/USA.

CCSDS 141.11-O-1 Page iii December 2018

CCSDS 141.11-O-1 Page iv

DOCUMENT CONTROL

Document Title Date Status

CCSDS

141.11-O-1

Optical High Data Rate (HDR) Communication—1064 NM, Experimental Specification, Issue 1

December

Original issue

EC1 Editorial change 1 January

Corrects graphics display problems

EC2 Editorial change 2 September

Corrects equation typography

September 2019

CONTENTS

Section Page

1 INTRODUCTION .......................................................................................................... 1-1

1.1 PURPOSE AND SCOPE ........................................................................................ 1-1

1.2 DOCUMENT STRUCTURE ................................................................................. 1-1

1.3 NOMENCLATURE ............................................................................................... 1-2

1.4 REFERENCES ....................................................................................................... 1-3

2 OVERVIEW ................................................................................................................... 2-1

2.1 GENERAL .............................................................................................................. 2-1

2.2 ARCHITECTURE .................................................................................................. 2-1

2.3 SPATIAL ACQUISITION ..................................................................................... 2-3

2.4 DATA LINK LAYER ............................................................................................ 2-8

2.5 ARCHITECTURE OF LIA .................................................................................. 2-15

3 PHYSICAL LAYER ...................................................................................................... 3-1

3.1 TERMINAL A OPTICAL TRANSMIT SIGNAL CHARACTERISTICS ............ 3-1

3.2 TERMINAL B OPTICAL SIGNAL CHARACTERISTICS ................................. 3-2

3.3 COMMUNICATIONS SIGNAL ............................................................................ 3-2

3.4 TERMINAL B OPTICAL COMMUNICATIONS SIGNAL

CHARACTERISTICS .......................................................................................... 3-21

4 CODING AND SYNCHRONIZATION ...................................................................... 4-1

4.1 TERMINAL A DATA LINK LAYER CHARACTERISTICS .............................. 4-1

4.2 TERMINAL B DATA LINK LAYER CHARACTERISTICS .............................. 4-5

ANNEX A SECURITY, SANA, AND PATENT CONSIDERATIONS

(INFORMATIVE) ......................................................................................... A-1

ANNEX B PHYSICAL LAYER AND CODING AND SYNCHRONIZATION

SUBLAYER IMPLEMENTATION (INFORMATIVE)............................B-1

ANNEX C ABBREVIATIONS AND ACRONYMS (INFORMATIVE) .................... C-1

Figure

2-1 Relationship with OSI and CCSDS Layers .................................................................. 2-2 2-2 Modes of Beaconless Acquisition According to a Master-Slave Approach ................ 2-6 2-3 Simplified Flow Chart of the Beaconless Spatial Acquisition Algorithm .................... 2-7 2-4 Layer Overview for the Example of EDRS Application .............................................. 2-8

CCSDS 141.11-O-1 Page v December 2018

CONTENTS (continued)

Figure Page

2-5 Layer Overview for the Example of a Symmetrical OISL between Two GEO Relays ........................................................................................................ 2-10

2-6 Block Diagram with Reference Points and Data Rates for the Example of EDRS Application ................................................................................... 2-11

2-7 Block Diagram with Reference Points and Data Rates for the Example of EDRS Application with Optimized Throughput (Denoted As 600 Mb/s Mode or Sentinel Mode) ....................................................... 2-12

2-8 Requirements on LIA=LIAU for Flexible Relay Network ......................................... 2-14 2-9 Architecture of LIA .................................................................................................... 2-15 2-10 Sequence of Operations in LIA for Framing .............................................................. 2-16 2-11 Backpressure Concept for LIA=LIAU to Adapt to Given Data Rates on RF Downlink.......................................................................................................... 2-17 3-1 Upper Limit for the Frequency Noise of the Tx Laser ................................................. 3-4 3-2 Mapping of LPC Encoder Input to 5-by-5 Input Matrix .............................................. 3-9 3-3 Mapping of 5-by-5 Output Matrix to Encoder Output ............................................... 3-10 3-4 Calculation of e(0,0) to e(3,3) ..................................................................................... 3-11 3-5 Definition of Subblocks within 5-by-5 Output Matrix ............................................... 3-13 3-6 System Channel Frame ............................................................................................... 3-16 3-7 Insertion of Inverted Unique Word, Scrambler Reset and Alignment of 3-Tuples .................................................................................................................. 3-17 3-8 Format of Service Channel Frame .............................................................................. 3-18 3-9 Serial Output Data Frame DatSerOut ......................................................................... 3-19 3-10 Spectral Mask of the Modulated Base-Band Tx Signal .............................................. 3-19 3-11 Transmit Eye Pattern .................................................................................................. 3-20 4-1 Data Rates in Flexible Relay Network ......................................................................... 4-1 4-2 LIA Frame Header for the General Case ...................................................................... 4-2 4-3 LIA Frame Header for the Specific Case of LIA=DRAU ............................................ 4-3

Table

3-1 Mux and Align Modes .................................................................................................. 3-5 3-2 Illustration of the Building Rule for the Parallel PRBS Generator .............................. 3-7 3-3 Scrambler Reset Definition ........................................................................................... 3-7 3-4 Disparity Calculation .................................................................................................. 3-14 3-5 Definition of Subblock Inversion ............................................................................... 3-15 3-6 Definition of Unique Word and Reserved Pattern ...................................................... 3-16 3-7 Short Scrambler Reset Mode Definition ..................................................................... 3-16 3-8 Service Channel Bit Encoding .................................................................................... 3-17 3-9 Definitions for the Transmit Eye Pattern in Figure 3-11 ............................................ 3-20

CCSDS 141.11-O-1 Page vi December 2018

1 INTRODUCTION

1.1 PURPOSE AND SCOPE

The purpose of this Experimental Specification is to define a recommendation for optical communication, taking as reference the implementation in ESA missions (EDRS series, Sentinel series) and the original DLR development. The key technical features are the use of the 1064 nm wavelength with Binary Phase-Shift Keying (BPSK) modulation. In addition, future evolutions with regard to dual-wavelength (1064 nm and 1550 nm), increased data rates (3.6 Gb/s with Reed-Solomon codes and BPSK and up to 10 Gb/s with QPSK), modulation, and coding schemes will be specified in the context of the ESA ScyLight program, a dedicated new ESA framework on optical communication technology, and in the frame of the ESA GlobeNet project.

The Experimental Specification contains the technical specification for implementing the Physical Layer and the Coding and Synchronization (sub)layer of optical systems supporting the High Data Rate (HDR) scenario.

ESA and DLR consider this Experimental Specification to be a candidate for a future CCSDS Recommended Standard for optical systems interoperable with the European Data Relay System (EDRS), for complementary missions like ESA GlobeNet, or even for other dedicated scenarios.

The described optical communications mechanisms will be useful in particular for LEO-GEO and GEO-GEO Inter-Satellite Link (ISL) operational scenarios. However, they can also be used for space-ground and airborne-space links if additional measures are taken, for example, adaptive optics, interleaving, and erasure coding.

This Experimental Specification provides additional proven options for the implementation of optical communication in cases of HDR transmissions, and it should be adopted by ESA for the above-mentioned missions and beyond.

Furthermore, this Experimental Specification will complement the optical communication Recommended Standards for High Photon Efficiency (HPE) and Low Complexity (LC), without overlapping them, but adding a sound candidate for future standardization.

1.2 DOCUMENT STRUCTURE

This document is structured as follows:

– Section 2 provides a brief description of the application scenarios and an overview of the selected Physical Layer characteristics and modulation, coding, and synchronization schemes.

– Section 3 contains the specification of the Physical Layer characteristics of both the transmit and receive terminal implementations.

CCSDS 141.11-O-1 Page 1-1 December 2018

– Section 4 contains the specification of the coding and synchronization sublayers of the transmit and receive terminal implementations.

– Annex A discusses security, Space Assigned Numbers Authority (SANA), and patent considerations.

– Annex B identifies existing implementations that demonstrate the technologies expounded in this Experimental Specification.

– Annex C is a glossary of abbreviations used in this document.

1.3 NOMENCLATURE

1.3.1 NORMATIVE TEXT

The following conventions apply for the normative specifications in this Experimental Specification:

a) the words ‘shall’ and ‘must’ imply a binding and verifiable specification;

b) the word ‘should’ implies an optional, but desirable, specification;

c) the word ‘may’ implies an optional specification;

d) the words ‘is’, ‘are’, and ‘will’ imply statements of fact.

NOTE – These conventions do not imply constraints on diction in text that is clearly informative in nature.

1.3.2 INFORMATIVE TEXT

In the normative sections of this document, informative text is set off from the normative specifications either in notes or under one of the following subsection headings:

– Overview;

– Background;

– Rationale;

– Discussion.

CCSDS 141.11-O-1 Page 1-2 December 2018

1.4 REFERENCES

The following publications contain provisions which, through reference in this text, constitute provisions of this Experimental Specification. At the time of publication, the editions indicated were valid. All publications are subject to revision, and users of this Experimental Specification are encouraged to investigate the possibility of applying the most recent editions of the documents indicated below. The CCSDS Secretariat maintains a register of currently valid CCSDS publications.

[1] Information Technology—Open Systems Interconnection—Basic Reference Model: The Basic Model. 2nd ed. International Standard, ISO/IEC 7498-1:1994. Geneva: ISO, 1994.

[2] TM Synchronization and Channel Coding. Issue 3. Recommendation for Space Data System Standards (Blue Book), CCSDS 131.0-B-3. Washington, D.C.: CCSDS, September 2017.

[3] TM Space Data Link Protocol. Issue 2. Recommendation for Space Data System Standards (Blue Book), CCSDS 132.0-B-2. Washington, D.C.: CCSDS, September 2015.

[4] TC Space Data Link Protocol. Issue 3. Recommendation for Space Data System Standards (Blue Book), CCSDS 232.0-B-3. Washington, D.C.: CCSDS, September 2015.

[5] AOS Space Data Link Protocol. Issue 3. Recommendation for Space Data System Standards (Blue Book), CCSDS 732.0-B-3. Washington, D.C.: CCSDS, September 2015.

CCSDS 141.11-O-1 Page 1-3 December 2018

2 OVERVIEW

2.1 GENERAL

ESA and DLR consider this Experimental Specification to be a candidate for a future CCSDS Recommended Standard for optical systems interoperable with the EDRS, complementary missions like ESA GlobeNet, or even for other dedicated scenarios.

The described optical communications mechanisms will be particularly useful for LEO-GEO and GEO-GEO Inter-Satellite Link (ISL) operational scenarios. However, they can also be used for space-ground and airborne-space links if additional measures are taken, for example, adaptive optics, interleaving, and erasure coding.

This Experimental Specification provides additional proven options for the implementation of optical communication in cases of HDR transmissions, which option should be adopted by ESA for the above-mentioned missions and beyond.

Furthermore, this Experimental Specification will complement the optical communication Recommended Standards for High Photon Efficiency (HPE) and Low Complexity (LC), without overlapping them, but adding a sound candidate for future standardization.

2.2 ARCHITECTURE

Figure 2-1 illustrates the relationship of this Recommended Standard to the Open Systems Interconnection reference model (reference [1]). Two sublayers of the Data Link Layer are defined for CCSDS space link protocols. The Data Link Protocol sublayer provides functions for producing Transfer Frames; examples are the TM Space Data Link Protocol (reference [3]), the AOS Space Data Link Protocol (reference [5]), and the TC Space Data Link Protocol (reference [4]).

The Optical Communications Coding and Synchronization protocol specified in this Recommended Standard provides the functions of the synchronization and channel coding sublayer of the Data Link Layer for transferring Transfer Frames over an optical space link.

CCSDS 141.11-O-1 Page 2-1 December 2018

Figure 2-1: Relationship with OSI and CCSDS Layers

CCSDS 141.11-O-1 Page 2-2 December 2018

2.3 SPATIAL ACQUISITION

2.3.1 BACKGROUND

In order to establish communication between two optical communication terminals, the communication terminals are required to perform a so-called ‘spatial acquisition’ sequence, which ends when spatial tracking is achieved. In coherent optical communication modes, a transition to coherent (frequency) tracking needs to be further executed by locking the transmit laser frequency coherently to the received frequency. In the specific case of homodyne communication modes, the frequency of the local oscillator needs to be adjusted to the signal carrier frequency (frequency acquisition), such that received signal and local oscillator are phase-locked to each other. If this state of homodyne tracking is reached, communication can be started.

Spatial acquisition is the process of co-aligning the receiver line of sight and the transmit-beam of the optical communication terminal precisely with the direction of the counter terminal’s position. If the direction of the counter terminal is known to a sufficient degree of precision, co-alignment can be achieved by pointing the terminal to the known direction by direct open-loop pointing. The estimated error on the counter terminal direction is called an ‘Uncertainty Cone’ (UC) and is available (usually) to a precision of a few milliradians. A constant of the propagation of electromagnetic waves is the so-called beam parameter product. For near-infrared light, the beam parameter product is in the order of ~mm mrad. As it is beneficial for the link budget to maximize the communication beam aperture, the UC of the terminal is often orders of magnitude larger than the beam divergence of the communication beam. Thus a direct open-loop pointing is in many cases not feasible, leading to reliance in the acquisition process on an optical feedback signal to which the counter terminal can align. Either an additional beam with a beam divergence larger than the communication beam (a so-called beacon) is employed for this purpose, or the communication beam with small beam divergence scans the UC to provide the necessary feedback to the counter terminal. Literature distinguishes between acquisition with beacon and beaconless acquisition if only the communication signal is employed to achieve spatial acquisition, either by direct pointing or scanning.

In beacon-based systems, a 2-D sensor is utilized to detect and center the beacon signal.

Mechanical co-alignment of the pixel and communication sensors’ coordinate systems needs to be guaranteed in space over a wide range of operating temperatures, which guarantee requires a balance between mechanical stability and light-weight construction. Quadrant photodiodes are an alternative design option, which can be used simultaneously as a receiver for acquisition and for communication. Avoiding pixel sensors has the advantage of reduced power and mass, and higher reliability since the part count is lower and quadrant photodiodes have better FIT rates than pixel sensors. If the wavelength of the beacon differs from the communication beam, then the optical system (e.g., coatings) has to be optimized for both wavelengths, which results in compromises and reduces system performance for the communication wavelength. The higher divergence of a beacon laser requires higher optical transmit power than a beaconless system, which increases the requirements of the system to cope with high optical power densities. For example, keeping receive-signal power constant, CCSDS 141.11-O-1 Page 2-3 December 2018 transmit power has to be 100 times higher if the beacon divergence is 10 times higher than the beaconless transmit beam, which increases the optical power from 0.7W to 70W for a LEO-LEO system.

Before designing a specific Pointing, Acquisition, and Tracking (PAT) scheme, it is important in any case to analyze and, if possible, to reduce the UC of the link. If a link is to be established between two different terminals, the link acquisition will be influenced by two main factors:

The first factor to be considered is the so-called Host Uncertainty Cone (HUC), which is derived from the position, attitude, and timing knowledge of the transmitting optical terminal. To determine the second factor, the so-called Total Uncertainty Cone (TUC), the position uncertainty of the receiving counter terminal, also needs to be taken into consideration.

Parameters that influence HUC and TUC and are recommended to be optimized for mission planning of optical links in context, for example, of an ICD are the following:

a) Timing accuracy

The precision of timing data determines how well the position of terminal and counter terminal are known.

b) Position knowledge

Depending on the location of the terminal (e.g., Earth, geostationary S/C, low orbit Earth observation S/C), the accuracy of position knowledge will differ. The position accuracy directly influences the size of the UC.

c) Attitude knowledge

Precision of the knowledge of orientation in space directly influences the size of the UC. To determine the attitude knowledge, internal contributors such as pointing precision of the Optics and external contributors such as alignment knowledge aboard a S/C and attitude knowledge of a S/C have to be determined.

d) (Micro)-vibration

In-orbit vibration is to be considered in the design of the beaconless spatial acquisition algorithm, so that spatial-acquisition probability and spatial-acquisition duration requirements are met. The design of the algorithm depends on the magnitude and frequency of vibrations.. The greatest contributors to in-orbit vibrations are reaction wheels and solar arrays. The design of the beaconless spatial acquisition algorithm is based on the predicted in-orbit vibration of both S/Cs, and therefore the performance of the algorithm depends on the in-orbit vibration conditions of not only the local S/C but of the counter S/C as well.

CCSDS 141.11-O-1 Page 2-4 December 2018

e) Planning cycle and telecommand opportunities

The precision of position knowledge may depend on the link planning cycle, since the position knowledge will degrade over time. The longer the planning cycle, the more safety margins have to be applied to counterbalance increasing TUC. Predicted S/Cs positions on ground are also used to inform the optical terminal where the counter terminal is at the time of a requested data transmission. The error of the predicted terminal position can be kept small using updated predictions.

2.3.2 ACQUISITION SEQUENCE

2.3.2.1 Introduction

The following beaconless PAT scheme is implemented in the EDRS and has previously been reliably verified in orbit with the TerraSar-X NFire optical LEO intersatellite links. It uses the communication beam (i.e., identical wavelength and beam divergence as the communication signal) and scans the UC to achieve spatial acquisition. Because of the scanning methodology, a time-tagged sequence has been chosen. Additionally, the transmitted beam is modulated to facilitate terminal identification and to improve the PAT link budget. To establish a link acquisition with the EDRS optical terminals, only the normative characteristics of the optical signal (wavelength, modulation, etc.—see below) are required. However, the knowledge of the time-tagged acquisition sequence is helpful and recommended to be agreed upon in a mission-specific ICD.

2.3.2.2 Beaconless PAT

In the first phase of the time-tagged PAT sequence, both optical terminals point in the estimated direction of their respective counter terminal in open loop. The estimated direction needs to be known, with limited accuracy, of the total UC, which will typically be in the order of milliradians; larger UCs increase the duration of the spatial acquisition. After initial open-loop pointing, the spatial acquisition starts in master-slave mode. The master and slave roles are determined during mission planning. The master optical terminal emits light and spirals the UC with its low divergent transmit beam, and the counter (slave) Laser Communication Terminal (LCT) should receive a light pulse once per scan. The receiving optical terminal in slave mode will successively reduce its UC with each light pulse, as it corrects its pointing with each received light pulse with a decreasing step size. Because of vibrations, the probability of hitting the counter terminal might be below 100 percent for a single scan.

After a predefined number of scans, the master terminal stops scanning and transmitting. The number of necessary scans depends on overall system characteristics, which define the total

UC.

The slave terminal is at this point well aligned to the master terminal, and the roles of master and slave are reversed: the former slave terminal takes on the role of master and starts to scan

CCSDS 141.11-O-1 Page 2-5 December 2018 the remaining UC. Since the UC is small during this second phase of acquisition, much shorter single scans allow the former master terminal (now slave) to align quickly by the same algorithm. At a predefined fine alignment—the remaining UC may be defined in the context of mission-specific ICDs—the former master also restarts to emit light and to scan.

Both terminals are now scanning the UC while reducing the scan angle from scan to scan.

The alignment is further improved until the tracking sensor responds. The terminal then stops scanning and stably tracks its counter terminal. At this point in time, spatial tracking is accomplished. Figure 2-2 shows a simplified flow chart of the beaconless spatial acquisition algorithm.

SSSSSS

MMMMMM

Coarse Acquisition Phase 1

Coarse Acquisition Phase 2

Fine AcquisitionPointing

Pointing Error Slave Terminal

Pointing Error Master Terminal

M: master terminal, S: slave terminal

Figure 2-2: Modes of Beaconless Acquisition According to a Master-Slave Approach

Figure 2-3 shows a simplified flow chart of the beaconless spatial acquisition algorithm.

CCSDS 141.11-O-1 Page 2-6 December 2018

BEACONLESS SPATIAL ACQUISITION ALGORITHM

Start heterodyne tracking Stop spiraling

Align to direction of receive signal

Align to receive signal Spiral UC with Tx-beam

Adapt spiral and UC when hit

Spiraling UC with Tx-beam

LCT B

Align to receive signal Spiral UC with Tx-beam

Adapt spiral and UC when hit

Spiraling UC with Tx-beam

Align to direction of receive signal

Start heterodyne tracking Stop spiraling

LCT A

Figure 2-3: Simplified Flow Chart of the Beaconless Spatial Acquisition Algorithm

The acquisition sequence then continues to achieve homodyne tracking by performing frequency acquisition. The laser frequencies of the respective local oscillators must be adjusted so they are phase-locked to the received signal. Each terminal is now coherently phase locked to the counter terminal; homodyne tracking is thus achieved and the terminals are ready to initiate communication.

2.3.3 ACQUISITION TIME

For the beacon-less acquisition method, the acquisition time is a time-tagged parameter. It is recommended to agree on the acquisition time within the context of an ICD, as it will depend strongly on the mission scenario. Determining factors for the acquisition time are the size of the total UC of the link. Based on the size of the UC, a trade-off between reliable link acquisition and fast acquisition will be done. 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 UCs of 1 milliradian, acquisition times of 55 s are guaranteed for the EDRS intersatellite and ground link (including a safety margin). In actuality, smaller acquisition times can be expected after initial in-orbit verification.

CCSDS 141.11-O-1 Page 2-7 December 2018

2.4 DATA LINK LAYER

2.4.1 TERMINAL A DATA LINK LAYER CHARACTERISTICS

2.4.1.1 General Layer Structure

The description of the coding and synchronization schemes for optical communication is compliant with the CCSDS layer structure as stated in 2.2 of this document.

2.4.1.2 Application Examples

Figure 2-4 displays an example of how the optical communication is embedded in a satellite network. The example is based on the EDRS, with which data is transmitted over an Optical Inter-Satellite Link (OISL), from a LEO satellite via laser to a GEO relay satellite, and from Relay to Ground via RF links. The communication is bidirectional, at least on the OISL (the uplink from ground to GEO is outside the scope of this document). Both LEO and GEO satellites contain one LCT each.

Mod Demod

Mux

Encod.

Shaping

Demux

Demod

Mux Demux

Mux Stuffing

Encoding Interleav.

Scrambling

Encoding Interleav.

Scrambling

Encap-sulation

Encap-sulation

MM Ch 1 MM Ch N

Encapsulation Stuffing

Encoding

Encryp-tion

Encryp-tion

Encoding

DRAU

Demod Demod

GEO frame sync

GEO frame sync

Decrypt.

LIAU Frame sync

Decoding

Demux

MM Ch 1 MM Ch N

Anti-

DRAU

LIAU frames

Bitstream BitstreamBitstream

Session-wise permanent OISL bidirectional, 2812.5 Mb/s gross

Immediate forward

MM frames

Async.

Bitstreams

Packets [= data content of GEO frames]

Packets

Permanent Ka-band downlinks unidirectional, each channel with 600 Mb/s gross

DRAU

frames

Bitstream

LEO

Ground Network/User

GS

GEO

LCT

LIAU

Anti-LIAU

Anti-GIAGIA provides session-wise permanent forward link, up to 1676 Mb/s (depending on UL feeder and continuous/block mode)

SCh logic

SCh logic

Optical I/F Optical I/F

De-coding

Demux

Decoding

Frame type ident.

Frame type ident.

De-stuff. De-stuff.

Decrypt.

Decoding

Frame type identif.

De-stuffing

LCT

Mux

Place of MM frame re-establishment and network I/F tbd.

GEO frames provides session-wise permanent return link, data rate = rOISL-net= 1800 Mb/s provides permanent return link, data rate = rDL-net provides return link with unlimited integrity, data rate = rMM

E nc od in g

De-coding

E nc od in g

E nc od in g

Encod.

Shaping

E nc od in g data rate < 600/1800

Mb/s

Mod ModMod

[= data content of LIAU frames]

Figure 2-4: Layer Overview for the Example of EDRS Application

As shown in figure 2-4, the data stream is not fed directly into the LCT:

– On the LEO satellite, the data from the source(s), also denoted as mass memory (MM), is fed into a device denoted as an LCT Interface Adaptation Unit (LIAU). This is called return service. The reverse counterpart to LIAU is denoted as Anti-LIAU (located on ground, but this is not relevant in this context).

CCSDS 141.11-O-1 Page 2-8 December 2018

– On the GEO satellite, the data to be transmitted as forward service is fed into a device denoted as Data Rate Adaptation Unit (DRAU). The reverse counterpart to DRAU is denoted as Anti-DRAU and is located in the LEO satellite.

The term LIA (LCT Interface Adaptation) is used here as a generic term for both LIAU and DRAU; the generic term for the reverse units is Anti-LIA.

It should be noted that the LIA accepts CCSDS frames as input data, but does not actually demand a specific formatting of the input data, as the LIA and Anti-LIA transparently encapsulate any input data for transport over the optical link, regardless of the source data format (e.g., raw mass-memory dumps or CCSDS frames).

The LCTs on LEO and GEO are denoted here as type A and type B, respectively. Typically, there is LIA=LIAU for type A and LIA=DRAU for type B, but in order not to exclude other scenarios, and for the sake of simplification and generality, a more general architecture for LIA is specified.

As a general principle, a lower layer provides a service to the layer above via a Service Access Point (SAP). The lower layer should be independent, as much as possible, from the higher layer. The term ‘layer’ does not exactly reflect the original OSI meaning, since all ‘layers’ mentioned here are basically Physical and Data Link Layers in the OSI sense.

For the sake of layer independence and technology independence, any data structures present in the input signal to LIA are ignored, and the input data is encapsulated into frames (known as bitstream service from CCSDS 732.0.B-3, subsection 3.4—reference [5]).

CCSDS 141.11-O-1 Page 2-9 December 2018

Onboard Processing

Mod Demod

Mux

Encod.

Shaping

Demux

Mux Stuffing

Encoding Interleav.

Scrambling

Encoding Interleav.

Scrambling

Encap-sulation

Encap-sulation

LIAU Frame sync

Decoding

Demux

LIA frames

A→B bitstream

Permanent OISL bidirectional, 2812.5 Mb/s gross

NA async.

streams

NA async.

streams

GEOA

LCTA LCTB

LIAA

provides NB permanent B→A links provides NA permanent A→B links total rate =rMM total rate =rMM

SCh logic

Optical I/F

De-coding

Mod Demod

Mux

Encod.

Shaping

Demux

SCh logic

Optical I/F

De-coding

Frame type identif.

De-stuffing

Mux Stuffing

Encoding Interleav.

Scrambling

Encoding Interleav.

Scrambling

Encap-sulation

Encap-sulation

LIAU Frame sync

Decoding

Demux

Frame type identif.

De-stuffing provides permanent bidirectional link, data rate = rOISL-net= 1800 Mb/s

(each direction)

Anti-LIAB LIAB Anti-LIAA

NB async.

streams

NB async.

streams

Onboard Processing

LIA frames

B→A bitstream

GEOB

E nc od in g

E nc od in g

E nc od in g

E nc od in g

Figure 2-5: Layer Overview for the Example of a Symmetrical OISL between Two GEO Relays

In figure 2-5, an OISL between two GEO relays is considered as a further example, in which a fully symmetrical relation between both satellites is assumed. NA independent and asynchronous links are supported from A to B. Vice versa, NB independent and asynchronous links are supported from A to B. Of course, NA and NB could be equal to 1 and LIA/Anti-LIA functions could be physically integrated into the ‘Onboard Processing’ block.

The next two figures display the EDRS satellite network architecture in terms of block diagrams. This information is provided for a better overview and to introduce reference points and data rates.

CCSDS 141.11-O-1 Page 2-10 December 2018

LEO Satellite (e.g., Sentinel)

Ground Segment

MM

Source

LIAU

Anti‐LIAU

MM

Sink

Relay Satellite (e.g., EDRS)

Ka‐Band DL n channels

DPU

Mod

Anti‐

DPU

A C C2' C1'

C1''

E1

A' potential MM frames ignored

LIAU

frames

Mb/s

Mb/s n*rs Mb/s

C2

OISL Line Dec.

Line Enc.

LCT‐TX

Mod

LCT ‐RX

Mod

Mod n*rs Mb/s rOISL‐gross = 2812.5 Mb/s

2812.5 Mb/s

F

E1' F' perhaps GEO frames rMM<1650 Mb/s rOISL‐net =1800 Mb/s

Figure 2-6: Block Diagram with Reference Points and Data Rates for the Example of EDRS Application

Figure 2-6 shows the EDRS application with maximum data rates.

NOTE – As shown in the figure 2-7, there are also other EDRS applications in which the throughput on the DownLink (DL) from Relay to Ground is limited to a net value of 600 Mb/s. It is possible to design the LIAU frames with a reduced header (of 2 bytes only instead of 8 bytes) such that the combination of rMM=560 Mb/s and rDL-net=600 Mb/s is supported. This mode is called ‘throughput optimized’ (also denoted as 600 Mb/s mode or Sentinel mode) and is included here to demonstrate the flexibility of the concept. However, the reduced header of 2 bytes is not possible for all cases.

CCSDS 141.11-O-1 Page 2-11 December 2018

LEO Satellite (e.g., Sentinel)

Ground Segment

MM

Source

LIAU

Anti‐LIAU

RS

Enc.

Inter-leaver

Rep.

Enc.

Rep.

Dec.

MM

Sink

RS

Dec.

De‐ Inter-leaver

Relay Satellite (e.g., EDRS, Alphasat)

Ka‐Band DL n channels

LIAU

framing Mux DPU

Mod

Anti‐

DPU

Frame search

Demux

LIAU

defram.

A'

A

C'''' C'' potential MM frames ignored

LIAU

frames

C''

C C1 C2 C2' C1' E1

E1'

F

F'

C'

C''' C''

2*280 Mb/s

2*299.56 Mb/s

Mb/s

Mb/s n*rs Mb/sOISL Line Dec.

Line Enc.

Mb/s

Mb/s

LCT‐TX

Mod

LCT‐RX

Mod

Mod n*rs Mb/s

2812.5 Mb/s

2812.5 Mb/s

B1 B2 B3 perhaps GEO frames

Figure 2-7: Block Diagram with Reference Points and Data Rates for the Example of EDRS Application with Optimized Throughput (Denoted As 600 Mb/s Mode or Sentinel Mode)

The most important reference points from the two figures above are summarized below (all data rates mentioned below refer to the current LCT technology):

– A is the interface between source (MM) and LIA=LIAU. The maximum data rate rMM is limited to a value slightly below 1800 Mb/s; for example, rMM = 1676 Mb/s, denoted as user data rate or MM data rate. The corresponding interface on the receiver side is denoted ‘A’.

– C is the (internal) interface between LIA and LCT. The data rate here is always exactly rOISL-net = 1800 Mb/s (or an integer multiple of 112.5 = 1800/16 Mb/s), denoted as OISL net data rate. The corresponding interface on the receiver side is denoted ‘C’.

– C2 is the ‘space (air)’ interface between the LCTs, including all overhead for coding and synchronization and control. The data rate here is always exactly rOISL-gross =

2812.5 = 1800 × 25/16 Mb/s, denoted as OISL gross data rate. By definition, a corresponding interface on the receiver side does not exist.

NOTES

1 For LIA=LIAU, the maximum user data rate @ A is in the order of 560 Mb/s, and the net OISL data rate @ C is 600 Mb/s (or an integer multiple of 37.5 = 600/16 Mb/s).

However, the gross OISL data rate @ C2 is always 2812.5 Mb/s.

CCSDS 141.11-O-1 Page 2-12 December 2018

2 For LIA = DRAU and the EDRS example, the data rate at the input to DRAU is very small (in the order of some kb/s), and the OISL net data rate is 112.5 Mb/s.

In summary, for the EDRS application with 600 Mb/s, LIA=LIAU on the LEO satellite and LIA=DRAU on the GEO satellite are different. For all other cases (like EDRS with 1800 Mb/s or the GEO-GEO link), a general concept for LIA is specified with no need to distinguish between different applications.

2.4.1.3 Objectives for LIA Design

The objectives for the LIA design are summarized as follows:

– main functions/output side (I/F to LCT):

• usage of the 1800 Mb/s mode of the LCT (rOISL-net = 1800 Mb/s);

• user-data rate as high as possible—but with support of

▫ enhanced coding gain together with LCT internal coding, ▫ adaptation (fix or variable) to µW-feeder DL capabilities;

• compatibility with EDRS relay and DTE setups and minimized footprint on relay;

• support of robust receiver operation;

– main function / input side (I/F to mass memory):

• support of 1...N data streams (multiplexing prior to or within LIA);

• support of variable (or switch on/off) data rates;

• support of LIA=LIAU integration into mass memory;

• support of unconstrained user-data integrity;

• additional requirements (e.g., very small data rates);

– clock concept:

• LIA to clock LCT-TX;

– LIA clock is available in LCT-RX. In case of LIA=LIAU, it can be either terminated (like EDRS) or forwarded (like Alphasat) in the relay satellite; conformity to CCSDS data processing schemes as far as possible.

CCSDS 141.11-O-1 Page 2-13 December 2018

2.4.2 DISCUSSION

Figure 2-8 shows more details for the support of DL channels with variable throughput. The basic idea is summarized as follows:

The input data rate from MM to LIA is reduced to a value such that after addition of overhead (because of LIA encapsulation and frame structure), the resulting data rate does not exceed the DL throughput.

Stuffing with LIA idle frames is required in LIA to achieve the fixed throughput rate on the OISL. This stuffing needs to be removed in the Relay satellite (this is somehow a footprint on GEO; details are outside the scope of this document).

If the available data rate from MM is even lower than the capacity of the DL, further stuffing is required. Hence, a part of the LIA idle frames has to be removed in GEO, and another part has to be transmitted in DL (to minimize the footprint on GEO, LIA can introduce two types of idle frames).

LEO Satellite

MM

NextGen Relay

Ka‐Band DL (1/2)LIAU GIA Mod

(TeTra: 2...6 bit/symb)

OISL User View (1800 Mb/s)

OISL

2812.5 Mb/s

Line Dec.

Line Enc.

rOISL-net = 1800 Mb/s rOISL-gross = 2812.5 Mb/s rMM < rDL*(0.8...0.9...0.99)

– MM protection (LIA could be part of MM);

– size of footprint on MIA.

variable in case of ACM/VCM, overhead depending on rDL-net < (1..2)*(113...862) Mb/s variable in case of ACM/VCM

General Considerations

– If the TeTra modulator is used with VCM/ACM to adapt to propagation conditions (e.g., rain, elevation):

• rDL-net is variable (selectable @ VCM, adaptive @ ACM);

• rMM is variable.

– OISL throughput is large enough to feed up to two TeTra DLs with 216 MHz (see below for exceptions).

– OISL throughput is fixed (to rOISL-net = 1800 Mb/s > rDL-net):

• stuffing in LIAU is required;

• de-stuffing in GIA is required → LEO leaves a footprint in MEO.

– Split of data to 2 DL channels in GIA → Framing is required, preferably together with stuffing in LIAU → Again, footprint in

MEO.

– Option: LIAU and MM could be integrated into one box.

Conclusions on LIAU Overhead

– Minimal overhead in LIAU is to be added for framing (framing enables stuffing in LIAU and split in GIA).

– More overhead in LIAU is to be added for OISL protection if not done in MM.

Figure 2-8: Requirements on LIA=LIAU for Flexible Relay Network

In summary, LIA frames and the concept of encapsulation are introduced for coding purposes (to enhance the link budget margin of the OISL) and for flexibility purposes (the stuffing concept does allow for the transmission of arbitrary user data rates over a link with fixed data rates).

The following subsections describe the specification of the LCT Interface Adapter (LIA).

CCSDS 141.11-O-1 Page 2-14 December 2018

2.5 ARCHITECTURE OF LIA

The general architecture of the LIA is displayed in the figure 2-9.

A number of N sources (mass memories) are connected to LIA on the input side, and a data stream of rOISL-net = 1800 Mb/s is created on the output side. If the incoming data stream has a frame structure like LIA frames, this structure is fully ignored in LIA.

Examples are N=1 for LIA=DRAU or N=2 for LIA=LIAU. The upper bound for N is given by the implementation only, but a general limit does not exist (however, the recommended LIA header provides 6 bits for the source ID, so 64 different sources can be distinguished).

The N inputs can have independent time-variant data rates (including on-off operation), supposing the aggregate rate is limited:

aggregated LIA input rate = rMM < rOISL-net × 1904/2044

= 1676 Mb/s (for rOISL-net = 1800 Mb/s).

The data rate at the output is always constant with rOISL-net = 1800 Mb/s, even in cases in which all inputs sources are inactive with rMM = 0.

rOISL-net= 1800 Mb/s

Source

LCT-TX

LIA

variable data rate allowed variable data rate allowed

Divide stream in blocks of 1904 bytes

Interleaving Scrambling Buffer

Mux

Add ASM (4) Add Header (8) Add RS (128)

Divide stream in blocks of 1904 bytes

Interleaving Scrambling

Interleaving Scrambling

Buffer Add ASM (4)

Add Header (8) Add RS (128)

Add ASM (4) Add Header (8) Add RS (128)

LIAU frames with data from Source 1

Idle frame content (fixed PN sequence of 1904 bytes)

Received clock(s) from source LIA local clock

Source N aggregated LIAU input rate = rMM is limited:

rMM < min{rOISL-net, rDL-net}*1904/2044 < 1676 Mb/s

LIAU frames with data from Source N

LIAU idle frames

Backpressure on rMM to respect rDL-net rMM

(fixed)

Figure 2-9: Architecture of LIA

CCSDS 141.11-O-1 Page 2-15 December 2018

As shown in the figure 2-9, the input data streams are divided (packetized) in data blocks.

These data blocks are equipped with a frame header. Then the concatenated field [data block, frame header] is together encoded with an R-S code, followed by interleaving and scrambling. The N chains are operated independently and asynchronously.

Another chain produces idle frames, as many as required, to generate at LIA output a constant data rate of rOISL-net = 1800 Mb/s. The multiplexer operates on N+1 chains, where the first N chains are served on a first-come-first-transmit basis, and the idle frames from the last chain have lowest priority (i.e., are inserted and transmitted only to increase the data rate to rOISL-net). This is denoted as a stuffing operation.

ASM

Content after Scrambling 8+1904+128 = 2040

ASM

CADU frame 2040 = 8 (header) + 1904 (TM data) + 128 (RS)

RS encoding

CADU frames ignored for LIA

ASM

CADU frame 2040 = 8 (header) + 1904 (TM data) + 128 (RS)

LIAU Superframe Data

Header

LIA frames

Division into blocks of length 1904 (independent of any present structure)

Superframe Data

Header

Content after Interleaving 8+1904+128 = 2040

RS checksum

Interleaving

Scrambling

Figure 2-10: Sequence of Operations in LIA for Framing

The figure 2-10 shows the sequence of operations to build up a LIA frame. The structure of the incoming data stream is fully ignored, and the data stream is divided into blocks of 1904 bytes (a byte structure of the incoming data shall be observed). Then a header of 8 bytes is added resulting in 1904+8=239×8 bytes, corresponding to 8 codewords of an R-S(255,239) code, in accordance with section 4 of reference [2]. The R-S parity symbols with a total length of 8×(255−239)=128 bytes are added. The resulting packet of 2040 bytes is interleaved and scrambled. Finally, an Attached Synchronization Marker (ASM) word of 4 bytes is added.

The concept of backpressure is described in more detail in the figure 2-11.

CCSDS 141.11-O-1 Page 2-16 December 2018

Adaptation to available date rate in μW-DL

– Basic idea:

• The source (or the aggregated sources) is commanded to present data with a limited rate to the LIAU → Backpressure from μW-DL to MM

• The LIAU generates a data rate of 1800 Mb/s by stuffing with idle frames

• The GEO relay removes the stuffing (partly) to reduce the data to the net rate of the μW-DL

– Note: this leaves a footprint of the LIAU on the GEO relay (drawback!)

• The GEO relay has to detect the LIAU frame structure

• The GEO relay has to remove the LIAU idle frames

Details

– Net rate of μW-DL = rDL-net [Mb/s]

– Each source @ LIAU input may have different and time-variant data rate, but rMM shall be bounded as

Aggregated LIAU input rate = rMM < min{rOISL-net, rDL-net} × 1904/2044 Mb/s

– Several alternatives/modifications are possible (see below)

– Alternatives for idle frame extraction in GEO relay

• Remove LIAU idle frames automatically as much as needed

• Introduce two types of idle frames in LIAU, one for extraction in relay and one for stuffing in LIAU

• GEO relay may introduce additional frame structure for coding purposes or for clock termination

Figure 2-11: Backpressure Concept for LIA=LIAU to Adapt to Given Data Rates on RF Downlink

CCSDS 141.11-O-1 Page 2-17 December 2018

3 PHYSICAL LAYER

3.1 TERMINAL A OPTICAL TRANSMIT SIGNAL CHARACTERISTICS

3.1.1 OVERVIEW

Optical transmit 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 sensor).

3.1.2 CENTER FREQUENCIES

The center frequency shall be equal to 281594.0 GHz ± 3 GHz.

NOTE – During the spatial acquisition process, there are no specific requirements for the Laser Tuning Range, Laser Tuning Range Rate, Laser Line Width, Laser Relative Intensity Noise, Laser Frequency Noise, and Laser Phase Noise.

3.1.3 POLARIZATION

3.1.3.1 Polarization Type

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.

3.1.3.2 Polarization Extinction Ratio

NOTE – While there is no specification of the polarization extinction ratio as such, the minimum irradiance levels refer to the nominal polarization state.

3.1.4 MODULATION

3.1.4.1 Modulation Scheme

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 percent.

3.1.4.2 Spectral Mask (LPC) Pulse Shape

The modulation waveform shall be sinusoidal.

NOTE –…