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We propose a novel soft-aided iterative decoding algorithm for product codes (PCs). The proposed algorithm, named iterative bounded distance decoding with combined reliability (iBDD-CR), enhances the conventional iterative bounded distance decoding (iBDD) of PCs by exploiting some level of soft information. In particular, iBDD-CR can be seen as a modification of iBDD where the hard decisions of the row and column decoders are made based on a reliability estimate of the BDD outputs. The reliability estimates are derived by analyzing the extrinsic message passing of generalized low-density-parity check (GLDPC) ensembles, which encompass PCs. We perform a density evolution analysis of iBDD-CR for transmission over the additive white Gaussian noise channel for the GLDPC ensemble. We consider both binary transmission and bit-interleaved coded modulation with quadrature amplitude modulation. We show that iBDD-CR achieves performance gains up to 0.51 dB compared to iBDD with the same internal decoder data flow. This makes the algorithm an attractive solution for very high-throughput applications such as fiber-optic communications.

The recently introduced 5G New Radio is the first wireless standard natively designed to support critical and massive machine type communications (MTC). However, it is already becoming evident that some of the more demanding requirements for MTC cannot be fully supported by 5G networks. Alongside, emerging use cases and applications towards 2030 will give rise to new and more stringent requirements on wireless connectivity in general and MTC in particular. Next generation wireless networks, namely 6G, should therefore be an agile and efficient convergent network designed to meet the diverse and challenging requirements anticipated by 2030. This paper explores the main drivers and requirements of MTC towards 6G, and discusses a wide variety of enabling technologies. More specifically, we first explore the emerging key performance indicators for MTC in 6G. Thereafter, we present a vision for an MTC-optimized holistic end-to-end network architecture. Finally, key enablers towards (1) ultra-low power MTC, (2) massively scalable global connectivity, (3) critical and dependable MTC, and (4) security and privacy preserving schemes for MTC are detailed. Our main objective is to present a set of research directions considering different aspects for an MTC-optimized 6G network in the 2030-era.

In this letter, we propose a short-frame (SF) approximation for the packet loss rate of Irregular Repetition Slotted ALOHA (IRSA) particularly suitable for very short frames, up to 50 slots. The reason for limiting the frame size is to allow low-latency communications, a typical requirement in Industrial Internet of Things (IIoT) applications. We extend the approximation of [1] (named EF) through a recursive evaluation of inter-related stopping sets (STs). The tighter approximation yields the user degree distribution that minimizes the packet loss rate (PLR). For a scenario with 10 slots and 5 users, the degree distribution optimized adopting the SF approximation results in a 20% lower PLR compared to the one optimized with the EF approximation.

A geographical routing scheme for LEO satellite constellations with intersatellite links is proposed, implemented, and analyzed for two Walker Star constellations. The approach targets reliable transmissions with low latency and high data rates even in scenarios with significant traffic load. An Iridium‐like constellation and a megaconstellation are investigated and compared regarding the address resolution procedures, the average end‐to‐end transmission delay, and the dropping and rerouting rates using a system level simulator.

In this paper, we provide an analysis of the performance of concatenation of polar codes with outer cyclic redundancy check (CRC) codes, separated by an interleaver, in the short and moderate block length regimes. The analysis addresses maximum likelihood decoding as a proxy to the code performance under successive cancellation list decoding. The analysis is carried out by introducing the concatenated polar code (CPC) ensembles, whose distance properties can be analyzed (for sufficiently short block lengths) by means of the uniform interleaver approach. At moderate block lengths, we resort to the Monte Carlo simulations. Results show that if the inner polar code possesses a low minimum distance and the outer CRC code has a sufficiently large amount of redundancy, then the choice of the outer code generator polynomial and the interleaver may yield to a large variability in the performance of the resulting CPC.

The HEIMDALL project aims to improve societies' preparedness to cope with complex crisis situations by providing a flexible platform for multi-hazard emergency planning and management for actors involved in disaster management. The result is a cooperative management tool that provides data exchange, scenario building and situation assessment functionalities for training, preparedness and response planning.

Caching at the edge of wireless networks is a key technology to reduce traffic in the backhaul link. However, ${a}$ concentrated amount of requests during peak-periods may cause the outage of the system, meaning that the network is not able to serve the whole set of demands. The outage probability is a fundamental metric to take into account during the network design. In this paper, we derive the analytical expression of the outage probability as a function of the total amount of users requests, library size, requests distribution, cache size and capacity constraints on the backhaul resources. In particular, we focus on a scenario where end-users have no direct connection to the master node which holds the complete library of content that can be requested. A general formulation of the outage is derived and studied for two relevant caching schemes, i.e. the random caching scheme and the most popular caching schemes. The exact closed form expressions presented in this paper provide useful insights on how requests, memory and resources can be balanced when the parameters of a cache-enabled network have to designed.

We speed up existing decoding algorithms for three code classes in different metrics: interleaved Gabidulin codes in the rank metric, lifted interleaved Gabidulin codes in the subspace metric, and linearized Reed-Solomon codes in the sum-rank metric. The speed-ups are achieved by new algorithms that reduce the cores of the underlying computational problems of the decoders to one common tool: computing left and right approximant bases of matrices over skew polynomial rings. To accomplish this, we describe a skew-analogue of the existing PM-Basis algorithm for matrices over ordinary polynomials. This captures the bulk of the work in multiplication of skew polynomials, and the complexity benefit comes from existing algorithms performing this faster than in classical quadratic complexity. The new algorithms for the various decoding-related computational problems are interesting in their own and have further applications, in particular parts of decoders of several other codes and foundational problems related to the remainder-evaluation of skew polynomials., Comment: 26 pages, accepted for publication in IEEE Transactions on Information Theory

In this paper upper and lower bounds on the probability of decoding failure under maximum likelihood decoding are derived for different (nonbinary) Raptor code constructions. In particular four different constructions are considered; (i) the standard Raptor code construction, (ii) a multi-edge type construction, (iii) a construction where the Raptor code is nonbinary but the generator matrix of the LT code has only binary entries, (iv) a combination of (ii) and (iii). The latter construction resembles the one employed by RaptorQ codes, which at the time of writing this article represents the state of the art in fountain codes. The bounds are shown to be tight, and provide an important aid for the design of Raptor codes., Comment: Accepted in IEEE Transactions on Information Theory

We explore the problem of deriving a posteriori probabilities of being defective for the members of a population in the non-adaptive group testing framework. Both noiseless and noisy testing models are addressed. The technique, which relies of a trellis representation of the test constraints, can be applied efficiently to moderate-size populations. The complexity of the approach is discussed and numerical results on the false positive probability vs. false negative probability trade-off are presented., Comment: To be presented at the special session on Data Science for COVID-19 at CISS 2021

Modern satellite missions like CubeSat-missions are characterized by extremely short development time and significant low resource requirements. This can only be reached by reducing classical standards to necessary levels, tailored down for the respective mission. It leads to a rethinking of system engineering in modern space missions following the new space approach, which tailors down the standard processes to a minimum but reasonable level. The Optical Communication Systems Group (OCS) of DLR develops solutions to break the bottleneck caused by limited data-rates of traditional RF-communication systems with Free-Space-Optics (FSO) technologies for earth orbiting platforms. Therefore DLR started 10 years ago the OSIRIS (Optical Space InfraRed downlInk System) program which concentrates on research and development of laser communication terminals for Low-Earth-Orbit (LEO) satellites. The development speed in laser communication accelerated in the last years due to the availability of compact and low-cost flying platforms like pico- and nanosatellites. Therefore OCS follows the new space approach to shorten development times and finish projects much earlier compared to traditional space missions. The OSIRIS4CubeSat (O4C) project has the goal to develop a high data-rate optical communication payload for CubeSats and demonstrates it in a quasi-operational scenario. The development of the payload is in close collaboration with Tesat-Spacecom who sells O4C under the name 'CubeLCT' as a commercial product. Beside the payload development, the functionality of O4C will be demonstrated in a direct to earth downlink from a CubeSat to an Optical Ground Station. Thus, the payload will fly in the PIXL-1 mission on a 3U CubeSat built by GomSpace. After the Launch and Early Operational Phase (LEOP) the satellite will be hand over to German Space Operation Center (GSOC) to demonstrate for the first a time a commanding of a CubeSat by a professional Ground System. The ambitious path from the development of the payload, which started from scratch, to a quasi-operational mission, shows the necessity of a working system engineering to observe all requirements, coordinate the different teams and manage the interfaces to the stakeholder. This paper describes the system engineering based on the new space approach for a modern CubeSat mission. In the beginning of the project the overall requirements for the whole project were defined. This includes the technical requirements for the payload, to ensure the functionality depending on the extreme environmental conditions in space and the requirements for the satellite. Furthermore the operational requirements were defined. Additionally to the internal requirements the needs of the commercialization partner and the possible launch opportunities had to be considered. Beside the requirements, the single work packages were defined to distinguish the several tasks and visualise the interfaces and connections in a work breakdown structure (WBS). Based on the WBS the technical teams for the development were formed. During the concept development and the integration of the payload, the system engineering had to monitor the requirements and coordinate the different technical teams with all their interfaces. Even though the teams were separated in optics, mechanics, electronics and software, their tasks were strongly connected. Beside the internal interface coordination the system engineering had to coordinate the communication on technical level to the external stakeholders like contractee (Tesat), satellite manufacturer (GomSpace), launch provider and operator (GSOC). This paper gives an overview over the processes in the OSIRIS4CubeSat project which represents modern system engineering following the new space approach.

This paper presents a finite length analysis of multi-slot type frameless ALOHA based on a dynamic programming approach. The analysis is exact, but its evaluation is only feasible for moderate number of users due to the computational complexity. The analysis is then extended to derive continuous approximations of its key parameters, which, apart from providing an insight into the decoding process, make it possible to estimate the packet error rate with very low computational complexity. Finally, a feedback scheme is presented in which the slot access scheme is dynamically adapted according to the approximate analysis in order to minimize the packet error rate. The results indicate that the introduction of feedback can substantially improve the performance of frameless ALOHA, Comment: Accepted for publication in IEEE Transactions on Communications

In the framework of error correction in space telecommand (TC) links, the Consultative Committee for Space Data Systems (CCSDS) currently recommends short block-length BCH and binary low-density parity-check (LDPC) codes. Other alternatives have been discarded due to their high decoding complexity, such as non-binary LDPC (NB-LDPC) codes. NB-LDPC codes perform better than their binary counterparts over AWGN and jamming channels, being great candidates for space communications. We show the feasibility of NB-LDPC coding for space TC applications by proposing a highly efficient decoding architecture. The proposed decoder is implemented for a (128,64) NB-LDPC code over GF(16) and the design is particularized for a space-certified Virtex-5QV FPGA. The results prove that NB-LDPC coding is an alternative that outperforms the standardized binary LDPC, with a coding gain of 0.7 dB at a reasonable implementation cost. Given that the maximum rate for TC recommended by the CCSDS is 2 Mbps, the proposed architecture achieves a throughput of 2.03 Mbps using only 9615 LUTs and 5637 FFs (no dedicated memories are used). In addition, this architecture is suitable for any regular (2,4) NB-LDPC (128,64) code over GF(16) independently of the H matrix, allowing flexibility in the choice of the code. This brief places NB-LDPC codes as the excellent candidates for future versions of the telecommand uplink standard. This work was supported by Spanish MICINN/AEI under Project TEC2017-86722-C4-3-R.

FSO systems present many advantages like high data rate, license-free bandwidth and tap-proof communication allowing the download of vast amounts of data from LEO satellites. However, the atmospheric channel is quite challenging, because of spurious effects such as absorption, scattering and scintillation that in turn vary the link losses in correspondence to the elevation. In order to maximize the downlink throughput, it should start around 5° elevation. This leads to a design with suboptimal performance for higher elevations when constant data rates are used. Therefore, DLR is developing a system to adjust the data rate according to elevation and atmospheric channel conditions. This data rate variation is achieved by determining the maximum rate for higher elevation and then for lowering the data rates a bit-level repetition is performed. The presented system enables a fast transition between the different data rates. Additionally, this system allows the satellite to transmit data at rates even lower than those nominally supported by the physical transceiver. At the receiver side, the system complexity increases as it should be able to acquire, detect, and filter the signal for different data rates. DLR proposes a system that mirrors the operation of its transmitter counterpart by sampling the acquired signal at the maximum data rate. Then an FPGA processes the signal by majority decision algorithm followed by voting system that filters and detects the intended data rate in real-time. This enables replication and parallelization of the filtering and detection processes enabling the automatic detection of the received data rate. In order to provide noise stability, the transition between data rates is governed by a hysteresis process. This scheme allows the detection and selection of the proper data rate in the range of few microseconds for a system operating between 10 Gbps and 1.25 Gbps in steps of factor of 2, ignoring the propagation delays.

The generated amount of data on high flying platforms like aircrafts, satellites and Unmanned Aerial Vehicles (UAV) increases continuously, due to the technical improvement of modern sensor systems. The resulting demands for higher data rates on airborne and space platforms motivates the development of Laser Communication terminals for aircrafts and satellites in the last years. DLRs Institute of Communications and Navigation has a successful track record in developing Free Space Optical (FSO) terminals for flying platforms like stratospheric balloons, aircrafts and small satellites to transfer data from moving platforms down to earth in real-time. Beside the advantages of FSO such as high data rates and a secure transfer channel against Radio Frequency (RF) interferences, a direct line of sight is mandatory for a successful link. Traditional RF-Communication is more robust and less effected by atmospheric disturbances or weather conditions. Thus, new system concepts have been developed to benefit from the provided high data rates of the FSO and the reliability of RF-Communication technologies. As part of this trend, DLR has developed and demonstrated a Hybrid FSO/RF-communication system capable of overcoming the spurious effects of the atmosphere. This paper gives an overview about DLRs current studies and developments with the goal to combine the advantages of FSO and RF-Communication. It discusses possible implementation concepts on different platforms and presents experimental results of the implemented FSO/RF hybrid communication system operating for airborne, optical downlinks at 1Gbps.

Space industry has undergone a significant change over the last years. The development moved from large and costly spacecrafts to cost-efficient designs and shorter development times. While the satellites became smaller, the resolution of high compact sensors increased which led to a high data-volume to be transmitted and increasing demands for higher data rates on small satellites. This motivated for a highly compact version of DLR’s optical communication payload OSIRIS for small LEO satellites. DLR’s Institute of Communications and Navigation has developed the OSIRIS (Optical Space Infrared Downlink System) program starting with payloads on the satellites Flying Laptop of Univ. of Stuttgart and BiROS of DLR. Combining miniaturization to the flight-proven developments with novel concepts, OSIRIS4CubeSat allows integration in a standard CubeSat bus. The development of OSIRIS4CubeSat (industrialized under the product name “CubeLCT”) is conducted in close collaboration with Tesat Spacecom, DLR’s commercialization partner. The first implementation will be demonstrated within the PIXL-1-Mission on a 3Unit CubeSat. Furthermore, OSIRIS4CubeSat (O4C) has been chosen to support scientific missions together with university partners in the field of Quantum Key Distribution (QUBE). In the future, the modular design will enable extensions for optical inter-satellite links. This paper will give an overview about the development of the O4C payload and the current status of the PIXL-1- Mission. Furthermore, it will show the adaptation of the payload for the scientific mission QUBE. Besides these projects, the paper will give an outlook for future extensions of the O4C payload and the necessity of high data-rates in other scenarios such as inter-satellite links.

A key agreement problem is considered that has a biometric or physical identifier, a terminal for key enrollment, and a terminal for reconstruction. A nested convolutional code design is proposed that performs vector quantization during enrollment and error control during reconstruction. Physical identifiers with small bit error probability illustrate the gains of the design. One variant of the nested convolutional codes improves on the best known key vs. storage rate ratio but it has high complexity. A second variant with lower complexity performs similar to nested polar codes. The results suggest that the choice of code for key agreement with identifiers depends primarily on the complexity constraint., To appear in ACM Workshop on Information Hiding and Multimedia Security 2020

Our ecosystems are facing increasingly extensive and complex natural disasters originating from natural or man-made hazards. Examples include the wild fires in Portugal 2017, Chile 2017, California 2018 and most recently Australia 2019/2020 as well as widespread flood events in Austria and the Czech Republic in 2013 and in Serbia and Croatia in 2014. These complex crisis situations highlight the increasing demands of stakeholders to monitor, anticipate, prepare for and learn from disasters. Research and innovation in this area needs to revolve around the expertise and guidance from practitioners in order to find solutions that are accepted and to benefit from their domain knowledge. In the European Commission (EC) H2020-funded project HEIMDALL on a Multi-Hazard Cooperative Management Tool for Data Exchange, Response Planning and Scenario Building we address the challenge of co-designing technological solutions for an improved adaptive emergency management at local, regional, national and European level with a multi-disciplinary group of experts including firefighters, police, emergency medical services, command and control and civil protection.In order to find the most practical scenario-based solutions we follow a three-step approach: 1) Identification of immediate and long-term prevention and response planning activities that involve complex multi-hazard scenarios and information that needs to be represented in a conceptual scenario model to improve these activities; 2) Extension of that scenario data model by a harmonized lessons learnt data structure which allows stakeholders to capture experience of the emergency management in complex disasters; 3) Development and implementation of a scenario matching tool which allows users to find situations with a similar context, environmental conditions, hazard behaviour and stressed capabilities, from local storage as well as shared by other organizations. We believe that the combination of recording and matching scenarios including lessons learnt from prior incidents can improve the ability of stakeholders to learn and evolve from complex situations and thereby allow them to respond more effectively and operate more efficiently during disasters. Results of successive user exercises and evaluations of the implemented products and tools throughout the project underpin this assumption and at the same time indicate future research needs.The HEIMDALL project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 740689.

In response to natural and man-made hazards multiple organisations usually are involved in a very complex situation. On the other hand, extreme weather situations due to the climate change create hazards in areas which were considered safe before. In order to improve the capabilities of involved organisations in responding and preparing for disaster events, the availability of an efficient information sharing approach is a key enabler. To this end, we propose a communication system based on a content oriented architecture tailored to disaster management. It includes a catalogue that is offering web services for publishing and subscribing of disaster information and for further collaboration amongst agencies and first responders. Moreover, the considered approach also allows for full content access control and enables a flexible system. The paper shows the current status of the system design. Next steps will include the implementation and evaluation of the approach.

A successive cancellation (SC) decoder with inactivations is proposed as an efficient implementation of SC list (SCL) decoding over the binary erasure channel. The proposed decoder assigns a dummy variable to an information bit whenever it is erased during SC decoding and continues with decoding. Inactivated bits are resolved using information gathered from decoding frozen bits. This decoder leverages the structure of the Hadamard matrix, but can be applied to any linear code by representing it as a polar code with dynamic frozen bits. SCL decoders are partially characterized using density evolution to compute the average number of inactivations required to achieve the maximum a-posteriori decoding performance. The proposed measure quantifies the performance vs. complexity trade-off and provides new insight into dynamics of the number of paths in SCL decoding. The technique is applied to analyze Reed-Muller (RM) codes with dynamic frozen bits. It is shown that these modified RM codes perform close to extended BCH codes., Accepted at the 2020 ISIT

In this paper, a low-complexity symbol-based equalizer that performs non-linear distortion cancellation is proposed for application at the user terminal in the DVB-S2X satellite forward link. The channel is comprehensively modeled, including the non-linear travelling wave tube amplifier characteristics, the input-multiplexing and output-multiplexing filter responses at the satellite transponder, and the phase noise at the user terminal, according to the very-small aperture terminal reference scenario. Two detectors in the cancellation loop are considered, comparing the packet-error rate (PER) performance of simple maximum likelihood demodulation with hard decision to soft information exchange with low-density parity-check decoder, and showing only marginal improvement with the latter solution. The PER performance is compared against a number of pre-distortion techniques at the transmitter, such as dynamic data pre-distortion, successive data pre-distortion, and static data pre-distortion. The novel receiver demonstrates superior performance even with one iteration of distortion cancellation, while the joint application of successive data pre-distortion and iterative symbol-based equalization shows up to 4.95-dB energy efficiency gain for 32-level amplitude and phase-shift keying (32-APSK). The computational complexity is also evaluated. The improved receiver is particularly suitable for application with higher order modulation, a wide-band carrier, and low roll-off factors.

Decoding complexity of convolutional and trellis codes by Viterbi decoder can be reduced by applying suggested merging algorithm to the Forney code trellis. The algorithm can be applied for every trellis section separately, which is convenient for time-varying codes, and it outputs the minimal trellis of the section. In case of convolutional codes, the same minimal trellis of every section can be obtained from the syndrome trellis of proposed split code.

In this paper, we explore the use of machine learning methods as an efficient alternative to correlation in performing packet detection. Targeting satellite-based massive machine type communications and internet of things scenarios, our focus is on a common channel shared among a large number of terminals via a fully asynchronous ALOHA protocol to attempt delivery of short data packets. In this setup, we test the performance of two algorithms, neural networks and random forest, which are shown to provide substantial improvements over {traditional} techniques. Excellent performance is demonstrated in terms of detection and false alarm probability also in the presence of collisions among user transmissions. The ability of machine learning to extract further information from incoming signals is also studied, discussing the possibility to classify detected preambles based on the level of interference they undergo.

Ground-based adaptive optics (AO) systems can use temporal control techniques to greatly improve image resolution. A measure of wind velocity as a function of altitude is needed to minimize the temporal errors associated with these systems. Spatio-temporal analysis of AO telemetry can express the wind velocity profile using the SLODAR technique. However, the limited altitude-resolution of current AO systems makes it difficult to disentangle the movement of independent layers. It is therefore a challenge to create an algorithm that can recover the wind velocity profile through SLODAR data analysis. In this study we introduce a novel technique for automated wind velocity profiling from AO telemetry. Simulated and on-sky centroid data from CANARY - an AO testbed on the 4.2 m William Herschel telescope, La Palma - is used to demonstrate the proficiency of the technique. Wind velocity profiles measured on-sky are compared to contemporaneous measurements from Stereo-SCIDAR, a dedicated high-resolution atmospheric profiler. They are also compared to European centre for medium-range weather forecasts. The software package that we developed to complete this study is open source.

From a geostationary Earth orbit (GEO) satellite's perspective a low Earth orbit (LEO) satellite is visible on more than half of its orbit. Albeit the free-space loss of an inter-satellite link is much higher than the one of a direct ground link, considerable data rates and download volumes can be achieved. In this paper we describe the system architecture of an integrated approach for a data relay satellite system and the development of LEO satellite and ground station modems. The approach allows serving several small and inexpensive LEO satellites at the same time both with low rate telemetry/telecommand links and with high rate download of sensor data.

We propose a decoding algorithm for tail-biting convolutional codes over phase noise channels. It can be seen as a reduced complexity approximation of maximum likelihood decoding. We target short blocks and extend the wrap-around Viterbi algorithm to trellises describing the random evolution of the phase impairment, for which we adopt two different models: a blockwise non-coherent and a blockwise Wiener channel model. Numerical results show that the performance of the proposed algorithm is within a few tenths of dB or less from maximum likelihood decoding for the setup studied in this letter.

We address the problem of decoding Gabidulin codes beyond their unique error-correction radius. The complexity of this problem is of importance to assess the security of some rank-metric code-based cryptosystems. We propose an approach that introduces row or column erasures to decrease the rank of the error in order to use any proper polynomial-time Gabidulin code error-erasure decoding algorithm. The expected work factor of this new randomized decoding approach is a polynomial term times \(q^{m(n-k)-w(n+m)+w^2+\min \{2\xi (\frac{n+k}{2}-\xi ),wk\} }\), where n is the code length, q the size of the base field, m the extension degree of the field, k the code dimension, w the number of errors, and \(\xi := w-\tfrac{n-k}{2}\). It improves upon generic rank-metric decoders by an exponential factor.

We show that the root-finding step in interpolation-based decoding of interleaved Gabidulin codes can be solved by finding a so-called minimal approximant basis of a matrix over a linearized polynomial ring. Based on existing fast algorithms for computing such bases over ordinary polynomial rings, we develop fast algorithms for computing them over linearized polynomials. As a result, root finding costs $O^{\sim}(\ell^{\omega}\mathcal{M}(n))$ operations in $F_{q^{m}}$, where l is the interleaving degree, n the code length, $F_{q^{m}}$ the base field of the code, $2 \leq \omega \leq 3$ the matrix multiplication exponent, and $\mathcal{M}(n) \in O(n^{1635})$ is the complexity of multiplying two linearized polynomials of degree at most n. This is an asymptotic improvement upon the previously fastest algorithm of complexity $O(\ell^{3}n^{2})$, in some cases $O(\ell^{2}n^{2})$.

Optical satellite links have gained increasing attention throughout the last years. Especially for the application of optical satellite downlinks, DLR's Institute of Communications and Navigation is developing a number of experimental payloads for various satellites. Within the OSIRIS program, DLR develops optical terminals and systems which are optimized for small satellites. This paper will show measurements conducted with DLR's OSIRISv1-payload hosted on University of Stuttgart's Flying Laptop satellite. Furthermore, a summary of the OSIRIS program's current status will be given as well.

The synthesis of numerical power vectors for optical satellite data downlinks through the atmosphere to optical ground stations is described. A set of standard time series is defined and their further application for estimation of transmission performance is shown.

Herausforderungen und Vorteile der CCSDS-Mitarbeit: - Zeitaufwendig und kostspielig (USA-Reisen, 2x Prototypenbau): ideal 41 Monate bis BB, in Praxis viel länger - Personen oder Agenturen sind später nicht sichtbar; Sichtbarkeit für Personen oder Institute existiert nur über separate Veröffentlichungen - Einstimmigkeit innerhalb der Gruppe für BBs erschwert Konsensfindung: gegenseitiges Überzeugen durch teils aufwendige Untersuchungen - politische Motivationen erschweren manchmal optimale technische Entscheidungen . . . + . . . andererseits gibt es OrangeBooks als kurzfristigen Ausweg + Nutzung der existierenden gut funktionierenden Organisation CCSDS für die Erarbeitung von Standarddokumenten + Übernahme durch andere Standardisierungs-Organisationen (ISO) + wichtige Diskussionen mit den besten Experten zum Thema

This letter proposes successive cancellation list (SCL) decoding of product codes with Reed--Muller (RM) component codes. SCL decoding relies on a product code description based on the $2\times 2$ Hadamard kernel, which enables interpreting the code as an RM subcode. The focus is on a class of product codes considered in wireless communication systems, based on single parity-check and extended Hamming component codes. For short product codes, it is shown that SCL decoding with a moderate list size performs as well as (and, sometimes, outperforms) belief propagation (BP) decoding. Furthermore, by concatenating a short product code with a high-rate outer code, SCL decoding outperforms BP decoding by up to $1.4$ dB., accepted for publication in IEEE Communications Letters

In this paper we investigate the performance of caching schemes based on fountain codes in a heterogeneous satellite network. We consider multiple cache-aided hubs which are connected to a geostationary satellite through backhaul links. With the aimof reducing the average number of transmissions over the satellite backhaul link, we propose the use of a caching scheme based on fountain codes. We derive a simple analytical expression of the average backhaul transmission rate and provide a tightupper bound on it. Furthermore, we show how the performance of the fountain code based caching scheme is similar to that of a caching scheme based on maximum distance separable codes., Comment: arXiv admin note: substantial text overlap with arXiv:1807.05619

The design and qualification of a retroreflector specifically designed for a CubeSat (CubeL) is described. The CubeSat will be launched to space in 2019 and demonstrate the latest generation of the optical space infrared downlink system developed by the German Aerospace Center together with the industrial partner Tesat-Spacecom. The retroreflector is optimized to allow for a coarse verification of the satellites attitude control system. By analyzing the returning photon count during satellite laser ranging (SLR) when the satellite is operated in station pointing mode attitude information is obtained. To achieve this goal, the entrance face of the retroreflector is recessed by a circular tube-shaped aperture. Due to this recession, the signal reflected from the retroreflector falls off rapidly when the retroreflector is tilted away from the SLR station. From measurements of the retroreflectors far-field diffraction pattern and calculations, we believe that it should be possible to determine the orientation accuracy of the satellite to within ± 2°. The proposed method is an effective and cheap way for coarse attitude control, e.g., for satellites of mega-constellations with any existing satellite laser ranging ground station.

The establishment of quantum communication links over a global scale is enabled by satellite nodes. We examine the influence of Earth's atmosphere on the performance of quantum optical communication channels with emphasis on the downlink scenario. We derive the geometrical path length between a moving low Earth orbit satellite and an optical ground station as a function of the ground observer's zenith angle, his geographical latitude, and the meridian inclination angle of the satellite. We show that the signal distortions due to regular atmospheric refraction, atmospheric absorption, and turbulence have a strong dependence on the zenith angle. The observed saturation of transmittance fluctuations for large zenith angles is explained. The probability distribution of the transmittance for slant propagation paths is derived, which enables us to perform the security analysis of decoy state protocols implemented via satellite-mediated links., Comment: 29 pages, 13 figures

Transmitter diversity is an effective fading mitigation scheme in an optical geostationary satellite feeder uplink. We quantify the performance of the scheme over a slow fading channel where the atmospheric turbulence causes scintillation and wandering of the optical beam resulting in deep fades at the satellite receiver. For given atmospheric conditions and residual beam pointing jitter, we optimize the transmit power of each beam to obtain the minimum overall power scintillation index and achieve a bit error rate gain of 0.46dB considering intensity modulation and direct detection.

International audience; Context. Laser guide stars (LGS) allow adaptive optics (AO) systems to reach greater sky coverage, especially for AO systems correcting the atmospheric turbulence on large fields of view. However LGS suffer from limitations, among which is their apparent elongation which can reach 20 arcsec when observed with large aperture telescopes such as the European Southern Observatory 39 m telescope. The consequences of this extreme elongation have been studied in simulations and laboratory experiments, although never on-sky, yet understanding and mitigating those effects is key to taking full advantage of the Extremely Large Telescope (ELT) six LGS. Aims: In this paper we study the impact of wavefront sensing with an ELT-scale elongated LGS using on-sky data obtained with the AO demonstrator CANARY on the William Herschel telescope (WHT) and the ESO Wendelstein LGS unit. CANARY simultaneously observed a natural guide star and a superimposed LGS launched from a telescope placed 40 m away from the WHT pupil. Methods: Comparison of the wavefronts measured with each guide star allows the determination of an error breakdown of the elongated LGS wavefront sensing. With this error breakdown, we isolate the contribution of the LGS elongation and study its impact. We also investigate the effects of truncation or undersampling of the LGS spots. Results: We successfully used the elongated LGS wavefront sensor (WFS) to drive the AO loop during on-sky operations, but it necessitated regular calibrations of the non-common path aberrations on the LGS WFS arm. In the off-line processing of the data collected on-sky we separate the error term encapsulating the impact of LGS elongation in a dynamic and quasi-static component. We measure errors varying from 0 nm to 160 nm rms for the dynamic error and we are able to link it to turbulence strength and spot elongation. The quasi-static errors are significant and vary between 20 nm and 200 nm rms depending on the conditions. They also increase by as much as 70 nm over the course of 10 m. We do not observe any impact when undersampling the spots with pixel scales as large as 1.95″, while the LGS spot full width half maximum varies from 1.7″ to 2.2″; however, significant errors appear when truncating the spots. These errors appear for fields of view smaller than 10.4″ to 15.6″, depending on the spots' elongations. Translated to the ELT observing at zenith, elongations as long as 23.5″ must be accommodated, corresponding to a field of view of 16.3″ if the most elongated spots are put across the diagonal of the subaperture. Data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/649/A158

We study the application of random linear network coding (RLNC) for cooperative coverage extension in land mobile satellite (LMS) vehicular networks. We perform an analytical assessment of the limits of cooperation in the presence of both a satellite and a terrestrial repeater (gap-filler). Using the Max-flow Min-cut theorem we derive exact expressions as well as closed-form lower bounds on the coverage in a setup of practical interest. Furthermore, we propose a practical implementation of the RLNC cooperative approach for the Digital Video Broadcasting - Satellite services to Handheld (DVBSH) standard. We evaluate numerically the performance of the proposed protocol using a simulator based on physical layer abstraction and widely adopted propagation channel models for both the satellite and the terrestrial segments. Our simulation results show that the proposed scheme extends the coverage with respect to a system in which simple cooperative relaying is used, making a more efficient use of the terrestrial channel resources. Additionally, the proposed solution can help keeping a relatively low outage probability while limiting the number of required gap-fillers.

We present the results from a Monte Carlo computer simulation of adaptive optics (AO) pre-compensated laser uplink propagation through the Earth’s atmospheric turbulence from the ground to orbiting satellites. The simulation includes the so-called point-ahead angle and tests several potential AO mitigation modes such as tip/tilt or full AO from the downlink beam, and a laser guide star at the point ahead angle. The performance of these modes, as measured by metrics relevant for free-space optical communication, are compared with no correction and perfect correction. The aim of the study is to investigate fundamental limitations of free-space optical communications with AO pre-compensation and a point-ahead angle, therefore the results represent an upper bound of AO corrected performance, demonstrating the potential of pre-compensation technology. Performance is assessed with varying launch aperture size, wavelength, launch geometry, ground layer turbulence strength (i.e. day/night), elevation angle and satellite orbit (Low-Earth and Geostationary). By exploring this large parameter space we are able examine trends on performance with the aim of informing the design of future optical ground stations and demonstrating and quantifying the potential upper bounds of adaptive optics performance in free-space optical communications.

A pilot-assisted transmission (PAT) scheme is proposed for short blocklengths, where the pilots are used only to derive an initial channel estimate for the list construction step. The final decision of the message is obtained by applying a non-coherent decoding metric to the codewords composing the list. This allows one to use very few pilots, thus reducing the channel estimation overhead. The method is applied to an ordered statistics decoder for communication over a Rayleigh block-fading channel. Gains of up to $1.2$ dB as compared to traditional PAT schemes are demonstrated for short codes with QPSK signaling. The approach can be generalized to other list decoders, e.g., to list decoding of polar codes., Comment: Accepted at the 12th International ITG Conference on Systems, Communications and Coding (SCC 2019), Rostock, Germany

For the next generation of very high throughput communication satellites, free-space optical (FSO) communication between ground stations and geostationary telecommunication satellites is likely to replace conventional RF links. To mitigate atmospheric turbulence, TNO and DLR propose Adaptive Optics (AO) to apply uplink pre-correction. In order to demonstrate the feasibility of AO pre-correction an FSO link has been tested over a 10 km range. This paper shows that AO pre-correction is most advantageous for low point ahead angles (PAAs), as expected. In addition, an optimum AO precorrection performance is found at 16 AO modes for the experimental conditions. For the specific test site, tip-tilt precorrection accounted for 4.5 dB improvement in the link budget. Higher order AO modes accounted for another 1.5 dB improvement in the link budget. From these results it is concluded that AO pre-correction can effectively improve high-throughput optical feeder links.

Recently, it has been shown how McEliece public-key cryptosystems based on moderate-density parity-check (MDPC) codes allow for very compact keys compared to variants based on other code families. In this paper, classical (iterative) decoding schemes for MPDC codes are considered. The algorithms are analyzed with respect to their error-correction capability as well as their resilience against a recently proposed reaction-based key-recovery attack on a variant of the MDPC-McEliece cryptosystem by Guo, Johansson and Stankovski (GJS). New message-passing decoding algorithms are presented and analyzed. Two proposed decoding algorithms have an improved error-correction performance compared to existing hard-decision decoding schemes and are resilient against the GJS reaction-based attack for an appropriate choice of the algorithm's parameters. Finally, a modified belief propagation decoding algorithm that is resilient against the GJS reaction-based attack is presented.

Optical Data Links are a very promising Technology for downlinking data from stratospheric platforms to ground or to satellite relais, as well as interconnecting these towards a network: The optical signal does not interfere with any radio communication on ground or from the HAP user links itself, and the free-space loss of such laser links is minimal compared to its RF counterparts. Still, the communication is very secure by physical nature, and even allows the application of QKD principles based on quantum effects. The impact of the atmospheric channel needs to be evaluated and, if necessary, counteracted. Dependent on the link scenario, the atmosphere can influence the optical signal by its index-of-refraction trubulence, leading to fading-like effects. Furthermore clouds can in certain link geometries cause outages which can be compensated by site- and link-diversity. DLR-IKN has evaluated the atmospheric impact both analytically and by experiments, and according mitigation techniques (like physical diversity, Forward Error Correction /FEC, as well as adaptive data repetition techniques) were developed such as high speed modems with FEC and interleaving, as well as ARQ techniques, and also physical diversity and receiver sensitivity slope techniques. German Aerospace Center's Institute of Communications and Navigation sees a great chance for the application of optical links with HAPS in certain application scenarios - either of commercial or institutional nature - and fosters cooperation based on our technology developments.

Some types of weak keys in the Faure-Loidreau (FL) cryptosystem are presented. We show that from such weak keys the private key can be reconstructed with a computational effort that is substantially lower than the security level. The proposed key-recovery attack is based on ideas of generalized minimum distance (GMD) decoding for rank-metric codes.

Low complexity decoding algorithms are necessary to meet data rate requirements in excess of 1 Tbps. In this paper, we study one and two bit message passing algorithms for belief propagation decoding of low-density parity-check (LDPC) codes and analyze them by density evolution. The variable nodes (VNs) exploit soft information from the channel output. To decrease the data flow, the messages exchanged between check nodes (CNs) and VNs are represented by one or two bits. The newly proposed quaternary message passing (QMP) algorithm is compared asymptotically and in finite length simulations to binary message passing (BMP) and ternary message passing (TMP) for spectrally efficient communication with higher-order modulation and probabilistic amplitude shaping (PAS). To showcase the potential for high throughput forward error correction, spatially coupled LDPC codes and a target spectral efficiency (SE) of 3 bits/QAM symbol are considered. Gains of about 0.7 dB and 0.1 dB are observed compared to BMP and TMP, respectively. The gap to unquantized belief propagation (BP) decoding is reduced to about 0.75 dB. For smaller code rates, the gain of QMP compared to TMP is more pronounced and amounts to 0.24 dB in the considered example., Accepted for IEEE/OSA Journal on Lightwave Technology

The railways industry is at the moment looking for innovations and solutions supporting their core business and increasing the capacity of the rail system. One aspect is the development of a new communication system that improves shortcomings at the European Train Control System (ETCS) with an adaptable multi-bearer train-to-ground communications system. The idea is to increase the capacity and improve the availability of the communication system by using multiple bearers or providers like, 5G, LTE, WiFi or SatCom. Testing these solutions can become cumbersome since multiple networks must be set up and especially in the SatCom case there are multiple options for bearers. SDR offers a solution for this: the bearer can be implemented in software and adapted if needed to model other technologies. We present here a prototype design that modules a satellite channel and can be used to model a satellite bearer.

This paper explores the application of physical-layer network coding (PNC) for short-packet transmissions. PNC can potentially reduce the communication delay in relay-assisted wireless networks and can thus be instrumental in realizing short-packet communication systems with stringent delay requirements. In this work, first, we first derive an achievability bound for channel-coded short-packet PNC systems. Based on the random-coding error-exponent, the bound serves as a benchmark for short-packet PNC operating with traditional preamble-aided channel estimation and XOR channel decoding. Second, we design a blind channel estimation algorithm and a code-aided channel estimation algorithm for short-packet PNC systems. Both outperform the traditional preamble-aided channel estimation for PNC systems operating with mismatched channel-state-information. As a case study, we compare the three algorithms for packets of 128 symbols over a two-way relay channel. The results show that the blind algorithm outperforms the code-aided algorithm and preamble-aided algorithm by almost 0.2 and 1.5 dB respectively. Furthermore, the blind algorithm achieves the target packet error rate of 10−4 within 0.5 dB of the random coding bound of an imaginary system in which perfect channel-state-information is available at the relay at no cost (i.e., channel estimation is not required in the imaginary system). The bound and the algorithms give us a fundamental framework for applying PNC to short-packet transmissions.

Managing forest fires and other disasters usually involves multiple emergency management organisations, even multiple jurisdictions and countries in case of cross-border events. Following the initial disaster event, cascading effects can further amplify the degree and complexity of disaster situations. This imposes a high need and degree of cross-organisational communication and cooperation, not only during response but also in the preparedness phase, between all stakeholders (command and control centres, civil protection units, medical services, police and fire fighting units). However, relevant studies have revealed that collective interoperability is not sufficiently achieved, which reduces the ability to perform collaborative activities, including decision making and action implementation (House, 2014). Moreover, information overload and uncertainty in a crisis situation lead to reduced situation awareness and decision making capabilities. Managing disasters begins before the disaster happens through being ready and aware of hazards, considering risks, possibilities and preventive measures, building scenarios and training. There is clearly a need to ensure efficient societal preparedness, to improve incident and emergency situation response mechanisms, in order to reduce impacts on people, property, the environment, and on society as a whole. An element of this improvement should be the provision to disaster risk management first responders of a flexible platform for multi-hazard emergency planning and management. Such a platform makes use of innovative technologies, for the definition of realistic multi-disciplinary scenarios and response plans. Implementing such a tool is the ambition of the HEIMDALL H2020 European project (HEIMDALL, 2017). In the following sections the concept of the HEIMDALL project is outlined and demonstrated within the context of wildfire management.

Recently, the availability of innovative and affordable COTS (Commercial Off-The-Shelf) technological solutions and the ever-improving results of microelectronics and microsystems technologies have enabled the design of ever smaller yet ever more powerful satellites. The emergence of very capable small satellites heralds an era of new opportunities in the commercial space market. Initially applied only to scientific missions, Earth observation and remote sensing, small satellites are now being deployed to support telecommunications services. This review paper examines the operational features of small satellites that contribute to their success. An overview of recent advances and development trends in the field of small satellites is provided, with a special focus on telecommunication aspects such as the use of higher frequency bands, optical communications, new protocols, and advanced architectures.