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Over the last decade, terms such as big data and IoT have become part of our everyday vocabulary, and as time goes by, more and more systems are collecting larger amounts of data in order to provide new services or improve quality, and aerospace sector is not an exception. Space probes and rovers, which originally communicated with ground stations using S-band, have moved to higher frequencies in order to be able to transmit more information per unit of time. As the frequency of the system increases, the optical band is reached, 40 years ago, the first experiment in aerospace to demonstrate laser communication, the Airbone Flight Test System (AFTS), was conducted. Numerous efforts have been made to demonstrate that optical communications are possible. When sending an exploration mission, the scientific community maximises the performance of the instruments by taking into account multiple criteria, such as whether the particular device has been previously tested in space and the likelihood of failure. Therefore, the use of new technologies requires a process of multiple demonstration missions prior to be accepted. This thesis compiles the state of the art, i.e. the knowledge acquired over the last four decades, and covers three main points: ground infrastructures, the flight terminal and the method of communication between both systems. In the first point, the study focuses on explaining the parameters that must be taken into account when designing an international ground station network, equivalent to its counterpart in the RF band, NASA’s DSN networks or ESA’s ESTRACK, among others. One of the most relevant variables that determines the location of a ground stations are the atmospheric conditions. For this reason, a series of files containing information about the planet’s atmosphere has been downloaded and processed from NASA’s LAADS DAAC database. Secondly, the link equation of a signal emitted in optical band has been studied. Each of the terms that make up the equation are presented in detail in several sections, in particular the obscuration losses in Cassegrain type antennas, the pointing losses and those due to atmospheric absorption and turbulence. Finally, two practical studies have been carried out in which it is possible to see how the mathematics described in the previous chapters have been applied to execute missions whose purpose is to communicate in deep space. To achieve this, the JPL library and toolkit called SPICE has been used in a fictitious but realistic Mars-Earth downlink mission. Thanks to the high reliability of SPICE, all the data related to the orbital mechanics of a space mission has been obtained and compared, in order of magnitude, with a mission called Psyche and DSOC, scheduled for launch in August 2022. Apart from didactically exemplifying the terms of the link equation in a specific mission, key elements such as capacity or bit rate have also been retrieved, which allow immediate conclusions to be drawn in favour of this technology and thus contribute to its consolidation in the field of deep space communications.

International audience; Carrier synchronization is a fundamental stage in the receiver side of any communication or positioning system. Traditional carrier phase tracking techniques are based on well-known phase-locked loop (PLL) closed-loop architectures, which are still the methods of choice in modern receivers. Those techniques are well understood, easy to tune, and perform well under benign propagation conditions, but their applicability is seriously compromised in harsh propagation environments, where the signal may be affected by high dynamics, shadowing, strong fadings, multipath effects, or ionospheric scintillation. From an optimal filtering standpoint, the Kalman filter (KF) is clearly a powerful alternative, but the synchronization community seems still reluctant to exploit all the potential it has to offer. The purpose of this article is twofold: i) to review the basics and state of the art on both PLL and KF-based tracking techniques and ii) to present and justify the reasoning behind the systematic use of KF-based tracking approaches instead of the well-established PLL-based architectures from both theoretical and practical points of view. To support the discussion, two specific scenarios of interest to the aerospace community are numerically evaluated: robust carrier tracking of global navigation satellite systems' signals and synchronization in a deep space communications system.

International audience; Deep space missions keep pushing for new frontiers affecting a wide spectrum of disciplines. To support the scientific achievements expected from new missions, communication technology is being pushed towards its limits [1]. A need to increase communication links data rate as well as to lower the operative signal-to-noise ratio (SNR) are identified. The adoption of advanced coding schemes such as turbo codes and low-density parity-check (LDPC) codes (e.g., Consultative Committee for Space Data Systems (CC-SDS) standards) allows receivers to operate at lower SNRs. However, in order to exploit the full potential of the coding gain, the receiver must be able to acquire and track a signal with a SNR much lower than expected in nominal conditions of state-of-the-art systems. The target operating point is given by the candidate LDPC codes [2], where the codeword error rate is set to WER ≤ 10 -5 , achieved at the bit energy to noise density ratio E b /N 0 ≥ 5.2 dB, ≥ 3.6 dB for LDPC(128,64) and LDPC(256,128), respectively. In [3] the first receiver bottleneck related with frame synchronization, a functionality required previous to channel decoding, was identified. Even though frame synchronization enhancements were proposed beyond standard correlation techniques [3], [4], [1], it was recommended to increase the synchronization word length in order to achieve the target performance. The recommendation was recently adopted by the CCSDS. In this work, the focus lies on the receiver synchronization stages (i.e., acquisition and tracking). Not only from a research standpoint, but also for the design of next generation Telemetry Tracking & Command (TT&C) transponders, it is of capital importance to understand the performance limitations of state-of-the-art deep space communications architectures, clearly identifying possible bottlenecks and the synchronization stages (i.e., acquisition and tracking) to be improved. Digital carrier and timing synchronization have been an active research field for the past three decades in applications such as satellite-based positioning or terrestrial wireless communications systems. In those scenarios, the limitations of standard delay, frequency, and phase-locked loop (delay-locked loop, frequency-locked loop (FLL), and phase-locked loop (PLL), respectively) architectures have been clearly overcome by Kalman filter (KF) based solutions [5], which provide an inherent adaptive bandwidth, robustness, flexibility, and an optimal design methodology. Despite the advances in the field, synchronization architectures for deep space communications links, implemented in current TT&C transponders, still rely on well-known conventional architectures, which may be insufficient if limits are pushed to extremely low SNR or harsh propagation conditions. With the advent of powerful software defined radio receivers and new system design rules, it is now possible to adopt new robust architectures that may enable going beyond the performance and reliability provided by legacy solutions.

Carrier synchronization is a fundamental stage in the receiver side of any communication or positioning system. Traditional carrier phase tracking techniques are based on well-known phase-locked loop (PLL) closed-loop architectures, which are still the methods of choice in modern receivers. Those techniques are well understood, easy to tune, and perform well under benign propagation conditions, but their applicability is seriously compromised in harsh propagation environments, where the signal may be affected by high dynamics, shadowing, strong fadings, multipath effects, or ionospheric scintillation. From an optimal filtering standpoint, the Kalman filter (KF) is clearly a powerful alternative, but the synchronization community seems still reluctant to exploit all the potential it has to offer. The purpose of this article is twofold: i) to review the basics and state of the art on both PLL and KF-based tracking techniques and ii) to present and justify the reasoning behind the systematic use of KF-based tracking approaches instead of the well-established PLL-based architectures from both theoretical and practical points of view. To support the discussion, two specific scenarios of interest to the aerospace community are numerically evaluated: robust carrier tracking of global navigation satellite systems' signals and synchronization in a deep space communications system. © 2017 IEEE.

Deep-space communications are characterized by extremely critical conditions; current standards foresee the usage of both turbo and low-density-parity-check (LDPC) codes to ensure recovery from received errors, but each of them displays consistent drawbacks. Code concatenation is widely used in all kinds of communication to boost the error correction capabilities of single codes; serial concatenation of turbo and LDPC codes has been recently proven effective enough for deep space communications, being able to overcome the shortcomings of both code types. This work extends the performance analysis of this scheme and proposes a novel hardware decoder architecture for concatenated turbo and LDPC codes based on the same decoding algorithm. This choice leads to a high degree of datapath and memory sharing; postlayout implementation results obtained with complementary metal-oxide semiconductor (CMOS) 90 nm technology show small area occupation (0.98 mm 2 ) and very low power consumption (2.1 mW).

In this paper we develop two new approaches for frame synchronization in the binary-input AWGN channel, in which we account for the sign ambiguity of the received symbols and exploit knowledge of an alternating sequence which precedes the synchronization word. We present an approach based on an extended sliding window and the appropriate decision metric. For the common case that the synchronization word is followed by encoded data we present a solution which exploits the error detection capability of the channel decoder and applies a list decoding approach for frame synchronization. The proposed methods are validated through computer simulations in the deep-space communication uplink and show significant performance gains compared to current solutions.

Deep space (DS) missions for interplanetary explorations are aimed at acquiring information about the solar system and its composition. To achieve this result a radio link is established between the space satellite and receiving stations on the Earth. Significant channel capacity must be guaranteed to such spacecraft-to-Earth link considering their large separation distance as well. Terrestrial atmospheric impairments on the space-to-Earth propagating signals are the major responsible for the signal degradation thus reducing the link's channel temporal availability. Considering the saturation and the limited bandwidth of the conventional systems used working at X-band (around 8.4 GHz), frequencies above Ku-band (12-18 GHz) are being used and currently explored for next future DS missions. For example, the ESA mission EUCLID, planned to be launched in 2020 to reach Sun-Earth Lagrange point L2, will use the K-band (at 25.5-27 GHz). The BepiColombo (BC) ESA mission to Mercury, planned to be launched in 2016, will use Ka-band (at 32-34 GHz) with some modules operating at X-band too. The W-band is also being investigated for space communications (Lucente et al., IEEE Systems J., 2008) as well as near-infrared band for DS links (Luini at al., 3 rd IWOW, 2014; Cesarone et al., ICSOS, 2011). If compared with X-band channels, K-band and Ka-band can provide an appealing data rate and signal-to-noise ratio in free space due to the squared-frequency law increase of antenna directivity within the downlink budget (for the same physical antenna size). However, atmospheric path attenuation can be significant for higher frequencies since the major source of transmission outage is not only caused by convective rainfall, as it happens for lower frequencies too, but even non-precipitating clouds and moderate precipitation produced by stratiform rain events are detrimental. This means that accurate channel models are necessary for DS mission data link design at K and Ka band. A physical approach can offer advanced radiopropagation models to take into account the effects due to atmospheric gases, clouds and precipitation. The objective of this work is to couple a weather forecast numerical model with a microphysically- oriented radiopropagation model, providing a description of the atmospheric state and of its effects on a DS downlink. This work is developed in the framework of the RadioMeteorological Operations Planner (RMOP) program, aimed at performing a feasibility study for the BC mission (Biscarini et al., EuCAP 2014). The RMOP chain for the link budget computation is composed by three modules: weather forecast (WFM), radio propagation (RPM) and downlink budget (DBM). WFM is aimed at providing an atmospheric state vector. Among the available weather forecast models, for RMOP purposes we have used the Mesoscale Model 5. The output of the WFM is the input of the RPM for the computation of the atmospheric attenuation and sky-noise temperature at the receiving ground station antenna. RPM makes use of radiative transfer solver based on the Eddington approximations well as accurate scattering models. Time series of attenuation and sky-noise temperature coming from the RPM are converted into probability density functions and then ingested by the DBM to compute the received data volume (DV). Using the BC mission as a reference test case for the Ka-band ground station at Cebreros (Spain), this work will show the advantages of using a coupled WFM-RPM approach with respect to climatological statistics in a link budget optimization procedure. The signal degradation due to atmospheric effects in DS links in terms of received DV will be also investigated not only at Ka band, but also at X, K and W for intercomparison. The quality of the DS downlink will be given in terms of received DV and the results at different frequencies compared showing the respective advantages and drawbacks

The polychromatic laser guide star (PLGS) provides adaptive optics (AO) with a phase referenceto correct corrugated wavefronts, including tip tilt. It relies on the chromatic dispersion of light returnedfrom the 2-photon resonant excitation of sodium in the mesosphere. Diffraction limited imaging in thevisible then becomes possible. This is mandatory for 80% of the prominent astrophysical cases for the EELT.A PLGS requires standard deviations of position measurements 26 times less than in classical cases. Thus Ihave studied the interferometric laser projector. I have designed a polychromatic base corrector to equalizethe fringe periods, a phase corrector to compensate atmospheric refraction and the optics for fringemeasurements and for keeping apart the PLGS from the science target images.The required accuracy leads me to study how the maximum likelihood algorithm approaches the Cramer-Rao bound.I have written an end-to-end code for numerical simulations of the PLGS, from the lasers to the Strehlmeasurement. I get for the VLT Strehl ratios larger than 40% at 500 nm if one uses an AO providing us a50% instantaneous Strehl (tip tilt Strehl : 80%). An analytical model validates these results.Finally I address the application of the PLGS to deep space communications and to space debris clearing., L’étoile laser polychromatique (ELP) fournit la référence de phase à une optique adaptative (OA)pour corriger les surfaces d’onde turbulentes, y compris leur pente. L’ELP, générée dans la mésosphère parune excitation résonnante à deux photons du sodium, repose sur la déviation chromatique des images. Uneimagerie dans le visible devient possible, et est indispensable pour 80% des programmes astrophysiquesprioritaires de l'E-ELT.L’ELP requiert un écart-type des mesures de position 26 fois inférieur au cas classique. Cela m’a amené àétudier le projecteur laser interférométrique. J’ai mis au point un correcteur de base polychromatique pourégaliser la période des franges et un correcteur de phase pour compenser la réfraction atmosphérique. J’aiétudié l'optique de mesure des franges, et de séparation entre l'ELP et l’objet observé.La précision requise m’a conduit à étudier dans quelles conditions l’algorithme du maximum devraisemblance tend vers la borne de Cramér-Rao.J’ai également développé un modèle numérique de bout en bout pour simuler l’ELP depuis les lasersjusqu’à la mesure du rapport de Strehl. Je montre que pour un VLT, les rapports de Strehl sont supérieurs à40% à 500 nm sans étoile de référence, en prenant une OA qui aurait donné 50% instantané (Strehl depente : 80%). Une approche analytique valide ces résultats.Enfin, j’aborde l’application de l’ELP aux télécommunications interplanétaires et à la destruction des débrisorbitaux.