Bastien Bechadergue

En réponse aux problèmes croissants liés aux transports routiers - accidents, pollutions,congestions - les véhicules à faibles émissions, équipés de systèmes de transports intelligents (ITS)sont progressivement développés. Si la finalité de cette démarche est le véhicule entièrementautonome, on peut néanmoins s'attendre à voir d'abord sur nos routes des véhicules automatisés surdes phases de conduite spécifiques. C'est le cas du convoi automatisé, qui permet à plusieursvéhicules de rouler en convois de manière automatique et donc d'augmenter la capacité des voies decirculation tout en réduisant la consommation de carburant. La fiabilité de cet ITS repose surplusieurs briques technologiques, et en particulier sur la mesure de distance et la transmission dedonnées véhicule-véhicule (V2V).De nombreux systèmes permettent de réaliser ces deux fonctions vitales comme, par exemple, lesradars ou lidars pour la mesure de distance et la technologie IEEE 802.11p pour la communicationvéhiculaire. Si ces différents dispositifs présentent de très bonnes performances, ils sont néanmoinsparticulièrement sensibles aux interférences, qui ne cessent de se multiplier à mesure que le nombrede véhicules équipés augmente et que le trafic est dense. Pour pallier les dégradations deperformances induites par de telles situations, des technologies complémentaires pourraient donc êtreutiles. Le récent développement des diodes électroluminescentes (LED) blanches, en particulier pourl'éclairage automobile, a permis l'émergence des communications optiques visibles sans fil (VLC).Les phares à LED sont alors utilisés pour transmettre des données entre véhicules et avec lesinfrastructures. Malgré la puissance limitée de ces éclairages, plusieurs études ont montré qu'unetransmission de qualité est possible sur quelques dizaines de mètres, faisant de la VLC uncomplément particulièrement intéressant à l'IEEE 802.11p, en particulier pour les convoisautomatisés. Par analogie, on peut alors se demander si les phares ne pourraient pas être aussi utiliséspour mesurer la distance V2V.Le but de cette thèse est donc de proposer et évaluer un système dédié aux situations de convoisautomatisés qui, à partir des phares avant et arrière des véhicules, transmet des données et mesuresimultanément la distance V2V. Dans un premier temps, une étude détaillée de l'état de l'art de laVLC pour la communication V2V est effectuée afin de déterminer l'architecture de base de notresystème. La fonction de mesure de distance est ensuite ajoutée, après une revue des différentestechniques usuelles. Une fois l'architecture générale du système établie, elle est dans un premiertemps validée par des simulations avec le logiciel Simulink. En particulier, les différents paramètressont étudiés afin de déterminer leur impact sur la résolution de mesure de distance et les performancesen transmission de données, puis afin de les optimiser. Si ces simulations fournissent des indicateursimportants pour la compréhension du système, elles ne peuvent cependant remplacer les tests d'unprototype réel. L'implémentation de ce prototype est alors détaillée ainsi que les tests réalisés dansdifférentes configurations. Ces différents tests démontrent l'intérêt des solutions proposées pour lamesure de distance et la communication V2V en convois automatisés.

Optical wireless communication (OWC) represents a promising option for overcoming spectrum limitations in radio frequency systems. OWC systems rely on cells generated by fixed access points, making them vulnerable to service degradation due to interference and frequent handovers. Steerable optical antennas, deployed both at the infrastructure and user levels, can mitigate these issues. Although their effectiveness has been experimentally verified, a thorough comparative study—particularly in terms of coverage—against traditional fixed antennas is still needed. In this article, simulations are first used to compare five scenarios corresponding to different beamsteering strategies. Each scenario is described, and the bit error rate and communication coverage are evaluated via Monte Carlo simulations, accounting for photobiological safety–compliant light source parameters and the effects of line-of-sight and non-line-of-sight optical paths. In a second step, an experimental test bench is proposed and then used to evaluate data rate and coverage with perfect or partial beamsteering and without beamsteering. The experimental results are consistent with the simulations and show that beamsteering significantly improves coverage compared to other pointing approaches, in particular by improving the quality of the received signal, thereby enabling better use of the entire available spectrum.

This study presents a detailed performance analysis of light-emitting diode (LED)–based optical wireless communication (OWC) systems for inter-satellite communication (ISC) in CubeSat constellations. Motivated by the stringent size, mass, and power constraints of small satellites, we investigate realistic system limitations, including LED modulation bandwidth, optical beam divergence, and environmental background noise from solar, lunar, and terrestrial sources. Analytical and simulation-based bit error rate models are developed for multiple modulation schemes, namely on-off keying (OOK), M-ary pulse position modulation (M-PPM), multiband carrierless amplitude and phase (m-CAP) modulation, and direct current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM). The proposed models consistently embed LED bandwidth limitations, inter-symbol interference, and realistic background-induced shot noise into all four modulation formats, and are validated against independent waveform-level Monte Carlo simulations. The results identify optimal operating regimes for each scheme based on data rate and power constraints, highlighting m-CAP as a strong candidate for high-throughput links and M-PPM for ultra-low-power telemetry. In particular, we quantify non-trivial design boundaries in terms of required Eb/N0 andtransmit power versus data rate, range, and background conditions, and show that, even under an intentionally optimistic avalanche photodiode model, PIN receivers remain more power efficient for the considered CubeSat LED links. Additionally, we quantify the influence of beamwidth and receiver field-of-view on alignment sensitivity and noise resilience. Our findings demonstrate that LED-based OWC can provide scalable, energy-efficient and spectrally agile ISC links, enabling robust communication within next-generation CubeSat missions

As 6G and beyond aim for sustainable, high-capacity wireless connectivity, optical wireless communication (OWC) has emerged as a compelling solution.Recent advances in vertical-cavity surface-emitting laser (VCSEL) arrays have significantly enhanced OWC performance, enabling high-speed, low-power data transmission. However, dense VCSEL deployments introduce challenges related to interference and energy efficiency (EE). This paper proposes a scalable precoding framework for EE maximization in fully cooperative VCSEL-based OWC broadcast systems. We formulate a non-convex optimization problem to design the precoding matrix under practical optical constraints while guaranteeing minimum user rates. To solve this, we apply Dinkelbach's method to handle the fractional objective and the inner approximation technique to iteratively convexify and solve the problem. Simulation results show that our approach consistently outperforms regularized zero-forcing in terms of EE, particularly in large-scale deployments, demonstrating its potential for next-generation sustainable dense OWC networks.

Positioning for optical wireless communications (OWC) has been the subject of numerous theoretical and experimental works in recent years, proposing various techniques for achieving sub-10 cm positioning errors. However, most of these techniques require multiple optical sources and/or multiple photoreceivers. In this paper, we take advantage of the growing interest in beam-steering techniques for OWC to propose a new positioning technique based on the possibility of changing the orientation of a single optical source to enable the two-dimensional positioning of a receiver equipped with a single photodetector, whatever its orientation and the optical power emitted. We detail the theoretical principles of this new method and then validate its operation, first using simulations to extract the main behavior, then experimentally on one dimension. The results obtained show that, in addition to the aforementioned advantages, the proposed method enables positioning with sub-10 cm errors, making it an interesting positioning technique for OWC with beam steering.

Whilethe contours of 6G are still being defined, integrated sensing and communication (ISAC) has been identified by the International Telecommunications Union (ITU) as a key feature of next-generation wireless communications. Given the maturity already demonstrated for data transmission on the one hand, and positioning on the other hand, optical wireless communications (OWC) could offer promising solutions for ISAC implementation, especially in indoor scenarios. In this paper, we propose and implement an OWC-based ISAC system that relies on multi-band carrierless amplitude and phase ( $m$ -CAP) modulation associated with received signal strength (RSS)-based positioning to achieve data transmission and localization from the same signal. This $m$ -CAP/RSS system is deployed in a 1.2 $\times\, 1.2\,\times$ 2.16 m $^{3}$ room using four access points installed on the ceiling, and can provide a communication link at a data rate of 12 Mbps with a bit error rate of less than $3.8\times 10^{-3}$ to any user in a reception plane 20 cm above the ground, while estimating its position with an error of less than 5.9 cm in 90% of cases.

As 5G devices and networks continue to roll out, new broadcasting services and capabilities have been introduced to the entire ecosystem, opening up additional new applications and granular business opportunities, where indoor joint communication and sensing are critical. Under this trend, in this paper, we propose a new system using multi-band carrierless amplitude and phase $(m$ -CAP) modulation associated with received signal strength (RSS)-based trilateration to achieve visible light sensing and communication from the same signal. The architecture of this system is first detailed, with an emphasis on how the light source limitations in terms of dynamic range and modulation bandwidth may be taken into account. The proposed set-up is then shown through simulations to provide an illuminance between 300 and 500 lux over the whole room, positioning with an error lower than 7.17 cm in 90% of the cases, and a continuous data connectivity at 32 Mbps. The influence of several parameters, including that of the main $m$ -CAP settings, on this performance is studied in order to define some general rules for the design of such a system.