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Optical wireless communication (OWC) offers several complementary advantages to radio-frequency (RF) wireless networks such as its massive available spectrum; hence, it is widely anticipated that OWC will assume a pivotal role in the forthcoming sixth generation (6G) wireless communication networks. Although significant progress has been achieved in OWC over the past decades, the outage induced by occasionally low received optical power continues to pose a key limiting factor for its deployment. In this work, we discuss the potential role of single-photon counting (SPC) receivers as a promising solution to overcome this limitation. We provide an overview of the state-of-the-art of OWC systems utilizing SPC receivers and identify several critical areas of open problems that warrant further research in the future.

International audience; Traditional IP networks lack the flexibility to respond to faults, network reconfiguration, and load changes in an ever-evolving digital society, which we call the Internet. To make matters worse, implementation of network policies requires configuration of each network device in which the control and data planes are coupled together using vendor specific commands. Software defined networking (SDN) is an emerging technology, which decouples the control plane from the data plane to provide flexibility in configuring/reconfiguring a network. In this manuscript, we present a SDN testbed using off-the-shelf components, write and deploy network applications onto the testbed, and demonstrate the functioning of the network application using a free space optical link.

International audience; We address the features channel characterization and performance evaluation for wireless body-area networks (WBANs) in medical applications during a walk scenario using optical wireless transmission. More specifically, we focus on optical extra-WBAN uplink communication between a central coordinator node (CN) placed on the patient's body and an access point (AP) in a typical hospital room. To characterize the optical wireless channel, we use a Monte Carlo ray tracing-based method and take into account the effects of body shadowing and mobility based on realistic models, in contrast to the previous simplistic models considered in the literature. Using this approach, we derive the dynamic behavior of the channel DC gain for different configurations of the CNs and APs. Furthermore, based on the obtained results, we develop a statistical channel model based on kernel density estimation, which we use to investigate the impact of CN and AP placement on the communication link parameters. Also, based on the outage probability criterion, we discuss the link performance and further analyze the improvement in performance achieved through spatial diversity, i.e., by using multiple APs in the room, for different photodetector types, under different background noise conditions. The presented results show that CN placement and user's local and global mobility significantly impact the performance of extra-WBAN links, which can nevertheless be reduced using spatial diversity. Finally, the presented performance analysis shows that a single AP equipped with an avalanche photodiode photodetector allows an acceptable link performance for low-to-moderate background noise conditions, whereas multiple APs equipped with PIN photodetectors should be used in the case of moderate-to-strong background noise.

International audience; Visible-light communication is a well known emerging technology, which enables high data rate wireless access in indoor environments, by making dual-use of light-emitting diode luminaires for providing lighting and communication. Managing the multiple access and addressing the users' mobility are among the current challenges of this technology. To manage the multipleaccess interference arising from non-intended received signals of the other users, different approaches have been proposed so far, including zero-forcing pre-coding and broadcasting of the users' signals. However, by this approach, the network performance is sensitive to the users' locations, since they affect the correlation properties of the network channel matrix; a higher correlation (e.g., for the case of users getting closer together) results in a performance degradation. To mitigate this, we propose a novel approach of optimizing the receivers' field-of-views based on the bio-inspired particle swarm optimization, in order to adapt to the users' locations, and hence improve the network robustness. The efficiency of the proposed method is demonstrated through numerical simulations.

International audience; Emerging maritime applications arising from the continued growth of the marine economy have an inherent need for high data rate underwater wireless links. Within this context, underwater wireless optical communication is known as a promising technology for data transmission over short-to-medium ranges; the current available technology provides a transmission span of about 100 m. In view of extending the transmission range, silicon photo-multipliers (SiPMs) have recently emerged as a photo-detection solution offering high receiver (Rx) sensitivity together with operational flexibility. In this paper, we introduce the use of pulse amplitude modulation (PAM) together with frequency-domain equalization (FDE) at the Rx to boost the communication rate beyond the bandwidth (BW) limitation of the optoelectronic components. For instance, for a link BW limited to 2 MHz and 2-PAM transmission with a target BER of 10 −4 , the link becomes nonoperational for data rates larger than ∼ 8 Mbps without equalization, whereas much higher data rates can be attained using FDE, e.g., 20 and 50 Mbps with maximum ranges of 28 and 10 m, respectively, in clear waters for the SensL MicroSB-30020 SiPM and an average transmit optical power of 0.6 W only. Meanwhile, the nonlinear distortion of the SiPM is shown to limit the modulation order and thus the data rate in relatively short ranges. We also propose appropriate processing for PAM modulation and demodulation, given the quantum-noise-limited Rx when using an SiPM. We show that the use of non-binary PAM is undeniably advantageous for moderate data-rates (symbol rate a few MHz larger than the overall link BW) when no channel equalization is performed at the Rx. However, when employing FDE, only for very high data rates (e.g., symbol rate ten times larger than the link BW), where the link frequency response becomes highly frequency selective, the non-binary PAM becomes practically interesting, outperforming 2-PAM.