Mohammad-Ali Khalighi

The increasing proliferation of internet-connected devices, together with the widespread reliance on wireless communication in daily activities, are limiting the capabilities of the radio frequency (RF) spectrum to meet data traffic demands. In particular, the rise in connectivity requirements to realize next generation networks, coupled with the growth in utilization of artificial intelligence (AI) and its associated transmission of massive amounts of data, contribute to the need to leverage the optical spectrum to complement the already-congested RF bands. Optical wireless connectivity encompasses a range of solutions that can support data transfer in various use cases, ranging from intra-chip interconnects to deep-space communication. They benefit from advantages in terms of operation within a broad unlicensed spectrum, minimization of RF interference, and inherent security. On the other hand, optical wireless communication (OWC) systems might experience a decline in performance as a result of factors like atmospheric conditions and link blockage. This requires customizing system designs according to the considered use cases and investigating new solutions for realizing optical wireless connectivity. In this article, we present an overview of OWC, encompassing both its conceptual frameworks and the scientific and technological advancements that hold the potential for shaping its future in next generation networks.

Underwater observatories have recently emerged as an efficient solution for marine biodiversity monitoring. The primary objective of this work is to enable efficient and cost-effective data muling from underwater sensors by investigating the use of optical wireless communications to transmit data from the underwater sensors to an aerial node close to the water surface, such as an unmanned aerial vehicle (UAV).More specifically, we utilize a direct water-to-air (W2A) optical communication link between the sensor node equipped with an LED emitter and the UAV equipped with an ultra-sensitive receiver, i.e., a silicon photo-multiplier. As a main contribution, we develop a comprehensive Monte Carlo–based ray-tracing algorithm to characterize this complex channel. This framework rigorously incorporates the impact of air bubbles modeled through the Mie scattering theory, a realistic sea surface representation derived from the JONSWAP spectrum, and an analytical derivation of the channel loss resulting from UAV instability under wind-induced perturbations. Furthermore, we conduct a comprehensive analysis of the W2A channel, examining the influence of key parameters such as wind speed, transmitter configurations, and receiver characteristics. The end-to-end performance evaluation demonstrates the practical feasibility of the proposed approach, achieving a bit-error rate of $10^{-3}$ at a data rate of 1 Mbps for a transmitter depth of 47 m and wind speeds up to 13 m/s.

This paper proposes handover-aware scheduling solutions for multi-cell small-and large-scale visible-light communication networks, enabling soft handover. For this, we coordinate the transmissions at the access points (APs), serving the users in different time slots based on their locations with respect to the AP coverage areas for an efficient utilization of the resources. For scenarios where coverage in large areas is needed, we additionally propose clustering solutions to decrease the handover rate. Compared with non-coordinated schemes, the proposed soft handover techniques offers improved performance in terms of user achievable throughput and link reliability.

Optimizing the energy efficiency (EE) of wireless networks is one of the key priorities in the design of beyond 5G mobile technologies. In this pursuit, the use of new frequency bands, in combination with advanced multiple access protocols and cooperative communications strategies, has recently shown promising results. To this end, this paper investigates an indoor wireless network that aggregates communication resources in visible light and radio-frequency (RF) bands, taking advantage of the complementary aspects of the two technologies. More specifically, a non-orthogonal multiple access (NOMA) scheme is introduced for the visible light communication (VLC) downlink, such that cell-edge users experiencing a weak VLC signal enhance their aggregated data rate with the aid of cooperative communications over RF sidelinks (i.e., device-to-device links). The optimal resource allocation strategy over both VLC and RF bands is derived aiming at EE maximization based on the Dinkelbach’s algorithm and successive convex approximation. Additionally, for the sake of flexibility, a weighted EE metric is proposed for the characterization of the aggregated VLC/RF network performance. Simulation results are provided to validate the proposed analysis, revealing the impact of various design and system parameters, such as the weighting factors, quality of service requirements, and channel conditions.

NEWFOCUS is an EU COST Action targeted at exploring radical solutions that could influence the design of future wireless networks. The project aims to address some of the challenges associated with optical wireless communication (OWC) and to establish it as a complementary technology to the radio frequency (RF)-based wireless systems in order to meet the demanding requirements of the fifth generation (5G) and the future sixth generation (6G) backhaul and access networks. Only 6G will be able to widely serve the exponential growth in connected devices (i.e., more than 500 billion) in 2030, real-time holographic communication, future virtual reality, etc. Space is emerging as the new frontier in 5 and 6G and beyond communication networks, where it offers high-speed wireless coverage to remote areas both in lands and sees. This activity is supported by the recent development of low-altitude Earth orbit satellite mega-constellations. The focus of this 2nd White Paper is on the use of OWC as an enabling technology for medium- and long-range links for deployment in (i) smart-cities and intelligent transportation systems; (ii) first- and last-mile access and backhaul/fronthaul wireless networks; (iii) hybrid free-space optics/RF adaptive wireless connections; (iv) space-to-ground, inter-satellite, ground-to-air, and air-to-air communications; and (v) underwater communications.

Wireless sensor networks (WSNs) are currently being deployed in everyday objects to collect and transmit information related to humidity, temperature, heartbeat, motion, etc. Such networks are part of the massive machine-type communication (mMTC) scenario within the fifth/sixth generation of wireless networks. In this paper, we consider the optimization and design of an optical WSN composed of multiple battery-powered sensor nodes based on light-emitting diode transmitters. Extending our previous work, we take into account both line-of-sight and diffuse-light propagation, and show that in indoor scenarios, diffuse radiation can improve link availability under shadowing/blocking and extend battery life. In order to optimize the optical wireless link parameters, we use a machine-learning approach based on a genetic algorithm to ascertain the performance limits of the system. The presented results indicate that the proposed system is a viable wireless option for WSNs within the context of mMTC.

The EU COST Action NEWFOCUS is focused on investigating radical solutions with the potential to impact the design of future wireless networks. It aims to address some of the challenges in OWC and establish it as an efficient technology that can satisfy the demanding requirements of backhaul and access network levels in 5G networks. This also includes the use of hybrid links that associate OWC with radiofrequency or wired/fiber-based technologies. The focus of this White Paper is on the use of optical wireless communication (OWC) as enabling technology in a range of areas outlined in HE's Pillar II including Health, Manufacturing, Intelligent Transportation Systems (ITS), Unmanned Aerial Vehicles and Network and Protocol.

The reliability of an underwater wireless optical communication (UWOC) network is seriously impacted by beam misalignment between transmitters (Txs) and receivers (Rxs). Also, the performance of UWOC systems can be affected by oceanic turbulence-induced fading due to fluctuations in the water refractive index as a result of variations in the pressure, water temperature, and salinity. In this work, we investigate the performance analysis of a vertical UWOC link subject to oceanic turbulence and pointing errors and further investigate the appropriate selection of link parameters to optimize link performance. This study is based on an accurate mathematical framework for link modeling while taking into account realistic Tx/Rx and channel parameters under different turbulence and beam misalignment conditions. We provide an analytical expression for calculating the link outage probability, whose accuracy is validated through numerical simulations. Last, the necessity of optimal Tx/Rx parameter selection to minimize the link outage is demonstrated. A laser beam is considered at the Tx, as well as an ultra-sensitive photodetector (silicon photo-multiplier) at the Rx to enable working at relatively long link ranges. The presented results give valuable insight into the practical aspects of deployment of UWOC networks.

The transfer of health monitoring data from multiple patients using wireless body-area networks requires the use of robust, and energy and bandwidth efficient multiple-access schemes. This paper considers the frequency-division multiple access for the wireless uplink to a fixed access point when using infrared signals to collect medical data from several patients inside an emergency waiting room. The conventional optical orthogonal scheme applies Hermitian symmetry to obtain real-valued signals, which implies increased computational complexity. We consider a new approach transmitting only the real part of a complex-valued signal, where no such constraint is imposed. Based on the proposed scheme, and taking into account the limited dynamic range of an infrared light-emitting diode, we study the performance of direct current biased and asymmetrically clipped schemes, and show their advantage in terms of energy efficiency and computational complexity, as compared with the conventional schemes. For instance, we show that by using asymmetric clipping, around 35mW less transmit power is needed to achieve a bit error rate of $\mathrm {10}^{-3}$ in the considered scenario. We also demonstrate the robustness of the proposed scheme against multiple access interference.