Augmentation of spectral efficiency in optical wireless communication networks using grid‐based elephant swarm optimization protocol

Guest Editorial

The growing need for underwater observation and subsea monitoring systems has stimulated considerable interest in advancing the enabling technologies of underwater wireless communication and underwater sensor networks. This communication technology is expected to play an important role in investigating climate change, in monitoring biological, biogeochemical, evolutionary, and ecological changes in the sea, ocean, and lake environments, and in helping to control and maintain oil production facilities and harbors using unmanned underwater vehicles (UUVs), submarines, ships, buoys, and divers. However, the present technology of underwater acoustic communication cannot provide the high data rate required to investigate and monitor these environments and facilities. Optical wireless communication has been proposed as the best alternative to meet this challenge. Models are presented for three kinds of optical wireless communication links: (a) a line-of-sight link, (b) a modulating retroreflector link, and (c) a reflective link, all of which can provide the required data rate. We analyze the link performance based on these models. From the analysis, it is clear that as the water absorption increases, the communication performance decreases dramatically for the three link types. However, by using the scattered light it was possible to mitigate this decrease in some cases. It is concluded from the analysis that a high-data-rate underwater optical wireless network is a feasible solution for emerging applications such as UUV-to-UUV links and networks of sensors, and extended ranges in these applications could be achieved by applying a multi-hop concept.

Optical wireless communication (OWC), the IEEE 802.15.7 standard (revised 2018) is developed in normative reference to low-rate wireless personal area networks IEEE 802.15.4 standard. One significant difference between the two standards is the highly directional transmitters in the OWC networks. This difference opens up the possibility of adding full-duplex communication to wireless networks. Our work proposes adding full-duplex functionality in the contention-free period (CFP) of the OWC media access control (MAC) layer. We justify the significance of our proposal by implementing IEEE 802.15.7 resource allocation scheme for both our proposed full-duplex optical MAC (FD-OMAC) and the IEEE 802.15.7 MAC. Our simulation results demonstrate that the proposed work improves the spectral efficiency in the CFP without compromising delays. We also discuss the minor changes required in the IEEE 802.15.7 MAC for implementing FD-OMAC. We further extend the FD-OMAC to a multiple access point network and evaluate its performance in comparison with IEEE 802.15.7 MAC.

Traditional device fingerprinting methods primarily rely on data-intensive deep learning models, treating devices as black boxes. However, these approaches suffer from high computational complexity and sensitivity to noise, making them impractical for large-scale Internet-of-Things (IoT) deployments that demand real-time processing and energy efficiency. To address these challenges, we propose a physics-based fingerprinting model for optical wireless communication (OWC) systems. Instead of relying solely on statistical features, small yet significant non-linear response variations in LEDs are quantified as lumped parameters in an equivalent circuit model, serving as the foundation for physical fingerprint features. This physics-based fingerprint is not only interpretable but also enables compact feature representation, reducing reliance on extensive training data. Experimental results demonstrate that our method achieves an average classification accuracy of 90.88% under varying signal-to-noise ratio (SNR) conditions. Furthermore, compared to convolutional neural network (CNN) and long short-term memory (LSTM)-based models, our approach achieves higher accuracy with significantly lower computational overhead, making it particularly well-suited for resource-constrained IoT environments. By reducing both dataset dimensionality and training sample requirements, our framework provides an efficient and scalable solution for device authentication in OWC networks.

We propose and experimentally demonstrate a full-duplex integrated passive optical network (PON) and indoor optical wireless communication (OWC) system. For the PON part, an external cavity laser (ECL) and a directly modulated laser (DML) are used as optical sources for downlink and uplink, respectively. The OWC subsystem utilizes a visible light-emitting diode (LED) for downlink and an infrared LED (IR-LED) for uplink transmission. To enable high spectral efficiency (SE), high-speed transmission, and flexible multiple access with simplified optical network unit (ONU)-side digital signal processing (DSP), multilevel, multiband quadrature amplitude modulation (QAM) and hybrid 128/64/16 Nyquist single-carrier frequency domain equalization (N-SC-FDE) modulation are implemented in this paper. In terms of 62.5 MHz OWC N-SC-FDE signals, the system successfully delivered a further 140 cm indoor distance after transmitting over a span of 25 km standard single mode fiber (SSMF) together with three subbands of 250 MHz PON signals. As a proof of concept, an integrated system of symmetrical full-duplex 5 Gb/s PON and 250 Mb/s OWC at each direction for three wired users and one wireless user is successfully achieved. The measured bit error ratios (BERs) for each user are all smaller than the 7% pre-forward-error-correction (pre-FEC) limit of 3.8 × 10−3, which shows the promising potential and feasibility of this proposal to extend multiple services from metro areas to suburban areas.

Optical wireless communications (OWC) in general and resource allocation in OWC networks particularly have gained lots of attention recently. In this work, we consider the resource allocation problem of a visible light communication downlink transmission system based on time division multiple access with the objective of maximizing spectral efficiency (SE). As for the operational conditions, we impose constraints on the average optical intensity, the energy consumption and the quality-of-service. To solve the non-convex problem, we transform the objective function into a difference of concave functions by solving a second order differential inequality. Then, we propose a low-complexity algorithm to solve the resource allocation problem. Finally, we show by simulations the SE performance gains achieved by optimizing the power allocation over equal power allocation in the considered system. Numerical results show the SE gains achieved by using this solution.

Free space, dynamic, optical wireless communications will require topology control for optimization of network performance. Such networks may need to be configured for bi- or multiple-connectedness, reliability and quality-of-service. Topology control involves the introduction of new links and/or nodes into the network to achieve such performance objectives through autonomous reconfiguration as well as precise pointing, acquisition, tracking, and steering of laser beams. Reconfiguration may be required because of link degradation resulting from obscuration or node loss. As a result, the optical transceivers may need to be re-directed to new or existing nodes within the network and tracked on moving nodes. The redirection of transceivers may require operation over a whole sphere, so that small-angle beam steering techniques cannot be applied. In this context, we are studying the performance of optical wireless links using lightweight, bi-static transceivers mounted on high-performance stepping motor driven stages. These motors provide an angular resolution of 0.00072 degree at up to 80,000 steps per second. This paper focuses on the performance characteristics of these agile transceivers for pointing, acquisition, and tracking (PAT), including the influence of acceleration/deceleration time, motor angular speed, and angular re-adjustment, on latency and packet loss in small free space optical (FSO) wireless test networks.

The demand for sixth-generation (6G) and future communication systems is pushing current wireless technologies, including the promising optical wireless communication (OWC), to their physical limits. For fundamental engineering breakthroughs, vectorial light rooted in optical physics provides a potential solution to OWC. The understanding of the physical essence of vectorial light and its use as a robust information carrier in disordered media touches upon the basic physical problem of seeking orders in disorders, thereby closely linking the future of OWC with advances in optical physics. Specifically, vectorial light fields, with different spatial modes loaded onto orthogonal polarizations, intrinsically multiplexes multiple degrees of freedom (DoFs) and enables a level of DoF control unattainable by traditional scalar modulation schemes, such as intensity modulation (IM) or homogeneous polarization modulation (PM). Furthermore, its inherent DoF coupling effect inspires novel vectorial modulation (VM) schemes, offering the possibility of a super-diversity gain. This opens up a development prospect for OWC and makes it different from conventional wireless technologies. To clarify this prospect, this article provides a systematic perspective rooted in optical physics, explaining how advances in this field are driving the evolution of scalar OWC into a vectorial era. Accordingly, we highlight the major challenges, opportunities, and preliminary solutions within this research trend. We further explore the new visions that vectorial OWC (VOWC) brings to the wireless community. For example, the multi-functional integration of optical communication, sensing, and imaging, driven by optical physics, is expected to upgrade the integrated sensing and communications functionality in 6G. Moreover, the systematic introduction of tools from cohomology theory and topological physics provides OWC with a physical perspective. We emphasize that by bridging optical physics and communication engineering, VOWC promises to greatly expand the technological vision and theoretical scope for 6G and beyond.

With the evolution in the information transmission technologies and rapidly augmenting requirement for high-speed, readily available, and long-haul links, optical communication is witnessed as one of the most prominent solutions to tackle to ever-growing user's demands. Optical communication links are further classified as optical fiber and optical wireless links based on the medium of information propagation. Optical wireless communication (OWC) links, which use free space as the propagation medium have gathered significant attraction nowadays because of it easy deployment and low cost installation process. One of the most crucial applications of OWC links is the transmission of information between two or more satellites, also referred to as inter-satellite optical wireless communication (IsOWC) link. In this work, we propose modeling and analysis of a 10 Gbps long-haul IsOWC link by incorporating Manchester encoding for improved link performance. Furthermore, the impact of increasing link distance, pointing errors, laser transmission power, and receiver lens diameter is investigated and faithful 18000 km-10 Gbps information transmission is reported.

With the escalation of heterogeneous data traffic, the research on optical wireless communication (OWC) has attracted much attention, owing to its advantages such as wide spectrum, low power consumption and high security. Ubiquitous optical devices, e.g. light-emitting diodes (LEDs) and cameras, are employed to support optical wireless links. Since the distribution of these optical devices is usually dense, multiple-input-multiple-output (MIMO) can be naturally adopted to attain spatial diversity gain or spatial multiplexing gain. As the scale of OWC networks enlarges, optical MIMO can also collaborate with network-level operations, like user/AP grouping, to enhance the network throughput. Since OWC is preferred for short-range communications and is sensitive to the directions/rotations of transceivers, optical MIMO links vary frequently and sharply in outdoor scenarios when considering the mobility of optical devices, raising new challenges to network design. In this work, we present an overview of optical MIMO techniques, as well as the cooperation of MIMO and user/AP grouping in OWC networks. In consideration of the challenges for outdoor OWC, key technologies are then proposed to facilitate the adoption of optical MIMO in outdoor scenarios, especially in vehicular ad hoc networks. Lastly, future applications of MIMO in OWC networks are discussed. This article is part of the theme issue 'Optical wireless communication'.

Optical wireless communication is emerging as a potential wireless networking alternative, made possible with the promising developments in the physical layer transmission. While the highspeed optical wireless transceivers have been demonstrated with data rates well over 10 Gbps, other technologies in the form of beam steering, optical localization and modulation/coding are also used to enhance the coverage and reliability of the optical wireless links. Given the ultra-high data rates and the complexity of these transceivers, existing access network architectures and protocols such as passive optical networks or Wi-Fi are not directly applicable to optical wireless communication. Thus, there is a necessity to develop a novel network architecture to gain all the benefits that can be provided by optical wireless communication. To this end, we propose, FLOWN, an architecture with a full-duplex data plane, which is assisted by a separate control plane. The FLOWN architecture includes a central office with the active devices, which is connected to individual access points in the coverage areas via optical fiber links. Simulation results demonstrate that the proposed centralized architecture coupled with advanced features including network function virtualization could realize future-oriented high-capacity optical wireless networks to support diverse next-generation mobile applications.

Underwater wireless optical communication (UWOC) has emerged as a key technology for next-generation underwater wireless data transmission. Semantic communication is regarded as a promising communication paradigm to improve the efficiency and robustness of UWOC systems. However, existing underwater wireless optical semantic communication (UWOSC) system lacks the capability to adapt the code rate to different channel states, leading to intelligence inadequacy and coding inefficiency. In this paper, we introduce environment semantics into the UWOSC system for the first time, and propose an environment semantics aided underwater wireless optical semantic communication (ESA-UWOSC) framework. Based on this framework, we develop a system leveraging computer vision and deep learning for adaptive rate transmission. The ESA-UWOSC system is realized by a channel state perception mechanism (CSPM) for extracting environment semantics from the channel environment image to obtain the channel gain, a link network (LinkNet) for enabling variable code rate transmission of source semantic information, and a prediction network (PreNet) for predicting the optimal code length that satisfies the transmission task requirement. The combined operation of these three modules enables the ESA-UWOSC system to actively perceive channel state and perform adaptive rate transmission accordingly. In a series of experiments conducted on an emulated UWOC experimental platform, the results show that the ESA-UWOSC system outperforms the baseline scheme, achieving superior performance with lower bandwidth consumption, especially in harsh channel environments. Moreover, the results also demonstrate that the ESA-UWOSC system can achieve adaptive rate transmission based on the perceived channel state to meet transmission task requirement.

Although many researchers have achieved wireless optical ranging and communication based on Avalanche Photon Diode (APD) detectors and PIN detectors. However, due to the low sensitivity of APD and PIN detectors, their working distances are limited. In order to achieve long-distance underwater wireless optical communication, a Single-Photon Avalanche Diode (SPAD) with photon-limited sensitivity is used to detect optical signals. In addition, most literatures do not specially design the data frames of ranging and communication, which makes it difficult to perform ranging and communication at the same time. In view of the fact that there is currently no systematic solution for simultaneous communication and high-precision ranging under underwater photon counting, this paper sorts out the relevant technical details, proposes an integrated ranging and communication scheme applied to photon counting, designs a special data frame that integrates ranging and communication, and proposes an extraction and recovery scheme for ranging and communication signals. Simulation shows that this scheme can achieve underwater photon counting wireless optical communication with a communication distance of 160m and an SER of 9.75×10-6, and the ranging accuracy is better than 1.59cm.

This paper presents hybrid RFID – OWC with an adaptive priority transmission scheme. In this model, we apply optical wireless communication (OWC) for transmitting confidential information to a radio frequency identification (RFID) reader. Since OWC provides high security, this improves the security of our system. The priority of information is assigned according to the level of confidentiality and significance of the information. The more confidential information is transmitted by OWC with adaptive data rate, and the rest of the information (if there is any) is transmitted by RFID. The energy harvesting of RFID is used to modulate the reflected optical signal by Corner Cube Retroreflector (CCR). Bit error rate (BER) is analyzed regarding the half-power angle of the transmitter, optical transmit power, data rate, and the angle between tag and reader. The analytical results indicate that by employing the adaptive priority transmission scheme, the required BER of OWC transmission is achieved.

Research in the field of optical wireless communications (OWC) has increased significantly over the past decade. As new researchers begin to explore this field, there are various hurdles related to developing a research program in OWC. This is particularly noticeable when comparing the breadth of available RF toolkits to the limited number of openly available OWC tools. Furthermore, many of the available OWC resources are standalone with limited capabilities for higher layer integration. In this work, we present gr-owc, an open source out-of-tree module for the widely used GNURadio signal processing toolkit. Within gr-owc, we have developed signal processing blocks for OWC channel simulation and common OWC modulation/demodulation techniques. We demonstrate use of this module to simulate a multi-cell/multi-user OWC network. We also describe how gr-owc signal processing blocks can be deployed in a physical implementation using Software Defined Radio (SDR) hardware, namely the universal software radio peripheral (USRP). Furthermore, methods for contribution to the project are described since the project is designed for continued development internally and with the goal of engaging the broader OWC research community.