Optical Access Points Research Articles

Обзор ключевых особенностей при построении подводной оптической беспроводной связи

Increased interest in the researches of the underwater environment of the oceans is required for the study of flora and fauna, the ocean floor, the search for minerals, monitoring existing oil rigs and other objects in the ocean, collecting the necessary information. All this cannot be done without high-quality and reliable communication in underwater oceanic conditions. Known methods of organizing underwater wireless communication considered communication systems using acoustic, radio frequency and optical waves. Foreign and Russian researchers note that underwater acoustic and radio frequency wireless communication is characterized by a low speed of information transmission and high latency, but at the same time, it allows you to transmit information over long distances. The need for high-speed information transmission has contributed to the development of underwater optical wireless communication. It allows you to organize communication at a high speed of information transmission with low latency over short distances. An increase in the communication range may provided with the help of network technology for building such communication systems. Purpose: the purpose is to review the scientific works of foreign researchers in the analysis of theoretical and experimental research in the field of underwater optical wireless communication. Results: It is shown, that underwater optical wireless communication maybe organized directly between the surface station and optical nodes, or using network technology to build a network to organize a multi-level communication system from the surface station to the optical nodes using optical access points and/or optical base stations. The analysis showed that when organizing underwater optical wireless communication, the main influence on the quality and reliability of communication is directly exerted by the underwater oceanic environment. Practical relevance: of the work lies in the systematization of scientific works of foreign researchers on the problems of underwater optical wireless communication and use as a basis for future applied research.

QoS-Aware Reliable Architecture for Broadband Fiber-Wireless Access Networks

In the era of continuous traffic demands, failure of fiber-wireless (FiWi) access network components, such as optical network unit (ONU), access point (AP), or fiber links, compromises the user connectivity and leads to enormous traffic loss. In this article, we propose a novel strategy for FiWi network planning to ensure reliability and survivability of the network. Moreover, our proposed FiWi planning strategy satisfies the required quality of service (QoS) to the users even in the case of failures. It has been shown that by deploying the proposed network framework, user services like received signal strength, throughput, delay, etc., are not significantly affected even when there is a failure. The position of backup ONU-AP is optimized in the FiWi network using a stochastic optimization algorithm. Furthermore, we compare different scenarios wherein backup ONU-AP is equipped with varying antenna configurations, such as omnidirectional antenna, sector antenna, and point-to-point (P2P) link to provide the required services to the users. Simulation results show that the P2P solution offers better services compared to sector or omnidirectional antenna configurations. Moreover, results demonstrate that the proposed survivable FiWi network can be successfully deployed without compromising the QoS requirement of the users. In addition, the article also provides reliability of the proposed survivable FiWi network.

Energy Resource Allocation for Green FiWi Network Using Ensemble Learning

In this paper, we utilize a random forest regression based ensemble learning to effectively predict the solar power available for the fiber-wireless (FiWi) network components, such as optical network units (ONUs) and access points (APs) which is collectively known ONU-AP. Thereafter, a joint energy resource allocation framework is proposed to minimize the required number of photovoltaic (PV) panels and batteries. To solve the joint energy resource allocation problem, we divide it into two sub-problems, minimum PV panel allocation for a fixed number of batteries and minimum battery allocation for a fixed number of PV panels. The two sub-problems are further solved using the proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MinBatAlloc</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MinPVAlloc</i> algorithms. Moreover, we introduce a system parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> , that signifies the ratio between solar power supplied to operate ONU-AP and to charge the batteries. The results are shown by varying <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> and its impact on the energy resource allocation and battery lifetime. We compare the performance of our proposed approach with non-ML based approaches, such as, maximum, minimum, median, and outage threshold based energy resource allocation. Through the obtained results it has been shown that the proposed approach considerably improves the performance in terms of outage, lifetime, carbon dioxide emissions, and cost.

Channel Modelling and Error Performance Investigation for Reading Lights Based In-Flight LiFi

The new generation of communication technologies are constantly being pushed to meet a diverse range of user requirements such as high data rate, low power consumption, very low latency, very high reliability and broad availability. To address all these demands, fifth generation (5G) radio access technologies have been extended into a wide range of new services. However, there are still only a limited number of applications for radio frequency (RF) based wireless communications inside aircraft cabins that comply with the 5G vision. Potential interference and safety issues in on-board wireless communications pose significant deployment challenges. By transforming each reading light into an optical wireless access point (AP), light-fidelity (LiFi), could provide seamless on-board connectivity in dense cabin environments without RF interference. Furthermore, the utilization of available reading lights allows for a relatively simple, cost-effective deployment with the high energy and spectral efficiency. To successfully implement the aeronautical cabin LiFi applications, comprehensive optical channel characterization is required. In this paper, we propose a novel Monte Carlo ray-tracing (MCRT) channel modelling technique to capture the details of in-flight LiFi links. Accordingly, a realistic channel simulator, which takes the cabin models, interior elements and measurement based optical source, receiver, surface material characteristics into account is developed. The effect of the operation wavelength, cabin model accuracy and user terminal mobility on the optical channel conditions is also investigated. As a final step, the on-board direct-current biased optical orthogonal frequency division multiplexing (DCO-OFDM) performance is evaluated by using obtained in-flight LiFi channels. Numerical results show that the location of a mobile terminal and accurate aircraft cabin modelling yield as much as 12 and 2 dB performance difference, respectively.

Secure reconfigurable intelligent surface aided heterogeneous VLC–RF cooperative NOMA networks

In this paper, we investigate the physical layer security for a reconfigurable intelligent surface (RIS)-aided heterogeneous visible light communication (VLC) and radio-frequency (RF) network with two legitimate user equipments (UEs) in cooperative nonorthogonal multiple access (NOMA). An external eavesdropper (Eve) tries to eavesdrop the information from the cooperative channel. Since VLC is mainly available for line-of-sight path, and the UEs and Eve under the worktable cannot directly receive signals from the optical access point, a device is naturally employed to perform optical–electrical conversion and RF transmission. Further the device and RIS are jointly employed to eliminate blind spots and extend communication coverage. With these settings, the statistical characteristics of the VLC link and RF link are determined based on the feature of the optical channel and the RIS-aided wireless channel, respectively. The close-form expression of the secrecy outage probability for the proposed RIS-aided heterogeneous VLC–RF cooperative NOMA network is derived. Simulation results show the secrecy outage performance of the proposed network depends on not only the reflecting meta-surface number of the RIS, the power allocation based on NOMA, but also the tradeoff design between the optical and electrical parameters.

Resource Allocation in User-Centric Optical Wireless Cellular Networks Based on Blind Interference Alignment

Visible light communications (VLC) have been recently proposed to enhance the capacity of next generation of wireless services. Moreover, VLC networks usually comprise a large number of overlapping optical access points (APs). Moreover, each of these APs provides a small and confined area of coverage in order to generate satisfactory illumination. In this work, a user-centric (UC) clustering formation based on the K-means algorithm is proposed to manage the inter-cell interference (ICI) and enhance the performance of VLC networks. Moreover, assuming that each user is equipped with a reconfigurable photodetector, the use of blind interference alignment (BIA) in each UC cluster is considered. Notice that the data rate demands are not the same for all the users. We formulate an optimization problem to maximize the utility of the network resources allocated to the users based on their demands. After that, a centralized algorithm is proposed to obtain an optimal solution through exhaustive search, which is subject to high complexity. To reduce the complexity of this optimization problem, the problem is divided into sub-problems based on the number of constructed UC clusters. Then, a distributed algorithm via Lagrangian multipliers is proposed within each UC cluster with the aim of providing a near optimal solution to the centralized algorithm. Simulation results demonstrate that the proposed resource allocation algorithms provide higher performance than a uniform resource allocation scheme among users.

User Localization and Upstream Signaling for Beam-Steered Infrared Light Communication System

Beam-steered infrared light can provide ultra-high wireless capacity to individual user devices for indoor communication systems. The optical beams used to obtain such high capacities are relatively narrow with the average beam divergence of less than 2.55°, hence an accurate localization system to pinpoint multiple user devices at the same time is required. In addition, an indoor communication should provide mobile coverage to all users, therefore a dynamic and fast localization equipped with a capability of conveying the channel link status of the user devices to optical access points is necessary. In this work, we propose a vision-based technique to simultaneously localize the user devices in a room. A LED-tag system positioned around a photodetector enables the access points to recognize active users. A localization accuracy of 0.018° is achieved within milliseconds. Furthermore, taking advantage of this vision-based system, upstream signaling for channel status information is proposed using M-ary intensity modulation. Experimental results show that an upstream signaling rate of 2.4kbps can be achieved with our simple and low-cost prototype, enabling >10Gbit/s link per user.

Preoperative Computer-Assisted Laparoscopy Planning for the Minimally Invasive Surgical Repair of Hiatal Hernia.

Minimal invasive surgical procedures such as laparoscopy are preferred over open surgery due to faster postoperative recovery, less trauma and inflammatory response, and less scarring. Laparoscopic repairs of hiatal hernias require pre-procedure planning to ensure appropriate exposure and positioning of the surgical ports for triangulation, ergonomics, instrument length and operational angles to avoid the fulcrum effect of the long and rigid instruments. We developed a novel surgical planning and navigation software, iMTECH to determine the optimal location of the skin incision and surgical instrument placement depth and angles during laparoscopic surgery. We tested the software on five cases of human hiatal hernia to assess the feasibility of the stereotactic reconstruction of anatomy and surgical planning. A whole-body CT investigation was performed for each patient, and abdominal 3D virtual models were reconstructed from the CT scans. The optical trocar access point was placed on the xipho-umbilical line. The distance on the skin between the insertion point of the optical trocar and the xiphoid process was 159.6, 155.7, 143.1, 158.3, and 149.1 mm, respectively, at a 40° elevation angle. Following the pre-procedure planning, all patients underwent successful surgical laparoscopic procedures. The user feedback was that planning software significantly improved the ergonomics, was easy to use, and particularly useful in obese patients with large hiatal defects where the insertion points could not be placed in the traditional positions. Future studies will assess the benefits of the planning system over the conventional, empirical trocar positioning method in more patients with other surgical challenges.

Modulation format and number of users classification in multipoint free-space optical communication using convolutional neural network

A methodology based on convolutional neural network (CNN) is proposed for joint classification of transmitting user number and modulation format in a multiuser free-space optical communication (FSOC) link. The proposed methodology relies on amplitude information of received mixed signal. In-phase and quadrature components of users that are sharing time and bandwidth resources transmitting into the same optical wireless access point and interfering within each other are analyzed. The proposed approach utilizes the constellation diagrams of the received mixed symbols to generate image data sets that are fed into CNN input. The designed CNN model with three convolutional layers was tested for: varying image resolutions, image-data set size, varying number of received symbols, and atmospheric turbulence to identify optimal parameters and processing time for system design and implementation. The results indicate that the CNN model can blindly and accurately identify the communicating device number and their optical modulation format with classification accuracy up to 100% for various SNRs. Moreover, the CNN demonstrated robustness against atmospheric turbulence and suggested immunity to additive noise. Therefore, the proposed methodology proved to be a promising and feasible solution for practical implementation of an intelligent optical wireless receiver for aerial and terrestrial FSOC links.

Physical-Layer Security for Mobile Users in NOMA-Enabled Visible Light Communication Networks

In view of the secrecy requirements of visible light communication (VLC) and the massive connectivity demand of future communication, this work investigates physical-layer security (PLS) for a VLC network based on nonorthogonal multiple access (NOMA). To date, however, research on PLS in NOMA-enabled VLC networks considers only users in a static state. The movements of users make it imperative to dynamically allocate optical access points (OAPs) and transmit power to mobile users (MUs). Such a resource allocation problem is transformed into the problem of dynamically allocating power in this paper. Thus, joint secure communication and power allocation optimization is formulated to maximize the network secrecy performance in each time frame subject to the constraint of the maximum power of OAPs and the constraint of power allocation based on NOMA among the associated MUs at each OAP. The formulated joint optimization problem is generally nonconvex because the logarithmic subtraction operation exists in the secrecy capacity, and we cannot directly find the optimal solution. A hierarchical power allocation algorithm is naturally proposed based on an iterative security-aware water-filling approach and the optimality conditions of Karush-Kuhn-Tucker. Convergence and effectiveness are investigated for the presented power allocation algorithms through simulations. The simulation results show that the network sum secrecy capacity depends on the number of MUs, the characteristics of the optical transceiver, and the number of OAPs deployed in the room.

Load Balancing in Hybrid VLC and RF Networks Based on Blind Interference Alignment

Visible light communications (VLC) are proposed for increasing the spectral efficiency and the number of devices served in indoor environments, while providing illumination through light emitting diodes (LED). For VLC, each optical access point (AP) provides a small and confined area of coverage. Since several sources of light are usually deployed in overlapping fashion in order to provide satisfactory illumination, VLC are limited by inter-cell interference. Moreover, transmission from a specific optical AP can be blocked by the elements of the scenario. On the other hand, radio-frequency (RF) systems such as WiFi are usually available in most of the indoor scenarios. In this work, we first propose a dynamic cell formation method for grouping the optical APs in multiple optical cells that cover a footprint each minimizing the inter-cell interference. After that, we use transmission based on blind interference alignment (BIA) in each optical cell. Considering the coexistence with RF systems based on orthogonal frequency division multiplexing (OFDM), a load balancing algorithm is proposed for managing the resources of the resulting hybrid VLC/RF network and determining the user association to each system. However, the complexity of this optimization problem is excessively high for practical VLC/RF networks. In order to obtain a suboptimal but tractable solution, we propose a decentralized optimization method based on Lagrangian multipliers. Simulation results show that the proposed scheme outperforms other approaches for user grouping and managing the resources of hybrid VLC/RF networks.

Dual-Axis Hanle Magnetometer Based on Atomic Alignment with a Single Optical Access

Optically pumped magnetometers are serious candidates to replace SQUIDs, and thus avoid the need for cryogenics, in applications like magnetoencephalography. In building magnetometer arrays for imaging, a compact yet multiaxis architecture is highly desirable. Here the authors present a scheme based on atomic alignment that only requires one optical access point, bearing both a pump beam and a probe beam at a small angle to it, and that allows measurement of two magnetic field components. Measuring the third component should be possible via partial depolarization of the pump beam. Such a compact scheme opens interesting perspectives for magnetometer arrays for medical imaging.

Novel Heterogeneous Attocell Network Based on the Enhanced ADO-OFDM for VLC

In this letter, an enhanced asymmetrically clipped dc-biased optical orthogonal frequency-division multiplexing (ADO-OFDM) scheme is proposed with asymmetrically clipped optical OFDM for the local network and dc-biased optical OFDM for the global network to avoid co-channel interference. Based on that, a novel visible light communication attocell adopting heterogeneous networks with optical access point using two light-emitting diode sources with different transmitter semiangles can be adopted. The signal-to-noise ratio and the average capacity are then investigated and formulated. Simulation results show that the average achievable capacity region of the enhanced ADO-OFDM can be greatly increased compared with that of the conventional ADO-OFDM.

Network coding multiuser scheme for indoor visible light communications

Visible light communication (VLC) is a unique alternative for indoor data transfer and developing beyond point-to-point. However, for realizing high-capacity networks, VLC is facing challenges including the constrained bandwidth of the optical access point and random occlusion. A network coding scheme for VLC (NC-VLC) is proposed, with increased throughput and system robustness. Based on the Lambertian illumination model, theoretical decoding failure probability of the multiuser NC-VLC system is derived, and the impact of the system parameters on the performance is analyzed. Experiments demonstrate the proposed scheme successfully in the indoor multiuser scenario. These results indicate that the NC-VLC system shows a good performance under the link loss and random occlusion.

Capacity Bounds for the Gaussian IM-DD Optical Multiple-Access Channel

Optical wireless communications (OWC) is a promising technology for closing the mismatch between the growing number of connected devices and the limited wireless network capabilities. Similar to downlink, uplink can also benefit from OWC for establishing connectivity between such devices and an optical access point. In this context, the incoherent intensity-modulation and direct-detection (IM-DD) scheme is desirable in practice. Hence, it is important to understand the fundamental limits of communication rates over an OWC uplink employing IM-DD, i.e., the channel capacity. This uplink, modeled as a Gaussian multiple-access channel (MAC) for indoors OWC, is studied in this paper, under the IM-DD constraints, which form the main difference with the standard Gaussian MAC commonly studied in the radio-frequency context. Capacity region outer and inner bounds for this channel are derived. The bounds are fairly close at high signal-to-noise ratio (SNR), where a truncated-Gaussian input distribution achieves the capacity region within a constant gap. Furthermore, the bounds coincide at low SNR showing the optimality of ON–OFF keying combined with successive cancellation decoding in this regime. At moderate SNR, an optimized uniformly spaced discrete input distribution achieves fairly good performance.

Remote Temperature Distribution Sensing Using Permanent Magnets

Remote temperature sensing is essential for applications in enclosed vessels, where feedthroughs or optical access points are not possible. A unique sensing method for measuring the temperature of multiple closely spaced points is proposed using permanent magnets and several three-axis magnetic field sensors. The magnetic field theory for multiple magnets is discussed and a solution technique is presented. Experimental calibration procedures, solution inversion considerations, and methods for optimizing the magnet orientations are described in order to obtain low-noise temperature estimates. The experimental setup and the properties of permanent magnets are shown. Finally, experiments were conducted to determine the temperature of nine magnets in different configurations over a temperature range of 5 °C to 60 °C and for a sensor-to-magnet distance of up to 35 mm. To show the possible applications of this sensing system for measuring temperatures through metal walls, additional experiments were conducted inside an opaque 304 stainless steel cylinder.

Distributed user-centric scheduling for visible light communication networks.

Visible light communication (VLC) networks, consisting of multiple light-emitting diodes (LEDs) acting as optical access points (APs), can provide low-cost high-rate data transmission to multiple users simultaneously in indoor environments. However, the performance of VLC networks is severely limited by the interference between different users. In this paper, we establish a distributed user-centric scheduling framework based on stable marriage theory, and propose a novel decentralized scheduling method to manage interference by forming flexible amorphous cells for all users. The proposed scheduling method has provable low computational complexity and requires only the exchange of a few 1-bit messages between the APs and the users but not the feedback of the channel state information of the entire network. We further show that the proposed method can achieve both user-wise and system-wise optimality as well as a certain level of fairness. Simulation results indicate that our decentralized user-centric scheduling method outperforms existing centralized approaches in terms of throughput, fairness, and computational complexity.

Gas property measurements in a supersonic combustor using nanosecond gated laser-induced breakdown spectroscopy with direct spectrum matching

Gas density and fuel mole fraction in a cavity flameholder of a supersonic combustor with ethylene (C 2 H 4 ) fueling are simultaneously measured using nanosecond gated (10 ns) laser-induced breakdown spectroscopy (n-LIBS). Emission spectra from the laser-induced plasma over a range (550 nm–830 nm) containing multiple emission lines of O, H, N, and C are captured and used to quantify the gas conditions. A direct spectrum matching (DSM) process is employed for the gas property quantification in which an unknown spectrum is matched to a spectrum from a database, constructed through n-LIBS analysis of well-known gas conditions. A back-scattering collection method is implemented to allow for measurements using a single optical access point. Fuel mole fraction and gas density are mapped within a cavity flameholder on planes parallel to the Mach 2 freestream flow above the cavity. With C 2 H 4 injection from the closeout ramp of the cavity toward the front step, a high fuel mole fraction region appears near the front step where density and flow velocity are low, and thus favorable for cavity flame ignition. The fuel mole fraction at a location in the cavity is found to be nearly proportional to fueling rate; the gas density, on the other hand, is not affected by the fueling rate, under the typical operating conditions.

A 50 Gb/s Transparent Indoor Optical Wireless Communications Link With an Integrated Localization and Tracking System

In this paper, we describe an optical wireless communications system that uses light from an optical fibre access point to provide transparent and bi-directional optical links to nomadic terminals. Full localization and tracking is implemented, and a 50 Gb/s link is demonstrated. The link operates in an indoor environment, with a $ \pm 30^\circ $ field-of-view covering a distance of up to 3 m, and a localization accuracy of 0.05° (2.5 mm pointing accuracy at 3 m) is achieved. This demonstration shows that it is feasible to use an automated system to achieve the required alignment for an ultrahigh data rate fibre-wireless-fibre link.

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.