Ultraviolet Communication Research Articles

Bi-directional ultra-violet communication with self-interference.

We investigate the self-interference characterization, achievable rate, signal detection and parameter estimation for bi-directional ultra-violet (UV) communication. We firstly characterize and experimentally demonstrate the self-interference of UV communication, which is non-negligible as the angle between the transmission and receiver directions is blow 60°. Then, we present the achievable rate and symbol detection under self-interference, which show that the offset between self-interference and desirable symbols can increase the achievable rate and decrease the symbol detection error probability. We propose the practical system design with parameter estimation under self-interference. Finally, we experimentally evaluate the receiver-side signal detection with self-interference generated by Field Programmable Gate Array, and the signal detection of a real bidirectional UV communication system. Lower symbol detection error probability can also be observed as the offset between desirable symbols and self-interference symbols increases to half-symbol length from both system-level simulation and real experiments, which further validates the theoretical results.

760 Mbps ultraviolet wireless communication based on a transmitter with AlGaN/InGaN MQWs

III-nitride LEDs offer a solution for ultraviolet (UV) high-speed communication as a transmitter with high performance. This paper focuses on a transmitter with AlGaN/InGaN multi-quantum wells (MQWs) for UV communication. The transmitter is realized on a GaN-on-silicon platform by a double etching process. The emission region of the transmitter with a small area is beneficial for improving the data rate of UV communication. The emission peak keeps stable at 376.48 nm in the UVA band. The transmission with 300 Mbps is obtained in a UV communication system setup with on-off keying (OOK) modulation. We realize a digital signal transmission up to 760 Mbps by bit-loading discrete multi-audio (DMT) modulation.

Ultraviolet-Based UAV Swarm Communications: Potentials and Challenges

Unmanned aerial vehicle (UAV) swarm communication has received increasing attention thanks to its intriguing advantages, such as low costs, high mobility, and deployment convenience. However, this technology is also facing certain new challenges, for example, RF spectrum scarcity, interference, and network connectivity. To this end, ultraviolet (UV) communication is introduced in this article to tackle these problems due to its distinctive benefits, such as license-free operation, immunity to electromagnetic interference, and the ability of non-line-of-sight transmission. First, a comparison between UV communication and other alternatives is presented. Then the structural designs of the high-capability UAV and the low-capability UAV, the system communication protocol and mutual interference, and the network topology of the UV-based UAV swarm are investigated. Further, the bit error rate performance, data rate, and communication range are analyzed. In the end, an artificial-intelligence-aided UV-based UAV swarm system is put forward to tackle users' complicated requirements. Simultaneously, the challenges are discussed to direct future research work.

Optimization of ultraviolet communication links based on finite difference stochastic approximation.

The ultraviolet communication (UV) channel has been shown to have unique features that could be exploited for covert ground-to-ground communications in complex non-line-of-sight (NLOS) scenarios. A key challenge is the determination of optimal configuration of pointing directions of the UV nodes in unknown NLOS environments to maximize the link performance. In this paper, we proposed a novel steering optimization approach based on Finite Difference Stochastic Approximation (FDSA) to simultaneously optimize the transmitter (Tx) and receiver (Rx) pointing directions without any knowledge about the locations and relative orientations of the two nodes. We perform parametric analysis using Monte Carlo channel simulations to investigate and select appropriate key algorithmic parameters and analyze the performance of the proposed algorithm. We also carry out experimentation using our custom designed UV Tx and Rx gimbal systems and demonstrate the utility and efficiency of the proposed steering optimization approach and show that the received photon count can be increased significantly.

GaN-Djoser Pyramidal Self Powered UV Photodetector for Optical Signal Detection in Rugged Environments

Wireless communication under harsh environment using ultraviolet radiation remains a vital field of research. We have reported the novel GaN pyramids of Djoser ultraviolet photodetector operable at high-temperature conditions. The GaN-pyramids of Djoser ultraviolet photodetector display extremely high performance, detect weak optical signals and display self-powered behavior even under challenging conditions. GaN-pyramids of Djoser was grown via modulating flux ratio (Ga/N) in molecular beam epitaxy. Two-terminal asymmetric Pt electrodes metal semiconductor metal-ultraviolet photodetector were fabricated for better thermal stability and low dark current. The device exhibits high responsivity of 11.1 × 103 mAW−1 at RT and 5.6 × 103 mAW−1 at 250 °C with a fast response time of ∼ 200 µs in self-power mode. In photoconductive mode, the device demonstrates very high responsivity ∼ 2.5 × 107 mAW−1, high detectivity (1012 Jones) at a weak optical signal, while the device shows very high responsivity ∼1 × 107 mAW−1 at 250 °C. The extraordinary performance of the device is attributed to its unique Djoser-pyramidal structure with decreased surface stress and dislocations. The self-powered device with significantly high responsivity and capability to detect weak optical signals demonstrates the feasibility of a highly efficient photoreceiver design of GaN- pyramids of Djoser for ultraviolet communication, which can work under harsh environmental conditions.

Fully Transparent and High‐Performance ε‐Ga2O3 Photodetector Arrays for Solar‐Blind Imaging and Deep‐Ultraviolet Communication

With the development of new broadband semiconductor materials and the expansion of solar‐blind deep‐ultraviolet (SBDU) optoelectronics, the demand for high‐performance fully transparent array integration has also increased. Herein, metal–semiconductor–metal (MSM)‐type fully transparent SBDU photodetector arrays (PDAs), based on commercially available ε‐Ga2O3 films, are constructed using indium tin oxide (ITO), indium gallium zinc oxide (IGZO), and aluminum zinc oxide (AZO) transparent conductive oxides as electrodes. The experimental results show that the overall performance of the fully transparent SBDU PDAs used in this study places them at the forefront of ε‐Ga2O3‐based photodetectors (PDs). All three PDs not only exhibit ultra‐high responsivity (286.2, 284.1, and 262.1 A W−1), remarkable detectivity (4.73 × 1014, 5.06 × 1014, and 2.16 × 1015 Jones), and excellent stability, but also fast photoresponse time (5.6/7.2, 6.9/9.5, and 70/200 ms). It is found that the resistivity and carrier concentration of transparent conductive oxides significantly influence device performance. Consequently, it is demonstrated, for the first time, that fully transparent ε‐Ga2O3‐based SBDU PDAs can be used as ultraviolet imagers and signal receivers integrated into a homemade solar‐blind ultraviolet communication (SBUC) system to transmit text data. These results indicate great potential for future applications of fully transparent ε‐Ga2O3 thin‐film solar‐blind photodetectors in next‐generation artificial intelligence eyes, smart windows, light field cameras, and solar‐blind imaging, among others.

QoS based enhanced lossless contention MAC protocol for ultraviolet network.

Ultraviolet (UV) communication, with its excellent characteristics of non-line-of-sight propagation, high confidentiality, and flexible networking, has gradually gained traction in the field of research. The UV media access control (MAC) protocol is relatively lacking at present, and the UV lossless contention MAC (UVLLC-MAC) protocol designed by our team earlier is limited by the predictability of communication network topology; hence, it is not applicable to multinode and multi-data networks. In order to be applicable to multinode network and satisfy the quality of service (QoS) for various data, an enhanced UVLLC-MAC (eUVLLC-MAC) protocol is proposed based on the binary exponential backoff (BEB) and UVLLC protocols. A two-dimensional Markov chain is established to analyze the network performance, and the throughput and delay expressions of the UV network are derived systematically. Subsequently, the effects of reset probability, maximum backoff order, and priority types on network performance are analyzed, and the protocol parameters are optimized to obtain the best network performance. Finally, it is observed that compared with the BEB and UVLLC-MAC protocols, the network under the eUVLLC-MAC protocol can obtain better performance in throughput, packet loss rate and delay comprehensively, which demonstrates the effectiveness of the proposed protocol. Additionally, the eUVLLC-MAC protocol can provide guidance for multinode and multi-data UV networking.

Research on transmission characteristics of wireless ultraviolet communication in floating dust weather based on the particle scale spectrum.

Floating dust weather has a great impact on wireless ultraviolet (UV) communication (UVC). In this paper, the distribution of floating dust particle spectrum is considered. And a wireless UV scattering communication model in floating dust weather is established. The transmission characteristics of UV channel are studied by the segmentation of floating dust particle spectrum. In order to reduce the complexity of particle spectrum segmentation algorithm and the simulation time, an equivalent particle size method is proposed based on the particle scale spectrum segmentation method. At the same time, the equivalent concentration of equivalent particles is given. The simulation results show that the path losses calculated by the two methods can be well fitted. Outdoor experiments of wireless UVC under different floating dust weather conditions are carried out. The simulation results are consistent with the experimental results, which verify the effectiveness of the equivalent particle size method based on particle spectrum distribution.

Wireless ultraviolet light MIMO assisted UAV direction perception and collision avoidance method

In order to solve the problem of UAV’s direction perception and collision prevention in the limited radio communication environment, we use wireless ultraviolet (UV) communication as an auxiliary communication method in UAVs. We improve the traditional artificial potential field (APF) method, design a UV- MIMO model installed on the UAV, and propose the improved artificial potential field (IAPF) method. On this basis, the determination of the threat source direction in IAPF algorithm is further simplified, and the improved artificial potential field based on ultraviolet MIMO (IAPF-UVMIMO) algorithm is proposed. Experimental results show that IAPF effectively solves the problems of unreachable targets, path oscillations and local minimums that exist in the traditional artificial potential field method. In addition, IAPF-UVMIMO also improves the tolerance of the threat source direction. Compared with IAPF, the number of collisions with actual collision threats is reduced by 22.6%.

Endogenous Synergistic Enhanced Self‐Powered Photodetector via Multi‐Effect Coupling Strategy toward High‐Efficiency Ultraviolet Communication

AbstractUltraviolet (UV) communication is a promising security optical wireless communication technology, and self‐powered photodetectors as their optical receivers offer formidable evolution opportunities. However, insufficient light harvesting and carrier separation of self‐powered photodetectors hinder them from achieving high‐efficiency UV communication. Herein, a multi‐effect coupling strategy is proposed to design an enhanced self‐powered Ag NPs@ZnO nanowires/PEDOT:PSS (AZP) UV photodetector. Taking full advantage of the plasmonic and pyro‐phototronic coupling effect, the endogenous synergistic enhancement of UV light utilization and charge separation efficiency is realized without external field. The responsivity and detectivity of the AZP photodetector are significantly increased more than two and three times respectively, and the response time is less than 0.1 ms. Furthermore, a UV communication system is integrated based on the self‐powered AZP photodetector that conducts synchronous, accurate, and rapid wireless data transmission. Notably, the integrated UV communication system presenting large communication bandwidth with 4800 baud exhibits desirable efficient information transmission potential. This work provides design strategies for the advanced self‐powered UV photodetector toward future energy‐saving and high‐efficiency optical wireless communication.

Characteristic Study of Non-Line-of-Sight Scattering Ultraviolet Communication System at Small Elevation Angle

Ultraviolet (UV) communication is considered an effective complement to traditional wireless communication. However, the scattering models of existing non-line-of-sight (NLOS) UV, which are complex, are difficult to combine with the test. In this paper, the single scattering isosceles model with a small elevation angle is proposed first. Then, the relationships between the path loss of single scattering isosceles and elevation angle, emission beam angle, receiving field angle, and transmission distance are studied. Finally, we consider outdoor NLOS UV solar-blind communications test at ranges of up to 100 m and 400 m, with different transmit and receive elevation angles. The results show that the isosceles model is in good agreement with the experiments. In addition, the UV isosceles model exhibits good properties compared with the existing scattering model. The proposed UV isosceles model can be employed as a reference for practical applications in outdoor tests.

On the construction of ultraviolet communication line and orientation for controlling a small unmanned aerial vehicle

The purpose of this work is to analyze methods for constructing an ultraviolet (UV) communication line and orientation for controlling a small unmanned aerial vehicle (UAV). In conditions of difficult terrain, the passage of radio waves is difficult, so it is necessary to use the optical range for communication and orientation. In the UV range, optical interference is significantly reduced and it is possible to create small-sized film antennas for UAVs. The characteristics of UV communication using film fluorescent antennas and multi-crystal semiconductor emitters are given. The UAV orientation method using onboard film antennas has been analyzed.

Single-collision-induced path loss model of reflection-assisted non-line-of-sight ultraviolet communications.

By considering both scattering and reflection events as collision-induced events (CIEs), an analytical path loss model of reflection-assisted non-line-of-sight (NLOS) ultraviolet communications (UVC) is proposed with single CIE incorporated, which refers to the single-collision-induced (SCI) path loss model. More specifically, the analytical expressions of the received optical energy resulting from single-scatter and single-reflection events in reflection-assisted NLOS UVC are respectively derived. Then, in terms of those two expressions, the expression of the proposed SCI path loss model is obtained. Finally, Monte-Carlo (MC) simulations and experimental results are given to verify the correctness and effectiveness of the proposed SCI path loss model. The results manifest that the proposed SCI path loss model can work well in both coplanar and noncoplanar geometry of the reflection-assisted NLOS UVC.

High-performance self-powered ultraviolet photodetector based on BiOCl/TiO2 heterojunctions: Carrier engineering of TiO2

For low-energy photoelectric devices, it is essential to develop self-powered photodetectors (PDs), because it can work independently, wirelessly and sustainably. The heterojunction PDs based on BiOCl nanoflakes (NFs) and anatase TiO2 film fabricated by the hydrothermal method demonstrate the excellent ultraviolet (UV) photoresponse properties without external power supply. The strong built-in electric field formed at the heterojunction interface and the efficient carrier transmission characteristic of TiO2 film can improve the self-powered performance of PDs. The optimized heterojunction device with TiO2 film grown for 1.75 h exhibits a high photocurrent-to-dark current ratio of 103, responsivity of 0.17 A/W, remarkable detectivity of 1.3 × 1012 Jones, linear dynamic range of 70 dB and fast response speed of 23 ms under 0 V bias and weak UV light irradiation (340 nm, 0.18 mW/cm2). These results demonstrate that the BiOCl/TiO2 heterojunction devices have great application potential in the future UV communications systems.

Reflection-Assisted Non-Line-of-Sight Ultraviolet Communications

Considering high path loss (PL) of the non-line-of-sight (NLOS) ultraviolet communications (UVC) realized by the atmospheric scattering effect of ultraviolet light, we propose to use a reflective plane to improve the received optical power and further reduce the PL. More specifically, a channel model for NLOS UVC with not only scattering but also reflection considered is proposed via Monte-Carlo (MC) photon-tracing method. Both scattering and reflective events are called collision-induced events (CIEs). The proposed channel model can obtain the PL and channel impulse response (CIR) performances of the NLOS UVC system with multiple-order CIEs. It is shown that the reflective plane could reduce the PL and the time delay of CIR, which could be a benefit for designing high data-rate NLOS UVC systems. Finally, experimental results in two representative scenarios are also given to verify the effectiveness of the proposed channel model for reflection-assisted NLOS UVC systems.

High-Dimensional Feature Based Non-Coherent Detection for Multi-Intensity Modulated Ultraviolet Communications

Ultraviolet communication (UVC) has been regarded as a promising supplement for overloaded conventional wireless communications. One challenge lies in the communication deterioration caused by the UV-photon scattering induced inter-symbol-interference (ISI), which will be even worse when encountering multilevel pulse amplitude modulation (multi-PAM) symbols. To address this ISI, traditional coherent detection methods (e.g., maximum-likelihood sequence detection, MLSD) require high computational complexities for UV channel estimation and sequential detection space formation, thereby making them less attractive. Current non-coherent detection, which simply combines the ISI-insensitive UV signal features (e.g., the rising edge) into a one-dimensional (1D) metric, cannot guarantee reliable communication accuracy. In this work, a novel high-dimensional (HD) non-coherent detection scheme is proposed, leveraging a HD construction of the ISI-insensitive UV signal features. By doing so, we transform the ISI caused sequential detection into an ISI-released HD detection framework, which avoids complex channel estimation and sequential detection space computation. Then, to compute the detection surface, a UV feature based unsupervised learning approach is designed. We deduce the theoretical bit error rate (BER), and prove that the proposed HD non-coherent detection method has a lower BER than that of the current 1D non-coherent scheme. Simulation results validate our results, and more importantly, demonstrate a BER that approaches that of the state-of-the-art coherent MLSD ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 1 dB in SNR at BER = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$4.5\times 10^{-3}$</tex-math></inline-formula> , the 7% overhead forward-error-correction limit), and also a reduction of computational complexity by at least two orders of magnitude.

Work‐Function‐Tunable MXenes Electrodes to Optimize p‐CsCu2I3/n‐Ca2Nb3‐xTaxO10 Junction Photodetectors for Image Sensing and Logic Electronics

AbstractTunable work function has a high profile for the MXene‐based optoelectronic devices, and surface modification provides the huge potential to shift its Fermi level and modulate the work function. In this work, the window of MXene's work function is engineered from 4.55 to 5.25 eV by surface modification with LiF, Se, and polyethylenimine ethoxylated (PEIE). The vertical p‐CsCu2I3/n‐Ca2Nb3‐xTaxO10 junction photodetectors are constructed on the basis of the above surface‐modified MXenes, which changes the Schottky barrier between n‐Ca2Nb3‐xTaxO10 and the electrodes. In particular, the rectification effect is significantly enhanced by utilizing PEIE‐decorated MXene electrodes, resulting in a high rectification ratio of 16 136 and improved UV responsivity of 81.3 A W–1. Such high‐performance devices based on MXenes electrodes are compatible with the standard clean room fabrication process, realizing large‐scale flexible UV detectors that maintain 80% of the original current after 5000 times bending. Meanwhile, a photodetector array stimulated with UV of different wavelengths is constructed to reveal its potential for image sensing. Finally, functional “AND” and “OR” optoelectronic logic gates are developed for UV communication using Au/CsCu2I3/Ca2Nb3‐xTaxO10/MXene–PEIE photodetectors, enriching the application of MXene‐based optoelectronic devices. This work on tuning MXene work function via surface modification demonstrates that MXene is a promising candidate for future optoelectronics.

Path loss of non-line-of-sight ultraviolet light communication channel in polydisperse aerosol systems

Path loss of non-line-of-sight ultraviolet light communication channel in polydisperse aerosol systems

On-channel characteristics of wireless ultraviolet communication with mobile terminals.

Most studies of ultraviolet communication do not consider the mobility of communication terminals. In this Letter, a single-scattering-channel model based on the Monte Carlo method is proposed for non-line-of-sight ultraviolet communication with mobile terminals. Our main contribution is to present an original method of evaluating the impulse response of communication channels given the relative moving speed and direction of the terminals. Using this method, the impact of the moving speed and direction of the terminals on the system response is simulated. Our simulation results show that the transmission distance plays a dominant factor in all scenarios, whether the communication terminals are coplanar or noncoplanar and with or without a height difference.

On the performance of a relay assisted hybrid RF-NLOS UVC system with imperfect channel estimation

Non-line-of-sight (NLOS) ultraviolet communication (UVC) is emerging as an attractive optical wireless communication technology that enables wireless connectivity in radio-frequency (RF) prohibited areas with no LOS availability. NLOS UVC, however, suffers from a very high path loss, thereby restricting its usage to smaller link distances. In this paper, we address the challenge of providing long-distance wireless connectivity to RF prohibited areas by mixing NLOS UVC with RF communication using a decode-and-forward relay. The RF link is modeled using Rayleigh distribution, and the NLOS UV link is modeled using lognormal distribution under weak turbulence conditions. A framework for analytical expressions of the outage probability and probability density function (PDF) of the end-to-end signal-to-noise ratio is presented by considering the practical scenario of imperfect channel state information (CSI) at the receiver. Subsequently, a PDF based novel closed-form analytical expression of the average symbol error rate is deduced for spectrally efficient higher-order modulation schemes, including rectangular quadrature modulation (RQAM), square QAM (SQAM), cross-QAM (XQAM), and hexagonal QAM (HQAM). Numerical investigations are conducted, and the impact of CSI imperfections on the system performance is evaluated. It is shown that the RF link is more vulnerable to channel estimation error (CEE) than the NLOS UV link. Further, it is illustrated that for constellation sizes greater than four, HQAM always performs better than the RQAM, SQAM, and XQAM schemes, irrespective of the amount of CEE present. Furthermore, it is shown that an elevation angle of 70° or less in the NLOS UVC link results in better outage performance. Correctness of the derived analytical expressions is supported through extensive Monte Carlo simulations.