Ultraviolet Communication System Research Articles

Spread spectrum for covert communication in ultra-violet communication system

In this paper, we propose a covert communication scheme based on a spread spectrum for ultra-violet communication. We first characterize the system model of the communication system, where Warden is adopted to monitor the legitimated user transmission based on the binary hypothesis test and Kolmogorov-Smirnov test. To avoid periodic transmission of the pilot sequence which potentially degrades covertness, we propose a blind synchronization approach, such that the pilot sequence does not need to be transmitted. It is observed from system-level simulation that the spread spectrum-based approach can achieve both low detection bit error rate and covertness under weak light intensity. Moreover, we experimentally evaluate the detection performance and covertness of the proposed approach.

Decoding Algorithm Based on LDPC for UAV MISO Ultraviolet Communication System

Decoding Algorithm Based on LDPC for UAV MISO Ultraviolet Communication System

Investigation of Characteristics of Ultraviolet Light Pulse Weak Signal Communication System Based on Fourth-Order Frequency-Shift Keying Modulation

In ultraviolet (UV) communication, On–Off Keying (OOK) is the primary modulation technique. Compared to OOK, frequency modulation offers stronger resistance to path attenuation. Currently, research on frequency modulation demodulation schemes for UV communication is limited, mainly employing waveform detection and laser pulse response methods, which require high detection sensitivity to light. This study presents a novel frequency modulation communication scheme using discrete Poisson channel distribution and optical pulse signal processing algorithms, enhancing the signal processing sensitivity of the existing frequency modulation scheme to the level of photons. The proposed system model is rigorously evaluated through theoretical derivations and simulations. Additionally, a hardware system integrating optical pulse counting, frequency detection, and clock data recovery algorithms is developed. Experimental results show the system achieving a 5 kbps transmission rate under frequency modulation. In non-line-of-sight (NLOS) scenarios, communication reaches up to 65 m, with the receiver elevation angle ranging from 10° to 25° and the bit error rate (BER) stabilized at 10−4, while in line-of-sight (LOS) situations, the BER remains at 10−5 up to 400 m and 10−4 up to 700 m, achieving the farthest distance and fastest communication rate achievable in the current FSK modulation scheme of ultraviolet communication systems. The integrated components enhance its applicability in communication systems. This study offers a valuable addition to UV communication technology.

Enhanced Performance of Gallium‐Based Wide Bandgap Oxide Semiconductor Heterojunction Photodetector for Solar‐Blind Optical Communication via Oxygen Vacancy Electrical Activity Modulation

AbstractGallium oxide (β‐Ga2O3) is a prominent representative of the new generation of wide‐bandgap semiconductors, boasting a bandgap of ≈4.9 eV. However, the growth process of β‐Ga2O3 materials introduces unavoidable oxygen vacancies (Vo), leading to persistent photoconductivity (PPC), a phenomenon that severely hinders device performance. In this study, an innovative approach is successfully developed by introducing high p‐orbital energy nitrogen (N). This leads to the formation of a hybridized state with O 2p orbitals in β‐Ga2O3, resulting in the creation of GaON and suppressing the electrical activity of Vo. Through meticulous experimentation and advanced computational methods, a comprehensive and insightful explanation of the regulation and mechanism underlying this passivation process is offered. Moreover, pn‐junction solar‐blind photodetectors are engineered using hybridized GaON thin films with p‐type CuPc. These photodetectors demonstrate exceptional characteristics, including ultra‐low dark current (10−14 A), high photo‐to‐dark current ratio (106), and rapid decay speed (0.008 s) even at zero bias. Based on these advancements, a solar‐blind ultraviolet communication system is designed, featuring straightforward and reliable encoding, easy implementation, and robust anti‐interference capabilities.

A New Photon-Counting MU-MISO Ultraviolet Communication System With MMSE Precoding in Turbulence Channels

A New Photon-Counting MU-MISO Ultraviolet Communication System With MMSE Precoding in Turbulence Channels

Implementation of large angle low error non-line-of-sight ultraviolet communication system

Due to the strong scattering of ultraviolet (UV) communication, it is particularly suitable for scenarios involving short distance and large angle scattering, such as communication between buildings and jungles. In this paper, a system based on a single scattering model and a discrete Poisson channel pulse counting signal processing algorithm is constructed, and the effects of the number of signal photons, noise photons, and elevation angle on the system's bit error rate (BER) are simulated and analyzed. The effect of sampling rate on the system's performance is numerically analyzed. The results show that the pulse counting algorithm is suitable for systems with a small number of signal photons and a high sampling rate. The BER of the system when the number of signal photons becomes large is more dependent on the sampling rate than the signal-to-noise ratio. Additionally, we designed an outdoor test system including hardware system, pulse counting, synchronization and data recovery algorithms. The test results are consistent with the simulation results. The communication rate of the outdoor system is designed to be 10 kbps at a distance of 50 m. The BER is 10-3 when the elevation angle is 85°, while the BER is 10-5 when the elevation angle is 50°.

Large‐Area 2D Perovskite Oxides/Organic Heterojunction Enables Highly‐Sensitive Self‐Powered Photodetector for Ultraviolet Light Communication

AbstractUltraviolet (UV)‐sensitive semiconductors play a key role in converting UV light into electric signals in a UV photodetector. Two‐dimensional (2D) oxide perovskite, as a kind of green and stable semiconductor materials, exhibits excellent UV detection capabilities. However, the non‐dense nanosheet thin film induces alternative shunts in vertical‐structured devices results in high ohmic leakage currents. Large number of oxygen vacancies in 2D oxide perovskite leads to the adsorption / desorption process of oxygen molecules that slows down the device's response speed. Therefore, an inorganic–organic heterojunction that effectively fills up the pinholes in nanosheet films, effectively suppressing the dark current of the device by 100 000 times are designed. Meanwhile, the construction of inorganic–organic heterojunctions can accelerate the charge carriers’ transporting process, resulting in a fast rise / decay response time of 0.7 ms / 8.5 ms. Moreover, the inorganic–organic heterojunction endows the device with excellent self‐powered performance, presenting a high responsivity of 60 mA W−1. This photodetector demonstrates application potential in a UV communication system with a detection angle of 30 degrees and a close‐range communication of 1.2 m.

Enhanced photoresponse of self-powered ZnO-based photoelectrochemical-type UV photodetectors via Ga-doping for optical communication application

Wide-bandgap metal-oxide semiconductors hold promise for self-powered photoelectrochemical (PEC) type UV photodetectors (PDs) due to their inherent photoelectric properties and durability. However, inadequate charge carrier separation and transport remain a fundamental challenge for practical applications. Herein, the extraordinary efficacy of introducing gallium (Ga) into ZnO nanowire to design high-performance PEC-type PDs is demonstrated. The obtained Ga-doped ZnO (ZnO:Ga) PEC-type photodetectors exhibit superior UV photoresponse performance, featuring an exceptionally high responsivity of 233.26mA/W, an excellent detectivity of 4.18 × 1012 Jones, and a fast response/recovery time of 159/150 ms under 365nm illumination without external bias voltages. These accomplishments outperform the majority of previously reported PEC-type UV PDs. It is found that the unique properties of ZnO:Ga nanowires, including improved donor density and steeper band bending at solid-liquid interface, significantly enhance the generation, transfer, and separation of photoexcited charge carriers, thus contributing to the superior photodetector’s performance. In addition, a secure UV communication system using international Morse code is set to demonstrate the feasibility of ZnO:Ga nanowires PEC-PD as a self-powered optical receiver. This study introduces a promising approach to develop self-powered photodetectors that are highly stable, cost-effective, and poised for integration into future multifunctional optoelectronic devices.

On the capacity of a SIM-based cooperative NLOS UVC system with best relay selection

Ultraviolet communication (UVC) is a promising technology due to its ability to operate in non-line-of-sight (NLOS) mode thereby eliminating the pointing acquisition and tracking (PAT) requirement as needed by infrared and visible light communications. However, NLOS UVC suffers from very high attenuation and turbulence-induced fading when operated over a long distance. Due to these limitations, the existing literature on the NLOS UVC is mostly restricted to short-distance communications only. Therefore, this paper addresses these challenges by proposing an outdoor subcarrier-intensity-modulation (SIM) based multi-relay cooperative communication system employing the best relay selection and decode-and-forward (DF) relaying protocol. The turbulence-induced fading is modelled using lognormal distribution under weak atmospheric turbulence conditions. We derive novel closed-form analytical expressions of outage probability and ergodic capacity. Correctness of the derived analytical expressions is validated through numerical simulations.

Boosting Charge Utilization in Self-Powered Photodetector for Real-Time High-Throughput Ultraviolet Communication.

Ultraviolet (UV) communication is a cutting-edge technology in communication battlefields, and self-powered photodetectors as their optical receivers hold great potential. However, suboptimal charge utilization has largely limited the further performance enhancement of self-powered photodetectors for high-throughput communication application. Herein, a self-powered Ti3 C2 Tx -hybrid poly(3,4 ethylenedioxythiophene):poly-styrene sulfonate (PEDOT:PSS)/ZnO (TPZ) photodetector is designed, which aims to boost charge utilization for desirable applications. The device takes advantage of photothermal effect to intensify pyro-photoelectric effect as well as the increased conductivity of the PEDOT:PSS, which significantly facilitated charge separation, accelerated charge transport, and suppressed interface charge recombination. Consequently, the self-powered TPZ photodetector exhibits superior comprehensive performance with high responsivity of 12.3mA W-1 and fast response time of 62.2 µs, together with outstanding reversible and stable cyclic operation. Furthermore, the TPZ photodetector has been successfully applied in an integrated UV communication system as the self-powered optical receiver capable of real-time high-throughput information transmission with ASCII code under 9600 baud rate. This work provides the design insight of highly performing self-powered photodetectors to achieve high-efficiency optical communication in the future.

The excellent performance of β-Ga2O3 Schottky photodiode under forward bias and its application in solar-blind ultraviolet communication

In this work, the planar β-Ga2O3 Schottky photodiodes on the sapphire substrates were manufactured by conventional photolithography and lift-off processes. Au and Ti/Au were used as Schottky and Ohmic contacts. After optimizing the geometry layout of β-Ga2O3 Schottky photodiode, R increased by 120%, EQE enhanced by 896.81% and D* gotten a 1540.88% increase. Particularly, β-Ga2O3 Schottky photodiode had exhibited the abnormally excellent performance under forward bias, contrary to most of conventional UV photodetectors. The origin of abnormally excellent performance in β-Ga2O3 Schottky photodiodes under forward bias have been researched systematically. Combined experiments with DFT calculations, we have attributed the ultra high EQE in β-Ga2O3 Schottky photodiode to its unique band structure. While the large photo-to-dark current ratio and D* under forward bias originate from deep-state intrinsic defects of β-Ga2O3. At last, the solar-blind ultraviolet communication system based on β-Ga2O3 Schottky photodiode was achieved and the message, “Hello, HIT!”, was successfully transmitted.

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.

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.

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.

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 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.

Flexible perovskite nanosheet-based photodetectors for ultraviolet communication applications

Ultraviolet (UV) photodetection has attracted much attention for applications like monitoring ozone holes and light communication. Although UV photodetectors based on conventional inorganic semiconductors have been widely investigated, fast response devices with high sensitivity remain needed for UV communication systems. This Letter reports on flexible ultrathin methylammonium lead bromide(MAPbBr3)-based UV photodetectors. In the UV regime, the response time reaches 3.3/4.0 μs, and the 3 dB bandwidth is 0.22 MHz. No current degradation is detected after repeated bending cycles, indicating the excellent mechanical flexibility and reliability of flexible high-speed UV photodetectors. Moreover, MAPbBr3 nanosheet-based photodetectors have been integrated into a UV communication system as signal receivers transmitting messages encrypted by international Morse codes. These results reveal the potential of ultrathin perovskite nanosheets in developing flexible optoelectronic devices for UV communications and related applications.

Wireless ultraviolet scattering channel estimation method based on deep learning.

Due to the strong scattering characteristics, there are serious problems of inter-symbol interference (ISI) and transmission attenuation in the none-line-of-sight (NLOS) wireless ultraviolet communication system. In this paper, a wireless ultraviolet scattering channel estimation method based on deep learning is presented. The learning model structure is designed by combining the one-dimensional convolutional neural network (1D-CNN) and the deep neural network (DNN). In the training stage, the network optimization process is improved by the differential evolution (DE) algorithm. The computer simulation results show that the proposed deep learning channel estimation scheme has better mean square error (MSE) performance and bit error rate (BER) performance compared with the traditional algorithms. Furthermore, we verify the stability of this scheme in different communication environments, and the constructed neural network model has good generalization ability.

The realization of a wide-angle voice transmission non-line-of-sight ultraviolet communication system

A 300 kbps wide-angle non-line-of-sight ultraviolet communication system with voice transmission function is designed here. Based on Poisson distribution theory, we design the symbol detecting method for the receiving discrete photon signals. Using 272 nm LED array as the light source and PMT as the detector, the voice transceiver is integrated into the carriable size of 200 × 90 × 65 mm3. An outfield test shows the system obtains the BER of 0.88% under 200 m. Under 10° wide-angle deviation of the transmitter, a BER below 1.33% is achieved.