Single and double scattering event analysis for ultraviolet communication channels

Ultraviolet communication with a large scattering angle via artificial agglomerate fog

Considering strong signal attenuation of the large-angle non-line-of-sight (NLOS) link achieved due to the ultraviolet (UV) scattering properties, we propose to increase the UV communication link gain under a large scattering angle via generating agglomerate fog within a certain range as a secondary light source. In this study, a channel model with locally strong scatterers from agglomerate fog is proposed based on Monte Carlo ray-tracing approaches. Mie theory is adopted to calculate the atmospheric channel parameters, to further evaluate the link gain of a channel under non-uniform atmosphere. The performance of scattering system in the presence of fog conditions depends on the relative positions of the light source to the fog and to the receiver. The link gain results reveal the transmission capabilities for different scattering channel geometries, and give the optimal spray point location within a 10 m communication range. We further establish a foggy NLOS system using an agglomerate fog generator to verify our research in the real environment. The results show that the received signal strength of the NLOS link can be effectively enhanced by constructing scatterers in the atmospheric channel, which significantly decreases the bit-error rate (BER).

266 nm ultraviolet communication under unknown interference using UVC micro-LED

Ultraviolet C (UVC) micro light-emitting diode (LED) can achieve symbol communication rate up to 100Msps at distance 40 meters without transmitter-side lens to guarantee certain communication mobility. We consider what we believe to be a new scenario where high speed UV communciation is realized under unknown low-rate interference. The signal amplitude properties are characterized, and the interference intensity is categorized into three cases, namely weak, medium and high interference intensity. The achievable transmission rates for the three cases are derived, where the achievable transmission rate for medium interference intensity can approach those in weak interference intensity and strong interference intensity cases. We provide Gaussian approximation and related log-likelihood ratio (LLR) calculation, which are fed into the subsequent message-passing decoder. In the experiment, the data is transmitted with symbol rate 20 Msps under unknown interference with symbol rate 1 Msps, received by one photomultiplier tube (PMT). Experimental results show that the proposed interference symbol estimation approach shows negligibly higher bit error rate (BER) compared with those with perfect knowledge on the interference symbols.

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.

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.

Laser triangulation measurement system with Scheimpflug calibration based on the Monte Carlo optimization strategy

We propose a linear laser triangulation measurement system using Scheimpflug calibration based on the Monte Carlo optimization strategy. A Scheimpflug inclination camera calibration model is introduced in the measurement system for improving the image definition in small-range measurements with a large depth-of-field. To address the nonlinear optimization problem between the instrument resolution and measurement range, the Monte Carlo method is adopted to determine the optimal optical parameters (scattering angle, Scheimpflug angle, and focus length) in a practical measurement system. Furthermore, we experimentally constructed the measurement system to demonstrate the measurement precision by measuring a standard step block (measurement range 15 mm). The performance parameters of the maximum measurement error, maximum standard deviation, and linearity are obtained as ±7 μm, 0.225 μm, and 0.046%, respectively. Finally, the proposed measurement system based on the Monte Carlo optimization strategy is promising for high-precision measurements in industrial applications and provides guidance for optimizing the design parameters of ranging measurement sensors.

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.

Single-scatter path loss model of LED-based non-line-of-sight ultraviolet communications

Light-emitting diodes (LEDs) are popularly used as light sources in non-line-of-sight (NLOS) ultraviolet communications (UVC). However, currently reported single-scatter path loss (PL) models of NLOS UVC links assume that the radiant intensity of the light source is uniformly distributed within the beam divergence angle, which cannot well characterize the light emission pattern of LEDs. In this Letter, we propose a single-scatter PL model for LED-based NLOS UVC systems, and the corresponding analytical expression is derived by modeling the LED emission pattern as a Lambertian distribution. Monte Carlo simulations and experimental results are provided to verify the effectiveness of the proposed PL model. Results show that the proposed model can accurately predict PL results in actual situations. The root-mean-square error of the proposed PL model is only about 1 dB in typical scenarios with experimental results as benchmarks. Also, the proposed model is much easier to implement than the currently reported PL model with the light source model of a uniformly distributed emission pattern.