Light Position Research Articles

Double‐Sided Bifunctional Blue‐Green Light Photodetector Based on Liquid Crystalline Polymer for Light Positioning and Health Monitoring

AbstractWearable blue‐green photodetectors have attracted considerable attention in underwater and medical applications. However, semiconductor‐based photodetectors generally suffer from inevitable performance deterioration because of elastic modulus mismatch between rigid inorganic materials and polymer matrixes. Besides, most of the photodetectors reported so far can't be used on both sides and the multiple functionalizations can only be realized by stacking different types of devices. Herein, an intrinsically flexible and size‐customizable blue‐green photodetector has been fabricated based on well‐designed composite fabrics with oriented electrospun fibers, consisting of pseudo‐stilbene azobenzene‐containing cross–linked liquid crystalline polymers (NAzo‐CLCP) and piezoelectric poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)] nanogenerator. Taking advantage of the synergistic effect between liquid crystalline alignment and polymer networks, the NAzo‐CLCP devices construct a consecutive and efficient conversion of illuminance – internal stress – electric signal. A responsivity of 233 mV W−1 is achieved in voltage signals and a comparable response time of 0.1 s in current signals compared to the reported wearable semiconductor‐based photodetectors. Benefiting from the inherent flexibility and compatibility of the hydrophobic fabrics, the NAzo‐CLCP devices exhibit robust stabilities under cyclic irradiations, humidity and temperature variations, and especially slightly dynamic conditions, fulfilling basic requirements for wearable electronics. For practical applications, a photodetector array for light positioning based on blue light and a bracelet for real‐time health monitoring based on green light are developed. Profiting from the uniformity of the fabrics and the consistency of detection performance, the integrated bifunction of code transmission and health monitoring over a double‐sided one‐piece photodetector has been realized for the first time, providing extensive potential for wearable electronics based on the NAzo‐CLCP fabrics.

Reconfigurable intelligent surface-aided positioning-centered multi-LED integrated visible light communication and positioning system

This paper investigates a reconfigurable intelligent surface (RIS)-aided integrated visible light communication and positioning (VLCP) system, which aims to reduce sensitivity to line-of-sight (LoS) blockage in visible light and simultaneously achieve capabilities for both visible light communication (VLC) and visible light positioning (VLP). The framework of this system is divided into three parts: positioning, channel state information (CSI) estimation, and data transmission. When the LoS links are present, due to the potential adverse positioning effects RIS caused in this scenario, the RIS only plays a role in assisting the communication. Meanwhile, the positioning process is based on the received signal strength (RSS) information from the LoS transmission. If the LoS links are blocked, the RIS provides added non-line-of-sight (NLoS) positioning signals and achieves subsidiary communications accordingly. The Cramer-Rao lower bound (CRLB) on the positioning result is derived and the CSI estimation is conducted based on the results provided by the positioning schemes to reduce the pilot overhead. The achievable rate is evaluated based on the estimated CSI. The configurations of RIS parameters and the power allocated to positioning and communication are jointly optimized to minimize the CRLB while satisfying constraints on the maximum tolerable outage probability, RIS parameter acquisition, and total transmit power. To address this non-convex optimization problem, we proposed an alternative optimization (AO) algorithm to optimize the RIS assignment matrix and the power coefficient alternatively. We employ the worst-case distribution of the Conditional Value-at-Risk (CVaR) along with successive convex approximation (SCA) techniques to derive feasible solutions of the power coefficient optimization subproblem. Meanwhile, we optimize the RIS assignment matrix based on the principle of maximum received power chosen (MRPC). Simulation results demonstrate the influence of RIS in the positioning process in our proposed VLCP system with or without the presence of LoS links, and meanwhile, the relationship between communication performance and positioning performance is validated through the simulations. From the simulation results, the RIS-aided VLCP system can be verified as a viable option for the upcoming era of sixth-generation (6G) technology.

DeepVLP: Graph Neural Network-based Denoising and Signals Optimization Framework for Visible Light Positioning

DeepVLP: Graph Neural Network-based Denoising and Signals Optimization Framework for Visible Light Positioning

Optimizing Daylight Integration through Light Pipes in Dhaka's Office Buildings: A Simulation and Field Study Approach

The rapid urbanization of Dhaka has resulted in the proliferation of middle and high-rise office buildings, often designed with deep plans and large open layouts to maximize economic and spatial efficiency. However, these designs typically rely heavily on artificial lighting, with core areas devoid of natural daylight, contributing significantly to energy consumption—up to 50% of total building energy use. While daylight has well-documented physiological and psychological benefits, its effective integration into deep office spaces remains a challenge. This study explores the integration of light pipes with HVAC systems, forming a dual ducting system to enhance daylight utilization in office buildings. Light pipes are innovative devices that transport and distribute daylight while minimizing heat transfer, providing an effective solution for illuminating deep, windowless areas. Using EnergyPlus software for simulation analysis along with field study, the research examines the optimal design parameters for light pipe installation, including length, width, number, and positioning. Findings reveal significant potential for daylight inclusion through light pipes, improving energy efficiency and workspace quality. The study synthesizes insights from literature, field observations, and simulations to propose design guidelines for consultants. These strategies aim to optimize the luminous environment of Dhaka’s office buildings, fostering sustainable, cost-effective, and occupant-friendly working environments.

Data-Efficient Training of Gaussian Process Regression Models for Indoor Visible Light Positioning.

A data-efficient training method, namely Q-AL-GPR, is proposed for visible light positioning (VLP) systems with Gaussian process regression (GPR). The proposed method employs the methodology of active learning (AL) to progressively update the effective training dataset with data of low similarity to the existing one. A detailed explanation of the principle of the proposed methods is given. The experimental study is carried out in a three-dimensional GPR-VLP system. The results show the superiority of the proposed method over both the conventional training method based on random draw and a previously proposed line-based AL training method. The impacts of the parameter of active learning on the performance of the GPR-VLP are also presented via experimental investigation, which shows that (1) the proposed training method outperforms the conventional one regardless of the number of final effective training data (E), especially for a small/moderate effective training dataset, (2) a moderate step size (k) should be chosen for updating the effective training dataset to balance the positioning accuracy and computational complexity, and (3) due to the interplay of the reliability of the initialized GPR model and the flexibility in reshaping such a model via active learning, the number of initial effective training data (m) should be optimized. In terms of data efficiency in training, the required number of training data can be reduced by ~27.8% by Q-AL-GPR for a mean positioning accuracy of 3 cm when compared with GPR. The CDF analysis shows that with the proposed training method, the 97th percentile positioning error of GPR-VLP with 300 training data is reduced from 11.8 cm to 7.5 cm, which corresponds to a ~36.4% improvement in positioning accuracy.

Performance Improvement by FRFT-OFDM for Visible Light Communication and Positioning Systems

In indoor visible light communication (VLC) and visible light positioning (VLP) systems, the performance of conventional orthogonal frequency-division multiplexing (OFDM) schemes is often compromised due to the nonlinear characteristics and limited modulation bandwidth of light-emitting diodes, the multipath effect in enclosed indoor environments, and the relative positions of transmitters and receivers. This paper proposes an OFDM scheme based on the fractional Fourier transform (FRFT) to address these issues, demonstrating promising results when applied to indoor VLC and VLP systems. The FRFT, a generalization of the conventional Fourier transform (FT) in the fractional domain, captures information in both the time and frequency domains, offering greater flexibility than the FT. In this paper, we first introduce the computation method of the reality-preserving FRFT for an intensity modulation/direct detection VLC system and integrate it with OFDM to optimize system performance. By adopting FRFT-OFDM under the optimal fractional order, we enhance both the bit error ratio (BER) performance and positioning accuracy. Simulation results reveal that the FRFT-OFDM scheme with an optimized fractional order significantly improves the BER and positioning accuracy compared to the FT-OFDM scheme across most receiver positions within the indoor observation plane. For communication, the FRFT-OFDM scheme achieves over 6 dB Eb/N0 gain compared to the FT-OFDM scheme at a BER of 3×10−4 when the receiver is positioned at most locations in the room. For positioning, the FRFT-OFDM scheme enhances positioning accuracy by more than 1 cm relative to the FT-OFDM scheme at most locations in the room. Notably, both systems maintain the same computational complexity and spectral efficiency.

Measuring the Potential Risk of Re‐identification of Imaging Research Participants from Open‐Source Automated Face Recognition Software

AbstractBackgroundResearch subjects can potentially be re‐identified from de‐identified MRI, CT, and PET brain scans with up to 98% accuracy using Microsoft Azure’s cloud‐based commercial facial recognition software. This showed the need to “de‐face” publicly shared research brain scans. Subsequently, Microsoft has begun restricting its face recognition services, intending to prevent misuse. This study tests a variety of popular open‐source computer vision and facial recognition software packages to measure the re‐identification risk with only unrestricted free software.MethodThis study used brain MRI from Siemens 3T scanners and face photographs from 182 participants (ages 30‐90+) in the Mayo Clinic Study of Aging. Each participant had photos taken with an iPad, which were cropped loosely around the head and converted to black and white. A total of 81 renders (2D reconstruction images; Figure 1) were made from each 3D T2‐FLAIR MRI, simulating various camera and lighting positions. These face renders approximate black and white photos, allowing use with software packages developed for matching faces/features between photographs.Open‐source Python packages (OpenCV, DeepFace, face_recognition, scikit‐learn) and their included pre‐trained models (designed for photographs) were used to match participant photographs to the labelled library of MRI‐based face renders. A correct match was recorded when the top‐scoring render or set of renders automatically chosen by the algorithm was from the MRI of the correct participant.ResultFeature matching with ORB and SWIFT (both from OpenCV) produced no correct matches, despite a prior publication reporting moderate success. The best match rates (Figure 2) were 58‐59% accuracy using face_recognition or DeepFace packages with support vector machines (SVMs). Without SVMs, these packages performed modestly worse (51%‐55%).ConclusionWhile the highest match rates obtained by widely available open‐source packages (roughly 60%) are much lower than those of a limited‐access commercial product (Microsoft Azure, with 98%), they show that actors with only access to no‐cost readily available software could still re‐identify a research subject from a brain scan most of the time. This further highlights the need for image refacing software, such as mri_reface, to protect the privacy and identifies of research volunteers.

Development of a light source position estimation system for accurate drone flight

Development of a light source position estimation system for accurate drone flight

SIC-Free Based Indoor Two-User NOMA-VLCP System

In this letter, an integrated dual-user visible light communication and positioning (VLCP) system based on non-orthogonal multiple access (NOMA) is proposed. The system consists of a single light-emitting diode (LED) and five photodiodes (PD), and the adaptive feedback threshold (AFT) algorithm is used to reduce error propagation (EP) to improve noise immunity. The particle swarm optimization (PSO) algorithm is employed to construct a joint optimization function that optimizes the power allocation factor of the two users and the roll-off coefficient of the square-root-raised-cosine(SRRC) filter. The simulation results demonstrate that, in the given indoor environment, the bit error ratio (BER) of each user in the proposed system is lower than the front error correction (FEC) limit and the average positioning errors of the two users are 4.62 cm and 5.74 cm respectively.

Design and implementation of broadband optical vortices in photonic crystal slabs

We propose and discuss a simple method to generate broadband optical vortices, utilizing the inherent topological vortex structures of polarization around bound states in the continuum supported by a photonic crystal slab in the momentum space to induce the generation of vortex beams. Since the proposed structure is composed of silicon pillars arranged periodically, it lacks a true optical geometric center. It is insensitive to the position of the incident light and does not require a specific optical alignment process compared to traditional spiral phase plates. Furthermore, because it is composed of dielectric pillars, it can achieve vortex beam generation at any desired working wavelength. We also discuss the robustness of its structure, showing that it can be immune to certain manufacturing defects. Therefore, the proposed structure not only provides a new method for manipulating the angular momentum of photons but also has potential new applications in integrated optical information processing and optical tweezers.

Rate Optimization Based on Successive Convex Approximation Algorithm in the Self-Powered Visible Light Communication and Positioning System

Rate Optimization Based on Successive Convex Approximation Algorithm in the Self-Powered Visible Light Communication and Positioning System

Ergonomic Workstation Design for Online Shop Live Streamers: Reducing Musculoskeletal Disorders (Pt. Xyz Case Study)

This study was conducted at PT. XYZ to evaluate and reduce the risk of musculoskeletal disorders among host streamers through the design of ergonomic workstations. The research method used was a quantitative case study approach, with the population consisting of employees at PT. XYZ who worked as host streamers. Purposive sampling was employed to select 10 respondents who frequently experienced fatigue and complaints in specific body areas. Primary data were collected through observation, questionnaires, guidelines, and interviews. Posture measurements were taken using the REBA (Rapid Entire Body Assessment) and RULA (Rapid Upper Limb Assessment) methods. The results indicated that prior to the intervention, host streamers had REBA and RULA scores that signified a high risk of musculoskeletal disorders, particularly in the neck, shoulders, back, and legs. After implementing an adjustable live streaming workstation design, along with adjustments to lighting and microphone positions, there was a significant decrease in the REBA and RULA scores. The REBA score decreased from 10 to 1, and the average RULA score dropped from 7 to 3. This indicated a significant reduction in the risk of musculoskeletal disorders. The conclusion of the study was that the design of an adjustable ergonomic workstation significantly reduced the risk of musculoskeletal disorders among host streamers at PT. XYZ, thereby enhancing worker comfort and health during live streaming.

A fast and stable calibration method for VLP system without any geometric measurement

Abstract. Visible light positioning (VLP) is one of the most promising technologies for providing high-precision, low-cost indoor positioning and navigation services. However, the traditional calibration methods of VLP are complex and unfriendly to users, which hinders the large-scale commercial deployment of VLP systems. In this letter, a fast and stable calibration method for Lambert model in the received signal strength (RSS)-based VLP system is proposed, which dispenses with geometric measurement and greatly simplifies the calibration procedures. The proposed method calibrates the Lambert model through two steps, firstly using a ratio method to calibrate the Lambert order, and then estimating the constant term. The actual processes only require moving a robot equipped with a photo-detector (PD) along a rectangular trajectory once, and then the program will automatically estimate the required parameters by analyzing the RSS during this period. Experimental results show a good stability of the calibrated parameters, as well as a excellent distance measuring accuracy within 12 cm. And the entire processes, including signal collection and processing, only take a total of no more than four minutes.

Asynchronous visible light communication and positioning system based on a multi-carrier orthogonal coding mechanism.

This paper presents an asynchronous visible light communication and positioning (VLCP) system leveraging the multi-carrier orthogonal coding mechanism (MC-OCM) based on complete complementary (CC) codes. Utilizing the superior correlation properties of CC codes, our system first achieves interference-free transmission from multiple access interference and inter-symbol interference, thus simultaneously enhancing the accuracy of data transmission and receiver location in asynchronous code division multiplexing-based VLCP systems. Numerical results confirm the proposed VLCP system's superiority, featuring an average BER below the FEC standard and an average PE less than 3 cm in challenging system settings with asynchronous transmission and multipath propagation.

Both the Positioned Supplemental or Night-Interruptional Blue Light and the Age of Leaves (or Tissues) Are Important for Flowering and Vegetative Growth in Chrysanthemum.

In this study, the effects of supplemental or night interruptional blue light (S-BL or NI-BL) positioning on morphological growth, photoperiodic flowering, and expression of floral genes in Chrysanthemum morifolium were investigated. Blue light-emitting diodes (LEDs) at an intensity of 30 μmol·m-2·s-1 photosynthetic photon flux density (PPFD) were used for 4 h either (1) to supplement the white LEDs at the end of the 10 h short-day (SD10 + S-BL4) and 13 h long-day conditions (LD13 + S-BL4), or (2) to provide night interruption in the SD10 (SD10 + NI-BL4) and LD13 (LD13 + NI-BL4). The S-BL4 or NI-BL4 was positioned to illuminate either the shoot tip, the youngest leaf (vigorously growing the third leaf from the shoot tip), or the old leaf (the third leaf from the stem base). In the text, they will be denoted as follows: SD10 + S-BL4-S, -Y, or -O; SD10 + NI-BL4-S, -Y, or -O; LD13 + S-BL4-S, -Y, or -O; LD13 + NI-BL4-S, -Y, or -O. Normally, the LD13 conditions enhanced more vegetative growth than the SD10 periods. The growth of leaves, stems, and branches strongly responded to the S-BL4 or NI-BL4 when it was targeted onto the shoot tip, followed by the youngest leaf. The SD10 + S-BL4 or +NI-BL4 on the old leaf obviously suppressed plant extension growth, resulting in the smallest plant height. Under LD13 conditions, the flowering-related traits were significantly affected when the S-BL4 or NI-BL4 was shed onto the youngest leaf. However, these differences do not exist in the SD10 environments. At the harvest stage, other than the non-flowered LD13 treatment, the LD13 + S-BL4 irradiating the youngest leaf induced the most flowers, followed by the shoot tip and old leaf. Moreover, LD13 + NI-BL4 resulted in the latest flowering, especially when applied to the shoot tip and old leaf. However, the SD10 + S-BL4 or + NI-BL4 irradiated the shoot tip, youngest leaf, or old leaf all significantly earlier and increased flowering compared to the SD10 treatment. Overall: (1) Generally, vegetative growth was more sensitive to photoperiod rather than lighting position, while, during the same photoperiod, the promotion of growth was stronger when the light position of S-BL4 or NI-BL4 was applied to the shoot tip or the youngest leaf. (2) The photoperiodic flowering of these short-day plants (SDPs) comprehensively responded to the photoperiod combined with blue light positioning. Peculiarly, when they were exposed to the LD13 flowering-inhibited environments, the S-BL4 or NI-BL4 shed onto the leaves, especially the youngest leaves, significantly affecting flowering.

Frequency division multiplexing-based light-emitting diode identification expansion design in visible light imaging positioning system

Frequency division multiplexing-based light-emitting diode identification expansion design in visible light imaging positioning system

IRS aided visible light positioning with a single LED transmitter

We propose a visible light positioning (VLP) system with a single light emitting diode (LED) transmitter and an intelligent reflecting surface (IRS) for estimating the position of a receiver equipped with a single photo-detector. By performing a number of transmissions from the LED transmitter and optimizing the orientation vectors of the IRS elements for each transmission, position information is extracted by the receiver based on power measurements of the signals reflecting from the IRS. The theoretical limit and the maximum likelihood (ML) estimator are presented for the proposed setting. In addition, an algorithm, named IRS focusing, is proposed for determining the orientations of the IRS elements during the localization process. The effectiveness of the proposed localization approach is demonstrated through simulations. Furthermore, extensions are provided to apply the proposed approach in the presence of partial prior information about the receiver position and when the IRS is located at the LED transmitter.

Three-dimensional visible light positioning through fisheye camera

Abstract Visible light can be utilized to achieve indoor high-precision positioning. However, most visible light positioning (VLP) systems only achieve two-dimensional (2D) positioning and require a dense LED layout as the transmitter. Therefore, we propose a novel three-dimensional (3D) visible light indoor positioning system, which uses the fisheye camera as the receiver, designs an LED width comparison method to reduce the requirement of LED density, and realizes 3D positioning. When images captured by the fisheye camera distort, we use the checkerboard calibration method to correct the distortion parameters of the fisheye camera. The parameters can be used to improve the impact of image distortion on the positioning effect. For the LED width comparison method, we set up a discrete height-width database, fit a curve between height and LED width, and calculate the receiver height according to the linear relationship. Extensive results show that the positioning system can achieve a 3D positioning with 9.66cm average error.

Acpro: fusion of embedded ambient light sensor and image sensor for visible light positioning

Abstract With the increasing demand for indoor positioning, visible light positioning (VLP) systems have become an optics technologies research hotspot due to their high accuracy and avoidance of electromagnetic interference. However, current photodiode (PD)-based and image sensor (IS)-based VLP systems still suffer from high costs at the receiver, and the problem of the trade-off between field of view (FoV) and positioning accuracy. Therefore, we propose a smartphone-based low-cost, and high-precision VLP system, Acpro. The system combines the smartphone’s embedded ambient light sensor and IS as the receiver for the positioning. First, for the low sampling rate of the ambient light sensor, we use the frequency aliasing characteristic to identify the LED’s beacon through the dynamic undersampling principle. Then, to increase the FoV and positioning accuracy, we use the standard distance information corrected by the IS to improve the noise distance calculated by the ambient light sensor. Further, the corrected distance information is used for positioning. Extensive results show that our system can achieve sub-meter positioning accuracy.

Delineating Regional BES–ELM Neural Networks for Studying Indoor Visible Light Positioning

Delineating Regional BES–ELM Neural Networks for Studying Indoor Visible Light Positioning