Multiple Photodiodes Research Articles

Dynamic range optimization of optoelectronic systems based on quantum mathematical models

A photodiode is a small and low-cost photosensitive sensor that can measure the solar vector through at least three combinations, making it a high-precision solar sensor. How to select the number of photodiodes and determine their layout is a challenge in order to solve the solar vector in any direction in a 360° field of view space as much as possible, the author first discretizes the equal surface area of the 360° field of view space, transforming the infinite sensor layout optimization problem into a finite combinatorial optimization (NP problem is difficult). Then, by establishing multi-objective optimization functions for coverage and uniformity, and combining quantum genetic algorithm to solve the optimal solution. The experimental analysis of the layout effects of different numbers of photodiodes and field of view ranges provides a theoretical basis for optimizing the layout of multiple photodiodes. The experimental results show that selecting 12 to 14 photodiodes can basically achieve a layout without coverage risk and uniform risk.

Hybrid Position and Orientation Estimation for Visible Light Systems in the Presence of Prior Information on the Orientation

Visible light communication (VLC) is seen as a potential access option for fifth-generation (5G) wireless communication (Wang <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2014) and (Ayyash <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2016) and beyond 5G (Strinati <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2019). A reliable VLC system benefits from an accurate estimate of the receiver’s position and orientation. In many cases, the orientation of the receiver is estimated with an external orientation estimation device. However, these devices generally suffer from drift and misalignment, causing an uncertainty in the orientation presented to the receiver. Hence, the external device can only provide a probability distribution of the orientation to the position estimator, which can be used as prior information for the position estimation. Since the orientation of a receiver greatly affects the performance of a visible light system, the orientation uncertainty will degrade the performance of standard positioning algorithms, implying it should be taken into account when designing a robust positioning algorithm. In this paper, we design an received signal strength (RSS)-based hybrid position and orientation estimation algorithm using the hybrid maximum likelihood (ML)/maximum <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a posteriori</i> (MAP) (HyMM) principle for a multiple LEDs - multiple photodiodes (PDs) (MLMP) system to take into account the presence of prior information on the orientation. The proposed HyMM estimator is compared with three existing estimators, i.e., the simultaneous position and orientation (SPO) estimator, the misspecified maximum likelihood (MML) estimator and the first-order-approximation-based positioning algorithm, subject to the orientation uncertainty. Further, in order to analytically assess the performance of the proposed estimator, the theoretical lower bound on the mean squared error (MSE), i.e. the hybrid Cramér-Rao bound (HCRB) for HyMM is derived. Computer simulations show an asymptotic tightness between the performance of the estimator and its associated theoretical lower bound.

Sub-Decimeter VLC 3D Indoor Localization With Handover Probability Analysis

This paper addresses the problem of Visible Light Communication (VLC)-based indoor localization and handover, where mobile users communicate with hybrid VLC/mmWave Access Points (APs). The VLC system consists of multiple Light-Emitting Diodes (LEDs) treated as VLC transmitters, multiple Photodiodes (PDs) on the user’s smart device, and multiple mmWave Radio Frequency (RF) transmitters used as complementary APs for the VLC system in the case of blockage. We propose a Convolutional Neural Network (CNN)-based algorithm consisting of offline and online modes. In the offline mode, we gather a data set by dividing the environment into fixed-sized elements where the received VLC signal along with the data attained from the smart device at each element represent a sample to train a CNN model for indoor localization. In the online mode, users employ the received VLC signals to estimate their locations. We then propose a virtual soft handover process according to the Coordinated Multiple Point (CoMP) transmission, where the HandOver Margin (HOM) and Waiting Time (WT) are dynamically set based on the change in Signal-to-Noise-Ratio (SNR) values in consecutive time slots. We derive a closed-form expression for the average effective throughput during the handover process, which shows the algorithm’s superior performance compared to conventional soft and hard handovers. Simulation results show an average positioning error of 4.31 centimeters for the proposed localization algorithm in a $5\times 4\times 3\,\,\text {m}^{3}$ smart environment.

An Artificial-Noise-Based Approach for the Secrecy Rate Maximization of MISO VLC Wiretap Channel With Multi-Eves

In this paper, we consider improving the secure performance of multiple-input single-output visible light communication channel in the presence of multiple eavesdroppers with multiple photodiodes. Our goal is to design an optimal artificial-noise (AN) aided transmission strategy to maximize the achievable secrecy rate subject to both sum power constraint and peak amplitude constraint. We consider a joint optimization of the transmit covariance and AN covariance for the non-convex secrecy rate maximization (SRM) problem. In order to solve it, the SRM problem is transformed into a series of single-variable semidefinite programming (SDP) problems without losing any optimality, and a one-dimensional search based algorithm is proposed to handle the converted problem, with polynomial complexity. By exploiting Karush-Kuhn-Tucker conditions of the problem, beamforming is found to be optimal for the confidential information transmission. Simulation results show the superior performance of the proposed AN-aided method compared with two other AN-aided methods and no AN-aided method.

Demonstration of Three-Dimensional Indoor Visible Light Positioning with Multiple Photodiodes and Reinforcement Learning.

To provide high-quality location-based services in the era of the Internet of Things, visible light positioning (VLP) is considered a promising technology for indoor positioning. In this paper, we study a multi-photodiodes (multi-PDs) three-dimensional (3D) indoor VLP system enhanced by reinforcement learning (RL), which can realize accurate positioning in the 3D space without any off-line training. The basic 3D positioning model is introduced, where without height information of the receiver, the initial height value is first estimated by exploring its relationship with the received signal strength (RSS), and then, the coordinates of the other two dimensions (i.e., X and Y in the horizontal plane) are calculated via trilateration based on the RSS. Two different RL processes, namely RL1 and RL2, are devised to form two methods that further improve horizontal and vertical positioning accuracy, respectively. A combination of RL1 and RL2 as the third proposed method enhances the overall 3D positioning accuracy. The positioning performance of the four presented 3D positioning methods, including the basic model without RL (i.e., Benchmark) and three RL based methods that run on top of the basic model, is evaluated experimentally. Experimental results verify that obviously higher 3D positioning accuracy is achieved by implementing any proposed RL based methods compared with the benchmark. The best performance is obtained when using the third RL based method that runs RL2 and RL1 sequentially. For the testbed that emulates a typical office environment with a height difference between the receiver and the transmitter ranging from 140 cm to 200 cm, an average 3D positioning error of 2.6 cm is reached by the best RL method, demonstrating at least 20% improvement compared to the basic model without performing RL.

Accurate Visible Light Positioning Using Multiple-Photodiode Receiver and Machine Learning

Visible light positioning (VLP) is a promising indoor localization method as it provides high positioning accuracy and allows for leveraging the existing lighting infrastructure. Photodiode (PD)-based receiver is a commonly used tag for VLP. However, a tag employing a single PD requires three or more luminaires to be visible. This article presents a VLP system that uses a custom-made tag utilizing multiple PDs. It applies received signal strength (RSS)-based fingerprinting using a weighted k-nearest neighbor (WkNN) algorithm for localization. Experimental results show that it is possible to localize using less than three luminaires with high accuracy. The Manhattan and Matusita distance metrics are found to provide lower localization accuracy than the Euclidean metric for the WkNN algorithm. The creation of a dense fingerprinting database through 2-D interpolation is presented as a method to reduce the cost of time and labor. The localization performance of the VLP system does not degrade noticeably with the fabricated database. The localization accuracy of the WkNN algorithm is shown to be better than that of a multilayer perceptron (MLP)-based regressor. The developed VLP system is also experimentally benchmarked against the HTC Vive showing comparable performance.

Simultaneous Position and Orientation Estimation for Visible Light Systems With Multiple LEDs and Multiple PDs

Visible light communication (VLC) is seen as a supplement for fifth-generation (5G) wireless communication in short-range high data rate communication applications [1]. A reliable VLC system relies on an accurate estimate of the position and orientation of the receiver, which corresponds to the six-dimensional positioning problem mentioned in [2]. In this paper, we investigate the simultaneous position and orientation estimation (SPO) problem using received signal strength (RSS), for a visible light system containing multiple LEDs and multiple photodiodes (PDs) (MLMP). Although in general, the position and orientation of the receiver can be represented by a vector and a rotation matrix, respectively, the constraints imposed by the rotation matrix make the numerical optimization in the estimation process cumbersome, e.g, the commonly used constrained optimization method is often very complex and non-robust. Therefore, in this paper, we design two SPO algorithms using the principle of optimization on manifolds, which alleviates the constraints from the rotation matrix. In addition, we propose an initialization algorithm, based on the direct linear transformation (DLT) principle, to obtain an initial estimate in closed-form for the iterative algorithms. To evaluate the performance of the proposed RSS-based SPO algorithms, we derive the Cramer-Rao bound (CRB). In particular, the orientation error component of the CRB corresponds to the intrinsic CRB or the CRB on manifolds, which measures the error in the estimated rotation matrix in a physically meaningful way. Finally, computer simulations show an asymptotic tightness between the performance of the proposed algorithms and the theoretical lower bound, demonstrating the effectiveness of the proposed solutions.

Theoretical bounds for the bit error rate for SAC OCDMA balanced detectors with multiple photodiodes

In this paper, we derive the theoretical lower and upper bounds for bit error rate (BER) for spectral amplitude coding OCDMA balanced detector (BD) employing multiple photodiodes. The purpose of this study is to find the maximum performance improvement that can be achieved when a multi-photodiode structure is used to reduce the intensity noise. Results show that when the split signals are independent, the lower bound for the BER is much lower than it is for the conventional BD. To further validate our study, Monte Carlo simulation and software simulation using Optisystem were performed.

Enabling Real-Time Indoor Tracking of IoT Devices Through Visible Light Retroreflection

Visible light communication (VLC)-based indoor localization approaches enjoy many advantages, such as utilizing ubiquitous lighting infrastructure, high location accuracy, and no interruption to RF-based devices. However, existing VLC-based localization methods lack a real-time backward channel from the device to landmarks and necessitate computation at the device, which make them unsuitable for real-time tracking of small IoT devices. In this paper, we propose and prototype RETRO, that establishes an almost zero-delay backward channel by retroreflection. RETRO localizes passive IoT devices without requiring computation and heavy sensing (e.g., camera) at the devices. Multiple photodiodes (i.e., landmarks) are mounted on any single unmodified light source to sense the retroreflected optical signal (i.e., location signature). We derive a closed-form expression, which is validated by experiments and ray tracing simulations, for the reflected optical power relative to the location and the orientation of the retroreflector. The expression is applied to a received signal strength indicator and trilateration based localization algorithm. Extensive experiments demonstrate centimeter-level location accuracy and single-digit angular error. For practicality concern, to mitigate the thickness problem of a single retroreflector, the capabilities of different retroreflector arrays are studied. The range of the localization system is theoretically evaluated for different light emission patterns.

Secrecy Performance of the MIMO VLC Wiretap Channel With Randomly Located Eavesdropper

We study in this paper the secrecy performance of the multiple-input multiple-output (MIMO) visible light communication (VLC) wiretap channel. The underlying system model comprises three nodes: one transmitter, equipped with multiple fixtures of LEDs, one legitimate receiver and one eavesdropper, each equipped with multiple photo-diodes (PDs). The VLC channel is modeled as a real-valued amplitude-constrained Gaussian channel and the eavesdropper is assumed to be randomly located in the coverage area. We propose a low-complexity precoding scheme that aims at enhancing the secrecy performance of the system. Specifically, assuming discrete input signaling, we derive an average achievable secrecy rate for the underlying system in a closed-form, and the derived expression is a function of the precoding matrix and the input distribution using stochastic geometry. Then, we propose a low-complexity design of the precoding matrix based on the generalized singular value decomposition (GSVD) of the channel matrices of the system. We examine the resulting average achievable secrecy rate using the truncated discrete generalized normal (TDGN) distribution, which is the best-known discrete distribution available in the literature. Finally, we validate the proposed scheme through extensive simulations and we demonstrate its superiority when compared to other schemes reported in the literature.

Differential laser Doppler velocimetry for cross-sectional velocity distribution measurements using 48-channel spatial encoding and nonmechanical scanning

A differential laser Doppler velocimeter using 48-channel spatial encoded measurement points is proposed for dense cross-sectional velocity distribution measurements. An asymmetrical push–pull configuration and multiple photodiodes are employed to increase the number of the measurement points. The functionality of the proposed structure is experimentally demonstrated. The results indicate that a cross-sectional velocity distribution is successfully measured with the proposed structure.

Low-Complexity Spatial Modulation for IM/DD Optical Wireless Communications

A bipolar pulse amplitude modulation (PAM)-based optical spatial modulation transmission scheme is developed for intensity modulation/direct detection optical wireless communications. In the proposed scheme, multiple light emitting diodes (LEDs) and multiple photodiodes are employed at the transmitter and receiver, respectively. The transmit LEDs are divided into two groups. The first group of LEDs transmits the positive part of the PAM symbol, while the second group of LEDs transmits the absolute value of the negative part of the bipolar PAM symbol. Besides, spatial shift keying is employed in the active LED group to improve data rate. According to the transmit strategy, a novel low-complexity receiver algorithm is developed.

A Reversed Visible Light Multitarget Localization System via Sparse Matrix Reconstruction

A reversed indoor multitarget localization system employing compressive sensing (CS) theory is proposed for the first time in terms of visible light positioning (VLP). Unlike conventional VLP systems, where targets process the received light signals to localize themselves, our system works reversely by using multiple photodiodes (PDs) mounted on the ceiling to localize mobile targets that carry light emitting diodes. By utilizing its nature of sparsity, the problem of multitarget localization is formulated as a problem of sparse matrix reconstruction, and a 3-step workflow is developed to solve the problem. In this workflow, first, a sensing matrix is redesigned by using QR decomposition to enable CS theory. Next, the conventional l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -minimization (l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> M) algorithm which is highly vulnerable to noise in solving a localization problem is theoretically analyzed and subsequently improved by adopting a reweighted l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> M approach. Finally, a subgrid localization algorithm is proposed to overcome a common unpractical assumption of on-grid locations, tackle the false peak problem in sparse matrix reconstruction, and ultimately improve the localization precision. The feasibility of our system and supporting algorithms is verified through extensive simulations. Our system demonstrates a good positioning accuracy of 7.4 cm by using 25 PDs when SNR = 20 dB. We also investigate the impact of various factors on the positioning performance, and the obtained results provide an insightful reference paving the way to a practical system design.

Interference Mitigation for Indoor Optical Attocell Networks Using an Angle Diversity Receiver

In this paper, interference mitigation techniques based on angle diversity receivers (ADRs) are studied for optical attocell networks. Consisting of multiple photodiodes (PDs), an ADR requires appropriate signal combining schemes in order to mitigate intercell interference (ICI) in optical attocell networks. Four signal combining schemes, namely select best combining, equal gain combining, maximum ratio combining, and optimum combining are investigated. To further mitigate ICI, a novel double-source cell configuration with two transmission modes is also proposed. Results show that the systems with ADRs significantly outperform those with single-PD receivers in terms of signal-to-interference-plus-noise ratio (SINR). Also, compared to the conventional single-source cell configuration, the double-source cell configuration can provide an SINR improvement of over $\text{20}$ dB. Furthermore, an analytical framework is proposed to analyze the performance of optical attocell networks with ADRs, where different propagation scenarios such as line-of-sight and nonline-of-sight are considered. The accuracy of the proposed analytical model is validated by Monte Carlo simulations.

Metameric MIMO-OOK transmission scheme using multiple RGB LEDs.

In this work, we propose a novel visible light communication (VLC) scheme utilizing multiple different red green and blue triplets each with a different emission spectrum of red, green and blue for mitigating the effect of interference due to different colors using spatial multiplexing. On-off keying modulation is considered and its effect on light emission in terms of flickering, dimming and color rendering is discussed so as to demonstrate how metameric properties have been considered. At the receiver, multiple photodiodes with color filter-tuned on each transmit light emitting diode (LED) are employed. Three different detection mechanisms of color zero forcing, minimum mean square error estimation and minimum mean square error equalization are then proposed. The system performance of the proposed scheme is evaluated both with computer simulations and tests with an Arduino board implementation.

The Uplink Visible Light Communication Beacon System for Universal Traffic Management

This paper presents a feasibility study of the uplink visible light communication (VLC) beacon system for the universal traffic management system (UTMS). The UTMS is a traffic management system beneath the National Police Agency of Japan. Currently, 55 000 UTMS infrared beacon systems have been installed, and they provide expressway and ordinary road information to cars. However, the data rate is 1 Mbps, and a faster data rate is necessary to support automotive and smart mobility devices. In this paper, we propose an uplink V2I system for the UTMS. The system is designed to match the current beacon system as closely as possible, so that the system can easily be replaced and still provide sufficient bandwidth for future automotive and smart mobility devices. We adopt a photo diode (PD) as the VLC receiver and a commercially available off-the-shelf LED headlight as a transmitter. Unfortunately, the bandwidth of such an LED is usually small, so we consider applying a bit-loading algorithm to direct-current-biased optical orthogonal frequency division multiplexing. To reduce strong background noise, such as from the sun, we narrow down the field-of-view by applying a lens to the PD, which forms a tiny communication area, smaller than the current infrared beacon system. We then consider multiple PDs with the lens to create a similar communication area as the infrared beacon system. As a result, we achieve 3.1-Mbps throughput.

Laser-Based Measurement of Gas–Liquid Two-Phase Flows in Micro and Mini Channels using Multiple Photodiode Arrangement

Two-phase flow measurement is important in process and chemical industries. In the present work, a measurement technique for the characterization of two-phase flows using a laser and an arrangement of the photodiodes is proposed and tested. Two-phase flow experiments were carried out in 1.80, 3.14, and 4.68-mm-diameter glass tubes. A high-speed camera was used to analyze the various optical patterns formed by a stationary laser beam on a screen during bubbly, slug, and stratified flows, which have been discussed in detail in Navisa et al. (2015). Photodiodes are arranged on the screen based on high-speed camera recordings. A procedure is demonstrated to calculate the flow regime velocity and length based on the photodiode outputs. The designed nonintrusive instrumentation determines the two-phase flow parameters in real time for flow in optically transparent mini channels. The accuracy of the measurement technique and the limitations are also discussed.

High-Q wavelength division multiplexed optoelectronic oscillator based on a cascaded multi-loop topology

A WDM optoelectronic oscillator (OEO) based on a cascaded optical multi-loop configuration and multiple photodiodes is proposed and demonstrated experimentally. By employing up to three lasers widely separated in wavelength along with two cascaded multi-loop fiber sections and two photodiodes, we demonstrate OEO topologies that scale up to six effective loops revealing an ultra-high quality factor in excess of 1010 and a phase noise performance down to −119dBc/Hz at 10kHz offset

Linear Precoding for Multiuser Visible-Light Communication With Field-of-View Diversity

The multiple-input–multiple-output (MIMO) indoor visible-light communication (VLC) system with multiple users, where several light-emitting diodes (LEDs) send messages to several photodiodes (PD), is studied. To enhance the diversity, each user is assumed to be equipped with multiple PDs with a different field of view. The objective is to minimize the LEDs' maximum power consumption subject to multiple constraints, including illumination constraint and capacity constraint. Under the assumption of maximum-ratio combining at the receivers, a linear precoding method is proposed. Detailed operation of this precoding method includes two steps: First, with matrix transformation and semi-definite relaxation, the original nonconvex optimization problem is transformed into solvable convex optimization subproblems. Afterward, based on the solution of the subproblems, it is proved that a linear precoding solution can be reformulated using a rank-1 decomposition theorem. Numerical results show that our proposed scheme with different system parameters outperforms the traditional method.

Study of an Optical Goniometer Using a Multi-Photodiode Sensor

The monitoring and measurement of the motion of a human joint is very important in screening for degenerative brain diseases and tracking the rehabilitation process. Since there are various medical fields to benefit from angular motion measurement, the necessity for monitoring of human joint movement is increasing. In this study, the optical sensor is composed of a light emission unit with a red LED and an optical fiber, and a reception unit with an arrangement of three photodiodes. The angular detection range was widened with the use of multiple photodiodes and the developed algorithm. The result will be useful for designing an effective angular sensor with low cost and small size.