Visible light positioning system based on a quadrant photodiode and encoding techniques

Visible light positioning systems (VLPSs) are a feasible alternative to local positioning systems due to the technology improvement and massive use of light-emitting diodes (LEDs). Compared to other technologies, VLPSs can provide significant advantages, such as the achieved accuracy, although they still present some issues, mainly related to the reduced coverage area or the high computational load. This article proposes the design of a VLPS based on four LED lamps as transmitters and a quadrant photodiode angular diversity aperture (QADA) as a receiver. As the shape of the QADA is circular and the aperture to be installed over it is square, we derive the corresponding general equations to obtain the currents through the different pads of the QADA, regarding the angle of incidence of the light (and, inversely, how to estimate the angle of incidence from the measured currents). An encoding scheme based on 1023-bit Kasami sequences is proposed for every transmission from the LED lamps, thus providing multiple access capability and robustness against low signal-to-noise ratios and harsh conditions, such as multipath and near-far effect. A triangulation technique has been applied to estimate the receiver's position, by means of the least-squares estimator (LSE), together with some geometrical considerations. The proposal has been validated by simulation and by experimental tests, obtaining 3-D positioning average errors below 13 and 5.5 cm for separations between the transmitters' plane and the receiver of 2 and 1 m, respectively

Estimation of the polar angle in a 3D infrared indoor positioning system based on a QADA receiver

2019 International Conference on Indoor Positioning and Indoor Navigation (IPIN), 30 September 2019 - 03 October 2019, Pisa, Italy.Three-dimension infrared positioning systems are a must on indoor local positioning systems, where those based on photodetectors are the most typically used in order not to have complex processing algorithms but a fast positioning computation. Most optical positioning systems are characterized by their low cost, low lifetime, and easy integration on the workplace. This work proposes an infrared positioning system based on four infrared LEDs and a QADA receiver. By applying encoding techniques to the infrared transmissions, the points of incidence from those transmitters on the QADA receiver are simultaneously obtained and the polar angle compensated, in order to finally estimate the receiver?s position. The geometrical considerations of the system have been derived, including the polar angle and its behaviour with regard to the receiver?s position, the angle of incidence and the aperture height. The proposal has been successfully validated by simulation and experimental tests, obtaining positioning errors below 10 cm.Ministerio de Economía y CompetitividadAgencia Estatal de Investigació

Experimental Evaluation of a Machine Learning-Based RSS Localization Method Using Gaussian Processes and a Quadrant Photodiode

The research interest on indoor Location-Based Services (LBS) has increased during the last years, especially using LED lighting, since they can deal with the dual functionality of lighting and localization with centimetric accuracy. There are several positioning approaches using lateration and angular methods. These methods typically rely on the physical model to deal with the multipath effect, environmental fluctuations, calibration of the optical setup, etc. A recent approach is the use of Machine Learning (ML) techniques. ML techniques provide accurate location estimates based on observed data without requiring the underlying physical model to be described. This work proposes an optical indoor local positioning system based on multiple LEDs and a quadrant photodiode plus an aperture. Different frequencies are used to allow the simultaneous emission of all transmitted signals and their processing at the receiver. For that purpose, two algorithms are developed. First, a triangulation algorithm based on Angle of Arrival (AoA) measurements, which uses the Received Signal Strength (RSS) values from every LED on each quadrant to determine the image points projected from each emitter on the receiver and, then, implements a Least Squares Estimator (LSE) and trigonometric considerations to estimate the receiver?s position. Secondly, the performance of a data-driven approach using Gaussian Processes is evaluated. The proposals have been experimentally validated in an area of 3 × 3m2 and a height of 1.3m (distance from transmitters to receiver). The experimental tests achieve p50 and p95 2D absolute errors below 9.38 cm and 21.94 cm for the AoA-based triangulation algorithm, and 3.62 cm and 16.65 cm for the Gaussian Processes.Agencia Estatal de Investigació

High-rate acquisition system for an infrared LPS

2023 38th Conference on Design of Circuits and Integrated Systems (DCIS), 15-17 November 2023, Málaga, Spain.In the last years, the demand for positioning systems based on visible light, infrared light or, in general, optical signals has increased considerably due to their high accuracy and low cost compared to positioning systems based on other technologies, as well as their ease of integration due to their wide presence in domestic and industrial environments. The main constraint of these solutions is that the high speed of light makes the acquisition process complex. This work proposes a complete acquisition architecture for the twelve signals coming from four QADA (Quadrature Angular Diversity Aperture) photoreceptors, based on an analog front-end for signal conditioning at the input, an analog-to-digital converter, and a final digital stage using an FPGA for the acquisition of the data coming from the converter with high data rates up to 16.25 Msps. To verify the system performance, LS (Loosely Synchronized) sequences, often used in positioning systems, are emitted by a LED, and, later, they are acquired and digitally processed successfully by the proposed architecture in some preliminary experimental tests.Agencia Estatal de InvestigaciónUniversidad de AlcaláJunta de Comunidades de Castilla-La ManchaEuropean Science Foundatio

Dynamic Adjustment of Measurement Noise Covariance Matrix in an Infrared-based Positioning and Tracking System

2022 IEEE 12th International Conference on Indoor Positioning and Indoor Navigation (IPIN), 5-8 September, 2022, Beijing, China.The accuracy of optical positioning systems can be compromised by multiple factors (reflections, calibration, etc.). As an alternative to the triangulation, multilateration, or fingerprinting techniques typically used in these systems, stochastic estimation techniques can be used, such as Kalman Filters (KF) in its different variants. They estimate the receiver position based on the acquired measurements and the estimated positions in previous iterations. This work presents the evaluation of a 3D optical positioning system, based on four LED beacons and a quadrant receiver, using an Extended Kalman Filter (EKF). The implementation of a measurement noise covariance matrix that is adjusted depending on the angle and distance between transmitters and receiver, obtained in the previous iteration, is analysed. The receiver position estimation using both a dynamic and a static measurement noise covariance matrix is evaluated and compared with simulations and experimental tests. In simulations, the achieved errors are below 6 cm and 12 cm in 75% of the cases when using a dynamic and a static noise matrix, respectively. In the experimental tests, the obtained errors in 75% of the cases for the position in plane XY and the rotation angle ? are smaller than 7.44 cm and 1.06 ? with a dynamic noise matrix; and below 7.59 cm and 1.62 ? for a static one.Agencia Estatal de InvestigaciónUniversidad de Alcal

Implementation of a High Measurement Rate VLP System

redOptical positioning systems have raised interest in recent years, due to the centimeter accuracy in three-dimension environments they are able to provide, thanks to the use of light emitting diodes (LED) and diode photoreceptors. This work is based on the design and implementation of the signal processing algorithms for an optical indoor positioning system. It is configured using some LED beacons placed at known positions and the corresponding receivers to be positioned moving in the coverage area. The definition and design of the hardware architecture for the processing associated to the receiver, for the case of a Quadrant Photodiode Angular Diversity Aperture (QADA) detector is proposed, analyzing different aspects involved in the final performance, such as the fixed-point notation used in the hardware definition. Furthermore, the implementation of the proposal includes an analog conditioning stage, an acquisition system, as well as a FPGA-based (Field-Programmable Gate Array) System-on-Chip (SoC) for implementing the necessary hardware and software elements, required to estimate the final position coordinates of the QADA receiver. In addition to the description of the positioning system and all its stages, some preliminary experimental tests are also shown, including position estimation for two specific locations, achieving the validation of a processing system associated with indoor positioning systems capable of handling high data rates (in the range of Msps)

Detecting relative amplitude of IR signals with active sensors and its application to a positioning system

Nowadays, there is an increasing interest in smart systems, e.g., smart metering or smart spaces, for which active sensing plays an important role. In such systems, the sample or environment to be measured is irradiated with a signal (acoustic, infrared, radio‐frequency…) and some of their features are determined from the transmitted or reflected part of the original signal. In this work, infrared (IR) signals are emitted from different sources (four in this case) and received by a unique quadrature angular diversity aperture (QADA) sensor. A code division multiple access (CDMA) technique is used to deal with the simultaneous transmission of all the signals and their separation (depending on the source) at the receiver’s processing stage. Furthermore, the use of correlation techniques allows the receiver to determine the amount of energy received from each transmitter, by quantifying the main correlation peaks. This technique can be used in any system requiring active sensing; in the particular case of the IR positioning system presented here, the relative amplitudes of those peaks are used to determine the central incidence point of the light from each emitter on the QADA. The proposal tackles the typical phenomena, such as distortions caused by the transducer impulse response, the near‐far effect in CDMA‐based systems, multipath transmissions, the correlation degradation from non‐coherent demodulations, etc. Finally, for each emitter, the angle of incidence on the QADA receiveris estimated, assuming that it is on a horizontal plane, although with any rotation on the vertical axis Z. With the estimated angles and the known positions of the LED emitters, the position (x, y, z) of the receiver is determined. The system is validated at different positions in a volume of 3 × 3 × 3.4 m3 obtaining average errors of 7.1, 5.4, and 47.3 cm in the X, Y and Z axes, respectively.Agencia Estatal de InvestigaciónUniversidad de AlcaláJunta de Comunidades de Castilla-La Manch

A Step-by-step Guide to the Realisation of Advanced Optical Tweezers

Since the pioneering work of Arthur Ashkin, optical tweezers have become an indispensable tool for contactless manipulation of micro- and nanoparticles. Nowadays optical tweezers are employed in a myriad of applications demonstrating the importance of these tools. While the basic principle of optical tweezers is the use of a strongly focused laser beam to trap and manipulate particles, ever more complex experimental set-ups are required in order to perform novel and challenging experiments. With this article, we provide a detailed step- by-step guide for the construction of advanced optical manipulation systems. First, we explain how to build a single-beam optical tweezers on a home-made microscope and how to calibrate it. Improving on this design, we realize a holographic optical tweezers, which can manipulate independently multiple particles and generate more sophisticated wavefronts such as Laguerre-Gaussian beams. Finally, we explain how to implement a speckle optical tweezers, which permit one to employ random speckle light fields for deterministic optical manipulation.Comment: 29 pages, 7 figure

3D Positioning system with optical sensors using encoding techniques

Esta tesis doctoral se centra en el desarrollo y la mejora de los Sistemas de Posicionamiento Locales (LPS) en interiores, los cuales se utilizan en entornos no compatibles con señales GNSS (Global Navigation Satellite Systems) para localizar, seguir y guiar a personas, objetos o vehículos. Se han realizado numerosos estudios para llevar a cabo un sistema de posicionamiento en entornos interiores, donde las personas pasan aproximadamente el 80% de su tiempo. Algunas de las técnicas propuestas emplean diversas señales, como acústicas, de radiofrecuencia, mecánicas u ópticas, entre otras. Por su bajo coste, facilidad de integración en el entorno de trabajo y ausencia de riesgos para la salud, la tecnología óptica es una alternativa viable que ha comenzado a expandirse rápidamente. Esta tesis aporta propuestas que permiten establecer las bases para el desarrollo de un LPS óptico basado en técnicas de codificación y sensores QADA. Se han propuesto dos diseños: un LPS orientado a la privacidad, basado en un conjunto de cuatro LEDs transmisores, aunque fácilmente extensible a más emisores, que actúan como balizas en ubicaciones conocidas y un único sensor QADA que actúa como el receptor a posicionar; y un LPS centralizado basado en un conjunto de transmisores móviles y al menos dos receptores QADA colocados en ubicaciones conocidas. Se han estudiado los módulos transmisor y receptor. En concreto, se propone un esquema de codificación para la emisión del transmisor, que proporciona capacidad de acceso múltiple, así como robustez frente a bajas relaciones señal a ruido y condiciones adversas como los efectos de multicamino y cerca-lejos. Además, para mejorar las prestaciones de la propuesta sin aumentar significativamente el tiempo de emisión, se han analizado diferentes secuencias y sus longitudes, como los códigos LS (Loosely Synchronized) o las secuencias pseudoaleatorias (Kasami). Por otro lado, el módulo receptor está compuesto por un sensor QADA, una apertura cuadrada y una etapa de filtrado para reducir las interferencias no deseadas. El sensor QADA y la apertura se han modelado para, en primer lugar, analizar la influencia de la longitud de la apertura en la linealidad de las ecuaciones de estimación del punto imagen y, en segundo lugar, determinar los parámetros intrínsecos que modelan el receptor (longitud, altura, desalineación y descentrado de la apertura respecto al sensor QADA), de forma que se pueda implementar un algoritmo de calibración para mejorar la precisión del sistema propuesto. El LPS tiene como objetivo estimar la posición 3D de un objeto estático o en movimiento. Para ello, se diseñan varios algoritmos basados en técnicas de triangulación con determinación de ángulos de llegada (AoA) y técnicas homograficas que resuelven el problema de la perspectiva de n puntos (PnP) del sistema pin-hole propuesto. Todas las propuestas han sido verificadas mediante simulaciones y pruebas experimentales en una gran variedad de situaciones: utilizando luz visible o infrarroja, secuencias LS o Kasami, diferentes longitudes de apertura, distintas distancias entre transmisores y receptores, diferentes algoritmos de posicionamiento y varias rotaciones del receptor. Finalmente, las pruebas experimentales han demostrado que es posible posicionar con errores de menos de 5 centímetros