Optical boundaries for LED-based indoor positioning system

Overlap of footprints of light emitting diodes (LEDs) increases the positioning accuracy of wearable LED indoor positioning systems (IPS) but such an approach assumes that the footprint boundaries are defined. In this work, we develop a mathematical model for defining the footprint boundaries of an LED in terms of a threshold angle instead of the conventional half or full angle. To show the effect of the threshold angle, we compare how overlaps and receiver tilts affect the performance of an LED-based IPS when the optical boundary is defined at the threshold angle and at the full angle. Using experimental measurements, simulations, and theoretical analysis, the effect of the defined threshold angle is estimated. The results show that the positional time when using the newly defined threshold angle is 12 times shorter than the time when the full angle is used. When the effect of tilt is considered, the threshold angle time is 22 times shorter than the full angle positioning time. Regarding accuracy, it is shown in this work that a positioning error as low as 230 mm can be obtained. Consequently, while the IPS gives a very low positioning error, a defined threshold angle reduces delays in an overlap-based LED IPS

Design, Calibration, and Evaluation of a Long-Range 3-D Infrared Positioning System Based on Encoding Techniques

Optical indoor positioning systems have experienced an increasing research interest during last years as they can provide 3D centimeter accuracy using LED lighting. In the case of having several LEDs emitting simultaneously and a receiver (e.g. the tag to be localized), these systems face important challenges, such as very high dynamic ranges with low Signal-to-Noise Ratios when the coverage area is increased, Multiple Access Interference (MAI), multipath and near-far effects, calibration issues (misalignments in the receiver and other intrinsic parameters), and so on. Previous work have already shown the feasibility of using LED emitters in combination with Quadrature Angular Diversity Aperture (QADA) receivers to implement positioning systems. This work further introduces new design considerations, tested on an experimental setup, to enlarge the emitter-receiver range, thus increasing the total coverage, while dealing with the aforementioned challenges. The system applies encoding techniques to each transmitter to solve the multiple access problem. The performance of two different types of codes has been compared, as well as their influence on the final estimation of the receiver?s position: one based on Kasami sequences and another based on Loosely Synchronous (LS) codes, derived from Complementary Sets of Sequences. At the receiver, the estimation of the incident point is constrained to angles at which the system can be linearized, and a specific calibration process for this type of sensor has also been defined and applied. The proposal has been finally validated with both, simulated and experimental results, in a large space of 2 2m2 (base), with a distance from transmitters to receiver of 3:4m (height). The experimental tests at distances up to 4 m, carried out after the calibration process, achieve average absolute errors bellow 10 cm for X and Y axis and around 20 cm for Z, and standard deviations below 4 cm for X and Y , and around 30 cm for Z.Agencia Estatal de InvestigaciónUniversidad de Alcal

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

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

An Assessment of Indoor Geolocation Systems

Currently there is a need to design, develop, and deploy autonomous and portable indoor geolocation systems to fulfil the needs of military, civilian, governmental and commercial customers where GPS and GLONASS signals are not available due to the limitations of both GPS and GLONASS signal structure designs. The goal of this dissertation is (1) to introduce geolocation systems; (2) to classify the state of the art geolocation systems; (3) to identify the issues with the state of the art indoor geolocation systems; and (4) to propose and assess four WPI indoor geolocation systems. It is assessed that the current GPS and GLONASS signal structures are inadequate to overcome two main design concerns; namely, (1) the near-far effect and (2) the multipath effect. We propose four WPI indoor geolocation systems as an alternative solution to near-far and multipath effects. The WPI indoor geolocation systems are (1) a DSSS/CDMA indoor geolocation system, (2) a DSSS/CDMA/FDMA indoor geolocation system, (3) a DSSS/OFDM/CDMA/FDMA indoor geolocation system, and (4) an OFDM/FDMA indoor geolocation system. Each system is researched, discussed, and analyzed based on its principle of operation, its transmitter, the indoor channel, and its receiver design and issues associated with obtaining an observable to achieve indoor navigation. Our assessment of these systems concludes the following. First, a DSSS/CDMA indoor geolocation system is inadequate to neither overcome the near-far effect not mitigate cross-channel interference due to the multipath. Second, a DSSS/CDMA/FDMA indoor geolocation system is a potential candidate for indoor positioning, with data rate up to 3.2 KBPS, pseudorange error, less than to 2 m and phase error less than 5 mm. Third, a DSSS/OFDM/CDMA/FDMA indoor geolocation system is a potential candidate to achieve similar or better navigation accuracy than a DSSS/CDMA indoor geolocation system and data rate up to 5 MBPS. Fourth, an OFDM/FDMA indoor geolocation system is another potential candidate with a totally different signal structure than the pervious three WPI indoor geolocation systems, but with similar pseudorange error performance

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

Fixed-point Processing for an IR Positioning System based on QADA Receivers

2022 IEEE 12th International Conference on Indoor Positioning and Indoor Navigation (IPIN), 5-8 September, 2022, Beijing, China.Indoor optical positioning systems have increased in popularity in recent years because they can provide centimeter accuracy in three dimensions (3D) utilizing light-emitting diodes (LEDs) and photoreceptors. This work presents the design of a positioning system, which is based on a set of four photoreceptors functioning as beacons at known places for a single LED to be positioned. However, it might be extended to additional emitters with some medium access control. The associated processing is explained, as well as the basic assumptions to be addressed when approaching its hardware implementation, such as the preliminary partitioning of tasks between hardware and software, and the fixed-point representation of the processing to be implemented in hardware. The system has been validated by simulation in a 2 × 2 × 3.4 m3 volume, yielding mean absolute errors around 0.004 m for the X and Y axes, and around 0.01 m for the Z-axis, as well as lower standard deviations than 0.004 m for the X and Y axes and 0.01 m for the Z-axis.Agencia Estatal de InvestigaciónUniversidad de Alcal

3D indoor positioning of UAVs with spread spectrum ultrasound and time-of-flight cameras

Este trabajo propone el uso de un sistema híbrido de posicionamiento acústico y óptico en interiores para el posicionamiento 3D preciso de los vehículos aéreos no tripulados (UAV). El módulo acústico de este sistema se basa en un esquema de Acceso Múltiple por División de Código de Tiempo (T-CDMA), en el que la emisión secuencial de cinco códigos ultrasónicos de espectro amplio se realiza para calcular la posición horizontal del vehículo siguiendo un procedimiento de multilateración 2D. El módulo óptico se basa en una cámara de Tiempo de Vuelo (TOF) que proporciona una estimación inicial de la altura del vehículo. A continuación se propone un algoritmo recursivo programado en un ordenador externo para refinar la posición estimada. Los resultados experimentales muestran que el sistema propuesto puede aumentar la precisión de un sistema exclusivamente acústico en un 70-80% en términos de error cuadrático medio de posicionamiento.This work proposes the use of a hybrid acoustic and optical indoor positioning system for the accurate 3D positioning of Unmanned Aerial Vehicles (UAVs). The acoustic module of this system is based on a Time-Code Division Multiple Access (T-CDMA) scheme, where the sequential emission of five spread spectrum ultrasonic codes is performed to compute the horizontal vehicle position following a 2D multilateration procedure. The optical module is based on a Time-Of-Flight (TOF) camera that provides an initial estimation for the vehicle height. A recursive algorithm programmed on an external computer is then proposed to refine the estimated position. Experimental results show that the proposed system can increase the accuracy of a solely acoustic system by 70–80% in terms of positioning mean square error.• Gobierno de España y Fondos para el Desarrollo Regional Europeo. Proyectos TARSIUS (TIN2015-71564-C4-4-R) (I+D+i), REPNIN (TEC2015-71426-REDT) y SOC-PLC (TEC2015-64835-C3-2-R) (I+D+i) • Junta de Extremadura, Fondos FEDER y Fondo Social Europeo. Proyecto GR15167 y beca predoctoral 45/2016 Exp. PD16030peerReviewe