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

Testing solar panels for small-size satellites: the UPMSAT-2 mission

At present, the development of small-size satellites by universities, companies and research institutions have become a usual practice, which is spread rapidly. In this kind of projects the cost play a significant role. One of the main points are the Assembly, Integration and Test (AIT) plans, which carries out an associated cost for simulating the environmental conditions. For instance, in the power subsystems test and, in particular in the solar panels testing, the irradiance and temperature conditions might be the optimum so the performances of the system are next to real operational conditions.
 To reproduce the environmental conditions in terms of irradiance, solar simulators are usually used, which carries an associated increase of cost for testing equipments. The aim of this paper is to present an alternative and unexpenssive way to perform the AIT plans on spacecraft power subsystems, from a testing campaign performed using outdoor clean-sky conditions and an isolation system to protect the panels. A post-process of the measured data is therefore needed, taking into account the conditions in which the test has been accomplished. The I-V characteristics obtained are compared with a theorical 1-diode/2-resistor equivalent electric circuit, achieving enough precision based solely in the manufacturer data

Combined infrared-ultrasonic positioning system to improve the data availability

Many indoor positioning applications related to accurate monitoring and tracking targets require centimeter precision. Infrared (IR)- and ultrasound (US)-based systems represent a feasible approach providing high robustness against interference. Furthermore, their combination may achieve better performance by mitigating their complementary drawbacks, covering larger areas, and improving the availability of positioning measurements. In this context, this work presents the proposal and experimental evaluation of a tightly coupled fusion method that uses an extended Kalman filter (EKF) to merge an IR- and a US-based positioning system. An outlier detection method is considered to select measurements with an adequate performance. Experimental results reveal that the IR and US systems are unable to position in 4.08% and 26.06% of locations, whereas the combined IR -US system has 100% of availability. In addition, the merged solution achieves less than 4 cm of positioning error in 90% of cases, outperforming the IR and US systems when they work independently

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

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

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

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

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

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)

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