Static and dynamic evaluations of acoustic positioning system using TDMA and FDMA for robots operating in a greenhouse

Acoustic positioning system has great potential to be applied in a greenhouse due to its centimeter-level accuracy, low cost, and ability of extensive greenhouse coverage. Spread Spectrum Sound-based local positioning system (SSSLPS) was proposed to be a navigation tool for multiple agricultural robots by the authors' research team. However, to increase the system capacity for positioning multiple robots in a greenhouse, the near-far problem caused by the interference between speakers needs to be overcome. The use of different access methods, Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA), is essential in the SSSLPS system for solving the near-far problem. The static positioning in a greenhouse was first evaluated by setting different parameters to determine the optimal signal setting for a dynamic experiment. From that, the moving robot tests were added with a motion capture system and tested the performance of TDMA and FDMA. The results demonstrated that TDMA can be used in a stationary sound-based positioning system with 12.2 mm accuracy, but it has a time delay problem in dynamic positioning. A simulation was designed to mimic the position error increases with different moving speeds. Although FDMA has the sound damping problem in high-frequency regions creating a peak detection issue, it achieved a higher accuracy with an average position error of 62.1 mm compared to 180.3 mm of TDMA. This study shows that the TDMA method is suitable for static measurements, while the FDMA method is suitable for measuring dynamic objects and controlling mobile robots

A survey on acoustic positioning systems for location-based services

Positioning systems have become increasingly popular in the last decade for location-based services, such as navigation, and asset tracking and management. As opposed to outdoor positioning, where the global navigation satellite system became the standard technology, there is no consensus yet for indoor environments despite the availability of different technologies, such as radio frequency, magnetic field, visual light communications, or acoustics. Within these options, acoustics emerged as a promising alternative to obtain high-accuracy low-cost systems. Nevertheless, acoustic signals have to face very demanding propagation conditions, particularly in terms of multipath and Doppler effect. Therefore, even if many acoustic positioning systems have been proposed in the last decades, it remains an active and challenging topic. This article surveys the developed prototypes and commercial systems that have been presented since they first appeared around the 1980s to 2022. We classify these systems into different groups depending on the observable that they use to calculate the user position, such as the time-of-flight, the received signal strength, or the acoustic spectrum. Furthermore, we summarize the main properties of these systems in terms of accuracy, coverage area, and update rate, among others. Finally, we evaluate the limitations of these groups based on the link budget approach, which gives an overview of the system's coverage from parameters such as source and noise level, detection threshold, attenuation, and processing gain.Agencia Estatal de InvestigaciónResearch Council of Norwa

Positioning aquatic animals with acoustic transmitters

Geolocating aquatic animals with acoustic tags has been ongoing for decades, relying on the detection of acoustic signals at multiple receivers with known positions to calculate a 2D or 3D position, and ultimately recreate the path of an aquatic animal from detections at fixed stations.This method of underwater geolocation is evolving with new software and hardware options available to help investigators design studies and calculate positions using solvers based predominantly on time-difference-of-arrival and time-of-arrival.We provide an overview of the considerations necessary to implement positioning in aquatic acoustic telemetry studies, including how to design arrays of receivers, test performance, synchronize receiver clocks and calculate positions from the detection data. We additionally present some common positioning algorithms, including both the free open-source solvers and the 'black-box' methods provided by some manufacturers for calculating positions.This paper is the first to provide a comprehensive overview of methods and considerations for designing and implementing better positioning studies that will support users, and encourage further knowledge advances in aquatic systems

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

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

잔향 환경에서의 인공 음향 신호를 이용한 음향 센서 위치 추정 기술

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 김남수.Widespread use of smart devices has brought a growth of user-customized services. In particular, localization techniques have been gaining attention due to increase of location-based services (LBS). Most of LBS services such as navigation systems, traffic alerts or augmented reality (AR) services depend on the GPS for its accuracy and speed, however, its operation is limited to the outdoor environments. The demand of indoor LBS is rapidly growing due to the growth of automated home and IoT technology. There have been studies via WiFi, Bluetooth or RFID, but their performance has been unsatisfactory for their limitation such as the requirement of additional equipment or guarantee of the line of sight. Among various sensors used for indoor localization, we focus on the acoustic sensors, i.e. microphones. There are several advantages in using the acoustic signals for indoor localization. There is no need for additional apparatus since loudspeakers are pre-installed in most of the buildings for the purpose of announcement or playing background music and mobile devices such as cellphones or tablets are equipped with microphones and loudspeakers. Even the prevailing popularity of IoT services helps accessibility of acoustical sensors and loudspeakers. In addition, acoustic signals have advantages of being able to detect signals through obstacles unlike cameras of RFID. In this thesis, we propose a position estimation system using acoustic signals to maximize these advantages. We aim to estimate the position of the target user with an acoustic sensor based on the recording of signals from the fixed loudspeakers installed around the room. We target to estimate the position of the acoustic sensor with high accuracy and low-complexity in a large space with high reverberation. Particularly, we try not to affect human hearing by using inaudible frequency bands. In order to estimate the position, it is important to estimate the direct path signal rather than the signal due to reverberation or reflection. To do this, we present various localization techniques as following. First, we propose the source data structure to operate in the large reverberant environments. In the large space, the consideration of the near-far effect is required which refers to a situation when the desired signal is far away, it is difficult to receive the desired signal due to the interference of closer unwanted signals. In wireless communications, it can be dealt with by interaction of transmitter and receiver by feedback of channel information. However, it is difficult in the acoustic system since there is no feedback between the transmitter and receiver. We borrowed the structure called OFDMA-CDM and modified it to deal with the near-far effect. In the reverberant environment, the amplitude of reverberation is often larger than the direct path signal. We proposed the technique to estimate the direct path signal. Second, we propose a method for accurate location estimation in the highly reverberant environments. In the high reverberation condition, more spurious reflections occur, which makes it difficult to estimate the time delay of the direct path signal. If the time delay estimation is wrong, it is likely that the position estimate does not converge by an estimation method. In the proposed method, position candidates are obtained from most of the received signals including signals even from spurious reflections. The unreliable candidates are filtered out by the agreement test and rank the rest candidates by their reliability to find accurate target position. We can estimate the receiver's position even in the condition of attenuated direct path signal or high reverberation by using the proposed method. Third, we proposed a low-complexity localization method to work in the highly reverberant environment. This method is based on the particle filter that estimates the position by weighted particles whose weights are computed by the likelihood. We designed likelihood function that efficiently calculates likelihood in the region with the direct path signal so that more reliable position can be obtained. The proposed method enables location estimation with high precision with a relatively small amount of computation in severe reverberation. The proposed methods are evaluated in simulated environments with different reverberation time. The performances are verified in different parameters and compared with other localization methods. In addition, the performance is evaluated in the real reverberant environment with a large space. A series of experiments has shown the superiority of the proposed methods and it is appropriate to apply in the actual environment.1 Introduction 1 2 Acoustic Receiver Localization System 7 2.1 Source data structure 8 2.2 Localization from the received signal 12 2.3 TDE in reverberant environments 16 2.4 Near-far effect 18 3 Indoor Localization using Inaudible Acoustic Signals 21 3.1 Introduction 21 3.2 Acoustic source design and synchronization 22 3.2.1 Reverberation in multipath environments 23 3.2.2 Source data structure for ARL 23 3.2.3 Signal presence detection 30 3.2.4 Direct path detection 30 3.3 Performance evaluation 32 3.3.1 Experimental setup and system configuration 33 3.3.2 Evaluation of acoustic data structure 34 3.3.3 Performance of the direct path detection algorithm 36 3.3.4 Performance in a real room 36 3.4 Summary 38 4 Robust Time Delay Estimation for Acoustic Indoor Localization in Reverberant Environments 39 4.1 Introduction 39 4.2 Robust TDE 40 4.3 Performance evaluation 45 4.3.1 Performance evaluation in a real room 46 4.3.2 Performance evaluation in simulated reverberant conditions 47 4.4 Summary 50 5 Indoor Localization Based on Particle Filtering 53 5.1 Introduction 53 5.2 A framework of positioning method using particle filter 54 5.2.1 State and dynamic models 55 5.2.2 Bayesian framework using particle filter 56 5.2.3 Likelihood function 57 5.3 ARL in reverberant environment 59 5.3.1 Peak quality 59 5.3.2 Efficient calculation of the likelihood function 60 5.3.3 Finding the direct path region 61 5.4 Performance evaluation 64 5.4.1 Performance in a simulated environment 65 5.4.2 Performance in the actual environment 87 5.5 Summary 89 6 Conclusions 91 Bibliography 95 요약 105Docto

A Robust High-Accuracy Ultrasound Indoor Positioning System Based on a Wireless Sensor Network

This paper describes the development and implementation of a robust high-accuracy ultrasonic indoor positioning system (UIPS). The UIPS consists of several wireless ultrasonic beacons in the indoor environment. Each of them has a fixed and known position coordinate and can collect all the transmissions from the target node or emit ultrasonic signals. Every wireless sensor network (WSN) node has two communication modules: one is WiFi, that transmits the data to the server, and the other is the radio frequency (RF) module, which is only used for time synchronization between different nodes, with accuracy up to 1 μs. The distance between the beacon and the target node is calculated by measuring the time-of-flight (TOF) for the ultrasonic signal, and then the position of the target is computed by some distances and the coordinate of the beacons. TOF estimation is the most important technique in the UIPS. A new time domain method to extract the envelope of the ultrasonic signals is presented in order to estimate the TOF. This method, with the envelope detection filter, estimates the value with the sampled values on both sides based on the least squares method (LSM). The simulation results show that the method can achieve envelope detection with a good filtering effect by means of the LSM. The highest precision and variance can reach 0.61 mm and 0.23 mm, respectively, in pseudo-range measurements with UIPS. A maximum location error of 10.2 mm is achieved in the positioning experiments for a moving robot, when UIPS works on the line-of-sight (LOS) signal