Ultrasonic Positioning System Research Articles

A Method for Correcting Signal Aberrations in Ultrasonic Indoor Positioning.

The increasing focus on the development of positioning techniques reflects the growing interest in applications and services based on indoor positioning. Many applications necessitate precise indoor positioning or tracking of individuals and assets, leading to rapid growth in products based on these technologies in certain market sectors. Ultrasonic systems have already proven effective in achieving the desired positioning accuracy and refresh rates. The typical signal used in ultrasonic positioning systems for estimating the range between the target and reference points is the linear chirp. Unfortunately, it can undergo shape aberration due to the effects of acoustic diffraction when the aperture exceeds a certain limit. The extent of the aberration is influenced by the shape and size of the transducer, as well as the angle at which the transducer is observed by the receiver. This aberration also affects the shape of the cross-correlation, causing it to lose its easily detectable characteristic of a single global peak, which typically corresponds to the correct lag associated with the signal's time of arrival. In such instances, cross-correlation techniques yield results with a significantly higher error than anticipated. In fact, the correct lag no longer corresponds to the peak of the cross-correlation. In this study, an alternative technique to global peak detection is proposed, leveraging the inherent symmetry observed in the shape of the aberrated cross-correlation. The numerical simulations, performed using the academic acoustic simulation software Field II, conducted using a typical ultrasonic chirp and ultrasonic emitter, compare the classical and the proposed range techniques in a standard office room. The analysis includes the effects of acoustical reflection in the room and of the acoustic noise at different levels of power. The results demonstrate that the proposed technique enables accurate range estimation even in the presence of severe cross-correlation shape aberrations and for signal-to-noise ratio levels common in office and room environments, even in presence of typical reflections. This allows the use of emitting transducers with a much larger aperture than that allowed by the classical cross-correlation technique. Consequently, it becomes possible to have greater acoustic power available, leading to improved signal-to-noise ratio (SNR).

Optimization of Ultrasonic Positioning Accuracy by Hybrid Algorithm of Time Compensation Factor and Kalman Filter

In the ultrasonic positioning system, the positioning system has a certain delay due to the sequential ranging at the ultrasonic receiver, the system's decoding time and the signal transmission time, which has a great impact on the positioning accuracy. The solution is to set a time compensation factor for the speed of the object to be positioned and the positioning time of the system unit to compensate for the error, so as to achieve the same positioning accuracy when the object to be positioned is stationary; then the Kalman filter algorithm is used to correct the positioning results at different speeds, so that the positioning accuracy of the ultrasonic positioning system can be further improved. The simulation results show that the positioning accuracy can be stabilized within 2cm at a certain speed, which is able to move and position the object to be positioned at a certain speed; finally, the experiments are conducted using the Arduino Uno as the core positioning system, and the experimental results verify the simulation results and show that the solution can The experimental results verify the simulation results and show that the solution is able to improve the positioning accuracy of moving objects, especially when the object to be positioned moves at a constant speed, the positioning accuracy tends to be stable, and the object to be positioned with a certain speed can be positioned well.

Fusing of a Continuous Output PDR Algorithm With an Ultrasonic Positioning System

The availability of inertial navigation sensors in smartphones has facilitated the development of pedestrian dead reckoning (PDR) models on a large scale. These models often consist of a step detection algorithm combined with a heading estimation routine. Common approaches to step detection include searching for peaks/valleys in the acceleration signal, principle frequency estimation, and machine learning techniques. Since the sensors embedded in smart devices are prone to noise, the position error grows unbounded if unchecked and requires periodical corrections based on external measurements. In this work, we propose a novel step detection algorithm based on sine-wave approximation of the acceleration signal. This method detects step fractions as well as full steps, which allows for continuous and real-time updates. The step detection algorithm is combined with a heading estimation routine described in our previous work to obtain a stand-alone PDR model. To mitigate error accumulation, we fuse the proposed model with position and heading measurements provided by a commercial indoor positioning system based on ultrasound. We evaluate the performance of the PDR and fused model in an open office environment, by walking along a trajectory while carrying a smartphone in hand or in the pocket. The results demonstrate the feasibility of the sine-wave approximation approach to step detection, as well as the expected benefits of fusing PDR with the ultrasonic system.

Comparison of Objectives in Multiobjective Optimization of Ultrasonic Positioning Anchor Placement

The position of anchors in an ultrasonic positioning system has a significant impact on the performance of that system. This impact on performance can be in the form of positioning error, how large of a space the system can cover, and then number of anchors required. A comparison of three different performance metrics for anchor position optimization in ultrasonic localization systems is presented. These metrics are geometric dilution of precision (GDOP), weighted GDOP (WGDOP), and simulated localization error (SLE). Each of these performance metrics is used as an objective in a multi-objective genetic algorithm. The optimal solutions found by the genetic algorithm were processed by a simulation that used a simulated received time series to localize the target position allowing a direct comparison of the three performance metrics. While the performance difference between all three metrics was small, it was found that solutions generated using WGDOP as a metric of performance outperformed those generated using the GDOP and the SLE objectives.

Indoor ultrasonic positioning system for mobile objects

At present, automation of many types of works is widely distributed. When solving the automation problem, it is often necessary to use methods for determining the position of individual parts of an industrial or other system, as well as controlling the moving elements of such a system. In the paper, one of the variants of solving such a problem is considered. The determination of the object coordinates is calculating from the computed distances to known points. There are several ways to implement this method. Authors offer a solution that provides real-time control of the mobile device, automatic location control and delivery of the moving part of the system to a specified point with high accuracy. The system provides scalability for solving the problem of positioning in various rooms.

Simulating Signal Aberration and Ranging Error for Ultrasonic Indoor Positioning.

Increasing efforts toward the development of positioning techniques testify the growing interest for indoor position-based applications and services. Many applications require accurate indoor positioning or tracking of people and assets, and some market sectors are starting a rapid growth of products based on these technologies. Ultrasonic systems have already been demonstrating their effectiveness and to possess the desired positioning accuracy and refresh rates. In this work, it is shown that a typical signal used in ultrasonic positioning systems to estimate the range between the target and reference points—namely, the linear chirp—due to the effects of acoustic diffraction, in some cases, undergoes a shape aberration, depending on the shape and size of the transducer and on the angle under which the transducer is seen by the receiver. In the presence of such signal shape aberrations, even one of the most robust ranging techniques, which is based on cross-correlation, provides results affected by a much greater error than expected. Numerical simulations are carried out for a typical ultrasonic chirp, ultrasonic emitter, and range technique based on cross-correlation and for a typical office room, obtained using the academic acoustic simulation software Field II. Spatial distributions of the ranging error are provided, clearly showing the favorable low error regions. The work demonstrates that particular attention must be paid to the design of the acoustic section of the ultrasonic positioning systems, considering both the shape and size of the ultrasonic emitters and the shape of the acoustic signal used.

Improved Obstacle Mitigation and Localization Accuracy in Narrowband Ultrasonic Localization Systems Using RoBCUL Algorithm

This article develops a method for mitigating the negative effects of obstacles in narrowband, time-division multiple access (TDMA), ultrasonic localization systems. The method builds upon the robust Bayesian classifier for ultrasonic localization (RoBCUL) algorithm that utilizes an iteratively reweighted least-squares (IRLS) scheme. This algorithm has the advantage of low computational cost but loses performance in the presence of obstacles. The improved version of the RoBCUL algorithm presented in this article uses a statistical test applied after each iteration of the regression, using a weighted-residual vector calculated from the weight matrix and residual vector. The technique was tested using experimental data with its performance being quantified by its ability to correctly classify all the signals received during a single TDMA cycle. The extended version performed significantly better in all obstacle scenarios than the original, correctly classifying 100% of TDMA cycles in the scenarios with no obstacles, 99.9% with one obstacle, and 98.7% with two obstacles.

Revitalizing Ultrasonic Positioning Systems for Ultrasound-Incapable Smart Devices

An ultrasonic positioning system (UPS) has demonstrated its high accuracy for years. However, few of the developed solutions have been deployed in practice to satisfy the localization demand of today’s smart devices, which lack ultrasonic sensors and were considered as being “deaf” to ultrasound. A recent finding demonstrates that ultrasound may be audible to the smart devices under certain conditions due to their microphone’s nonlinearity. Inspired by this insight, this work revisits the ultrasonic positioning technique and builds a practical UPS, called UPS+, for ultrasound-incapable smart devices. The core concept is to deploy two types of indoor beacon devices, which will advertise ultrasonic beacons at two different ultrasonic frequencies respectively. Their superimposed beacons are downconverted to a low-frequency by exploiting the nonlinearity effect at the receiver’s microphone. This underlying property functions as an implicit ultrasonic downconverter without inflicting harm to the hearing system of humans. We demonstrate UPS+, a fully functional UPS prototype, with centimeter-level localization accuracy using custom-made beacon hardware and well-designed algorithms.

Quasi-Spherical PVDF Ultrasonic Transducer With Double-Cylindrical PVDF Structure

In this paper, a quasi-spherical PVDF airborne ultrasonic transducer for three-dimensional (3D) ultrasonic location systems is designed and fabricated using two strips of cylindrical PVDF film. The 3D solid model of the transducer was created and the acoustic directivity pattern of the transducer was simulated using the finite-element method and the COMSOL Multiphysics™ software. Measurements of the frequency response, pulse response and beam directivity performance are presented. The measurement and simulation results show that the proposed transducer has a spherical beam pattern, and its resonant frequency is consistent with that of the cylindrical PVDF transducers. Because of its spherical beam pattern, it is very suitable for 3D ultrasonic location systems as a transducer to achieve wide coverage.

Locating Ultrasonic Signals Employing MEMS-On-Fiber Sensors.

Sound sensing finds wide applications in various fields, such as underwater detection, structural health monitoring, and medical diagnosis, to name just a few. Based on our previously developed MEMS-on-fiber sensors, showing the advantages of low cost, small volume, and high performance, a three-dimensional ultrasonic localization system employing four such sensors was established in this work. A time difference of arrival (TDOA) algorithm was utilized to analyze the acquired data and then calculate the accurate position of the ultrasonic signal source. Plenty of practical measurements were performed, and the derived localization deviation in the region of 2 m × 2 m × 1 m was about 2–5 mm. Outside this region, the deviation tended to increase due to the directional sensitivity existing in these sensors. As a result, for a more accurate localization requirement, more sensing probes are needed in order to depict a completely suitable application situation for MEMS technology.

A Narrowband Ultrasonic Ranging Method for Multiple Moving Sensor Nodes

Accurate ranging using narrow-band ultrasonic transducers in small-scale environments can be used for indoor localization, human motion capture, and robotic navigation. One of the main problems faced by the ultrasonic localization systems is the ranging error due to the Doppler shift. Existing methods for Doppler correction employ a bank of matched filters at the receiver end which is computationally intense and complex. On the other hand, enabling multiple access for the ultrasonic localization systems is a challenging task due to multiple access interference. We propose a method to measure the range between multiple ultrasonic mobile nodes and static anchors in which we track the Doppler velocity and correct the errors between the transmitted and the received signals due to the Doppler effect. We utilize range-Doppler coupling to estimate the Doppler shift and adjust the range values calculated by correlation. In our method, a unique set of two chirp signals are used for each transmitter to get one sample reading. The simulation results show high ranging accuracy and robustness using the proposed method as the Doppler velocity increases. A pendulum experiment was conducted to validate the method using narrowband ultrasonic sensors. The multiple access interference problem was tackled by orthogonal coding, the chirp signals and Doppler correction. An improvement in the ranging accuracy was observed over traditional methods using chirp signals without Doppler correction.

Semicool Temperature Compensation Algorithm Based on the Double Exponential Model in the Ultrasonic Positioning System

This paper proposes a semicool temperature compensation algorithm based on the double exponential model of the transient temperature rise curve to improve the performance of the 3-D ultrasonic positioning system. The error model of the 3-D ultrasonic positioning system is derived and the importance of temperature to the positioning accuracy is demonstrated. Then, the double exponential model of the transient temperature rise curve derived by the difference principle is established through a dynamic system identification method. On this basis, the semicool temperature compensation algorithm is proposed, which includes the estimation of the initial time $t_{0}$ , the principle of the choice of parameter $k$ . The effectiveness of the algorithm is verified by temperature measurement experiments. The impact of the ambient temperature on the algorithm is also analyzed qualitatively. In the end, the semicool temperature compensation algorithm is proved to be able to improve the performance of the 3-D ultrasonic positioning system by the comparison experiments respectively under static measurement of a fixed point and dynamic measurement of a fixed line.

A review of techniques for ultrasonic indoor localization systems

Accurate localization in indoor environments is crucial for the correct operation of location-aware and augmented reality applications, indoor navigation, and inventory management, among others. Magnetic, radiofrequency and inertial navigation systems typically provide room or meter-level accuracy. Despite being the most widely used, they are affected by error drifts or changes in the environment where they operate, and their accuracy is a drawback for certain applications, such as navigation. Optical-based systems provide better accuracy, but they can be expensive, and they are not privacy-oriented. Ultrasonic positioning systems can also give room-level accuracy, as acoustic propagation is contained within the room walls, helping resolve room or floor-level ambiguities of radio systems. They can even achieve centimeter-level accuracy and ensure privacy, while being low cost. These properties highlight acoustics as a versatile technology for different indoor localization applications, as stated by the research published almost over the last three decades. In this work, the operating principles of the different techniques employed by acoustic positioning systems are reviewed, covering narrowband and wideband systems (including the differences between coded and uncoded transmissions), fingerprinting, and the most recent systems based on machine learning.

A Robust Algorithm for Classification and Rejection of NLOS Signals in Narrowband Ultrasonic Localization Systems

This paper develops a novel algorithm for classifying and rejecting non-line-of-sight ultrasonic signals for use in indoor positioning and measurement systems. The algorithm consists of two parts, an initial probability estimate based upon signal amplitude followed by an iteratively reweighed least squares regression that utilizes the probabilities in the weight update step. This method allows for reflections to be identified and rejected while simultaneously calculating the position of a receiving node. The algorithm has been tested on a data collected during experiments designed to generate many challenging specular reflections. The experiments were conducted with transducers in a variety of different positions, and amplitude-modulated ultrasonic signals were used with four different envelopes. The algorithm was capable of correctly classifying over 96% of narrowband signals with severe multipath effect at low computational cost.

Application of Optimized Ultrasonic Localization System for Radial Artery Puncture by Intern Doctors: A Randomized Trial.

BackgroundUltrasound with developing line may by suitable for medical personnel who are inexperienced in the use of ultrasound-guided radial artery puncture. In this trial, we assessed whether this technology could increase the success rate of radial artery puncture performed by interns.Material/MethodsSeventy-seven patients undergoing general anesthesia were enrolled and randomly divided into 2 groups: an ultrasound with developing line group and a traditional ultrasound group. All radial artery punctures were performed by interns who received theoretical explanation (including video demonstration of puncture) and on-site guidance puncture once. The primary end-point was the success rate of cannulation at the first attempt and the secondary end-point was cannulation failure rate.ResultsThe success rate of cannulation at the first attempt in ultrasound in the developing line group was significantly higher than that in the traditional ultrasound group (proportion difference: 34.21%, 95% confidence interval [CI], −0.5483 to −0.1334; P=0.0025). However, no significant between-group difference was observed with respect to failure rate (mean difference 95% CI, (−0.0084 to 0.2743; P=0.0866). The ultrasonic location time in the ultrasound with developing line group was significantly lower than that in the traditional ultrasound group (mean difference −12.4 seconds, 95% CI, 10.64 to 13.98 s; P<0.0000).ConclusionsUse of ultrasound with developing line significantly improved the success rate of radial artery puncture performed by interns as compared to that with use of traditional dynamic ultrasound guidance technology.

Calibration of Beacons for Indoor Environments based on a Digital Map and Heuristic Information

This paper proposes an algorithm for calibrating the position of beacons which are placed on the ceiling of an indoor environment. In this context, the term calibration is used to estimate the position coordinates of a beacon related to a known reference system in a map. The positions of a set of beacons are used for indoor positioning purposes. The operation of the beacons can be based on different technologies such as radiofrequency (RF), infrared (IR) or ultrasound (US), among others. In this case we are interested in the positions of several beacons that compose an Ultrasonic Local Positioning System (ULPS) placed on different strategic points of the building. The calibration proposal uses several distances from a beacon to the neighbor walls measured by a laser meter. These measured distances, the map of the building in a vector format and other heuristic data (such as the region in which the beacon is located, the approximate orientation of the distance measurements to the walls and the equations in the map coordinate system of the line defining these walls) are the inputs of the proposed algorithm. The output is the best estimation of the position of the beacon. The process is repeated for all the beacons. To find the best estimation of the position of the beacons we have implemented a numerical minimization based on the use of a Genetic Algorithm (GA) and a Harmony Search (HS) methods. The proposal has been validated with simulations and real experiments, obtaining the positions of the beacons and an estimation of the error associated that depends on which walls (and the angle of incidence of the laser) are selected to make the distance measurements.

Ultrasonic positioning system for the calibration of central detector

A thorough detector response calibration using radioactive sources is necessary for the Jiangmen Underground Neutrino Observatory. Herein, we discuss the design of a source positioning system based on ultrasonic technology, aiming for a 3-cm precision over the entire 35-m diameter detector sphere. A prototype system is constructed and demonstrated for the experiment.

Ultrasonic localization method based on receiver array optimization schemes

Ultrasonic localization system using trilateration has been adopted in various types of full-enclosed and semi-enclosed space. For small-scale or enclosed scenarios, there is an important phenomenon, that is, the ultrasonic wave may rapidly reflect back and forth between the walls to form different normal waves during the process of propagation, which may break the inverse square law of sound intensity (the sound intensity in free space is inversely proportional to the square of the distance). The other problem is that the sound intensity of some local corner points are obviously stronger than those points near the acoustic source, which may confuse the ultrasonic receivers and bring significant differences in measurement errors. To avoid excessive errors influence for the positioning accuracy, in this article, a novel ultrasonic localization method based on receiver array optimization schemes is reported. The main purpose is to activate the ultrasonic receiver in the area as well as shield the ultrasonic receiver outside the area. The system error will be reduced based on this method, and most of the redundant data will be eliminated. The simulation results are visualized and compared with the existing methods. The positioning accuracy measured by our method is increased significantly.

An Indoor Ultrasonic Positioning System with Fast TOA Approach in Distance Space

An Indoor Ultrasonic Positioning System with Fast TOA Approach in Distance Space

Design of Chirp Waveforms for Multiple-Access Ultrasonic Indoor Positioning

In ultrasonic positioning systems (UPSs) chirp waveforms have attracted much attention due to its high range resolution. However, the multiple-access schemes for the chirp-based UPS are limited. In its application to multiple-access ultrasonic positioning, effective waveform diversity design is a prerequisite. In a multiple-access UPS, each transmitter should transmit a unique waveform with impulse-like auto-correlation and relatively flat cross-correlations to the waveforms transmitted by other transmitters. Proposed in this paper is a methodology whereby multiple transmitters can transmit chirp signals simultaneously. The chirp waveforms are constructed by concatenating a number of linear sub-chirps of the same durations and bandwidths but different starting and stopping frequencies. This process is optimized by selecting sequences with impulse-like auto-correlations and relatively flat cross-correlations. First, the efficiency of the proposed methodology is evaluated by several metrics and, then, in an indoor environment, through simulations and experiments for ultrasonic positioning.