Simulating Signal Aberration and Ranging Error for Ultrasonic Indoor Positioning

Abstract

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.

Advanced Sensors and Systems Technologies for Indoor Positioning

“…In [ 10 ], the use of software Field II is proposed to simulate signal aberration and ranging error in ultrasonic indoor positioning applications. Ultrasonic systems have already been demonstrating their effectiveness in achieving high positioning accuracy and refresh rates, but attention must be paid to certain aspects of signal propagation.…”

Comparison of Direct Intersection and Sonogram Methods for Acoustic Indoor Localization of Persons

“…This array records the incoming echo wave with different time of arrival, depending on the incoming signal direction. Since unsuitable hardware can affect the system’s performance [ 53 ], both the microphones and speaker were tested for correct signal generation and reception in an anechoic box.…”

Ranging with Frequency Dependent Ultrasound Air Attenuation

“…The received signal r by the sensor at point P ( d , θ , φ ) (see Figure 1 ) first undergoes geometric attenuation, which depends point-by-point on the emission diagram of the emitter: where represents the radiation diagram of the emitter including the effect of geometric attenuation. Due to the presence of energy absorption in the propagation medium, an exponential term must be considered in addition [ 26 ], included in the following equation: where is the amplitude of the received sinusoidal signal r and α is the attenuation coefficient, the latter assumed constant throughout the space of interest for all the time necessary for completion of ranging operations. This is an acceptable assumption when considering an air-conditioned home or office without particularly humid or dry areas.…”

“…Moreover, it is worth noting that it is not possible to find the emitter–receiver distance by using only one emitter–receiver pair without having any kind of synchronization. From what has been described, it therefore can be seen that to obtain a reliable distance measurement it is necessary to use a technique that requires shaped signals and a significant computational resource to calculate their cross-correlation [ 26 ]. Inevitably, from the realization point of view, this translates into a sensor equipped with a processor capable of performing the cross-correlation at three or four times the positioning rate, since three or four distances are needed to calculate the positioning.…”