Carotenuto Riccardo, Iero Demetrio, Merenda Massimo
Department of Information Engineering, Infrastructure and Energy Sustainable (DIIES), Mediterranea University of Reggio Calabria, 89124 Reggio Calabria, Italy.
HWA srl, Spin-off Mediterranea University of Reggio Calabria, Via R. Campi II tr. 135, 89126 Reggio Calabria, Italy.
Sensors (Basel). 2024 Mar 21;24(6):2017. doi: 10.3390/s24062017.
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).
对定位技术发展的日益关注反映出人们对基于室内定位的应用和服务越来越感兴趣。许多应用需要精确的室内定位或对人员及资产进行跟踪，这导致基于这些技术的产品在某些市场领域迅速增长。超声波系统已被证明在实现所需的定位精度和刷新率方面是有效的。用于估计目标与参考点之间距离的超声波定位系统中使用的典型信号是线性调频脉冲。不幸的是，当孔径超过一定限度时，由于声衍射的影响，它会发生形状畸变。畸变的程度受换能器的形状和尺寸以及接收器观察换能器的角度影响。这种畸变还会影响互相关的形状，使其失去易于检测的单个全局峰值的特征，该峰值通常对应于与信号到达时间相关的正确延迟。在这种情况下，互相关技术产生的结果误差比预期的要高得多。实际上，正确的延迟不再对应于互相关的峰值。在本研究中，提出了一种替代全局峰值检测的技术，利用在畸变互相关形状中观察到的固有对称性。使用学术声学模拟软件Field II进行的数值模拟，采用典型的超声波调频脉冲和超声发射器，在标准办公室房间中比较了经典测距技术和所提出的测距技术。分析包括房间内声反射的影响以及不同功率水平下的声学噪声的影响。结果表明，即使存在严重的互相关形状畸变以及办公室和房间环境中常见的信噪比水平，甚至存在典型反射时，所提出的技术也能实现准确的距离估计。这允许使用比经典互相关技术允许的孔径大得多的发射换能器。因此，有可能获得更大的声功率，从而提高信噪比（SNR）。
