Abstract
Ultrasonic local positioning systems (ULPS) have been brought to the attention of researchers as one of the possibilities that can be used for indoor localization. Acoustic systems combine a suitable trade-off between precision, ease of development, and cost. This work proposes a method for measuring the time of arrival of encoded emissions from a set of ultrasonic beacons, which are used to implement an accurate ULPS. This method uses the generalized cross-correlation technique with PHAT filter and weighting factor β (GCC-PHAT-β). To improve the performance of the GCC-PHAT-β in encoded emission detection, the employment is proposed of mixed-medium multiple-access techniques, based on code division and time division multiplexing of beacon emissions (CDMA and TDMA respectively), and to dynamically adjust the PHAT filter weighting factor. The receiver position is obtained by hyperbolic multilateration from the time differences of arrival (TDoA) between a reference beacon and the rest, thus avoiding the need for receiver synchronization. The results show how the dynamic adaptation of the weighting factor significantly reduces positioning errors from 20 cm to 2 cm in 80% of measurements. The simulated and real experiments prove that the proposed algorithms improve the performance of the ULPS in situations with lower signal-to-noise ratios (SNR) than 0 dB and in environments where the multipath effect makes it difficult to correctly detect the encoded ultrasonic emissions.
Highlights
Technology dedicated to determining the position of an object, robot, or person, either in an outdoor or indoor space has experienced a rapid growth during the last decade
This work has proposed and validated an algorithm based on the use of the GCCPHAT(β), for improving the detection of times-of-arrival in an Ultrasonic local positioning systems (ULPS)
The performance of the detection of time of arrival (ToA) is improved whether the weighting factor of the PHAT filter is dynamically adjusted
Summary
Technology dedicated to determining the position of an object, robot, or person, either in an outdoor or indoor space (building, premises, or room) has experienced a rapid growth during the last decade. The position calculation time is independent of the number of devices to localize In those LPS based on a group of transmitter beacons located at known positions, which transmit simultaneously and periodically, the DS-CDMA (Direct-Sequence Code Division Multiple-Access) technique is often considered to be a feasible approach to avoid any crosstalk interference [14,16]. The authors in [23] proposed the use of generalized cross-correlation with PHAse Transform filtering (GCC-PHAT) for the detection of ultrasonic encoded emissions, showing an improvement in the TDoA estimations and, in the final positioning. The estimation of the time of arrival for each beacon, when applying the GCC with PHAT filtering, requires a more complex analysis than the standard cross-correlation This is because the received signal is a composition of as many “signals” as available beacons. More detail can be found in the previous work presented in [23]
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