Abstract
Self-calibrated Acoustic Local Positioning Systems (ALPS) generally require a high consumption of hardware and software resources to obtain the user’s position at an acceptable update rate. To address this limitation, this work proposes a self-calibrated ALPS based on a software/hardware co-design approach. This working architecture allows for efficient communications, signal processing tasks, and the running of the positioning algorithm on low-cost devices. This fact also enables the real-time system operation. The proposed system is composed of a minimum of four RF-synchronized active acoustic beacons, which emit spread-spectrum modulated signals to position an unlimited number of receiver nodes. Each receiver node estimates the beacons’ position by means of an auto-calibration process and then computes its own position by means of a 3D multilateration algorithm. A set of experimental tests has been carried out where the feasibility of the proposed system is demonstrated. In these experiments, accuracies below 0.1 m are obtained in the determination of the receptor node position with respect to the set of previously-calibrated beacons.
Highlights
The applications and services of people and object localization and context analysis are a growing demand in consumer society, so it is necessary to investigate and develop alternative and complementary technologies to existing global location [1] to cover indoor environments with better performance, precision, and robustness [2,3].Most indoor positioning systems proposed so far can be classified into three main categories
The transfer of the 1023-bit code, BPSK modulated with an oversampling factor ( f cs = 6), was carried out by associating a buffer with 6138 samples to a DMA channel connected to the Serial Audio Interfaces (SAI), making possible a direct transmission from memory without the need for a CPU intervention
The samples acquired by the Serial Peripheral Interface (SPI) block, in I2S half-duplex master mode, were stored into a buffer memory using a DMA channel with interrupt signaling through the receive data register configured to provide 16 contiguous bits in MSB–first format
Summary
The applications and services of people and object localization and context analysis are a growing demand in consumer society, so it is necessary to investigate and develop alternative and complementary technologies to existing global location [1] to cover indoor environments with better performance, precision, and robustness [2,3]. The only way to extend the operational area of these systems is to deploy new beacons at known and precise locations, whose coordinates will be used to solve the trilateration or multilateration equations, provided that the simultaneous coverage of a minimum of three or four beacons is always ensured, respectively Needless to say, this is a tedious task prone to multiple errors during the beacons’ placement procedure, even more given the usually wired infrastructure of these beacons. In [15], the authors proposed the LOSNUS system (Localization of Sensor Nodes by Ultrasound) based on the measurement of the ToFs of a set of six transmitters and four receivers that together with the speed of sound allow defining a system of 24 equations that, once solved through a minimization algorithm, allows the definition of a system of coordinates Using this method, calibration accuracies of less than one centimeter were achieved.
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