Abstract
Indoor positioning systems have become a feasible solution for the current development of multiple location-based services and applications. They often consist of deploying a certain set of beacons in the environment to create a coverage volume, wherein some receivers, such as robots, drones or smart devices, can move while estimating their own position. Their final accuracy and performance mainly depend on several factors: the workspace size and its nature, the technologies involved (Wi-Fi, ultrasound, light, RF), etc. This work evaluates a 3D ultrasonic local positioning system (3D-ULPS) based on three independent ULPSs installed at specific positions to cover almost all the workspace and position mobile ultrasonic receivers in the environment. Because the proposal deals with numerous ultrasonic emitters, it is possible to determine different time differences of arrival (TDOA) between them and the receiver. In that context, the selection of a suitable fusion method to merge all this information into a final position estimate is a key aspect of the proposal. A linear Kalman filter (LKF) and an adaptive Kalman filter (AKF) are proposed in that regard for a loosely coupled approach, where the positions obtained from each ULPS are merged together. On the other hand, as a tightly coupled method, an extended Kalman filter (EKF) is also applied to merge the raw measurements from all the ULPSs into a final position estimate. Simulations and experimental tests were carried out and validated both approaches, thus providing average errors in the centimetre range for the EKF version, in contrast to errors up to the meter range from the independent (not merged) ULPSs.
Highlights
Global positioning systems are nowadays fully integrated into daily life in many fields of application, mainly based on global navigation satellite systems (GNSSs), due to their performance in terms of availability, coverage, compact size, and the low cost of receivers.GNSSs do not match so well in all the scenarios and applications due to certain constraints, such as the degradation or lack of satellite signals in closed environments
Taking into account the previous independent results with significant errors and dispersions in the perpendicular axes to the ULPSs, we propose hereinafter the aforementioned fusion of information at two different levels: a loosely coupled fusion and a tightly coupled one
With regard to previous works dealing with the design of ultrasonic positioning systems, a proposal based on a single ULPS was described in [18] for 2D positioning, with errors below 20 cm in 90% of the cases for a grid of points on the ground with a size of 4 × 4 m2
Summary
Global positioning systems are nowadays fully integrated into daily life in many fields of application, mainly based on global navigation satellite systems (GNSSs), due to their performance in terms of availability, coverage, compact size, and the low cost of receivers. A 3D positioning system presented in [16] was composed of a single mobile emitter and a set of six fixed and coplanar receivers at known positions; it proposed a linear ultrasonic chirp and the phase correlation approach to calculate the corresponding TOAs, with a spherical trilateration technique to obtain the estimated positions. In order to achieve a large coverage volume with enough accuracy in the three coordinates, several ultrasonic LPSs are deployed on different planes This fact implies that several TDOA measurements or position estimates can be obtained for a single receiver’s position, being necessary to merge all of them in an efficient way to obtain suitable accuracy.
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