Infrastructure-less indoor positioning in 3D (completed)

• Sosa, Joaquin Aparicio; Alvarez, Fernando J.; Hernandez, Alvaro & Holm, Sverre (2022). A Survey on Acoustic Positioning Systems for Location-Based Services. IEEE Transactions on Instrumentation and Measurement. ISSN 0018-9456. doi: 10.1109/TIM.2022.3210943. Full text in Research Archive Show summary

  Positioning systems have become increasingly popular in the last decade for location-based services, such as navigation, and asset tracking and management. As opposed to outdoor positioning, where the global navigation satellite system became the standard technology, there is no consensus yet for indoor environments despite the availability of different technologies, such as radio frequency, magnetic field, visual light communications, or acoustics. Within these options, acoustics emerged as a promising alternative to obtain high-accuracy low-cost systems. Nevertheless, acoustic signals have to face very demanding propagation conditions, particularly in terms of multipath and Doppler effect. Therefore, even if many acoustic positioning systems have been proposed in the last decades, it remains an active and challenging topic. This article surveys the developed prototypes and commercial systems that have been presented since they first appeared around the 1980s to 2022. We classify these systems into different groups depending on the observable that they use to calculate the user position, such as the time-of-flight, the received signal strength, or the acoustic spectrum. Furthermore, we summarize the main properties of these systems in terms of accuracy, coverage area, and update rate, among others. Finally, we evaluate the limitations of these groups based on the link budget approach, which gives an overview of the system’s coverage from parameters such as source and noise level, detection threshold, attenuation, and processing gain.

• Aguilera, Teodoro; Aparicio, Joaquin & Alvarez, Fernando J. (2021). High Availability Acoustic Positioning for Targets Moving in Poor Coverage Areas. IEEE Transactions on Instrumentation and Measurement. ISSN 0018-9456. 70. doi: 10.1109/TIM.2021.3106684. Full text in Research Archive Show summary

  Currently, most acoustic positioning strategies are based on broadband coding and the pulse compression technique to obtain better accuracy and robustness against in-band noise. However, the accuracy and robustness of these systems are often seriously damaged in areas of low coverage and/or affected by multipath. This work proposes a high availability positioning algorithm (HAPA) that optimally processes the received signal to improve positioning results throughout the whole location area. This algorithm validates the Time-of-Arrival (ToA) from each beacon, corrects their Doppler shift, and compensates for multipath when it exists. If the number of validated beacons is enough to obtain a position, the algorithm tries to position with their optimal combination; if not, it tries to position by incorporating additional ToA candidates for the nonvalidated beacons. The HAPA performance has been evaluated through a set of experimental tests to compare its results with those obtained by the robust positioning algorithm (RPA) developed by the authors in previous work, and by a classical positioning algorithm (CPA) based on the emission of chirps. In particular, when using a mobile robot to follow trajectories that cross areas with low coverage and affected by multipath, the HAPA maintains availability of 97.89%, while the RPA drops to 83.25% and the CPA to 50.19%.

• Aparicio, Joaquin & Holm, Sverre (2021). Obtaining range measurements from ambient noise cross-correlations for the self-calibration of nodes. CEUR Workshop Proceedings. 3097. Full text in Research Archive Show summary

  The calibration of nodes in a sensor network or in a positioning system is a time-consuming process. This is especially relevant in indoor environments, where GPS signals are not available. Usually, it involves a user making transmissions either at known points, or by transmitting while moving under the area of interest. Some self-calibration methods have already been proposed for acoustic sensor network systems, that require range calculation between the nodes, to later apply a positioning algorithm. In this work, we evaluated a range mechanism based on the cross-correlation of the ambient noise naturally available indoors, so no active transmissions were required. Results from experimental tests show a minimum Mean Absolute Error (MAE) of 0.93 cm and a maximum MAE of 1.37 cm, when calculating the range between two microphones separated 18.8 cm.

• Thio, Vincent Martello Kwie Hoe; Aparicio, Joaquin; Ånonsen, Kjetil Bergh & Bekkeng, Jan Kenneth (2021). Experimental Evaluation of the Forkbeard Ultrasonic Indoor Positioning System. IEEE Transactions on Instrumentation and Measurement. ISSN 0018-9456. doi: 10.1109/TIM.2021.3136261. Full text in Research Archive Show summary

  Indoor positioning systems are crucial to provide location based services in areas that are not covered by a Global Navigation Satellite System. Among the many technologies applied to this field, ultrasound has emerged as a potential low-cost, high-accuracy approach to positioning based on trilateration. Several ultrasonic systems have been proposed over the years. Of these, academic systems are typically prototypes that are unavailable to the public, whereas commercial systems generally do not provide characterization test results. In this work, we have conducted a detailed characterization study of a commercial indoor positioning system for smart devices developed by Forkbeard Technologies AS. We tested the system under static and dynamic conditions in a motion capture lab of approximately 150 m2. We considered different room occupancies, beacon configurations, and device positions. The results, given in terms of 2D absolute errors at different confidence levels, show great variation depending on the aforementioned conditions. The worst case scenario corresponds to a pedestrian in motion in an office setup with 4 beacons, with the phone placed in the pocket. In this case, 80% of the errors were below 143 cm. The best results were obtained under static conditions using 10 beacons, for which 80% of the errors were below 44 cm.

• Thio, Vincent Martello Kwie Hoe; Aparicio, Joaquin; Ånonsen, Kjetil Bergh; Bekkeng, Jan Kenneth & Booij, Wilfred (2021). Fusing of a continuous output PDR algorithm with an ultrasonic positioning system. IEEE Sensors Journal. ISSN 1530-437X. doi: 10.1109/JSEN.2021.3134468. Full text in Research Archive Show summary

  The availability of inertial navigation sensors in smartphones has facilitated the development of pedestrian dead reckoning (PDR) models on a large scale. These models often consist of a step detection algorithm combined with a heading estimation routine. Common approaches to step detection include searching for peaks/valleys in the acceleration signal, principle frequency estimation, and machine learning techniques. Since the sensors embedded in smart devices are prone to noise, the position error grows unbounded if unchecked and requires periodical corrections based on external measurements. In this work, we propose a novel step detection algorithm based on sine-wave approximation of the acceleration signal. This method detects step fractions as well as full steps, which allows for continuous and real-time updates. The step detection algorithm is combined with a heading estimation routine described in our previous work to obtain a stand-alone PDR model. To mitigate error accumulation, we fuse the proposed model with position and heading measurements provided by a commercial indoor positioning system based on ultrasound. We evaluate the performance of the PDR and fused model in an open office environment, by walking along a trajectory while carrying a smartphone in hand or in the pocket. The results demonstrate the feasibility of the sine-wave approximation approach to step detection, as well as the expected benefits of fusing PDR with the ultrasonic system.

• Thio, Vincent; Ånonsen, Kjetil Bergh & Bekkeng, Jan Kenneth (2021). Relative Heading Estimation for Pedestrians Based on the Gravity Vector. IEEE Sensors Journal. ISSN 1530-437X. doi: 10.1109/JSEN.2021.3052430. Full text in Research Archive Show summary

  Inertial navigation of pedestrians carrying a smart device is a core component of many indoor positioning systems. While infrastructure-based solutions typically depend on an installation of dedicated hardware, inertial navigation depends only on sensors embedded in the device itself. A single solution can thus be applied to a large range of use cases. This work focuses on one of the main challenges in inertial navigation: user heading estimation. We describe a complete statistical model for heading estimation based on the IMU and magnetometer, assuming a fixed device pose on the pedestrian. Our aim is to provide a stand-alone solution, suitable for direct implementation into a larger positioning framework. The method consists of two consecutive parts. The first focuses on gravity vector estimation based on IMU data. We describe a method for obtaining independent estimates under dynamic conditions, thereby removing the quasi-static initialization phase required by conventional methods. The second part combines the gravity vector with gyro and magnetic measurements to estimate user heading. The proposed method is tested against a motion capture system, and against an alternative method based on attitude. We find that both methods produce similar results in terms of accuracy.

• Aparicio, Joaquin; Aguilera, Teodoro & Alvarez, Fernando J. (2020). Robust airborne ultrasonic positioning of moving targets in weak signal coverage areas. IEEE Sensors Journal. ISSN 1530-437X. 20(21), p. 13119–13130. doi: 10.1109/JSEN.2020.3003523. Full text in Research Archive Show summary

  Current ultrasonic Local Positioning Systems (LPS) based on an infrastructure of beacons can provide centimeter-level accuracy employing the spread spectrum technique, which also adds robustness against noise. However, the strong attenuation of the acoustic waves at high frequencies, the high directionality of ultrasound transducers, and the Doppler effect caused by moving targets still affect the correct performance of LPS. These phenomena reduce the availability of these systems in weak signal coverage areas, as they are no longer able to distinguish weak arrivals from spurious peaks, failing to calculate the position of the target. In this work, the aforementioned problems are dealt with by transmitting Doppler resilient waveforms together with a validation code based on Complementary Set of Sequences. This validation code is leveraged at the receiver after Doppler compensation to reduce the number of spurious arrival candidates and therefore increase the system availability. Compared to a system with no validation, experimental tests with a moving robot have shown that the proposed system increased the availability in weak coverage areas between 20 and 25%. The robot's average 2D positioning error at rest and in motion was 4.6 cm and 6 cm, respectively.

View all works in NVA

• Aparicio, Joaquin; Thio, Vincent Martello Kwie Hoe & Holm, Sverre (2022). Range evaluation between indoor microphones obtained from acoustic ambient noise cross-correlations. Full text in Research Archive
• Aparicio, Joaquin & Holm, Sverre (2021). Evaluation of acoustic ambient noise cross-correlations in indoor environments. Full text in Research Archive
• Aparicio, Joaquin; Alvarez, Fernando; Hernandez, Alvaro & Holm, Sverre (2019). A review of techniques for ultrasonic indoor localization systems. Full text in Research Archive
• Aparicio, Joaquin (2019). Acoustic daylight: Concept and applications on different fields. Full text in Research Archive

View all works in NVA