{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,21]],"date-time":"2026-03-21T19:28:18Z","timestamp":1774121298524,"version":"3.50.1"},"reference-count":50,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2021,3,10]],"date-time":"2021-03-10T00:00:00Z","timestamp":1615334400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100011698","name":"Junta de Comunidades de Castilla-La Mancha","doi-asserted-by":"publisher","award":["FrailCheck project, SBPLY\/17\/180501\/000392"],"award-info":[{"award-number":["FrailCheck project, SBPLY\/17\/180501\/000392"]}],"id":[{"id":"10.13039\/501100011698","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100012818","name":"Comunidad de Madrid","doi-asserted-by":"publisher","award":["CM\/JIN\/2019-043"],"award-info":[{"award-number":["CM\/JIN\/2019-043"]}],"id":[{"id":"10.13039\/100012818","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100014440","name":"Ministerio de Ciencia, Innovaci\u00f3n y Universidades","doi-asserted-by":"publisher","award":["RTI2018-095168-B-C51, PID2019-105470RA-C33"],"award-info":[{"award-number":["RTI2018-095168-B-C51, PID2019-105470RA-C33"]}],"id":[{"id":"10.13039\/100014440","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Indoor positioning remains a challenge and, despite much research and development carried out in the last decade, there is still no standard as with the Global Navigation Satellite Systems (GNSS) outdoors. This paper presents an indoor positioning system called LOCATE-US with adjustable granularity for use with commercial mobile devices, such as smartphones or tablets. LOCATE-US is privacy-oriented and allows every device to compute its own position by fusing ultrasonic, inertial sensor measurements and map information. Ultrasonic Local Positioning Systems (U-LPS) based on encoded signals are placed in critical zones that require an accuracy below a few decimeters to correct the accumulated drift errors of the inertial measurements. These systems are well suited to work at room level as walls confine acoustic waves inside. To avoid audible artifacts, the U-LPS emission is set at 41.67 kHz, and an ultrasonic acquisition module with reduced dimensions is attached to the mobile device through the USB port to capture signals. Processing in the mobile device involves an improved Time Differences of Arrival (TDOA) estimation that is fused with the measurements from an external inertial sensor to obtain real-time location and trajectory display at a 10 Hz rate. Graph-matching has also been included, considering available prior knowledge about the navigation scenario. This kind of device is an adequate platform for Location-Based Services (LBS), enabling applications such as augmented reality, guiding applications, or people monitoring and assistance. The system architecture can easily incorporate new sensors in the future, such as UWB, RFiD or others.<\/jats:p>","DOI":"10.3390\/s21061950","type":"journal-article","created":{"date-parts":[[2021,3,10]],"date-time":"2021-03-10T20:51:42Z","timestamp":1615409502000},"page":"1950","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":31,"title":["LOCATE-US: Indoor Positioning for Mobile Devices Using Encoded Ultrasonic Signals, Inertial Sensors and Graph-Matching"],"prefix":"10.3390","volume":"21","author":[{"given":"David","family":"Gualda","sequence":"first","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, Alcal\u00e1 de Henares, 28801 Madrid, Spain"},{"name":"Signal Theory and Communications Department, King Juan Carlos University, M\u00f3stoles, 28933 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8271-6843","authenticated-orcid":false,"given":"Mar\u00eda Carmen","family":"P\u00e9rez-Rubio","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, Alcal\u00e1 de Henares, 28801 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5326-0752","authenticated-orcid":false,"given":"Jes\u00fas","family":"Ure\u00f1a","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, Alcal\u00e1 de Henares, 28801 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Sergio","family":"P\u00e9rez-Bachiller","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, Alcal\u00e1 de Henares, 28801 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5900-0978","authenticated-orcid":false,"given":"Jos\u00e9 Manuel","family":"Villadangos","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, Alcal\u00e1 de Henares, 28801 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9308-8133","authenticated-orcid":false,"given":"\u00c1lvaro","family":"Hern\u00e1ndez","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, Alcal\u00e1 de Henares, 28801 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7121-8651","authenticated-orcid":false,"given":"Juan Jes\u00fas","family":"Garc\u00eda","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, Alcal\u00e1 de Henares, 28801 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0713-0054","authenticated-orcid":false,"given":"Ana","family":"Jim\u00e9nez","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, Alcal\u00e1 de Henares, 28801 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,3,10]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"598","DOI":"10.3390\/ijgi2030598","article-title":"Indoor Positioning for Smartphones Using Asynchronous Ultrasound Trilateration","volume":"2","author":"Filonenko","year":"2013","journal-title":"Isprs Ing. J. Geo-Inf."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1155\/2017\/2630413","article-title":"Evolution of Indoor Positioning Technologies: A Survey","volume":"17","author":"Brena","year":"2017","journal-title":"J. Sens."},{"key":"ref_3","unstructured":"(2021, January 10). Google Indoor Navigation. Available online: https:\/\/www.indoornavigation.com\/knowledge\/indoor-navigation-by-google-what-you-should-know-about-it."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Vanclooster, A., and De Maeyer, P. (2012). Combining indoor and outdoor navigation: The current approach of route planners. Advances in Location-Based Services, Springer.","DOI":"10.1007\/978-3-642-24198-7_19"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"9263","DOI":"10.1016\/j.eswa.2015.08.013","article-title":"Comprehensive Analysis of Distance and Similarity Measures for WiFi Fingerprinting Indoor Positioning Systems","volume":"42","author":"Montoliu","year":"2015","journal-title":"Expert Syst. Appl."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"101","DOI":"10.1016\/j.inffus.2016.06.004","article-title":"An improved inertial\/wifi\/magnetic fusion structure for indoor navigation","volume":"34","author":"Li","year":"2017","journal-title":"Inf. Fusion"},{"key":"ref_7","unstructured":"Gualda, D., Villadangos, J.M., Ure\u00f1a, J., Jim\u00e9nez, A., Seco, F., and Hern\u00e1ndez, A. (October, January 30). Indoor Positioning in Large Environments: Ultrasonic and UWB Technologies. Proceedings of the International Conference of Indoor Positioning and Indoor Navigation (IPIN), Pisa, Italy."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Qi, J., and Liu, G.-P. (2017). A Robust High-Accuracy Ultrasound Indoor Positioning System Based on a Wireless Sensor Network. Sensors, 17.","DOI":"10.3390\/s17112554"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Yang, L., Feng, X., Zhang, J., and Shu, X. (2019). Multi-Ray Modeling of Ultrasonic Sensors and Application for Micro-UAV Localization in Indoor Environments. Sensors, 19.","DOI":"10.3390\/s19081770"},{"key":"ref_10","unstructured":"Rowe, A., and Lazik, P. (2012, January 6\u20139). Indoor Pseudo-ranging of Mobile Devices using Ultrasonic Chirps. Proceedings of the 10th ACM Conference on Embedded Network Sensor System, Toronto, Canada."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Peng, C., Shen, G., Zhang, Y., Li, Y., and Tan, K. (2007, January 6\u20139). BeepBeep: A High Accuracy Acoustic Ranging System using COTS Mobile Devices. Proceedings of the 5th International Conference on Embedded Networked Sensor Systems, Sydney, Australia.","DOI":"10.1145\/1322263.1322265"},{"key":"ref_12","first-page":"1","article-title":"Acoustic Self-Calibrating System for Indoor Smart Phone Tracking","volume":"2015","author":"Ens","year":"2015","journal-title":"Intern. J. Navig. Obs."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Langheinrich, M. (2001, January 30\u20132). Privacy by design- principles of privacy-aware ubiquitous sytems. Proceedings of the Ubiquitous Computing, Atlanta, GA, USA.","DOI":"10.1007\/3-540-45427-6_23"},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Aguilera, T., Paredes, J.A., \u00c1lvarez, F.J., Su\u00e1rez, J.I., and Hern\u00e1ndez, A. (2013, January 28\u201331). Acoustic Local Positioning System Using an iOS device. Proceedings of the International Conference on Indoor Positioning and Indoor Navigation (IPIN), Montbeliard, France.","DOI":"10.1109\/IPIN.2013.6817872"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"3248","DOI":"10.1109\/JSEN.2018.2807412","article-title":"Acoustic Signal-Based Indoor Global Coordinates System for Smartphones","volume":"18","author":"Oh","year":"2018","journal-title":"IEEE Sens. J."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"38","DOI":"10.1016\/j.dsp.2016.11.001","article-title":"CDMA-based acoustic local positioning system for portable devices with multipath cancellation","volume":"62","author":"Aguilera","year":"2017","journal-title":"Digit. Signal Process."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"832","DOI":"10.1109\/JSTSP.2009.2027795","article-title":"High-Precision Robust Broadband Ultrasonic Location and Orientation Estimation","volume":"3","author":"Bleackley","year":"2009","journal-title":"IEEE J. Sel. Top. Signal Process."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"347","DOI":"10.1016\/S0957-4174(01)00019-7","article-title":"Fuzzy expert systems with double knowledge base for ultrasonic classification","volume":"20","author":"Llata","year":"2001","journal-title":"Expert Syst. Appl."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1042","DOI":"10.1109\/JPROC.2018.2819938","article-title":"Acoustic Local Positioning with Encoded Emission Beacons","volume":"106","author":"Hernandez","year":"2018","journal-title":"Proc. IEEE"},{"key":"ref_20","unstructured":"Ure\u00f1a, J., Villadangos, J.M., Gualda, D., P\u00e9rez, M.C., Hern\u00e1ndez, A., Garc\u00eda, J.J., Jim\u00e9nez, A., Garc\u00eda, J.C., Arango, A., and Jim\u00e9nez, J.C. (2016, January 4\u20137). Technical description of LOCATE-US: An Ultrasonic local positioning system based on encoded beacons. Proceedings of the International Conference on Indoor Positioning and Indoor Navigation (IPIN), Alcal\u00e1 de Henares, Spain."},{"key":"ref_21","first-page":"629","article-title":"Indoor positioning based on foot-mounted IMU","volume":"63","author":"Guo","year":"2015","journal-title":"Bull. Pol. Acad. Sci. Tech. Sci."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Bousdar\u2013Ahmed, D., Munoz\u2013Diaz, E., and Kaiser, S. (2016, January 4\u20137). Performance comparison of foot- and pocket-mounted inertial navigation systems. Proceedings of the International Conference on Indoor Positioning and Indoor Navigation (IPIN), Alcal\u00e1 de Henares, Spain.","DOI":"10.1109\/IPIN.2016.7743673"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Kuang, J., Niu, X., and Chen, X. (2018). Robust Pedestrian Dead Reckoning Based on MEMS-IMU for Smartphones. Sensors, 18.","DOI":"10.3390\/s18051391"},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Solin, A., Cortes, S., Rahtu, E., and Kannala, J. (2018, January 10\u201313). Inertial Odometry on Handheld Smartphones. Proceedings of the 21st International Conference on Information Fusion, Cambridge, UK.","DOI":"10.23919\/ICIF.2018.8455482"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"143","DOI":"10.1109\/JSEN.2020.3014955","article-title":"Pedestrian Dead Reckoning with Wearable Sensors: A Systematic Review","volume":"21","author":"Hou","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_26","unstructured":"(2021, January 10). SHIMMER 3 EMG. Available online: https:\/\/www.shimmersensing.com\/products\/shimmer3-emg-sensor."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"2949","DOI":"10.1007\/s11277-016-3759-x","article-title":"Seamless Positioning Using a Smart Device","volume":"94","author":"Bahillo","year":"2019","journal-title":"Wirel. Pers. Commun."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Xia, M., Xiu, C., Yang, D., and Wang, L. (2019). Performance Enhancement of Pedestrian Navigation Systems Based on Low-Cost Foot-Mounted MEMS-IMU\/Ultrasonic Sensor. Sensors, 19.","DOI":"10.3390\/s19020364"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"7606","DOI":"10.3390\/s110807606","article-title":"Indoor Pedestrian Navigation Using Foot-Mounted IMU and Portable Ultrasound Range Sensors","volume":"11","author":"Girard","year":"2011","journal-title":"Sensors"},{"key":"ref_30","unstructured":"School of Engineering, University of Alcala (2021, January 10). Available online: http:\/\/escuelapolitecnica.uah.es."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1304","DOI":"10.1109\/TVT.2015.2391296","article-title":"Indoor Positioning Using Efficient Map Matching, RSS Measurements, and an Improved Motion Model","volume":"64","author":"Zampella","year":"2015","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"283","DOI":"10.1016\/j.eswa.2016.10.061","article-title":"Implementation of generic algorithm in map-matching model","volume":"72","author":"Nikolic","year":"2017","journal-title":"Expert Syst. Appl."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1954","DOI":"10.1109\/TIM.2017.2682938","article-title":"FPGA-Based Architecture for Managing Ultrasonic Beacons in a Local Positioning System","volume":"66","author":"Gualda","year":"2017","journal-title":"IEEE Trans. Instrum. Meas."},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"P\u00e9rez-Bachiller, S., Gualda, D., P\u00e9rez, M.C., Villadangos, J.M., Ure\u00f1a, J., and Cervig\u00f3n, R. (2018, January 24\u201327). Android application for indoor location using sensor fusion: Ultrasounds and inertial devices. Proceedings of the International Conference on Indoor Positioning and Indoor Navigation (IPIN), Nantes, France.","DOI":"10.1109\/IPIN.2018.8533785"},{"key":"ref_35","unstructured":"(2021, January 10). Pro-Wave Electronics Corporation. Available online: http:\/\/www.prowave.com.tw\/pdf\/txall.pdf."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1016\/j.sigpro.2014.07.002","article-title":"Spreading sequences in active sensing: A review","volume":"106","author":"Paredes","year":"2015","journal-title":"Signal Process."},{"key":"ref_37","unstructured":"(2021, January 10). Knowles Acoustics Application Note. Available online: https:\/\/media.digikey.com\/pdf\/Data%20Sheets\/Knowles%20Acoustics%20PDFs\/SiSonic_Design_Guide.pdf."},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Kasami, T. (1966). Weight Distribution Formula for Some Class of Cyclic Codes, Coordinated Science Lab, University of Illynois. Technical Report R-285.","DOI":"10.21236\/AD0632574"},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"Piccinni, G., Avitabile, G., and Coviello, G. (2016, January 10\u201313). An improved technique based on Zadoff-Chu sequences for distance measurements. Proceedings of the 2016 IEEE Radio and Antenna Days of the Indian Ocean (RADIO), Reunion, France.","DOI":"10.1109\/RADIO.2016.7772043"},{"key":"ref_40","doi-asserted-by":"crossref","unstructured":"Chen, C., Lu, X., Markham, A., and Trigoni, N. (2018, January 2\u20137). IONet: Learning to Cure the Curse of Drift in Inertial Odometry. Proceedings of the International Conference on Artificial Intelligence, New Orleans, LA, USA.","DOI":"10.1609\/aaai.v32i1.12102"},{"key":"ref_41","first-page":"393","article-title":"Proposal for a building accessibility service (BASE)","volume":"Volume 29","author":"Amaral","year":"2011","journal-title":"Everyday Technology for Independence and Care (AAATE)"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"5231","DOI":"10.1109\/TSP.2013.2276440","article-title":"Convergence and applications of a gossip-based gauss-newton algorithm","volume":"61","author":"Li","year":"2013","journal-title":"IEEE Trans. Signal Process."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"220","DOI":"10.1016\/j.sna.2012.12.021","article-title":"Efficient trilateration algorithm using time differences of arrival","volume":"193","author":"Villadangos","year":"2013","journal-title":"Sens. Actuators A Phys."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"35","DOI":"10.1115\/1.3662552","article-title":"A New Approach to Linear Filtering and Prediction Problems","volume":"82","author":"Kalman","year":"1960","journal-title":"Trans. ASME J. Basic Eng."},{"key":"ref_45","doi-asserted-by":"crossref","unstructured":"Munoz\u2013Diaz, E., and Mendiguchia\u2013Gonzalez, A.L. (2014, January 27\u201330). Step Detector and Step Length Estimator for an Inertial Pocket Navigation System. Proceedings of the International Conference of Indoor Positioning and Indoor Navigation (IPIN), Busan, Korea.","DOI":"10.1109\/IPIN.2014.7275473"},{"key":"ref_46","doi-asserted-by":"crossref","unstructured":"Gualda, D., Ure\u00f1a, J., Garc\u00eda, J.C., Alcal\u00e1, J., and Miyadaira, A.N. (2016, January 4\u20137). Reduction of Ultrasonic Indoor Localization Infraestructure based on the use of Graph Information. Proceedings of the International Conference on Indoor Positioning and Indoor Navigation (IPIN), Alcal\u00e1 de Henares, Spain.","DOI":"10.1109\/IPIN.2016.7743638"},{"key":"ref_47","unstructured":"(2021, January 10). Samsung Galaxy Tab S2. Available online: http:\/\/www.samsung.com\/es\/tablets\/galaxytab-s2-9-7-t810\/SM-T810NZKEPHE\/."},{"key":"ref_48","unstructured":"(2021, January 10). Apple, Iphone 11. Available online: https:\/\/www.apple.com\/jo\/iphone-11\/."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"1347","DOI":"10.1109\/COMST.2016.2637663","article-title":"A Survey of Selected Indoor Positioning Methods for Smartphones","volume":"19","author":"Davidson","year":"2017","journal-title":"IEEE Commun. Surv. Tutor."},{"key":"ref_50","doi-asserted-by":"crossref","unstructured":"Zhou, L., Fischer, E., Tunca, C., Brahms, C.M., Ersoy, C., Granacher, U., and Arnrich, B. (2020). How We Found Our IMU: Guidelines to IMU Selection and a Comparison of Seven IMUs for Pervasive Healthcare Applications. Sensors, 20.","DOI":"10.3390\/s20154090"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/6\/1950\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T05:33:45Z","timestamp":1760160825000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/6\/1950"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,3,10]]},"references-count":50,"journal-issue":{"issue":"6","published-online":{"date-parts":[[2021,3]]}},"alternative-id":["s21061950"],"URL":"https:\/\/doi.org\/10.3390\/s21061950","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,3,10]]}}}