{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,29]],"date-time":"2026-05-29T19:43:36Z","timestamp":1780083816640,"version":"3.54.0"},"reference-count":50,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2017,12,30]],"date-time":"2017-12-30T00:00:00Z","timestamp":1514592000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Spanish Government (TARSIUS)","award":["TIN2015-71564-C4-4-R"],"award-info":[{"award-number":["TIN2015-71564-C4-4-R"]}]},{"name":"European Regional Development Fund (REPNIN)","award":["TEC2015-71426-REDT"],"award-info":[{"award-number":["TEC2015-71426-REDT"]}]},{"name":"Spanish Government (SOC-PLC)","award":["TEC2015-64835-C3-2-R"],"award-info":[{"award-number":["TEC2015-64835-C3-2-R"]}]},{"name":"Regional Government of Extremadura and ERDF-ESF","award":["GR15167"],"award-info":[{"award-number":["GR15167"]}]},{"DOI":"10.13039\/501100014181","name":"Regional Government of Extremadura","doi-asserted-by":"publisher","award":["Pre-doctoral scholarship (45\/2016 Exp. PD16030)"],"award-info":[{"award-number":["Pre-doctoral scholarship (45\/2016 Exp. PD16030)"]}],"id":[{"id":"10.13039\/501100014181","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>This work proposes the use of a hybrid acoustic and optical indoor positioning system for the accurate 3D positioning of Unmanned Aerial Vehicles (UAVs). The acoustic module of this system is based on a Time-Code Division Multiple Access (T-CDMA) scheme, where the sequential emission of five spread spectrum ultrasonic codes is performed to compute the horizontal vehicle position following a 2D multilateration procedure. The optical module is based on a Time-Of-Flight (TOF) camera that provides an initial estimation for the vehicle height. A recursive algorithm programmed on an external computer is then proposed to refine the estimated position. Experimental results show that the proposed system can increase the accuracy of a solely acoustic system by 70\u201380% in terms of positioning mean square error.<\/jats:p>","DOI":"10.3390\/s18010089","type":"journal-article","created":{"date-parts":[[2018,1,3]],"date-time":"2018-01-03T12:00:06Z","timestamp":1514980806000},"page":"89","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":73,"title":["3D Indoor Positioning of UAVs with Spread Spectrum Ultrasound and Time-of-Flight Cameras"],"prefix":"10.3390","volume":"18","author":[{"given":"Jos\u00e9","family":"Paredes","sequence":"first","affiliation":[{"name":"Sensory System Research Group, University of Extremadura, 06006 Badajoz, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7610-1452","authenticated-orcid":false,"given":"Fernando","family":"\u00c1lvarez","sequence":"additional","affiliation":[{"name":"Sensory System Research Group, University of Extremadura, 06006 Badajoz, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9436-5999","authenticated-orcid":false,"given":"Teodoro","family":"Aguilera","sequence":"additional","affiliation":[{"name":"Sensory System Research Group, University of Extremadura, 06006 Badajoz, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jos\u00e9","family":"Villadangos","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, Alcal\u00e1 de Henares, 28805 Madrid, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2017,12,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Tiemann, J., Schweikowski, F., and Wietfeld, C. 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