{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T21:16:31Z","timestamp":1760217391780,"version":"build-2065373602"},"reference-count":23,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2015,7,30]],"date-time":"2015-07-30T00:00:00Z","timestamp":1438214400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>This paper describes a new approach and implementation methodology for indoor ranging based on the time difference of arrival using code division multiple access with ultrasound signals. A novel implementation based on a field programmable gate array using finite impulse response filters and an optimized correlation demodulator implementation for ultrasound orthogonal signals is developed. Orthogonal codes are modulated onto ultrasound signals using frequency shift keying with carrier frequencies of 24.5 kHz and 26 kHz. This implementation enhances the possibilities for real-time, embedded and low-power tracking of several simultaneous transmitters. Due to the high degree of parallelism offered by field programmable gate arrays, up to four transmitters can be tracked simultaneously. The implementation requires at most 30% of the available logic gates of a Spartan-6 XC6SLX45 device and is evaluated on accuracy and precision through several ranging topologies. In the first topology, the distance between one transmitter and one receiver is evaluated. Afterwards, ranging analyses are applied between two simultaneous transmitters and one receiver. Ultimately, the position of the receiver against four transmitters using trilateration is also demonstrated. Results show enhanced distance measurements with distances ranging from a few centimeters up to 17 m, while keeping a centimeter-level accuracy.<\/jats:p>","DOI":"10.3390\/s150818641","type":"journal-article","created":{"date-parts":[[2015,7,30]],"date-time":"2015-07-30T11:21:59Z","timestamp":1438255319000},"page":"18641-18665","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":15,"title":["An Ultrasonic Multiple-Access Ranging Core Based on Frequency Shift Keying Towards Indoor Localization"],"prefix":"10.3390","volume":"15","author":[{"given":"Laurent","family":"Segers","sequence":"first","affiliation":[{"name":"Department of Industrial Sciences and Technology (INDI), Vrije Universiteit Brussel, Pleinlaan 2, Elsene 1050, Belgium"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"David","family":"Van Bavegem","sequence":"additional","affiliation":[{"name":"Department of Industrial Sciences and Technology (INDI), Vrije Universiteit Brussel, Pleinlaan 2, Elsene 1050, Belgium"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Sam","family":"De Winne","sequence":"additional","affiliation":[{"name":"Department of Industrial Sciences and Technology (INDI), Vrije Universiteit Brussel, Pleinlaan 2, Elsene 1050, Belgium"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9965-915X","authenticated-orcid":false,"given":"An","family":"Braeken","sequence":"additional","affiliation":[{"name":"Department of Industrial Sciences and Technology (INDI), Vrije Universiteit Brussel, Pleinlaan 2, Elsene 1050, Belgium"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Abdellah","family":"Touhafi","sequence":"additional","affiliation":[{"name":"Department of Industrial Sciences and Technology (INDI), Vrije Universiteit Brussel, Pleinlaan 2, Elsene 1050, Belgium"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kris","family":"Steenhaut","sequence":"additional","affiliation":[{"name":"Department of Industrial Sciences and Technology (INDI), Vrije Universiteit Brussel, Pleinlaan 2, Elsene 1050, Belgium"},{"name":"Department of Electronics and Informatics (ETRO), Vrije Universiteit Brussel, Pleinlaan 2, Elsene 1050, Belgium"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2015,7,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"187","DOI":"10.1023\/A:1013767926256","article-title":"The anatomy of a context-aware application","volume":"8","author":"Harter","year":"2002","journal-title":"Wirel. Netw."},{"key":"ref_2","unstructured":"Fukuju, Y., Minami, M., Morikawa, H., and Aoyama, T. (2003, January 15\u201316). Dolphin: An autonomous indoor positioning system in ubiquitous computing environment. Proceedings of the 2003 IEEE workshop on Software Technologies for Future Embedded Systems, Hakodate, Japan."},{"key":"ref_3","unstructured":"Priyantha, N.B., Balakrishnan, H., Demaine, E., and Teller, S. (2003, January 5\u20137). Anchor-free distributed localization in sensor networks. Proceedings of the 1st International Conference on Embedded Networked Sensor Systems, Los Angeles, CA, USA."},{"key":"ref_4","unstructured":"Knauth, S., Hussmann, J.S., Jost, C., and Klapproth, A. (2010, January 21). Applications of the iLoc indoor localization system in the area of assistance systems. Proceedings of the 5th BMI, Workshop on Behaviour Monitoring and Interpretation, Karlsruhe, Germany."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Alloulah, M., and Hazas, M. (2010, January 15\u201317). An efficient CDMA core for indoor acoustic position sensing. Proceedings of 2010 International Conference on Indoor Positioning and Indoor Navigation (IPIN), Z\u00fcrich, Switzerland.","DOI":"10.1109\/IPIN.2010.5648279"},{"key":"ref_6","unstructured":"Aly, O.A.M., and Omar, A.S. (2005, January 17). Spread spectrum ultrasonic positioning system. Proceedings of the 2nd Workshop on Positioning, Navigation and Communication (WPNC05), Magdeburg, Germany."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1284","DOI":"10.1109\/JSEN.2010.2084568","article-title":"Low-cost, wideband ultrasonic transmitter and receiver for array signal processing applications","volume":"11","author":"Bleakley","year":"2011","journal-title":"IEEE Sens. J."},{"key":"ref_8","unstructured":"Hazas, M., and Ward, A. (2002). UbiComp 2002: Ubiquitous Computing, Springer."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"3172","DOI":"10.3390\/s140203172","article-title":"Ultrasonic multiple-access ranging system using spread spectrum and mems technology for indoor localization","volume":"14","author":"Segers","year":"2014","journal-title":"Sensors"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Lanzisera, S., Lin, D.T., and Pister, K.S.J. (2006, January 30). RF time of flight ranging for wireless sensor network localization. Proceedings of the 2006 International Workshop on Intelligent Solutions in Embedded Systems, Vienna, Australia.","DOI":"10.1109\/WISES.2006.329127"},{"key":"ref_11","unstructured":"Huang, X., Barralet, M., and Sharma, D. (2009, January 18\u201320). Accuracy of location identification with antenna polarization on RSSI. Proceedings of the International MultiConference of Engineers and Computer Scientists, Hong Kong, China."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"221","DOI":"10.1007\/s11276-006-5064-1","article-title":"Indoor location tracking using rssi readings from a single Wi-Fi access point","volume":"13","author":"Huber","year":"2007","journal-title":"Wirel. Netw."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Peng, R., and Sichitiu, M.L. (2006, January 28). Angle of arrival localization for wireless sensor networks. Proceedings of the 3rd Annual IEEE Communications Society on Sensor and Ad Hoc Communications and Networks (SECON\u201906), Reston, VA, USA.","DOI":"10.1109\/SAHCN.2006.288442"},{"key":"ref_14","unstructured":"Xu, J., Ma, M., and Law, C.L. (December, January 30). AOA cooperative position localization. Proceeding of the Global Telecommunications Conference, New Orleans, LO, USA."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"3501","DOI":"10.3390\/s130303501","article-title":"Ultrasound indoor positioning system based on a low-power wireless sensor network providing sub-centimeter accuracy","volume":"13","author":"Medina","year":"2013","journal-title":"Sensors"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Gonzalez Hernandez, J.R., and Bleakley, C.J. (2007, January 1\u20134). Accuracy of spread spectrum techniques for ultrasonic indoor location. Proceedings of the 2007 15th International Conference on Digital Signal Processing, Cardiff, UK.","DOI":"10.1109\/ICDSP.2007.4288574"},{"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":"Bleakley","year":"2009","journal-title":"IEEE J. Sel. Top. Signal Process."},{"key":"ref_18","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 Int. J. Geo-Inf."},{"key":"ref_19","unstructured":"MEMS SPU0410LR5H-QB Datasheet. Available online: http:\/\/www.knowles.com\/kor\/content\/download\/5755\/91802\/version\/3\/file\/SPU0410LR5H-QB+revH.PDF."},{"key":"ref_20","unstructured":"Atlys FGPA Board. Available online: http:\/\/www.digilentinc.com\/Products\/Detail.cfm?NavPath= 2,400,836&Prod=ATLYS&CFID=10184552&CFTOKEN=d9dfb5bdd2b5e41a-9D1D2398-5056- 0201-0209778A50D40CB5."},{"key":"ref_21","unstructured":"ADC101S021 Datasheet Texas Instruments. Available online: http:\/\/www.ti.com\/product\/adc101s021."},{"key":"ref_22","unstructured":"Prowave 250ST180 Piezo Crystal Transducer Datasheet. Available online: http:\/\/www.farnell.com\/datasheets\/81154.pdf."},{"key":"ref_23","unstructured":"Xilinx ISE Development Environment. Available online: http:\/\/www.xilinx.com\/products\/design-tools\/ise-design-suite.html."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/15\/8\/18641\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T20:49:55Z","timestamp":1760215795000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/15\/8\/18641"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2015,7,30]]},"references-count":23,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2015,8]]}},"alternative-id":["s150818641"],"URL":"https:\/\/doi.org\/10.3390\/s150818641","relation":{},"ISSN":["1424-8220"],"issn-type":[{"type":"electronic","value":"1424-8220"}],"subject":[],"published":{"date-parts":[[2015,7,30]]}}}