{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T04:08:18Z","timestamp":1760242098194,"version":"build-2065373602"},"reference-count":35,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2018,12,19]],"date-time":"2018-12-19T00:00:00Z","timestamp":1545177600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100005073","name":"Agency for Defense Development","doi-asserted-by":"publisher","award":["UD170022DD"],"award-info":[{"award-number":["UD170022DD"]}],"id":[{"id":"10.13039\/501100005073","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>In this paper, we propose a covert underwater acoustic communication method that is robust to fading using a chirp signal combined with a frequency-hopping spread spectrum scheme. A fractional Fourier transform, which estimates the slope of the signal frequency variation, is applied to the receiver to enable a robust and reliable symbol estimation with respect to the frequency and irregular phase variations. In addition, since the recursive symbol synchronization can be implemented using a chirp signal, compression and expansion effects due to the Doppler shift can be mitigated. Simulation and lake trials were performed to verify the performance of the proposed method. The simulation was performed by two different methods.<\/jats:p>","DOI":"10.3390\/s18124498","type":"journal-article","created":{"date-parts":[[2018,12,19]],"date-time":"2018-12-19T12:12:44Z","timestamp":1545221564000},"page":"4498","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["Chirp-Based FHSS Receiver with Recursive Symbol Synchronization for Underwater Acoustic Communication"],"prefix":"10.3390","volume":"18","author":[{"given":"Geunhyeok","family":"Lee","sequence":"first","affiliation":[{"name":"Department of the Radio Communication Engineering, Korea Maritime and Ocean University, Busan 49112, Korea"}]},{"given":"Woongjin","family":"Park","sequence":"additional","affiliation":[{"name":"Department of the Radio Communication Engineering, Korea Maritime and Ocean University, Busan 49112, Korea"}]},{"given":"Taewoong","family":"Kang","sequence":"additional","affiliation":[{"name":"Department of the Radio Communication Engineering, Korea Maritime and Ocean University, Busan 49112, Korea"}]},{"given":"Kiman","family":"Kim","sequence":"additional","affiliation":[{"name":"Department of the Radio Communication Engineering, Korea Maritime and Ocean University, Busan 49112, Korea"}]},{"given":"Wanjin","family":"Kim","sequence":"additional","affiliation":[{"name":"Agency for Defense Development, Changwon 51678, Korea"}]}],"member":"1968","published-online":{"date-parts":[[2018,12,19]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"205","DOI":"10.1109\/48.107149","article-title":"Performance limitations in underwater acoustic telemetry","volume":"15","author":"Catipovic","year":"1990","journal-title":"IEEE J. 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