{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T19:43:17Z","timestamp":1760211797967,"version":"build-2065373602"},"reference-count":48,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2016,7,19]],"date-time":"2016-07-19T00:00:00Z","timestamp":1468886400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Entropy"],"abstract":"<jats:p>A millimeter wave (MMW) radar sensor is employed in our laboratory to detect human speech because it provides a new non-contact speech acquisition method that is suitable for various applications. However, the speech detected by the radar sensor is often degraded by combined noise. This paper proposes a new perceptual wavelet packet method that is able to enhance the speech acquired using a 94 GHz MMW radar system by suppressing the noise. The process is as follows. First, the radar speech signal is decomposed using a perceptual wavelet packet. Then, an adaptive wavelet threshold and new modified thresholding function are employed to remove the noise from the detected speech. The results obtained from the speech spectrograms, listening tests and objective evaluation show that the new method significantly improves the performance of the detected speech.<\/jats:p>","DOI":"10.3390\/e18070265","type":"journal-article","created":{"date-parts":[[2016,7,19]],"date-time":"2016-07-19T09:48:22Z","timestamp":1468921702000},"page":"265","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Noise Suppression in 94 GHz Radar-Detected Speech Based on Perceptual Wavelet Packet"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3189-6482","authenticated-orcid":false,"given":"Fuming","family":"Chen","sequence":"first","affiliation":[{"name":"Department of Biomedical Engineering, Fourth Military Medical University, Xi\u2019an 710032, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chuantao","family":"Li","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, Fourth Military Medical University, Xi\u2019an 710032, China"},{"name":"Laboratory of Aviation Medicine, Naval Medical Research Institute, Shanghai 200433, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Qiang","family":"An","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, Fourth Military Medical University, Xi\u2019an 710032, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Fulai","family":"Liang","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, Fourth Military Medical University, Xi\u2019an 710032, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Fugui","family":"Qi","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, Fourth Military Medical University, Xi\u2019an 710032, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Sheng","family":"Li","sequence":"additional","affiliation":[{"name":"College of Control Engineering, Xijing University, Xi\u2019an 710123, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jianqi","family":"Wang","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, Fourth Military Medical University, Xi\u2019an 710032, China"},{"name":"Department of Physics and Information Engineering, Shaanxi University of Technology, Hanzhong 723001, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2016,7,19]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/0924-4247(94)00790-X","article-title":"A review of silicon microphones","volume":"44","author":"Scheeper","year":"1994","journal-title":"Sens. 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