An improved least mean square/fourth direct adaptive equalizer for under-water acoustic communications in the Arctic
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An improved least mean square/fourth direct adaptive equalizer for under-water acoustic communications in the Arctic Yanan Tian1, 2, 3, Xiao Han1, 2, 3*, Jingwei Yin1, 2, 3, Hongxia Chen4, Qingyu Liu5 1 Acoustic Science and Technology Laboratory, Harbin Engineering University, Harbin 150001, China 2 Key Laboratory of Marine Information Acquisition and Security (Harbin Engineering University), Ministry of
Industry and Information Technology, Harbin 150001, China 3 College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001, China 4 First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China 5 Naval Research Academy, Beijing 100161, China
Received 13 October 2019; accepted 13 November 2019 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
An improved least mean square/fourth direct adaptive equalizer (LMS/F-DAE) is proposed in this paper for underwater acoustic communication in the Arctic. It is able to process complex-valued baseband signals and has better equalization performance than LMS. Considering the sparsity feature of equalizer tap coefficients, an adaptive norm (AN) is incorporated into the cost function which is utilized as a sparse regularization. The norm constraint changes adaptively according to the amplitude of each coefficient. For small-scale coefficients, the sparse constraint exists to accelerate the convergence speed. For large-scale coefficients, it disappears to ensure smaller equalization error. The performance of the proposed AN-LMS/F-DAE is verified by the experimental data from the 9th Chinese National Arctic Research Expedition. The results show that compared with the standard LMS/F-DAE, AN-LMS/F-DAE can promote the sparse level of the equalizer and achieve better performance. Key words: underwater acoustic communication, the Arctic, direct adaptive equalizer, adaptive norm Citation: Tian Yanan, Han Xiao, Yin Jingwei, Chen Hongxia, Liu Qingyu. 2020. An improved least mean square/fourth direct adaptive equalizer for under-water acoustic communications in the Arctic. Acta Oceanologica Sinica, 39(9): 133–139, doi: 10.1007/s13131-0201653-6
1 Introduction With the rapid development of various applications in the Arctic in recent years, more and more ocean observation equipment such as underwater unmanned vehicle (UUV) is being used in the Arctic to gain insight into the temporal and spatial processes below the ice surface (Wang et al., 2017; Li et al., 2019). However, the thick ice covered in the Arctic prevents underwater platforms from communicating with the satellites, which makes acoustics the only means of data transmissions under ice surface. Different from open-water environment, under-ice environment can introduce some new problems for acoustic communication such as larger transmission loss, severe Doppler effect, and impulsive noise. The key feature of the typical Arctic sound speed profile is that the minimum sound speed resides at the ice-water interface (Freitag et al.
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