Time-Varying Channel Equalization in Underwater Acoustic OFDM Communication System
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-Varying Channel Equalization in Underwater Acoustic OFDM Communication System Anfu Zhu1*
1
North China University of Water Resources and Electric Power, Zhengzhou, China *ORCID: 0000-0003-3412-264X, e-mail: [email protected] Received October 17, 2018 Revised June 5, 2020 Accepted June 15, 2020
Abstract—In this paper, three time-varying channel equalization schemes are studied in the underwater acoustic (UWA) Orthogonal Frequency Division Multiplexing (OFDM) communication system. The equalization algorithms are the zero-forcing (ZF) equalization algorithm, and the minimum mean square error equalization (MMSE) algorithm and the serial interference cancellation (SIC) equalization algorithm. Among the schemes, there is a problem of needing a large amount of operation when obtaining the inversion of the channel matrix. Then, to reduce the computation complexity of channel matrix inversion, the band approximation of the channel matrix, the serial equalization and the LDLH decomposition are also studied. To evaluate the efficacy of the algorithms studied in this paper, numerical simulation and the field experiment are both conducted. The simulation results proof that each equalization algorithm can work appropriately under different time-varying conditions, and valid the reliability of each simplified algorithm under the same Doppler factor. The results of two sets of field experiment also prove that the simplified algorithm eliminates the influence of the residual narrow band Doppler to a certain extent, and a better effect is obtained while a channel estimation algorithm with higher accuracy is combined. DOI: 10.3103/S0735272720080038
1. INTRODUCTION With the development of communication technology, the demand for communication through the time-varying underwater acoustic (UWA) channel is gradually increased. Under the condition of the time-varying UWA channel, the Doppler effect generated by the scatterers in the water or the high-speed motion of the transmitter and the receiver will affect the performance of the UWA communication system seriously. In this case, the estimation of the channel matrix of the time-varying UWA channel and the channel equalization technique are necessary to be used to suppress the ICI, especially for the Orthogonal Frequency Division Multiplexing (OFDM) communication system, which is more sensitive to the ICI than the single-carrier communication system. The channel estimation and equalization algorithms for the time-invariant UWA channel are no longer valid when the channel is time-varying. Therefore, a corresponding system model needs to be established for the time-varying channel, in which time-varying channel estimation and equalization algorithms can be studied. Typically, the equalization techniques should be based on accurate channel estimation. Many researchers have studied the time-varying channel estimation methods and proposed a variety of channel estimation methods for time-varying channels. Among them, the representative methods are Basis Expansion Model (BEM), and Compress
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