Research on the Adaptive OFDM Hydroacoustic Communication

Abstract

Due to the complexity and variability of hydroacoustic channels with long delay multipath propagation, Doppler shift, spectral distortion and non-smoothness, adaptive techniques are used to efficiently use the hydroacoustic channel information to change some parameters of the transmit signal to adapt to the changing channel and thus improve the communication performance. The efficiency of underwater communication systems may be further enhanced by combining the high communication rate, frequency band usage, and multipath resistance of orthogonal frequency division multiplexing (OFDM) technology with multi-carrier wireless communication. We review the development process of adaptive techniques in hydroacoustic communication, and introduce AM based on channel information, power allocation adaptive techniques, joint adaptive bit, modulation and power allocation, combined with reinforcement learning adaptive techniques, respectively. And we analyze the research results of using them in recent years to solve the effects of rapidly changing multipath propagation, fast time-varying, and extended propagation delay in hydroacoustic communication. Our analysis concludes that a multi-carrier OFDM system using link-level adaptive techniques has greater flexibility and can achieve better system performance than a conventional single-carrier system. The basic parameters that can be adjusted include modulation, coding, transmit power, spread spectrum gain and signaling bandwidth. Inaccurate channel state information (CSI) can lead to incorrect modulation schemes, resulting in inefficient communication. Therefore, it is important to effectively obtain accurate CSI as the basis for efficient modulation selection, regardless of the AM method used.