基于短时傅里叶变换的水声通信自适应OFDM均衡

由于水声环境时变特性，在水声信道中进行正交频分复用(orthogonal frequency division multi plexing,OFDM)信号传输，子载波间的正交性易受到破坏，从而产生载波间干扰，使得水声通信的误码率性能变差。针对这个问题，提出一种适用于水下时变信道的自适应OFDM均衡算法，该算法采用滑动窗口进行子块短时傅里叶变换获得接收信号的二维时频谱，进而对该二维时频谱进行自适应时-频域联合合并均衡。该自适应均衡算法中采用最小均方误差算法跟踪信道时变特性，并通过自适应判决反馈均衡更新二维时频谱的加权合并系数，提高了OFDM系统抗载波间干扰的性能。仿真分析表明,所提出的OFDM均衡算法可在时变信道下，有效降低水声通信的误码率。

Adaptive OFDM equalization in underwater acoustic communication based on short time Fourier transform

For orthogonal frequency division multiplexing (OFDM) signal transmission over underwater acoustic channel, the subcarrier orthogonality is quite easily destroyed by the time varying characteristic of underwater environment, which will cause great inter carrier interference, and increase the bit error ratio of the underwater acoustic communication system. An adaptive underwater acoustic OFDM equalization algorithm is proposed, which adopts adaptive joint time frequency combination of the two dimension spectrum of the received signal obtained by a sliding window based subblock short time Fourier transform (STFT). The adaptive equalization algorithm is implemented by adaptively tracking the time varying channel characteristic by least mean square (LMS) method, then adaptively combine the time frequency sequences with the coefficients updated by adaptive decision feedback equalization. Simulation results show that the proposed OFDM equalization method over time varying channel can decrease the bit error ratio of the underwater acoustic communication effectively.