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恶劣情况下的非相干水声通信信道模型为随机相位Rayleigh衰落,推导了该模型的信道容量曲线。为实现接近非相干信道容量的可靠通信,提出多进制低密度校验码(LDPC)和恒重码级联码的多进制非相干概率域迭代处理算法。在信道幅度和相位完全未知的情况下,根据矩估计得到信号和噪声频点幅度的统计参量,进而得到恒重码的码字后验概率,再对多进制LDPC码进行因子图迭代译码。仿真证明本算法与现有的最大能量检测非迭代译码算法相比,与信道容量曲线的差距从4.5 dB缩小至1.5 dB。给出了实际海试湖试通信效果,频段为6~10 kHz,数据速率为357 bps,海试时近似垂直通信距离为5 km,湖试时水平通信距离近3 km、多径超过50 ms,两种情况下无差错通信的信噪比门限为2 dB,验证了本算法的优势。
The incoherent underwater acoustic communication channel model is random phase Rayleigh fading, and the channel capacity curve of the model is deduced. In order to achieve reliable communication close to the incoherent channel capacity, a multi-band noncoherent probability domain iterative processing algorithm of multi-ary low density parity check codes (LDPC) and constant weight codes is proposed. Under the circumstance that the channel amplitude and phase are completely unknown, the statistical parameters of the amplitude of the signal and the noise frequency point are obtained according to the moment estimation, then the posterior probability of the codeword of the constant weight code is obtained, and the iterative decoding of the multi-ary LDPC code is carried out. The simulation results show that compared with the existing maximum energy detection non-iterative decoding algorithm, the proposed algorithm reduces the gap from the channel capacity curve from 4.5 dB to 1.5 dB. The actual sea trial communication results are given in the band of 6 ~ 10 kHz with a data rate of 357 bps. The approximate vertical communication distance is 5 km for sea trials, horizontal communication distance is about 3 km for lake trials, and the multipath is more than 50 ms , SNR threshold of error-free communication is 2 dB in both cases, which verifies the advantages of this algorithm.