接近非相干水声通信信道容量的信号处理算法

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4.5dB缩小至1.5dB。给出了实际海试湖试通信效果,频段为6~10kHz,数据速率为357bps,海试时近似垂直通信距离为5km,湖试时水平通信距离近3km、多径超过50mS,两种情况下无差错通信的信噪比门限为2dB,验证了本算法的优势。 

Signal processing algorithm for noncoherent underwater acoustic communication approaching channel capacity

Noncoherent underwater acoustic communication channel in adverse condition is modeled as phase-random Rayleigh fading channel, and its capacity curve is derived. To approach channel capacity curve, concatenated code of nonbinary LDPC code and constant weight code is proposed for noncoherent communication and iteratively decoded in probability domain. Without information of channel amplitude or phase in the receiver, statistic parameters of signal and noise bins were estimated based on moment estimation method, posterior probabilities of constant weight code words were further calculated, and nonbinary LDPC code was decoded with nonbinary factor graph algorithm. It is verified by simulation that by utilizing the proposed concatenated code and its processing algorithm, gap to channel capacity curve is reduced from previous 4.5 dB to 1.5 dB. Underwater communication experiments were carried out in both deep ocean (vertical communication, 5 kin) and shallow lake (horizontal communication, near 3 km, delay spread larger than 50 ms), signal frequency band was 6 to 10 kHz, and data transmission rate was 357 bps. The proposed scheme can correctly transmit in both experiments with a signal noise ratio threshold of 2 dB. The performance of proposed algorithm was well verified by experiments.