水下甚低频MSK信号最大似然多符号差分解调算法

水下甚低频（VLF）最小频移键控（MSK）信号受脉冲噪声、海水衰减和海面起伏的共同影响。为了降低对相位同步的要求，提高解调算法的适应性，该文研究了水下甚低频MSK信号的差分解调算法，建立了甚低频MSK调制信号在海水中的传播模型。考虑脉冲噪声处理算法的影响，基于最大似然（ML）原理推导了水下甚低频MSK信号多符号差分解调算法。仿真结果表明:水下甚低频MSK信号最大似然多符号差分解调算法在相位同步下可获得逼近相干解调的性能，在相位不同步下可获得优于相干解调的性能，具有显著的优势。

Maximum Likelihood Multiple Symbol Differential Demodulation Algorithms for Underwater VLF MSK Signal

Underwater very low frequency (VLF) minimum shift keying (MSK) signals are distorted by the impulsive noise, the propagation attenuation of sea water and the fluctuation of sea wave. In order to reduce the requirement for carrier phase synchronization and improve the robustness of demodulation algorithm, the differential demodulation algorithm of the underwater VLF MSK signal is investigated in this paper. The propagation attenuation of sea water is first modeled. By considering the impact of suppressing impulsive noise, the multiple-symbols differential demodulation of the underwater VLF MSK signal is then derived based on the principle of maximum likelihood (ML) detection. Extensive simulation results show that the performance of the ML multiple-symbols differential demodulation algorithm can closely approach that of the coherent demodulation algorithm if the carrier phase is recovered and a relative large amount of symbols are utilized. On the other hand, the differential demodulation algorithm is superior to the coherent demodulation algorithm if the carrier phase is not recovered.