基于蒙特卡罗方法对水下激光脉冲长距离传输进行了模拟仿真。根据激光脉冲在水下的展宽情况及脉冲能量的变化规律, 系统采用波长为532 nm、单脉冲能量为1 mJ的全固态脉冲激光器作为发射光源, 采用口径为100 mm、接收视场角为15°的望远镜作为接收机。采用现场可编程门阵列(FPGA)进行低密度奇偶校验码(LDPC)编码和脉冲位置调制(PPM), 经光电转换及采样后的接收端信号被发送到上位机进行后处理。最后, 基于研制的实验系统开展了水池实验, 以验证系统性能。理论与实验结果表明, 在Jerlov Ⅱ类水质条件下, 误码率情况相同时LDPC编码与PPM相结合的通信系统可获得2.34 dB的编码增益。实验证明该系统可以实现水下130 m处误码率低于10-5的可靠通信。

The long distance transmission of underwater laser pulse is simulated based on Monte Carlo method. According to the underwater broadening of laser pulse and the variation of pulse energy, the system uses a solid-state laser with the wavelength of 532 nm and the single pulse energy of 1 mJ as the emission source, and uses a telescope with the aperture of 100 mm and the field angle of 15° as the receiver. Low-density parity check codes (LDPC) and pulse-position modulation (PPM) are accomplished based on a field-programmable gate array (FPGA). The received signal after photoelectric conversion and sampling is transmitted to the host computer for post-processing. Finally, a pool experiment is used to verify the system performance based on the developed experimental system. The theoretical and experimental results demonstrate that the designed system with LDPC and PPM can obtain 2.34 dB coding gain at the same bit error rate (BER) under the condition of Jerlov Ⅱ water quality. Experiment shows that the system can achieve reliable underwater communication with BER of 10-5 and distance of 130 m.