基于数字信号处理机的水下光通信收发系统设计及分析

Design and Analysis of Underwater Optical Communication Transceiver System Based on Digital Signal Processor

设计了一种基于数字信号处理机(DSP)的高速高可靠性水下光通信收发系统,并分析了调制时序和信号处理过程。在收发机中,DSP完成待发送信息的里德-所罗门码编码和接收信息的滤波、门限判决、解调解码,现场可编程门阵列(FPGA)完成编码后信息的脉冲位置调制(PPM)。针对激光脉冲水下传输后脉宽展宽小于100ns,激光重复频率偏离均值小于15%的情况,讨论了不同伽罗华域和PPM信息发送速率的关系;分析了收发机的各环节信号处理速度和各接口通信速度。结果表明,收发系统能够实现全双工的实时通信,通信速率可达73kbit/s,可用于实时传输语音和图像等多媒体信息。最后利用Matlab对激光脉冲在Ⅱ类水质中传输100m后到的激光脉冲形状进行了仿真,同时对FPGA发送的一帧数据的电平时序以及模数转换器(ADC)采样得到的一帧数据的采样序列进行了模拟。设计的收发系统为今后水下光通信系统的设计与实现提供了一定的参考。

A high speed and high reliable underwater optical communication transceiver system based on digital signal processor （DSP） is proposed, and the modulation timing sequence and signal processing procedure is analyzed. In the transmitter, the DSP accomplishes Reed-Solomon codes encoding of the information need to be sent and filtering, threshold decision, the decoding and demodulation of the received information. The field-programmable gate array （FPGA） accomplishes the modulation of the information encoded in the DSP. Under the condition that the pulse width after underwater propagation is less than 100 ns and the frequency deviation from the mean is less than 15 %, the dependence of the pulse position modulation （PPM） modulation rate on the chosen Galois field is discussed and the signal processing speed as well as the interfaces communication speed are analyzed. The analytical results show that the designed transmitter system can accomplish full-duplex and real time communication with a speed as high as 73 kbit/s, which can be used for real-time communication of multi-media information, such as voice and images. The pulse shape of laser after a propagation of 100 m in case II water is simulated through Matlab as well as the timing sequence of a frame of data transmitted through FPGA and sampled sequence of a frame of data obtained through analog-to-digital converter （ADC）. The structure of the designed transceiver provides a certain reference to the design and accomplishment of underwater optical communication system in the future.