A design of underwater wireless laser communication system based on PPM modulating method

Underwater laser communication has been developed in the field of deep-sea exploration, also become a highlight of modern communication technology research. It has the edges of hidden, safe, non-contact and rapid mobility. By now, most data exchange and transmission between underwater sensors and devices are achieved by RS-232 serial ports communication. But it is not able to meet the demands of present underwater communication due to the limitations of transmitting rate and distance. For the first version of our laser system the signals flowing through the RS-232 ports had not been modulated. Therefore, the bit error rate of our previous work was adversely high. In this paper, we progress our system by introducing in a novel signal modulating module, which mainly consists of FPGAs and PPM method. Considering with the effect of absorption and scattering [1], a series of experiments are performed in this paper: unmodulated and modulated underwater laser communication experiments under different visibility water. By comparing the bit error rate results, we suggest that the whole underwater laser communication system is compact, efficient and reliable. Finally, we based on multiple of visibility, the theoretical communication distance of the system can be estimated.