Asynchronous Underwater Acoustic Communication Based On The Initial Signal Time-lapse Modulation

Because of the population explosion and the land resource shortages, the international marine resource competitions become more and more drastic. The requirements of the development of underwater acoustic communication technologies are increasingly urgent in both military and civilian areas. The human being pays more attention to the research and design on underwater communication system. However, underwater communications are much more complex than land communications. The signal frequency shift, which is caused by underwater acoustic environment, multipath interferences and Doppler effects, affects the performance of underwater acoustic communication seriously. Additionally, as the attenuation of underwater acoustic communications signal increases while the frequency increases, the frequency tends to extend to the low frequency, which leads to the limitation of the available bandwidth of underwater acoustic communication.Nowadays several common methods of underwater acoustic communication have some shortages. For example, spread spectrum communications technology is limited by the limitation of the available bandwidth. M-ary Chirp Linear Frequency Modulation has less spectrum capacity. As the development of technology, these problems can be solved in some way, but that increase the loss of soft and hardware resources, which add the costs of engineering application.Inspired by the idea that different dots and dashes in Morse code represent different information, this article uses adjacent two different time span transmitted waves to modulate digital information and propose a method of asynchronous underwater acoustic communication based on the initial signal time-lapse modulation.This method can be used to any stationary initial signal. It uses adjacent two different time span transmitted waves to represent different information, and obtain the modulation of digital signal. As to the modulation of primitive signal at the receiving end, time-lapse estimation algorithm, which uses the cross correlation function of receiving signal and initial signal to calculate the time delay, can be used to estimate the time span of adjacent transmitted waves. According to the pre-set relation between the figure and time span to judge the receiving digital information. Just a kind of initial signal can modulate M-ary figure. The method is simple and easy, and has a strong anti-interference, that can help to decrease the costs of engineering application.The simulation results show that this method can effectively combat Doppler frequency shift of underwater acoustic communication, and obtain a higher communication data rate. Moreover, it doesn’t have a specific restriction on the initial signal, so the most suitable type of primitive signal can be chosen based on engineering application.