How do clouds affect blue-green laser communication
Since the attenuation of blue-green laser is very small under water, it has become the future direction of communication between air target and underwater target. However, if there are clouds on the link, the communication performance will become worse. Figure 1 is a schematic diagram of the presence of clouds on the link. There are several hypotheses about the mechanism by which clouds affect the communications: 1. Clouds attenuate laser energy; 2. Clouds bring extra noise; 3. Clouds expand the time domain of the pulse signal. Different influencing mechanisms correspond to different methods to improve communication quality: 1. Increase transmission power, and reduce divergence angle or increase receiving aperture; 2. More efficient coding and modulation techniques are adopted so that the signal still has a smaller bit error rate at a lower SNR; 3. Reduce transmission rate, adopt MIMO technology or channel equalization technology, etc. In order to reduce the influence of cloud on blue-green laser communication more effectively, it is necessary to find out how cloud affects blue-green laser communication to determine the future research direction of technology.
The team of Professor MAO Zhongyang of Naval Aviation University analyzed and studied this problem through simulation, which showed that the time domain expansion of the pulse signal was the most important factor . Although the cloud attenuates the laser energy, it can still communicate normally for systems with large link margins. However, turbulence is still the factor that affects SNR in the atmospheric channel, and the influence of cloud on SNR can be ignored. Nevertheless, from the perspective of maximum communication rate, when the pulse passes through the cloud layer, the time domain is extended due to multipath effect, and when the communication rate is too high, inter-code crosstalk is caused, so the maximum communication rate is limited. When the communication rate exceeds the maximum value, inter-code crosstalk is caused, which increases the bit error rate and results in the decline of communication quality. One of the advantages of blue-green laser communication is high-speed communication, so it is more affected by clouds than other forms of communication.
This work is funded by the National Natural Science Foundation of China (6170012154) and theShandong Province "Taishan Scholar" Construction Project Special Fund Project (ts20081130).
About The Group
The research team has been engaged in the research work of laser communication for a long time. It is one of the earliest teams to carry out the offshore wireless optical communication technology in China, and has undertaken a number of pre-research and model development tasks. Focusing on the application of the wireless optical communication system in the offshore environment, there is a rich accumulation of technology in the modeling and testing of the characteristics of the wireless optical communication channel, wireless optical modulation coding technology and so on. At present, the research on the characteristics of wireless laser channel in offshore environment is in a leading position in China. The team has built the first offshore wireless optical communication channel test system in China, and established the channel model and basic database of infrared band communication channel. In recent years, the team has won 1 second prize of national scientific and technological progress, 1 first prize and 4 second prizes of military scientific and technological progress, 1 first prize of Shandong provincial scientific and technological progress, more than 20 authorized invention patents, published more than 100 papers, nearly 50 papers have been included in SCI and EI, and two papers have been selected as the “F5000" top academic papers of China's high-quality scientific and technological journals.
Li Songlang, Mao Zhongyang, Liu Chuanhui, et al. Analysis of the effect of cloud thickness on the performance of blue-green laser communication[J]. Opto-Electronic Engineering, 2020, 47(3): 190389.