Adaptive Coding For Laser Communication In Atmosphere

Presently, in intensity modulation wireless optical communication, atmospheric attenuation and atmospheric turbulence could cause light signal to generating random fading.Through increasing power to conquer fading was feasible in theory. But for high rate modulation and high power output laser apparatus, it was not only difficult but also not economical. Otherwise, the output optical power must ensure eyes safety. So the study of channel coding had gained recognition. Channel coding technique could improve transmitting quality, but different coding scheme which occupied resource was also different, affected transmitting quality and transmitting rate directly. Therefore, traditional simplex channel coding had not been the same with gaining the best transmitting rate in actual wireless optical communication system.Adaptive modulation coding technique was able to improve transmitting quality and make the best of channel resource. It mainly via estimating channel quality to change send power,baud rate,encode scheme or all of above. This paper applied adaptive technique on atmosphere optics communication, especially studied on adaptive channel estimate arithmetic.This paper firstly expounded the purpose of adaptive technique in atmosphere optics communication from the viewpoint of transmission quality and transmission efficiency. Secondly, this paper analyzed atmosphere wireless channel, indicated that atmospheric attenuation and atmospheric turbulence had affection on laser signal. Designed open-loop adaptive encoding scheme which using channel estimate technique. Then, profound studied various channel estimate technique,such as LS,MMSE,Weiner-MMSE,SVD arithmetic and put forward improved arithmetic. Otherwise, stress studied four SNR estimation arithmetics. Finally, with experimentation measure data, the analysis and the corresponding simulations also confirmed arithmetic feasibility. Experimental result indicated that channel estimate and SNR estimate technique adopted in this paper could distinguish weather variations, experimental result could provide theory reference for adptive channel coding system to select switchover judgement threshold.