【作者】 张宇峰；

【导师】 柯熙政；

【作者基本信息】 西安理工大学 ， 通信与信息系统， 2008， 硕士

【摘要】 在目前强度调制式的无线光通信系统中,由于存在大气湍流和衰减致使光信号产生随机衰落。从理论上来讲,可通过提高发射功率来克服衰落,但在实际中大功率、高速率的激光器制造很困难,而且也不经济。另外输出的光功率太大对人眼的安全会造成伤害。所以信道编码技术应用于无线光通信的研究已得到重视。信道编码技术可以有效提高传输质量,但会占用系统带宽,且不同的编码方式其纠错能力不同,直接影响通信传输质量和速率。因此,传统单一形式的信道编码设计已不适用于在实际的无线光通信系统中取得最佳传输速率。自适应调制编码技术是一种既能改善传输质量,又能充分利用信道资源的技术。它不以牺牲系统的误码性能为代价,而是通过对信道的准确估计来改变发送功率、波特率、编码方式等或者是综合改变前面所述的各种参数,最终达到提高频谱效率,充分利用信道资源的目的。本文将自适应调制编码技术应用于大气激光通信中,重点研究了各种自适应信道估计算法对无线光通信编码方案的影响,并提出了改进方案。本文首先从传输质量和传输效率的角度,阐述了自适应调制编码技术的作用并将其应用于大气激光通信。其次,在分析大气衰减和大气湍流对激光信号的影响之后,通过比较各种自适应编码方案,设计了一种适用于大气激光通信的自适应信道编码方法——基于信道估计技术的开环自适应信道编码方案。然后,深入研究了各种信道估计技术,如LS(最小二乘)、MMSE(最小均方误差)、基于MMSE准则的维纳滤波、SVD(奇异值分解)等算法,并结合无线光通信的特点,对算法提出了改进。另外,还重点研究了以信噪比作为衡量参数的信道估计方法——基于子空间自相关的估计、基于噪声方差的估计、基于最小二乘的估计、基于相关系数的估计。最后,将自适应信道估计算法应用于大气激光通信,并结合实验测量数据进行了仿真,验证了方案的可行性。实验结果表明,文中所采用的信道估计和信噪比估计技术可以比较好的区分各种天气变化,本文所得到的结果,可以为实现自适应信道编码系统选择切换判决门限提供了适合的理论依据。更多还原

【Abstract】 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.更多还原