Zhang Yu, Li Xinyang, Rao Changhui
The Key Laboratory on Adaptive Optics, Chinese Academy of Sciences, Chengdu, China.
Appl Opt. 2012 Apr 1;51(10):C144-51. doi: 10.1364/AO.51.00C144.
An accurate pointing system is required in free-space optical (FSO) communication links. Low energy-transmission efficiency caused by pointing errors would decline the communication system's performance. The statistics of the detected signal or return signal values could be used to estimate the pointing parameters, whereas atmospheric turbulence brings in serious challenges. A modified moment-matching estimation method is presented in this paper. The irradiance fluctuation caused by the atmospheric turbulence is considered, and the probability density function (PDF) in a weak turbulence condition is assumed to be lognormal. This modified approach is evaluated with wave-propagation simulation data and shows significant improvement over the conventional approach. The estimation accuracy and the properties of this new approach are also discussed. Although our method is based on lognormal irradiance PDF under a weak turbulence condition, the irradiance PDF would tend to be lognormal with aperture averaging effect under moderate to strong turbulence, and the ideas can be extended with appropriate PDF models to satisfy different conditions.
自由空间光（FSO）通信链路需要一个精确的指向系统。指向误差导致的低能量传输效率会降低通信系统的性能。检测信号或返回信号值的统计数据可用于估计指向参数，而大气湍流带来了严峻挑战。本文提出了一种改进的矩匹配估计方法。考虑了大气湍流引起的辐照度波动，并假设弱湍流条件下的概率密度函数（PDF）为对数正态分布。该改进方法通过波传播模拟数据进行评估，与传统方法相比有显著改进。还讨论了这种新方法的估计精度和特性。虽然我们的方法基于弱湍流条件下的对数正态辐照度PDF，但在中等到强湍流条件下，辐照度PDF在孔径平均效应下会趋于对数正态分布，并且这些想法可以通过适当的PDF模型进行扩展以满足不同条件。
