自由空间光通信中的数字喷泉码方法

Research on digital fountain code method of free space optical communication

为了克服大气衰减和光强起伏对自由空间光通信性能的影响,信道编码是解决大气湍流信道影响的关键技术.数字喷泉码是一种无固定码率的信道编码方法,其中度分布是数字喷泉码设计的基础,本文采用开关度分布的方法,并给出其开关点最佳值.实验仿真结果表明,分别在自由空间光通信系统的弱湍流和强湍流环境条件下,数字喷泉码相比于RS码有较好的编码增益,数字喷泉码中的开关度分布相较于二进制指数度分布、鲁棒孤子度分布,在相同的信噪比条件下,开关度分布的误码率更低,信息速率的下降趋势也最少,同时双开关度分布与单开关度分布相比,对于自由空间光通信系统的性能提升更大.因此,双开关度分布数字喷泉码能有效抑制大气湍流的影响,大幅度地提高自由空间光通信系统性能.

Channel coding is the key technology to solve the atmospheric turbulent channel influence, which can overcome the weakening on the performance of free space optical communication caused by atmospheric attenuation and light intensity fluctuation. Digital fountain code is a channel coding method without fixed rate, based on the distribution design. This paper presents the method of switch degree distribution and gives the optimal value of the switching point. The simulation result shows that regardless the turbulent environment of free space optical communication system is weak or strong, digital fountain code compared with RS code has the better coding gain. Also, under the same SNR, free space optical communication system with the lowest bit error rate and the least information rate decline is under digital fountain code of switch distribution compared to binary exponential distribution and robust soliton distribution. At the same time, the double switch degree distribution compared with the single degree distribution improves more on the performance of free space optical communication system. Therefore, digital fountain code of the double switch distribution can effectively suppress the influence of atmospheric turbulence, significantly improve the performance of free space optical communication system.