ABSTRACT

OFDM-based Radio on Free space optical (RoFSO) system gained attention of technocrats and researchers due to high data rates, license-free spectrum and ease of installation among the others. However, it is noteworthy to mention that turbulence-induced fading and pointing error are the major challenges of RoFSO system. Although various literatures include pointing error and/or turbulence induced fading to present different performance measures of RoFSO system, none of them includes all the turbulence condition from weak to strong. In contrary, Double Generalized Gamma (DGG) distribution shows perfect fit over the entire range of turbulence conditions from weak to strong. This research work presents various closed form expressions of BER for M-QAM and K-PSK schemes over DGG distribution under weak, moderate and strong turbulence conditions for the system with and without pointing error. Furthermore, as DGG distribution includes different fading channels such as Double Weibull and Gamma-gamma distribution as its special case. Therefore, we reproduce BER of M-QAM and K-PSK modulation schemes with and without pointing error over Double Weibull and Gamma-gamma fading channels. Simulation shows that irrespective of severity of turbulence, pointing error and/or increase in the order of modulation scheme deteriorate the system performance.

摘要

基于 OFDM 的自由空间光无线电 (RoFSO) 系统由于高数据速率、免许可频谱和易于安装等优点而受到技术专家和研究人员的关注。然而，值得注意的是，湍流引起的衰落和指向误差是 RoFSO 系统的主要挑战。尽管各种文献包括指向误差和/或湍流引起的衰落以呈现 RoFSO 系统的不同性能度量，但它们都没有包括从弱到强的所有湍流条件。相反，双广义伽马 (DGG) 分布在从弱到强的整个湍流条件范围内显示出完美的拟合。这项研究工作提出了 M-QAM 和 K-PSK 方案在弱、具有和不具有指向误差的系统的中度和强湍流条件。此外，由于 DGG 分布包括不同的衰落通道，例如双威布尔分布和 Gamma-gamma 分布作为其特例。因此，我们在 Double Weibull 和 Gamma-gamma 衰落信道上重现了具有和不具有指向误差的 M-QAM 和 K-PSK 调制方案的 BER。仿真表明，无论湍流的严重程度如何，指向误差和/或调制方案阶数的增加都会使系统性能恶化。我们在 Double Weibull 和 Gamma-gamma 衰落信道上重现了具有和不具有指向误差的 M-QAM 和 K-PSK 调制方案的 BER。仿真表明，无论湍流的严重程度如何，指向误差和/或调制方案阶数的增加都会使系统性能恶化。我们在 Double Weibull 和 Gamma-gamma 衰落信道上重现了具有和不具有指向误差的 M-QAM 和 K-PSK 调制方案的 BER。仿真表明，无论湍流的严重程度如何，指向误差和/或调制方案阶数的增加都会使系统性能恶化。