In this paper, we have presented the cooperative free space optical (FSO) communication system with radio frequency (RF) backup as an application to the level crossing warning systems for Railways. Reliability and bit error rate (BER) performance has been carried out to ensure the performance improvement over single link. Cooperative FSO link continues to work in the presence of rain in which the RF system fails. BER performance improvement includes the study of various combining schemes including multiple gain combiner (MGC) which is simple and provides close to optimum performance. FSO system fails in the presence of fog whereas the RF system continues to work. The complementary nature of the system ensures that one of them gives desired performance in the presence of rain/fog. The effect of equipment failure, turbulence, pointing error, fog and rain has been studied in reliability analysis. Different relaying techniques and various combining techniques are the part of study in BER analysis. With the use of reflect and forward relaying scheme including cyclic redundancy check and 3 out of 5 majority voting scheme, we can achieve the desired tolerable hazard rate which meets the international standards of safety integrity level 4.

中文翻译：

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具有 RF 备份的协作 FSO 通信系统作为铁路平交道口警告系统的应用

在本文中，我们提出了具有射频 (RF) 备份的协作自由空间光 (FSO) 通信系统，作为铁路平交道口警告系统的应用。进行了可靠性和误码率（BER）性能测试，以确保在单链路上的性能提升。协作 FSO 链路在出现 RF 系统故障的雨中继续工作。BER 性能改进包括研究各种组合方案，包括简单且接近最佳性能的多增益组合器 (MGC)。FSO 系统在有雾的情况下发生故障，而 RF 系统继续工作。该系统的互补性质确保其中之一在有雨/雾的情况下提供所需的性能。设备故障、湍流、指向错误的影响，在可靠性分析中研究了雾和雨。不同的中继技术和各种合并技术是BER分析研究的一部分。通过使用反射和转发中继方案，包括循环冗余校验和 3 of 5 多数表决方案，我们可以达到理想的可容忍危险率，满足安全完整性等级 4 的国际标准。