A Tutorial on Fiber Monitoring for Applications in Analogue Mobile Fronthaul

Radio access networks must evolve to meet future communication requirements. One of the development directions is the future radio base station architecture and its functional splits. The very last connectivity segment to a simple antenna unit is analogue in nature and, to centralize the important and expensive radio access network resources, one would potentially want to extend it to several kilometers. This sort of requirement calls for development of new fiber-based transport technologies with strong emphasis on reach improvement, bandwidth efficiency, and link reliability. With regards to the later aspect, efficient monitoring of physical links would become essential. It should provide rapid and detailed in-service link quality assessment and troubleshooting while imposing minor additional costs and preserving signal integrity. While link monitoring possibilities in baseband transmission for backhaul or digital radio over fiber for fronthaul have been extensively studied, the analogue radio over fiber transmission brings opportunities for application of novel and potentially more efficient transceiver-embedded techniques. It is the objective of this paper to emphasize the critical importance of analogue radio over fiber link monitoring in the era of rapidly developing mobile communications. Our aim in this communication is to define requirements, which an efficient monitoring solution is expected to satisfy, and provide an overview of recent developments. It is assumed that the readers possess general knowledge of fiber optic transmission, reflectometry, passive optical networks and are familiar with various optical components. Set of selected references is provided for those willing to deepen their knowledge of aspects addressed in this paper.