Design a 5G Backhaul Network Based on Free Space Optics and Analyze the Link Performances

The leading mobile operator in several regions of the world has already launched the 5G networks with midfrequency bands (i.e., 3-6 GHz) and achieved a significant performance boost over 4G networks. However, the 5G network still needs to evolve to unfold the full potential where the network will use the higher frequency bands (i.e., millimeter-wave band) for the additional spectrum (i.e., 400~800 MHz) and boost the network capacity by several folds. The cell site coverage reduces significantly in higher frequency bands which is 100m radius compared to several kilometers in 4G networks. Therefore, the small cell densification will be the key to meet the high availability requirements of 5G networks. But each cell site will need to have a direct connection with the core network called the backhaul network, and it must meet the ultra-low latency requirements of the 5G network, which will be a new challenge. This paper introduces a backhaul network for 5G based on free-space optics and analyzes the backhaul link performances. It is found that there are several mechanisms that negatively affect the optical backhaul link while some of them are climate-related (e.g., rain, fog, and snow), others are related to atmospheric constituents (e.g. gaseous molecules).