*Article* **Rainfall Monitoring Based on Next-Generation Millimeter-Wave Backhaul Technologies in a Dense Urban Environment**

**Congzheng Han 1,2,\*, Juan Huo 1,2, Qingquan Gao 1, Guiyang Su 3 and Hao Wang 1,2**


3 Zhejiang Provincial Meteorological Observatory, Hangzhou 310002, China; sgy52401314@126.com

**\*** Correspondence: c.han@mail.iap.ac.cn

Received: 31 January 2020; Accepted: 17 March 2020; Published: 24 March 2020

**Abstract:** High-resolution and accurate rainfall monitoring is of grea<sup>t</sup> importance to many applications, including meteorology, hydrology, and flood monitoring. In recent years, microwave backhaul links from wireless communication networks have been suggested for rainfall monitoring purposes, complementing the existing monitoring systems. With the advances in microwave technology, new microwave backhaul solutions have been proposed and applied for 5G networks. Examples of the latest microwave technology include E-band (71–76 and 81–86 GHz) links, multi-band boosters, and line-of-sight multiple-input multiple-output (LOS-MIMO) backhaul links. They all rely on millimeter-wave (mmWave) technology, which is the fastest small-cell backhaul solution. In this paper, we will study the rain attenuation characteristics of these new microwave backhaul techniques at different mmWave frequencies and link lengths. We will also study the potential of using these new microwave solutions for rainfall monitoring. Preliminary results indicate that all the test mmWave links can be very effective for estimating the path-averaged rain rates. The correlation between the mmWave link measurement-derived rain rate and the local rain gauge is in the range of 0.8 to 0.9, showing a grea<sup>t</sup> potential to use these links for precipitation and flood monitoring in urban areas.

**Keywords:** rainfall monitoring; remote sensing; rain rate estimation; 5G; millimeter-wave; E-band; LOS-MIMO
