# Opportunistic Weather Sensing by Smart City Wireless Communication Networks
## 2 OISAC of Weather--Current Situation  
In recent years, many researchers in universities, in state-wise meteorological services, and in the private sector, dealt with different aspects of OISAC for weather; see, for example, EU COST Action OpenSense ([[https://opensenseaction.eu/](https://opensenseaction.eu/)]([https://opensenseaction.eu/](https://opensenseaction.eu/)), accessed on 25 September 2024), connecting more than 150 members from over 30 countries. When dealing with terrestrial communications, one can divide the communication into two groups: terrestrial CMLs used mainly in backhaul cellular networks, and SCWNs--for dense smart city connectivity. It is worth noting here that satellite communication usage for OISAC is also an evolving field [19; 24; 25]; however, in this paper we focus on near-ground weather monitoring. In Figure 1, we present an illustration of these two main groups, which emphasize their different deployment and application properties. Note that the division of these groups can be somewhat mixed, as in recent applications, especially under the IoTframework (and IoT in smart cities specifically), different technologies work in harmony as additional parts of a full SCWN, adding a diversity of opportunistic sensor-types, but on the other hand, introducing the challenges of working with different data-sources and devices, each with its own characteristics.  
In general, an IoT framework consists of three layers [26; 27; 28]: The perception (or sensing) layer, the communication (or the connectivity) layer, and the processing (or the data) layer. In the ISAC paradigm for IoT, the sensing capabilities (which corresponds to the end-user hardware itself, such as the transmitted/receiver modules, e.g., with additional hardware aimed for sensing phenomena of interest) are integrated with the communication layer (for further background details regarding OISAC and IoT, the reader is referred to Supplementary Materials).  
The OISAC approach is used to add the sensing of the weather to the existing communication layer. In smart cities, where a vast number of connected devices are available, the number of channels is high, which raises the potential for high spatiotemporal weather products (such as rain-field maps [14; 29]).  
We focus on wireless communication in the microwave and mmWave frequency bands (i.e., 5 GHz to 100 GHz), as the signal level in these frequencies is more affected by weather, as shown in Figure 2. Luckily, this frequency range is the one used mainly in the backhaul CMLs and also in modern fronthaul and xhaul CMLs and SCWNs.  
Figure 1: Opportunistic ISAC for weather using terrestrial wireless communication links, divided into two groups: (**a**) CMLs—point-to-point terrestrial microwave and mmWave channels (e.g., in cellular backhaul networks); (**b**) SCWNs—smart city wireless networks at mmWave frequencies (e.g., wireless communication mesh of smart IoT sensors at street level such as security cameras, traffic lights, bus stations, vehicles, and public facilities such as street trash cans and fire poles).  
Figure 2: The expected signal attenuation (in dB/km) as a function of the channels frequency due to rain, water vapor, and fog. This image is taken from [30] and is based on the ITU recommendation P.838-3 [31].