# Rainy Environment Identification Based on Channel State Information for Autonomous Vehicles
## 3 Wireless Communication Vehicle Network
The channel model is the foundation of wireless communication system design and must consider specific factors under various vehicular environments, such as urban congestion, highway travel, tunnel crossing, and suburban areas. Each environment exhibits unique channel characteristics, including multipath effects, shadowing losses, reflection, and scattering. To accurately model the channel characteristics in these environments, five main vehicular environments [27], namely Rural Line of Sight (Rural LOS), Urban Line of Sight (Urban LOS), Urban Non-Line of Sight (Urban NLOS), Highway Line of Sight (Highway LOS), and Highway Non-Line of Sight (Highway NLOS) are considered. The channel models for these environments are based on characteristics such as power attenuation, time delay spread, and Doppler frequency shift. Power attenuation describes the energy loss during signal propagation, time delay spread reflects the signal delay variation caused by multipath propagation, and the Doppler frequency shift characterizes the frequency variation due to the change in the relative position of moving vehicles. The comprehensive consideration of these characteristics allows the channel model to more accurately reflect the actual communication environment, providing a solid theoretical foundation for the design of wireless communication systems. These vehicular environments are shown in Table 1.  
Under rainy conditions, the characteristics of the V2X channel indeed undergo significant changes. To accurately simulate these changes in the V2V channel model, a new multipath component is introduced. This component contains independent parameters for gain, delay, and Doppler frequency shift to reflect the specific variations in signal propagation under rainy conditions. Specifically, raindrops may cause additional attenuation and scattering of the signal, affecting its gain and delay. Moreover, rainy conditions may also change the moving speed of vehicles, thereby affecting the Doppler frequency shift. By precisely adjusting these parameters, the vehicle communication performance under rainy weather conditions can be simulated, providing theoretical support for the stable operation of autonomous driving systems in rainy environments. Based on the existing multipath components in each vehicular communication environment, the introduced new multipath components to simulate the channel characteristics under rainy conditions. For path gain, it can be calculated by considering the attenuation effect of raindrops on electromagnetic waves. This typically involves calculating the impact of the scattering and absorption of raindrops on electromagnetic waves. \[G=G_{0}e^{-k_{r}\cdot R\cdot d} \tag{5}\]  
In the formula, \(G_{0}\) is the gain under no-rain conditions, \(k_{r}\) is the rain attenuation coefficient, \(R\) is the rainfall rate (mm/h), and \(d\) is the propagation distance (km). \begin{table}
\begin{tabular}{c c c c c} \hline  & **Taps** & **Power [dB]** & **Delay [ns]** & **Doppler [Hz]** \\ \hline \multirow{3}{*}{U-LOS} & Tap 1 & 0 & 0 & 0 \\  & Tap 2 & \(-8\) & \(117\) & \(236\) \\  & Tap 3 & \(-10\) & \(183\) & \(-157\) \\  & Tap 4 & \(-15\) & \(333\) & \(492\) \\ \hline \multirow{3}{*}{U-NLOS} & Tap 1 & 0 & 0 & 0 \\  & Tap 2 & \(-3\) & \(267\) & \(295\) \\  & Tap 3 & \(-4\) & \(400\) & \(-98\) \\  & Tap 4 & \(-10\) & \(533\) & \(591\) \\ \hline \multirow{3}{*}{R-LOS} & Tap 1 & 0 & 0 & 0 \\  & Tap 2 & \(-14\) & \(83\) & \(492\) \\ \cline{1-1}  & Tap 3 & \(-17\) & \(183\) & \(-295\) \\ \hline \multirow{3}{*}{H-NLOS} & Tap 1 & 0 & 0 & 0 \\  & Tap 2 & \(-2\) & \(200\) & \(689\) \\ \cline{1-1}  & Tap 3 & \(-5\) & \(433\) & \(-492\) \\ \cline{1-1}  & Tap 4 & \(-7\) & \(700\) & \(886\) \\ \hline \multirow{3}{*}{H-LOS} & Tap 1 & 0 & 0 & 0 \\ \cline{1-1}  & Tap 2 & \(-10\) & \(100\) & \(689\) \\ \cline{1-1}  & Tap 3 & \(-15\) & \(167\) & \(-492\) \\ \cline{1-1}  & Tap 4 & \(-20\) & \(500\) & \(886\) \\ \hline \end{tabular}
\end{table} 
Table 1: Vehicular environment characteristics.