## 1 Introduction  
The fifth-generation (5G) wireless system is in the rapid development stage of China's mobile telecommunication standards. Moreover, 5G relies on unique advantages, such as high speed, low latency, large capacity, and wide connectivity to rapidly integrate applications in various fields of production and life, and its application scope will eventually range from mobile broadband services to next-generation car and device networking services [1]. Meanwhile, in the sixth-generation mobile communication technology planning, satellite internet communication will play an important role in realizing the transition from the interconnection of everything to the intelligent connection of everything. With the rapid development of coastal cities, the surrounding sea-land junction meteorological environment and the distribution of ground objects will change and become more complex. The modeling requirements for the forward-propagation of communication signals when mixed ducts and non-uniform turbulence occur are more accurate. The 5G network must coordinate high, medium, and low frequencies according to user service coverage and speed requirements to form an efficient and coordinated layered coverage. According to public data, by the end of 2020, operators have opened a total of 718,000 5G base stations, and the number of 5G mobile terminal connections has exceeded 200 million. The dense distribution of base stations has higher requirements for accurate reception and anti-interference of communication links. We selected three sub-6 GHz in the 5G plan for the simulation, and evaluated the weather-induced intercity CCI that may have occurred in different urban links when ducts and tropospheric turbulence existed. An atmospheric duct is mainly caused by the increase of atmospheric temperature with the increase of altitude or the rapid decrease of water vapor density with the increase of altitude. [PERSON] [2] proposed five synoptic processes that can form atmospheric ducts--radiative temperature inversion, subsidence temperature inversion on land surface, temperature advection inversion at the sea-land interface, topographic inversion in local valleys, and frontal temperature inversion are prone to occur. According to data statistics, communication disconnections and other phenomena often occur at night after rain in the plains of China. The monitoring found that it was related to the interference of ducts. This paper selected urban links in the East China Plain (where ducts are prone to occur) to analyze the CCI of over-the-horizon communications. In 1946, [PERSON] and [PERSON] [3] proposed a forward full-wave analytical method--the parabolic equation (PE) method--to solve the problem of forward-propagation in vertically layered inhomogeneous tropospheric ducts. In 1973, [PERSON] and [PERSON] [4] developed a split-step Fourier transform (SSFT) algorithm suitable for underwater acoustic transmission to solve parabolic equations. Subsequently, the PE model has been theoretically deduced and optimized by a series of scholars. Based on its framework, the Feit-Fleck wide-angle parabolic equation (WAPE) [5] method that can calculate a larger range of grazing angles was proposed. The grazing angle can reach 30\({}^{\circ}\). In 1983, [PERSON] and [PERSON] [6] formally proposed a new WAPE form based on the Feit-Fleck method, and [PERSON] [7] verified the good performance of WAPE at wide elevation angles. The PE method takes into account the refraction and diffraction effects of radio wave propagation. Moreover, it can simply and accurately describe the dielectric parameters of the irregular surface and the refractive index distribution of non-uniform atmospheric structures to simulate the propagation characteristics of radio waves in a complex environment. The step-by-step iterative solution method can predict the propagation loss of point-to-point links, and can further realize regional propagation loss prediction.