# UAV Dynamic Non-Terrestrial Transmission Channel Analysis Based on SSCM-RT Model
## 1 Introduction  
The fifth-generation (5G) wireless communication technology has developed quickly and has been used continually as a result of the ongoing advancement of the global information process. As shown in Figure 1, all kinds of UAVs have become an important component and effective supplement to realize the 6G air-space-ground-sea integrated communication system [1] and have become an important part of building a space-air-ground integrated network (SAGIN) [2]. Full-spectrum resources, such as sub-6 GHz, millimeter wave (mmWave), terahertz, and optical bands, will be increasingly explored [3]. To fulfill the increased demand for higher data rates, millimeter wave bands and broadband wireless communication links both offer new facilities for 5G mobile communication networks [4]. Due to the substantial propagation losses that millimeter waves experience due to long-distance communication, these losses are typically reduced by using highly directed antennas or antenna arrays [5; 6]. Omnidirectional antennas perform better in terms of communication performance during movement from the perspective of UAV control, while directional antennas struggle [7]. To better satisfy the demands of long-distance communication, Multiple-Input Multiple-Output (MIMO) antenna arrays can be used. Multiple antennas in a MIMO system can be used in many ways to maximize efficiency. MIMO antenna arrays can increase channel reliability and channel capacity [8]. Spatial multiplexing (SM) and beamforming (BF) are the most popular of these [9]. Low-altitude and high-altitude UAVs can cooperate to complete challenging targeting missions. In complex battlefield scenarios with potent electronic jamming and anti-aircraft firepower, as well as those that include non-terrestrial network (NTN) communication issues, micro UAVs have clear advantages such as indestructibility, low cost, and function distribution [10; 11]. NTNs can provide us with multicast opportunities over very large areas as well as can serve users even in remote areas or during times of natural calamities [12]. It is suggested that NTN can conduct high-capacity millimeter wave transmission in the 3 GPP specification, which calls for enormous bandwidth and can achieve high-speed connection using high-directional antennas [13]. Meanwhile, high-altitude UAVs have broader coverage than low-altitude UAVs and have lower path loss than high-altitude platforms. This mainly depends on the altitude of the flights. Therefore, the research into the communication channel characteristics of high-altitude UAVs and the non-terrestrial network transmission characteristics of UAV relays is relevant to the national military and security. Statistical, deterministic, and semi-deterministic models are the primary types of wireless channel models used today. A vast number of observed data are used in the statistical modeling method to determine the channel impulse response, which is then used to generalize the channel's statistical properties and empirical formula to other scenarios with comparable structural elements. Common statistical channel models such as the spatial statistical channel model have trouble adequately describing the conditions of dynamic communication channels [9]. The deterministic model is based on the electromagnetic wave propagation mechanism, predicts and analyzes the wireless channel characteristics by particular environmental conditions, but has significant computational complexity on air attenuation. The diffusion angle of some scattering components usually does not affect end-to-end channel transmission, but ray-tracing algorithms still take it into account. The complexity can be reduced using the semi-deterministic model. However, there is a significant error in simulating the propagation's environmental conditions. The fundamental tenet of the ray-tracing (RT) technique is that the ray approximation of geometrical optics can be used to study electromagnetic wave rays when their wavelength is sufficiently small in comparison to the size of the building.