## 1 Introduction
Secondly, due to the high maneuverability of the aircraft, it can be extremely difficult to effectively align the TT&C communication station with the vehicle antenna window. (2) Using lower frequency electromagnetic waves for communication can reduce the electromagnetic shielding effect of the plasma sheath. When the electromagnetic wave length is greater than the physical size of the plasma sheath, the electromagnetic wave frequency is much lower than the plasma frequency and collision frequency. At this point, the electromagnetic wave electric field component is severely attenuated by the plasma sheath, while the magnetic field component can penetrate the plasma sheath with minimal attenuation [27; 28]. Therefore, magnetic receiving devices can be deployed inside the vehicle to sense magnetic field component signals for communication. In addition, compared to high-frequency electromagnetic waves, short waves (3 MHz-20 MHz) are less affected by path loss and atmospheric loss and can use ionospheric reflection to achieve OTH (over-the-horizon) communication. The shortwave beam has a wide coverage range, eliminating the need for the widespread deployment of ground TT&C communication stations and saving satellite communication resources. However, the ionosphere changes with time and space, making the propagation of skywaves more complex. The focus of this study is to explore the characteristics and laws of the impact of ionospheric spatiotemporal changes on the skywave ionosphere communication channel of hypersonic vehicles. Since the 20 th century, there has been growing interest in research on skywave ionospheric propagation [29; 30]. In terms of skywave channel modeling, researchers have made further improvements based on the following two types of models: The first type of model is the Gaussian scattering model, proposed by [PERSON] et al. based on long-term measurement research on ionospheric reflection channels [31]. This model later became the standard channel model recommended by the International Telecommunication Union (ITU) for testing skywave communication performance [32]. However, in applications that are restricted to narrowband channel models, the effective bandwidth of the [PERSON] model cannot exceed 12 kHz [33; 34; 35; 36]. The second type of model is a statistical model developed by the Institute of Telecommunication Sciences (ITS) in the United States. This model includes three modules, namely, a delay power spectrum, Doppler frequency shift, and Doppler spread, making it suitable for both broadband and narrowband communication [37]. However, the above research focused on the channel characteristics of the time-varying ionosphere within a fixed airspace, specifically the reflection propagation from one fixed point to another (where both the receiver and transmitter are stationary). For a hypersonic vehicle moving across a large airspace, the ionosphere can be considered a stationary, non-drifting scattering/reflection surface. In this case, the channel characteristics depend on the structure of the ionospheric reflection surface and the maneuvering characteristics of the vehicle. Due to differences in flight altitude, the significant delay caused by OTH propagation, the multipath variations induced by irregular ionospheric structures, and the Doppler effect resulting from vehicle motion, the conditions differ from those of traditional channels. The fundamental differences in the physical factors causing channel variations make it impossible to directly apply traditional skywave channel models to hypersonic vehicle skywave ionospheric channels. Furthermore, in the future, hypersonic vehicles will require high-bandwidth communication systems capable of supporting long-distance (above 1000 km) flight control operations. According to the ITU's recommendations for selecting frequencies throughout the day based on the lowest usable frequency (LUF) and the highest usable frequency (MUF), the commonly used radio frequency bands are 7 MHz and 14 MHz.