在航空卫星移动服务(AMSS)应用之前,高频(HF)空地通信系统是超视距航空移动通信的唯一手段.无论在越洋、边远陆地和远程航线飞行的飞机都用HF电台与地面通信.高频电波传播主要靠电离层反射,而电离层的特性随着昼夜交替、季节变化和太阳黑子的活动产生扰动,很不稳定.通常认为HF是变参数的信 Prior to the application of Aeronautical Satellite Mobile Services (AMSS), HF HF communications systems were the only means of over-the-horizon aeronautical mobile communications where HF aircraft were used to communicate with terrestrial communications, regardless of whether the aircraft flying over the ocean, remote land and long-haul routes High-frequency radio waves are mainly reflected by the ionosphere, and the characteristics of the ionosphere are disturbing with the alternation of day and night, seasonal variations and sunspots’ activity, and it is generally unstable to believe that HF ​​is a variable parameter