## 1 Introduction  
The near space (NS), also known as the sub-orbit, is located in the airspace range from 20 km to 100 km [1]. Generally, the flight altitude of aviation aircraft is below 20 km, while the flight altitude of satellites is usually above 100 km. Therefore, it is difficult for aircraft and satellites to stay in the NS for a long time, and it is in an \"awkward\" altitude range where \"aircraft can't reach it and satellites can't come down to it\". Due to its special spatial position, it is of great significance both in scientific research and practical applications. Precisely because of this, the development and utilization of the NS has attracted extensive attention from scientists around the world. Correspondingly, a NS vehicle refers to a sub-orbital vehicle that can only fly or is capable of flying in the NS for a long time and continuously, or a hypersonic cruise vehicle flying in the near space, such as airships, high-altitude floating balloons, high-altitude long-endurance unmanned aerial vehicles (UAV), long-distance remotely controlled gliding vehicles, and space shuttles (including reusable ones), etc. They have great development potential in emergency support, scientific investigation, space exploration, agriculture, and other aspects, and possess advantages that aviation and aerospace vehicles do not have [2; 3; 4]. With the gradual rise of manned spacecraft, especially commercial aerospace, in the foreseeable future, NS vehicles may play a greater role in human exploration of space and the universe. However, spacecraft all face the problem of communication interruption with ground stations when re-entering the atmosphere. In order to meet the communication, navigation and tracking, telemetry and command (TT&C) requirements of spacecraft during re-entry into the atmosphere, we are compelled to consider an integrated communication, navigation, and TT&C (ICNT) signal that can adapt to the NS, so as to alleviate this problem from the perspective of signal design. To this end, scholars in relevant fields within the industry have successively put forward reference suggestions or solutions. At the national level, the National Aeronautics and Space Administration (NASA) of the United States (2019, 2020, 2024) has mentioned the development that will cover aspects such as broadband Ka band, optical radio frequency (RF) hybrid antennas, and user-initiated services (UIS) [5; 6; 7]. It hopes to leverage the commercial satellite communication services in low Earth orbit (LEO) to expand and potentially replace the tracking and data relay satellite service (TDRSS), and plans to gradually discontinue the use of TDRSS. The State Council Information Office (SCIO) of the People's Republic of China released a white paper titled \"Full text: China's Space Program: A 2021 Perspective\". In addition to introducing the main achievements of China's space industry development since 2016, it also mentioned that in the next five years, China will continue to improve its space infrastructure, promote the integrated development of satellite technologies such as remote sensing, communication, and navigation and positioning, advocate good and efficient governance of outer space, expand the cause of human progress, and make positive contributions to world peace and development [8]. The European Union and its member states attach great importance to the strategic value of NS. They have issued plans such as the \"Horizon\" program and the European space program, providing financial and policy support for the research of high-speed aircraft, NS platforms, etc., so as to help the sustainable development of Europe's space capabilities and related infrastructure by promoting technological innovation in the industrial and scientific communities [9; 10]. As a pioneer inspace projects and programs for exploring space beyond the Earth, Russia plays a crucial role in the development of satellite technology and the conduct of international cooperation.