Communication In the Gap—Helicopter Satellite Communication System
Helicopters have always been an important maneuvering platform, both in terms of military applications and in terms of everyday economic activities. At present, helicopters mainly communicate with ground towers through ultra-shortwave methods, which are affected by the curvature of the earth so that the communication distance is generally between 50 km and 200 km.
With the deepening of application in forest, emergency and disaster relief, emergency and other aspects, the scope of helicopter activities continues to expand. However, the traditional communication mode limits this kind of wide area application, and the traditional communication mode has very limited speed, which is difficult to adapt to the requirements of the development of the information age.
Among the current multiple means of communication, satellite communication is the most effective means without limitation of distance. Geostationary communication satellites in synchronous orbit can achieve rapid communication across thousands of kilometers; And the rate of satellite communication can reach hundreds of megabytes. These advantages of satellite communication have made it an important means of helicopter information transmission in the future.
The communication environment of helicopters is very different from that of general satellite communications. General satellite communications need to maintain terminal-to-satellite visibility, while helicopter communications have propeller occlusion of wireless signal transmission, and this occlusion period and occlusion time are also related to helicopter models. Therefore, anti-rotor occlusion has become a key technology for satcom in the field of helicopters.
The first anti-rotor occlusion technology is to use the rotor detection method to achieve the reception of burst signals at the interval between the propeller and the antenna occlusion. In this technology, rotor detection and signal burst reception are at the core.
The second anti-rotor occlusion technology is to use the diversity method, according to the rotor occlusion period to send the signal twice, if one of them is blocked by the rotor, it can ensure that the other time is correctly received. In this technology, the correct setting of the diversity period and the effective consolidation of the receiver signal are important contents.
In recent years, many studies have shown that the influence of rotor shielding on radio signals can be overcome by coding. These coding technologies mainly include low bit rate LDPC coding technology, fountain coding technology and so on. This kind of signal receiving way is different from two previous technology. It can not only adapt to different helicopter models, but also ensure good universality.
The trend of the development of next-generation helicopter satellite communication is high-speed channel transmission, high-performance phased array antenna, terminal miniaturization and low power consumption. These “communication in the gaps” technology can not only be applied in conventional helicopters, but also usher in faster development in the field of unmanned helicopters in the future.
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