Research On Information Transmission Scheme Under Plasma Sheath Channel

When space vehicles,satellites,and missiles etc aircrafts pass through the atmosphere over the Earth,due to the supersonic speed of the aircraft,a high temperature of up to 3000degrees Celsius is generated,resulting in ionization of the surrounding air molecules.These ionized ions and electrons will attach to the surface of the aircraft,forming a layer of high-density plasma,the so-called“plasma sheath”.Usually this layer of plasma's electron density can be as high as10^{2 0}m^-3,which will seriously interfere with the communication between the aircraft and the satellite or ground station.In severe cases,the communication will be interrupted,that is,the so-called“blackout”phenomenon,which has become one of the bottlenecks in the space field.To solve this problem,it is necessary to conduct research on the information transmission scheme under the plasma sheath.In this paper,we will find a suitable information transmission scheme through the study of the characteristics of the transmission signal in the plasma sheath,so as to lay a good foundation for the measurement,control and communication of super-high-speed air vehicles in the near space.1.The channel characteristics of the plasma sheath are analyzed.Firstly,the formation mechanism of the plasma sheath is explained.Then,based on the analysis of the characteristic parameters of the plasma sheath channel,the characteristics of the plasma sheath channel are studied,including the parasitic modulation effect and the existed Doppler effect in the plasma sheath.The amplitude attenuation and phase characteristics of the plasma sheath channel are studied.Finally,the coherence bandwidth and coherence time of the channel are analyzed,which lays a foundation for the design of the subsequent information transmission system.2.The information transmission scheme based on Chirp signal in plasma sheath channel is studied.Firstly,the characteristics of the Chirp signal and the fractional Fourier transform are analyzed.Then two modulation schemes based on Chirp signals are introduced,and two kinds of non-coherent demodulation schemes of the Chirp spread spectrum system are deeply analyzed,and the bit error rate performance under the additive Gauss white noise channel is derived.On this basis,the Chirp spread spectrum system is simulated.The simulation results show that the Chirp-2FSK system based on FrFT demodulation has more excellent performance than the existing 2FSK system.On this basis,the adaptive filter scheme based on the fractional Fourier transform is improved to make it suitable for the information transmission under the plasma sheath.Finally,based on the characteristics of the Chirp signal,a unequal error modulation system is proposed.When the attenuation of the channel is serious,the system can give priority to the high-priority data of the aircraft.3.An adaptive modulation and coding system for information transmission under plasma sheath channel is designed.The simulation verification and detailed analysis of the system are performed,which proves that the system has good adaptability to the plasma sheath channel.First,the feasibility of designing an adaptive modulation and coding system in a plasma sheath channel is analyzed.Then,the simulation of the direct sequence spread spectrum system based on Chirp-2FSK is performed,and its performance improvement under the plasma sheath channel is determined.At last,in view of the low transmission rate and low frequency bandwidth of the spread spectrum Chirp-2FSK system,the adaptive modulation and coding technology is introduced,and an adaptive modulation and coding system is designed and verified by simulation.The simulation results show that the system can work well under the plasma sheath channel.Through the adaptive adjustment of the system's information transmission rate,the system reliability is guaranteed,while ensuring the throughput of the system.