Research On The Relay Communication Method Of Near-space High-speed Aircraft Based On LEO Satellites

A near-space aircraft is a type of aircraft that can or can only continue to fly for a long time in the near space.Near space has a unique geographical advantage,so the near-space aircrafts show a very broad application prospects with the continuous development of modern science and technology.However,the development of near-space high-speed aircraft is faced with the problem of plasma sheath "black barrier".At present,the research on solving the "black barrier" problem at home and abroad mainly focuses on weakening or restraining the plasma sheath with some physical or chemical means,or weakening the signal attenuation of the plasma sheath by studying the signal transmission characteristics of the plasma sheath or other methods,but these methods can not really solve the problem of near-space high-speed aircraft communication interruption.The main idea of this paper is different from the above methods,it does not directly overcome the problem of weakening or restraining the plasma sheath,but avoids the windward surface with the larger plasma electron density of the near-space high-speed aircraft,emits electromagnetic waves from the leeward side with the smaller plasma electron density,and then forwards to the ground station via LEO satellites.This method can ease the impact of the aircraft by the plasma,and ensure the communication link is connected.In order to analyze the feasibility of the relay communication method of near-space high-speed aircraft based on LEO satellites,the Shannon theorem is used to estimate the link capacity between the aircraft and the LEO satellites.The results show that the channel capacity can meet the requirements of the communication.The dynamic change of the plasma sheath and the relative motion between the aircraft and the satellites make the channel condition between the aircraft and the satellites constantly changing.Aiming at the problem of relay selection of the near-space high-speed aircraft relay communication under the time-varying channel,this paper adopts a method based on channel attenuation coefficient to select the best relay.The method first calculates the incident angle on the plasma surface of the electromagnetic wave sent by the aircraft to each potential relay,then uses the equivalent wave impedance method to calculate the attenuation coefficient of the electromagnetic wave in the plasma sheath channel,and then obtains the attenuation coefficient of each channel to choose the best relay.Aiming at the problem of relay forwarding strategy in the case that the relay received signal power changes strongly with the plasma attenuation,this paper adopts a dynamic amplification/decoding forwarding strategy based on the SNR to forward the signal,the relay forwarding mode combines the advantages of AF and DF.Firstly,the SNR is estimated based on the decomposition of the autocorrelation matrix singular value at the relay.Then,the estimated value is compared with the SNR threshold,when the SNR estimate is greater than the SNR threshold,the decoding forwarding strategy is adopted.Otherwise,the amplification forwarding strategy is adopted.The SNR threshold is determined to be 0.6d B by the simulation result.Finally,in order to evaluate the performance of the relay communication of near-space high-speed aircraft based on LEO satellites,the paper establishes a communication scenario with Iridium satellite as the relay system,and uses the STK software to analyze the coverage of the satellites to the aircraft and the ground station,and select the potential relay.By comparing the channel capacity and the communication error rate of the direct communication and the relay communication based on LEO satellites,it is shown that the method of communication between the aircraft and the ground station based on LEO satellites can relieve the serious impact of the plasma sheath on the aircraft.