Design Of Modulation Method And Joint Demodulation And Decoding Method For Hypersonic Vehicle Telemetry Channel

When a hypersonic vehicle flies in the near space,a shock wave with high temperature is formed under the impact of rapid air compression.The high temperature ionizes the gas and forms a plasma that coats the vehicle,which is called the “plasma sheath”.The plasma sheath will scatter and absorb the electromagnetic wave,causing serious amplitude attenuation and phase shift of the electromagnetic waves,that is,the parasitic modulation effect;the plasma sheath has high dynamic and fast time-varying characteristics,which also affect the hypersonic vehicle telemetry channel.The existing telemetry modulation and demodulation methods are difficult to adapt to the hypersonic vehicle telemetry channel,so it is necessary to study the corresponding modulation methods and joint demodulation and decoding algorithms to obtain modulation and coding gains.Therefore,this paper develops the modulation and demodulation methods for hypersonic vehicle SISO(Single Input Single Output,SISO),SIMO(Single Input Multiple Output,SIMO),and 2×N MIMO(Multiple Input Multiple Output,MIMO)telemetry channels and design the corresponding joint demodulation and decoding methods.The main work and contributions are as follows:1.The adaptive demodulation method and detection performance of typical modulation in the SISO telemetry channel are studied.For the highly dynamic telemetry channel,the detection performances of a PSK(Phase-Shift Keying,PSK)demodulation method with pilot correction,an adaptive ASK(Amplitude-Shift Keying,ASK)demodulation method with ML(Maximum Likelihood)detection,and the non-coherent FSK(Noncoherent Frequency-Shift Keying,NC-FSK)demodulation method are analyzed.The simulation results show that the PSK demodulation method can correct the large-scale phase shift;the ASK demodulation method can adapt to the dynamic changes of the channel;the NC-FSK demodulation method can effectively reduce the influence of the phase shift,and compared with the first two methods,at least 3d B gain can be obtained.2.A power modulation with an adaptive ML detection method for the SIMO telemetry channel is proposed.Aiming at the highly dynamic and fast time-varying characteristics of the telemetry channel,a power modulation with a progressively optimized constellation and an adaptive ML detection method are designed by using the criterion of minimizing the bit error rate.This method uses the RJ-MCMC(Reversible Jumping Markov Chain Monte Carlo)algorithm to estimate the probability density function(PDF)of the average power of the received signals,and realizes the adaptive ML detection in the highly dynamic and fast time-varying telemetry channel.The simulation results show that compared with the diversity receiving method of the traditional modulation method,the optimized power modulation with ML detection can improve the performance by at least8 d B,and significantly reduce the bit error rate.3.A space-frequency modulation with an efficient non-coherent detection method for the 2×N MIMO telemetry channel is proposed.Based on the analysis of the asymptotic correlation between the 2×N MIMO link from the vehicle to the receiving station,a spacefrequency modulation method and a detection method are proposed.The method uses dual antennas and dual carriers to transmit QPSK co-directional and quadrature components;in the process of signal detection,the noncoherent detection problem based on ML criterion is converted into a parameter optimization problem,and then an efficient fast noncoherent detection method is given.Meanwhile,an optimal transmit power allocation algorithm is proposed to improve the system performance.The simulation results show that the spacefrequency modulation and detection method proposed in this paper can effectively suppress the parasitic modulation effect,and the efficiency of the optimal transmit power allocation algorithm is verified.4.Protograph-BICM-ID systems based on NC-FSK,power modulation,and space frequency modulation are proposed.The new systems introduce the Protograph LDPC coding and the Protograph-BICM-ID joint demodulation and decoding framework.For the SISO,SIMO,and 2×N MIMO telemetry channels,the adaptive Protograph-BICM-ID systems based on NC-FSK,power modulation,and space frequency modulation are constructed,respectively.The systems use the RJ-MCMC algorithm to calculate soft information for iterative decoding,realize joint demodulation and decoding processing,and obtain a performance gain of at least 3d B(compared with the hard-decision decoding scheme).The system efficiency is verified.In this paper,the modulation and demodulation,joint demodulation and decoding methods of hypersonic vehicle SISO,SIMO and 2×N MIMO telemetry channels are studied.The research results deepen the understanding of the transmission characteristics of electromagnetic signals in dynamic plasma.The communication method designed to adapt to the telemetry channel of the hypersonic aircraft provides a key theoretical method support for alleviating the“radio barrier” and improving the telemetry performance.