Fast Acquisition And Tracking Method Of Carrier Signal In Hypersonic Flying Environment

In recent years,hypersonic vehicle as an important carrier for the development of near space has been rapidly developed,when a hypersonic vehicle is flying in the near space,the carrier signal in the tracking telemetry and command(TT&C)link not only generates big Doppler frequency offset,but also a high rate of change of the Doppler frequency due to the maneuvering flight of the hypersonic vehicle,which seriously affects the reliability of the TT&C communication.In addition,the friction between aircraft surface and air leads to ionization of air molecular and generation of plasma sheath with variable parameters.And,the research shows that this dynamic plasma sheath can produce parasitic amplitude-phase modulation effect on signal.What's more,under the influence of fluctuating pressure,the phase change caused by antenna vibration and signal coupling will also pose great challenges to the reliable TT&C communication of hypersonic vehicle.In light of continuous and reliable TT&C communication requirements for hypersonic vehicles,a fast acquisition and tracking method of carrier signal in hypersonic flight environment is studied in this paper.The influence mechanism of hypersonic flight environment on synchronization of TT&C signal is emphatically analyzed,including the influence of large dynamic Doppler shift,phase noise generated by dynamic plasma sheath and phase noise caused by antenna vibration.On the basis of the above mechanism analysis,at the large scale level,the fast acquisition method under the constraints of low signal-to-noise ratio and large dynamic Doppler is studied.At the small scale level,aiming at the problem that the tracking speed and tracking accuracy of carrier signal are contradictory under the influence of amplitude and phase jitter,fast and accurate tracking methods of carrier signal with nonlinear carrier tracking and assisted by smoothing constraints algorithm are studied respectively.Finally,the adaptive carrier synchronization method in hypersonic flight environment is studied.This study will provide methodological support and engineering application guidance for continuous and reliable TT&C communication of hypersonic vehicle.The main contributions of the thesis are listed as follows:1.The influence mechanism of hypersonic flight environment on synchronization of TT&C signal is investigated from large and small scale aspects,respectively.Firstly,the large dynamic Doppler model(large scale)is established and its influence on carrier synchronization is analyzed.Secondly,the effects of two typical phase noise sources(small scale)on dynamic plasma sheath and antenna vibration are studied respectively,a computational model of dynamic plasma phase noise is proposed.Aiming at single frequency signal,BPSK and QPSK phase modulation signal,the influence mechanism of dynamic plasma phase noise on carrier synchronization error and carrier tracking loop robustness of different telemetry signals is studied,and the influence of dynamic plasma phase noise on carrier tracking loop lock-out threshold is quantitatively analyzed.The coupling effect between the antenna vibration of hypersonic vehicle and the TT&C signal is found.The influence of antenna vibration intensity on carrier tracking loops of different telemetry systems is quantitatively analyzed.2.A joint acquisition method of Doppler shift and Doppler rate based on the correction of the search range of spectrum peak assisted by blind estimation of Doppler rate is developed.In the light of acquisition and tracking of carrier signal under the condition of big Doppler shift as well as big Doppler rate,this method achieves a fast acquisition method of dynamic Doppler in hypersonic flight environment.A fast blind estimation method of Doppler rate is proposed,combining the advantages of parallel Doppler rate matching acquisition method under multi-channel condition,and draw lessons from the idea of spectral peak search range correction,realizing the joint acquisition of Doppler shift and Doppler rate.The simulation results show that the acquisition error of Doppler shift is less than 100 Hz and the acquisition error of Doppler rate is less than 1 kHz/s when the Doppler shift is 1.5 M and the Doppler rate is �200 kHz/s in Ka band,and the acquisition speed is 75.47% higher than that of the multi-channel acquisition method.3.A new tracking loop structure coupled with a non-linear element is proposed.Under the influence of jitter effect of frequency and phase,a fast and accurate tracking method based on Type3-phase-locked loop(PLL)is investigated.Referring to the idea of non-linear control,the non-linear model of the new loop is constructed,and a mathematical model describing the dynamic process of the new loop is established,and a feedback iteration method is proposed to optimize parameters of the loop.The results show that the output frequency of the new loop jitters much smaller than that of the traditional Type3-PLL when the input signal-to-noise ratio(SNR)equals-15dB.The standard deviation of the frequency-phase error is reduced from 0.6198(rad/s)~2 to 0.2264(rad/s)~2.Under the optimum parameters,the performance of the new loop is obviously improved,and the lock-out threshold is reduced from-20 dB to-23 dB.4.A new tracking method based on smoothing constraint algorithm is developed to suppress the amplitude modulation effect.The received signal amplitude is constrained in a reasonable range by the smoothing constraint algorithm,and then the Type3-PLL is utilized to track the carrier,which realizes the suppression of dynamic plasma amplitude modulation effect and improves the performance of carrier tracking loop.The simulation results show that,the jitter of output phase error is obviously suppressed when the jitter intensity of plasma sheath is 8%,and the lock-out threshold of the loop is reduced by 4 dB.Moreover,the loop has strong robustness when its bandwidth varies from 5 Hz to 15 Hz.5.A new adaptive carrier signal synchronization method is proposed,which combines the fast acquisition method of large dynamic Doppler and the tracking method under the condition of small scale jitter effect.The results show that when the loop noise bandwidth is 15 Hz,the dynamic plasma electron density jitter intensity is 2%,the standard deviation of antenna vibration displacement is 0.01 times of the electromagnetic wave wavelength,and the signal-to-noise ratio is as low as-22 dB,the new synchronization method can track the Doppler shift of 1.5 M and the Doppler change rate of �200 kHz/s.In conclusion,the thesis research results of this paper provide effective method support and engineering application guidance for the continuous and reliable TT&C communication of hypersonic vehicle,which is of great significance to solve the problem of TT&C communication of hypersonic vehicle.