Doppler Diversity Method For High-speed Aircraft In Large Dynamic Doppler Environment

In recent years,hypersonic vehicles have become a research hotspot in the aerospace field.And reliable measurement and control communication technology,as its"eyes and ears"during flight,has also become one of the key technologies.There is a high-speed radial relative motion between the hypersonic vehicles and monitoring and control station on the ground,resulting in the received signal to have a very large Doppler shift and Doppler rate of change.When the hypersonic vehicle is flying at a high speed in the Ka communication band at a speed of Mach 10 to 25,the Doppler shift can be as high as 453kHz to 1.133 MHz,Doppler rate of change up to 100 kHz/s.Large dynamic Doppler will bring huge challenges to the existing measurement and control communication system,which will lead to the correct demodulation of the measurement and control information and the failure of the aircraft to perform tasks.This paper focuses on the challenges brought by the large dynamic Doppler in the measurement and control communication of hypersonic vehicles,and explore different research ideas from conventional methods,a fast transmission scheme and overall idea that combines Doppler diversity with Doppler shift fast coarse capture is proposed.The specific idea of the program is as follows.Firstly,the Doppler frequency shift fast coarse acquisition method is used to roughly estimate the Doppler frequency offset and the Doppler primary change rate.The Doppler frequency offset is reduced by the compensation to within the Doppler diversity processing capability.The signal carrying the residual Doppler shift is then handed over to the Doppler diversity system for processing.Finally,the data is accurately demodulated.The traditional frequency-locked phase-locked loop capture tracking method has the disadvantages of high precision and loss of lock.the advantage of this method is that the Doppler frequency shift coarse capture requires low capture accuracy and can save a lot of capture time.The use of Doppler diversity instead of the real-time tracking of the frequency-locked phase-locked loop,which ingeniously avoids high complexity and that the problem of loss of lock caused by the dynamic change Doppler frequency shift.Under the guidance of the overall plan and ideas,this paper further explores two specific methods for implementing Doppler diversity transmission.1.A Doppler diversity receiving method based on frequency offset is proposed.The method performs a frequency offset on the compensation signal,which with residual Doppler shift,to generate multiple copies of the branch signal.The Doppler diversity gain is obtained by the signal energy that is enhanced by merging.Simulation results show,at low SNR?-5 dB?,the fast coarse capture method can achieve 100%coarse capture of Doppler shift and its rate of change.Reducing the normalized Doppler shift to 0.01,when the residual Doppler frequency is at 1 kHz,which can achieve better Doppler diversity performance when corrects the frequency shift to 0.4/T.Therefore,under certain conditions,compared with the traditional acquisition and tracking method,the Doppler frequency offset is coarse captured to within 1 kHz,then the measurement and control communication of the hypersonic vehicle can be completed faster.2.A Doppler diversity transmission method for precoding joint block feedback equalization is proposed.In view of the poor performance of the system performance of the Doppler diversity reception method due to channel estimation errors,the method further improves system performance by jointly designing transmission and reception.The method spreads each symbol information to the entire transport block by transmitting precoding,and uses the soft decision block feedback equalizer to iteratively collect each symbol information for the entire data block to obtain a Doppler diversity gain.Simulation results show,When the residual Doppler shift is 1 kHz,the bit error rate performance can reach 10^-3 by 5 iterations.Compared with Doppler diversity receiving method,the system performance is improved.