Research On Key Techniques Of M-ary Spread Spectrum Communication For Hypersonic Aircraft

In recent years,hypersonic vehicles have played an increasingly important role in modern warfare.The stable transmission of hypersonic aircraft information needs to rely on highperformance communication technology.Spread spectrum communication technology has been highly valued in the field of hypersonic aircraft communication because of its strong antiinterference and concealment performance.In view of the particularity of the hypersonic transmission environment,starting from reducing the complexity and the stability of transmission performance,a high-performance M-ary orthogonal spread spectrum communication scheme is proposed in this paper.And the bit error performance of the proposed communication scheme is calculated through strict mathematical derivation.The anti-noise performance of the M-ary single orthogonal spread spectrum communication scheme and the M-ary bi-orthogonal spread spectrum communication scheme under different channels are analyzed respectively,and the analytical expressions of the bit error rate under several different channel environments are deduced.Aiming at the adverse effects of the time-varying motion state of hypersonic aircraft on the communication receiver,a Partial Matching Filter-Double Hamming-Fast Fourier Transform fast synchronous capture algorithm(PMF-DH-FFT)is proposed.The main work and contributions of the paper are summarized as follows:1)In order to improve the communication quality of hypersonic aircraft,a highperformance M-ary orthogonal spread spectrum communication scheme is proposed.The M orthogonal spread spectrum code sequences required in this scheme are obtained by cyclically shifting the prototype spread spectrum code sequence.During the transmission process,the information data is divided into one symbol per k bit.Then,according to the information content of each input symbol,a spreading code sequence is selected from the M-ary spread code selector for information transmission.The power spectrum of the transmitted signal in this way will be smoother,the concealment of the signal will be significantly improved,the bit error performance can be significantly improved,and the Eb/N0 value in the bit error characteristic curve can be reduced essentially.2)In order to accurately evaluate the performance of th e proposed M-ary orthogonal spread spectrum communication scheme,the bit error rate analytical formulas of the proposed M-ary orthogonal spread spectrum communication scheme under AWGN and Nakagami-m and Rayleigh fading channel are obtained through strict mathematical derivation.And through simulation experiments,the influence of noise power,modulation method,spread spectrum code sequence length,cyclic shift length and other parameters on the performance of M-ary orthogonal spread spectrum communication scheme is analyzed.The bit error performance of the proposed scheme after fading channels is simulated and analyzed.The results show that the proposed scheme can significantly improve the bit error performance,reduce the normalized signal-to-noise ratio in the bit error rate curve,which is very suitable for the application scenarios of hypersonic aircraft with strict requirements on communication performance and signal-to-noise ratio.3)Aiming at the problems of long acquisition time and low acquisition accuracy under the high-speed motion environment of hypersonic aircraft,a PMF-DH-FFT fast synchronization acquisition algorithm is proposed.Through rigorous mathematical derivation,the effects of doppler frequency offset,doppler frequency offset change rate,correlation loss and other parameters on the performance of the proposed algorithm are analyzed.At the same time,the analytical formulas of false alarm probability,detection probability and average capture time are deduced.Theoretical analysis and simulation results show that the proposed acquisition algorithm completes the correct search of the code phase and the accurate estimation of the frequency deviation.The performance is better than the traditional synchronous acquisition algorithm,and it is more suitable for the acquisition of hypersonic aircraft signals.