Research On SC-FDE Based Troposcatter Communication Scheme

In recent years, troposcatter communication has occupied an important position in emergency communication. It not only can communicate between far distances, but also have high quality of secrecy. In this paper, the design and analysis of troposcatter communication scheme based on single carrier frequency domain equalization(SC-FDE) is proposed.Firstly, the characteristics of the troposphere scattering channel are analyzed: large channel transmission loss and high efficient nonlinear power amplifier in the transmitter, meanwhile, the multipath delay spread causes the frequency selective fading, and the Doppler effect leads to the channel time variation. Furthermore, the model of the tapped delay line is used to establish the mathematical model of troposphere scattering channel, and simulation model of the seven path Rayleigh channel is established, which provides the basis for the design of the troposcatter communication scheme.Secondly, SC-FDE combines the advantages of frequency domain equalization and low peak to average ratio, which can solve the problems of severe multipath delay extended and power constrained in the troposphere scattering channel. According to the characteristics of the troposphere scattering channel, the system model and the transmission frame of the SC-FDE based communication scheme are designed. The transmission frame structure is designed by composed preamble and data frame. The cyclic prefix and cyclic suffix are inserted in the front and behind of each symbol in order to overcome the inter symbol interference caused by multipath effects. The Zadoff-Chu sequence is used as the sequence of the preamble and unique word(UW). According to the simulation channel model, the parameters of the SC-FDE based communication scheme are selected, including the length of FFT, the encoded and modulated method and so on.Finally, the key technologies of SC-FDE based communication scheme are studied and simulated. In the aspect of frame synchronization, preamble is divided into multiple CAZAC sequences to prevent the loss of useful data. Since CAZAC sequence has strong autocorrelation features, the receive sequence and the local sequence are correlation processed and can succeed in capturing the transmission data arrival time by the correlation peak constantly superimposed. In the aspect of frequency synchronization, the effect of carrier frequency offset on system is introduced, and the common frequency offset estimation algorithms are simulated and theoretical analyzed. According to analyze the advantages and disadvantages of different algorithms, the estimation algorithm combined cyclic prefix and UW sequence is established. The simulation results show that the algorithm has greatly improved in frequency offset estimation accuracy and performance of the system. In the aspect of frequency domain equalization, the channel estimation, channel interpolation and equalization criterion are introduced. In this paper, the minimum mean square error criterion is used for frequency domain equalization, and it is optimized by segmenting UW sequence in Least-Square channel estimation algorithm. The simulation results show that the algorithm can improve the performance of the system.