Synchronization And Anti-interference Tecnology Of Spread Spectrum Signal In Large Frequency Offset And High Dynamic And Its Implementation

Spread spectrum communication is widely used in the field of space-based measurement and control beause of its strong ability of anti-interference.Ka-band communications has the characteristics of widely available bandwidth, high speed and strong anti-jamming performance.Therefore, measurement and control is developing toward this band.Since the high frequency in Ka-band(26.5-46GHz),and there is often a large relative velocity and acceleration between transmitter and receiver.So the receiver will bear a large doppler shift and its rate of change.Further,since the complexity of transmission path, signal is susceptible to the interference, so the SNR of input signal is low.Therefore,how to demodulate signal in the case of large frequency offset, high dynamic and low SNR is the key of completing the communication and measurement and control for the receiver.Acquisition and tracking are the key technologies of a receiver.We will mainly research on how to complete acquisition and tracking in the situation of large frequency offset and high dynamic in this paper. The main contents are as follows:(1): The basic principle and system models of spread-spectrum communication system will be briefly introducted.The main contents include the concepts of spreading codes,pseudo-random code,m sequence and Gold sequence of direct sequence spread spectrum system.Simultaneously,the correlation of the sequence is analyzed.Finally,the structure of the transmitter and receiver is introduced.(2):A variety of acquire methods are introduced in detail.In this paper,the traditional time-frequency search,parallel code phase and parallel frequency search are introduced.Finally,in order to solve the problem of large frequency offset and low signal to noise ratio,we introduce a parallel Tong detection scheme based on PMF-FFT.(3): The basic knowledge of frequency locked loop,PLL and code loop are introduced in detail.In order to overcome the high dynamics,we present a structure of a two order frequency locked loop parallel assisting three order phase locked loop.And we compare an analysis it with the single PLL and FLL.Subsequently,in order to further improve the anti-interference ability of the system,some interference suppression methods are introduced.(4): The FPGA implementation of the system is described in detail.And the performance of the system was tested on the KC705 Xilinx development board.By comparing with the requirements of the index, the feasibility and reliability of our overall scheme is verified.