A Fast Acquisition And Tracking Tecnology Of Spread Spectrum Signal In Large Frequency Offset And High Dynamic Circuments And Its FPGA Implementation

Spread spectrum communication technology has been widely used in many fields forits multiple advantages. Under certain circumstances，there is often a high relative velocityand acceleration between the transmitter and the receiver, and the carrier frequency is high,so the receiving end is subjected to great doppler shift and doppler frequencyrate-of-change. Further, since the transmission path is complex and the signal is susceptibleto strong interference, so the signal to noise ratio (SNR) at the receiving end is low.Therefore, how to a achieve signal demodulation and other functions at the receiver in largefrequency offset, high dynamic and low SNR environment is the key issue to completecommunication, monitoring and control and other purposes. In spread spectrum receiversystem, acquisition and tracking are the key tecnologies. This paper studies how to achievefast acquisition and tracking in large frequency offset, high dynamic and low SNRenvironment and be summarized as follows:(1)The paper introduces the basic principles of spread spectrum and the basic structureof the receiver. Mainly introduce the concepts of spreading codes, pseudo-random sequence,m sequence, Gold sequence. For spread spectrum receiver, there is a brief mention of itsfront end, DSP processing part, and the paper emphasizes the importance of acquisition andtracking.(2)The paper introduces the concept of spread spectrum signal acquisition. Theacquisition techniques based on sliding correlation and serial search in time-domain andbased on FFT cycle-related are analyzed. The fast acquisition technique based on PMF-FFTis designed for the circumstance with large frequency offset and high dynamic. And thedetection method based on Tong detector is designed for the environment with low SNR.And there is a detailed presentation about CFAR and other related technology. This paperpresents the simulation results for the method and the results verify that the method iseffective.(3)For high dynamic situation, the paper designs a second-order FLL assitingthird-order PLL carrier tracking loop. The method takes advantage of good dynamicperformance, good noise performance of FLL and the advantages of high tracking accuracy of PLL, so that the two complement each other. The results of simulation and experimentshow that the method can effectively track50g dynamic.(4)The scheme is implemented on the Xilinx KC705development board. The resultsshow that this scheme can achieve fast acquisition and tracking of signal with800kHzfrequency offset,50g dynamic,10k data rate,3.069M spread spectrum code rate and7dBsymbol SNR.