Research And FPGA Implementation Of The Synchronization Technology Of Multiple Modes Airborne Spread-Spectrum Data-Link

In this thesis,the synchronization issues of digitized direct-sequence spread-spectrum(DSSS)receiver under conditions of large frequency offset and low signal-to-noise ratio environment have been researched based on the background in the design of the battlefield Data-link and the development of the communication terminal.The paper discuss from three aspects: large frequency offset capture,pseudo-code synchronization and carrier synchronization.The design of the Data-link and the realization of synchronization algorithms of the program on the background for this study is given.This paper first introduces the development status of the Unmanned Aerial Vehicle(UAV)Data-link and the advantages to adopt spread-spectrum technology in UAV systems,and introduces the fundamental principle of Spread-Spectrum technology.Then introduces the design of the Data-link with the analysis of the Doppler effects on the background for this study.After the establishment of frequency offset model of the system,we discuss the synchronization algorithm for Network mode,first we introduce the traditional time-frequency two-dimensional serial search algorithm following with presenting a FFT-based frequency-domain pre-compensation method which is suitable for large frequency offset and low signal-to-noise(SNR)environment.In order to increase the SNR,we propose differential coherent accumulation algorithm whose performance is much better than the traditional non-coherent accumulation algorithm.And then gives the pseudo-code tracking strategies and carrier tracking strategies of Network mode.As for Data-Transmission mode,consider that the length of pseudo-code is short and the symbol rate is high in this mode,we adopt the synchronization method based on matched filter which is able to accomplish the synchronization fast without using lots of hardware resources.Finally,the paper gives the implementation of the hardware platform according to the demand of the terminal,it also gives the block diagram of the software and the test results of the implementation.