Research On Synchronization Technology In DS/FH Hybrid Spread Spectrum System

The direct sequence spread spectrum technology is generally adopted in radio navigation system. But with the development of the electronic counter measures and the improvement of system performance requirements, the radio navigation system adopting the direct sequence spread spectrum technology is facing a serious threat. There are many weak points in the direct sequence spread spectrum system, as its process gain is limited, the near-far effect is severe, and the suppression capability of narrowband interference and spot jamming is poor, so it is vulnerable to enemy interference in actual war. To improve the capability of anti-jamming, anti-intercepting and anti-destruction, it is a trend to develop DS/FH hybrid spread spectrum.On that background, this thesis propose to use DS/FH hybrid spread spectrum technology in radio navigation system in order to improve the ensurence capability in essence. This thesis studies the overall plan and the synchronization technology in radio navigation system adopting DS/FH hybrid spread spectrum technology. The primary content of this thesis is as follows:The signal form of DS/FH hybrid spread spectrum is analyzed and studied. It is been discussed in two aspects. First, the suitable modulation type of DS/FH hybrid spread spectrum is selected in radio navigation system. Second, the overall plan of the system is designed, including FH sequences, direct sequence spread spectrum sequences and fequency synthesizer.The synchronization technology in the receiver is studied in detail. By the analysis and comparison of common DS synchronization methods and FH synchronization methods, a kind of synchronization method combined DS synchronization with FH synchronization is proposed. Firstly, the initial acquisition of FH sequences is achieved by the method of detecting energy. Then, the acquisition of DS sequences is realized according to the position correlation between DS sequence and FH sequence. At last, the precise synchronization of local FH sequence is obtain by the result of DS sequence acquisition. In the end of the thesis, the hardware description language VHDL and the principle diagram are used to design the synchronization circuit in Altera's Quartus II software.