Research Of Frequency Synthesizer And Synchronization In Frequency-hopping System

As the fast development of communication technology, single-frequency or simple multi-frequency communication can not meet the demand of modern electronic war. Spreading Spectrum (SS) system is a new type of communication system built on the basis of Shannon Information Theory. It is widely used for its strong capabilities of anti-jamming, multi-accesses, secrecy and anti-multipaths. As a branch of SS system, Frequency-Hopping (FH) system has excellent anti-jamming capability by changing the carrier wave frequency randomly. Now it is widely used in military communication.This dissertation conducts an in-depth study of SS system, DS(direct-spreading) system and FH system ,which includes discussion of pseudo-random sequence and synchronization theory. FH function module is added to a VHF fixed frequency communication system to enhance the anti-jamming performance. The key technology in the system is the design of FH synthesizer and Synchronizer.DDS regarded as the third generation synthesizer is an ideal choice in the FH system for its excellent appearance in phase-noise, frequency resolution and frequency changing time. The DDS device AD9852 of this synthesizer has a valuable function that it can generate linearity FM signal through changing its working model. FM modulation is achieved by changing its time and frequency step.This dissertation designed a synchronizer that combined "Reference Time" and "Synchronous Head" method together. The receiver's working frequency is got from system's TOD time by complicated nonlinear operation. The synchronous head is set at the forefront of the HF signal and is inserted in divergently throughout transmitting process. The synchronizer of receiver can recognize the synchronous head signal and use it to adjust local time and PN codes. The main profit of the scheme includes high speed, good credibility and high confidentiality.