Research And Implementation Of Modulation And Synchronous Technology In FH System

As there are many kinds of radios, complex interference and very crowdedspectrum in very high frequency (VHF) band, anti-jamming has been one of the mostimportant issues for VHF communication systems. Frequency hopping (FH)communication technology has strong anti-interference ability, anti-multipath ability,anti-fading ability, high spectral efficiency, good confidentiality and easy networkingetc., which make it be widely used in military communications. And it is also one of themajor anti-jamming technologies in VHF band. Achieving efficient and reliable datatransmission is a hot and difficult research in VHF FH communication system, is ofgreat significance.Firstly, FH date transmission scheme is given, and analysis of the key technologiesin it, such as FH control, modulation and coding, system synchronization and AGC, ismade.Secondly, modulation and synchronization technique in the system scheme areresearched emphatically. Practical problems, such as phase ambiguity, bad errorperformance of conventional differential modulation and contradiction of effectivenessand reliability, are taken into consideration. Theory of multiple-symbol differentialdetection of QPSK and TCM8PSK modulation is researched, and then a systemsynchronization method which uses Gardner algorithm and frame synchronization ofcoherent insert is designed. The simulation performance of modulation algorithm andsynchronization method well overcomes the above problems and meets the technicalrequirements.Finaly, an implementation scheme based on DSP&FPGA hardware platform hasbeen put forward. Data transmission process of intermediate frequency (IF) andimplementation scheme of master are designed in this thesis, and then characteristics ofIF signal are analysed. Next, two indoor experiments on BER and digital sensitivity ofthe system are made. The results of the experiments show that the key technologiesresearched and performance of the hardware system satisfy the requirements that VHFFH communication data should be transmitted efficiently and reliably under low SNRcondition.