Research And Implementation Of Duplex Direct Spread Spectrum System

Spread spectrum communication technology is a means ofcommunication, which is to send the signal by expanding the spectrum ofthe baseband signal to a wide one in the transmitting terminal. Wihile inthe receiving terminal, the expanded spectrum returns to the baseband one.It is the spread spectrum communication technology that possesses thestronger anti–noise jamming, anti–multipath jamming and also the higherspectral efficiency, which makes the technology widely used both inmilitary and civil field.The main work of the dissertation is to research and implement thespread spectrum code modulation of the transmitting terminal andsynchronization technology of the receiving terminal in the DirectSequence Spread Spectrum Duplex Communication System. In order toimprove the anti-jamming capability of spread spectrum systems, longerspreading code sequence is put into use in the transmittingterminal.During the coarse synchronization of the spreading codesynchronization in the receiving terminal, the acquisition algorithm ofsliding correlation is introduced.While in the process of finesynchronization, non-coherent delay locked loop is used in the trackingalgorithm,with COSTAS loop producing the copy of the local carrier inthe carrier synchronization.The data transition in the spread spectrumreceiver is solved by changing the spread spectrum modulation scheme.What s more, in order to improve system stability, after researching the algorithm of phase discriminator and loop filter in the code ring andcarrier ring, the algorithm suitable for the system is proposed.The projectmentioned above, having been simulated by Matlab, is implemented byVHDL.Finally, the project is simulated based on Modelsim,with a fineeffect after debugging on the board.At last, the next researching directions are put forward. Furthermore,several suggestions are offered to optimize the system.