Research On Acquisition Technologies Of PN Code Based On DMF And Narrowband Interference Suppression In DSSS

Direct-Sequence Spread-Spectrum communication technique has developed with the development of Spread-Spectrum technique and communication technique.It has been widely used in both military and civilian communication system due to good immunity to interference and interception,resistance to multipath fading,and robust multiple access capability,etc.And what's more,it is impossible to exist without Spread-Spectrum communication technique in military wireless ommunication system.In the spread spectrum receiving system,the acquisition for PN code is the most important technical problems,especially,it works under the condition of low sgnal noise ratio,low signal interference ratio and high dynamic.Comparing with other acquisition method of PN code,the acquisition of PN code based on digital matched filter(DMF) has many advantages,for example,acquisition time is short,it is implemented easily and works stably.therefore it has been widely used in satallite communication and moblie communication system.At first,the acquisition of PN code based on digital matched filter is introduced and then the acquisition performance of PN code based on DMF is analysed in non-fading AWGN channel,rayleigh fading channe and narrowband interference environment.The detection probability,false alarm probability and mean acquisition time are derived.The computer simulation and analysis is given.Contraposing the different condition,the acquisition circuit of PN code is designed.In order to improve acquisition performance in Rayleigh fading channel,the method of post-integral is proposed.In order to improve acquisition performance under the large frequency-offset, a high precise method to measure carrier frequency-offset complex vector with FFT is proposed.In order to improve acquisition performance and bit-error-ratio in the narrowband interference environment,two method of narrowband interference suppression is given in the paper.Contraposing the different condition,the acquisition circuit of PN code is designed.Therefore the research of this paper provides the theory basis for the better acquisition performance in DSSS.Because the fixed threshold can not meet the requirements of interference rejection and anti-fading in the process of PN code acquisition,we discussed the necessity to use adaptive threshold at first,and then we give two method of adaptive threshold estimation.A new adaptive threshold estimation algorithm for PN code acquisition with limitative false alarm rate is proposed. it is very fit for practical application.Finally,we give the circuit design based on FPGA of acquisition PN code according to acquisition method on the different conditions based on theoretical analysis and computer simulation,and the design method of key technical mould is given in detail. In the end of the paper,we carried on the summary to the full text,pointing to the shortcoming and the practical problems encountered in the research work,and discussed the method to improve the future work.