Reseach On Direct Sequence Spread Spectrum Technology And FPGA Implementation

From preliminarily explorated in the military confrontation fields to widely used in the civilian communication fields,Spread Spectrum Communication shows superior performances on the aspects of anti-multipath-fading,anti-interception and anti-jamming.Because its spreading sequence has well pseudo-randomness,Direct Sequence Spread Spectrum technology which belongs to Spread Spectrum technology shows the advantages of concealing information and accomplishing multi-address communication.How to design synchronization link and data link with stable performance becomes the key link to resist the complex channel environment,to complete tracking frame head and to compensate channel distortion in the Direct Sequence Spread Spectrum Systems.In this paper,I analyze the system performance in AWGN channel,Rayleigh channel and COST207 channel according to the technical characteristics of Direct Sequence Spread Spectrum Systems,complete the hardware implementation of this system with the xc5vsx95 t chip which produced by Xilinx company and test the performance of this hardware system.The specific steps include:Firstly,I complete the design of synchronization link and test the link performance by using Matlab simulation software.The design mainly includes selection of spreading sequence,design of filter,frame synchronization,frequency offset estimation and so on.In the design,system uses two kinds of spread factor.When SF is 4,the system can achieve the fast data transmission in high-quality channel environment.When SF is 128,the system can achieve the reliable data transmission in strong interference and noise channel environment.In the process of frame synchronization,I use the method of sliding correlation to complete tracking frame head.And then,with the phase difference between the adjacent two correlation peaks,the system can estimate the frequency offset and compensate the frequency distortion brought by radio frequency equipment.On the basis of the design,I select threshold factors and test the performance of synchronization link by Matlab simulation in AWGN channel,Rayleigh channel and COST207 channel.Secondly,with the ISE hardware design tool,I complete the design of data link and the implementation of the whole hardware system.The hardware system which has modular construction needs FPGA cooperating with DSP to accomplish digital signal processing.DSP mainly completes modulation and demodulation,coding and decodingl,error statistics and other symbolic data processings.FPGA mainly completes spreading and despreading spectrum,scrambling and descrambling,synchronization and other sampling data processings.The EMIF interface between FPGA and DSP completes data and information interactions with the interrupt mode.At last,I test and analyze the performance of the hardware system.In order to test the performance of the system under the different environment,I calculate the bit error rate from hardware system by importing different environments which are designed by Matlab.And then,I compare the curves of error rate between from the hardware system and software simulation system to analyze the performance of hardware system.