Research On Spread Spectrum Parameters Estimation And Anti-interference,and Code Space Joint Transmission Scheme

The direct sequence spread spectrum technology adopts pseudo-random sequence for spectrum spreading.It has low power spectral density,good concealment performance,strong secrecy,and strong anti-interference ability,thus has been widely used.A Direct Sequence/Frequency Hopping(DS/FH)hybrid spread spectrum communication system combines direct sequence spread spectrum technique with frequency hopping spread spectrum technology to allow the signal to have the advantage of direct-spread signal and to have frequency-hopping signal like ultra-wide spectrum,strong anti-interference ability.And this technology is usually used in military communications.In the communication confrontation,intercepting and knowing the enemy's transmission data is very important,so it is necessary to study the blind estimation of the parameters of the DS/FH hybrid signal.In addition,Multiple Input Multiple Output(MIMO)technology is equipped with multiple antennas at both ends of the wireless link,and can utilize the space resources provided by multiple antennas to enhance the system transmission capacity and transmission reliability without increasing frequency domain resources and additional transmit power.Therefore,the design of transmission scheme based on the combination of spread spectrum and space resource is also the main work of this thesis.The main work of this thesis is as follows:A DS/HF hybrid communication system simulation model was built in SIMULINK,and then extended to the LABVIEW platform.Firstly,SIMULINK and LABVIEW simulation platform are briefly introduced,and SIMULINK is used to build direct sequence spread spectrum and DS/FH hybrid spread spectrum communication system model.This thesis analyze the key sub-modules and common interference modules in the DS/FH system model,and use the data collected in the DS/FH hybrid spread spectrum communication system built by SIMULINK to estimate the spread spectrum parameters.The spectrum-reprocessing method and cepstrum method are used to estimate the duration of the spreading code,and the spreading chip rate is estimated by using the delay and multiply approach and the cyclic spectrum analysis method.In addition,based on the established model,the ability of the system to resist sweep frequency interference,tracking interference,and monophonic interference under gaussian channel is simulated and analyzed.The wireless communication signals intercepted in non-cooperative communication system are detected and analyzed,and the two parameters of the duration of the spreading code and the spreading chip rate in the signal are estimated.Combining MIMO technology with spread spectrum technology,we design a joint transmission scheme.In the scheme,by distinguishing different communications through different sub-domains and spaces,a flexible trade-offs between frequency domain and space resources can be implemented,which can alleviate the problem of too wide spectrum occupied by spread spectrum,increase transmission capacity,and effectively control co-channel interference between signals.Simulation analysis was performed on the proposed transmission scheme and compared with the Code Division Multiple Acess(CDMA)system.