Research On Narrowband Interference Suppression Technology For Direct Sequence Spread Spectrum Systems

Spread spectrum communication technology has the advantages of anti-jamming,low interception,good concealment and so on,which is widely used in civil and military communication fields.However,when the malicious interference is encountered,the DSSS cannot guarantee the normal operation of the system only by its own processing gain.In order to solve this problem,this paper designs a direct sequence spread spectrum receiving system which can suppress narrowband interference.First of all,the narrowband interference suppression techniques commonly used in time domain and frequency domain are studied and analyzed.In the narrowband interference suppression method of transformation domain,the method based on chisquare distribution and spectrum accumulation is adopted to solve the problem of inaccuracy in single frequency spectrum detection,and the detection threshold setting method under different accumulation times is analyzed and demonstrated in detail by setting double threshold coefficient for detection and suppression of interference.Secondly,this paper uses PMF-FFT method to capture spread spectrum signals transmitted in the channel.Compared with the traditional acquisition algorithm,this algorithm has more advantages in the case of low signal-to-noise ratio and high dynamic Doppler.PMF-FFT acquisition algorithm is improved in view of scallop loss and large Doppler frequency offset.By using the sweep method to estimate the residual frequency offset algorithm,it can realize the high precision and fast acquisition of spread spectrum signal under the condition of high dynamic Doppler,and the implementation of this algorithm in FPGA can achieve the performance index.Third,in order to solve the frequency carrier wave doppler frequency shift cases low tracking precision,double loop tracking method is proposed in this paper,the method combined with the second order frequency lock loop fast track carrier frequency error and the third order phase-locked loop steady-state phase error is zero,the advantages of constitute the second order frequency lock and the third order phase-locked parallel operation of the carrier tracking loop,the loop in a large dynamic doppler frequency shift can rapidly and accurately under the condition of carrier phase tracking receiving signal.In the end,this article gives the specific hardware design and implementation scheme,and the design index of this scheme is verified and tested,the experiment shows that this scheme can complete the acquisition and tracking of spread spectrum signal under the condition of eliminating narrowband interference.