Study Of Uppressing The Narrowband Interference In DSSS System

As one of core technologies,the Direct sequence spread spectrum is used widely in military and civilian communications, the basic principles of DS-SS communication determines its own narrow-band interference (NBI) suppression capability in a certain degree,and this could usually able to meet the needs of normal communications. But when the narrow-band interference power is too large in the channel, it will seriously affect the normal communication. Therefore studying the Narrowband interference suppression technology in DSSS Communication System to improve the communication capacity of the system has important practical significance.In this paper, the receiver's signal model in DSSS Communication System is Given, based on the given model, the DSSS Communication System's own performance of suppressing several typical interference such as occlusion Gaussian interference, sine wave interference and narrowband interference is analyzed, and two important indicators such as processing gain and interference tolerance is introduced.The least square lattice (LSL) theory of time-domain adaptive filtering system is studied, the performance of the LSL prediction algorithm and the LSL interpolation algorithm which suppress the NBI in DSSS Communication is analyzed, the "media forward and backward prediction error" of small dynamic range is introduced and involved in recursive computation instead of "forward and backward prediction coefficients" of relatively bigger dynamic range, the improved interpolation algorithm that is based on the orthogonal triangular decomposition (QRD-LSL) is present. The simulation results show that: the steady-state error of the QRD-LSL interpolation algorithm is 7dB smaller than LSL interpolation algorithm, and 10dB smaller than LSL prediction algorithm. Therefore the algorithm of QRD-LSL is a more effective filter algorithm.The technique of NBI suppression based on the DFT transform domain is studied, the loss of SNR produced by adding window to input datum is analyzed. The paper present that the signal which is composed of DSSS signal and awgn is a narrowband gauss process in DFT transform domain, the square of its magnitude spectrum submits to the exponential distribution, based on it, the paper proposes the adaptive detection threshold algorithm for suppressing the NBI, and simulates the performance of the algorithm for suppressing the single frequency sine wave interference, several frequency sine wave and AR model interference. The simulation results shows that the algorithm could effectively suppress them, and make the BER maintain on the level of about 0.01 when the SNR equals 0, Combining overlapping windowing technique, the ERB could reduce to less than 0.001.