The Research Of Direct Spread System Narrow Band Interference Suppression Technology

Spread spectrum technology is the technology of spreading the information signalspectrum and sending it out. Spread spectrum technology including a variety of methods, themost widely used technique is direct sequence spread spectrum technology. However, there isan interference tolerance for DSSS system, when NBI goes beyond it, the syetemperformance will be greatly reduced, narrow-band interference is a typical form ofinterference, so it is necessary to research the narrow-band interference resistance for DSSSsystem.DSSS narrowband interference suppression technology including two major categoriesof time-domain interference suppression technology and transform domain interferencesuppression technology, time-domain interference suppression technology is the one of theearliest technology of studing the interference suppress, which use the strong autocorrelationof the narrowband interference signal and the wake autocorrelation characteristic of thespread spectrum signal to predict the narrow-band interference, thus achieving a separation ofinterference and signal. Transform domain interference suppression technology is differentfrom the time-domain interference suppression, the technology first will transform thereceived signal to the transform domain, and then use the different characteristics of the signaland interference in the transform domain to suppress interference by a certain degree ofinterference suppression algorithm.The papers focused on three narrow-band interference suppression algorithms.First is thetime-domain interference suppression technology, mainly including interference suppressiontechnology based on prediction and interference suppression technology based on spreadspectrum code auxiliary.Depending on the implementation of different types, it can bedivided into prediction filter and interpolation filter.The interference suppression of thelinear interpolation filter has been simulated effectively.Next is the despread respread algorithm, the despread respread algorithm is atime-domain adaptive filtering algorithm.The received signal was despreaded, filtered andrespreaded, the information signal was unaffected,but the most of the narrow-band interference was filtered, the despread respread algorithm use this nature to put the respreadsignal as the reference signal of the adaptive filter, the DSSS system narrowband interferencerejection capability was improved.the improved algorithm has a better ability to suppressnarrowband interference, the algorithm was improved by the addition of synchronization.Despread respread algorithm and the improved algorithm was simulated by the computer, theimproved despread respread algorithm has a better performance.Finally is the side correlation replacement algorithm, the side correlation replacementalgorithm (SCR) is a real-time interference suppression technology to suppres narrowbandinterference effectively, which uses the symmetry of the DSSS signal frequency spectrum.Then narrow-band interference is eliminated when it is replaced by side correlation value, thesignal has been transferred into the frequency range, it has created the frequency spectrumrevelation,so making the improvement to the side correlation replacement algorithm.first ofall,the narrowband interference model was selectived as AR model, the ariginal algorithm’snarrowband interference is the single frequency interference,in order to make the algotihmmore popular,the narrowband interference model was selectived as AR model; setting up aninterference detection threshold, the amplitude of the transform domain signal was comparedwith threshold, if the amplitude greater than the threshold, the signal was polluted byinterference,then rejecting the interference, if the amplitude is less than the threshold, thereis not interference then the signal was directly sending into the next processing.DCT-2surpasses DFT,this is because it has one kind nature, which is because the energy compressionnature.specially, the finite sequence’s DCT-2coefficient usually more centralisms in the lowserial number’s part compared to the DFT, therefore based on the DCT transformation sidecorrelation replacement algorithm was proposed. The simulation confirmed the improvementalgorithm have the better interference suppression performance.