Research And Implement Of Narrow-Band Interference Rejection In DSSS

With the development of wireless communications and the rapid deterioration of electromagnetic environment, it is becoming more and more important for the interference rejection in wireless communication system. Direct Sequence Spread Spectrum (DSSS) technology is one of the most widely used technologies of interference rejection, which has ability to reject narrow-band interference (NBI) and suppress multiple access interference or decline. However, there is an interference- tolerance for DSSS system, which means that the system performance will be reduced greatly when NBI goes beyond it. It is necessary to research on the interference rejection for DSSS system.Adaptive filter is a popular technology to reject narrowband interference, which can suppress NBI effectively by learning and tracking the NBI characteristics adaptively.Three methods of NBI rejection have been discussed in this thesis, which are time-domain linear prediction adaptive algorithm, frequency-domain adaptive algorithm and adaptive de-spread spectrum re-spread spectrum (SS-SP) decision algorithm. The performances of three algorithms have been researched and simulated in the thesis. Based on the simulation results, it is found that an adaptive SS-SP filter is suitable for FPGA realization.The adaptive filter is designed and implemented on FPGA, which is a 31- order time-domain filter. The filter is updated by LMS algorithm. It is shown by the test on hardware circuit that the filter had a capacity of 15-28dB for NBI rejection which satisfies the requirement. Also the filter has a better stability, scalability and maintainability.