Study On The Jamming Of Receivers With Adaptive Nulling Antenna In Spread Spectrum System

Communication confrontation is used to protect one’s own wireless communication system, and weaken or destroy the effectiveness of wireless communication system of the other side. Researches on communication jamming and anti jamming technology are the core of communication countermeasures. The adaptive nulling antenna can weaken the energy of interference, thus improving the ratio of signal power to interference power, so it is an effective measure to develop the ability of anti-jamming of receivers; and an effective interference on adaptive nulling antenna can significantly reduce the anti-jamming effectiveness of receivers with this kind of antenna.Aiming at jamming this kind of terminals with adaptive nulling antenna, researches on jamming patterns and strategies are conducted in this thesis. The main research contents are listed as follows:1. The theory analysis and simulation of the adaptive nulling antenna, especially the MVDR(minimum variance distortion response) adaptive algorithm which is recursive implemented in RLS and LMS algorithms are presented.2. A kind of LMS algorithm with improved step factor which can change continuously is given, and it can adjust step factor continuously according to average power of received signals, and it is able to balance convergence speed and steady-state error.Then the formula is given to calculate the step factor. It indicates that the LMS algorithm with this kind of step factor has both fast convergence speed and good steady-state error via simulation of convergence curve of antenna weight in many different conditions compared to the LMS algorithm with fixed step factor.3. The influence of different jamming patterns based on chirplet atoms on the adaptive nulling antenna system implemented in LMS is studied. The simulation model of receivers with adaptive nulling antenna in spread spectrum system is shown. The result shows that: For the jamming pattern of continuous wave jamming, the performance of the chirplet atoms is almost the same with white Gaussian noise. For the jamming pattern of blinking jamming, the smaller the ratio of jamming duration to the total time,the better the jamming effect will be. For the jamming pattern of mixed jamming, if the average power of chirplet atoms is the same, then the smaller the ratio of jamming duration to the total time, the better the jamming effect will be. If the average power of chirplet atoms is different, and the atom with higher power is sent in delay, then the longer the time delayed is, the better the jamming effect will be.