Cognition Based Interference Detection And Recognition Technology Research In Wireless Communication System

Frequency Hopping System is widely used in military and civilian fields for its good anti-jamming, anti-interception capability. However, in highly dynamic and mutational electromagnetic environment, the performance of conventional frequency hopping is limited due to its fixed anti-jamming pattern. To solve this shortcoming, in recent years, people have done continual improvement on frequency-hopping technology. Firstly, increasing frequency hopping rate. The rate of the frequency-hopping communication system JTIDS is as high as 38000-hop/sec. But the dwell time of high-speed frequency hopping is very short, the bandwidth needed will be broader, and its sidelobes will cause adjacent channel interference. Secondly, proposing adaptive frequency-hopping technology. It combines frequency set with disturbed frequency bands. When a wide range of interference occurs in the frequency-hopping band, the system removes these bad frequencies adaptively according to the bit error rate of the signal received at the receiving end, thereby changing the frequency hopping pattern adaptively. Then the system overcomes the effects on communication which is bought by interference. But the real-time performance is unsatisfied, especially the poor anti-jamming performance under time-varying channel will lead to an intolerable long time for the system to be stable if the amount of bands which are disturbed is quite a lot. Thirdly, expanding operating bands, whereas the spectrum resource is finite.In this paper, we combine cognitive radio technology with frequency hopping system, and we use spectrum sensing technology in cognitive radio to detect the interference which is occurred in the communication band, then identify the type of the detected interference and extract its parameters. So we can take effective avoidance strategy, and then improve anti-jamming performance of frequency-hopping system, which can guarantee the reliability of communication system.The main contents and contributions of this paper contain following several aspects:1. In order to achieve full probability interception of interference in the entire communication band, and achieve fast accurate sensing of the frequency-hopping communication band, we use channelized receiver mechanism based on polyphaser filter,and show the simulation diagram based on the polyphaser filter in this paper.2. Introduce two interference identification algorithms: Feature extraction method and wavelet analysis method. Different interference has different eigenvalues in time domain, frequency domain or time and frequency domain, so we can use this property to distinguish the type of interference. To a signal, its local singularity is closer with its modulus maxima of wavelet transform. We can detect the signal's local singularity based on the rate of decay of the modulus maxima of wavelet transform. According to this theory, we propose wavelet analysis method, and prove it is feasible in theory.3. Propose a method to extract parameters of sweeping interference. We use WVD distribution of sweeping interference to extract the values of sweeping rate, sweeping bandwidth and so on. And we propose differential descrambling algorithm. After we know the type of the interference, and its center frequency, bandwidth, we can take appropriate anti-jamming measures, thereby enhance the reliability of the system.4. Introduce the realization of the sensing module in frequency-hopping system.