To minimize damage from network security problem, an improved network security situation assessment model based on Fuzzy Analytic Hierarchy Process (FAHP) was proposed. First, a set of index system in conformity with actual environment which consists of index layer, criterion layer and decision layer was established in consideration of the large-scale network environment in the future. Aiming at the influence on evaluation by data distribution uncertainty and fuzziness in situation assessment, the proposed model used Fuzzy C-Means (FCM) clustering algorithm and the best clustering criterion for data preprocessing to get the optimal cluster number and cluster center. Finally, multi-factor secondary assessment model was established for situation assessment vector. The simulation results show that, compared with the present situation assessment method based on FAHP, the improved method takes the factors which have small weights into consideration better, so the standard deviation is smaller and evaluation results are more objective and accurate.
The conventional threshold function in wavelet noise reduction of chaotic signals has its shortages, such as low resolution of high frequency and restraint limit of quantitative method to hard and soft thresholds. Concerning these shortages, a wavelet packet noise reduction method of chaotic signals was proposed based on a high-order threshold function. The method could further decompose high frequency part by wavelet packet and retained useful high-frequency information, so it was more precious in partial analysis. Furthermore the threshold function was continuous and derivable. There was a smooth transiting area between noise wavelet coefficient and chaotic signal wavelet coefficient. As a result, it is more consistent with the continuous characteristics of the signal. The comparative simulation shows that, compared with soft threshold noise reduction method and semi-soft threshold wavelet packet noise reduction method, the effect of noise reduction to chaotic signals has been significantly improved, and Signal-to-Noise Ratio (SNR) increased 3.7-7dB.