Since the pilot overhead using traditional channel estimation methods in the Reconfigurable Intelligent Surface (RIS)-assisted wireless communication systems is excessively high, a block sparseness based Orthogonal Matching Pursuit (OMP) channel estimation scheme was proposed. Firstly, according to the millimeter Wave (mmWave) channel model, the cascaded channel matrix was derived and transformed into the Virtual Angular Domain (VAD) to obtain the sparse representation of the cascaded channels. Secondly, by utilizing the sparse characteristics of the cascaded channels, the channel estimation problem was transformed into the sparse matrix recovery problem, and the reconstruction algorithm based on compressive sensing was adopted to recover the sparse matrix. Finally, the special row-block sparse structure was analyzed, and the traditional OMP scheme was optimized to further reduce pilot overhead and improve estimation performance. Simulation results show that the Normalized Mean Squared Error (NMSE) of the proposed optimized OMP scheme based on the row-block sparse structure decreases about 1 dB compared with that of the conventional OMP scheme. Therefore, the proposed channel estimation scheme can effectively reduce pilot overhead and obtain better estimation performance.
The accurate flight delay prediction results can provide a great reference value for the prevention of large-scale flight delays. The flight delays prediction is a time-series prediction in a specific space, however most of the existing prediction methods are the combination of two or more algorithms, and there is a problem of fusion between algorithms. In order to solve the problem above, a Convolutional Long Short-Term Memory (Conv-LSTM) network flight delay prediction model was proposed that considers the temporal and spatial sequences comprehensively. In this model, on the basis that the temporal features were extracted by Long Short-Term Memory (LSTM) network, the input of the network and the weight matrix were convolved to extract spatial features, thereby making full use of the temporal and spatial information contained in the dataset. Experimental results show that the accuracy of the Conv-LSTM model is improved by 0.65 percentage points compared with LSTM, and it is 2.36 percentage points higher than that of the Convolutional Neural Network (CNN) model that only considers spatial information. It can be seen that with considering the temporal and spatial characteristics at the same time, more accurate prediction results can be obtained in the flight delay problem. In addition, based on the proposed model, a flight delay analysis system based on Browser/Server (B/S) architecture was designed and implemented, which can be applied to the air traffic administration flow control center.
K-anonymous algorithm makes the data reached the condition of K-anonymity by generalizing and suppressing the data. It can be seen as a special feature selection method named K-anonymous feature selection which considers both data privacy and classification performance. In K-anonymous feature selection method, the characteristics of K-anonymity and feature selection are combined to use multiple evaluation criteria to select the subset of K-anonymous features. It is difficult for the filtered K-anonymous feature selection method to search all the candidate feature subsets satisfying the K-anonymous condition, and the classification performance of the obtained feature subset cannot be guaranteed to be optimal, and the wrapper feature selection method has very high-cost calculation. Therefore, a hybrid K-anonymous feature selection method was designed by combining the characteristics of filtered feature sorting and wrapper feature selection by improving the forward search strategy in the existing methods and thereby using classification performance as the evaluation criterion to select the K-anonymous feature subset with the best classification performance. Experiments were carried out on multiple public datasets, and the results show that the proposed algorithm can outperform the existing algorithms in classification performance and has less information loss.
For the vital arc problem of maximum dynamic flow in time-capacitated network, the classic Ford-Fulkerson maximum dynamic flow algorithm was analyzed and simplified. Thus an improved algorithm based on minimum cost augmenting path to find the vital arc of the maximum dynamic flow was proposed. The shared minimum augmenting paths were retained when computing maximum dynamic flow in new network and the unnecessary computation was removed in the algorithm. Finally, the improved algorithm was compared with the original algorithm and natural algorithm. The numerical analysis shows that the improved algorithm is more efficient than the natural algorithm
A printing module based on COM was designed and realized. It could print 2D bar code of high resolution and microform effectively in appointed geometric area and form. The principle of COM technology was introduced, and the elementary method of using ATL to realize the COM module in VC was described.