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    20 June 2022 Volume 49 Issue 3
      
    Information and Communications Engineering
    Impact of cooperative jamming time-frequency synchronization errors on secure communication performance
    XIAO Shanghui,CHEN Yanming,WANG Ziyu,GUO Wenbo,SHAO Shihai
    Journal of Xidian University. 2022, 49(3):  1-9.  doi:10.19665/j.issn1001-2400.2022.03.001
    Abstract ( 386 )   HTML ( 752 )   PDF (1144KB) ( 336 )   Save
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    The premise of secure communication is to accurately reconstruct and cancel cooperative interference signals in authorized receivers.However,due to the influence of hardware and propagation environment,and restricted by actual engineering accuracy,a time-frequency synchronization error always exists.Therefore,aiming at the problem of imperfect time-frequency synchronization of the cooperative interference transceiver in physical layer secure communication,the residual interference power with a time-frequency synchronization error is derived under the Gaussian eavesdropping channel model.The influence of the time-frequency synchronization error on the system performance is analyzed theoretically,and the closed expressions for the authorized user interference suppression ratio,demodulation bit error rate and secure communication security capacity are obtained,while the theoretical performance is verified by computer simulation.Simulation results show that the suppression degree of the cooperative interference signal decreases,that the interference suppression ratio and security capacity of authorized users decrease,and that the demodulation bit error rate increases with the increase of time delay or frequency offset.In a certain range,the time-frequency synchronization error will not affect the performance of the three indicators.When the signal-to-noise ratio is 10 dB,it is shown that the normalized delay is less than 0.06,that the normalized frequency offset is less than 10-5,that the delay and frequency offset have a little impact on the system security communication performance,and that the loss of security capacity is less than 16%.Accordingly,analyzing the influence of the time-frequency synchronization error of cooperative interference can provide guidance and theoretical support for the design of a secure communication system.

    MAC protocol for the dense wireless network of UAV assisted communication
    YANG Xin,MAO Yaqi,WANG Ling
    Journal of Xidian University. 2022, 49(3):  10-20.  doi:10.19665/j.issn1001-2400.2022.03.002
    Abstract ( 526 )   HTML ( 43 )   PDF (2782KB) ( 95 )   Save
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    Facing the dense wireless network communication scene assisted by unmanned aerial vehicles (UAVs),Aiming at the problem of a limited network throughput caused by transmission of fixed base stations on the ground,and focusing on the improvement of communication network performance within the coverage of UAVs,a UAV Assisted Dense network Medium Access Controlprotocol (UAD-MAC) is proposed.First,based on the heterogeneous communication of different devices in a dense network,we propose a novel UAV assisted dense wireless network communication model.Second,the concepts of initial competition window coefficient,sub-coefficient and their weights are introduced.We design a new MAC protocol by combining the design of the initial contention window and the nodes quitting probability in UAV mobile environment.Finally,a three-dimensional Markov model is used to evaluate the normalized saturated throughput and access fairness,and then we determine the sub-coefficient weights of the initial contention window to maximize the throughput.Simulation results show that the average normalized saturated throughput of the UAD-MAC protocol is nearly doubled under the basic access mechanism and increased by about 51% under the RTS/CTS mechanism compared with the existing protocol.Moreover,the loop with a smaller access time can obtain a higher throughput and lower delay.

    Algorithm for tracking adaptive context-aware correlation filter targets
    SUN Yamei,XIAO Song,QU Jiahui,DONG Wenqian
    Journal of Xidian University. 2022, 49(3):  21-27.  doi:10.19665/j.issn1001-2400.2022.03.003
    Abstract ( 370 )   HTML ( 100 )   PDF (2190KB) ( 90 )   Save
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    In the traditional correlation filter object tracking algorithm,due to the limitation of the cosine window and the search area,a tracking drift can easily occur in complex scenes.A framework is proposed in the context-aware algorithm to allow global contextual information to be incorporated into the correlation filter tracker,but the same suppression weight is directly used instead of calculating the interference degree of the context information to the target and it cannot adapt to giving background information with different degrees of interference,on the basis of which we propose a context suppression weight adaptive correlation filter target tracking algorithm.First,the background information arpond the target is learned into the filter,enhancing the classification ability of the filter template for target and context background information,and the adaptive weight coefficient vector is introduced.Second,a formula for the context information interference coefficient is proposed to quantitatively evaluate the interference degree of the context information to the target.Third,according to the proposed formula,the interference degree of context information is calculated,and then it is matched with the adaptive weight coefficient vector,so as to lead to the effect that,the greater the interference degree of the context information to the target,the greater the suppression degree.Finally,we rely on the OTB100 dataset to verify the effectiveness of the algorithm in this paper,with experimental results showing that the success rate and accuracy of the algorithm in this paper are improved by 5.7% and 4.3%,respectively compared with the benchmark algorithm,and that it has strong robustness.

    Thermal target detection method introducing an attention mechanism
    YANG Zixuan,XIAO Song,DONG Wenqian,QU Jiahui
    Journal of Xidian University. 2022, 49(3):  28-35.  doi:10.19665/j.issn1001-2400.2022.03.004
    Abstract ( 363 )   HTML ( 25 )   PDF (1452KB) ( 136 )   Save
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    In view of the problems of less texture details and low detection accuracy of infrared targets,we propose a Cascade-RCNN algorithm introducing an attention mechanism in thermal detection scenes,and design an attention mechanism suitable for infrared scenes.Because the attention mechanism is commonly used for performance verification on visible-light datasets,we first experiment the detection accuracy of other attention mechanisms on the thermal detection dataset,and meanwhile,propose an attention mechanism that interacts with explicit and implicit channels.In this method,the factorization machine method and the fully connected layer method are adopted,using this method to make all features go into the same Hilbert space.We propose a local pooling method to replace the global pooling method to obtain more image spatial information,using multi-scale convolution in the spatial dimension to extract target information in different receptive fields.An experiment is conducted on the FLIR thermal dataset.Without many parameters,the detection performance is improved by about 2% on different backbone networks compared to the Cascade R-CNN.

    Performance analysis for the improved multiuser high-efficiency DCSK communication scheme
    ZHANG Gang,DONG Jiangtao,ZHANG Tianqi,WU Xueshuang
    Journal of Xidian University. 2022, 49(3):  36-47.  doi:10.19665/j.issn1001-2400.2022.03.005
    Abstract ( 237 )   HTML ( 10 )   PDF (1694KB) ( 44 )   Save
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    Aiming at the disadvantages of high bit error rate (BER) and low transmission rate in the traditional high efficiency differential chaos shift keying (HE-DCSK) system,an improved multiuser high-efficiency differential chaos shift keying communication scheme is proposed.The scheme introduces an orthogonal chaotic signal generator that can generate two mutually orthogonal chaotic signals.The transmitter signal is divided into two time slots:the first time slot transmits a linear combination of two orthogonal chaotic signals as the reference signal,and the second time slot modulates the information bits of the two chaotic signals separately and then superimposes them for transmission,and finally the transmission rate is doubled by the quadrature modulation technique.The system also introduces an orthogonal Walsh code sequence for the purpose of transmitting multi-user information.At the receiver,the reference and information signals are separated from the received signal and the transmitted information bits are recovered using correlation demodulation.The system BER performance is further improved by introducing a mean filter to average some of the received signals.The theoretical BER formulation of the system is derived for additive Gaussian white noise channels and multipath Rayleigh fading channels and verified by Monte Carlo experimental simulations.The results show that the design of the scheme can effectively improve the transmission rate and BER performance of the system.When the number of users is 2,the transmission rate of this system is improved by about 300% and the BER performance is improved by nearly 1dB compared to the HE-DCSK system.

    QoE-awarevideo transmission resource allocation strategy for V-CRAN
    ZHANG Hong,HUANG Chuang,ZOU Hong,WANG Ruyan,XU Ruixin,LI Zhidu
    Journal of Xidian University. 2022, 49(3):  48-58.  doi:10.19665/j.issn1001-2400.2022.03.006
    Abstract ( 263 )   HTML ( 13 )   PDF (1482KB) ( 51 )   Save
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    Under the development trend of increasing video service requirements,to solve the problem of unbalanced distribution of optical and wireless resources,and poor user experience quality in cloud wireless access network transmission,a transmission resource allocation strategy of video experience quality perception in the virtual cloud wireless access network is proposed.First,according to the bandwidth requirements of different users,the fronthaul bandwidth efficiency model for optical transmission wavelength assignment,the wavelength tuning overhead model,and load balance evaluation model between optical networks are constructed respectively.Based on the alliance game theory,an iterative algorithm for optical network unit alliance formation based on merging and splitting rules is proposed to construct the virtual cloud wireless access network.An optical network unit coalition formation algorithm based on the merge and split rule is proposed to construct a virtualized cloud radio access network.Furthermore,the influence trend of the transmission rate and video interruption risk on user experience quality is analyzed,with a two-stage Stackelberg game between users and virtual cloud wireless access network established.The existence and uniqueness of its Nash equilibrium solution are proved.Finally,while improving the quality of user experience,the limited wireless resource allocation is optimized to guarantee the utility of service providers.Extensive simulation results validate that in scenarios with different user numbers and load rates,the proposed strategy not only meets the experience quality of users watching video but also effectively improves the resource utilization in the optical and wireless domains.

    Research on deployment strategy of multiple controllers in the software-defined satellite network
    CHEN Jintao,LIANG Jun,GUO Zizhen,XIAO Nan,LIU Bo
    Journal of Xidian University. 2022, 49(3):  59-67.  doi:10.19665/j.issn1001-2400.2022.03.007
    Abstract ( 299 )   HTML ( 94 )   PDF (1306KB) ( 67 )   Save
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    Software-defined networking (SDN) relies on the concept of programmable and reconfigurable,and will play an important role in the development of future satellite networks.By decoupling the control plane and data plane,the software-defined networking approach simplifies network management and accelerates network innovation.With the comprehensive deepening of the satellite "orbital revolution" and the growing demand for satellite communications,attention to and research on software-defined satellite networks are constantly deepening and make it a new paradigm.And the programmability required is offered to dynamically manage a satellite network.As the key concern of network performance,controller deployment is the basis of SDSN.In the current research,the impact of processing delay and link states on network performance is often ignored,which may lead to unreasonable control domain partitions which leads to unbalanced controller loads,poor network reliability and other problems.Therefore we take the processing delay and link states into account and design a Multi-controller reliability deployment strategy based on control delay (CDS-R) in the Software defined satellite network.In order to demonstrate its performance,a controlled experiment is designed.Experimental results show that CDS-R could significantly improve the network load balancing performance with an acceptable reassignment expense.CDS-R can decrease the control delay by nearly 35% and improve reliability obviously compared with other schemes.

    Improved method for energy efficient clustering of the wireless sensor network
    DOU Peipei,ZENG Yuqin,LU Yi,MA Hongliang,XU Mengying,ZHOU Jie
    Journal of Xidian University. 2022, 49(3):  68-73.  doi:10.19665/j.issn1001-2400.2022.03.008
    Abstract ( 264 )   HTML ( 79 )   PDF (1257KB) ( 56 )   Save
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    The wireless sensor network (WSN) is mainly used to collect and process data,so it is widely used in many fields.However,most battery-powered sensor nodes in the WSN are small in size,which makes them unable to work for a long time.Therefore,designing a clustering method that can effectively improve energy utilization and reduce network communication energy consumption is one of the important research directions of the WSN.Aiming at the problem of high communication energy consumption of the cluster head node selected by the traditional clustering method,an energy-efficient clustering method based on the clone elite genetic algorithm for the WSN is proposed.In clustering,the clone elite genetic algorithm is used to select some sensor nodes as cluster head nodes in the monitoring range,and then the network communication energy consumption is optimized.In the iterative process,the cluster head node scheme with low energy consumption is retained as much as possible through the clone operator and the elite operator.The method reduces the running time and increases the possibility of obtaining a better cluster head node scheme.The proposed method is compared with the clustering method based on the elite genetic algorithm and the clustering method based on the shuffled frog leaping algorithm.Simulation results show that compared with the two other methods,the clustering method based on the clone elite genetic algorithm significantly reduces the network communication energy consumption,improves the energy utilization efficiency,and effectively prolongs the network life.

    Denoising autoencoder-aided downlink MIMO-SCMA codec method
    JIANG Fang,HUANG Xing,HU Mengyu,WANG Yi,XU Yaohua,HU Yanjun
    Journal of Xidian University. 2022, 49(3):  74-82.  doi:10.19665/j.issn1001-2400.2022.03.009
    Abstract ( 229 )   HTML ( 9 )   PDF (2114KB) ( 50 )   Save
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    Aiming to improve the bit error rate (BER) performance of sparse code multiple access (SCMA)systems in multi-antenna applications,deep learning is introduced in a MIMO-SCMA system and a denoising autoencoder-aided Codec method (DAE-MIMO-SCMA) is proposed.Multiple deep neural network (DNN) units are used by the transmitter to construct the MIMO-SCMA encoder.The codebook of each user on different transmitting antennas is obtained through neural network (NN) learning.Moreover,the noise layer is used at the transmitter so that the output of the encoder is more robust.At the receiver is designed a fully connected DNN as a decoder,which combines multi-antenna detection and multi-user detection to obtains the original data of all users at one time.An end-to-end training method is used to train the Codec,optimizing the structure and parameters of the NN,which improves the convergent rate.Experimental results show that the proposed Codec method can lower the BER of the MIMO-SCMA system and reduce the detection time at the receiver.

    Power control and antenna selection for themulti-antenna transmitter with energy harvesting
    NING Xiaohan,LEI Weijia
    Journal of Xidian University. 2022, 49(3):  83-92.  doi:10.19665/j.issn1001-2400.2022.03.010
    Abstract ( 191 )   HTML ( 14 )   PDF (1555KB) ( 50 )   Save
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    Aiming at the rate maximization in the MISO system with energy harvesting,we propose an online joint power control and antenna selection strategy based on the Lyapunov optimization framework.The source node is a multi-antenna node powered by an energy harvesting device.The power consumption of the radio frequency (RF) circuit for each antenna is not negligible.The more antennas are activated,the larger the gain of the antenna array,but the larger the power consumption of the RF circuit,so it is necessary to balance between the gain and the power consumption.The source node should choose the appropriate transmit antenna and transmit power according to the available energy and the channel state.Since the energy arrival and the channel fading are stochastic processes,the rate maximization problem is a stochastic optimization problem.The energy virtual queue is constructed from the power level of the rechargeable battery,the negative value of the rate is modeled as the penalty term,and then the optimization problem of power control and antenna selection is transformed into the minimization of the instantaneous queue drift-plus-penalty function by using the Lyapunov optimization framework.During each time slot,the corresponding transmit power is optimized for each active antenna number that the power stored in the battery can support,and then the number of active antennas and the transmission power with the minimum drift-plus-penalty are selected as the optimal solution.Simulation results show that compared with the three comparison algorithms,the proposed algorithm can achieve a significantly higher transmission rate.The proposed algorithm only makes decisions based on the current channel state and battery power state,and has a very low computational complexity.

    Signal two-scale nearest neighbor positioning method under dynamic correction
    SUN Shunyuan,ZHU Hongzhou,QIN Ningning
    Journal of Xidian University. 2022, 49(3):  93-100.  doi:10.19665/j.issn1001-2400.2022.03.011
    Abstract ( 279 )   HTML ( 14 )   PDF (1577KB) ( 36 )   Save
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    Among indoor position scenarios,the positioning method based on the Received Signal Strength has several problems such as unstable signal propagation,high computational complexity and low positioning accuracy caused by large target areas.In order to solve these problems,this paper proposes a signal two-scale nearest neighbor with dynamic correction method,according to the connectivity structure of the target area,and the system uses the one-vs-rest support vector machine to construct a partition model of the target area in order to predict the subarea with signal changes.This paper trains the AP signal-distance model based on Gaussian process regression in partition.It is important to realize the correction of signal fluctuation value by predicting the path-loss characteristics in partition.In order to improve the positioning accuracy,by combining signal similarity with signal difference,a two-scale nearest neighbor algorithm is established.The k value of the nearest neighbor is adaptively calculated by combining the environmental parameter in order to reduce the influence of environmental noise.Through simulation experiments,the average localization error of the proposed algorithm is less than 0.5173 m,indicating that the algorithm causes a lower error than the traditional algorithm by more than 25 percent.

    Research on the drones single station opportunistic signal positioning method aided by motion parameters
    BIAN Zhi’ang,LU Hu,SHI Haodong
    Journal of Xidian University. 2022, 49(3):  101-110.  doi:10.19665/j.issn1001-2400.2022.03.012
    Abstract ( 168 )   HTML ( 11 )   PDF (2478KB) ( 42 )   Save
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    The current estimation of the position of drones relies heavily on the Global Navigation Satellite System (GNSS).To solve this problem,a Single Station Positioning of Opportunity Signals Aided by Kinetic Parameters (SPoKP) is proposed.This paper gives the detailed steps of establishing the motion state transfer equation and position estimation output equation,deduces the observability condition for drones position estimation,and gives the method for motion parameter estimation and error suppression by setting the variable adaptive smoothing window,with the decision threshold for window setting given.Finally by relying on the recursion of the motion state and a single ranging radio frequency signal station,the estimation of positions of the drones in different motion states is realized.Theoretical simulation shows that in the environment where the navigation satellite system refuses,the single-station positioning algorithm for the radio frequency opportunistic signal assisted by dynamic parameters can achieve robust positioning of drones in different motion states,which can meet routine tasks such as delivery,drones cruise and reconnaissance and that the actual test using the ultra-wideband (UWB) signal beacon further verifies the accuracy and effectiveness of the proposed method.Compared with the navigation satellite system,the positioning root mean square error of the proposed algorithm is only 2.7 m,which verifies the feasibility of drones using opportunistic signals to achieve higher-precision positioning in a denial environment,and reduces the drones’ dependence on sensors of traditional navigation and positioning systems.

    Algorithm for fingerprint database construction under the dual beacon mechanism
    QIN Ningning,WU Yisong,SUN Shunyuan
    Journal of Xidian University. 2022, 49(3):  111-119.  doi:10.19665/j.issn1001-2400.2022.03.0013
    Abstract ( 205 )   HTML ( 11 )   PDF (2322KB) ( 38 )   Save
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    Considering the problem that the construction of fingerprint database in indoor positioning research requires a lot of manpower and time for signal acquisition,this paper proposes an algorithm for fingerprint database expansion based on the dual beacon mechanism and radial basis neural network.This algorithm can flexibly adjust the sampling ratio of beacon points according to the needs of the scene,and obtain the lowest sampling overhead under the premise of ensuring the accuracy of prediction.The algorithm uses the radial basis neural network to mine the deep connection between the position of the beacon and the signal to predict the signal strength of the position to be estimated,and achieve the purpose of expanding the fingerprint database.Tested by the actual scene,on the premise of ensuring the accuracy of prediction,the proposed algorithm expands the fingerprint database by 140%.Through experimental verification,the average prediction error is reduced by more than 12% compared with the existing algorithms.

    Multipath parameter estimation realized by an improved particle filter algorithm
    GUO Qiang,LIU Xuemeng,ZHOU Kai
    Journal of Xidian University. 2022, 49(3):  120-128.  doi:10.19665/j.issn1001-2400.2022.03.014
    Abstract ( 302 )   HTML ( 10 )   PDF (2165KB) ( 53 )   Save
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    In a static environment,to solve the problems of particle degradation and reduced particle diversity in the parameter estimation process of the particle filter algorithm,a new algorithm combining the unscented Kalman filter algorithm and improved differential evolution algorithm is proposed to optimize the particle filter.The algorithm first introduces the unscented Kalman filter in the importance sampling stage of the particle filter to calculate the mean and covariance of each particle,and uses the mean and covariance to "guide" sampling to avoid particle degradation.Second,an adaptive strategy is adopted in the mutation and crossover process of traditional differential evolution to avoid premature convergence.At the same time,the improved differential evolution algorithm is used to replace the particle filter's resampling process,which overcomes the problem of reduced particle diversity.Finally,the new algorithm is used to realize multipath parameter estimation.Simulation results show that the new algorithm can effectively reduce the fluctuation range of the parameter estimation results and reduce the root mean square error while meeting the real-time requirements.

    Targeted password guessing scheme combined with GAN
    DU Lixuhong,CHEN Jie,YANG Xiaoxue
    Journal of Xidian University. 2022, 49(3):  129-136.  doi:10.19665/j.issn1001-2400.2022.03.015
    Abstract ( 240 )   HTML ( 12 )   PDF (1000KB) ( 46 )   Save
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    In order to improve the success rate of directional password guessing,this paper proposes a directional password guessing scheme based on the probabilistic context-free grammar (PCFG) combined with generative adversarial networks (GAN).First,this scheme matches the user’s real password with his personal information,and further divides the tags on the basis of the TarGuess-I model,and uses the divided tags to parse the real password.Second,the parsed passwords are input into the confrontation network,and an expanded rule set that follows the real password distribution is obtained after training.Finally,the guessed password set of the target user is generated according to the expanded rule set generated by training and the frequency table of the L (Letters),D (Digits),and S (Symbols) fields obtained from the user's personal information and the password parsing process.This paper adopts the method of demonstration based on the statistical results of the data to propose ideas and verification through experiments,and optimizes the innovative matching of the type-based personal identifiable information PII (Personal Identifiable Information):“numbers +letters” and “letters +special characters”.A series of studies on “numbers +special characters” (which should generally be “letters” and “numbers”) is carried out.Through guessing attack experiments on the railway 12306 data set containing users’ personal information,compared with other targeted password guessing schemes,this scheme has a higher success rate of password guessing.

    Computer Science and Technology & Artificial Intelligence
    Algorithm for clarification of the underwater image combining saliency information
    WANG Zhaoyu,GUO Jichang,WANG Tianbao,ZHENG Sida,ZHANG Yi
    Journal of Xidian University. 2022, 49(3):  137-146.  doi:10.19665/j.issn1001-2400.2022.03.016
    Abstract ( 194 )   HTML ( 17 )   PDF (3253KB) ( 64 )   Save
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    Due to the selective absorption of light by water and the scattering effect of particles in water,underwater images usually have some defects,such as color distortion,low contrast and blurred details.Considering the color distortion and low contrast in the underwater images,an underwater image clarification algorithm combining saliency information is proposed.First,the background light is estimated by a hierarchical search algorithm based on quadtree segmentation.Second,in combination with the underwater imaging model,the perliminary clarification of the underwater image is performed.Furthermore,the superpixels are achieved via the Simple Linear Iterative Clutering algorithm.The global distance matrixes are constructed according to the feature similarity of each superpixel and the boundary background clusters.Then,the global distance matrixes are integrated to generate a saliency map by the Multi-Layer Cellular Automata.Finally,based on the saliency map,the color of underwater images is corrected in the Lab color space.In the experiment,1500 underwater images in UFO-120 dataset are selected as research objects.The algorithm has a significant improvement in the Patch-based Contrast Quality Index,Entropy,Underwater Image Sharpness Measure,Underwater Image Contrast Measure and subjective color restoration.Extensive experiments show that the proposed algorithm outperforms state-of-the-art methods in color correction and contrast enhancement of underwater images.

    Matrix decomposition recommendation model incorporating item attribute preference
    HAN Lifeng,CHEN Li,SHI Xiaolong
    Journal of Xidian University. 2022, 49(3):  147-159.  doi:10.19665/j.issn1001-2400.2022.03.017
    Abstract ( 223 )   HTML ( 11 )   PDF (1523KB) ( 46 )   Save
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    In order to solve a series of problems such as sparse data,especially cold start,the traditional collaborative filtering algorithm can not accurately calculate the similarity between users and articles,so that it cannot accurately recommend corresponding articles for users.Combined with the advantages of the nearest neighbor based collaborative filtering algorithm and model-based collaborative filtering algorithm,this paper proposes a recommendation model based on matrix decomposition.The model uses model-based collaborative filtering,which is based on matrix decomposition and integrates other auxiliary information,in order to optimize the effect of matrix decomposition and make more accurate score prediction.Based on the traditional matrix decomposition algorithm,in the existing recommendation model,first,the similarity is calculated based on the user attribute and project attribute information,and the scoring matrix is constructed to predict the user's initial score.Then,the user interest matrix is constructed by integrating the user’s preferences for project attributes.At the same time,the user attribute information and project attribute information are integrated into the new matrix decomposition model to predict the score of cold start users.Compared with the traditional personalized recommendation model,the new model has a better recommendation accuracy.Through simulation experiments,it is also confirmed that the recommended model mentioned in this paper can alleviate the cold start problem to a certain extent and improve the accuracy.At the same time,good results have been achieved in the scalability of the model.

    Feature enhanced single-stage remote sensing image object detection model
    WANG Xili,LIANG Min,LIU Tao
    Journal of Xidian University. 2022, 49(3):  160-170.  doi:10.19665/j.issn1001-2400.2022.03.018
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    Purpose:The performance of remote sensing object detection has been largely improved with the development of the convolutional neural network.However,the complexity of the scene and the diversity of the target size and shape are still challenging in the remote sensing object detection task.Thus,the deep detection model of different sizes’ objects in a complex scenario is studied.Methods:Feature pyramids are an effective method for detecting objects with different sizes.But the way of transferring the feature layer by layer may lose information in the feature pyramids.Therefore,this paper proposes a feature pyramid network with shortcut connections,which can enhance the semantic and detailed information on each feature layer in the feature pyramid.Moreover,using the spatial attention weight to strengthen the possible target area is an effective method to improve the target detection rate,and it is helpful for object detection in the complex scene.But the available spatial attention will strengthen the imprecise prediction results simultaneously,so that it may interfere with the final prediction results.For this purpose,this paper proposes an anchor-based spatial attention module which mainly strengthens feature regions that are more likely to produce accurate prediction results.In this paper,the feature pyramid network with shortcut connections and the anchor-based spatial attention module are embedded into the Retina Net to form an end-to-end feature enhanced single-stage remote sensing object detection model,namely FENet (Feature Enhanced Network).Results:Experimental results show that the FENet model is 1.78% higher in mAP than the FAN (Feature Enhanced Network) on UCAS-AOD remote sensing dataset,and 1.48% higher than the FAN model on RSOD dataset.And the mAP results of the FENet are superior to those of the comparable models.In addition,the test time of the FENet for an image of 800800 pixel in a single Titan X GPU is 0.058s.Conclusions:Experimental results show that the proposed model can effectively enhance the object feature extraction ability,and thus improve the detection performance.

    Novel deep matrix factorization and its application in the recommendation system
    SHI Jiarong,LI Jinhong
    Journal of Xidian University. 2022, 49(3):  171-182.  doi:10.19665/j.issn1001-2400.2022.03.019
    Abstract ( 376 )   HTML ( 16 )   PDF (1220KB) ( 69 )   Save
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    Personalized recommender systems are playing an increasingly important role in the online consumption platform.Low-rank and deep matrix factorization have been widely used in recommendation systems to optimize the recommendation performance.In order to overcome the bilinear property of traditional matrix factorizations,deep matrix factorizations establish the deep neural network models based on the feature vectors of users and items.The existing methods show a poor performance and a long running time when the data scale is large and the sparsity is high.For this purpose,a new deep matrix factorization model is proposed whose input is the latent feature vectors of users and items.The network structure is composed of two parallel multi-layer perceptrons and a weighted inner product operator for prediction.For the proposed model,a two-stage solution method is designed.First,the low-rank matrix fitting algorithm is used to complete the missing data so that two latent feature matrices are determined simultaneously.Then,the generated feature engineering is fed into the deep neural network and a nonlinear mapping is established with the output as the prediction score.The effectiveness of the proposed method is verified in public recommendation data sets.Experimental results show that the proposed method greatly improves the recommendation performance compared with the traditional matrix factorization methods and that compared with the existing deep matrix factorization methods,the running time is significantly reduced.

    Convolutional quasi-recurrent network for real-time speech enhancement
    SHI Yunlong,YUAN Wenhao,HU Shaodong,LOU Yingxi
    Journal of Xidian University. 2022, 49(3):  183-190.  doi:10.19665/j.issn1001-2400.2022.03.020
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    To improve the speech enhancement performance of deep neural networks under the premise of ensuring the real-time performance,a convolutional quasi-recurrent network for real-time speech enhancement is proposed.The network uses a causal input,and it only uses the time-frequency domain features of the current and past frames of the noisy speech to meet the input requirements of the real-time speech enhancement method.The network uses the quasi-recurrent neural network to model the correlation of the noisy speech in the time domain,and uses its parallel calculations capability for the noisy speech sequences to improve the computational efficiency of the model.The network uses the convolutional layer to improve the feature extraction method of the quasi-recurrent neural network for the frequency domain feature of the noisy speech,which enables the network to better utilize the local correlation between the adjacent frequency bands of the noisy speech and improve the performance of speech enhancement.Experimental results show that,compared with the speech enhancement method based on the quasi-recurrent network,the speech enhancement method based on the convolutional quasi-recurrent network not only improves the speech enhancement performance,but also reduces the parameter number of the network model.Compared with existing methods,the convolutional quasi-recurrent network effectively suppresses the interference of background noise on the target speech,reduces the distortion of the target speech,and has a better speech enhancement performance under the premise of ensuring the causal input.The real-time performance of the speech enhancement method based on the convolutional quasi-recurrent network is verified on different computing platforms.

    EEG emotion recognition based on the 3D-CNN and spatial-frequency attention mechanism
    ZHANG Jing,ZHANG Xueying,CHEN Guijun,YAN Chao
    Journal of Xidian University. 2022, 49(3):  191-198.  doi:10.19665/j.issn1001-2400.2022.03.021
    Abstract ( 386 )   HTML ( 26 )   PDF (2384KB) ( 107 )   Save
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    Currently,many deep learning methods have been proposed for EEG-based emotion recognition.However,most of them do not fully consider the correlated information from temporal,spatial,and frequency dimensions of EEG signals,on the basis of which a three-dimensional convolutional neural network based on the spatial-frequency attention mechanism (FSA-3D-CNN) is proposed to improve the accuracy of emotion recognition,in which the emotion correlated information on EEG can be learned from temporal,spatial,and frequency perspectives effectively.First,the differential entropy features are extracted from the time-domain segmented EEG signals,and a novel 4D feature structure is designed to obtain the four-dimensional feature matrix for training the deep learning model according to the characteristics of the EEG signals.Then,the existing 3D-CNN is improved according to the 4D feature structure,which makes full use of the information on temporal,spatial,and frequency dimensions of EEG signals.Finally,a spatial-frequency attention mechanism is designed to adaptively allocate the weights to the spatial and frequency channels of the EEG signals,and extract the spatial and frequency information on EEG signals that can more significantly reflect changes in emotional state.The DEAP emotion dataset is used to test the performance of our method.Experimental results have demonstrated that the proposed FSA-3D-CNN method can achieve the average accuracy of 95.87% and 95.23% for the two classifications between arousal and valence dimension and the average accuracy of 94.53% for four classifications of arousal-valence dimension,which has achieved significant improvement than that of the existing CNN and LSTM emotion recognition methods.

    Efficient method for designing optimal control sequences in Petri nets
    ZOU Minqiang,MA Ziyue
    Journal of Xidian University. 2022, 49(3):  199-205.  doi:10.19665/j.issn1001-2400.2022.03.022
    Abstract ( 146 )   HTML ( 69 )   PDF (733KB) ( 30 )   Save
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    An algorithm for designing optimal control sequences in Petri nets based on basic marking analysis is proposed,which drives a plant net from a given source marking to a given target marking set with a least-cost control sequence.The algorithm performs Dijkstra search in the basic marking space of the Petri net so that only a small subset of the reachability set is explored with the unpromising branches discarded,which can alleviate the state explosion problem to a great extent.The entire basic reachability graph is initially unknown and revealed stepwise during the search process.It is proved that the proposed algorithm is optimal,since the nodes relaxed in each iteration is identical to that in the standard Dijkstra search,which guarantees the optimality of the outputted control sequence.Moreover,a rule for selecting the set of explicit transitions is developed so that the verification of implicit reachability can be done by checking the validity of a simple inequality.By doing so,it is now possible to quickly determine the implicit reachability of the target set without solving exhaustive integer linear programming problems.Experimental results show that,compared with the method based on integer linear programming in the literature,the method proposed in this paper has a high computational efficiency and can be used in cases where a plant must respond promptly to a request of reconfiguration.

    Electronic Science and Technology & Others
    The effect of nitrogen passivation on gate dielectric reliability of SiC MOS capacitors
    BAI Zhiqiang,ZHANG Yimeng,TANG Xiaoyan,SONG Qingwen,ZHANG Yuming,DAI Xiaoping,GAO Xiuxiu,QI Fang
    Journal of Xidian University. 2022, 49(3):  206-212.  doi:10.19665/j.issn1001-2400.2022.03.023
    Abstract ( 368 )   HTML ( 13 )   PDF (2356KB) ( 64 )   Save
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    Nitric oxide annealing is currently the mainstream interface passivation process in industry,and the passivation effect is severely affected by the annealing conditions of the nitric oxide,so it is important to select appropriate annealing conditions to improve the interface quality.In this paper,the influences of different nitric oxide passivation time on the traps near gate oxide interface and the reliability of gate dielectrics are investigated by the use of n-type and p-type SiC MOS capacitors.The interface traps,near-interface traps,oxide traps and the reliability of gate dielectrics are characterized by the parallel conductance peak test,capacitance-voltage hysteresis test,gate bias stress test and gate leakage test,respectively.The results show that increasing the nitric oxide annealing time can reduce the interface electron trap density of the n-type MOS capacitor and improve the interface quality.In addition,increasing the nitric oxide annealing time can reduce the near-interface electron traps that affect the positive shift of the threshold voltage,but at the same time it will introduce excess hole traps,which can improve the threshold voltage positive stability and worsen the threshold voltage negative stability.Similarly,increasing the nitric oxide annealing time will reduce the effective fixed charge density that is negatively charged in the oxide layer,but will increase the effective fixed charge density that is positively charged in the oxide layer.The results of gate leakage characteristics show that the nitric oxide annealed time has different effects on the gate oxide reliability during the on-state and off-state operation of the device.The results in this paper provide a useful annealing process reference for improving the performance of SiC MOSFETs.

    Design of the line calculation circuit based on capacitive coupling of interconnection lines
    LI Lin,ZHANG Huihong,ZHANG Yuejun
    Journal of Xidian University. 2022, 49(3):  213-221.  doi:10.19665/j.issn1001-2400.2022.03.024
    Abstract ( 194 )   HTML ( 13 )   PDF (3721KB) ( 35 )   Save
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    With the continuous development of integrated circuit technology nodes,the influence of the parasitic effect between interconnects becomes more and more obvious.The interconnection line has become one of the key factors restricting the ability of chip computing,and the design method of using the interconnection line as logical calculation has aroused the designer's wide concern.Based on the study of the coupling effect of capacitance between metal interconnectors,a circuit scheme which uses the deterministic signal interference between metal interconnectors to carry out logic calculation is proposed.First,the capacitive coupling relationship between metal interconnections is analyzed to construct a capacitive coupling model.Then nano metal wires are used to form coupling capacitors,and further to design NAND,NOR,XOR and XNOR gates by adjusting the coupling strength between the interference line and the victim line and adjusting the inverter threshold.After that,a 3-wire-8-wire decoder based on capacitive coupling of interconnection lines is realized.Finally,by using TSMC 65 nm CMOS technology for simulation verification under Cadence Spectre environment,the results show that the designed line calculation circuit functions correctly.Compared with the standard unit of the TSMC 65 nm technology library,the number of transistors used in the two-input line calculation NAND is reduced by 25%,the power consumption of the two-input line calculation XNOR is reduced by 29.1%,and the area and power delay product of the four-input line calculation NAND are reduced by 46.4% and 55%,respectively.Therefore,the line calculation logic gate has the characteristics of a low hardware overhead,thus providing a new way to realize digital integrated circuits intensively,which is conducive to the miniaturization of chips.

    High-precision compacted X-band 6-bit digital phase shifter
    CHEN Ning,LIANG Yu,ZHANG Wei
    Journal of Xidian University. 2022, 49(3):  222-229.  doi:10.19665/j.issn1001-2400.2022.03.025
    Abstract ( 360 )   HTML ( 15 )   PDF (2074KB) ( 59 )   Save
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    X-band active phased array radars are widely used in missile defense,weather monitoring and other fields.The phase shifter is the critical function circuit in the transceivers with an active phased array,and exists widely in the whole active phased array.In view of the problem that high-integration and high-precision cannot be simultaneously met under the broadband of a large phase-shifting unit,a compacted 6-bit digital phase shifter applied in the X-band is designed based on the 0.18 μm SiGe BiCMOS process.By means of cascade 6 different phase shifting units,the phase shifter can achieve a minimum phase shifting step of 5.625° in the range of 360° phase shifting.In addition,in order to reduce the area of the chip,this design proposes an embedded switching structure for the 90°phase shifting unit,which greatly reduces the area of the chip compared with the traditional structure where the large unit chooses the path by switching.The deep-well NMOS transistor is used as the switch to control the working state of each phase shift unit with the floating body technology which is used to improve the switch isolation by reducing the parasitic capacitance of the transistor to the ground.Simulation results show that within the 8.3~12.0 GHz,the RMS phase error is less than 2.5°,that the insertion loss is less than -16.73 dB,and that the RMS amplitude error is less than 1.25 dB.The chip core layout area is 1.68 mm×0.64 mm.

    Analysis of thermally induced vibration of space slender rod-beam structures
    FENG Yuqing,MA Xiaofei,WANG Hui,FAN Chao,WANG Jing
    Journal of Xidian University. 2022, 49(3):  230-237.  doi:10.19665/j.issn1001-2400.2022.03.026
    Abstract ( 184 )   HTML ( 10 )   PDF (3427KB) ( 51 )   Save
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    To solve the unknown problem of thermally induced vibration (TIV) of slender rod-beam structures without cross-section temperature gradients under temperature loads,the “L-shaped” right-angle beam is taken as the object,and the TIV mathematical model and the equivalent axial force method are proposed.Based on the finite element method,the nodes’ temperature changes of different elements are equivalent to the thermal axial force for loading,with dynamic analyses carried out.It is verified that TIV occurs as long as the temperature changes cause the structure to deform and that the temperature fields change rapidly,even if there are no cross-section temperature gradients.The theory of “only the temperature gradients in the cross-section can cause TIV” is improved,and this paper provides a new method for studying TIV of complex structures.Then in the “L-shaped” right-angle beam study,the results calculated by this method are compared with those by the equivalent displacement method,with the results indicating that their error is within 0.002 2%,but the time required by the equivalent axial force method is 79% less than that by the equivalent displacement method,which verifies the rationality and effectiveness of this method.What is more,the interaction between the rods can cause the structure to bend,which can lead to TIV under a certain temperature condition.Finally,TIV of the hoop-truss is analyzed based on the method in this paper.

    Quantum ozone emission effect in needle-to-plate negative ion generators
    HAO Jiaxue,LIU Bo,HUANG Xunan,XU Wenhua,ZHANG Hongliang,WANG Guohua,MIAO Qiguang,LI Tanping,JIA Guang
    Journal of Xidian University. 2022, 49(3):  238-244.  doi:10.19665/j.issn1001-2400.2022.03.027
    Abstract ( 275 )   HTML ( 11 )   PDF (1319KB) ( 41 )   Save
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    Ozone is a highly effective and broad-spectrum non-residual gas disinfectant.The global COVID-19 pandemic has significantly affected public safety and health,and low concentrations of ozone can inactivate the novel coronavirus.The negative ion generator is a safe and efficient method to generate ozone.Through corona discharge on the needle plate,an ion current can be formed between the needle-plate electrodes and a certain concentration of ozone can be released.In the research on the relationship between the electrode-to-plate distance and ozone release in the negative ion generator,different experimental observations show contradictory results,making the theoretical explanation very difficult and complicated.As the needle-to-plate electrode distance increases,the continuous exponential decreasing trend of ozone emission rate changes to a non-continuous step-wised decreasing pattern,which is defined as the Quantum Ozone Emission Effect (QOEE).The QOEE was observed in all negative ion generators when the plate material was aluminium,stainless steel,yellow brass,or copper.The observed quantum ozone emission effect in negative ion generators may be related to the gas ionization potential of the oxygen molecule and to the electron avalanche theory.The quantum effect of ozone emission is a manifestation of the quantum behavior of the microscopic electron world in the macroscopic world.The ozone emission quantum effect provides a novel technical method for measuring the microscopic properties and corona discharge characteristics of materials.