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    Research on the multi-objective algorithm of UAV cluster task allocation
    GAO Weifeng, WANG Qiong, LI Hong, XIE Jin, GONG Maoguo
    Journal of Xidian University    2024, 51 (2): 1-12.   DOI: 10.19665/j.issn1001-2400.20230413
    Abstract550)   HTML44)    PDF(pc) (2779KB)(328)       Save

    Aiming at the cooperative task allocation problem of UAV swarm in target recognition scenario,an optimization model with recognition cost and recognition benefit as the goal is established,and a multi-objective differential evolution algorithm based on decomposition is designed to solve the model.First,an elite initialization method is proposed,and the initial solution is screened to improve the quality of the solution set on the basis of ensuring the uniform distribution of the obtained nondominated solution.Second,the multi-objective differential evolution operator under integer encoding is constructed based on the model characteristics to improve the convergence speed of the algorithm.Finally,a tabul search strategy with restrictions is designed,so that the algorithm has the ability to jump out of the local optimal.The algorithm provides a set of nondominated solution sets for the solution of the problem,so that a more reasonable optimal solution can be selected according to actual needs.After obtaining the allocation scheme by the above method,the task reallocation strategy is designed based on the auction algorithm,and the allocation scheme is further adjusted to cope with the unexpected situation of UAV damage.On the one hand,simulation experiments verify the effectiveness of the proposed algorithm in solving small,medium and large-scale task allocation problems,and on the other hand,compared with other algorithms,the nondominated set obtained by the proposed algorithm has a higher quality,which can consume less recognition cost and obtain higher recognition revenue,indicating that the proposed algorithm has certain advantages.

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    Smooth interactive compression network for infrared small target detection
    ZHANG Mingjin, ZHOU Nan, LI Yunsong
    Journal of Xidian University    2024, 51 (4): 1-14.   DOI: 10.19665/j.issn1001-2400.20231203
    Abstract353)   HTML41)    PDF(pc) (3393KB)(208)       Save

    Infrared Small Target Detection is a critical focus of various fields,including earth observation and disaster relief efforts,receiving considerable attention within the academic community.Since infrared small targets often occupy just a few dozen pixels and are scattered within complex backgrounds,it becomes paramount to extract semantic information from a broad range of image features to distinguish targets from their surroundings and enhance detection performance.Traditional convolutional neural networks,due to their limited receptive fields and substantial computational demands,face challenges in effectively capturing the shape and precise positioning of small targets,leading to missed detections and false alarms.In response to these challenges,this paper proposes a novel Smooth Interactive Compression Network comprising two main components:the Smooth Interaction Module and the Cross Compression Module.The Smooth Interaction Module extends the feature map's receptive field and enhances inter-feature dependencies,thus bolstering the network’s detection robustness in complex background scenarios.The Cross Compression Module takes into account channel contributions and the interpretability of pruning,dynamically fusing feature maps of varying resolutions.Extensive experiments conducted on the publicly available SIRST dataset and IRSTD-1K dataset demonstrate that the proposed network effectively addresses issues such as target loss,a high false alarm rate,and subpar visual results.Taking the SIRST dataset as an example,compared to the second-best performing model,the proposed model achieved a remarkable improvement in metrics:IoU,nIoU,and Pd are increased by 3.05%,3.41%,and 1.02%,respectively.Meanwhile,Fa and FLOPs are decreased by 33.33% and 82.30%,respectively.

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    Superimposed pilots transmission for unsourced random access
    HAO Mengnan, LI Ying, SONG Guanghui
    Journal of Xidian University    2024, 51 (3): 1-8.   DOI: 10.19665/j.issn1001-2400.20230907
    Abstract337)   HTML64)    PDF(pc) (856KB)(312)       Save

    In unsourced random access,the base station(BS) only needs to recover the messages sent by each active device without identifying the device,which allows a large number of active devices to access the BS at any time without requiring a resource in advance,thereby greatly reducing the signaling overhead and transmission delay,which has attracted the attention of many researchers.Currently,many works are devoted to design random access schemes based on preamble sequences.However,these schemes have poor robustness when the number of active devices changes,and cannot make full use of channel bandwidth,resulting in poor performance when the number of active devices is large.Aiming at this problem,a superimposed pilots transmission scheme is proposed to improve the channel utilization ratio,and the performance for different active device numbers is further improved by optimal power allocation,making the system have good robustness when the number of active devices changes.In this scheme,the first Bp bits of the sent message sequence are used as the index,to select a pair of pilot sequence and interleaver.Then,using the selected interleaver,the message sequence is encoded,modulated and interleaved,and the selected pilot sequence is then superimposed on the interleaved modulated sequence to obtain the transmitted signal.For this transmission scheme,a power optimization scheme based on the minimum probability of error is proposed to obtain the optimal power allocation ratio for different active device numbers,and a two-stage detection scheme of superimposed pilots detection cancellation and multi-user detection decoding is designed.Simulation results show that the superimposed pilot transmission scheme can improve the performance of the unsourced random access scheme based on the preamble sequence by about 1.6~2.0 dB and 0.2~0.5 dB respectively,and flexibly change the number of active devices that the system carries and that it has a lower decoding complexity.

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    GaN-based LLC resonant converter with a 2.5 MHz resonant frequency
    ZHANG Runyu, HE Yunlong, ZHENG Xuefeng, ZHANG Junjie, ZHOU Xiang, MA Xiaohua, HAO Yue
    Journal of Xidian University    2024, 51 (5): 1-8.   DOI: 10.19665/j.issn1001-2400.20240910
    Abstract337)   HTML64)    PDF(pc) (2926KB)(232)       Save

    The DC-DC converter plays a pivotal role in secondary power supplies for aerospace applications.The ongoing development trend for aerospace power supply converters emphasizes compact size,lightweight,and high-power output.To achieve these goals,enhancing the “power-to-weight ratio” and increasing the switching frequency are critical strategies.Notably,the pursuit of higher frequencies is a significant focus for future DC-DC converters.In this paper,GaN(Gallium Nitride) based HEMTs(High Electron Mobility Transistors) is employed as a switching device to investigate the impact of device characteristics on the maximum achievable operating frequency when the LLC resonant converter operates in the soft-switching mode.It is found that reducing the output capacitance of GaN devices leads to higher switching frequencies.However,it is essential to consider the tradeoff between frequency and power losses.To address this problem,we establish an accurate loss model for GaN devices,providing valuable insights for optimizing efficiency.Finally,a 200W 270 V~28 V LLC resonant converter is realized and the detailed analysis is carried out.By utilizing GaN devices as a switching component,a high-frequency converter operating at 2.5 MHz is achieved.The resulting power-to-weight ratio reaches 3.1 kW/kg,with a peak conversion efficiency of 92.8%.Our prototype validates the feasibility of designing higher-frequency LLC converters,and provides a design reference for the future production of a high-frequency converter.

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    Survey of routing technologies for the satellite Internet
    WEI Wenting, FU Liying, WANG Kun, LU Xueyu, ZHOU Zhaojun
    Journal of Xidian University    2024, 51 (5): 9-23.   DOI: 10.19665/j.issn1001-2400.20240503
    Abstract302)   HTML41)    PDF(pc) (2816KB)(140)       Save

    With its evolution of global coverage,flexible access,and reliable transmission,the satellite Internet is the key to constructing a space-air-ground integrated information network.Due to the rapid expansion of constellation scale,complex network topology and diverse service requirements,there is increasing pressure on transmission over the satellite Internet.Routing is responsible for path selection and data forwarding between satellites,which is important to improving the efficiency of inter-satellite transmission and ensuring the quality of service.By considering inter-satellite routing,first,the basic structure and working mechanisms of the satellite Internet are reviewed.According to the challenges of inter-satellite networking,routing technologies are systematically reviewed from the perspectives of dynamic information perception,network failures model,and cross-layer hybrid networking.In addition,the research on routing technologies in different scenarios is analyzed,with the applicability of various existing solutions studied when the on-board computing and storage capabilities are limited.Finally,by combining the bottlenecks of current satellite Internet routing and emerging network technology,future research hotspots are prospected.

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    Time series anomaly detection based on multi-scale feature information fusion
    HENG Hongjun, YU Longwei
    Journal of Xidian University    2024, 51 (3): 203-214.   DOI: 10.19665/j.issn1001-2400.20230906
    Abstract277)   HTML28)    PDF(pc) (2089KB)(92)       Save

    Currently,most time series lack corresponding anomaly labels and existing reconstruction-based anomaly detection algorithms fail to capture the complex underlying correlations and temporal dependencies among multidimensional data effectively.To construct feature-rich time series,a multi-scale feature information fusion anomaly detection model is proposed.First,the model employs convolutional neural networks to perform feature convolution on different sequences within sliding windows,capturing local contextual information at different scales.Then,position encoding from the Transformer is utilized to embed the convolved time series windows,enhancing the positional relationships between each time series and its neighboring sequences within the sliding window.Time attention is introduced to capture the temporal autocorrelation of the data,and multi-head self-attention adaptively assigns different weights to different time series within the window.Finally,the reconstructed window data obtained through the down-sampling process is progressively fused with the local features and temporal context information at different scales.This process accurately reconstructs the original time series,with the reconstruction error used as the final anomaly score for anomaly determination.Experimental results indicate that the constructed model achieves improved F1 scores compared to the baseline models on both the SWaT and SMD datasets.On the high-dimensional and imbalanced WADI dataset,the F1 score decreases by 1.66% compared to the GDN model.

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    Efficient semantic communication method for bandwidth constrained scenarios
    LIU Wei, WANG Mengyang, BAI Baoming
    Journal of Xidian University    2024, 51 (3): 9-18.   DOI: 10.19665/j.issn1001-2400.20240203
    Abstract241)   HTML40)    PDF(pc) (1035KB)(161)       Save

    Semantic communication provides a new research perspective for communication system optimization and performance improvement.However,current research on semantic communication ignores the impact of communication overhead and does not consider the relationship between semantic communication performance and communication overhead,resulting in difficulty in improving semantic communication performance when the bandwidth resource is limited.Therefore,an information bottleneck based semantic communication method for text sources is proposed.First,the Transformer model is used for semantic and channel joint encoding and decoding,and a feature selection module is designed to identify and delete redundant information,and then an end-to-end semantic communication model is constructed in the method;Second,considering the tradeoff between semantic communication performance and communication cost,a loss function is designed based on the information bottleneck theory to ensure the semantic communication performance,reduce the communication cost,and complete the training and optimization of the semantic communication model.Experimental results show that on the proceedings of the European Parliament,compared with the baseline model,the proposed method can reduce communication overhead by 20%~30% while ensuring communication performance.Under the same bandwidth conditions,the BLEU score of this method can be increased by 5%.Experimental results prove that the proposed method can effectively reduce the semantic communication overhead,thereby improving semantic communication performance when the bandwidth resource is limited.

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    Research on lightweight and feature enhancement of SAR image ship targets detection
    GONG Junyang, FU Weihong, FANG Houzhang
    Journal of Xidian University    2024, 51 (2): 96-106.   DOI: 10.19665/j.issn1001-2400.20230407
    Abstract218)   HTML19)    PDF(pc) (2728KB)(110)       Save

    The accuracy of ship targets detection in sythetic aperture radar images is susceptible to the nearshore clutter.The existing detection algorithms are highly complex and difficult to deploy on embedded devices.Due to these problems a lightweight and high-precision SAR image ship target detection algorithm CA-Shuffle-YOLO(Coordinate Shuffle You Only Look Once) is proposed in this article.Based on the YOLO v5 target detection algorithm,the backbone network is improved in two aspects:lightweight and feature refinement.The lightweight module is introduced to reduce the computational complexity of the network and improve the reasoning speed,and a collaborative attention mechanism module is introduced to enhance the algorithm's ability to extract the detailed information on near-shore ship targets.In the feature fusion network,weighted feature fusion and cross-module fusion are used to enhance the ability of the model to fuse the detailed information on SAR ship targets.At the same time,the depth separable convolution is used to reduce the computational complexity and improve the real-time performance.Through the test and comparison experiments on the SSDD ship target detection dataset,the results show that the detection accuracy of CA-Shuffle-YOLO is 97.4%,the detection frame rate is 206FPS,and the required computational complexity is 6.1GFlops.Compare to the original YOLO v5,the FPS of our algorithm is 60FPS higher with the required computational complexity of our algorithm being only the 12% that of the ordinary YOLOv5.

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    Study of EEG classification of depression by multi-scale convolution combined with the Transformer
    ZHAI Fengwen, SUN Fanglin, JIN Jing
    Journal of Xidian University    2024, 51 (2): 182-195.   DOI: 10.19665/j.issn1001-2400.20230211
    Abstract216)   HTML11)    PDF(pc) (2907KB)(86)       Save

    In the process of using the deep learning model to classify the EEG signals of depression,aiming at the problem of insufficient feature extraction in single-scale convolution and the limitation of the convolutional neural network in perceiving the global dependence of EEG signals,a multi-scale dynamic convolution network module and the gated transformer encoder module are designed respectively,which are combined with the temporal convolution network,and a hybrid network model MGTTCNet is proposed to classify the EEG signals of patients with depression and healthy controls.First,multi-scale dynamic convolution is used to capture the multi-scale time-frequency information of EEG signals from spatial and frequency domains.Second,the gated transformer encoder is used to learn global dependencies in EEG signals,which effectively enhances the ability of the network to express relevant EEG signal features using the multi-head attention mechanism.Third,the temporal convolution network is used to extract temporal features available for EEG signals.Finally,the extracted abstract features are fed into the classification module for classification.The proposed model is experimentally validated on the public data set MODMA using the Hold-out method and the 10-Fold Cross Validation method,with the classification accuracy being 98.51% and 98.53%,respectively.Compared with the baseline single-scale model EEGNet,the classification accuracy of the proposed model is increased by 1.89% and 1.93%,the F1 value is increased by 2.05% and 2.08%,and the kappa coefficient values are increased by 0.0381 and 0.0385,respectively.Meanwhile,the ablation experiments verify the effectiveness of each module designed in this paper.

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    High precision time synchronization between nodes under motion scenario of UAV platforms
    CHEN Cong, DUAN Baiyu, XU Qiang, PAN Wensheng, MA Wanzhi, SHAO Shihai
    Journal of Xidian University    2024, 51 (3): 19-29.   DOI: 10.19665/j.issn1001-2400.20231207
    Abstract213)   HTML18)    PDF(pc) (1363KB)(94)       Save

    Time synchronization is the foundation for transmission resource scheduling,cooperative localization and data fusion in UAV clusters.Two-way time synchronization is commonly used to synchronize time between nodes in scenarios with high synchronization accuracy requirements.However,the relative motion of the UAVs will cause the propagation delays of the two synchronization messages to be unequal,thereby causing time synchronization errors.To solve this problem,the causes of synchronization deviation are analyzed from the perspective of solving linear equations.A method is proposed to increase the number of equations by conducting two-way time synchronization twice,with the number of unknown quantities being reduced under the premise of the uniform motion of nodes.The solution formula for the clock deviation under uniform motion of nodes is derived,and the derivation results show that the clock deviation solution is independent of the speed of the nodes.Synchronization performance is compared with that of existing compensation methods under the additive Gaussian white noise channel.The effect of time stamp deviation and speed changing on the accuracy of the clock deviation solution is analyzed.Finally,the effectiveness of the dual-trigger two-way time synchronization is verified through field experiments.Simulation and experiment results show that,compared with conventional two-way time synchronization,the dual-trigger two-way time synchronization does not cause systematic deviations by the uniform motion of nodes.

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    UAV swarm power allocation strategy for resilient topology construction
    HU Jialin, REN Zhiyuan, LIU Anni, CHENG Wenchi, LIANG Xiaodong, LI Shaobo
    Journal of Xidian University    2024, 51 (2): 28-45.   DOI: 10.19665/j.issn1001-2400.20230314
    Abstract207)   HTML9)    PDF(pc) (5173KB)(87)       Save

    A topology construction method of the Unmanned combat network with strong toughness is proposed for the problem of network performance degradation and network paralysis caused by the failure of the Unmanned combat network itself or interference by enemy attack.The method first takes the edge-connectivity as the toughness indicator of the network;second,the minimum cut is used as the measure of the toughness indicator based on the maximum flow minimum cut(Max-flow min-cut) theorem,on the basis of which considering the limited power of a single UAV and the system,the topology is constructed by means of power allocation to improve the network toughness from the physical layer perspective,and the power allocation strategy of the Unmanned combat network under power constraint is proposed;finally,particle swarm optimization(PSO) algorithm is used to solve the topology toughness optimization problem under the power constraint.Simulation results show that under the same modulation and power constraints,the power allocation scheme based on the PSO algorithm can effectively improve the toughness of the Unmanned combat network compared with other power allocation algorithms in the face of link failure mode and node failure mode,and that the average successful service arrival rate of the constructed network remains above 95% in about 66.7% of link failures,which meets the actual combat requirements.

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    Fall detection algorithm based on the improved YOLOv8 combined with key points
    WANG Xiaopeng, SHI Huan
    Journal of Xidian University    2024, 51 (5): 149-164.   DOI: 10.19665/j.issn1001-2400.20240403
    Abstract202)   HTML7)    PDF(pc) (7965KB)(77)       Save

    To solve the problems of insufficient feature extraction,a single fall detection method,and weak real-time performance of traditional fall detection algorithms,an improved YOLOv8 fall detection algorithm combined with human skeleton key points is proposed.First,the backbone network of YOLOv8 is replaced by a ShuffleNetV2 network,and the mixed attention mechanism(Shuffle Attention,SA) is added in the neck,so that the model can extract the behavioral characteristics better and realize the static posture matching of a human body.Second,by analyzing the information on position change of skeletal key points,the decline speed of the center of mass,the angle speed between the trunk and the ground and height-to-width ratio of the body are taken as the basis of the fall behavior to improve the accuracy of fall judgment.Experimental results show that the algorithmic accuracy,F1 value,and mAP50 value on COCO Key Points datasets are 78.3%,67.9%,and 70.0% respectively,that the algorithmic accuracy is 95.85%,92.8% and 96.52% on UR Fall Detection,Fall Detection Datasets and self-built datasets,and that the proposed algorithm outperforms the traditional algorithm in distinguishing daily life behavior and falling behavior.

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    Design and measurement of reconfigurable intelligent surface-aided millimeter-wave coverage enhancement with wide beam
    TENG Xiaokun, MENG Shengguo, CHEN Weicong, TANG Wankai, JIN Shi
    Journal of Xidian University    2024, 51 (5): 189-200.   DOI: 10.19665/j.issn1001-2400.20241002
    Abstract186)   HTML4)    PDF(pc) (5137KB)(60)       Save

    To address the issue of weak signal coverage of the millimeter-wave in wireless communication systems,the method for using the reconfigurable intelligent surface(RIS) to reflect wide beams is proposed,which enhances the signal strength in weak coverage areas.First,an RIS is introduced between the transmitter and receiver,with no direct line-of-sight path between them,to enhance the received signal strength in weak coverage areas.A general electromagnetic wave propagation model for RIS-aided millimeter-wave communication is established,with an analytical expression for the received signal power derived.Subsequently,based on different levels of prior information about the area,a general design framework for the reflection phase shift of RIS is proposed.For the optimization problem of discrete phase shifts of RIS,a heuristic algorithm is employed for efficient optimization.Simulation results demonstrate that the proposed algorithm can synthesize reflection beams with any width based on RIS.Additionally,further optimization based on specific information about the area shape can further improve the millimeter-wave signal coverage performance in the target area.Finally,a radiation pattern measurement system and a RIS-based millimeter-wave communication prototype system are set up.Measurement campaigns are conducted in the 35 GHz frequency band,yielding results that match those in the simulations.Radiation pattern measurement results in an anechoic chamber validate the effectiveness of the wide beam synthesis algorithm.In real-world signal coverage measurements,the signal coverage rate is improved from 1.5% to 90% after deploying RIS and the proposed algorithm,as compared to the scenario without RIS.

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    Time series prediction method based on the bidirectional long short-term memory network
    GUAN Yepeng, SU Guangyao, SHENG Yi
    Journal of Xidian University    2024, 51 (3): 103-112.   DOI: 10.19665/j.issn1001-2400.20231205
    Abstract175)   HTML17)    PDF(pc) (2614KB)(65)       Save

    Time series prediction means the use of historical time series to predict a period of time in the future,so as to formulate corresponding strategies in advance.At present,the categories of time series are complex and diverse.However,existing time series prediction models cannot achieve stable prediction results when faced with multiple types of time series data.The application requirements of complex time series data prediction in reality are difficult to simultaneously meet.To address the problem,a time series prediction method is proposed based on the Bidirectional Long and Short-term Memory(BLSTM) with the attention mechanism.The improved forward and backward propagation mechanisms are used to extract temporal information.The future temporal information is inferred through an adaptive weight allocation strategy.Specifically,an improved BLSTM is proposed to extract deep time series features and explore temporal dependencies of context by combining BLSTM and Long Short-term Memory(LSTM) networks,on the basis of which the proposed temporal attention mechanism is fused to achieve adaptive weighting of deep time series features,which improves the saliency expression ability of deep time series features.Experimental results demonstrate that the proposed method has a superior prediction performance in comparison with some representative methods in multiple time series datasets of different categories.

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    Efficient seed generation method for software fuzzing
    LIU Zhenyan, ZHANG Hua, LIU Yong, YANG Libo, WANG Mengdi
    Journal of Xidian University    2024, 51 (2): 126-136.   DOI: 10.19665/j.issn1001-2400.20230901
    Abstract174)   HTML5)    PDF(pc) (1912KB)(59)       Save

    As one of the effective ways to exploit software vulnerabilities in the current software engineering field,fuzzing plays a significant role in discovering potential software vulnerabilities.The traditional seed selection strategy in fuzzing cannot effectively generate high-quality seeds,which results in the testcases generated by mutation being unable to reach deeper paths and trigger more security vulnerabilities.To address these challenges,a seed generation method for efficient fuzzing based on the improved generative adversarial network(GAN) is proposed which can flexibly expand the type of seed generation through encoding and decoding technology and significantly improve the fuzzing performance of most applications with different input types.In experiments,the seed generation strategy adopted in this paper significantly improved the coverage and unique crashes,and effectively increased the seed generation speed.Six open-sourced programs with different highly-structured inputs were selected to demonstrate the effectiveness of our strategy.As a result,the average branch coverage increased by 2.79%,the number of paths increased by 10.35% and additional 86.92% of unique crashes were found compared to the original strategy.

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    Drone identification based on the normalized cyclic prefix correlation spectrum
    ZHANG Hanshuo, LI Tao, LI Yongzhao, WEN Zhijin
    Journal of Xidian University    2024, 51 (2): 68-75.   DOI: 10.19665/j.issn1001-2400.20230704
    Abstract173)   HTML7)    PDF(pc) (1621KB)(82)       Save

    Radio-frequency(RF)-based drone identification technology has the advantages of long detection distance and low environmental dependence,so that it has become an indispensable approach to monitoring drones.How to identify a drone effectively at the low signal-to-noise ratio(SNR) regime is a hot topic in current research.To ensure excellent video transmission quality,drones commonly adopt orthogonal frequency division multiplexing(OFDM) modulation with cyclic prefix(CP) as the modulation of video transmission links.Based on this property,we propose a drone identification algorithm based on the convolutional neural network(CNN) and normalized CP correlation spectrum.Specifically,we first analyze the OFDM symbol durations and CP durations of drone signals,on the basis of which the normalized CP correlation spectrum is calculated.When the modulation parameters of a drone signal match the calculated normalized CP correlation spectrum,several correlation peaks will appear in the normalized CP correlation spectrum.The positions of these peaks reflect the protocol characteristics of drone signals,such as frame structure and burst rules.Finally,for identifying drones,a CNN is trained to extract these characteristics from the normalized CP correlation spectrum.In this work,a universal software radio peripheral(USRP) X310 is utilized to collect the RF signals of five drones to construct the experimental dataset.Experimental results show that the proposed algorithm performs better than spectrum-based and spectrogram-based algorithms,and it remains effective at low SNRs.

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    Hyperspectral image denoising based on tensor decomposition and adaptive weight graph total variation
    CAI Mingjiao, JIANG Junzheng, CAI Wanyuan, ZHOU Fang
    Journal of Xidian University    2024, 51 (2): 157-169.   DOI: 10.19665/j.issn1001-2400.20230412
    Abstract172)   HTML6)    PDF(pc) (2394KB)(71)       Save

    During the acquisition process of hyperspectral images,various noises are inevitably introduced due to the influence of objective factors such as observation conditions,material properties of the imager,and transmission conditions,which severely reduces the quality of hyperspectral images and limits the accuracy of subsequent processing.Therefore,denoising of hyperspectral images is an extremely important preprocessing step.For the hyperspectral image denoising problem,a denoising algorithm,which is based on low-rank tensor decomposition and adaptive weight graph total variation regularization named LRTDGTV,is proposed in this paper.Specifically,Low-rank tensor decomposition is used to characterize the global correlation among all bands,and adaptive weight graph total variation regularization is adopted to characterize piecewise smoothness property of hyperspectral images in the spatial domain and preserve the edge information of hyperspectral images.In addition,sparse noise,including stripe noise,impulse noise and deadline noise,and Gaussian noise are characterized by l1-norm and Frobenius-norm,respectively.Thus,the denoising problem can be formulated into a constrained optimization problem involving low-rank tensor decomposition and adaptive weight graph total variation regularization,which can be solved by employing the augmented Lagrange multiplier(ALM) method.Experimental results show that the proposed hyperspectral image denoising algorithm can fully characterize the inherent structural characteristics of hyperspectral images data and has a better denoising performance than the existing algorithms.

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    Highly dynamic multi-channel TDMA scheduling algorithm for the UAV ad hoc network in post-disaster
    SUN Yanjing, LI Lin, WANG Bowen, LI Song
    Journal of Xidian University    2024, 51 (2): 56-67.   DOI: 10.19665/j.issn1001-2400.20230414
    Abstract170)   HTML6)    PDF(pc) (1608KB)(93)       Save

    Extreme emergencies,mainly natural disasters and accidents,have posed serious challenges to the rapid reorganization of the emergency communication network and the real-time transmission of disaster information.It is urgent to build an emergency communication network with rapid response capabilities and dynamic adjustment on demand.In order to realize real-time transmission of disaster information under the extreme conditions of "three interruptions" of power failure,circuit interruption and network connection,the Flying Ad Hoc Network can be formed by many unmanned aerial vehicles to cover the network communication in the disaster-stricken area.Aiming at the channel collision problem caused by unreasonable scheduling of FANET communication resources under the limited conditions of complex environment after disasters,this paper proposes a multi-channel time devision multiple access(TDMA) scheduling algorithm based on adaptive Q-learning.According to the link interference relationship between UAVs,the vertex interference graph is established,and combined with the graph coloring theory,and the multi-channel TDMA scheduling problem is abstracted into a dynamic double coloring problem in highly dynamic scenarios.Considering the high-speed mobility of the UAV,the learning factor of Q-learning is adaptively adjusted according to the change of network topology,and the trade-off optimization of the convergence speed of the algorithm and the exploration ability of the optimal solution is realized.Simulation experiments show that the proposed algorithm can realize the trade-off optimization of network communication conflict and convergence speed,and can solve the problem of resource allocation decision and fast-changing topology adaptation in post-disaster high-dynamic scenarios.

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    Secure command delivery protocol for drone networks in emergency scenarios
    LIU Luyao, ZHOU Yuchen, CAO Jin, MA Ruhui, YOU Wei, LI Hui
    Journal of Xidian University    2024, 51 (5): 201-216.   DOI: 10.19665/j.issn1001-2400.20241007
    Abstract166)   HTML3)    PDF(pc) (2831KB)(46)       Save

    Drones play an increasingly important role in emergency scenarios.When drones perform long-distance missions,the flight distance is long,which makes it impossible for the ground control center to communicate directly with the drones.Emergency scenarios such as sudden fires and earthquakes require timely instructions to respond.Aiming at the scenario of secure issuance of drone network data instructions in emergency scenarios,a command authority issuance mechanism based on a multi-receiver encryption protocol and a secure instruction issuance mechanism based on proxy signcryption are designed.When the ground control center issues command authority,it issues command authority to several mobile command centers through a multi-receiver encryption protocol and dispatches them to the emergency site.When the instruction is securely issued,the mobile command center sends the signed instruction to the aerial platform which verifies the identity and command authority of the mobile command center and sends the signed instruction to the drone.The drones in the network are pre-configured under the jurisdiction of the aerial platform.The drone verifies the identity of the aerial platform,decrypts and executes the instruction.A security analysis of the scheme is carried out using a variety of methods such as the formal verification tool Scyther,BAN logic and informal security analysis.The results show that the proposed scheme can meet the necessary security requirements.Compared with multiple schemes,the results show that the proposed scheme has a good performance.

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    Doppler frequency shift estimation and the tracking algorithm for air-to-air high-speed mobile communications
    ZHANG Xin, LI Jiandong
    Journal of Xidian University    2024, 51 (3): 30-37.   DOI: 10.19665/j.issn1001-2400.20240304
    Abstract165)   HTML17)    PDF(pc) (1484KB)(70)       Save

    Under air-to-air high-speed mobile communications,the Doppler frequency shift of the Aerial platform has characteristics of a large range and rapid change.It is difficult for existing frequency estimation algorithms to tackle both high estimation accuracy and engineering realization feasibility.In this paper,the time-varying Doppler frequency shift model is first constructed according to the traditional frequency offset model and the spatiotemporal correlation of Doppler frequency shift versus time.Based on this model,the coarse frequency offset estimation values of adjacent short preambles are associated.The optimization problem of frequency offset estimation is transformed into a classic optimization problem of overdetermined linear equations,which reduces the estimation variance to the maximum extent and improves the estimation accuracy.Simulation results show that the residual frequency offset of the proposed algorithm is reduced significantly compared with the traditional algorithm.Simulation results show that the root mean square error(RMSE) of the proposed algorithm is less than 100 Hz when the SNR is greater than 5 dB.Aiming at the numerical stability problem existing in the proposed algorithm,the corresponding engineering realizable method is given in the paper.Unlike the traditional phase-locked loop feedback tracking scheme,the proposed algorithm adopts a feedforward compensation scheme,thereby improving the system stability and timeliness.

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    Adaptivedensity peak clustering algorithm
    ZHANG Qiang, ZHOU Shuisheng, ZHANG Ying
    Journal of Xidian University    2024, 51 (2): 170-181.   DOI: 10.19665/j.issn1001-2400.20230604
    Abstract161)   HTML7)    PDF(pc) (3821KB)(74)       Save

    Density Peak Clustering(DPC) is widely used in many fields because of its simplicity and high efficiency.However,it has two disadvantages:① It is difficult to identify the real clustering center in the decision graph provided by DPC for data sets with an uneven cluster density and imbalance;② There exists a "chain effect" where a misallocation of the points with the highest density in a region will result in all points within the region pointing to the same false cluster.In view of these two deficiencies,a new concept of Natural Neighbor(NaN) is introduced,and a density peak clustering algorithm based on the natural neighbor(DPC-NaN) is proposed which uses the new natural neighborhood density to identify the noise points,selects the initial preclustering center point,and allocates the non-noise points according to the density peak method to get the preclustering.By determining the boundary points and merging radius of the preclustering,the results of the preclustering can be adaptively merged into the final clustering.The proposed algorithm eliminates the need for manual parameter presetting and alleviates the problem of "chain effect".Experimental results show that compared with the correlation clustering algorithm,the proposed algorithm can obtain better clustering results on typical data sets and perform well in image segmentation.

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    Algorithm for estimation of the two-dimensional robust super-resolution angle under amplitude and phases uncertainty background
    LIU Minti, ZENG Cao, HU Shulin, CHENG Jianzhong, LI Jun, LI Shidong, LIAO Guisheng
    Journal of Xidian University    2024, 51 (3): 55-62.   DOI: 10.19665/j.issn1001-2400.20231201
    Abstract157)   HTML10)    PDF(pc) (2186KB)(50)       Save

    In order to address the issues of low angle resolution in elevation and azimuth dimensions of the 4D vehicle-mounted millimeter wave radar,as well as the biased angle measurement when the array includes amplitude and phase defects.A robust two-dimensional super-resolution angle estimation method based on fast sparse Bayesian Learning(FSBL) is suggested as a solution to this issue.First,a two-dimensional super-resolution angle signal model with amplitude and phase errors is built by using grids to split the angle domain space depending on spatial sparsity.Then,the two-dimensional angle estimation for spatial proximity targets is obtained using the fixed-point updated based MacKay SBL reconstruction algorithm,with the phase error and biased angle compensation calibrated using the self-correcting algorithm based on vector dot product.Finally,the computational complexity of the proposed algorithm is analyzed,and the Cramer-Rao Lower Bound(CRB) for two-dimensional angle estimation under MIMO non-uniform sparse arrays is provided.By comparing six distinct categories of super-resolution algorithms,simulation results demonstrate that the proposed method has a high angle resolution and a low root mean square error(RMSE) in a low SNR and few snapshot numbers under the actual layout of 12 transmitting and 16 receiving antennas for the continental ARS548 radar.

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    New method for calculating the differential-linear bias of the ARX cipher
    ZHANG Feng, LIU Zhengbin, ZHANG Jing, ZHANG Wenzheng
    Journal of Xidian University    2024, 51 (2): 211-223.   DOI: 10.19665/j.issn1001-2400.20230404
    Abstract156)   HTML6)    PDF(pc) (1106KB)(63)       Save

    The ARX cipher consists of three basic operations,additions,rotations and XORs.Statistical analysis is currently used to calculate the bias of the ARX cipher differential-linear distinguishers.At CRYPTO 2022,NIU et al.gave a method for evaluating the correlation of the ARX cipher differential-linear distinguishers without using statistical analysis.They gave a 10-round differential-linear distinguisher for SPECK32/64.This paper gives the definition of differential-linear characteristics.It presents the first method for calculating the bias of differential-linear distinguishers using differential-linear characteristics based on the methods by BLONDEAU et al.and BAR-ON et al.Also,a method for searching for differential-linear characteristics based on Boolean Satisfiability Problem(SAT) automation techniques is proposed,which is a new method for calculating the bias of the ARX cipher differential-linear distinguisher without statistical analysis.As an application,the bias of the 10-round differential-linear distinguisher for SPECK32/64 given by NIU et al.is calculated with the theoretical value 2-15.00 obtained,which is very close to the experimental value 2-14.90 from the statistical analysis and better than the theoretical value 2-16.23 given by NIU et al.Also,the first theoretical value 2-8.41 for the bias of the 9-round differential-linear distinguisher for SIMON32/64 is given,which is close to the experimental value 2-7.12 obtained by statistical analysis.Experimental results fully demonstrate the effectiveness of this method.

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    New prediction strategy based evolutionary algorithm for dynamic multi-objective optimization
    WAN Mengyi, WU Yan
    Journal of Xidian University    2024, 51 (3): 124-135.   DOI: 10.19665/j.issn1001-2400.20230902
    Abstract155)   HTML13)    PDF(pc) (3026KB)(85)       Save

    Dynamic multi-objective optimization problems(DMOPs) where the environments change over time require that an evolutionary algorithm be able to continuously track the moving Pareto set or Pareto front.Response strategies based prediction has received much attention.However,these strategies mostly use historical environmental information for prediction,which will make the predicted results inaccurate.In this paper,we strengthen the mining and utilization of new environmental information and propose a new prediction strategy based evolutionary algorithm for dynamic multi-objective optimization(RAM),which includes mainly two core parts,namely,response mechanism and acceleration mechanism.The response mechanism reinitializes the population after the environmental changes,some individuals are generated by the prediction strategy,which is close to the new environmental PS to improve the optimization ability of this algorithm,and the remaining individuals are generated by the local search strategy to increase the population diversity.The acceleration mechanism is used in the static optimization process to accelerate the convergence speed of the RAM.Finally,the RAM is compared with other three advanced dynamic multi-objective optimization algorithms on a series of test functions with different dynamic characteristics.The results show that the RAM has more advantages than other three algorithms in solving dynamic multi-objective optimization problems.

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    Blockchain searchable encryption scheme for multi-user environment
    ZHAI Sheping, ZHANG Ruiting, YANG Rui, CAO Yongqiang
    Journal of Xidian University    2024, 51 (4): 151-169.   DOI: 10.19665/j.issn1001-2400.20240205
    Abstract155)   HTML8)    PDF(pc) (2449KB)(38)       Save

    How to perform search and realize data sharing on encrypted data that have lost the original features of a plaintext is the key issue in the research on searchable encryption technology.In view of the problems existing in traditional asymmetric searchable encryption schemes,it is difficult to support multi-user multi-keyword search,semi-honest third-party search service,and centralized authorization management,so this paper proposes a searchable encryption scheme for multi-user environment based on blockchain.First,the traditional asymmetric searchable encryption scheme is combined with conditional broadcast proxy re-encryption technology.By encrypting the ciphertext for user groups,verifying user authorization and re-encrypting search results for users meeting the conditions,the secure search and controllable sharing of secret data is realized in multi-user environment.Second,smart contracts are called on the alliance chain to perform multi-keyword ciphertext search,thus reducing the risk of semi-honest third-party false search,and the improved PBFT algorithm is used to elect consensus nodes to rotate as authorization managers,thereby reducing the threat of single point failure or malicious attacks of traditional central authorities.Finally,by analyzing the security and correctness of the scheme,it is shown that the scheme can effectively improve the problems existing in the traditional scheme.Simulation shows that compared with the existing searchable encryption schemes,the proposed scheme has obvious advantages in ensuring the privacy of data search,with the computing cost relatively low.

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    Algorithm for optimization of joint spatial and power resources for cooperative active and passive localization
    LYU Peixia, ZHAO Yue, LI Zan, BAI Dou, HAO Benjian
    Journal of Xidian University    2024, 51 (4): 29-38.   DOI: 10.19665/j.issn1001-2400.20240102
    Abstract151)   HTML18)    PDF(pc) (2429KB)(49)       Save

    The rapid development of UAVs has brought great convenience to today's society,but their potential misuse poses a risk to public safety.As a result,in recent years,surveillance and localization technologies for UAVs have been widely studied.In response to the application problem of difficulty in accurate localization of long-range low-flying UAVs,a cooperative localization framework is proposed,mainly for passive localization,and it is supplemented by active detection.Based on the passive localization using the time difference of arrival(TDOA),the active detection equipment supporting round-trip time of arrival(RT-TOA) measurement is introduced to locate the UAVs opportunistically and actively.These devices compensate for the missing target elevation information of passive localization,to improve the three-dimensional localization accuracy of UAVs.This paper delves into the spatial and power sources allocation methods for active localization nodes under the pre-deployment of passive localization nodes.Under the framework of cooperative localization,it derives the localization accuracy measurement indicator and formulates the joint optimization problem for spatial and power resources.A resource optimization algorithm for improved gray wolf optimization based on nonlinear convergence factors and memory guidance(CM-IGWO) is proposed.Simulation results show that the active and passive cooperative localization effect is better than the passive localization effect,and that the elevation localization accuracy in typical scenarios is significantly improved by 96.33%.In addition,the proposed CM-IGWO algorithm is superior to the gray wolf optimization(GWO) and IGWO when solving the joint optimization problem for spatial and power resources.

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    Workflow deployment method based on graph segmentation with communication and computation jointly optimized
    MA Yinghong, LIN Liwan, JIAO Yi, LI Qinyao
    Journal of Xidian University    2024, 51 (2): 13-27.   DOI: 10.19665/j.issn1001-2400.20231206
    Abstract149)   HTML16)    PDF(pc) (3074KB)(106)       Save

    For the purpose of improving computing efficiency,it becomes an important way for cloud data centers to deal with the continuous growth of computing and network tasks by decomposes complex large-scale tasks into simple tasks and modeling them into workflows,which are then completed by parallel distributed computing clusters.However,the communication bandwidth consumption caused by inter-task transmission can easily cause network congestion in data center.It is of great significance to deploy workflow scientifically,taking into account both computing efficiency and communication overhead.There are two typical types of workflow deployment algorithms:list-based workflow deployment algorithm and cluster-based workflow deployment algorithm.However,the former focuses on improving the computing efficiency while does not pay attention to the inter-task communication cost,so the deployment of large-scale workflow is easy to bring heavy network load.The latter focuses on minimizing the communication cost,but sacrifices the parallel computing efficiency of the tasks in the workflow,which results in a long workflow completion time.This work fully explores the dependency and parallelism between tasks in workflow,from the perspective of graph theory.By improving the classic graph segmentation algorithm,community discovery algorithm,the balance between minimizing communication cost and maximizing computation parallelism was achieved in the process of workflow task partitioning.Simulation results show that,under different workflow scales,the proposed algorithm reduces the communication cost by 35%~50%,compared with the typical list-based deployment algorithm,and the workflow completion time by 50%~65%,compared with the typical cluster-based deployment algorithm.Moreover,its performance has good stability for workflows with different communication-calculation ratios.

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    Bidirectional adaptive differential privacy federated learning scheme
    LI Yang, XU Jin, ZHU Jianming, WANG Youwei
    Journal of Xidian University    2024, 51 (3): 158-169.   DOI: 10.19665/j.issn1001-2400.20230706
    Abstract147)   HTML7)    PDF(pc) (2749KB)(45)       Save

    With the explosive growth of personal data,the federated learning based on differential privacy can be used to solve the problem of data islands and preserve user data privacy.Participants share the parameters with noise to the central server for aggregation by training local data,and realize distributed machine learning training.However,there are two defects in this model:on the one hand,the data information in the process of parameters broadcasting by the central server is still compromised,with the risk of user privacy leakage;on the other hand,adding too much noise to parameters will reduce the quality of parameter aggregation and affect the model accuracy of federated learning.In order to solve the above problems,a bidirectional adaptive differential privacy federated learning scheme(Federated Learning Approach with Bidirectional Adaptive Differential Privacy,FedBADP) is proposed,which can adaptively add noise to the gradients transmitted by participants and central servers,and keep data security without affecting the model accuracy.Meanwhile,considering the performance limitations of the participants hardware devices,this model samples their gradients to reduce the communication overhead,and uses the RMSprop to accelerate the convergence of the model on the participants and central server to improve the accuracy of the model.Experiments show that our novel model can enhance the user privacy preserving while maintaining a good accuracy.

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    Collaborative resource allocation method for multiple jammers in formation penetration
    YAN Junkun, ZHANG Congrui, LI Wanping, DAI Jinhui, ZHANG Peng, LIU Hongwei
    Journal of Xidian University    2024, 51 (5): 24-34.   DOI: 10.19665/j.issn1001-2400.20240501
    Abstract146)   HTML8)    PDF(pc) (2291KB)(84)       Save

    The essence of jamming countermeasure is competition in the resource dimension.The single node with limited jamming resources is no longer able to meet practical needs.Multi node collaborative jamming can introduce higher dimensional jamming resources,which has become an important form of combat in the future.However,in traditional collaborative jamming scenarios,the use of preset transmission modes by each node can lead to redundant configuration of jamming resources,resulting in poor jamming effects in the context of formation penetration.In response to the above issues,a performance-driven method for collaborative resource allocation of multiple jammers is proposed.Its core is to allocate the transmission resources of multiple jammers in real time,so as to reduce the tracking accuracy of enemy radars on our penetration targets under the same resource consumption.First,this article derives the Bayesian Cramér-Rao Lower Bound for tracking penetration targets in jamming scenarios and evaluates the performance of multi jammer collaborative jamming; Then,based on the resource constraints of our jammers,a multi jammer collaborative resource optimization model including dwell time variables is established,which proves to be a convex optimization problem.The Augmented Lagrangian Multiplier Method is used for fast optimization and solution.Simulation results show that compared to other benchmark methods,the proposed jamming resource allocation method can effectively suppress enemy networked radars,reduce their tracking accuracy towards our penetration targets,and still have a good jamming effect and a fast solving ability under the constraint of a limited number of beams.

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    Graph neural network vulnerability detection for ethernet smart contracts
    LI Xiaohan, YANG Yanbo, ZHANG Jiawei, LI Baoshan, MA Jianfeng
    Journal of Xidian University    2024, 51 (4): 139-150.   DOI: 10.19665/j.issn1001-2400.20240306
    Abstract143)   HTML7)    PDF(pc) (2352KB)(44)       Save

    A smart contract is an important part of the blockchain,and the Ethereum platform enables decentralized applications by deploying a large number of smart contracts,which is associated with billions of dollars worth of digital currency.However,a smart contract is a piece of code written in a high-level language,which can be vulnerable to attacks and cause huge economic losses.Currently,smart contract vulnerabilities are one of the serious threats to Ethereum.Traditional smart contract vulnerability detection methods rely heavily on fixed expert rules,resulting in low accuracy and time-consuming.In recent years,some researchers have used machine learning methods for vulnerability detection,but the detection methods they use do not fully utilize the semantic information of smart contract source code.In this paper,the smart contract source code is constructed as a smart contract graph with a data flow and control flow information,and the attention mechanism is utilized to assign different weights to the nodes in the graph according to their criticality to update the graph node features for contract vulnerability detection.In the paper,experiments are conducted on reentrant vulnerabilities and timestamp vulnerabilities.Experimental results show that compared with the traditional graph neural network detection model,the model in the paper improves the accuracy in the two vulnerability detections by 11.18% and 10.06%,respectively.The experiments demonstrate that smart contract vulnerabilities are not only related to the structural features of the contract code,but also closely related to different functions and data variables.

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    Multi-objective optimization offloading decision with cloud-side-end collaboration in smart transportation scenarios
    ZHU Sifeng, SONG Zhaowei, CHEN Hao, ZHU Hai, QIAO Rui
    Journal of Xidian University    2024, 51 (3): 63-75.   DOI: 10.19665/j.issn1001-2400.20230802
    Abstract141)   HTML11)    PDF(pc) (3027KB)(55)       Save

    With the rapid development of intelligent transportation,the cloud computing network and the edge computing network,the information interaction among vehicle terminal,road base unit and central cloud server becomes more and more frequent.In view of how to efficiently realize vehicle-road-cloud integration fusion sensing,group decision making and reasonable allocation of re-sources between each server and the servers under the cloud-edge-terminal collaborative computing scenario of intelligent transportation,a network architecture based on the comprehensive convergence of the cloud-edge-terminal and intelligent transportation is designed.A network architecture based on the comprehensive integration of cloud-side-end and intelligent transportation is designed.Under this architecture,by reasonably dividing the task types,each server selectively caches and offloads them;under the collaborative computing scenario of the cloud-side-end of intelligent transportation,an adaptive caching model for tasks,a task offloading delay model,a system energy loss model,a model for evaluating the dissatisfaction of in-vehicle users with the quality of service,and a model for the multi-objective optimization problem are designed in turn,and a multi-objective optimization task offloading decision-making scheme is given based on the improved non-dominated genetic algorithms.Experimental results show that the proposed scheme can effectively reduce the delay and energy consumption brought by the task offloading process,improve the utilization rate of system resources,and bring better service experience to the vehicle user.

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    Hyperspectral image denoising based on superpixel segmentation and band segmentation
    LI Huajun, JIANG Junzheng, ZHOU Fang, QUAN Yinghui
    Journal of Xidian University    2024, 51 (5): 122-135.   DOI: 10.19665/j.issn1001-2400.20240502
    Abstract140)   HTML3)    PDF(pc) (5826KB)(50)       Save

    Existing hyperspectral image denoising algorithms adopt a band-by-band or full-band approach to denoising,which fails to make full use of the similarity of hyperspectral image bands.To address this problem,this paper proposes a hyperspectral image denoising algorithm based on superpixel segmentation and band segmentation.In this paper,we construct a two-layer graph,including the upper and lower layer graphs.First,superpixel segmentation is applied to the hyperspectral image to obtain a series of superpixels.In order to utilize the spatial information on the hyperspectral image and retain the boundary information,the pixels within the superpixels are modeled as nodes with the pixels connected with edges to construct a series of lower layer graphs.In order to utilize the band similarity of the hyperspectral image,superpixel volumes are formed by segmenting along the band dimension based on the superpixel segmentation results with the superpixel volumes modeled as nodes,and the superpixel volumes connected with edges to construct an upper layer graph.Based on the graph structure and graph segmentation,the hyperspectral image denoising problem is reduced to a series of optimization problems,in which the graph Laplacian regularization is redefined using the Kronecker graph product.Finally,experimental results show that the proposed algorithm has a higher mean signal-to-noise ratio,mean structural similarity index measure and erreur relative globale adimensionnelle de synthese compared with the existing algorithms.

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    Beacon-aided CPD indoor positioning method for the BeiDou pseudo-satellite
    ZHANG Heng, YU Baoguo, PAN Shuguo
    Journal of Xidian University    2024, 51 (2): 107-115.   DOI: 10.19665/j.issn1001-2400.20230409
    Abstract139)   HTML2)    PDF(pc) (3360KB)(55)       Save

    In order to solve the problem of high-precision positioning of the BeiDou pseudo-satellite signal in indoor small-scale space,how to save the cost of network construction on the basis of small-scale space to improve the timeliness and positioning accuracy of indoor positioning technology is an important link in the future.In this paper,a method of BeiDou pseudo-satellite carrier phase difference(CPD) localization assisted by indoor node beacons is proposed,which fully combines the characteristics of small-scale space in indoor environment.First,the problem of large-scale fingerprint construction is transformed into a fingerprint beacon,and the concept of indoor node beacon is proposed.The connection between small-scale space and surrounding space is realized by beacon nodes,and the construction and processing of the beacon characteristic spectrum based on the carrier-to-noise ratio(CN0) and carrier phase are analyzed.Then,based on the indoor node beacon,the process of position estimation based on CPD is presented.Finally,a location search algorithm considering the constraints of pedestrian location and velocity space is proposed based on particle swarm optimization(PSO).Experimental results in real environment show that the dynamic positioning accuracy of 30cm and the positioning accuracy of 25cm in a suspended state can be achieved by the indoor node beacon.Compared with inertial navigation,it has a more relaxed attitude condition and is suitable for high-precision positioning processing in small-scale space.The proposed algorithm has a better applicability in small-scale space.

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    Novel artificial noise generation and suppression method for unmanned aerial vehicle networking
    LIN Lang, ZHAO Hongzhi, SHAO Shihai, TANG Youxi
    Journal of Xidian University    2024, 51 (5): 35-45.   DOI: 10.19665/j.issn1001-2400.20240803
    Abstract138)   HTML7)    PDF(pc) (2121KB)(62)       Save

    Wireless communication faces the risk of eavesdropping due to the natural characteristics of the broadcast channel.Aiming at the physical layer security of the unmanned aerial vehicle(UAV) networks,and considering that UAV platforms are limited in signal processing capability due to their limited size and power consumption,a novel artificial noise(AN) generation and suppression method adapted to UAV platforms is proposed.The transmitter takes the desired signal as a reference,and uses the phase information of the symbols in the past signal segments to construct the multiplicative artificial noise of the current signal segment.And the past signal segments are superimposed with different weights to construct the additive artificial noise of the current signal segment.The artificial noise is suppressed at the authorized receiver by phase compensation and differential operation.The two artificial noises can be designed either jointly or independently,and the appropriate AN waveforms are selected according to channel environments.Theoretical analysis and simulation show that the method has a low algorithm complexity,and that it can effectively deteriorate the signal-to-noise ratio of the eavesdropping channel,improve the security capacity of the system,and enhance the physical layer security.This method can also be applied to other large-scale networking systems whose nodes are limited in signal processing capacity and provide a means of secure transmission at the physical layer.

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    Electromagnetic modeling of general waveports with the method of moments
    DING Ning, HOU Peng, ZHAO Xunwang, LIN Zhongchao, ZHANG Yu
    Journal of Xidian University    2024, 51 (3): 38-45.   DOI: 10.19665/j.issn1001-2400.20230908
    Abstract137)   HTML17)    PDF(pc) (2095KB)(67)       Save

    For the problems of electromagnetic modeling of waveports with irregular cross-sections by the integral equation method,a general waveport modeling method based on the higher-order method of moments is proposed.We establish the waveport surface integral equations based on the equivalence principle and the mode matching(MM) method.Additionally,we utilize the two-dimensional finite element method(2-D FEM) to accurately analyze the modes of irregular waveports,thereby extending the modeling capability of the MoM from the regular waveport model to a general waveport model suitable for both regular and irregular waveports modeling,on the basis of which the adoption of the higher-order basis functions defined on quadrilateral elements instead of lower-order basis functions reduces the unknown of the MoM,thus significantly reducing the memory requirements and computation time.The proposed method is tested through numerical examples,and the comparison of the tested results with the numerical results of the FEM verifies the correctness of the proposed method,and the comparison with RWG-MoM verifies the efficiency.Numerical results show that the proposed method has the advantages of high efficiency and high numerical accuracy for the general waveport modeling.

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    Study of the parallel MoM on a domestic heterogeneous DCU platform
    JIA Ruipeng, LIN Zhongchao, ZUO Sheng, ZHANG Yu, YANG Meihong
    Journal of Xidian University    2024, 51 (2): 76-83.   DOI: 10.19665/j.issn1001-2400.20230504
    Abstract135)   HTML4)    PDF(pc) (2873KB)(60)       Save

    In view of the current development trend of the domestic supercomputer CPU+DCU heterogeneous architecture,the research on the CPU+DCU massively heterogeneous parallel higher-order method of moments is carried out.First,the basic implementation strategy of DCU to accelerate the calculation of the method of moments is given.Based on the load balancing parallel strategy of the isomorphic parallel moment of methods,an efficient heterogeneous parallel programming framework of "MPI+openMP+DCU" is proposed to address the problem of mismatch between computing tasks and computing power.In addition,the fine-grained task division strategy and asynchronous communication technology are adopted to optimize the design of the pipeline for the DCU computation process,thus realizing the overlapping of computation and communication and improving the acceleration performance of the program.The accuracy of the CPU+DCU heterogeneous parallel moment of methods is verified by comparing the simulation results with those by the finite element method.The scalability analytical results based on the domestic DCU heterogeneous platform show that the implemented CPU+DCU heterogeneous co-computing program can obtain 5.5~7.0 times acceleration effect at different parallel scales,and that the parallel efficiency reaches 73.5% when scaled from 360 nodes to 3600 nodes(1,036,800 cores in total).

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    EVD clutter suppression method based on the self-organizing neural network
    SHI Jiaqi, YANG Minglei, LIAN Hao, YE Zhou, XU Guanghui
    Journal of Xidian University    2024, 51 (5): 46-57.   DOI: 10.19665/j.issn1001-2400.20240602
    Abstract135)   HTML16)    PDF(pc) (5420KB)(70)       Save

    The subspace decomposition method is a common method for clutter suppression of slow moving targets in strong clutter environment.But the traditional subspace decomposition method has a poor adaptability.The SVD clutter suppression algorithm based on K-means clustering makes up for the above defects,but when the slow-moving target is close to the clutter Doppler or aliasing,the feature set discrimination decreases and the clustering results are unstable.Therefore,an eigenvalue-decomposition(EVD) clutter suppression algorithm based on self-organizing neural networks is proposed,with the differences between targets,clutter and noise analyzed deeply,and the features with high differentiation between slow-moving targets and clutter extracted to construct the feature set.Then,the self-organizing neural network,which is less affected by the initial value and has stable clustering results,is used for clustering,adaptive selection of clutter basis to construct clutter subspace.Finally,the clutter is suppressed by orthotropic subspace projection.Simulation and measured data are used to verify the performance of the algorithm.By combining with the target tracking algorithm,it is further verified that the algorithm has strong robustness and engineering practicability.

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    Application of the high-order S21 fitting strategy in coupling-matrix-extraction methods
    XIE Hanyu, WU Bian, YANG Yimin, ZHAO Yutong, CHENG Yingxin, CHEN Jianzhong, SU Tao
    Journal of Xidian University    2024, 51 (4): 15-28.   DOI: 10.19665/j.issn1001-2400.20240204
    Abstract135)   HTML11)    PDF(pc) (3782KB)(57)       Save

    Fitting the measured or simulated sampled data by a rational function model is an important step in a filter coupling-matrix-extraction method.A high-order transmission coefficient(S21) fitting strategy is proposed to address the problem of the deviation between the fitted and sampled data near the transmission zeros with small amplitudes.This strategy achieves a high fitting accuracy by fitting the sampled transmission coefficient with a rational function with a numerator polynomial of Nth-order(N being the order of filter) to accurately locate the transmission zeros.Then,the numerator polynomial of the transmission coefficient is reconstructed by selecting the Nz(Nz being the number of transmission zeros of the real filter) desired transmission zeros among the N fitted transmission zeros to guarantee that the number of transmission zeros of the extracted coupling matrix is the same as that of the real filter.For verification,a ninth-order coaxial filter with three transmission zeros is used as an example to validate the conventional Cauchy method,the Cauchy method that applies the higher-order transmission coefficient fitting strategy,and the model-based vector fitting method(MVF).The results show that this strategy can improve the fitting accuracy near the transmission zeros.Since the robustness of the Cauchy method is not high enough,a coupling-matrix-extraction method by identifying the zeros of S-parameters using vector fitting is proposed in this paper by consisting the operation steps of the Cauchy method and MVF,this method can fit the zero of S-parameters more accurately than MVF and has a less influence by noise than the Cauchy method.

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    Knowledge graph assisted spectrum resource optimization algorithm for UAVs
    WANG Yulai, LIAO Xiaomin, HE Haiguang, YE Guojun
    Journal of Xidian University    2024, 51 (5): 58-70.   DOI: 10.19665/j.issn1001-2400.20240505
    Abstract131)   HTML7)    PDF(pc) (1793KB)(68)       Save

    In response to the scarcity of available spectrum resources in UAV swarms and the difficulties in solving multi-objective optimization problems,as well as the challenges of obtaining complete channel information and poor real-time performance during the resource optimization process,a knowledge graph-assisted spectrum resource optimization algorithm for UAV swarms is proposed.Firstly,a relation-aware graph multi-head attention network(RGMAN) encoder is constructed to aggregate communication parameters,performance parameters,and electromagnetic environment information of the UAV swarm,and allocate different weights to neighbor information based on the importance of the nodes.Then,an improved layer-attention-based InteractE(SE-IE) model is developed to predict the channel access and transmit power for the UAVs,which utilizes a squeeze-and-excitation module to obtain layer attention information and extracts deep-level interactive information from the results of circular convolutions.The simulation results indicate that the proposed algorithm exhibits rapid convergence capability,excellent performance in link prediction,and notable stability and robustness on public datasets.Additionally,on the dataset for UAV swarm spectrum management,the proposed algorithm can generate an approximately optimal spectrum resource optimization scheme for UAV swarms,in the premise of channel distribution information and partial environmental information.

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    Secure K-prototype clustering against the collusion of rational adversaries
    TIAN Youliang, ZHAO Min, BI Renwan, XIONG Jinbo
    Journal of Xidian University    2024, 51 (2): 196-210.   DOI: 10.19665/j.issn1001-2400.20230305
    Abstract129)   HTML4)    PDF(pc) (1874KB)(61)       Save

    Aiming at the problem of data privacy leakage in cloud environment and collusion between cloud servers in the process of clustering,an cooperative secure K-prototype clustering scheme(CSKC) against the adversaries of rational collusion is proposed.First,considering that homomorphic encryption does not directly support nonlinear computing,secure computing protocols are designed based on homomorphic encryption and additive secret sharing to ensure that the input data and intermediate results are in the form of additive secret share,and to achieve accurate calculation of the security comparison function.Second,according to the game equilibrium theory,a variety of efficient incentive mechanisms are designed,and the mutual condition contract and report contract are constructed to constrain cloud servers to implement secure computing protocols honestly and non-collusively.Finally,the proposed protocols and contracts are analyzed theoretically,and the performance of the CSKC scheme is verified by experiment.Experimental results show that compared with the model accuracy in plaintext environment,the model accuracy loss of the CSKC scheme is controlled within 0.22%.

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    A self-attention sequential model for long-term prediction of video streams
    GE Yunfeng, LI Hongyan, SHI Keyi
    Journal of Xidian University    2024, 51 (3): 88-102.   DOI: 10.19665/j.issn1001-2400.20240202
    Abstract128)   HTML17)    PDF(pc) (3703KB)(38)       Save

    Video traffic prediction is a key technology to achieve accurate transmission bandwidth allocation and improve the quality of the Internet service.However,the inherent high rate variability,long-term dependence and short-term dependence of video traffic make it difficult to make a quick,accurate and long-term prediction:because existing models for predicting sequence dependencies have a high complexity and prediction models fail quickly.Aiming at the problem of long-term prediction of video streams,a sequential self-attention model with frame structure feature embedding is proposed.The sequential self-attention model has a strong modeling ability for the nonlinear relationship of discrete data.Based on the difference of correlation between video frames,this paper applies the time series self-attention model to the long-term prediction of video traffic for the first time.The existing time series self-attention model cannot effectively represent the category features of video frames.By introducing an embedding layer based on the frame structure,the frame structure information is effectively embedded into the time series to improve the accuracy of the model.The results show that,compared with the existing long short-term memory network model and convolutional neural network model,the proposed sequential self-attention model based on frame structure feature embedding has a fast inference speed,and that the prediction accuracy is reduced by at least 32% in the mean absolute error.

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    Task scheduling method for minimizing completion time in edge collaborative environment
    ZHANG Chao, ZHAO Hui, ZHANG Zhifeng, WANG Jing, WAN Bo, WANG Quan
    Journal of Xidian University    2024, 51 (4): 114-127.   DOI: 10.19665/j.issn1001-2400.20240308
    Abstract127)   HTML6)    PDF(pc) (1349KB)(31)       Save

    The uneven geographical distribution of users may lead to unbalanced load on edge servers,which makes it difficult to provide satisfactory service quality for users.In addition,the available resources of the edge server are limited,and some large tasks may be difficult to offload to the edge server.To solve the above problems,this paper proposes a task scheduling method to minimize the completion time in the edge collaboration environment by utilizing the collaboration among multiple edge servers and combining the task partial offloading technology.First,by combining the edge of horizontal collaboration and task partial offloading technology and considering the position relationship between users and edge servers in multi-user multi-edge server scenario,a task partial offloading and scheduling model is established to minimize the task completion time.Second,a task scheduling algorithm based on the Improved Group Teaching Optimization Algorithm(IGTOA) is proposed to jointly optimize the edge server computing resource allocation,user-edge server association decision,task offloading ratio and execution location decision.With minimizing the task completion time as the goal,efficient task scheduling is achieved under edge computing environment.Finally,the proposed task scheduling algorithm is compared with DTOSO,HJTORA and ACS algorithms under multiple indexes.Experimental results show that the proposed method can effectively reduce the task completion time.

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    K-anonymity privacy-preserving data sharing for a dynamic game scheme
    CAO Laicheng, HOU Yangning, FENG Tao, GUO Xian
    Journal of Xidian University    2024, 51 (4): 170-179.   DOI: 10.19665/j.issn1001-2400.20240201
    Abstract127)   HTML3)    PDF(pc) (1512KB)(24)       Save

    Aiming for fact that the deep trained learning model has some problems,such as lack of a large amount of labeled training data and data privacy leakage,a k-anonymity privacy-preserving data sharing for the dynamic game(KPDSDG) scheme is proposed.First,by using the dynamic game strategy,the optimal data k-anonymization scheme is designed,which achieves secure data sharing while protecting data privacy.Second,a data anonymization evaluation framework is proposed to evaluate data anonymization schemes based on the availability,privacy,and information loss of anonymous data,which can further improve the privacy and availability of data and reduce the risk of reidentification.Finally,owing to adopting the conditional generative adversarial network to generate data,the problem that model training lacks a large amount of labeled training samples is solved.The security analysis shows that the entire sharing process can ensure that the privacy information of the data owner is not leaked.Meanwhile,experiment shows that the accuracy of the model trained on the data generated after privacy in this scheme is higher than that of other schemes,with the optimal situation being 8.83% higher,that the accuracy of the proposed solution in this paper is basically consistent with the accuracy of the model trained based on raw data,with a difference of only 0.34% in the optimal situation and that the scheme has a lower computing cost.Therefore,the scheme satisfies data anonymity,data augmentation,and data security sharing simultaneously.

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    Optimization of light sources for the IRS-assisted indoor VLC system considering HPSA
    HE Huimeng, YANG Ting, SHI Huili, WANG Ping, BING Zhe, WANG Xing, BAI Bo
    Journal of Xidian University    2024, 51 (2): 46-55.   DOI: 10.19665/j.issn1001-2400.20240103
    Abstract126)   HTML11)    PDF(pc) (2522KB)(65)       Save

    Aiming at the problem of unevenness of optical power distribution on the receiving plane in a visible light communication(VLC) system,a light source optimization method for an intelligent reflecting surface(IRS)-assisted indoor VLC system based on the hybrid particle swarm algorithm(HPSA) is proposed.Taking the two layout schemes of rectangular and hybrid arrangements with 16 light-emitting diodes(LEDs) as examples,the variance of received optical power on the receiving plane is set as the fitness function,and the proposed HPSA is combined with the IRS technology to optimize the half-power angle and positional layout of LEDs as well as the yaw and roll angles of IRS.Subsequently,initial(unoptimized) optimization using the HPSA,and optimization using the HPSA for the IRS-aided VLC systems are simulated and compared.The results indicate that when considering the first reflection link,compared to the original VLC system,the fluctuations of received optical power and signal-to-noise ratio of the VLC system optimized with the HPSA significantly decrease for both light source layouts;the HPSA optimized IRS-aided indoor VLC system improves the received optical power fluctuations in the rectangular layout as well as the HPSA optimized VLC system,and its performance is significantly better than that of the HPSA optimized VLC system only in the hybrid layout for optical power fluctuations improvement.Among the three VLC systems,the IRS-aided VLC system based on HPSA optimization has the largest average received optical power.Besides,the average root mean square delay spread performance of the above three VLC systems using a hybrid layout is better than that of a rectangular layout.This work will benefit the study of light source distribution in indoor VLC systems.

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    Integration of pattern search into the grasshopper optimization algorithm and its applications
    XIAO Yixin, LIU Sanyang
    Journal of Xidian University    2024, 51 (2): 137-156.   DOI: 10.19665/j.issn1001-2400.20230602
    Abstract125)   HTML2)    PDF(pc) (2873KB)(61)       Save

    In the process of applying intelligent optimization algorithms to solve complex optimization problems,balancing exploration and exploitation is of great significance in order to obtain optimal solutions.Therefore,this paper proposes a grasshopper optimization algorithm that integrates pattern search to address the limitations of traditional grasshopper optimization algorithm,such as low convergence accuracy,weak search capability,and susceptibility to local optima in handling complex optimization problems.First,a Sine chaotic mapping is introduced to initialize the positions of individual grasshopper population,reducing the probability of individual overlap and enhancing the diversity of the population in the early iterations.Second,the pattern search method is employed to perform local search for the currently found optimal targets in the population,thereby improving the convergence speed and optimization accuracy of the algorithm.Additionally,to avoid falling into local optima in the later stages of the algorithm,a reverse learning strategy based on the imaging of convex lenses is introduced.In the experimental section,a series of ablative experiments is conducted on the improved grasshopper algorithm to validate the independent effectiveness of each strategy,including the Sine chaotic mapping,pattern search,and reverse learning.Simulation experiments are performed on two sets of test functions,with the results analyzed using the Wilcoxon rank-sum test and Friedman test.Experimental results consistently demonstrate that the fusion mode search strategy improved grasshopper algorithm exhibits significant enhancements in both convergence speed and optimization accuracy.Furthermore,the application of the improved algorithm to mobile robot path planning further validates its effectiveness.

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    Research on the construction and application of polar codes for shallow water acoustic communication
    XING Lijuan, LI Zhuo, HUANG Yanbiao
    Journal of Xidian University    2024, 51 (2): 116-125.   DOI: 10.19665/j.issn1001-2400.20230505
    Abstract124)   HTML6)    PDF(pc) (2313KB)(55)       Save

    To realize high speed and high-reliability communication in shallow water environments,the performance of polar code encoding and decoding technology in shallow water acoustic communication is studied.The Monte Carlo algorithm construction is used to complete the construction of polar codes on the time-invariant,quasi-stationary,and time-variant channel models established based on the ray acoustic theory,and the complexity and performance are compared with those of the channel polarization and channel degradation construction algorithms and the base-symmetric extended polarization weight construction algorithm.The constructed polar code is adopted as the channel coding scheme for the underwater acoustic communication system based on Orthogonal Frequency Division Multiplexing and the decoding scheme uses a Cyclic Redundancy Check-Aided Successive Cancellation List decoding algorithm.The performance of polar codes on these three channels is determined by simulation in comparison with the performance of Low-Density Parity Check codes with the same code length and code rate.Experimental results show that in these three channels and the range of the signal-to-noise ratio of interest,polar codes have a gain of about 0.5 dB ~ 1.2 dB relative to Low-Density Parity Check codes.Simulation comparison results of the three channels show that polar codes based on channel construction coding have better gain effects in harsh channel environments compared to Low-Density Parity Check codes,and that polar codes have a lower encoding and decoding complexity,which proves the competitiveness and broad application prospect of the polar code in energy and resource-limited shallow sea acoustic communication.

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    Retinal image quality grading for fused attention spectrum non-local blocks
    LIANG Liming, DONG Xin, LEI Kun, XIA Yuchen, WU Jian
    Journal of Xidian University    2024, 51 (4): 102-113.   DOI: 10.19665/j.issn1001-2400.20231101
    Abstract124)   HTML2)    PDF(pc) (4323KB)(34)       Save

    Retinal image quality assessment(RIQA) is one of the key components of screening for diabetic retinopathy.Aiming at the problems of large differences in retinal image quality and insufficient generalization ability of quality evaluation models,a multi-feature algorithm that combines non-local blocks of the attention spectrum is proposed to predict and rank RIQA.First,the ResNet50 network of fused spectral non-local blocks is used to extract the features of the input images;Second,efficient channel attention is introduced to improve the model's ability to express data and effectively capture the characteristic information relationship between channels;Then,the feature iterative attention fusion module is used to fuse the local feature information.Finally,the combined focus loss and regular loss further improve the effect of quality classification.On the Eye-Quality dataset,the accuracy rate is 88.59%,the precision is 87.56%,the sensitivity and F1 value are 86.10% and 86.74%,respectively.The accuracy and F1 values on the RIQA-RFMiD dataset are 84.22% and 67.17%,respectively,and simulation experiments show that the proposed algorithm has a good generalization ability for retinal image quality assessment tasks.

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    Joint feature approach for image-text cross-modal retrieval
    GAO Dihui, SHENG Lijie, XU Xiaodong, MIAO Qiguang
    Journal of Xidian University    2024, 51 (4): 128-138.   DOI: 10.19665/j.issn1001-2400.20240302
    Abstract123)   HTML6)    PDF(pc) (1931KB)(26)       Save

    With the rapid development of deep learning,cross-modal retrieval performance has been significantly improved.However,existing methods only match the image text as a whole or only use local information for matching,there are limitations in the use of graphic and textual information,and the retrieval performance needs to be further improved.In order to fully exploit the potential semantic relationship between images and texts,this paper proposes a cross-modal retrieval model based on joint features.In the feature extraction part,two sub-networks are used to deal with the local features and global features of images and texts respectively,and a bilinear layer structure based on the attention mechanism is designed to filter redundant information.In the loss function part,the triplet ranking loss and semantic label classification loss are used to realize feature joint optimization.And the proposed model has a wide range of generality,which can effectively improve the performance of the model only based on local information.A series of experimental results on the public datasets Flickr30k and MS COCO show that the proposed model effectively improves the performance of cross-modal image-text retrieval tasks.In the Flickr30k dataset retrieval task,the proposed model improves 5.1% on the R@1 metric for text retrieval and 2.8% on the R@1 metric for image retrieval.

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    Spatial-temporal graph convolutional networks foranomaly detection in multivariate time series
    WANG Jing, HE Miaomiao, DING Jianli, LI Yonghua
    Journal of Xidian University    2024, 51 (3): 170-181.   DOI: 10.19665/j.issn1001-2400.20230804
    Abstract122)   HTML10)    PDF(pc) (1548KB)(108)       Save

    To address the problem that the existing multivariate time series anomaly detection models have an insufficient ability to capture local and global spatial-temporal dependencies,a multivariate time series anomaly detection model based on spatial-temporal graph convolutional networks is proposed.First,in the temporal dimension,the short-term and long-term temporal dependencies in time series data are captured by using dilated causal convolution and multi-headed self-attention mechanisms,respectively.And the channel attention is introduced to learn the importance weights of different channels.Second,in the spatial dimension,a graph adjacency matrix is constructed by the static graph learning layer according to the node embedding,which is used to model the global spatial dependencies.Meanwhile,a series of evolutionary graph adjacency matrices is constructed by using the dynamic graph learning layer,so as to capture the local dynamic spatial dependencies.Finally,the reconstruction model and the prediction model are jointly optimized,and the anomaly score is calculated by the reconstructed error and the prediction error.Then,the relationship between the threshold and the anomaly score is compared to detect the anomaly.Experimental results on three public datasets,MSL,SMAP,and SwaT,show that the model outperforms the relevant baseline models such as OmniAnomaly,MTAD-GAT,and GDN in terms of the anomaly detection performance metric F1 score.

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    Trajectory optimization method for the OFDM-UAV relay broadcast communication system
    LI Dongxia, MENG Yan, HUANG Gengming, LIU Haitao
    Journal of Xidian University    2024, 51 (4): 91-101.   DOI: 10.19665/j.issn1001-2400.20240305
    Abstract121)   HTML5)    PDF(pc) (1102KB)(30)       Save

    To improve the performance of the unmanned aerial vehicle (UAV) relay broadcast communication system,taking into consideration the entire communication links from the base station to the UAV and from the UAV to the users,the orthogonal frequency division multiplexing (OFDM) based trajectory optimization method is proposed for the UAV relay broadcast communication system with frequency selective fading channels.First,the OFDM-based UAV relay broadcast communication model is provided.Then,approximate calculation formula for the interruption probability for a single-user node and that for the system average interruption probability are theoretically derived.Furthermore,two trajectory methods for the relay UAV are proposed based on the optimization criteria of minimizing the average interruption probability and minimizing the maximum user interruption probability.The effectiveness and correctness of the proposed optimization method are demonstrated by computer simulations,which indicates that the OFDM-based UAV relay broadcasting communication system can effectively overcome frequency-selective fading,and achieve better connectivity under the decode-and-forward transmission mode than the amplify-and-forward mode in multipath channels.The interruption performance of the system,derived based on the criterion of minimizing average interruption probability,surpasses that obtained by minimizing the maximum user interruption probability criterion.

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