Table of Content

30 November 2019, Volume 37 Issue 6

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Signal and Information Processing

Power System Low Frequency Oscillation Mode Identification Based on Improved EMD Denoising and Matrix Pencil Algorithm

SHEN Zhongting, DING Renjie

2019, 37(6):  761-774.  doi:10.3969/j.issn.0255-8297.2019.06.001

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The paper proposes a mode identification method for low frequency oscillations in power system. First, an improved empirical mode decomposition (EMD) denoising algorithm is employed for signal preprocessing. The algorithm superimposes a cosine wave onto the signal and conducts a second decomposition after implementing the interval thresholding. It overcomes the shortcomings of serious aliasing noise and long computing time, which exist in the conventional algorithms, and separates the signal and noise in a fast and effective manner. After signal denoising, the matrix pencil (MP) algorithm is used to extract mode parameters. Introducing relative difference of singular values can solve the key problem of order determination in MP algorithm, thus leading to an accurate estimation for model order. Lastly, numerical signals, system simulation signals and tested power grid signals are analyzed. Simulation results show that the proposed method achieves excellent performance in anti-noise ability, parameter accuracy and computing speed.

Altered Fingerprint Detection Based on Orientation Field

YANG Gaoqiang, LI Sheng, ZHANG Xinpeng

2019, 37(6):  775-782.  doi:10.3969/j.issn.0255-8297.2019.06.002

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Automatic fingerprint identification system (AFIS) has been widely used in visas, customs, criminal investigations. In order to avoid AFIS-based identification, some criminals change the ridge structure of their fingerprints by cutting, transplanting, burning, etc. The resulting fingerprints are called altered fingerprint. At present, AFIS can't effectively detect altered fingerprints. In this paper, an altered fingerprint detection method based on orientation field discontinuity and orientation field difference map discontinuity is proposed, and an operator for extracting this discontinuity is proposed. Firstly, the orientation field of fingerprint and its difference map are calculated, and the difference map is enhanced. Then, the proposed operator extracts the discontinuous features from the orientation field and the enhanced difference map. Finally, based on the discontinuous features, altered fingerprints and real fingerprints are classified using support vector machines (SVM). In addition, this paper also builds an altered fingerprint database, and tests the performance of the method on this library. The results show that the proposed scheme can detect the altered fingerprint effectively.

Dodging Method Based on Camera Response Functions for UAV Image

ZHANG Chunsen, ZHANG Hui, GUO Bingxuan, DU Shenbin, ZHANG Yueying

2019, 37(6):  783-794.  doi:10.3969/j.issn.0255-8297.2019.06.003

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Aiming at the imbalance of brightness and color in unmanned aerial vehicle (UAV) images captured over a large area, this paper proposes a method of uniforming light and color based on camera response functions. First, referred to two images taking by digital cameras in the same static scene, a multi-parameter image brightness error function is constructed. Then by using the Levenberg-Marquardt algorithm to estimate the optimal parameters and applying the estimated parameters into DOM processing, the uniforming of light and color of DOMs will be achieved. Experiments show that compared with the adaptive template method and the Waillis-filter method, the proposed method can ensure the uniformity of brightness and color in the image mosaic process with high efficiency and quality.

A Calibration Method Based on Defocused Image for Stereo Vision Sensor with Large FOV

YU Shuzhen, OU Qiaofeng, XIONG Bangshu, CHEN Yaofeng

2019, 37(6):  795-805.  doi:10.3969/j.issn.0255-8297.2019.06.004

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A calibration method based on defocused image is proposed for stereo vision sensor with large field of view (FOV) to simplify operation process and gain accurate and steady camera calibration. First, a defocusing position is selected between the stereo vision system and the measurement position. The intrinsic parameters of cameras are obtained by using the template images at the defocusing position. Second, the external parameters of the stereo vision are obtained by using the template images at the measurement position. Finally, a laboratory calibration experiment and an experiment of measuring the helicopter blade motion parameters are conducted to verify the proposed method. Experimental results show that the method features in simple operation, high accuracy and reliability. In a field of 4.6 mm×2.3 mm, the mean error and the RMS error of a 505.00 mm distance between two feature points on the target are 0.647 mm and 0.780 mm respectively. Therefore this method can meet the requirements of onsite calibration with high-precision for the measurement of helicopter blade motion parameters.

Multiple-center Points Incremental Fuzzy Clustering Algorithm

HU Bengu, DAI Muhong

2019, 37(6):  806-814.  doi:10.3969/j.issn.0255-8297.2019.06.005

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Incremental clustering algorithm has the ability to solve the problem that large data volume cannot be read into memory at one time. The traditional incremental multiple medoids based fuzzy clustering (IMMFC) algorithm selects only one or a fixed number of center points for each data block, thus leading to a poor clustering performance when the object weights in the cluster are small. A new incremental fuzzy clustering algorithm is proposed for processing large data sets. Firstly, the algorithm divides the large data set into multiple small data blocks and performs fuzzy clustering on each small data block. Then, the target center point is selected from each cluster of each small data block. The number of center points is the minimum number of objects whose sum of weights of objects in the cluster is greater than a threshold. Finally, all selected center points are merged, and the final data block is fuzzy clustered to obtain the final center point. Experimental results show that the algorithm works superior to IMMFC algorithm in the case that the data block accounts for more than 10% of the total data.

Hybrid Moving Object Localization with EKF Based on Measurement Techniques of UWB and ZigBee

WANG Yan, CHANG Xiaopeng, ZHANG Jianping

2019, 37(6):  815-824.  doi:10.3969/j.issn.0255-8297.2019.06.006

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In wireless sensor networks, either single tracking algorithm or single measurement technique cannot obtain high positioning accuracy for moving target tracking. To solve the problem, a hybrid localization technology composed of a tracking algorithm and different measuring techniques is proposed. The tracking algorithm based on the principle of extended Kalman filter is analyzed. By combining the distance values measured by ultra band width (UWB) technology and the receiving signal strength measured by ZigBee measuring technology, and applying them into the tracking algorithm based on extended Kalman filter, we achieve an approach of hybrid position tracking for moving objects in indoor environments. Experiment for indoor moving objects shows that the proposed position-tracking approach performs high localization accuracy.

Satellite Time Autonomous Integrity Monitoring Technology Based on Inter-satellite Link

CHEN Tingting, LIN Baojun, GONG Wenbin, FENG Lei, CHANG Jiachao, LIN Xia

2019, 37(6):  825-834.  doi:10.3969/j.issn.0255-8297.2019.06.007

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In view of the fact that the Beidou satellite system is difficult to deploy globally, this paper proposes an autonomous integrity detection method using Kalman filter based on satellite time. A model of atomic clock and time-frequency system is established to analyze errors in inter-satellite measurement data using real in-orbit data of Beidou. Time information is calculated from the distance measurement value of inter-satellite link, and relative clock difference is obtained through the ergodic regression calculation, Kalman filter monitoring algorithm is designed to monitor phase hopping and frequency hopping. Through simulation, monitoring performance of Kalman filter for the phase jump and frequency jump of Beidou satellite in the real inter-orbit link ranging value is analyzed. And according to the range of the abnormal jump, a suitable detection threshold is put forward for engineering practice.

Trajectory Privacy Protection Method Using LSTM Network

YAN Shaojun, WANG Zichi, ZHANG Xinpeng

2019, 37(6):  835-843.  doi:10.3969/j.issn.0255-8297.2019.06.008

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With the popularity of the mobile Internet, location query has become an important way for users to enjoy services. However, in the location query, the server can obtain the user location and trajectory information, which threaten the user's privacy. In order to improve the privacy of user trajectory, this paper proposes a method to protect user trajectory privacy by using improved long short-term memory (LSTM) networks. First, the trusted third party uses the improved LSTM network to predict the later position of the user. While constructing the anonymous area, the third party places the predicted location point information into the current moment to make a request. It can disrupt the timing information in the trajectory and obscure the user trajectory sequence on the server side, and therefore protects the privacy of user trajectory. Meanwhile, by placing the future moments into the current moment, the unreasonable problem of the anonymous area in the location privacy protection is overcome. Thus, the effectiveness of the system service is ensured. Experimental results show that the privacy of the user trajectory in this method is better than existing method.

Automatic Orientation Method for Rail Weld Based on Computer Vision

LIU Song, XIONG Bangshu

2019, 37(6):  844-850.  doi:10.3969/j.issn.0255-8297.2019.06.009

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In order to detect the edge misalignment of rail weld in real time, an automatic positioning method for the rail weld based on computer vision is proposed. First, the method of median filtering is used to remove the noise in a weld image. Second, the weld image is enhanced by using the contrast limited adaptive histogram equalization (CLAHE) algorithm and the histogram equalization method. Third, the image is segmented by the double threshold OTSU method to highlight the rail head and the weld region, and the contours of the rail head and the weld region are extracted by using the method of connected-domain. Finally, the weld fitting line is obtained by multiple least squares fitting, and the intersection of the fitted straight line and the top edge line of the rail head are calculated as the positioning point, accordingly, the rail weld is automatic positioned. Through a test of the weld region of 60 kg/m rail, the method performs with high precision and stability, and can be used for measuring the rail weld automatically in real-time on line.

Computer Science and Applications

Research and Implementation of Car Rental Alliance Based on Blockchain and Internet of Vehicles

REN Peng, XU Jingjing, WANG Yi, MA Xiaofeng

2019, 37(6):  851-858.  doi:10.3969/j.issn.0255-8297.2019.06.010

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There are many pain points need to be solved, such as large-scale asset investment, high market entry threshold and poor trading information flow in the traditional car rental industry. To solve the pain points we design a car rental alliance solution based on internet of vehicles technology and blockchain technology. The car rental alliance consists of vehicles renters, vehicle rental service platforms, vehicle providers, vehicle insurance agencies and vehicle maintenance agencies. It can reduce the transaction costs and market entry threshold, increase the flexibility of car shared, and promote personalized innovation in related businesses.

Cost-Efficient Task Scheduling in Geo-distributed Datacenters

YANG Yanan, LI Yiming, NIE Lihai, ZHANG Ning, ZHAO Laiping

2019, 37(6):  859-874.  doi:10.3969/j.issn.0255-8297.2019.06.011

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In this paper, we study the cost minimization for cloud users in geo-distributed cloud systems. By modeling it as a general assignment problem (GAP), we use the augmented Lagrangian multiplier method (ALMM) to obtain the optimal schedule solution. We additionally apply an Adjusting algorithm that adjusts the solution produced by ALMM to make it more feasible. We further use a decreased value density scheduling algorithm (DVDS) to speed up the convergence of ALMM. Experimental results show that DVDS algorithm can work out solutions in a much shorter period than ALMM does with costs similar to ALMM's in the case of small task, and only 10% more in the case of large task.

Control and system

Wireless Temperature Control System for High Temperature Heating Furnace Based on PFC-PID Algorithm

LIU Yangyi, SU Chengli, SHI Huiyuan, LI Ping, BO Guihua

2019, 37(6):  875-886.  doi:10.3969/j.issn.0255-8297.2019.06.012

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Address to the complicacy and difficulty of wiring installation for wired process control in harsh industrial site environment, this paper develops a wireless temperature control system for high temperature heating furnace based on predictive functional control-proportion integration differentiation (PFC-PID). First, a wireless communication network based on WirelessHart protocol is built to replace the traditional wired network. The wireless network uses the monitor and control generated system (MCGS) configuration software as application platform to measure and analyze the industrial high-temperature heating furnace. Then the wireless temperature control system is developed by integrating the improved predictive functional control (PFC) with the traditional proportion integration differentiation (PID), to realize wireless monitoring and real-time control of the temperature of the heating furnace. The results of engineering implementation show that the designed control system can solve the problem of packet loss in the wireless communication process. It works with satisfied reliability, control accuracy and response speed required in industrial sites. The designed system can also solve the problems of low scalability and poor mobility of wired network effectively.