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百年期刊
ISSN 1000-0585
CN 11-1848/P
Started in 1982
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, Volume 55 Issue 8
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ELECTRONIC ENGINEERING
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Jamming detection and erasing method based on the rate-enhanced JTIDS waveform
ZHANG Yu, WU Zhao, SONG Jian
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 821-825.
Abstract
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Joint tactical information distribution system (JTIDS) is a kind of widely used situational awareness data-link. To solve the performance deterioration problem of the rate-enhanced JTIDS in the presence of partial-band barrage jamming, a low complexity method for interference detection and erasure is proposed. First of all, the signal-to-noise ratio (SNR) of each pulse is estimated and the pulse is classified roughly. Then, the average SNR of all the normal pulses in the time slot is estimated. Finally, a fine pulse classification is performed, and each pulse is given an erasure-factor in a certain strategy. Simulation shows that this method greatly eases the effects of the partial-band barrage jamming on the reception performance and significantly reduces the bit error rate. The method is low complexity and easy to implement.
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Joint optimization algorithm combining source and channel coding for multi-stage vector quantization
XU Jingde, CUI Huijuan, TANG Kun
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 826-830.
Abstract
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Source optimized multi-stage vector quantization can have poor quality due to channel errors. This paper presents a joint optimization algorithm combining source and channel coding for multi-stage vector quantization. The joint optimization of the codebook with unequal error protection optimizes each codeword in each iteration using unequal bit error rates to reduce the distortion in the whole system by taking advantage of the connections between each codeword in each stage and the characteristics of unequal error protection. Simulations using linear spectral pairs of low bit speech coding show that the average spectral distortion is reduced 0.1 dB for an 8% bit error rate compared to combined channel optimized multi-stage individual vector quantization and unequal error protection. The average spectral distortion is much less than with using multi-stage codebook joint optimization of equal bit error rates.
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Security of a position-based secret key generation method
LUAN Fengyu, ZHANG Yan, ZHENG Fanfan, XU Xibin, ZHOU Shidong
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 831-837.
Abstract
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With the increasing demand for security, many systems take advantage of channel randomness to generate secret keys. However, when an eavesdropper has good knowledge of the environmental information and the position information of legal users, this method is not absolutely safe. The scattering environmental information cannot be kept secret but the system can still be secure based on the uncertainty of the positions of legal users due to the users movements and the limited observation ability of the eavesdroppers. This study analyzes the security of the position-based secret keys generation method with the security measured by the secret key rates. The calculational errors of the positions of the legal users in different scenarios (LOS, NLOS and different numbers of scattering objects) are analyzed first. Then, the impacts of the distance observation error, the azimuth observation error and the number of observations in each secret key generation period on the secret key rates are analyzed in simulations. The results show that the uncertainty of the positions of legal users can be used to provide security for the secret keys.
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Onboard interconnected parallel Clos-network
LIU Kai, YAN Jian, LU Jianhua
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 838-843.
Abstract
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Onboard switches in harsh space radiation environments can suffer serious reliability degradation. An interconnected parallel Clos (IP-Clos) network was developed to resist crosspoint faults and switch element faults. The IP-Clos consists of multiple Clos-network planes. Adjacent Clos-network planes are connected by inter-plane links to create multiple paths in each stage connecting to the next stage. Theoretical analyses demonstrate that the IP-Clos network has better reliability than parallel Clos networks for both crosspoint faults and switch element faults at the expense of the link overhead between switching elements. Numerical results indicate that the mean time to failure (MTTF) of an IP-Clos network in a geosynchronous orbit (GEO) satellite with space-grade field programmable gate arrays (FPGA) for crosspoint faults is more than 2.1×10
5
d. The MTTF for switch element faults is 6.86×10
3
d.
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Ship detection in SAR images by robust principle component analysis
SONG Shengli, YANG Jian
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 844-848.
Abstract
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Single polarization SAR ship detection using a constant false alarm rate (CFAR) detector does not have a standard clutter model, so the system often gives incomplete targets and misses weak targets in multitarget detection. A ship detection method was developed based on robust principle component analysis (RPCA) to improve the detection. This method leverages the intrinsic properties of SAR images that the sea area is approximately low rank and there are few ships. SAR images can be decomposed into the sum of a low rank component, a noise component and a sparse component via RPCA, with the sum of the first two corresponding to the sea surface and the third corresponding to ships. Thus, ship detection and clutter suppression are achieved in one step without a clutter model or statistics. The augmented Lagrange multiplier method for RPCA is verified by simulations. For comparison, cell averaging CFAR (CA-CFAR) and mean square error CFAR (MSE-CFAR) are also used. Tests with real data show that this method correctly detects ships from sea clutter with robust detection performance.
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Small harbor detection in polarimetric SAR images based on coastline feature point merging
LIU Chun, YIN Junjun, YANG Jian
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 849-853.
Abstract
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A method was developed to automatic detect small harbors in polarimetric synthetic aperture radar (polSAR) images using coastline feature point merging based on analyses of structural characteristics of harbors. The coastline is accurately extracted by level set segmentation algorithm of polSAR with the coastline feature points then detected with a split and merge algorithm for digital curves. Then, the algorithm takes advantage of the characteristic that feature points along small harbor contour are denser than those along other coastline contours using a merging algorithm to detect the small harbors. The detection scheme was tested using polarimetric SAR images acquired by RADARSAT-2 over Singapore and the Zhanjiang area of China. The results show that almost all the harbors along the coastline are correctly detected by this method.
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Spill detection based on polarimetric SAR decomposition models
YANG Fan, YANG Jian, YIN junjun, SONG Jianshe
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 854-859.
Abstract
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Spill detection using polarimetric SAR is proposed by using Bragg scattering energy proportion based on the polarimetric decomposition model. The Bragg scattering energy proportion is small in a spill region but larger in sea clutter or an Oleyl alcohol (OLA) region. Thus, this feature can detect oil spills from sea clutter while excluding false OLA alarms. The feature can be easily extended to HH\VV dual-polarimetric and compact polarimetric configurations which give wider radar coverage. Experiments with multi-look complex C band SAR data show that for all polarimetric modes, the feature gives state-of-art spill detection and false-alarm exclusion of spills.
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Radial velocity estimation based on Radon transforms for SAR images of moving ground targets
WANG Zhirui, ZHANG Xudong, XU Jia
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 860-865.
Abstract
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With synthetic aperture radar (SAR), the radial velocity of a moving ground target may cause Doppler ambiguities and spectrum split, which seriously affect the detection and velocity estimates. A Radon transform (RT) based method was developed to efficiently resolve the Doppler ambiguities and spectrum split to obtain precise estimates of the Doppler centroid and radial velocity. First, the inclination angles of the range walk are determined for all possible ambiguity numbers based on the radar and platform parameters to project the ambiguity number to the inclination angle. Since the radial velocity is unknown, the RT for all prior angles are computed with the ambiguity number obtained by searching for the peak value. A Doppler spectrum detector is used to solve the spectrum split and to accurately estimate the baseband Doppler centroid using the energy balance approach. Numerical simulations demonstrate the effectiveness of this method.
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Anti partial-band noise jamming interleaved hybrid spread spectrum system design and capacity analysis
REN Yinpeng, NI Zuyao, KUANG Linling, WU Sheng, LU Jianhua
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 866-872.
Abstract
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Anti partial-band noise jamming (PBNJ) is improved by an interleaved direct sequence/frequency-hopping (IDS/FH) system based on the traditional direct sequence/frequency-hopping (DS/FH) spread spectrum method. An interleaver crossing multiple hops improves the time-frequency diversity gain. The system capacities with PBNJ are compared to a single-input multiple-output (SIMO) system with additive Gaussian white noise (AWGN) in a fading environment. An optimum IDS/FH receiver is also given. Theoretical analyses indicate that, when the PBNJ occupies 50% of the entire frequency band and the SNR is 10 dB, the IDS/FH capacity is 49% higher than that of DS/FH. Simulations show that the achievable lowest bit error rate of IDS/FH is two orders of magnitude lower than that of DS/FH with 50% PBNJ.
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Character model optimization for segmentation-free Uyghur text line recognition
JIANG Zhiwei, DING Xiaoqing, PENG Liangrui
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 873-877,883.
Abstract
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(1484KB) (
548
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A text line recognition method was developed without pre-segmentation using a hidden Markov model (HMM) for simultaneously segmenting and recognizing text line images. The algorithm uses a probability graph to reduce recognition error from failed pre-segmentation results. However, the HMM design and training is complicated and the HMM generalization performance can not be easily improved in multi-font texts. Therefore, a character model optimization method with reasonably clustered observations was developed based on the most common HMM state in images. Then, a method was developed to optimize the model structure and parameters together for a multi-font Uyghur text line recognition system. Tests show that this method improves the state allocation, the generalization performance and the state efficiency of the character model for multi-font texts.
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Radar echo generation for hyperbolic frequency-modulation waveforms
ZHOU Wei, YE Chunmao, JIN Kan, LU Yaobin, YANG Jian
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 878-883.
Abstract
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The hyperbolic frequency-modulation (HFM) waveform is more conducive to high speed moving target detection and imaging than the commonly used linear frequency-modulation (LFM) waveform, due to its inherent Doppler-invariant property. However, the generation of radar echoes is computationally intensive when using high frequency algorithms for complex electrically large targets. A fast method was developed for generating HFM radar echoes using static electromagnetic data for HFM waveforms in wideband radar imaging with the computational complexity effectively reduced by phase-matched filtering and frequency domain down-sampling. The result is used to study the influence to HFM signal matched filtering for high-speed movements. This method is also suitable for LFM waveforms. Simulations verify the accuracy and effectiveness of this method.
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COMPUTER SCIENCE AND TECHNOLOGY
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Impact of space rotation on shell miss distances for serpentine flight path maneuvering
FU Qiang, ZHU Jihong, WANG Chunping
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 884-888.
Abstract
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(1057KB) (
758
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Targets maneuver along serpentine paths to avoid naval or antiaircraft gun fire. A method was developed to track a target's path and identify the target's rectangular coordinates and rotation angles. Least square filter models are then defined assuming first-order and second-order motion to predict the target motion, bomb impact points and shell miss distances in functional forms. Rotations of the flight path do not affect the filtered parameters for the target motion, but do affect the miss distance. Rotations of the bomb impact point change the shell's flight time. If the change in the flight time is ignored, the miss distance and the rotations do not affect the calculations. Finally, targeting of gun emplacements was simulated to verify the conclusions.
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Scan segmentation test architecture for power controllability
JIANG Zhou, XIANG Dong, SHEN Kele
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 889-894.
Abstract
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(1260KB) (
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As chip sizes reach micro-nano levels, the increasing power consumption during chip testing is becoming a bottleneck for chip production and testing. Prior work has mainly focused on reducing the power dissipation in either the shift cycle or the capture cycle with little work on reducing the peak power for both the shift and capture cycles at the same time. Moreover, there has been no work on the capture power controllability. This paper presents a power-aware scan segment architecture which controls the power during the shift and capture cycles at the same time with small area overhead. Meanwhile, the dependency checking and scan segment partitioning algorithms directly reduce the switching activity of flip-flops by iteratively optimizing the scan segment grouping. This method analyzes the power controllability in terms of both the structure dependency and the clock tree impact. Tests on reference circuits ISCAS89 and IWLS2005 verify the effectiveness of this architecture.
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Subnet convex hull merging algorithm for reconstructing digital terrain models
ZHENG Jitao, HE Honghong, ZHANG Tao, ZHU Jihong
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 895-899,905.
Abstract
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790
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There are many digital terrain reconstructing methods based on divide and conquer. This study analyzes all possible cases of the merging of two subnet convex hulls. A subnet merging algorithm is then developed to overcome the limitations and drawbacks of traditional algorithms. The public support line and support points are found from the projection position of the vertices of the convex hulls. Then, the convex hull vertices between the support points are linked to generate new triangles so that no two triangles are intersect. Tests show that the algorithm is stable and reliable and that any two subnet convex hulls can be successfully merged.
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Fast mobility solutions in software-defined networks
SUN Wenqi, LI Hewu, WU Jianping
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 900-905.
Abstract
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(1142KB) (
1093
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Software-defined networks (SDN) will be important in the future Internet. Measurements and analyses show the current SDN mobility management problems including long packet delays during handoff and considerable control overhead for supporting the mobility. The packet delay and control overhead are reduced by a fast mobility management scheme which uses tunnel and flow tables to decrease the communication between the control plane and the data plane. Simulations show that the fast IP mobility management scheme reduces the packet delay ten folds compared with the current SDN mobility management scheme with the control overhead during user handoff reduced by more than half.
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Chinese word segmentation method for short Chinese text based on conditional random fields
LIU Zewen, DING Dong, LI Chunwen
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 906-910,915.
Abstract
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Chinese word segmentation is a prerequisite for information retrieval. With the arrival of big data, information retrieval needs more precise word segmentation and recall. This paper presents a Chinese word segmentation method for short Chinese texts. The method first uses a conditional random field model to label the words with special tags to obtain preliminary results. Then, it uses the traditional dictionary-based method to improve the initial result to complete the word segmentation. This method improves recognition of “out of vocabulary” words and overlap ambiguities over the traditional method, with F-Scores over 0.95 with the 4 corpora of the Sighan 2005 bakeoff. Tests show that this method is better for short text Chinese word segmentation for information retrieval.
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Requirement characteristics for kernel services of Linux device drivers
MAO Junjie, CHEN Yu
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 911-915.
Abstract
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(1018KB) (
636
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Reuse of Linux device drivers allows new operating systems to be deployed over a wider range of hardware platforms. However, there are few tools to help developers reuse device drivers due to the lack of a thorough understanding of the requirement characteristics for kernel services by device drivers. The source codes of 271 device drivers in 6 categories were analyzed to identify their required kernel services. The results show that the drivers prefer generic interfaces over specialized ones. In addition, drivers in the same category have similar requirements while drivers in different categories do not. The conclusions will guide the reuse of Linux device drivers and the design of tools to help developers reuse drivers.
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Vector field based depth acquisition algorithm
LU Haiming, WANG Yijiao, XIE Zhaoxia
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 916-920.
Abstract
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(1091KB) (
712
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Scene foregrounds and backgrounds can be separated according to their depth to greatly improve human-computer interaction (HCI). Depth sensors using surface structured light are practical and widely used. The depth information is obtained using an image block matching algorithm, which searches for the optimal matching block in the image. However, the complex computations require high-performance computers or special chips to achieve real-time performance which increase the depth sensor cost. This paper describes a depth acquisition method based on vector field pattern recognition. The scene depth information is obtained by feature recognition of the vector field for every depth point. The vector field is first generated based on the depth features, then the depth information hidden in the vector field is converted to feature information by the pattern recognition algorithm. The depth information is then obtained by feature matching after an inverse transformation. The inverse transformation uses a searching strategy similar to Hash mapping, which avoids the complexity of a linear search. A smart TV with an infrared transmitter can easily realize natural HCI using this method.
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MECHANICAL ENGINEERING
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Efficient Hough transform based cylinder feature detection algorithm
YANG Xiangdong, RUI Xiaofei, XIE Ying
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 921-926.
Abstract
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Ellipse Hough transform method is a significant research topic in the field of feature extraction. Efficient Hough transform (EHT) is proposed to improve the algorithm's accuracy and timeliness. This method is suitable for detecting the ellipse contour in cylindrical feature. The algorithm mainly consists of estimating other parameters' approximation by single parameter's approximation. EHT's failure model is proposed to give the security error range of preset parameter. Synthetic images of ellipse contour are tested to demonstrate EHT's effectiveness.
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PHYSICS AND ENGINEERING PHYSICS
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Evacuation systems using decentralized building control strategies
MA Yaping, WU Nan, GAO Yuan, ZHANG Hui, LI Lihua
Journal of Tsinghua University(Science and Technology). 2015,
55
(8): 927-932.
Abstract
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(2764KB) (
580
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Automated building control systems are essentially centralized control systems with some field control that do not work well in large, complicated buildings. This paper describes a decentralized building control strategy that is more effective than centralized control strategies in terms of the control result and the system robustness. The building zones and communication network are related to the physical building design and entire communication system design. The decentralized building control strategy then gives a more efficient dynamic evacuation guidance system. This system consists of zone controllers, sensors and dynamic guidance signs and takes into account various factors such as the occupant distribution. Drills and simulation results show that this system balances the number of evacuees going to different exits and reduces the total evacuation time with a quick, orderly evacuation.
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