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ISSN 1000-0585
CN 11-1848/P
Started in 1982
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  • Table of Content
      , Volume 55 Issue 5 Previous Issue    Next Issue
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    ELECTRONIC ENGINEERING
    Overlapped frequency/code division multiple access (O-FCDMA) system framework
    GU Na, KUANG Linling, WU Sheng, LU Jianhua
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 485-490.  
    Abstract   PDF (1103KB) ( 998 )
    An overlapped frequency/code division multiple access (O-FCDMA) system framework was developed with the equivalent isotropic radiated power (EIRP) mask restraint to improve the spectral efficiency of multiple access systems for very small aperture terminals (VSATs) in the reverse link at the Ku band. Each user's information bits are spread by different sequences and then modulated on different subcarriers, with adjacent spectra partially overlapping. The system reduces the receiver complexity and improves the spectral efficiency. Simulations show that the reduced multiple access interference (MAI) improves the O-FCDMA system performance so that it outperforms the hybrid frequency/code division multiple access (H-FCDMA) system and approximates the optimal performance achieved by the belief propagation (BP) based joint iterative detection and decoding algorithm in direct-sequence code division multiple access (DS-CDMA) systems, with similar performance to single user systems. Moreover, the O-FCDMA system has a good compatibility with conventional DS-CDMA systems, so it can be easily implemented.
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    Multi-satellite and multi-antenna TDRSS dynamic scheduling method
    LIN Peng, YAN Jian, FEI Ligang, KOU Baohua, LIU Huafeng, LU Jianhua
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 491-496,502.  
    Abstract   PDF (1680KB) ( 1214 )
    A dynamic scheduling method was developed for tracking and data relay satellite systems (TDRSS) to maximize use of the space network (SN). The algorithm includes a service model for multi-satellite and multi-antenna TDRSS for satellites with constellation formations and two types of servable antennas. A population joint evolution algorithm was developed for the random temporal occurrences and spatial distributions of the tasks based on priority differences and time-delay tolerances. The dynamic topology of the SN is separated into the multi-satellite and multi-antenna service model and the population joint evolution algorithm to provide better service capabilities. Simulations show that the average scheduling failure is 18.7% less than with the greedy algorithm.
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    Sentiment classification based on multi-granularity computing and multi-criteria fusion
    WANG Bingkun, HUANG Yongfeng, LI Xing
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 497-502.  
    Abstract   PDF (1167KB) ( 657 )
    The large amount of online user-generated content on the Web has created a need for unsupervised sentiment classification methods. Unsupervised sentiment classification methods based on sentiment words do not work well because the complex sentence structures and sentence types are seldom taken into account. Unsupervised sentiment classification methods based on self-learning have many errors when generating pseudo-labelled datasets. These limitations are reduced by the current method based on multi-granularity computing and multi-criteria fusion. The multi-granularity computing improves the accuracy of unsupervised sentiment classification methods based on sentiment words. The multi-criteria fusion reduces the number of errors in the pseudo-labelled data from the self-learning. Tests using three real Chinese review datasets show that the classification accuracy is 6.5% more accurate on average than with existing unsupervised sentiment classification methods.
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    Sidelobe suppression of isolated strong scatterers based on extrapolated notch filtering
    LI Zenghui, CHANG Wen, YANG Jian
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 503-507.  
    Abstract   PDF (3271KB) ( 955 )
    A two-dimensional extrapolated notch filtering method was developed to suppress sidelobes due to isolated strong scatterers in polarimetric synthetic aperture radar (SAR) images and to maintain the statistical and polarization scattering characteristics. A Chirp-Z transform is used for the AR(1) parameter identification with two-dimensional signal extrapolation based on steady-state Kalman prediction theory. The strong scatterer signals are eliminated by filtering the extrapolated signal with a linear-phase equiripple notch filter. The mainlobes of the strong scatterer signals are recovered in the frequency domain and the image amplitude error is accurately compensated in the filtering process. Unlike both spatially variant apodization (SVA) and adaptive sidelobe suppression (ASS), this method preserves the image resolution, the statistics and the polarization scattering characteristics with a simpler procedure. The effectiveness of this method is demonstrated by simulated and real data.
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    Improved lattice-based speech keyword spotting algorithm
    XIAO Xi, WANG Jingqian
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 508-513.  
    Abstract   PDF (995KB) ( 801 )
    An improved lattice-based speech keyword spotting system was developed from the Gaussian mixture model and an improved N-best speech recognition algorithm. First, tests were used to evaluate different simplified structures of Gaussian mixture models. Then, an N-best token passing algorithm was developed from the classic token passing algorithm using some unique pronunciation rules for the Chinese language. These two modifications improve the performance of both the 1-best and N-best speech recognition candidates. Finally, a key word spotting system was developed based on an N-best lattice to show the effectiveness of these improvements.
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    Multipath-based probabilistic fingerprinting method for indoor positioning
    LI Jiahui, ZHANG Yan, LUAN Fengyu, LI Xueru, ZHOU Lai, ZHOU Shidong
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 514-519,525.  
    Abstract   PDF (1723KB) ( 875 )
    The space-alternating generalized expectation-maximization (SAGE) algorithm provides efficient, accurate indoor channel multipath estimation. This paper describes a multipath-based probabilistic fingerprinting method for indoor positioning that utilizes the channel multipath parameters obtained by the SAGE algorithm as fingerprinting data to achieve better positioning accuracy and robustness. Tests of measurements in a typical indoor environment show that this method is more accurate than traditional indoor positioning methods.
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    Rate-enhanced JTIDS waveform based on LDPC
    WU Zhao, ZHANG Yu, SONG Jian
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 520-525.  
    Abstract   PDF (1144KB) ( 827 )
    Joint tactical information distribution systems (JTIDS) have attracted much attention due to their anti-interference capabilities, security, long communication range, flexible deployment, etc. This paper describes a rate-enhanced JTIDS waveform based on the low density parity check code (LDPC). The optimized MSK soft demodulation method is combined with the LDPC code in the waveform to give significantly improved performance. Simulations demonstrate that the transmission rate of this waveform is an order of magnitude higher than the original JTIDS signal with only a slight decrease in the demodulation threshold and communication range. This scheme is better than several conventional rate-enhanced schemes and can be used in high data rate JTIDS terminals.
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    Impact of multi-cell pilot reuse on the achievable uplink rate for massive MIMO systems
    HE Qiang, ZHANG Xiujun, XIAO Limin, ZHOU Shidong
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 526-531.  
    Abstract   PDF (953KB) ( 779 )
    In massive multiple-input multiple-output (MIMO) systems, multi-cell pilot reuse is an important factor affecting the achievable system uplink rate. A generalized channel model with adaptable power control was used to derive the lower bound on the achievable uplink rate for both least square (LS) and minimum mean square error (MMSE) channel estimations. Then, the impact of pilot reuse as the number of base station (BS) antennas tends to infinity is analyzed based on these bounds. For uncorrelated channels, the ultimate achievable uplink rate of a user is mainly limited by pilot contamination and partially by the large-scale fading coefficients from a pilot interfering with users communicating to their base stations of their own cells due to power control. For correlated channels, pilot contamination is not the only factor that constrains the ultimate achievable system uplink rate, but always exists when LS channel estimation is used, but may vanish when MMSE is used.
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    AUTO MATION
    Battery DC internal resistance test method based on the constant current external characteristics and SOC
    HE Zhichao, YANG Geng, LU Languang, Wu Haisang
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 532-537.  
    Abstract   PDF (1809KB) ( 2256 )
    The direct current internal resistance (DCIR) is the sum of a battery's ionic and electronic resistances. The DCIR test indicates the battery's power characteristics and reflects the batteries' aging and uniformity characteristics. Thus, it is important for battery modeling and applications. This paper describes a DCIR test method based on the battery's constant current external characteristics. This method normalizes the battery's state of charge (SOC) changes for different constant current conditions. Then, the DCIR for different operating currents and SOC are obtained using constant current charge/discharge curves. This method is easier to implement than existing methods and has good accuracy.
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    Service composition analysis with collaboration
    XIN Le, FAN Yushun
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 538-542,549.  
    Abstract   PDF (1328KB) ( 517 )
    In business service networks, service composition often involves cooperation. A service composition model was developed that includes the effects of collaboration to facilitate selection of the service composition method with collaboration. This model describes the service flow as the main logic and expands the definition of the support impact factor for various types of supporting services. Service composition structure correlation indexes are used to optimize the selection approach based on the users' preferences and to predict the supporting services' utility, which gives a more comprehensive assessment of the service delivery effect. A numerical example shows the effectiveness of this model.
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    Fuzzy synthetic evaluation of the operational status of offshore direct-drive wind turbines
    HUANG Biqing, HE Yan, WANG Tingyan
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 543-549.  
    Abstract   PDF (1040KB) ( 847 )
    Direct drive motor systems for offshore wind turbines will improve reliability and reduce maintenance costs. This paper describes a real-time status evaluation model for offshore direct-drive wind turbines. This model integrates the correlation coefficient method, deterioration analyses and fuzzy synthetic evaluation. The correlation coefficient method determines the weights of various indexes. The deterioration analysis normalizes the indicator parameters. The bottom-up, step-by-step, multi-level fuzzy synthetic evaluation method assesses the status of each subsystem of the offshore direct-drive wind turbine. An analysis of online inspection data for a direct-drive wind turbine shows that the model results are consistent with real operational data. This model is helpful for managing routine operations and maintenance for offshore direct-drive wind turbines to improve the operational efficiency of offshore wind farms.
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    Solutions of the single elevator scheduling problem for emergency evacuations
    WANG Jing, WANG Shuning
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 550-557.  
    Abstract   PDF (960KB) ( 552 )
    This study considers the minimization of the evacuation time for a single elevator for emergency conditions when all the evacuees are waiting in the elevator halls before the evacuation begins. Integer programming (IP) and a heuristic algorithm are used to formulate the problem as an equivalent integer linear programming problem that includes the elevator operation constraints and linearizes the nonlinear constraints. The heuristic algorithm maximizes the number of evacuees evacuated in each roundtrip while minimizing the number of visits to the floors. Numerical tests verify the improved evacuation speed given by this algorithm relative to existing algorithms.
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    Transaction rating credibility based on user group preference
    CHEN Yuanlin, CHAI Yueting, LIU Yi, XU Yang
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 558-564,571.  
    Abstract   PDF (1505KB) ( 828 )
    Transaction and rating data can be used to evaluate credit as a key underlying service provided by online transaction platforms. However, credit evaluation methods pay little attention to user rating preferences, so rating manipulations can expand arbitrarily. A method is given here to determine transaction rating credibility based on group preferences. This method uses the K-means clustering algorithm to divide all the users into three groups and analyzes and validates each group's rating preferences. Then, the algorithm provides three steps to determine the credibility of ratings on different levels for different user groups based on these preferences. This paper also provides a strategy to dynamically update the group division and credibility to effectively restrict credit manipulation.
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    COMPUTER SCIENCE AND TECHNOLOGY
    Performance analysis of star topology wireless sensor networks based on IEEE 802.15.4
    CAI Jie, GU Ming
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 565-571.  
    Abstract   PDF (1115KB) ( 1271 )
    Performance analyzes are difficult in wireless sensor networks (WSNs). This study analyzes the performance of a star topology WSN based on the IEEE 802.15.4 standard. The probability of data collision is analyzed for the hidden terminal problem caused by channel fading. Then, the model is used to derive the packet reception rate (PRR), the average delay and the average energy consumption. Simulation results are within 5% of the theoretical results which validate the correctness and accuracy of the theoretical expressions.
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    Detection and analysis of size controlled heap allocation
    XIAO Qixue, CHEN Yu, QI Lanlan, GUO Shize, SHI Yuanchun
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 572-578.  
    Abstract   PDF (1083KB) ( 871 )
    Improper memory operations are one of the main causes of software vulnerabilities. This study analyzes controlled memory allocation (CMA) errors which occur when key elements of the memory allocation method are affected by elaborately designed input data. This paper presents a CMA detection approach that uses static analyzes and optimized symbolic execution with a path-guided algorithm. These algorithms are combined with a state-of-the-art symbolic execution engine named KLEE in a CMA detection tool. The tool was tested on commonly used applications like Coreutils, where it found 10 CMA related bugs including 3 previously unknown bugs. Tests show that the tool's path guided searcher reaches an assigned target faster and with more paths than the other path searchers provided by KLEE. The tool executes faster for memory allocation related code with better coverage than conventional symbolic execution engines.
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    Fast cross-datacenter virtual machine migration algorithm based on duplication
    LIU Shengzhuo, JIANG Jinlei, YANG Guangwen
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 579-584.  
    Abstract   PDF (1102KB) ( 891 )
    Live migration of virtual machines (VM) over wide-area networks (WAN) is key to cloud computing operations in a multi-datacenter environment. Compared with the migration over a local-area network (LAN), the live migration over a WAN faces more technical challenges due to the limited bandwidth. A live cross-datacenter VM migration infrastructure was developed in a fast live image migration cross-datacenters (FlimCD) method, which makes full use of dirty blocks deduplication, block pre-fetching and hot-area scheduled transmissions to reduce the overall migration time and the impact of the VM migration on the performance. Tests show that, for moderately I/O intensive workloads, the migration time is reduced by 64.3% compared with that of the pre-copy algorithm. The current optimization mechanisms reduce the block miss rate by 49% in the post-copy phase.
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    ELECTRICAL ENGINEERING
    Electric field around the outer insulator of a 10 kV solid insulation vacuum circuit breaker
    LUO Ling, YANG Zhaoxiang, MEI Hongwei, ZHAO Chenlong, WANG Liming, GUAN Zhicheng
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 585-591.  
    Abstract   PDF (2280KB) ( 1080 )
    10 kV solid insulation vacuum circuit breakers are widely used in electrical distribution networks. The effects of the space between the insulator and the metal cover and the cover itself on the electric field intensity around the outer insulator were analyzed for a solid sealed pole. Realistic 3-D simulation models were built in Solidworks. A simplified model of an aluminum solid sealed pole was set up with the external shielding grounded. The electric field intensity was predicted using Ansoft Maxwell 3D. The results indicate that the electric field intensity around the outer insulator has a large range. A metal shield increases the electric field intensity of the solid sealed pole. If there are some bubbles in the solid epoxy sealed pole, the metal shield may aggravate the partial discharges.
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    Improved gray-color transform method for MFL images
    PENG Lisha, WANG Shen, LIU Huan, HUANG Songling, ZHAO Wei
    Journal of Tsinghua University(Science and Technology). 2015, 55 (5): 592-596.  
    Abstract   PDF (1117KB) ( 910 )
    Magnetic flux leakage (MFL) systems using pseudocolor images give better identification than grayscale images. This study combines two traditional pseudocolor coding methods into an improved gray-color transform method. Firstly, the initial transform piecewise linear expression is determined from the magnetic flux leakage characteristics. Then, the Ostu method for grey value clustering is used to get the expression node values. The transformed pseudocolor images are then obtained using the improved expression. This method based on the actual gray value to get the specific expression has good adaptability. Real tests show that this method gives clearer, more vivid images, which give better MFL characteristics identification.
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