Table of Content

30 May 2016, Volume 34 Issue 3

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Communication Engineering

Optimization of Electronic Control Scheme of Multi-layer Phase-Modulated Surface and Its Influence on Scattering Properties

FU Yi, HONG Tao

2016, 34(3):  237-250.  doi:10.3969/j.issn.0255-8297.2016.03.001

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To improve absorbing properties of phase-modulated surface (PMS), a method for optimizing the switching scheme of PMS using a differential evolution (DE) algorithm is proposed. The number of active layers in PMS is increased. Scattering properties of PMS are theoretically studied using a time-modulation theory. The switching scheme of PMS is optimized using the DE algorithm. The results indicate that the optimized switching scheme can minimize the spatial coverage of scattered echo at the incident frequency. The effect is further enhanced as the number of active layers in PMS increases. The floor effect occurs when the number of active layers reaches a certain value, limiting the PMS structure conversely. This research is meaningful for the design of PMS by balancing its absorbing properties and structure complexity.

Impact of Antenna Characteristic on MIMO Channel Spatial Correlation

XUE Cui-wei, ZHU Qiu-ming, CHEN Xiao-min, LIAO Zhi-zhong, LIU Xing-lin

2016, 34(3):  251-262.  doi:10.3969/j.issn.0255-8297.2016.03.002

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In view of the influence of physical characteristics of an antenna on spatial correlation of a MIMO channel, this paper establishes a MIMO channel model including both coupling and polarization by analyzing and modeling the mechanism of mutual coupling and antenna polarization. Based on this model, a theoretical expression of spatial correlation for the MIMO channel model is derived, and applied to 3GPP SCM standard channel propagation. Simulation results show that the mutual coupling effect becomes significant as the antenna spacing decreases, and the polarization factor varies due to different polarization angle combinations. Moreover, both mutual coupling and polarization can reduce spatial correlation to some degree, but they cannot improve system capacity.

Secrecy Scheme of Two-Way Space Hopping Transmission in Physical Layer

QIN Wei, XU Jia-ping, LI Tao

2016, 34(3):  263-274.  doi:10.3969/j.issn.0255-8297.2016.03.003

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In this paper, a bidirectional training based technique is proposed for multiantenna space hopping transmission, which ensures information security of two-way transmission in the physical layer. The proposed scheme can guarantee the identity of channel characteristics obtained by two legitimate transceivers via bidirectional training. A space hopping pattern generation algorithm is presented, which calculates the pattern according to channel characteristics. The antenna switching mode is controlled by the pattern that selects several antennas for fast switching transmission. Conventional schemes resort to a backward training method, hiding the channel between transceiver and eavesdropper so that an eavesdropper cannot receive correctly with wrong weighting, thus achieving security of transceivers. The default mode is that a receiver only receives. Contrarily, the proposed scheme uses a switching mode to ensure transmission secrecy. To improve training efficiency, a spatial frequency multiplexing training method is used, with almost identical accuracy and significantly enhanced efficiency. Simulation results show that the proposed scheme has good performance in anti-eavesdropping as it causes a high bit error rate for the eavesdropper.

Power-Efficient Clustering-Based Spectrum Allocation in Heterogeneous Cellular Networks

XIANG Wei, ZHANG Jian-feng, XIE Wei, MA Wen-feng

2016, 34(3):  275-285.  doi:10.3969/j.issn.0255-8297.2016.03.004

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To solve the interference and power consumption problems between the macrocell base stations (MBSs) and the femto-cell base stations (FBSs), and that among FBSs, the paper proposes a power-efficient clustering-based spectrum allocation strategy (CSAS). According to outage probability of femto-cell users (FUEs), the maximum number of femtocell base stations contained in a cluster is derived. Under the restriction of the cluster capacity and OP, SIR of FUEs and minimum interference distance between FBSs in a cluster is further derived to strictly guarantee each FUE's SINR. A clustering algorithm and a spectrum allocation algorithm are proposed. Simulation results show that the proposed strategy improves power efficiency of the network and spectral efficiency of the femto-cell network.

Improved Blind Channel Estimation for MIMO-OFDM Systems

LI Guo-min, LIU Xin, KANG Xiao-fei, LIAO Gui-sheng

2016, 34(3):  286-292.  doi:10.3969/j.issn.0255-8297.2016.03.005

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Channel estimation for MIMO-OFDM systems by linear precoding requires repeated calculation of ambiguity matrices. To solve the problem, a blind channel estimation algorithm is proposed. It unifies different channel ambiguity matrices by processing crosscorrelation matrices of received signal, and then estimates the channel using an iterative method. Simulation results show that the proposed algorithm has good mean square error performance and convergence, and less computational complexity compared with existing channel estimation methods based on linear precoding.

Outage Probability Analysis for Multi-sensor Backscatter Communication

YAN Ting-ting, HU Sheng-bo, SHI Yan-feng, SONG Xiao-wei

2016, 34(3):  293-301.  doi:10.3969/j.issn.0255-8297.2016.03.006

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Outage probability is a vital index in analyzing wireless multi-sensor backscatter communication. A classical model of multi-sensor backscatter communication system is used for analyzing outage probability. A closed-form solution of outage probability for a lognormal shadow channel is given. Using Monte Carlo simulation and numerical integration, factors affecting outage probability are analyzed. The result of Monte Carlo simulation is consistent with that of numerical integration. The outage probability error of numerical analysis is less than 1.481%. Meanwhile, with increase of the SINR threshold, the outage probability increases. If the SINR threshold is too large, mutual interference among sensors becomes severe. On the contrary, if SINR threshold is too small, mutual interference is greatly reduced. These conclusions provide a reference for analyzing reliability and designing of backscatter communication systems.

Signal and Information Processing

Application of GNSS Based on Orthogonal Test

QI Yong-qiang, ZHANG Yan-zhong, ZHANG Bo, LI Shu-jian

2016, 34(3):  302-308.  doi:10.3969/j.issn.0255-8297.2016.03.007

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With rapid development and improvement of four satellite navigation systems, multi-systems are widely used in global navigation satellite system (GNSS) applications. This paper studies combination navigation of GNSS multi-systems. A navigation test of GNSS multi-systems is designed with orthogonal experiments of three factors at different levels. In the test, the RMS and PDOP mean value of position error are evaluated as indicators of GNSS positioning accuracy. Three factors, combined system, frequency and masking angle, are selected. As there are different levels for 3 factors, a mixed-level orthogonal array is selected. A test is carried out with the appropriate receiver according to the design. Optimal application of GNSS multi-system combination under a specific environment in a specific region is obtained by an overall equilibrium method based on the test result. The test shows that the described method is feasible and effective in solving the problem of optimization combination of GNSS multi-system. Calculation and analysis of the result are simple and objective.

Adaptive Print-Scan Resilient Image Watermarking Based on Fourier Transform

LIAO Ting, LI Zhi-jiang

2016, 34(3):  309-316.  doi:10.3969/j.issn.0255-8297.2016.03.008

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A robust blind watermarking scheme that combines uniform log-polar mapping and perceptual band decomposition of Fourier domain is proposed, which can resist general print-scan attacks. The proposed scheme can guarantee invisibility and increase robustness of the watermark. Perceptual band decomposition that splits the Fourier domain into overlapping sub-bands is used to locate the mid-frequency domain. Uniform log-polar mapping is applied to mid-frequencies in the Fourier domain. Watermark embedding in the mid-frequencies is adaptively controlled by the local spectrum property. Finally, a spatial perceptual mask is used to compensate distortion after the embedded image is inversely transformed back to the spatial domain. Both the theoretical analysis and experimental results show that the proposed scheme is invisible, and robust against general print-scan attacks.

Improving Atmospheric Correction Precision of Remote Sensing Image Inversion in Southeast Rocky Desertification Area of Yunnan

LI Su-min, YUAN Li-wei, YUAN Xi-ping

2016, 34(3):  317-328.  doi:10.3969/j.issn.0255-8297.2016.03.009

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Based on the aerosols spatial distribution and the near effect of the earth's surface, the paper studies the influence of different calibration files for spectral reflectance, determines appropriate calibration information, takes into account humidity, and determines reasonable visibility through spectral analysis. These values are used in the calculation of atmospheric correction to improve precision of atmosphere correction. The results show that they can effectively reduce the effects of air molecules, water vapor, aerosol particles, and ozone on the satellite remote sensing images, and improve remote sensing information inversion accuracy in the rocky desertification area. The performance of this method is better in winter than in autumn and spring.

Computer Science and Applications

Impact of Discontinuous Immunity on SIR Computer Virus Model

ZHANG Dao-xiang, LI Xun

2016, 34(3):  329-338.  doi:10.3969/j.issn.0255-8297.2016.03.010

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This paper studies the impact of discontinuous immunity on global dynamics of a computer virus model. Using differential inclusion, we define the solution of Filippov, and study existence and uniqueness of equilibrium. We get the basic reproduction number R₀ by calculation. By constructing a Lyapunov function, we show that all solutions converge to disease equilibrium in a finite time when R₀ > 1. Similarly, all solutions converge to free disease equilibrium in a finite time when R₀ < 1. Numerical simulations are carried out to illustrate and expand the theoretical results.

Control and System

Adaptive Backstepping Sliding Mode Approach to Flight Attitude of Quadrotor UAVs

XU Ya-peng, SU Cheng-li, SUN Xiao-ping

2016, 34(3):  339-351.  doi:10.3969/j.issn.0255-8297.2016.03.011

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To overcome the problems of nonlinearity and under-drive with six degrees-offreedom in controlling attitude and position of quadrotor UAVs, an adaptive backstepping sliding mode method is proposed. An adaptive law is derived to make online estimation of control parameter variations and external disturbances. The assessment is used to compensate the backstepping sliding mode control. With the Lyapunov stability theorem, it is shown that the design method is asymptotically stable for tracking error. Numerical simulation of a quadrotor UAV using the setting parameters shows that the proposed approach achieves attitude stabilization and fixed hanging stop of UAVs with parameter variations and external disturbance.

Remote Intelligent Monitoring Strategy of Heat-Supply Network Based on Kingview

SUI Xiu-wu, YU Bao-fu, GE Hui, TIAN Song

2016, 34(3):  352-360.  doi:10.3969/j.issn.0255-8297.2016.03.012

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To deal with control difficulties of coupling, nonlinearity and hysteresis in a centralized heat supply system of a heat-supply network, a remote monitoring system of heat-supply network based on Kingview is designed. It combines the concepts of energy conservation and environmental protection. Advanced control strategies are developed based on Kingview and a local PLC to realize site collection of district heating system parameters such as temperature, pressure, flow and valve opening. Thus accuracy of the heating control and quality of heating are improved. It is possible to achieve a good running condition of thermal water conservancy via fuzzy-PID control, temperature compensation control, thermal load budget, wireless remote, and other techniques. An optimization objective function and a nonlinear programming algorithm are established, and optimal operation solutions obtained with heating network parameters that can improve energy efficiency and system stability. Operation of a whole year shows that the design enhances the system's intelligent control, and has excellent energy efficiency. It is significant in adjusting quality, improving energy efficiency, and raising operation and management standards of urban central heating systems.