Loading...
Office

Table of Content

    20 December 2007 Volume 34 Issue 6
      
    Original Articles
    Remotely sensed image segmentation based on the wavelet-domain HMTseg algorithm with daptive fusion mechanism
    SUN Qiang;JIAO Li-cheng;HOU Biao
    J4. 2007, 34(6):  853-858. 
    Abstract ( 2460 )   PDF (1282KB) ( 1372 )   Save
    Related Articles | Metrics
    An HMTseg algorithm with the adaptive fusion mechanism is proposed for the segmentation of remotely sensed images. In this algorithm, the statistical correlation properties between wavelet coefficients across different scales are well employed. The initial segmentation results on coarse and fine scales are fused adaptively by the assignment of different contextual weights. This algorithm not only lays emphasis on the advantage of region consistency from the coarse-scale segmentation, thus preserving the main outlines of individual homogeneous regions, but takes into account the advantage of boundary location accuracy from the fine-scale segmentation, thereby favoring the discrimination of small targets within an image. Experimental results on remotely sensed images, including aerial photos and SAR images, demonstrate that the algorithm can improve the segmentation performance of remotely sensed images.
    Symbol rate estimation of orthogonal frequency division multiplexing (OFDM) signals
    ZHENG Wen-xiu;ZHAO Guo-qing;LUO Ming
    J4. 2007, 34(6):  859-863. 
    Abstract ( 2815 )   PDF (735KB) ( 1309 )   Save
    Related Articles | Metrics
    Aiming at the real application of OFDM signals’ parameter estimation and demodulation, a method is proposed for the accurate estimation of the symbol rate. The OFDM sub-carriers, accurately estimated by the high-order cyclic cumulants, are used to construct an auxiliary signal, of which the symbol jumping information is abstracted by the wavelet transform. Furthermore, its spectrum analysis can perform the accurate symbol rate estimation. The method needs no prior information so that it is easy for the communication reconnaissance and receiving equipments to implement. And simulation indicates that the proposed method has the correction of 99% for the symbol rate estimation of OFDM signals modulated by PSK and star-QAM with SNR> 0dB when the estimation error is within 0.1%.
    Face detection algorithm fusion of the skin-color model and wavelet transform
    HAO Lin-bo;NIU Hai-jun;LU Chun-mei
    J4. 2007, 34(6):  864-868. 
    Abstract ( 2249 )   PDF (1001KB) ( 1289 )   Save
    Related Articles | Metrics
    In view of the defect of high misdetection rate in the current Face Detection, this paper presents a new algorithm which is fusion of the skin-color model and wavelet. First, we use the skin color model to determine the potential facial position, and then separately carry on the examination to the eyes and the mouth, thus finally ensuring the real facial position. The eyes are detected based on the geometry location after the wavelet transformation, while the mouth is detected based on the Fisher classifier. This method realizes fast and accurate single face localization in the complex background. Compared with the traditional YCbCr skin color model, the combination of color space, the wavelet transformation, and the Fisher classification in face detection enhances the examination precision. Experimental results show that the correct detection rate is 91% and that the error probability is only 2%.
    A motion object detection algorithm for MPEG-4 video
    WANG Quan;DONG Bao-yuan;TIAN Yu-min
    J4. 2007, 34(6):  869-872. 
    Abstract ( 2299 )   PDF (741KB) ( 1166 )   Save
    Related Articles | Metrics
    Focusing on the problem of moving object detection and tracking on MPEG-4 compressed streams by a stationary camera, an algorithm for detecting the moving object using DC coefficients and motion vectors of the motion information in MPEG is presented. The algorithm is first to mark the moving regions based on the motion vectors, then get the moving macro blocks by obtaining the DC coefficient of each marked block in MPEG data and calculating the fourth-order detector of inter-frame difference, and finally obtain the moving object by region growth. The computational complexity of only computing DC coefficients and the detection error only through motion vectors are reduced by the method. The algorithm presented makes the real detecting and tracking of the moving object possible.
    Multi-class classifier of non-linear SVM decision tree
    YAO Yong;ZHAO Hui;LIU Zhi-jing
    J4. 2007, 34(6):  873-876. 
    Abstract ( 2153 )   PDF (507KB) ( 1147 )   Save
    Related Articles | Metrics
    A classification algorithm of non-linear support vector machine (SVM) decision tree is presented. The presented method extends the SVM to the non-linear SVM by using kernel functions and calculates the relativity separability measure between classes after non-linear mapping. This method is introduced on the basis of the SVM decision tree. As a result, the iterative error is effectively restrained and the efficiency improved accordingly. Experimental results have shown that, compared with the original SVM decision tree algorithm, the classification rate has increased greatly and that the classification time decreased apparently.
    A novel anonymous authentication scheme over the insecure channel
    CAO Xue-fei;ZENG Xing-wen;KOU Wei-dong;YU Yong
    J4. 2007, 34(6):  877-880. 
    Abstract ( 1949 )   PDF (518KB) ( 1054 )   Save
    Related Articles | Metrics
    Firstly, an ID-based signature scheme is proposed based on pairings. The bilinearity and non-degeneration of pairings are explored to make the verification result of the signature vary only with the identity of the signer. Then an anonymous authentication scheme is proposed based on the signature scheme. During the authentication, a user chooses a pseudonym by him/herself; then server computes the user’s account index from the pseudonym in order to identify and authenticate the user. With our scheme, users are able to travel incognito and to change their passwords at will. Furthermore, there is no need for server to maintain a table of users’ passwords or pseudonyms. To the best of our knowledge, the proposed scheme realizes for the first time both user anonymity and authentication security requirements over the insecure channel.
    An energy efficient data coding method and timing extraction for the RFID system
    WANG Hong-gang;PEI Chang-xing;CHEN Nan
    J4. 2007, 34(6):  881-886. 
    Abstract ( 1817 )   PDF (823KB) ( 1096 )   Save
    Related Articles | Metrics
    A data coding method for carrying more energy to the passive tag is presented for the RFID system. The basic idea of the coding is to set adjustable and asymmetric high and low level durations within a symbol cycle, and a longer duration for the high level. The performance analysis results show the energy of baseband data transmitted from reader to tags increases by 84% at most, compared with that of Manchester coding at typical 40kb/s. The coding achieves the same BER performance of ASK system with non-coherent demodulation as Manchester coding. For the coding, a clock recovery scheme in which an IIR filter is combined with a PLL is proposed. The scheme maintains the accurateness of PLL, and especially for the feedback of the IIR filter, it can recover the clock quickly with long data dropouts. The scheme can withstand data dropouts of 10 baud, which is correlated with the parameters of the filter.
    Reform of the Snort system by the multithreading technique
    LIN Guo-qing;WANG Xin-mei
    J4. 2007, 34(6):  887-894. 
    Abstract ( 2178 )   PDF (865KB) ( 1067 )   Save
    Related Articles | Metrics
    The Snort system is a lightweight network intrusion detection system based on rules. In this paper, the principle, the basic structure and the workflow of this system are analyzed. Aiming at the Snort system working in a single thread, a reform scheme based on the multithreading technique for developing its performance is put forward, including a queue between two function modules and a busy sign flag in every decoder and chain node. The workflow of the reformed system is described then. Finally, the performance of the reformed system is analyzed theoretically associating with the result of a simulated experiment with a simplified model, which shows the detection efficiency is increased and the rate of miss-detection is decreased, but the workloads of CPU and the computer memory are increased.
    Soft in soft out demapper for the BICM-ID system with multi-dimensional mappings
    GONG Feng-kui;GE Jian-hua;WANG Yong
    J4. 2007, 34(6):  895-899. 
    Abstract ( 2210 )   PDF (1043KB) ( 1035 )   Save
    Related Articles | Metrics
    By modifying the probability function of the MAX-LOG-MAP algorithm of two-dimensional mappings, a soft in soft out demapper is derived for BICM-ID with multi-dimensional mapping. By combining with the tree-searching algorithm of multi-antenna systems, a simplified multi-dimensional tree-searching algorithm (MD-TS) is also proposed, whose computational complexity is decreased significantly by selecting the symbol vectors with high probability. The reduced complexity is in proportion to the list length. Computer simulations show that the asymptotic BER performance is improved compared with two-dimensional mappings and that the simplified MD-TS algorithm brings only about 02dB performance degradation.
    Compression of interferential multispectral images based on empirical data decomposition
    WANG Ke-yan1;WU Cheng-ke1;DENG Jia-xian2;KONG Fan-qiang1;GUO Jie1
    J4. 2007, 34(6):  900-905. 
    Abstract ( 2776 )   PDF (1131KB) ( 1088 )   Save
    Related Articles | Metrics
    Due to the non-stationary property of interferential multispectral image data, a novel compression algorithm for interferential multispectral images with proposed Empirical Data Decomposition (EDD) is presented. EDD can make a multi-resolution analysis of the non-stationary interferential data. With its local characteristic and variation tendency, the non-stationary interferential data are decomposed by EDD into two parts: the sum of local region data and the difference data. In this paper, EDD is first utilized for interferential multispectral image data de-correlation, and a corresponding 2-D decomposition structure is presented as well. The decomposition coefficients are finally coded with the modified EBCOT. Experimental results show that, compared with the JPEG2000 standard, the proposed algorithm decreases the average output ratio by about 0.15 bit/pixel for lossless compression, and improves the reconstructed images by 1.1~2.5dB. The algorithm also reduces the Relative spectral Quadratic Error(RQE) and protects the spectral information efficiently.
    Time and frequency synchronization for OFDM systems
    GUO Yi;LIU Gang;GE Jian-hua;ZHANG Wu-jun
    J4. 2007, 34(6):  906-910. 
    Abstract ( 2606 )   PDF (638KB) ( 1135 )   Save
    Related Articles | Metrics
    A new training symbol is designed and a novel time and frequency synchronization scheme for orthogonal frequency division multiplexing systems is proposed. The timing synchronization is accomplished by using the symmetric conjugate of the training symbol in the time domain and the frequency synchronization is finished by utilizing the good autocorrelation of the training symbol in the frequency domain. Simulation results show that the scheme gives very accurate estimates of symbol timing and carrier frequency offset and provides a very wide range of acquisition for the carrier frequency offset, outperforming other available methods.
    Immune clonal optimization clustering technique
    MA Wen-ping;SHANG Rong-hua;JIAO Li-cheng
    J4. 2007, 34(6):  911-915. 
    Abstract ( 2287 )   PDF (1006KB) ( 1071 )   Save
    Related Articles | Metrics
    A new immune clonal clustering algorithm based on the clonal selection optimization of the artifical immune system is proposed for solving unsupervised classification and recognition problems. The new algorithm can carry out the global search and the local search in many directions around the same antibody simultaneously, and make the most of antibodies in population adequately in order to search for global optimal cluster centers in the feature space quickly. It avoids the local optimum of the classical clustering algorithm. Theoretical analysis shows that the new algorithm can converge to the global optimum. Experiments on seven benchmark clustering problems of artificial data sets and two texture images segmentation problems show that the average correct rate of the new algorithm is higher than that of the K-means algorithm by 20.9%, and is higher than that of a genetic algorithm based clustering method by 20.3%.
    Deployment kinematic analysis and control of hoop truss deployable antenna
    LI Tuan-jie;ZHANG Yan;DUAN Bao-yan
    J4. 2007, 34(6):  916-921. 
    Abstract ( 1993 )   PDF (784KB) ( 1104 )   Save
    Related Articles | Metrics
    Based on the structural characteristics of the hoop truss deployable space antenna, body-fixed coordinates are attached at the hoop modules, and the motion transformation relation between two hoop modules is derived using the method of coordinate transformation. The general model for deployment kinematic analysis is established. The model can be applied to carry out the position, velocity and acceleration analysis of any point on the structure. In order to avoid too large an impact in the deployable process, the deployment velocity of the hoop module is planned. The motion relation between the driving cable and the hoop module is given. The motion planning of the hoop module is transformed into the motion control of the driving cable, which can realize the deploying position control of the antenna. Finally, numerical simulations show the control method can make the antenna calmly deploy following the specified deployable motion.
    Geometric-pattern dynamic Bayesian networks reasoning gene regulatory networks
    WANG Kai-jun;ZHANG Jun-ying;ZHAO Feng;ZHANG Hong-yi
    J4. 2007, 34(6):  922-925. 
    Abstract ( 2021 )   PDF (508KB) ( 1128 )   Save
    Related Articles | Metrics

    Trend correlations (i.e., two genes are correlated in their varying trends that rise and descend with time) between genes are very important but usually neglected in reconstruction of gene regulatory networks (GRN). To mine trend correlations to enhance the reconstruction performance of GRN, we propose geometric-pattern dynamic Bayesian networks (Gp-DBN). In Gp-DBN the time series of each gene is transformed to a geometric pattern, by which potential regulators and time lags are estimated, and regulatory relations between genes are discovered by reasoning correlations between these geometric patterns. Gp-DBN realizes the mining of regulatory relations with trend correlations so that it can improve the performance of GRN reconstruction. Experimental results on Yeast and E. coli data sets show that Gp-DBN improves greatly the performance of GRN reconstruction in the cases with/without prior knowledge, compared with traditional dynamic Bayesian networks.

    Cryptanalysis of a (t, N-2)-resilient Mix Net
    LI Long-hai1;2;FU Shao-feng1;XIAO Guo-zhen2
    J4. 2007, 34(6):  926-929. 
    Abstract ( 2157 )   PDF (508KB) ( 959 )   Save
    Related Articles | Metrics
    We analysed Gao et al.’s (t, N-2)-resilient Mix Net scheme and found some serious security flaws in their design. In order to break Mix Net’s privacy, an active attacker can construct a list of ciphertexts with some relativity by utilizing the malleability of the ElGamal encryption scheme, and then observe the corresponding relativity of plaintexts to get the relationship between input and output elements. The malicious servers from two different groups can initiate collusion attacks proposed by this paper to make the Mix Net system output wrong and cheat the verifying protocol with non-negligible probability of success. The result of analysis shows that Gao et al.’s scheme does not satisfy (t, N-2)-resilience and that the electronic voting application based on their Mix Net is also insecure.
    Data lengthening and improved NFL classifier for HRRP recognition
    CAO Xiang-hai;LIU Hong-wei;WU Shun-jun
    J4. 2007, 34(6):  930-934. 
    Abstract ( 1906 )   PDF (562KB) ( 965 )   Save
    Related Articles | Metrics
    In the target identification based on the radar high resolution range profile(HRRP), data extrapolation changes the amplitude of HRRP, so the recognition performance of HRRP is deteriorated. In this paper, we first present a new HRRP preprocessing method-data lengthening, which can reduce the aligned error of HRRP. Then, for the nearest feature line(NFL) classifier, samples are expanded in a local region according to the distribution character of HRRP, so the NFL can achieve a better performance with reduced computation complexity. Finally the two methods are combined for identification of HRRP. Experiments based on measured and simulated data demonstrate the efficiency of the presented algorithm.
    Image spectrum segmentation and de-noising based on multi-channel nonuniform filter banks
    ZHONG Wei;XIE Xue-mei;SHI Guang-ming
    J4. 2007, 34(6):  935-938. 
    Abstract ( 2029 )   PDF (1371KB) ( 1165 )   Save
    Related Articles | Metrics
    A simple method for image spectrum segmentation and de-noising is proposed, due to the fact that the input image cannot be decomposed flexibly in a transform domain. Multi-channel linear-phase nonuniform filter banks with proper sampling factors are designed which are applied to rows and columns of the input image, respectively, according to its power spectrum distribution. By this procedure, the image can be segmented nonuniformly in the frequency domain. In addition, provided that the power spectrum of the noise involved concentrates on the low power part of the original image, it can be detected and removed easily by using the proposed idea of spectrum segmentation. This method performs efficiently when the power spectrum of the original image is distributed concentratedly. A design example is given to demonstrate the simplicity and effectiveness of the proposed method.
    Study of removal of artifacts in MEG using PCA and ICA
    GAO Li1;HUANG Li-yu1;DING Cui-ling2
    J4. 2007, 34(6):  939-943. 
    Abstract ( 1917 )   PDF (1936KB) ( 923 )   Save
    Related Articles | Metrics
    Principal Component Analysis (PCA) and Independent Component Analysis (ICA) are two representative algorithms in Blind Source Separation. In this paper, a novel method for removal of artifacts in Magnetoencephalography (MEG) by combining PCA and ICA is presented. The basic concepts and algorithms of PCA and ICA are introduced firstly, MEG data are decomposed by PCA method in order to reduce the dimension of the original signals and take the redundancies out for getting the main components of data. Then the de-dimensioned data are further processed by using the adaptive Infomax algorithm of ICA. The study shows that the various artifacts can be separated from the MEG successfully and that removal of artifacts can be realized by signal reconstruction.
    Statistics model for IR radiance of bare terrain and analysis of texture characteristics
    SHAO Xiao-peng;ZHENG Hong-bin;XU Jun;ZHANG Jian-qi
    J4. 2007, 34(6):  944-946. 
    Abstract ( 1691 )   PDF (706KB) ( 985 )   Save
    Related Articles | Metrics
    The radiant temperature field of the natural terrain is one of the key factors in the synthesis of its infrared textures. A statistical calculating model of infrared radiance of the bare terrain is developed based on its statistical analysis. And the Monte-Carlo method is applied to calculate the parameters of the infrared radiant temperature field of the bare terrain. Finally, the infrared textures of the bare terrain in a day are simulated by the Gaussian-Markov random field models using the temperature field data. Simulation results show that the models and the method in this study can be used to generate the real infrared textures of the bare terrain, which can be widely used in the application of the infrared scenes simulation.
    Energy dissipation in tapping-mode atomic force microscopy
    FAN Kang-qi;JIA Jian-yuan;ZHU Ying-min
    J4. 2007, 34(6):  947-952. 
    Abstract ( 1486 )   PDF (647KB) ( 956 )   Save
    Related Articles | Metrics
    Based on Hamaker hypotheses and Lennard-Jones potential, the interaction between an atom and a sphere is obtained to investigate the energy dissipation in tapping-mode atomic force microscopy (AFM). By considering the interaction between a sphere and an atom of a plane as the distributing adhesion force between a sphere and a plane, and combining with the elastic theory, a novel elastic model is established of adhesive contact between a sphere and a plane. With the adhesive model established, the variation of the adhesive force with the AFM tip-sample distance is obtained. Simulation results indicate that the variation of the adhesive force with the distance in the load process is different from that in the unload process, i.e., the adhesive hysteresis is demonstrated, which is the indication of the energy dissipation. So the energy dissipation is shown by the proposed model in the tapping-mode AFM.
    Research on attenuation and the two-frequency mutual coherence function for millimeter wave propagation in the sand and dust storm
    YANG Rui-ke;JIAN Dian-jun;YAO Rong-hui
    J4. 2007, 34(6):  953-957. 
    Abstract ( 1798 )   PDF (621KB) ( 1120 )   Save
    Related Articles | Metrics
    The attenuation and the two-frequency mutual coherence function (Γ) for millimeter wave propagation in the sand and dust storm are studied. According to the log-normal size distribution of the sand particles, the millimeter wave attenuations induced by the sand and dust storm of different water contents are studied by the Mie theory and the effective permittivity method. On considering particles size distribution and effective permittivity, the Γ differential equation is solved using the analysis and Fourier transform technique. The Γ solution is numerically analyzed. The influence of the sand and dust storm for different water contents on Γ is studied. It is shown that the attenuation evidently increases with the water content in sand particles increasing, when the water content is over 1.00%. Generally, the attenuation can only be neglected for the electromagnetic wave frequency below 10GHz. The influence of the sand and dust storm on Γ is smaller below 100GHz, but the influence of the water content change on Γ is relatively obvious. At 220GHz, the influence on Γ is apparent, but the change of the influence is small with the change of the water content. Therefore, for the exploitation and application channel of higher millimeter wave band, the attenuation and the influence on Γ induced by the sand and dust storm need be considered.
    Investigation on the electromagnetic scattering interaction between the sea surface and the two-dimensional target above it
    WANG Rui;GUO Li-xin;WANG Yun-hua
    J4. 2007, 34(6):  958-963. 
    Abstract ( 2087 )   PDF (704KB) ( 1093 )   Save
    Related Articles | Metrics
    A hybrid method is proposed for the analysis of compound scattered fields between the sea surface and a 2-D target. The Kirchhoff current and scattered field of the rough sea surface are evaluated by using the MOMI (Method of Ordered Multiple Interactions), the polarization current on the target and the scattered field are given by MOM. Associating with the reciprocity theorem, the second-order coupling scattered fields between the rough sea surface and a 2-D cylinder above it are calculated. The size of the system of linear equations produced by the hybrid method becomes much smaller than that by the conventional MOM, so the hybrid method saves the computer memory and reduces the computation time. Numerical results show the validity of the hybrid method and the computational time of our method is only about 12% that by MOM.
    The quantum effect in the inductance-coupling mesoscopic circuit with the charge discreteness
    CUI Yuan-shun
    J4. 2007, 34(6):  964-968. 
    Abstract ( 1646 )   PDF (518KB) ( 1034 )   Save
    Related Articles | Metrics
    In the inductance-coupling mesoscopic circuit, by taking account of the charge discreteness, a method for calculating quantum effects is proposed in the new Fock space that is formed by the eigenstate of charge operator. In this method, by introducting the minimum shift operator, the system Hamilton and the physics current are expressed according to the charge operator and the ladder operator, and the quantum fluctuations of the charge, current and energy are calculated directly by the character of the ladder operator. The obtained results are related with self-inductance closely. In designing the quantum circuit and the nanoelectroic devices, the considerable factors are given for the quantum noise reduction.
    A new and accurate frequency estimation approach based on the phase difference
    ZHANG Hai-ying1;2;YUAN Chao-wei1
    J4. 2007, 34(6):  969-973. 
    Abstract ( 1925 )   PDF (584KB) ( 1595 )   Save
    Related Articles | Metrics
    A method for estimating the frequency of signals based on the phase difference between long and short delay matches is proposed. This method uses the interferometer direction finder principle for reference, that is, small frequency offset estimation by measuring the interframe phase difference of the short delay is used to resolve the indistinct phase problem, and at the same time, estimation by long delay is used to improve precision. A great deal of simulation for various algorithms shows that the new algorithm not only has a good estimation accuracy, but also has a good frequency stability, which can be utilized for hardware implementation of the receiver system.
    A non-certificated Ad hoc key management and authentication model
    LIU Chun1;LIU Jian-wei1;ZHANG Qi-shan1;LI Hui2
    J4. 2007, 34(6):  974-979. 
    Abstract ( 2051 )   PDF (638KB) ( 1075 )   Save
    Related Articles | Metrics
    A new key management and authentication model for Ad hoc networks is proposed. In this model, the elliptic curve combined public key is applied, and the trusted authentication center support is needed only in the key initialization phase. In the operation phase, the self-organized public/private key update, revocation, and shared-private-key-matrix update are implemented with threshold cryptograph. An authentication and key agreement protocol is designed. The interlocutor’s public key is produced by computing, and two-time certificate transmission and verification are therefore reduced in the protocol. Compared with the certificate-based and the identity-based models, the new model is more secure, flexible and efficient. And it is more suitable for the self-organized and resource-constrained features of Ad hoc networks.
    A fast and efficient bind beamforming method for CDMA systems
    LI Jia-jing;JIN Rong-hong;GENG Jun-ping
    J4. 2007, 34(6):  980-985. 
    Abstract ( 2120 )   PDF (988KB) ( 977 )   Save
    Related Articles | Metrics
    A fast and efficient blind beamforming algorithm for DS-CDMA systems is presented. It utilizes the Powell algorithm to determine conjugate searching directions, so as to maximize the combined output of correlators and to form a beam toward the DOA of the desired user by shifting the phase of each element. It simplifies the beamforming system and simulation results show that the proposed algorithm enhances the stability of beamforming and immensely reduces the computational load compared with available methods in literature. Furthermore, it leads to a better beampattern with fewer requirements for the convergence criteria. The number of iterations and multiplications required by this method is approximately 10% that required by the available methods when only one path is received and this will be further reduced to 2% that when two paths exist.
    The jamming mechanism for intense light bomb antagonizing infrared imaging guided-missiles
    Hong Ming1;LIU Shang-qian2;WANG Da-peng3;GAO Guo-wang2
    J4. 2007, 34(6):  986-988. 
    Abstract ( 2139 )   PDF (513KB) ( 1342 )   Save
    Related Articles | Metrics
    The effect and threat of infrared guided-missiles in modern wars are expounded. Aiming at the weakness of an infrared imaging guided-missile with a vulnerable information link, a jamming scheme against infrared imaging guided-missiles is proposed in which the tracking algorithm module in its information link is attacked by using an incoherent intense light bomb, its normal work is misadvised or restrained, the information link from the optical circuit is cut and so on. In virtue of the intense light bomb with a wide radiation wave band and a large action field of view, the jamming method has a few advantages of strong adaptability, high ratio of capability to price, easy operation and so on.
    Prediction of the electromagnetic shadow zone under the atmospheric duct
    JIAO Lin;ZHANG Yong-gang
    J4. 2007, 34(6):  989-994. 
    Abstract ( 1469 )   PDF (1551KB) ( 1116 )   Save
    Related Articles | Metrics
    Atmospheric duct environment changes the normal path of electromagnetic wave propagation, affects the detection of radar and causes the electromagnetic shadow zone of radar. In this paper, we establish two coupling numerical forecasting models to solve the problems on forecasting the radar shadow zone, based on the mesoscale numerical prediction model and the electromagnetic wave propagation mechanism in atmospheric duct environment. The coupling model A is used to predict the top hole in the evaporation duct, the coupling model B is to predict the skip zone in the surface duct. It is concluded that the coupling models are effective to predicting the radar shadow zone.
    Self-adaptive backoff algorithm in IEEE 802.11 with optimum parameter approaching
    ZHU Ying;WU Mu-qing
    J4. 2007, 34(6):  995-1000. 
    Abstract ( 2274 )   PDF (745KB) ( 3033 )   Save
    Related Articles | Metrics
    In order to improve the network performance in congestion status and to achieve or approach the optimum performance in different network scales, a self-adaptive backoff algorithm named SAOP is proposed based on Optimum Parameter approaching. By taking the approximate invariability character of the optimum sending load(ratio of count in collision and success sending), every WLAN station adjusts the self minimum contention window periodically, making current sending load approach the optimum value, to improve the network congestion status. Simulation proves that SAOP can enhances the IEEE 802.11 WLAN saturation throughput by 48%, decreases the delay by 31% when the network scale is 80 stations in the basic access mode, and is close to the theoretical max throughput in the network scale-throughput curve (98% the max throughput on average).

    Genetic algorithm for nonlinear equalization

    JIANG Bo;LI Ai-hong;ZHU Jiang;ZHANG Er-yang
    J4. 2007, 34(6):  1001-1006. 
    Abstract ( 2648 )   PDF (695KB) ( 1042 )   Save
    Related Articles | Metrics
    This paper proposes an improved genetic algorithm for determining the optimal structure of the sparse Volterra filter. The algorithm defines chromosomes as the components of possible solutions instead of possible solutions in the classic genetic algorithm. The chromosomes are encoded with integer, which results in high efficiency. The genetic evolution process starts from the lower-order and short memory nonlinear model, and optimal setting is obtained at the end of the evolution process. Thus, the order and memory length of the nonlinear model needn’t be determined in advance, which avoids the booming expansion of the searching space for the high-order and long memory nonlinear model. The algorithm estimates the sparse kernel vector by the LMS algorithm, and therefore avoids repetitive estimation of the same vector and reduces computation. The simulation is finally carried out by applying the algorithm to nonlinear equalization for the data relay satellite channel, and the results show that the size of seeds group is largely reduced and that the genetic evolution converges faster.
    Research on the equivalent circuit model of the spiral defected ground structure and its applications to microwave circuits
    YANG Jin-ping;WU Wen
    J4. 2007, 34(6):  1007-1010. 
    Abstract ( 2133 )   PDF (1109KB) ( 1133 )   Save
    Related Articles | Metrics
    The tri-order lumped equivalent circuit model and modeling method for a spiral defected ground structure (SP-DGS) are proposed, which are used in novel designs of an elliptic function low-pass filter and a dual-band Wilkinson power divider. Simulations agreement with measured results show the validity of the proposed approach and its benefits to implement microwave circuits effectively.
    Particle simulation of a GW compact L-band coaxial relativistic backward wave oscillator
    GE Xing-jun;YANG Yi-ming;ZHONG Hui-huang;QIAN Bao-liang
    J4. 2007, 34(6):  1011-1014. 
    Abstract ( 2110 )   PDF (758KB) ( 921 )   Save
    Related Articles | Metrics
    A coaxial compact L-band coaxial relativistic backward wave oscillator is investigated using the 2.5 D particle simulation code. Detailed physical interaction pictures of the oscillator are presented. Simulation results show that for an electron beam of 700keV and 10kA, a microwave of coaxial TM<sub>01</sub> mode is generated with power of 2.2GW and frequency of 1.60GHz when the external guiding magnetic field is about 0.9T. The beam to microwave efficiency is about 30%. The optimized electromagnetic structure of the device is only 100mm×520mm.
    Application of the Mean shift algorithm in steel strip image segmentation
    YANG Shui-shan1;HE Yong-hui2;ZHAO Wan-sheng1;PENG Tie-gen2
    J4. 2007, 34(6):  1015-1018. 
    Abstract ( 2654 )   PDF (904KB) ( 1070 )   Save
    Related Articles | Metrics
    Defect segmentation results affect the precision of classification in the automatic strip surface defect detection system. In order to obtain a better result, the mean shift algorithm is presented to segment the defects in strip images. The mean shift algorithm is used to smooth the region of interest in the image and detect the defect’s edge, and its effectiveness is compared with that of the median filter. Test results show that it can smooth strip images effectively and can detect the edges of defect objects accurately. The mean shift algorithm can work effectively in strip image segmentation.