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Table of Content

    20 December 2008 Volume 35 Issue 6
      
    Original Articles
    Robust MIMO zero-forcing receiver in the presence of the channel estimation error
    CHEN Liang;LI Jian-dong;DONG Wei
    J4. 2008, 35(6):  957-962. 
    Abstract ( 2108 )   PDF (819KB) ( 1169 )   Save
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    A robust zero-forcing receiver in the Multiple Input Multiple Output (MIMO) channel with a channel estimation error is presented. By considering the statistics of channel estimation errors, the coefficient of zero-forcing filter is modified with the estimated channel information. The presented receiver is more robust than the traditional ZF receiver in the presence of inaccurate channel information in the receiver. Simulation results show that the BER (bit error rate) is improved and that the error floor is lower than that of the traditional receiver with the same estimation error. In the uncoded 4×4MIMO system with QPSK modulation and if the channel estimation error coefficient equals 0.05, the BER of the traditional ZF receiver is 5×10-3 and that of the presented receiver is 1.8×10-3 at a high SNR. It is also shown that the system with QPSK modulation can work effectively when the estimated channel error is smaller than three times the real channel error.
    Novel timing synchronization algorithm for the uplink of an OFDMA system
    GUO Yi;LIU Gang;GE Jian-hua
    J4. 2008, 35(6):  963-967. 
    Abstract ( 1879 )   PDF (660KB) ( 1080 )   Save
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    The effect of timing offset on OFDMA signals is exploited and a least squares algorithm of timing offset is proposed for OFDMA uplink systems. The phase difference between the sub-carriers of pilot symbols is used to estimate the timing offset. Compared with the conventional algorithms, all the users’ timing offsets are estimated simultaneously and the algorithm suits both the interleaved OFDMA and the sub-band based OFDMA, providing a faster acquisition of synchronization with a lower complexity.
    IP flow-based variable sampling method for network traffic measurement
    PAN Qiao1;2;PEI Chang-xing1
    J4. 2008, 35(6):  968-972. 
    Abstract ( 1468 )   PDF (613KB) ( 1138 )   Save
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    The random packet sampling method is usually employed by traffic sampling measurement. But the accuracy of anomaly detection is affected by the fact that it biases a large IP flow. Based on the IP flow arrival process, a variable sampling method is proposed. According to the attribute of the IP flow, the incoming packets are classified by their flow identifiers and sampling rates are set by their positions in the IP flow. Experimental results show that sampled traffic data improve the accuracy of anomaly detection because the variable sampling method increases the sampling rate of packets in a small IP flow.
    Analysis of a constrained LMS algorithm for MMSE combination
    ZHAO Li;SUN Xian-pu;ZHANG Hai-lin
    J4. 2008, 35(6):  973-977. 
    Abstract ( 1498 )   PDF (532KB) ( 956 )   Save
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    A Constrained least-mean-square (LMS) algorithm is proposed, which is used for an adaptive optimum combination(MMSE criterion) of diversity signals in orthogonal frequency-division multiplexing (OFDM) systems. Compared with the conventional algorithm, the proposed algorithm has no drawback of slow convergence speed when the input signals are highly correlated. Before the received diversity signals are fed to the adaptive filter, they are transformed to have the identical desired response. Then, the transformed signals are optimally combined in the adaptive filter subject to the proposed constraints. The derived analytical expressions indicate that regardless of the input signal correlation matrix, the convergence behavior of the proposed algorithm, in all cases, is only governed by the normalized step size.
    Optimal training design for MIMO-OFDM systems
    LIU Gang;GUO Yi;GE Jian-hua
    J4. 2008, 35(6):  978-982. 
    Abstract ( 1954 )   PDF (596KB) ( 1040 )   Save
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    The problem of optimal training design for channel estimation in MIMO-OFDM systems is investigated. The optimality condition and training structure based on minimizing the channel estimation MSE is analyzed, and a new training sequence is presented. This sequence combines the optimal structures of frequency division multiplexing, time division multiplexing and code division multiplexing, and retains the orthogonality in the time domain, frequency domain and space domain, thus decreasing the effect of the multiple antennas interference and reducing the channel estimation complexity effectively. With a flexible structure, it can be transformed according to channel environment, system parameters, system performance, etc.
    On the number of shortest cycles of Tanner graphs
    CHEN Ru-wei1;2;HUANG Hua-wei3;DU Xiao-ni4;DING Yong2;XIAO Guo-zhen1
    J4. 2008, 35(6):  983-985. 
    Abstract ( 2112 )   PDF (450KB) ( 976 )   Save
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    By the method for investigating the relation between parity-check matrixes and cycles of associated Tanner graphs proposed by Chen et al., the one-to-one correspondence between k-row-combinations satisfying a certain condition in a parity-check matrix of grith k and shortest cycles in the associated Tanner graph is proved. As a consequence, the algorithm for counting the shortest cycels of Tanner graphs proposed by Chen et al. is improved. The improved algorithm is as accurate as the original one while omitting one of the main steps.
    Novel parameter estimation principium about trajectory invariable-information of target elevation information
    LIU Jing-mang1;2;YANG Wan-hai1;YANG Bai-sheng1;ZUO Tao2
    J4. 2008, 35(6):  986-991. 
    Abstract ( 1995 )   PDF (677KB) ( 1129 )   Save
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    According to the author’s Cotangent relations theorem, bearings-only target tracking with linear motion is achieved. For the single/multiple senor measurements including elevations based target tracking problem, theorems for both target trajectory parameters estimation and tracking are proposed. With the supports from the single sensor bearings, and the elevation constants, target elevations are predicted by estimations of target heading angles and the deduced invariable-information of ratios. Then, target parameters estimation by two sensors measurements is analyzed, and the tracking principium by three-sensor synchronous measurements is discussed. Simulation results show the reliability and the practicability of the peoposed algorithms.

    Clutter analysis and range-ambiguous clutter suppression for bistatic airborne radar

    MENG Xiang-dong;WU Jian-xin;WANG Tong;BAO Zheng
    J4. 2008, 35(6):  992-998. 
    Abstract ( 2119 )   PDF (1750KB) ( 1134 )   Save
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    The geometry of every bistatic airborne radar configuration is analysed. A clutter mode with the variable azimuth angle and bistatic range is presented. A formula for calculating the Doppler frequency of receiving clutter in any bistatic configuration is deduced. It is an efficient tool for bistatic clutter analysis. And then a STAP approach to compensating the angle-Doppler difference of mainlobe clutter according to every ambiguous range apart is proposed. The problem of bistatic clutter suppression is solved perfectly.
    Adaptive Least-Squares method for blind source separation with an equivariant property
    ZHANG Wei-tao1;LOU Shun-tian1;ZHANG Yan-liang1;2
    J4. 2008, 35(6):  999-1002. 
    Abstract ( 1810 )   PDF (534KB) ( 976 )   Save
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    Equivariant adaptive blind source separation algorithms require a serial update rule for the demixing matrix. From the point of view of relative gradient proposed by Cardoso, we optimize a nonlinear principal component analysis criterion. Then a modified recursive least-squares (RLS) algorithm for serial updating of the demixing matrix is presented. The equivariant property is guaranteed due to the serial updating rule used at each iteration. To speed up the convergence, the singular value decomposition is employed together with the stiefel manifold projection of the demixing matrix. Computer simulation results demonstrate the effectiveness of the algorithm.
    Study of OSTBC and eigen-beamforming with antenna array groups
    WANG Yong1;LIAO Gui-sheng1;YE Zi2;WANG Xi-yuan1
    J4. 2008, 35(6):  1003-1008. 
    Abstract ( 1868 )   PDF (686KB) ( 1036 )   Save
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    This paper investigates a novel scheme combining spatial multiplexing with beamforming in spite of the contradictive requirement of antenna element spacing. The proposed scheme combines spatial multiplexing with beamforming of space-time block coding, which has the advantages of both techniques. The diversity gain is achieved by beamforming, and the multiplexing gain by spatial multiplexing according to different antenna array groups. The performance analysis and simulation results of the single antena array are shown to be dependent on the DOA and AS. However, the multiple antenna array is shown to have a stable performance independent of DOA and AS. Simulation results indicate that multiple antenna array can improve performnace by 12dB compared with the single antenna arrays when the direction of arrival is 0 angles and the angular spread is 50 angles. The performance will be improved obviously if the angular spread becomes smaller.
    Estimation of the number of sources based on spatial smoothing
    AN Zhi-juan1;2;SU Hong-tao2;BAO Zheng2
    J4. 2008, 35(6):  1009-1014. 
    Abstract ( 2253 )   PDF (594KB) ( 1754 )   Save
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    In the context of a small number of snapshots or unequal noise levels the noise eigenvalues of the covariance matrix are spreading, which results in the performance deterioration of the Akaike information criterion(AIC) and the Minimum Description Length(MDL). In this paper the Spatial Smoothing AIC(SSAIC) and Spatial Smoothing MDL(SSMDL) are presented. By spatial smoothing the spreading of the noise eigenvalues can be reduced remarkably, and hence the probability of correct detection can be increased, in addition, the consistency of the SSMDL is proved in detail. Finally, simulation results show that the SSAIC and SSMDL can improve the probability of correct detection remarkably.
    Difference-frequency coupling in nonlinear left-handed metamaterials
    CHEN Liang;LIANG Chang-hong;WU Bian;ZHU Cheng
    J4. 2008, 35(6):  1015-1019. 
    Abstract ( 1591 )   PDF (974KB) ( 1164 )   Save
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    Based on the nonlinear electromagnetic theory, general coupled-mode equations for difference-frequency coupling in nonlinear left-handed metamaterials(LHM) are studied. The co-directed energy conversion process and spatial distribution of the signal wave and difference-frequency wave under the phase-matching condition are investigated. It is shown that through a finite LHM slab, more output power of the signal wave and difference-frequency wave than through an RHM slab with the same thickness can be obtained. For this peculiar property, the nonlinear LHM may be utilized to design novel compact RF/microwave amplifiers. And through parameters adjustment of the material to control left-handed or right-handed properties, compact microwave amplifiers of the tunable output direction may be realized.
    Design of a highly efficient Doherty power amplifier for the OFDM system
    CHEN Xiao-qun;GUO Yu-chun;SHI Xiao-wei
    J4. 2008, 35(6):  1020-1025. 
    Abstract ( 1757 )   PDF (852KB) ( 1116 )   Save
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    An inverted Doherty power amplifier is proposed for the OFDM with the characteristic of high power to average power ratio (PAPR). The inverted structure changes its combining node from the end of the peak amplifier to the carrier amplifier, which improves the efficiency of load modulation in the carrier amplifier. Compared with the conventional Doherty power amplifier, the power added efficiency (PAE) of the proposed amplifier is improved by 3% due to its effective impedance modulation. Measurement results show that the PAE of the proposed amplifier remains about 27.8% with 10dB output power back-off. Its third-order intermodulation distortion (IMD3) and adjacent channel power ratio (ACPR) are improved by 2.5dB and 2dB respectively,which could be applied to OFDM communication well.
    Analysis and calculation of ground loss resistance for a VLF T-type antenna array with the ground screen
    LIU Chao1;2;LIANG Yu-jun2;LIU Qi-zhong1;FU Yun2
    J4. 2008, 35(6):  1026-1030. 
    Abstract ( 2025 )   PDF (685KB) ( 1231 )   Save
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    The methods for calculating the ground loss resistance of a very low frequency (VLF) T-type antenna array with the ground screen are studied. The magnetic field loss produced by the currents on antenna top wires of an arbitrary length is introduced to the classical analytical method. Based on the numerical simulation results of the near fields by the method of moments, the numerical integration of the ground loss power for an antenna array are calculated and a numerical method for computing the loss resistance of the ground screen is established. The loss resistance of the grounding system of a typical antenna array is computed using these two methods respectively. Results agree well with the measured data, and the precision is 30%~50% better than that of the classical analytical method.
    Echo cancelling algorithm for the LFM radar
    WANG Yu-jun1;2;ZHAO Guo-qing1;WANG Hong-wei1
    J4. 2008, 35(6):  1031-1035. 
    Abstract ( 1662 )   PDF (753KB) ( 1192 )   Save
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    A new algorithm is proposed for radar echo cancelling based on the group delay of the LFM (Linear Frequency Modulated) signal. Firstly, the received signal is multiplied by the conjugation of its delayed version to get the frequency difference between them. The received signal’s frequency is then shifted using the frequency difference. According to the target’s RCS(Radar Cross Section), phase and amplitude modulation are made in order to get the signal having the same frequency as the echo pulse but with the opposite phase. This signal cancels the radar echo signals. One of the jammer structures which can realize the algorithm is given and the method for reducing nonlinear phase errors is presented. Theoretical analysis and simulation show that the novel algorithm effectively reduces the signal power received by the radar receiver even when the chirp rate is unknown.The algorithm is also workable when the jammer has a large time delay.
    Novel 0.5V bulk driven full differential Amp
    ZHANG Huan-qian1;2;YANG Yin-tang1;ZHU Zhang-ming1
    J4. 2008, 35(6):  1036-1040. 
    Abstract ( 1855 )   PDF (689KB) ( 1151 )   Save
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    In oder to meet the needs of the low voltage-low power circuit application, a full differential amplifier operating at the 0.5V power supply with bulk inputs is introduced. A prototype was designed in a standard 0.18μm CMOS process using 0.5V threshold voltage devices. This amplifier uses the bulk driven as the input stage and the subthreshold operating device as the output stage. The two stages have their own local common mode feedback. Simulation results indicate that this amplifier has a 60dB DC gain, a 5.4MHz gain-bandwidth and consumes 138μW.
    Measurement and analysis of RTS noise in nano-MOS devices
    ZHANG Peng;ZHUANG Yi-qi;BAO Li;MA Zhong-fa;BAO Jun-lin;LI Wei-hua
    J4. 2008, 35(6):  1041-1045. 
    Abstract ( 1695 )   PDF (732KB) ( 1006 )   Save
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    A virtual-instrument based measurement and analysis method for RTS noise in nano-MOS devices is presented. After a systematic computation of both difference analysis and Gaussian function fitting, and digital filtering and exponential function fitting, the relative amplitudes and time constants of RTS noise are obtained, respectively. Verified by experimental characterization of RTS noise in 90nm MOSFETs, this new method not only manifests higher efficiency, but also needs just 1/10 sample points of the traditional method under the same requirements of measuring precision.
    Study of photoconductive switches transmission line based on D’Alembert’s method
    ZHU Yan-wu1;SHI Shun-xiang1;SUN Yan-ling1;FENG Xiang-chu2;LIU Ji-fang1
    J4. 2008, 35(6):  1046-1050. 
    Abstract ( 1851 )   PDF (653KB) ( 1193 )   Save
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    D’Alembert’s method is used to analyze the Photoconductive Switches transmission line. A total reflection border and the implementation of a new field source excitation for the finite-difference time-domain method are built to satisfy D’Alembert’s method. The electrical pulse generation and propagation by Photoconductive Switches (PCSS) microstrip line are simulated by the finite-difference time-domain method and the effect of Blumlein line geometrics on the pulse amplitude is acquired An ultra short bipolar pulse generator based PCSS is developed and analyzed. The good agreement of experimental results with the simulated values shows that D’Alembert’s method coupled with the finite-difference time-domain method could be used to study and accurately analyze the pulse circuit from the electromagnetic viewpoint.
    Improved two-frequency method with the four-element circuit model for the novel HfO2 as the gate dielectric
    LIU Hong-xia;CAI Nai-qiong
    J4. 2008, 35(6):  1051-1055. 
    Abstract ( 1626 )   PDF (776KB) ( 937 )   Save
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    For the MOS capacitance with the ultra thin hafnium oxide, an equivalent four-element circuit model including the additional series resistance and series inductance is proposed to be employed in the two-frequency C-V correction. These extracted parameters by independently measuring the capacitor at two different frequencies eliminate the frequency dispersion at high frequencies. The corrected C-V curves agree with the theoretical calculation very well. The parameters are extracted, and the relationships between the components’ values, the capacitance area and the inversion layer thickness are also presented in the paper. Experimental and theoretical results show that the model can be incorporated in the routine C-V measurement procedure and provide more accurate data.

    Study of algorithm on data race and deadlock detection for BPEL process
    CHEN Sheng;BAO Liang;CHEN Ping;HU Sheng-ming;WANG Meng
    J4. 2008, 35(6):  1056-1062. 
    Abstract ( 1607 )   PDF (796KB) ( 1004 )   Save
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    The business process always suffers from notorious problems, such as data race and deadlock. Moreover, these problems are extremely difficult to track down by testing and debugging. This paper proposes a novel detection approach for the BPEL process, which is based on the graph theory. The approach first transforms the BPEL process into a graphic model-BSG (BPEL Segment Graph). Then, the deadlocks are detected by finding strongly connected components of BSG. Meanwhile, data races are detected by determining the partial order among nodes in BSG, which in turn can be attained by deciding the reachability among them. It also employs the technique of constraint solving to enhance the accuracy of the detection result. Data races and deadlocks can be effectively detected by this approach, as demonstrated by practical application, thus enhancing the reliability of BPEL processes.
    Analysis of provably secure on-demand distance vector routing in MANET
    MAO Li-qiang1;MA Jian-feng1;2
    J4. 2008, 35(6):  1063-1068. 
    Abstract ( 1590 )   PDF (704KB) ( 944 )   Save
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    Based on the simulation paradigm, Acs et al proposed a formal model tailored to the security analysis of on-demand distance vector routing protocols in MANET, and a routing protocol, called ARAN, was proven secure in the model. We indicate the improper manipulations such as mergence of the adjacent adversarial nodes, the improper definition of the correct system state in the model, and the flaw in the proof for ARAN. A new attack to ARAN is presented, which shows that ARAN is not provably secure even in their model.
    Pointers in framing projection temporal logic programming languages
    WANG Xiao-bing;DUAN Zhen-hua
    J4. 2008, 35(6):  1069-1074. 
    Abstract ( 1626 )   PDF (550KB) ( 976 )   Save
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    A new method is presented for formalizing pointers and its implementation in Framed Tempura which is a framing Projection Temporal Logic programming language. It extends the Projection Temporal Logic and gives formal definitions of pointers reference and dereference based on name constants, and then by use of the frame operator and minimal model gives the implementing way in Framed Tempura which is an executable subset of the Projection Temporal Logic. An example for in place reversal of a singly linked list shows this method is workable.
    Image de-noising algorithm based on total variation and wavelet transform
    CHEN Li-xia1;2;DING Xuan-hao2;SONG Guo-xiang1;SUN Xiao-li1
    J4. 2008, 35(6):  1075-1079. 
    Abstract ( 1919 )   PDF (1163KB) ( 1260 )   Save
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    Based on the standard ROF model, an improved method for image de-noising is proposed. In order to overcome the weakness that edge information is sensitive to noise and prone to blur of the ROF model while de-noising, in the new algorithm, the anisotropic diffusion function is introduced, and the magnitude of wavelet transform is substituted for the module of the gradient operator, which makes the new model more robust and diffuse according to the characteristic of the image, and therefore, the edges are preserved better. Experiments show that there is an increase of about 1.5dB on average in the signal to noise ratio and a remarkable improvement on the visual effect.
    Space support vector domain classifier
    LIANG Jin-jin1;LIU San-yang1;WU De2
    J4. 2008, 35(6):  1080-1083. 
    Abstract ( 1734 )   PDF (541KB) ( 965 )   Save
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    A space support vector domain classifier (SSVDC) is proposed. In the training process, the support vector domain description (SVDD) is applied to both the positive and negative classes, disconnect regions are obtained according to the description boundaries and different classification rules are erected for the corresponding regions. In the test phase, the distances from the test sample to each hypersphere centers are computed, the region that the test samples belong to is confirmed according to the relations between their central distances and the hyperspheres radii, so that corresponding rules can be adopted. Numerical experiments on UCI data show that compared with existing algorithms SVM and SVDC, SSVDC has better robustness, a shorter training time of about 20.6% SVM and a classification accuracy which is about 45.9% higher than that of SVDC in the best case.
    Analysis and design of a phased array antenna with a shaped pattern
    GAO Jun;CAO Xiang-yu;ZHANG Guang;WEN Xi
    J4. 2008, 35(6):  1084-1088. 
    Abstract ( 1593 )   PDF (807KB) ( 1627 )   Save
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    A phased array antenna, which scans in the elevation plane with the shaped pattern in the azimuth plane, is analyzed and designed. The printed dipole is used as radiating elements. The fed current distribution in the scan plane adopts the Taylor amplitude illumination function in order to obtain a low sidelobe lever. The technology of virtual displacement with 4bit digital phase shifters instead of 9bit is used to satisfy the smallest steering increment of 0.2°, which simplifies facilities and lowers the cost. It is proved by reliable tests that within the scanning range of ±15°, the half power beamwidth is less than 2.3°, that the gain is higher than 25dB, that the sidelobe lever is lower than -25dB, and that the shaped beam width is 33°, which perfectly satisfs the requirements.
    On the computation of the distance spectrum for punctured convolutional codes
    NIU Lan-qi1;2;ZHANG Tai-yi1;ZHANG Jing1
    J4. 2008, 35(6):  1089-1093. 
    Abstract ( 1753 )   PDF (591KB) ( 1217 )   Save
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    For the optimum design problem of punctured convolutional codes based on the distance spectrum, an efficient computing method of the distance spectrum for punctured convolutional codes is proposed. A state transition matrix sequence is constructed with the state graph and punctured pattern, and the product of the matrix sequence is used to compute the transfer function and distance spectrum; furthermore, a state reduction algorithm for computing the transfer function is proposed to avoid the inverting operation of the symbolic matrix. Analyses and simulation results show that this method for computing the distance spectrum can provide efficiency and practicability, and may be used for optimal design or theoretical analysis.
    Improved certificateless signature scheme
    MING Yang1;ZHAN Yang2;WANG Yu-min2;PANG Liao-jun2
    J4. 2008, 35(6):  1094-1099. 
    Abstract ( 1638 )   PDF (530KB) ( 1050 )   Save
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    Based on the bilinear pairing, an improved certificateless signature scheme is presented to overcome the Yap-Heng-Goi scheme’s drawback that it is vulnerable to public key replacement attacks. This proposed scheme uses a short signature to generate the user’s partial private key which straightly constructs the private key with the secret value chosen by the user. Two Hash functions are used to generate signatures in the signature algorithm. The correction of the public key can be checked implicitly by verifying the signature, and thus the Yap-Heng-Goi scheme’s security problem is solved. In the proposed scheme, no pairing computation is needed in the signing algorithm and the verification algorithm requires only three pairings computations. A security analysis shows that the proposed scheme is proved secure against existential forgery on an adaptively chosen message attack under the assumption of Computational Diffie-Hellman in the random oracle model.
    New design of ternary low correlation zone sequence sets
    LI Sheng-qiang1;2;HUANG Hua-wei2;ZHANG Ning2;XIAO Guo-zhen2
    J4. 2008, 35(6):  1100-1104. 
    Abstract ( 1383 )   PDF (472KB) ( 904 )   Save
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    A column sequence set of period 3m+1-1 is devised by the idea of confusion and balance from the ternary sequences of period 3m-1 with the ideal autocorrelation property proposed by Helleseth et al., and new ternary low correlation zone sequence sets of period 3n-1 are constructed by using the column sequence set, where m and n are different positive integers with (m+1)|n. The conclusion shows that the low correlation zone sequence sets are optimal with respect to the Tang-Fan-Matsufuji bound and can be applied to practical quasi-synchronous(QS) CDMA systems.
    Water-filling precoder for single-carrier communication systems
    LI Hai-tao;LIN Xiao-kang
    J4. 2008, 35(6):  1105-1109. 
    Abstract ( 1913 )   PDF (677KB) ( 1343 )   Save
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    A water-filling precoder is proposed for shaping the spectrum of transmitted signals in single-carrier systems over inter-symbol interference (ISI) channels. This precoder can be efficiently implemented in the frequency domain without incurring extra receiver complexity. Furthermore, it does not increase the required length of the cyclic prefix (CP). It is proved in the information theory that with the water-filling precoder, superposition codes can achieve the ISI channel’s capacity with linear-minimum-mean-square-error (LMMSE)-based frequency domain equalization. Simulation results based on single-layer convolutional codes show that a power gain of 1~2dB can be achieved by the water-filling precoder.
    Digital forward sampling on the transient pulsant signal
    CHENG Xiao-lei1;2;FAN Ru-yu1;2
    J4. 2008, 35(6):  1110-1114. 
    Abstract ( 1475 )   PDF (1291KB) ( 1070 )   Save
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    This paper describes the trouble and the limitations of common sampling on the transient pulsant signal. To solve these troubles, this paper mainly introduces the theory and example design of digital forward sampling. The delay of the key signal in an analog circuit is substituted by a technology called’forward circulatory storing’ in the digital circuit. We can get the whole pulse of the input signal and keep the signal integrality synchronously thanks to the digital forward sampling theory. This design is validated by FPGA simulation and used in the work of “Transient Pulse’s A/D Conversion”. This conversion system can store 4kbyte data with the rate of 500Mbyte/s by the best FPGA we have chosen.
    Adaptive leaky factor selection algorithm for AR-FGS
    DENG Yun1;2;PENG Qiang1;ZHU Chang-qian1
    J4. 2008, 35(6):  1115-1120. 
    Abstract ( 1981 )   PDF (702KB) ( 927 )   Save
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    AR-FGS (Adaptive Reference for Fine Granular Scalable) adopts leaky prediction to achieve a better tradeoff between coding efficiency and robustness. The leaky factor is crucial to the performance of leaky prediction. This paper proposes an adaptive method for determining the optimal leaky factor for each frame. First, the disadvantage of the bit-stream extraction method used in the current JSVM (Joint Scalable Video Model) is analyzed that the bit-rate of extracted sub-steam is not smooth at the frame level. To guarantee the smoothness, a modified extraction method is presented which truncates each frame at the fixed total bit-rate. The proposed leaky factor determination algorithm sets the optimal leaky factor for each frame according to the ratio of current reference frame’s base layer bit-rate to that of the first I-frame’s. The optimal leaky factor is further adjusted according to the ratio of several previous frames’ average base layer bit-rate to that of current reference frame’s. Simulation results show that the proposed algorithm can further improve the PSNR over a wide range of bit-rate, compared with the use of the fixed leaky factor. Additionally, the bit-rate of sub-stream extracted by the modified bit-stream extraction method is smooth at the frame level.
    Novel proactive spectrum selection algorithm for cognitive radio networks
    GUO Cai-li;ZENG Zhi-min;FENG Chun-yan;LIU Fang-fang
    J4. 2008, 35(6):  1121-1126. 
    Abstract ( 2268 )   PDF (659KB) ( 1224 )   Save
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    To improve the persistence of spectrum allocations in cognitive radio networks, a primary user spectrum-usage model based on the alternative renewal process is given, and the spectrum utilizable rate and stability are defined as parameters to evaluate the quality of the usable spectrums, on the basis of which a novel Proactive Spectrum Selection Algorithm (PSSA) is proposed. By estimating the spectrum availability metric and the probability of a spectrum opportunity satisfying application requirements of cognitive radio users, the PSSA selects a spectrum with higher availability and opportunity probability to access. It achieves a cross-layer optimization between PHY/MAC and application layers. Simulation results show that the PSSA significantly reduces the collision rate and that it also has been proved to be a well self-adaptive method by adjusting weights of spectrum parameters and the spectrum usability threshold.
    Digital image watermark algorithm based on Hermit matrix perturbation
    ZHANG Bo1;LI Xiao-bin2;HOU Biao3
    J4. 2008, 35(6):  1127-1130. 
    Abstract ( 1936 )   PDF (739KB) ( 1024 )   Save
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    In order to solve the contradiction between the robustness and invisibility of the digital image watermark, a new digital image watermarking algorithm is presented. Based on the character that the greater singular value of the Hermit matrix is not sensitive under some perturbation, the algorithm chooses the greater singular value of the original image as the watermark, which is both invisible and has better resistivity to the attack of noise, geometry and filt on the image.