Email alert
2004 Vol. 26, No. 9
Display Method:
2004, 26(9): 1345-1350.
Abstract:
An effective algorithm is proposed to estimate multipath time delays in a CDMA chip under low SNR environment. Firstly, a power delay profile of multipath is constructed which can restrain effect of noise. Then the estimation algorithm that has super resolution is deduced based on the function. A detailed estimation process and analysis of the performance of this approach are given. Finally, comparsion and performance simulation demonstrate that the method can effectively estimate the delay of multipath in a CDMA chip under low SNR environment.
An effective algorithm is proposed to estimate multipath time delays in a CDMA chip under low SNR environment. Firstly, a power delay profile of multipath is constructed which can restrain effect of noise. Then the estimation algorithm that has super resolution is deduced based on the function. A detailed estimation process and analysis of the performance of this approach are given. Finally, comparsion and performance simulation demonstrate that the method can effectively estimate the delay of multipath in a CDMA chip under low SNR environment.
2004, 26(9): 1351-1357.
Abstract:
A new expression for the Bit Error Rate(BER) of a Direct-Sequence Code-Division Multiple-Access (DS-CDMA) system with non-ideal channel estimation in a frequency-selective Rayleigh fading channel is derived and evaluated. The analysis assumes an arbitrary number of independent, but non-identical resolvable paths combined by the conventional Maximal Ratio Combining(MRC) algorithm which is known to produce maxi-mal signal-to-noise ratio for diversity channels with equal noise powers and perfect channel estimates. The results obtained show that in such systems, the effects of non-identical fading and the channel estimation error on system performance cannot be ignored.
A new expression for the Bit Error Rate(BER) of a Direct-Sequence Code-Division Multiple-Access (DS-CDMA) system with non-ideal channel estimation in a frequency-selective Rayleigh fading channel is derived and evaluated. The analysis assumes an arbitrary number of independent, but non-identical resolvable paths combined by the conventional Maximal Ratio Combining(MRC) algorithm which is known to produce maxi-mal signal-to-noise ratio for diversity channels with equal noise powers and perfect channel estimates. The results obtained show that in such systems, the effects of non-identical fading and the channel estimation error on system performance cannot be ignored.
2004, 26(9): 1358-1363.
Abstract:
This paper proposes a general model and approach to analyze the bidirectional call-overflow scheme for an arbitrary Hierarchical Cellular System (HCS) with N layers, as illustrated by a 4-layer HCS. By setting different parameters, the proposed approach can be used to analyze various overflow schemes in any HCS with multiple layers, such as unidirectional or bidirectional overflows or partial overflows.
This paper proposes a general model and approach to analyze the bidirectional call-overflow scheme for an arbitrary Hierarchical Cellular System (HCS) with N layers, as illustrated by a 4-layer HCS. By setting different parameters, the proposed approach can be used to analyze various overflow schemes in any HCS with multiple layers, such as unidirectional or bidirectional overflows or partial overflows.
2004, 26(9): 1364-1370.
Abstract:
A method of position locating and tracking using pilot .sequence transmitted by the single CDMA Base Stations(BS) for 3-D moving targets is presented in this paper. First, based on the fact that the interfering component is different from the signal reflected by the moving target in the Doppler shift and the property of the auto-correlation function of PN sequence, the interfering component is filtered and the Time Difference Of Arrival(TDOA) is estimated. Then, position location is obtained using the method similar to Chan(1994). Finally, considering the fact that the motion of target is linear with constant speed vector in short duration, the accuracy of position location is improved and the velocity of target is estimated. Its effectiveness is verified by the simulation results.
A method of position locating and tracking using pilot .sequence transmitted by the single CDMA Base Stations(BS) for 3-D moving targets is presented in this paper. First, based on the fact that the interfering component is different from the signal reflected by the moving target in the Doppler shift and the property of the auto-correlation function of PN sequence, the interfering component is filtered and the Time Difference Of Arrival(TDOA) is estimated. Then, position location is obtained using the method similar to Chan(1994). Finally, considering the fact that the motion of target is linear with constant speed vector in short duration, the accuracy of position location is improved and the velocity of target is estimated. Its effectiveness is verified by the simulation results.
2004, 26(9): 1371-1375.
Abstract:
In mobile communication systems, the work upon grouping multipath signal is very important always. An algorithm is proposed which firstly separates user signals and multipath signals in system, then estimates DOA of them. Because this algorithm does not need spread spectrum to identify multipath signals, it not only can be adopted in CDMA system, but also can be applied to GSM system.
In mobile communication systems, the work upon grouping multipath signal is very important always. An algorithm is proposed which firstly separates user signals and multipath signals in system, then estimates DOA of them. Because this algorithm does not need spread spectrum to identify multipath signals, it not only can be adopted in CDMA system, but also can be applied to GSM system.
2004, 26(9): 1376-1382.
Abstract:
The time-varying channel estimation methods for OFDM systems based on pilot tones are investigated. Grouped and equispaced pilot tones are used to estimate the Channel Impulse Response (CIR) of some given moments. The CIR of other moments over one OFDM symbol are estimated by a new low-pass interpolation method proposed in this paper. The simulation results show that the Normal Mean-Square Error (NMSE) of the proposed method is smaller than the linear interpolation method and model-based interpolation method.
The time-varying channel estimation methods for OFDM systems based on pilot tones are investigated. Grouped and equispaced pilot tones are used to estimate the Channel Impulse Response (CIR) of some given moments. The CIR of other moments over one OFDM symbol are estimated by a new low-pass interpolation method proposed in this paper. The simulation results show that the Normal Mean-Square Error (NMSE) of the proposed method is smaller than the linear interpolation method and model-based interpolation method.
2004, 26(9): 1383-1388.
Abstract:
Based on the Least Mean Squares (LMS) principle, an online calibration algorithm with an auxiliary signal source is presented, and its improved algorithm is also given. These algorithms can be applied to the non-uniform array, and to the number of user greater than the number of antenna as well. Computer simulation demonstrates that they are effective.
Based on the Least Mean Squares (LMS) principle, an online calibration algorithm with an auxiliary signal source is presented, and its improved algorithm is also given. These algorithms can be applied to the non-uniform array, and to the number of user greater than the number of antenna as well. Computer simulation demonstrates that they are effective.
2004, 26(9): 1389-1394.
Abstract:
In this paper the optimum design of an adaptive modulation based on uncoded MQAM modulation assisted by wireless channel prediction for the flat Rayleigh fading chan-nel is discussed. By studying how a known prediction error variance will affect the optimized transmission properties, optimum solutions for the rate are derived based on the predicted SNR and the prediction error variance. And the data rate is adapted to maximize the spectral efficiency subject to average bit error rate constraints. The numerical results by simulations show that it adjusts the link adaptation better to the true channel conditions and improves the overall system performance.
In this paper the optimum design of an adaptive modulation based on uncoded MQAM modulation assisted by wireless channel prediction for the flat Rayleigh fading chan-nel is discussed. By studying how a known prediction error variance will affect the optimized transmission properties, optimum solutions for the rate are derived based on the predicted SNR and the prediction error variance. And the data rate is adapted to maximize the spectral efficiency subject to average bit error rate constraints. The numerical results by simulations show that it adjusts the link adaptation better to the true channel conditions and improves the overall system performance.
2004, 26(9): 1395-1400.
Abstract:
By using an m-sequence controlling a traditional feedforward stream cipher, this paper constructs a new feedforward network whose sequences have ideal balance, large period and linear complexity, it can also resist on linear approaching attack and correlation attack, at the same time it inherits the virtues of Bent functionss even Walsh spectra.
By using an m-sequence controlling a traditional feedforward stream cipher, this paper constructs a new feedforward network whose sequences have ideal balance, large period and linear complexity, it can also resist on linear approaching attack and correlation attack, at the same time it inherits the virtues of Bent functionss even Walsh spectra.
2004, 26(9): 1401-1406.
Abstract:
In this paper, the encryption property of the chaotic system in terms of the techniques developed in the analysis of chaotic time series is studied. Then, the typical Lorenz system is analyzed. It is found that the larger sampling interval is of huge help for improving the encryption property. The VWK(Volterra-Wiener-Korengerg) method is used to analyze and test. Finally, simulation on the computer gets the same result.
In this paper, the encryption property of the chaotic system in terms of the techniques developed in the analysis of chaotic time series is studied. Then, the typical Lorenz system is analyzed. It is found that the larger sampling interval is of huge help for improving the encryption property. The VWK(Volterra-Wiener-Korengerg) method is used to analyze and test. Finally, simulation on the computer gets the same result.
2004, 26(9): 1407-1412.
Abstract:
This article analyzes the main security problems that current mobile agent sys-tems face with and existing solving methods, then a secure transport model of mobile agent based on hybrid encryption HESTM is brought forward. The model comprises two parts: (1) Using hybrid encryption encrypt mobile agent; (2) Using TLS encrypts communication channel. The simulation and performance analysis show that HESTM can eiRciently pro-tect the transport security of mobile agent indeed, thus enhance the security and robustness of the whole system. This algorithm has been successfully applied in authors developed prototype-mobile agent based intrusion detection system.
This article analyzes the main security problems that current mobile agent sys-tems face with and existing solving methods, then a secure transport model of mobile agent based on hybrid encryption HESTM is brought forward. The model comprises two parts: (1) Using hybrid encryption encrypt mobile agent; (2) Using TLS encrypts communication channel. The simulation and performance analysis show that HESTM can eiRciently pro-tect the transport security of mobile agent indeed, thus enhance the security and robustness of the whole system. This algorithm has been successfully applied in authors developed prototype-mobile agent based intrusion detection system.
2004, 26(9): 1413-1419.
Abstract:
In order to solve problems of modular algorithm, a multi-dimensional packet classification algorithm that uses trees divided by value is presented in this paper. It supports increment of rules dimension and scale. Moreover, it can deal with prefix match and range match. The simulation result shows that the algorithm is scalable and practical for large-scale rules.
In order to solve problems of modular algorithm, a multi-dimensional packet classification algorithm that uses trees divided by value is presented in this paper. It supports increment of rules dimension and scale. Moreover, it can deal with prefix match and range match. The simulation result shows that the algorithm is scalable and practical for large-scale rules.
2004, 26(9): 1420-1425.
Abstract:
The cascades model proposed recently from self-similar and multifractal model stem can be used to analyze network traffic comprehensively. This- paper, therefore, puts forward an integrated process using cascades model in pattern of wavelet transform to analyze network traffic and further justifies the feasibility of the method. Meanwhile, it emphasizes specifically that, the cumulant sequences of the sequences denoting the number of packet arrivals in unit time and that of inter-arrival time between packets, instead of either of both.should be considered as the stochastic process of the model.
The cascades model proposed recently from self-similar and multifractal model stem can be used to analyze network traffic comprehensively. This- paper, therefore, puts forward an integrated process using cascades model in pattern of wavelet transform to analyze network traffic and further justifies the feasibility of the method. Meanwhile, it emphasizes specifically that, the cumulant sequences of the sequences denoting the number of packet arrivals in unit time and that of inter-arrival time between packets, instead of either of both.should be considered as the stochastic process of the model.
2004, 26(9): 1426-1432.
Abstract:
By using the relation of neighboring data, an improved Viterbi algorithm is proposed and extended it to SOVA decoding of Turbo code in this paper. Simulation results show that, the improved algorithm has reduced-implementation-complexity and lower power consumption. With the proposed algorithm, it is achieved that reduction of 20% in the size and power consumption of survivor memory and reduction of 30% in the size and power consumption of trace back unit in Viterbi decoding. Furthermore, the improvement can achieve reduction of about 15% in the size and power consumption of reliability metric memory and output unit or save half iterations in soft-decision output Viterbi algorithm of Turbo code.
By using the relation of neighboring data, an improved Viterbi algorithm is proposed and extended it to SOVA decoding of Turbo code in this paper. Simulation results show that, the improved algorithm has reduced-implementation-complexity and lower power consumption. With the proposed algorithm, it is achieved that reduction of 20% in the size and power consumption of survivor memory and reduction of 30% in the size and power consumption of trace back unit in Viterbi decoding. Furthermore, the improvement can achieve reduction of about 15% in the size and power consumption of reliability metric memory and output unit or save half iterations in soft-decision output Viterbi algorithm of Turbo code.
2004, 26(9): 1433-1439.
Abstract:
This paper proposes the optimum detection algorithm for a multiple antenna system based on the Maximum A Posteriori (MAP) criterion. It makes symbol-by-symbol decisions so that the probability of a symbol error is minimized. It also shows that the radial basis function neural network has an identical structure to the proposed MAP algorithm and, therefore, can be employed in a multiple antennas system.
This paper proposes the optimum detection algorithm for a multiple antenna system based on the Maximum A Posteriori (MAP) criterion. It makes symbol-by-symbol decisions so that the probability of a symbol error is minimized. It also shows that the radial basis function neural network has an identical structure to the proposed MAP algorithm and, therefore, can be employed in a multiple antennas system.
2004, 26(9): 1440-1448.
Abstract:
In this paper, an image content based perceptual watermarking model using ridgelet transform is presented. It provides a new visual model, which can exactly evaluate the Just Noticeable Distortion (JND) tolerance of human visual system. The watermarking algorithm is designed to address the issue of how to improve the robustness and the security of the embedded watermark according to the image content. In order to improve the robustness and transparency, the watermark bits are inserted in the visual significant ridgelet coefficients without exceeding the maximum strength of JND. With the spread spectrum technique and the secret key protection, the security of the embedded watermark is also guaranteed very well. Through analyzing the statistical property of the watermarked image, a threshold selection method based on Neymann-Pearson principle is presented and then the embedded watermark can be blindly detected by correlation coefficients between the original image and the watermark sequence. Experiments show that the proposed method can achieve a better tradeoff between the robustness and transparency.
In this paper, an image content based perceptual watermarking model using ridgelet transform is presented. It provides a new visual model, which can exactly evaluate the Just Noticeable Distortion (JND) tolerance of human visual system. The watermarking algorithm is designed to address the issue of how to improve the robustness and the security of the embedded watermark according to the image content. In order to improve the robustness and transparency, the watermark bits are inserted in the visual significant ridgelet coefficients without exceeding the maximum strength of JND. With the spread spectrum technique and the secret key protection, the security of the embedded watermark is also guaranteed very well. Through analyzing the statistical property of the watermarked image, a threshold selection method based on Neymann-Pearson principle is presented and then the embedded watermark can be blindly detected by correlation coefficients between the original image and the watermark sequence. Experiments show that the proposed method can achieve a better tradeoff between the robustness and transparency.
2004, 26(9): 1449-1454.
Abstract:
Based on the analyzing of the relation between interferoinetric SAR coherence map classification and two-dimensional phase unwrapping, coherence map classification is applied in two-dimensional phase unwrapping. A K-mean and Markov random field combined classification algorithm is presented for the coherence map classification. The classified coherence map is used to confine the propagation of the local phase errors of low coherence! regions during the two-dimensional phase unwrapping. The experiments on airborne X-band InSAR data show the validity of this approach.
Based on the analyzing of the relation between interferoinetric SAR coherence map classification and two-dimensional phase unwrapping, coherence map classification is applied in two-dimensional phase unwrapping. A K-mean and Markov random field combined classification algorithm is presented for the coherence map classification. The classified coherence map is used to confine the propagation of the local phase errors of low coherence! regions during the two-dimensional phase unwrapping. The experiments on airborne X-band InSAR data show the validity of this approach.
2004, 26(9): 1455-1460.
Abstract:
This paper analyzes ambiguities in Synthetic Aperture Radar(SAR) and its impact on the image quality. The definition of ambiguities is described in detail. The influence of system parameters on ambiguities is analyzed and the relationship between ghost and system parameters is given.
This paper analyzes ambiguities in Synthetic Aperture Radar(SAR) and its impact on the image quality. The definition of ambiguities is described in detail. The influence of system parameters on ambiguities is analyzed and the relationship between ghost and system parameters is given.
2004, 26(9): 1461-1467.
Abstract:
In a transient signal system, the TX/RX coupled interference is one of principle interferences and has great influence to the system capability, especially to the near field remote sensing system such as Surface Penetrating Radar(SPR). Suppression of the coupled interference is very important for the system performance. With consideration of the sys-tem operating condition, the signal and system character, realization object of the signal processing ,thc Principal Component Analysis (PCA) method is employed. The validity of the method for the engineering application is demonstrated with theoretical analysis and experiments in this paper, and it can bo applied to real-time processing.
In a transient signal system, the TX/RX coupled interference is one of principle interferences and has great influence to the system capability, especially to the near field remote sensing system such as Surface Penetrating Radar(SPR). Suppression of the coupled interference is very important for the system performance. With consideration of the sys-tem operating condition, the signal and system character, realization object of the signal processing ,thc Principal Component Analysis (PCA) method is employed. The validity of the method for the engineering application is demonstrated with theoretical analysis and experiments in this paper, and it can bo applied to real-time processing.
2004, 26(9): 1468-1473.
Abstract:
In this paper, the applicability of biomimetic pattern recognition to informa-tion processing of abstract objects is studied, and then a DOA estimation method based on biomimetic pattern recognition is advanced. In this method, the output signals of an-tenna array are collected in practical conditions and expressed as feature vectors. These feature vectors are studied with the method of high dimensional geometry and the principle of biomimetic pattern recognition. By using the feature vectors as training samples ANN models are constructed. In our experiments, when SNE, is 20dB or OdB, the correct estima-tion rate is 100%; when SNR is -20dB, the correct estimation rate is 83%. The experimental results show that the proposed method has the great advantage of preferably robust and fast computation.
In this paper, the applicability of biomimetic pattern recognition to informa-tion processing of abstract objects is studied, and then a DOA estimation method based on biomimetic pattern recognition is advanced. In this method, the output signals of an-tenna array are collected in practical conditions and expressed as feature vectors. These feature vectors are studied with the method of high dimensional geometry and the principle of biomimetic pattern recognition. By using the feature vectors as training samples ANN models are constructed. In our experiments, when SNE, is 20dB or OdB, the correct estima-tion rate is 100%; when SNR is -20dB, the correct estimation rate is 83%. The experimental results show that the proposed method has the great advantage of preferably robust and fast computation.
2004, 26(9): 1474-1479.
Abstract:
In this paper, a new method of hyperspectral anomaly detection based u* project pursuit is presented. The Generalized Likelihood Ratio Test(GLRT) is used to estab-lish a binary hypotheses detector and estimates the unknown parameters that represent tit* background in the detector from the image. Target information, the key paxameter, is got h using project pursuit approach to search anomaly information. The algorithm reduces the dependence of pre-information, enhances the arithmetic practicability. At the same time, project pursuit approach can extract target information efficiently and improve the effect of anomaly detection.
In this paper, a new method of hyperspectral anomaly detection based u* project pursuit is presented. The Generalized Likelihood Ratio Test(GLRT) is used to estab-lish a binary hypotheses detector and estimates the unknown parameters that represent tit* background in the detector from the image. Target information, the key paxameter, is got h using project pursuit approach to search anomaly information. The algorithm reduces the dependence of pre-information, enhances the arithmetic practicability. At the same time, project pursuit approach can extract target information efficiently and improve the effect of anomaly detection.
2004, 26(9): 1480-1486.
Abstract:
A simulation computation method for calculating the impedance matrix of cou-pling double gap cavity of broadband klystron is developed in this paper. The method is used to calculate the impedance matrix and equivalent gap impedance of the double gap cavity with overlap modes of a practical S band broadband klystron. The calculated re-sults are compared with cold test data. The relative difference between two kinds of data is small, only about 10% to 15%, which is a powerful proof for reliability of the simulation computation method.
A simulation computation method for calculating the impedance matrix of cou-pling double gap cavity of broadband klystron is developed in this paper. The method is used to calculate the impedance matrix and equivalent gap impedance of the double gap cavity with overlap modes of a practical S band broadband klystron. The calculated re-sults are compared with cold test data. The relative difference between two kinds of data is small, only about 10% to 15%, which is a powerful proof for reliability of the simulation computation method.
2004, 26(9): 1487-1494.
Abstract:
Considering azimuthal higher order modes in non-vane area and helical tape thickness, using field matching method and boundary condition of the ridge-loaded ring-piano slow wave structure, the dispersion equation of vane-load helical slow-wave structure is obtained. The numerical simulation for the vane-loaded helical slow-wave structure using MAFIA software is done. The theory calculation results are compared with the simulation results. Their errors reach the request of design precision. The effect of the dispersion is discussed in the different parameters of the vane structure. The instruction method also is provided for other types vane-load helical slow-wave structure.
Considering azimuthal higher order modes in non-vane area and helical tape thickness, using field matching method and boundary condition of the ridge-loaded ring-piano slow wave structure, the dispersion equation of vane-load helical slow-wave structure is obtained. The numerical simulation for the vane-loaded helical slow-wave structure using MAFIA software is done. The theory calculation results are compared with the simulation results. Their errors reach the request of design precision. The effect of the dispersion is discussed in the different parameters of the vane structure. The instruction method also is provided for other types vane-load helical slow-wave structure.
2004, 26(9): 1495-1503.
Abstract:
Robustness is the key issue of digital watermarking technology. Up to now, various watermarking algorithms are proposed with much emphasis on the robustness. However, the robustness claimed in most of algorithms is only against common signal processing operations such as compression and signal filtering. It is now clear that even very small geometric distortions can prevent the detection of a watermark. In this paper the current methods against geometric attacks are analyzed and summarized, and some probable development directions of digital watermarking at next stage axe introduced which are the key issues to improve and design watermarking algorithms.
Robustness is the key issue of digital watermarking technology. Up to now, various watermarking algorithms are proposed with much emphasis on the robustness. However, the robustness claimed in most of algorithms is only against common signal processing operations such as compression and signal filtering. It is now clear that even very small geometric distortions can prevent the detection of a watermark. In this paper the current methods against geometric attacks are analyzed and summarized, and some probable development directions of digital watermarking at next stage axe introduced which are the key issues to improve and design watermarking algorithms.
2004, 26(9): 1504-1508.
Abstract:
After summarizing and analyzing the existing signal detection methods in a-stable noise, several innovative signal detection methods based on Fractional Low Order Moments (FLOMs) are proposed in this paper, which are the improved moment-type method and the new locally suboptimum method respectively. And these detectors are available in both the Symmetric a-stable (SaS) interference and the mixture of Gaussian and SaS interference. At the same time, Monte Carlo simulations demonstrate that all these detectors are efficient and they outperform the existing methods.
After summarizing and analyzing the existing signal detection methods in a-stable noise, several innovative signal detection methods based on Fractional Low Order Moments (FLOMs) are proposed in this paper, which are the improved moment-type method and the new locally suboptimum method respectively. And these detectors are available in both the Symmetric a-stable (SaS) interference and the mixture of Gaussian and SaS interference. At the same time, Monte Carlo simulations demonstrate that all these detectors are efficient and they outperform the existing methods.
2004, 26(9): 1509-1512.
Abstract:
Considering the uncertain for rotating velocity of spatial target and sample period of radar observation, there exists sampling rate variance between radar returns and template data, which decreases the degree of matching. In this paper, the ARMA model in multirate is provided, through which the model parameters of radar turns in the scale of template data can be gotten, and then data can be matched in the same scale. Experimental result shows the validity of proposed method.
Considering the uncertain for rotating velocity of spatial target and sample period of radar observation, there exists sampling rate variance between radar returns and template data, which decreases the degree of matching. In this paper, the ARMA model in multirate is provided, through which the model parameters of radar turns in the scale of template data can be gotten, and then data can be matched in the same scale. Experimental result shows the validity of proposed method.
