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2003 Vol. 25, No. 11
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2003, 25(11): 1441-1446.
Abstract:
For the QPSK-modulated OFDM system, the channel estimation accuracy can be improved using of the soft information which is based on the iterative decoder principle of Turbo. Meanwhile, in order to avoid serious error propagation due to the error decision of the decoder, the weighted iterative estimation algorithm is proposed. The simulation results show that the proposed algorithm improves the system performance dramatically compared with the conventional scheme.
For the QPSK-modulated OFDM system, the channel estimation accuracy can be improved using of the soft information which is based on the iterative decoder principle of Turbo. Meanwhile, in order to avoid serious error propagation due to the error decision of the decoder, the weighted iterative estimation algorithm is proposed. The simulation results show that the proposed algorithm improves the system performance dramatically compared with the conventional scheme.
2003, 25(11): 1447-1451.
Abstract:
This paper deals with pilot-based channel estimation of space-time coded OFDM system in frequency selective channels. DFT-based LS and LMMSE method are studied. A practical channel estimation method is proposed. In proposed method the complexity of LS and LMMSE methods is greatly reduced by optimally designing the pilot symbols. And the performance demonstrated by simulation is close to idea channel information.
This paper deals with pilot-based channel estimation of space-time coded OFDM system in frequency selective channels. DFT-based LS and LMMSE method are studied. A practical channel estimation method is proposed. In proposed method the complexity of LS and LMMSE methods is greatly reduced by optimally designing the pilot symbols. And the performance demonstrated by simulation is close to idea channel information.
2003, 25(11): 1452-1462.
Abstract:
This paper proposes a decoding scheme in space-time block code system with three transmitting antennas and one receiving antenna for frequency-selective fading channels, which does not require channel estimation at the transmitter or receiver. By applying the subspace method to space-time codes, the direct decoding is accomplished from both a signal processing and space-time coding perspective. With the special orthogonal design of space-time block codes, the input of the space-time block code system is obtained from the subspace. The direct decoding is addressed for frequency-selective fading channels from a single carrier perspective. Monte Carlo simulations show the performance of direct decoding and the performance com-parison with the decoder using the perfect channel information.
This paper proposes a decoding scheme in space-time block code system with three transmitting antennas and one receiving antenna for frequency-selective fading channels, which does not require channel estimation at the transmitter or receiver. By applying the subspace method to space-time codes, the direct decoding is accomplished from both a signal processing and space-time coding perspective. With the special orthogonal design of space-time block codes, the input of the space-time block code system is obtained from the subspace. The direct decoding is addressed for frequency-selective fading channels from a single carrier perspective. Monte Carlo simulations show the performance of direct decoding and the performance com-parison with the decoder using the perfect channel information.
2003, 25(11): 1463-1468.
Abstract:
A Time-Of-Arrival(TOA) estimation method for CDMA system with high reso-lution is proposed. The integrate-dump circuits are used to sample the received signals while the sampling rate is not raised, then the Discrete-Fourier-Transform(DFT) is used to transform the discrete signals to frequency domain. Based upon the CDMA signal model, the multipath channel model and the discrete frequency spectrum of the known spreading codes, the integer part of TOA with multiples of a chip interval is estimated. Then least square method in discrete frequency domain is used to estimate the remainder fractional part of TOA. This method has the high resolution with low operation volume while the sampling rate is not high, so it is an effective and high precise TOA estimation method.
A Time-Of-Arrival(TOA) estimation method for CDMA system with high reso-lution is proposed. The integrate-dump circuits are used to sample the received signals while the sampling rate is not raised, then the Discrete-Fourier-Transform(DFT) is used to transform the discrete signals to frequency domain. Based upon the CDMA signal model, the multipath channel model and the discrete frequency spectrum of the known spreading codes, the integer part of TOA with multiples of a chip interval is estimated. Then least square method in discrete frequency domain is used to estimate the remainder fractional part of TOA. This method has the high resolution with low operation volume while the sampling rate is not high, so it is an effective and high precise TOA estimation method.
2003, 25(11): 1469-1474.
Abstract:
Based on eigenvalue distributing of input signal, the convergent necessary, condi-tions for LMS and Normalized LMS(NLMS) algorithm are again researched through the accu-rate analysis of the misadjustment. To avoid blindness for applying LMS and NLMS algorithm, the convergent threshold and the simple adaptive calculating formula for the step-size of them are proposed. The influence of eigenvalue distributing of input signal and order of filter on the threshold of step-size is also analyzed. Compared with an existing algorithm, the characters of lower computational complexity, practicality and stronger adaptive are shown and the satisfied misadjustment is achieved by adopting the presented method for calculating the step-size.
Based on eigenvalue distributing of input signal, the convergent necessary, condi-tions for LMS and Normalized LMS(NLMS) algorithm are again researched through the accu-rate analysis of the misadjustment. To avoid blindness for applying LMS and NLMS algorithm, the convergent threshold and the simple adaptive calculating formula for the step-size of them are proposed. The influence of eigenvalue distributing of input signal and order of filter on the threshold of step-size is also analyzed. Compared with an existing algorithm, the characters of lower computational complexity, practicality and stronger adaptive are shown and the satisfied misadjustment is achieved by adopting the presented method for calculating the step-size.
2003, 25(11): 1475-1481.
Abstract:
Both chaotic sequences and nonlinear feed-forward logic (NLFFL) sequences based on linear shift register almost have the same properties: the ease of their generation and various families with a large family size and long sequence period, as well as their broadband noise-like and non-linear nature. Their generation methods, correlation properties, Code Division Multi-ple Access (CDMA) properties and their resistance against correlation attack are compared in the paper. By simulation, it shows that most of their properties are comparable, but chaotic sequences are less vulnerable to correlation attack and jamming than some NLFFL sequences when their period is less than or equal to 1023, so they have more practical value than these nonlinear sequences based on shift register.
Both chaotic sequences and nonlinear feed-forward logic (NLFFL) sequences based on linear shift register almost have the same properties: the ease of their generation and various families with a large family size and long sequence period, as well as their broadband noise-like and non-linear nature. Their generation methods, correlation properties, Code Division Multi-ple Access (CDMA) properties and their resistance against correlation attack are compared in the paper. By simulation, it shows that most of their properties are comparable, but chaotic sequences are less vulnerable to correlation attack and jamming than some NLFFL sequences when their period is less than or equal to 1023, so they have more practical value than these nonlinear sequences based on shift register.
2003, 25(11): 1482-1487.
Abstract:
In this paper, a novel fragile watermark technique is proposed, which is based on the method of Yeung-Mintzers (1997). To resolve the existing security problem, a chaotic key which is based on image feature is used to control the embedding of fragile watermark. Theoretical analysis and experimental results demonstrate its effectiveness in resisting possible attacks. And because the watermark is embedded in pixel-wise order, the technique has good ability of detecting local alterations.
In this paper, a novel fragile watermark technique is proposed, which is based on the method of Yeung-Mintzers (1997). To resolve the existing security problem, a chaotic key which is based on image feature is used to control the embedding of fragile watermark. Theoretical analysis and experimental results demonstrate its effectiveness in resisting possible attacks. And because the watermark is embedded in pixel-wise order, the technique has good ability of detecting local alterations.
2003, 25(11): 1488-1493.
Abstract:
In this paper, a new classification method is proposed that is based on HMM and SVM using FingerCode. This technique uses FingerCode as representation of fingerprint, first, using five HMM classifiers to classify originally, furthermore, basing on the most possible two results of classification by HMM, the corresponding SVM classifier is selected to make final decision. Through experiments, the performance of this method reaches or exceeds many popular ones and has value to a certainty in practice.
In this paper, a new classification method is proposed that is based on HMM and SVM using FingerCode. This technique uses FingerCode as representation of fingerprint, first, using five HMM classifiers to classify originally, furthermore, basing on the most possible two results of classification by HMM, the corresponding SVM classifier is selected to make final decision. Through experiments, the performance of this method reaches or exceeds many popular ones and has value to a certainty in practice.
2003, 25(11): 1494-1498.
Abstract:
Support Vector Machines (SVMs) are a new generation learning system based on recent advances in statistical learning theory. SVMs have many well features that make them attractive for small samples, nonlinear and high dimensional pattern recognition. However, choice of Support Vectors(SVs) is difficult in SVMs, which is a bottleneck problem. In this paper, a novel method using bi-color Voronoi diagram is proposed to pre-extract SVs based on Voronoi diagram. Considering the distribution feature of samples space, this method determi-nates SVs based on the bi-color Voronoi diagram before training SVMs. Learning is based on these pre-extracted vectors. Experiments show that this method is feasible and effective.
Support Vector Machines (SVMs) are a new generation learning system based on recent advances in statistical learning theory. SVMs have many well features that make them attractive for small samples, nonlinear and high dimensional pattern recognition. However, choice of Support Vectors(SVs) is difficult in SVMs, which is a bottleneck problem. In this paper, a novel method using bi-color Voronoi diagram is proposed to pre-extract SVs based on Voronoi diagram. Considering the distribution feature of samples space, this method determi-nates SVs based on the bi-color Voronoi diagram before training SVMs. Learning is based on these pre-extracted vectors. Experiments show that this method is feasible and effective.
2003, 25(11): 1499-1504.
Abstract:
In this paper, a new kind of two-dimensional Cellular Automata (CA) is studied. Several algorithmic rules are discovered that can be used to design new Cellular Neural Networks (CNN) which can implement shadow detector and overstriking for character recognition. Their Boolean expressions and learning algorithms are introduced detailedly. The results of computer simulation confirm that this new approach is simpler and more effective than that given in the literature. Furthermore, these results also confirm that new CNN can be designed with CA rules and find a novel method to design CNN.
In this paper, a new kind of two-dimensional Cellular Automata (CA) is studied. Several algorithmic rules are discovered that can be used to design new Cellular Neural Networks (CNN) which can implement shadow detector and overstriking for character recognition. Their Boolean expressions and learning algorithms are introduced detailedly. The results of computer simulation confirm that this new approach is simpler and more effective than that given in the literature. Furthermore, these results also confirm that new CNN can be designed with CA rules and find a novel method to design CNN.
2003, 25(11): 1505-1513.
Abstract:
This paper presents some modeling methods for CDMA network planning applica-tions. Linear equations are used for modeling CDMA multi-cell networks and iterative methods are adopted for solving the equations. The simulation results based on these models are pre-sented in this paper. The analysis shows that the results are fairly accurate, so the models can be used in real networks perfectly. Whats more, the methods are easy to be implemented on computer platforms. Thus, these modeling methods can be used as the core algorithms of planning softwares, perspectively.
This paper presents some modeling methods for CDMA network planning applica-tions. Linear equations are used for modeling CDMA multi-cell networks and iterative methods are adopted for solving the equations. The simulation results based on these models are pre-sented in this paper. The analysis shows that the results are fairly accurate, so the models can be used in real networks perfectly. Whats more, the methods are easy to be implemented on computer platforms. Thus, these modeling methods can be used as the core algorithms of planning softwares, perspectively.
2003, 25(11): 1519-1524.
Abstract:
In this paper, the interferomtric experiments on airborne L-SAR system of IECAS is demonstrated. And data obtained from experiments are processed, and Chinese first DEM with repeat-pass airborne SAR, which nearly accords with the real topographic map, is obtained, and its height accuracy is about 10m. A new imaging coregistration method for crossed-orbit is presented and its effectiveness is tested by airborne data.
In this paper, the interferomtric experiments on airborne L-SAR system of IECAS is demonstrated. And data obtained from experiments are processed, and Chinese first DEM with repeat-pass airborne SAR, which nearly accords with the real topographic map, is obtained, and its height accuracy is about 10m. A new imaging coregistration method for crossed-orbit is presented and its effectiveness is tested by airborne data.
2003, 25(11): 1525-1530.
Abstract:
This paper puts forward a new method of detecting three-aperture Synthetic Aperture Radar (SAR) ground moving targets after studying Displaced Phase Center Antenna (DPCA) and interferometric processing technique. This method can not only discover moving targets but also estimate the targets parameters such as real positions and velocities. Furthermore it is simpler and needs fewer computations. Finally some typical computer simulation results are presented which illustrate the methods validity.
This paper puts forward a new method of detecting three-aperture Synthetic Aperture Radar (SAR) ground moving targets after studying Displaced Phase Center Antenna (DPCA) and interferometric processing technique. This method can not only discover moving targets but also estimate the targets parameters such as real positions and velocities. Furthermore it is simpler and needs fewer computations. Finally some typical computer simulation results are presented which illustrate the methods validity.
2003, 25(11): 1531-1535.
Abstract:
Microwave imaging techniques which can provide all-weather, day-and-night imag-ing capability have important applications to many scientific fields. It is an active area to ex-plore new microwave imaging ideas, systems and techniques. In this paper, a new microwave imaging method for earth observation is proposed. In this method, the signal transmitter and receiver are located in different platforms, and only a monochromatic microwave is required to illuminate the earth surface. Numerical simulation results show that this method can produce a microwave image with high spatial and radiation resolutions.
Microwave imaging techniques which can provide all-weather, day-and-night imag-ing capability have important applications to many scientific fields. It is an active area to ex-plore new microwave imaging ideas, systems and techniques. In this paper, a new microwave imaging method for earth observation is proposed. In this method, the signal transmitter and receiver are located in different platforms, and only a monochromatic microwave is required to illuminate the earth surface. Numerical simulation results show that this method can produce a microwave image with high spatial and radiation resolutions.
Extremal solution of the target\s brightness temperature in millimeter wave radiometric measurements
2003, 25(11): 1536-1541.
Abstract:
The near sensing techniques with millimeter wave play important role in many fields. To make precise measurements of the radiometric brightness temperature of a target, one must set up model of the interaction between the electromagnetic radiation properties of the antenna and the incident radiation from the environment. This interaction can be described by Fredholm integral equation of the first kind which is extremely unstable. In this paper, a inversion method is presented and is then applied to retrieve armored targets brightness temperature in millimeter wave radiometric measurements.
The near sensing techniques with millimeter wave play important role in many fields. To make precise measurements of the radiometric brightness temperature of a target, one must set up model of the interaction between the electromagnetic radiation properties of the antenna and the incident radiation from the environment. This interaction can be described by Fredholm integral equation of the first kind which is extremely unstable. In this paper, a inversion method is presented and is then applied to retrieve armored targets brightness temperature in millimeter wave radiometric measurements.
2003, 25(11): 1542-1547.
Abstract:
This paper presents a finite element method for the analysis of waveguide system without spurious modes. Prom the operator theory of the vector wave function space, a succinct and complete electromagnetic wave equation set is derived and the electiic field intensity vector can be expressed by two scalar functions. These two scalar functions are numerically computed by using finite element method so that the parameters of the waveguide system can be obtained. The method is demonstrated by the calculation of the reflection coefficients of the rectangular waveguide with an inductive diaphragm and the rectangular waveguide with an E-plane step respectively.
This paper presents a finite element method for the analysis of waveguide system without spurious modes. Prom the operator theory of the vector wave function space, a succinct and complete electromagnetic wave equation set is derived and the electiic field intensity vector can be expressed by two scalar functions. These two scalar functions are numerically computed by using finite element method so that the parameters of the waveguide system can be obtained. The method is demonstrated by the calculation of the reflection coefficients of the rectangular waveguide with an inductive diaphragm and the rectangular waveguide with an E-plane step respectively.
2003, 25(11): 1564-1569.
Abstract:
Ultra-wideband impulse radio is a developing high speed wireless access technology. In this paper, the principle of ultra-wideband multiaccess communication is analyzed with the transmitting signal. In order to study the system performance in mulitpath channels, the deterministic two-path model and the statistical S-V model are employed for evaluating the bit error rates of the system by simulation. The results indicate that the intersymbol interference and multiple access interference are the main factors that degrade the system performance, which, on the other hand, may be improved by antenna diversity.
Ultra-wideband impulse radio is a developing high speed wireless access technology. In this paper, the principle of ultra-wideband multiaccess communication is analyzed with the transmitting signal. In order to study the system performance in mulitpath channels, the deterministic two-path model and the statistical S-V model are employed for evaluating the bit error rates of the system by simulation. The results indicate that the intersymbol interference and multiple access interference are the main factors that degrade the system performance, which, on the other hand, may be improved by antenna diversity.
2003, 25(11): 1570-1574.
Abstract:
This paper presents a novel blind audio digital watermark algorithm. It makes full use of the multi-resolution of DWT and the energy compression of DCT and embeds binary image watermark in the audio by quantification process. The watermark can be extracted without the original audio signal. Experimental results demonstrate the algorithm is robust and imperceptible.
This paper presents a novel blind audio digital watermark algorithm. It makes full use of the multi-resolution of DWT and the energy compression of DCT and embeds binary image watermark in the audio by quantification process. The watermark can be extracted without the original audio signal. Experimental results demonstrate the algorithm is robust and imperceptible.
2003, 25(11): 1575-1577.
Abstract:
In this paper, echoes are decomposed based on wavelet multiresolution analysis. It is shown that the energy of wavelet coefficients is exponential to the decomposed scale in some degree, which is similar to the definition of fractal dimension. Hence, two sorts of features are extracted and applied to recognizing five classes of echoes. The recognition results are satisfactory.
In this paper, echoes are decomposed based on wavelet multiresolution analysis. It is shown that the energy of wavelet coefficients is exponential to the decomposed scale in some degree, which is similar to the definition of fractal dimension. Hence, two sorts of features are extracted and applied to recognizing five classes of echoes. The recognition results are satisfactory.
2003, 25(11): 1578-1580.
Abstract:
In the paper, an improved secret sharing scheme based on elliptic curve cryptography is proposed. It guarantees the mutual identity authentication between the legal dealer and the participating parties and can protect against the cheating action. The problems of renew and reuse are properly treated. The scheme may be applicable in practical network communication.
In the paper, an improved secret sharing scheme based on elliptic curve cryptography is proposed. It guarantees the mutual identity authentication between the legal dealer and the participating parties and can protect against the cheating action. The problems of renew and reuse are properly treated. The scheme may be applicable in practical network communication.
2003, 25(11): 1581-1584.
Abstract:
In this paper, a new edge-reserve filtering algorithm is presented. It adaptively adjusts the size of the filters supporting area according to the local variance of the interested area. The bigger the local variance is, which means the more high frequency texture information is contained in this area, the smaller the support area will be. In order to protect the edges of the image when it is filtered, this algorithm will divide the pixels in its supporting area into several groups according to the angle between its direction and the mean gradient of this area. By this way, pixels along the content edges will be given a bigger weight factors than pixels that are vertical to the image edge. Thus protect the edges from being blurred by the filtering process. The simulation results show that this algorithm is better than median filter both in terms of PSNR values and subjective image qualities. For pictures that are rich in texture information, the PSNR gain could reach 3dB higher.
In this paper, a new edge-reserve filtering algorithm is presented. It adaptively adjusts the size of the filters supporting area according to the local variance of the interested area. The bigger the local variance is, which means the more high frequency texture information is contained in this area, the smaller the support area will be. In order to protect the edges of the image when it is filtered, this algorithm will divide the pixels in its supporting area into several groups according to the angle between its direction and the mean gradient of this area. By this way, pixels along the content edges will be given a bigger weight factors than pixels that are vertical to the image edge. Thus protect the edges from being blurred by the filtering process. The simulation results show that this algorithm is better than median filter both in terms of PSNR values and subjective image qualities. For pictures that are rich in texture information, the PSNR gain could reach 3dB higher.
2003, 25(11): 1514-1518.
Abstract:
Under Kirchhoff principle, the security property of digital chaotic encryption system is discussed using chosen-ciphertext attacking. The key of the encryption system can be got by chosen-ciphertext attacking. The digital chaotic encryption system based on digital filter does not have high privacy.
Under Kirchhoff principle, the security property of digital chaotic encryption system is discussed using chosen-ciphertext attacking. The key of the encryption system can be got by chosen-ciphertext attacking. The digital chaotic encryption system based on digital filter does not have high privacy.
2003, 25(11): 1548-1557.
Abstract:
A Digital Audio Broadcasting(DAB) system, which is based on advanced technique of Coded Orthogonal Frequency Division Multiplexing (COFDM), can provide improved per-formance of high robustness and virtual CD-like quality. In-Band On-Channel(IBOC) digital audio systems have the capability of simultaneously transmitting both analog and digital signals (in hybrid mode)within the allocated channel mask, allowing full compatibility with existing analog receivers, and will accomplish smooth transition from analog broadcasting to all-digital mode DAB at low cost. The authors analyze the spectrum of Frequency Modulation (FM) IBOC DAB, and presents basic structures of FM IBOC DAB transmitting system and receiver, introducing key technologies of Perceptual Audio Codcr(PAC), Forward Error Coding(FEC), OFDM, First-Adjacent Canceling(FAC), Time Diversity Delay (TDD)and Audio Blend(AB). By careful comparison and analysis, some advice on development of Chinese IBOC DAB is given.
A Digital Audio Broadcasting(DAB) system, which is based on advanced technique of Coded Orthogonal Frequency Division Multiplexing (COFDM), can provide improved per-formance of high robustness and virtual CD-like quality. In-Band On-Channel(IBOC) digital audio systems have the capability of simultaneously transmitting both analog and digital signals (in hybrid mode)within the allocated channel mask, allowing full compatibility with existing analog receivers, and will accomplish smooth transition from analog broadcasting to all-digital mode DAB at low cost. The authors analyze the spectrum of Frequency Modulation (FM) IBOC DAB, and presents basic structures of FM IBOC DAB transmitting system and receiver, introducing key technologies of Perceptual Audio Codcr(PAC), Forward Error Coding(FEC), OFDM, First-Adjacent Canceling(FAC), Time Diversity Delay (TDD)and Audio Blend(AB). By careful comparison and analysis, some advice on development of Chinese IBOC DAB is given.
2003, 25(11): 1558-1563.
Abstract:
H. R. Walker presented a high spectral efficiency modulation (VMSK). It can reach 30 bit/(sHz) simply without loss of SNR in his analysis. There are papers introduce this technology in China too. But, through deeply analysis based on the engineering point, a very regrettable conclusion is obtained, i.e, this technology is a beautiful rainbow!
H. R. Walker presented a high spectral efficiency modulation (VMSK). It can reach 30 bit/(sHz) simply without loss of SNR in his analysis. There are papers introduce this technology in China too. But, through deeply analysis based on the engineering point, a very regrettable conclusion is obtained, i.e, this technology is a beautiful rainbow!
