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In Orthogonal Frequency Division Multiplexing (OFDM) system, Carrier frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality between carriers and degrade the system performance significantly. On the basis of traditional frequency offset estimation algorithm, an improved carrier frequency offset estimation algorithm is presented in this paper, which uses one complex training sequence, can effectively estimate fractional frequency offset in the time domain and the integer frequency offset in the frequency domain. Simulation results show that the improved carrier frequency offset estimation algorithm performs better than conventional P. Moose and Schmidl algorithm, which can effectively improve the frequency estimation accuracy and provides a wide acquisition range for the carrier frequency offset with low complexity.

A novel constellation mapping VBLAST zero forcing detection algorithm in MIMO-OFDM system is proposed in this paper. First, the signal is cycled and successively mapped from the whole space of constellation points and is regarded as the first the underlying detection signals to maximize the performance of the first detection layers at the receiver. Then, the traditional ZF detection algorithm is used for the remaining received signal. At last, a set of the optimal detection signal is determined as the decoding result based on the maximum likelihood criterion. The proposed algorithm is mainly to overcome the complexity of ML algorithm and the poor performance of ZF algorithm. Simulation results show that the proposed algorithm is superior to the traditional ZF algorithm

In this paper, considering the error propagation effect and high complexity of spatial multiplexing based vertical bell labs layered space time(VBLAST), a novel nonlinear MMSE-THP algorithm for VBLAST in MIMO-MC-CDMA downlink system is proposed in this paper. In the proposed algorithm, the nonlinear THP precoding is used between the sub-carrier channels of the MC-CDMA to eliminate interference from other signals at the transmitter so as to obtain frequency diversity gain and effectively eliminate the error propagation effect of layered space-time codes. At the receiver, minimum mean square error criterion is used and the complexity of the receiver is reduced. Simulation results show that the proposed algorithm is superior to the traditional minimum mean square error algorithm and the linear precoding algorithm.

In recent publications, some special detectors were proposed to improve the performance and complexity gaps between the optimal detector and the suboptimal detector. In this paper, we propose a multistage chase detection algorithm for MIMO-OFDM systems, which use chase detection framework to design sub-detector, so the nest chase detection was implemented that can further decrease the error spread and improve the BER performance. Simulation results show that the proposed schemes performs better than BLAST and conventional chase detection, which can achieve near-ML performance with lower complexity compared with ML algorithm.

In this paper, to solve the problem of feedback cost and performance loss for precoded spatial multiplexing MIMO OFDM with limited feedback, an improved nonlinear detection method based on limited feedback for precoded vblast is proposed, the corresponding criteria is used for select optimal codeword from the Grassmannian codebook at the receiving according to the channel state information, and feedback the precoding word index to the transmitter, thereby forming the equivalent channel. At the receiving, recycle and successive mapping from the entire space of constellation points as the first the underlying detection signals at the receiver, in order to maximize the performance of first detection layer, and then using the traditional detection algorithm for the remaining received signal, and determine a set of the optimal detection signal as decoding result based on the maximum likelihood criterion. Simulation results show that the proposed method to ensure system throughput, the cost of the feedback link and BER performance are improved some extent.

GPS-based twin antennas real-time attitude determination system realized with TMS320C6713 is presented in this paper. The direct computation method used to estimate attitude parameter is introduced firstly. Then the position, velocity and float ambiguity are estimated using kalman filter, the integer ambiguity is resolved based on Z-transformation augmented FASF algorithm. In the end, the software flow chart and hardware block diagram of attitude determination system were presented. The experiment results show that yaw accuracy about 0.04 degrees and pitch accuracy about 0.1 degrees at the output rate of 10Hz can be achieved.

A novel union detection algorithm based on the iterative cyclic QR decomposition (IQRD) algorithm and Bi-Directional ZF (BED-ZF) algorithm is proposed in this paper. By combining the advantage of BID with the IQRD, the proposed algorithm overcomes the error propagation of the conventional QR algorithm and the performance is improved effectively. Simulation results show that the proposed BID-IQRD algorithm is superior to the pure IQRD algorithm and BID-ZF algorithm.

As the feature based detection and classification of microcalcifications (MCs) in digital mammograms is considered here as a machine-leaning problem, we investigate an approach using immune algorithm (IA) and support vector machine (SVM), called IA-SVM, to solve it. Firstly, because only support vectors (SVs) are needed to build the classification hyperplane, we compress the training set according to their intra-class and inter-class Euclidean distances without losing any SVs. Meanwhile, an IA based MCs' features selector is provided to select an optimal feature subset, which can construct the input vectors for the latter SVM training; Secondly, the compressed and optimized training samples are fed to a SVM based classifier to make the optimal classification hyperplane more efficiently and more effectively. Experiments demonstrate that our method has better computing performance than other traditional classifiers (training samples were compressed by about 15%) and yields a satisfying Az value (about 0.83).

Selecting hundreds of thousands of particles from low contrast and low SNR Cryo-electron micrograph (Cryo-EM) images is one of the major bottle-necks in advancing toward achieving atomic resolution reconstruction of biological macromolecules. To recognize true particles from impurities and other invalid particles, shape information plays a significant role. This paper provide a new method based on multi-resolution analysis to detect the main edges of objects in Cryo-EM image, which can be the pre-processing operations of next step of particle identification.

To reduce the computation complexity of discrete cosine transform (DCT) and quantization in H.264 video coding, a highly effective algorithm to detect all-zero DCT coefficient blocks (AZB) before DCT is proposed, after analyzing the distribution model of DCT coefficients and the properties of the integer DCT and quantization. Experimental results show that the detection ratio of the proposed algorithm achieves up to 98% and up to 47% higher than that of the existing methodologies.

There still exist two key problems required to be solved in the classification rule extraction, i.e. how to select attributes and discretize continuous attributes effectively. The lack of efficient heuristic information is the fundamental reason that affects the performance of currently used approaches. In this paper, a new measure for determining the importance level of the attributes based on the trained SVM is proposed, which is suitable for both continuous attributes and discrete attributes. Based on this new measure, a new approach for rule extraction from trained SVM and classification problems with continuous attributes is proposed. The performance of the new approach is demonstrated by several computing cases. The experimental results prove that the approach proposed can improve the validity of the extracted rules remarkably compared with other rule extracting approaches, especially for the complicated classification problems.

All the previous methods for detecting all-zero discrete cosine transform (DCT) coefficient blocks (AZB) prior to DCT and quantization are SAD-based methods. In this paper, two improved AZB early detection methods for SSD-based video coding are proposed. Based on the analysis of DCT coefficient distribution and Paseval energy conservation theorem, we derive an efficient condition under which each quantized coefficient becomes zero. Experiment results show that the energy conservation method achieves up to 32% higher detection ratio without degrading video quality and DCT distribution method up to 47% higher than the existing methodologies

The assessment of wheat hardness is very important in each of its production stages. A new kind of detection method of wheat hardness based on the erosion effect of laser ultrasonics is proposed in this paper. The numeric model of laser ultrasonics excited by the erosion effect is established based on the classical theory of heat conduction and the wave equation. Then five characteristic parameters of the longitudinal ultrasonic wave are extracted both in the time domain and the frequency domain by wavelet transform, which include the parameters of TF5, TF6, TF7, WF1 and WF2. Finally, a back propagation neural network is designed using these five parameters as the input of the network to test the hardness of the wheat. Numerous experiments are performed using 20 wheat samples with different hardness index. The results show that the maximal relative measurement error is about −2.24%, that the mean relative error is about 0.15%, and that the measurement method of wheat hardness based on the erosion effect of laser ultrasonics is feasible.

This paper presents a general model of a two-stage vibration isolation system involving a flexible base plate with arbitrary boundary conditions. The dynamic behavior of the coupling system was obtained by using an impedance method in which the impedance matrix of the base plate was derived from a combined use of an improved Fourier series expansion and the Rayleigh-Ritz method. Subsequently, with the purpose of attenuation of sound radiation from the base plate structure, the optimal force information is formulated under various active control strategies including: 1) minimizing the total vibratory power of the coupled structure, 2) minimizing the sound power radiation from the base plate, 3) minimizing the vibratory power transmitted to the base plate, and 4) minimizing the mean square velocities at the isolator locations on the flexible plate. Numerical results were presented and discussed in detail. Finally, some concluding remarks are made.

In this paper, an improved Fourier series method is proposed for the free vibration analysis of moderately thick rectangular plates with uniform elastic restraints along each edge. The effect of shear deformation is considered by using Mindlin plate theory (namely, the first order shear deformation theory). The transverse deflection and rotation displacement functions are invariantly expressed as the superposition of a double Fourier cosine series and four supplementary functions in the form of the product of a polynomial function and a single cosine series expansion introduced to ensure (accelerate) the uniform and absolute convergence (rate) of the series representation on the plate including four edges. The unknown expansion coefficients are determined using the Rayleigh-Ritz procedure in conjunction with the energy formulation of Mindlin plate system. Several numerical examples are presented to demonstrate the effectiveness and reliability of the proposed method for predicting the modal parameters of ...

In this study, the energy distributions and power flows between some basic structural components such as beams, plates, and shells are studied using a so-called Fourier Spectral Element Method (FSEM). Similar to the SEA modeling, a complex system is here also considered as an assembly of subsystems or components. The FSEM, however, is deterministic in nature in that the solution is obtained by directly and faithfully solving the governing equations for each component under the actual boundary and coupling conditions. What make this model powerful and unique lie in its capability and flexibility of effectively dealing with model uncertainties (due to the probabilistic/stochastic natures of some model parameters) and engineering and manufacturing errors which tend to become critically important at higher frequencies. Since this method does not involve any artificial assumptions or simplifications, it potentially offers a whole frequency solution with adaptive spatial and frequency resolutions.

Similar to a diesel engine, the main vibration sources of an air-compressor are to and fro inertial forces of its piston, rod, and crankshaft. An active vibration isolation system is developed for an air-compressor in a tug boat. This system consists of four inertial actuators and a DSP processor. A four-input and four-output adaptive control strategy is applied and the reference input signal comes from a laser tachometer on the shaft of the motor. The active vibration isolation experiment is conducted in a tug boat when only the air-compressor is working. The experimental results demonstrate that good vibration reductions are obtained at not only error sensor's locations but also the hull under the compressor. Some discussion and conclusions are given at last.

Acoustic radiation modes have received increasing attention in the areas of structural acoustic radiation and active structural acoustic control during the past few years. In this paper, a comparative study on the acoustic radiation modes of several typical structures and their associated radiation efficiencies is presented. The present work is also undertaken to extend the acoustic radiation modes into more complex structures, i.e. a thin cylindrical shell, since it was rare described in the literatures. The two analytic approaches for deriving acoustic radiation modes are reviewed briefly first. Numerical examples and comparative analysis are performed from one-dimensional problem to two-dimensional and three-dimensional problems. A grouping characteristic of acoustic radiation modes and their corresponding radiation efficiencies is observed. The shapes of the acoustic radiation modes follow the order of uniform variation, linear, quadratic and high-order variation. It is interesting that the acoustic r...

Combing the subsystem modal coupling theory and the impedance‐mobility approach, a general analytical model is developed for the analysis and active control of structural acoustic transmission through the double panel‐cavity structure into the free field, in which control methods including incident panel piezoelectric (PZT) actuator, acoustic actuator in cavity, and radiating panel PZT actuator are considered. The matrix formulae for the modal response of the coupled structural acoustic system and optimal secondary source strengths are obtained. On the basis, active control of sound transmission is studied analytically and numerically in detail. Simulations and analyzes are conducted to compare the control effects between different control strategies and examine the dominant control mechanisms involved in each control case, and the effect of system parameters on control effect is also examined. The results demonstrate that the incident panel actuator can obtain sound attenuation by modal suppression or re...

Background-free third-order harmonic generation is observed from dynamic gratings induced by dual laser filaments in argon gas. The filaments were generated by focusing two intense 60 fs laser pulses noncollinearly into a gas cell. The optimal result is achieved with gas pressure of 2 atm and zero relative delay. It seems that the off-axis third-harmonic generation is mainly due to the interaction between the two interfering fundamental pulses and their filaments.

This paper presents an investigation into the active control of sound transmission into a structural-acoustic coupled system. An enclosure with four acoustically rigid walls and two flexible plates is considered. One of the two plates through which a harmonic sound wave is transmitted into the enclosure, is called the incident plate, and the other as the receiving plate. Based on a fully coupled vibro-acoustic model, seven different control strategies, i.e. control configurations, are considered. They are: (a) use of the incident plate actuator, (b) applying acoustic control source in the cavity (called as cavity control), (c) use of the receiving plate actuator, (d) hybrid control system combining the incident plate actuator and the cavity control source, (e) hybrid control system combining the receiving plate control and the cavity control source, (f) simultaneous use of both the incident plate actuator and the receiving plate actuator, and (g) use of the combined acoustic actuator and structural actuators on both flexible panels. The effectiveness and performance of the control system corresponding to each configuration are compared and discussed through numerical simulations. The results show that two control system configurations, that is, the hybrid control system combining the incident plate actuator and the cavity control source and simultaneous use of both the incident plate actuator and the receiving plate actuator are desirable configurations in terms of the acoustic potential energy inside the enclosure.