Duan Fajie

A Universal Two-Dimensional Direction of Arrival Estimation Method Without Parameter Match

In this paper, based on the subspace method, a novel algorithm, which does not require match procedure, is proposed to estimate 2-D direction of arrival (DOA) with the L-shaped array. The novel train of thought for DOA estimation includes the following two steps: using the 1-D uniform linear subarray (ULSA) along the z axes, obtain the elevation angle estimates based on the polynomial root method and with the elevation angle estimates and using the 2-D ULSA along the x axes, achieve the estimation of the azimuth angles based on the subspace method. Finally, the proposed algorithm is extended to adapt to the more general array structure. The proposed algorithm obtains much higher detection probability of successful pair matching than the existing algorithms. Simulation results illustrate the validity of the proposed algorithm.

Fiber-optic interferometer fringe projection using integrating bucket modulation

A new fiber-optic interferometer fringe projection with the integrating bucket method is presented. This method is based on the sinusoidal phase-modulating technique and makes use of Mach-Zehnder interferometer structure and Youngs double pinhole interference principle to achieve interference fringe projection. Here, we consider the modulated signal with the modulation intensity of laser (companion amplitude modulation) m in the calculation directly, adjust the optimal value of z to accommodate different m, and calculate the initial phase with phase generated carrier technology at the same time. Preliminary results from the optimum phase modulation z and initial phase φ(0) are discussed.

Closed-loop phase stabilizing and phase stepping methods for fiber-optic projected-fringe digital interferometry

Closed-loop active homodyne control can be used to make an interferometer steady against phase fluctuating followed by, for example, temperature gradients. This technology is introduced to stabilize π/2 -rad phase steps in a full-field interferometer. Two beams emitted from a fiber-optic coupler are combined to form an interference fringe pattern on a diffusely reflecting object. Fresnel reflections from the distal fiber ends undergo a double pass in the fibers and interference at the fourth port of the coupler which formed a Michelson interferometer. We suggested two means of ac phase tracking (PTAC) and dc phase tracking (PTDC) to maintain the interference intensity at quadrature by feedback control. Stepping between quadrature positions forces a π/2 -rad phase step. A method based on the ratio of harmonic of the interference signal was proposed to estimate phase step accuracy. A root-mean-square phase stability of 1.5 mrad and phase step accuracy of 2.6 mrad were measured with PTAC and a root-mean-square phase stability of 2 mrad and phase step accuracy of 13.8 mrad were measured with PTDC for the fiber-optic projected-fringe digital interferometry following the same condition. It worked well in two hours without resetting the integrator.

An Efficient Classification Method of Mixed Sources

A simple but effective classification and localization method is presented to distinguish the near- and far-field sources from mixed sources, and estimate the range parameters of near-field sources. To distinguish the near- and far-field sources, He et al. fall back on the oblique projection technique (OPT), which would yield extra estimation errors. In this paper, we do not resort to any other estimation technique (such as OPT), but make good use of known information, so as to achieve the separation of both near-field sources and far-field sources as well as estimation of range of near-field sources. Therefore, the proposed method obtains higher estimation accuracy than the method of He et al. Simulation and comparison results with the method of He et al. show the performance of the proposed method in this paper.

Study of defect feature dimension reduction based on principal component analysis

Feature extraction is an important link of visual defects detection, for it can transform high dimension space of image data into low dimension space of feature. But for the pattern classifier, high dimension input will lead the increasing of identification complexity. Therefore, it is necessary to select one group of features that can most express the defect essential characteristics. Principal component analysis makes use of the thought of statistical variance, which can remove the correlation between the statistical variables and keep all or most of the information. With the example of steel plate surface defects detection, this paper studies the feature dimension reduction based on principal component analysis. Select 7 types steel plate surface defects, acquire 20 sample images from each defect and extract 128 eigenvalues from each sample image. The experiment results show that the principal component analysis can effectively remove the correlation between the feature e data, and keep the necessary information effectively.

Notice of Retraction Design of odd number rational coefficients symmetric compactly-supported biorthogonal wavelet filters

Most wavelet filters that constructed based on Daubechies compactly-supported wavelet construction theory have nonlinear phase and irrational number coefficients. Nonlinear phase may cause distortion in image processing, and irrational filter coefficients will cause much inconvenience for wavelet applications on computer, especially for embedded processor applications. With thought of the theory of perfect-reconstruction filter banks, this paper does a study for linear phase biorthogonal perfect-reconstruction wavelet filter banks, and through of detail derivation, makes a conclusion for the procedure of odd number rational coefficients symmetric compactly-supported biorthogonal wavelet filter construction, which can be achieved by adding some vanishing moments conditions. With the example of length 7-5 biorthogonal wavelet filters design, this paper makes a detail discussion on the value selection for free variable appears in design equations, and then deduces the length 7-5 rational biorthogonal wavelet filters models.

An Effective Frequency-Spatial Filter Method to Restrain the Interferences for Active Sensors Gain and Phase Errors Calibration

In the conventional active calibration algorithms for sensors gain and phase errors, the interference did not be considered. However, the interferences are unavoidable in the practical application. In this paper, an effective frequency-spatial filter (SF) method to restrain the interferences for active sensors gain and phase errors calibration is presented. The proposed method first search the frequency range of the lowest power from the interferences, and then filter out the interferences out of the frequency range through a group of bandpass filter (BF) groups. Further, the proposed method uses an SF to suppress the interferences with nonzero power in the frequency range of the selected BF. Through the above two steps, almost all of interferences can be filtered out. Simulation results illustrate the validity of the proposed method.

A Novel Offshore Acoustic Sensing Array: Unifying Clock Source to Every Hydro-phones Acquisition Node

A high-precision clock source (±2.0 ppm) in the head of array was used to generate unified acquisition and transmission clock, each hydro-acoustic acquisition node recovered local standard clock from the unified source via PLLs. The real-time transmission path of clock and data was pipelined, which is based on RS-485 and positive emitter coupled logic (PECL). Synchronous serial data communicated at 196.608 Mbps by non-shielded twisted-pair (Cat 6) in the length of 100 meters, which can guarantee a strong anti-jamming capability and good real-time features. Clock transmission and data acquisition experiments were carried out in the laboratory, and results show that the hydrophones array can be a good system for real-time undersea acoustic exploration.