Advanced Materials Research Vols. 989-994

Abstract: A radar compressed sensing imaging method with 2-D separable sampling is proposed in this paper. Instead of converting the radar imaging problem into two 1-D compressed sensing problem, we use the 2-D Separable Projections to solve it directly. Unlike the 2-D separable sampling in visible imaging, the range and azimuth which are the two dimensions of the radar imaging couple with each other. This Coupling increases the storage and computation in radar compressed imaging, therefore some de-coupling processing using in Range Doppler algorithm are adopted in the proposed method to construct the 2-D separable sampling data. Accordingly the two dimensional scene has been reconstructed with the proposed 2-D compressed sensing algorithms. Compared with conventional compressed sensing imaging methods, the new method has reduced the memory usage and complexity with imaging performance improvement.

Abstract: An orthogonal frequency division multiplexing (OFDM) is one of the effective techniques used in wireless communications. In OFDM systems, channel impairments due to multipath dispersive wireless channels can cause deep fades in wireless channels. The OFDM receiver also requires an accurate and computationally efficient channel state information when coherent detection is involved. Therefore, it needs a good robust estimation method of the channel in wireless communication for OFDM systems. And one of these channel estimation methods is minimum mean square error (MMSE) channel estimation. MMSE channel estimation one most used method in OFDM systems. In this work we enhanced robustness of MMSE channel estimation by using it in base of quasi-cyclic low density parity check (QC-LDPC) coded OFDM system.

Abstract: A novel fusion algorithm based on Nonsubsampled Contourlet Transform (NSCT) is proposed, according to the characteristics of infrared and visible images. Firstly, the registered infrared and visible images from the same scene were transformed by NSCT transforms; then the low frequency coefficient is fused by the combination of local energy and normalised correlation matrix, the high frequency coefficient fusion is fused by regional energy matching with regional variance; finally, the target image is obtained by performing inverse NSCT transforms. experimental results indicate that the proposed algorithm can effectively get more detail information and the fusion performance is dramatically better than traditional fusion methods.

Abstract: This paper presents a new method to achieve effective text extraction using mathematical morphology. Firstly, the document is segmented and divided into several parts based on the layout. And then, every part is dilated to big connected regions, whose biggest skeleton will be extracted and serve as a structure element (SE). Finally, a proposed region-concatenated operation with the SE will be employed, whose result can be the input of subsequent OCR system. Experimentally, the proposed method is robust to noise, the text orientation, font style and size, language and layout.

Abstract: HF communication is a very important tactical communication method, which can achieve thousand-miles away communication through the ionosphere reflections without any infrastructure support. But HF communication quality is not stable for the ionosphere disturbance, multipath fading and propagation loss. In this paper, we propose a new long-range communication scheme based on majority combing. In the scheme, we use multi-point receiving and multi-copying transmission, which can significantly improve the communication success rate by utilizing the land-sites’ space diversity and the multi-packet’s time diversity.

Abstract: In this paper, an improved complex image method to derive closed form periodic Green’s function for problem of scattering from perfectly conducting periodic surfaces is considered. The complex image technique represents a close-form periodic Green’s function consisting of a finite series of real sources and two finite series of complex sources with complex locations and amplitudes. Then the integral equation with the complex images periodic Green’s function in the kernel is solved by the method of moments. Results and computational times obtained by this improved complex image method and the previous one are compared with those obtained by the spectral Kummer-Poisson’s method. Results show that the improved complex image method is more accurately than the previous one.

Abstract: The full-wave band CCD system is widely used for military,civil or photography of criminal image and extraction analysis,its wavelength is range between 200 nm and 1200 nm,including ultraviolet,visible light and infrared.Through translating blanck visibleimage into optical image,and realizing collecting of weak signal under low illumination case and collecting and processing of high quality image,it makes Full-wavelength CCD system the powerful features such as the topography and landform scaning,traces exploration,file inspection,holographic photography and image processing.The whole band CCD system structure,characteristic and the application of the image interpretation technology were briefly introduced in this paper,and experiment band CCD selected was validated.

Abstract: An improved discrete Fourier transform DFT-based channel estimation for OFDM systems is proposed. Conventional DFT-based channel estimator improved its performance by suppressing noise, but it does not completely suppress noise. In order to overcome the disadvantage, this paper proposed a gate method without requiring any channel statistical information. This method comprehensively considersthe effects of the power of the strongest path and the noises. Computer simulation demonstrates the performance of the proposed algorithms in terms of bit error rate.

Abstract: Bandwidth enhancement and response flattening of wavelength conversion based on single-pass and double-pass cascaded second harmonic generation and difference frequency generation in step-segmented quasi-phase matched (QPM) gratings are investigated. For the same waveguide length, high conversion efficiency, flat response and broad signal bandwidth can be obtained simultaneously by optimizing the poling period of the step-segmented QPM structure. The conversion bandwidths in a 3-cm-long five-step-segmented waveguide are 134 nm for single-pass scheme and 132 nm for the double-pass one, respectively, which are both over the whole conventional band and long-wavelength band. The ripple on the matching response can keeps less than 0.2 dB as well.

Abstract: We report difference frequency generation-based wavelength conversion in step-segmented quasi-phase matched (QPM) gratings. It is shown that both the pump bandwidth and the signal bandwidth are efficiently widened by adding the segment number of QPM grating and optimizing the poling period of the first segment and the period shifts between adjacent sections. Especially, flattop conversion efficiency response with peak-to-peak ripples less than 0.2 dB, which is very helpful to multichannel conversion in WDM systems, can be achieved simultaneously. For 3-cm-long waveguide, the signal conversion bandwidth and the pump bandwidth reach 166 nm and 0.88nm, respectively, meanwhile the maximum efficiency is-0.55dB.