Wang Yiding

The maximum phase error of a reflected signal in an active coded transponder

This letter is devoted to investigate the active coded transponder (ACT), which is designed to add a phase shifter to an active transponder (AT). Since a phase shifting error of a phase shifter is inevitable, there is additional phase error in reflected signal from ACT to synthetic aperture radar (SAR). This letter presents the theoretical study of the phase error of reflected signal. A method is proposed to determine the maximum phase error of the reflected signal. Moreover, images of ACT with different maximum phase errors are simulated. Peak-value and integral methods are used also to evaluate the accuracy of SAR radiometric calibration.

Application of inverse chirp-z transform in wideband radar

Pulse stepped frequency radar is a kind of wideband radar technique. It can obtain high range resolution by correct signal processing methods. One of most important methods is the inverse Fourier transform method. This method can realize pulse compression by the coherent sum of a series of echoes. Although the inverse Fourier transform method is very useful, the number of echo series limits the sampling resolution. In order to improve the sampling resolution at a fixed number of echo series, a special inverse chirp-z transform method is presented in this paper. This special inverse chirp-z transform method has all the features of the inverse Fourier transform method. It can compress a series of pulse signals and increase sampling resolution within a range profile window.

A modified apodization method in SAR/ISAR processing

SAR/ISAR image processing involves a 2D Fourier transform that produces high intensity sidelobes which obscure low intensity scatters in the image. Although the sidelobe can be reduced using parametric windows, the image resolution becomes worse. The apodization technique can reduce sidelobe level while maintaining the image resolution. In this paper, based on the analysis of the apodization algorithm, a modified apodization method was present via stronger constraint. The modified method has higher resolution and lower sidelobe level than the original method. This method was proved correct with a real ISAR image.

A New Method of Progressive Images Transmission Based on Lagrange Interpolation Polynomials over Finite Fields

Progressive images transmission is a very important technique in the area of information exchange over low speed channels. A new progressive images transmission method based on Lagrange interpolation polynomials over finite fields is proposed in this paper, the new method is a flexible parameters method, and which method can apply digital images of any types. In addition, the proposed method can extend to audio and video areas easily, so we take an option that the method will have a good perspective.

Errors Analysis of Spectrum Inversion Methods

Two kinds of spectrum inversion methods are investigated. One is analog mixing method; another is digital undersampling method, which is put forward in this paper. In order to prove the digital undersampling method is better than the analog mixing method. The error models of these two methods are set up. Based on the error models, simulation experiments are carried out. The results prove that the digital undersampling method is of much more precision than the analog mixing method.

Phase shifting error of active coded transponder in SAR external radiometric calibration

This paper investigated active coded transponder (ACT), which designed with a phase shifter, in SAR external radiometric calibration. Because of the error of phase shifting, ACT caused additional phase error in azimuth reflected signal to SAR. Based on pair echoes’ theory, this phase error changed signal and clutter ratio of ACT in SAR external radiometric calibration image and influenced SAR external radiometric calibration precision. In this paper, the phase shifting error of ACT was studied in detail. Under the condition of signal and clutter ratio, a method how to calculate phase shifting error (maximum phase shifting error) was put forward. The images of active coded transponder with different phase shifting error were simulated. Peak-value method was used to extract SAR external radiometric calibration coefficients. Finally the relationship between the phase shifting error of ACT and SAR external radiometric calibration precision was established.

A new storage scheme for streaming media server cluster

We report on the design, implementation of a non-equal scheme in streaming media data storage. According to the characteristics of the streaming media and considering the human beings usage, our scheme combines n-way mirroring and erasure-coding together to storage streaming media data. It is make good tradeoffs between system fault-tolerance and sufficient quality of service streams. The system has the optimal storage efficiency and the remarkably fault-tolerant capability. At last the design of the non-equal streaming media data cluster storage system is introduced in detail, and an intensive performance evaluation study on it is performed.

Secret Image Sharing Based on Array Codes

A new secret image sharing scheme is proposed in this paper, and which scheme is based on array codes. Any type digital images can be shared by the new method, and compared to other secret image sharing schemes, all the calculations of the new scheme only uses XOR operations, so it is very efficiently. And more, the new scheme can share multi secret images, all shadow images can have clear visual significance, and pixels of all images including secret images and shadow images would not be expanded. In addition, the new method can extend to audio and video areas easily, so we think this method will have a good perspective.

An Efficient Copyright Protection Technique for Digital Images Based on Finite Groups

It is well known that a digital signature scheme and digital timestamp are two well-defined security methods for copyright protection. However, these techniques are not suitable for dealing with digital images directly because of some intrinsic features of digital images such as large amount of data, highly redundancy, and strong correlation among pixels. For this reason, digital watermarking has received considerable attention for copyright protection. In this paper, a robust copyright protection scheme for digital image is proposed. In the new scheme, Color images can be used as the watermark is an important characteristic and the watermark does not require to be embedded into the protected image but is used to generate a secret image by addition operations over finite groups, then the secret image is registered to certified authority (CA) for further protection. The experimental results show that the proposed scheme not only can clearly verify the copyright of the digital image, but also is robust to withstand many image processing attacks.

A new encoding transponders for SAR calibration

A transponder can encode the signal transmitted by synthetic aperture radar (SAR). The reflected signal from the encoding transponder to SAR can be imaged with the background signals suppressed. One type of encoding transponder is to make the linear frequency modulation (LFM) signal transmitted by SAR inverted. To realize this aim, there are the analog mixing method and the digital undersampling method, which is put forward in this paper. The error models of these two methods are studied. Simulation experiments about an input LFM signal are carried out. The results prove that the precision of the digital undersampling method is better than that of the analog mixing method.