Zhu Yaoting

On the testing for alpha-stable distributions of ethernet network traffic

The modeling of network traffic is important for the design and application of networks, but little is known as to the characteristics of distribution of packets in network traffic. In this letter the distribution of packets in network traffic is explored.

A visual model weighted cosine transform for hiding watermark in images

Watermarking is a technique for labeling digital pictures by hiding secret information into images. Watermark embedding is a method to discourage unauthorized copying and identify the owner or distributor of digital data. In this paper, a new method is proposed. The watermark is processed as a visually recognizable pattern—binary image, which includes more information than the traditional symbol or ID number and is “extracted” instead of only “detected” to characterize the owner. The watermark is hidden in the host image by selectively modifying the middle-frequency part of the host image in conjunction with the human visual system(HVS) and the image discrete cosine transform(DCT). The experimental results show that this method can survive image cropping and image compression, and get better results, this is also a prospective method.

The performance analysis of direct sampling microwave radiometer

L-band direct sampling digital total power microwave radiometer (DSDTPMR) is a novel radiometer, which trades analog complexity for digital ditto. This article considered the low noise amplifier (LNA) gain fluctuation, analog-to-digital converter (ADC) sampling rates and quantization resolution, to derive a general mathematical expression of sensitivity of the DSDTPMR; Analyzed the influence of sampling rate, quantization on sensitivity of DSDTPMR; The simulation result indicating, when the sampling frequency is bigger than two times of signal bandwidth, the multi-bit quantization resolution has very small effect on the sensitivity; when the gain fluctuation obeys the Gaussian distribution, the gain fluctuation may reduce to radicN times.

A study on fractal properties of Mandarin speech

In this paper, fractal theory is successfully applied to the analysis of fractal properties of Mandarin speech. First, a new algorithm of the arithmetical progression scales gridding dimension, based on the conventional Box Dimension, is presented to reduce the computational cost. Second, the distribution laws of fractal dimension of Mandarin speech have been obtained by calculating and statistically analyzing the arithmetical progression scales gridding dimension of 21 consonants and 38 vowels of Mandarin speech. The preliminary results in our experiment show that Mandarin speech has the scale-invariant property and that the arithmetical progression scales gridding dimension can indicate the complexity and irregularity degree of the waveform of Mandarin speech signals. The novel discoveries in our studies imply that fractal theory has a good potential in the field of speech signals processing.

Development and Evaluation of a Distance Learning System Based on CSCW

This paper described a distance learning system, which allows Internet users to conduct a lesson in real-time from any kinds- attached computers. Participants can jointly view and edit relevant multimedia information distributed through Internet. Teachers and students can also simultaneously communicate by voice and text to discuss the problems. Teacher can broadcast streaming PowerPoint presentation in real time to network users. In addition to sliders, presenters can broadcast video and audio simultaneously to deliver a live multimedia show online, and store their presentations for on-demand playback. Teachers distributed in different places can also use cooperative editing tool to edit and encode existing digital content. We discussed some important design principles of the system. Then, the system configuration and the results of evaluation are also presented. The system has proved to be applicable to the distance learning based on CSCW (Computer Support Cooperative Work) in Internet.

Throughput analysis considering capture effect in IEEE 802.11 networks

The impact of capture effect on the IEEE 802.11 networks with different transmission speeds is investigated in this paper. A new Markov chain model considering capture effect for the binary exponential back-off scheme in the MAC layer has been proposed in the first time. Based on the new Markov chain model, a new throughput model is proposed, and then the impact of capture effect on throughput has been analyzed in the condition of different transmission speeds. The performance analysis shows that, in the RTS/CTS scheme, the improvement throughput of high speed networks caused by capture effect is more than that of low speed networks.The impact of capture effect on the IEEE 802.11 networks with different transmission speeds is investigated in this paper. A new Markov chain model considering capture effect for the binary exponential back-off scheme in the MAC layer has been proposed in the first time. Based on the new Markov chain model, a new throughput model is proposed, and then the impact of capture effect on throughput has been analyzed in the condition of different transmission speeds. The performance analysis shows that, in the RTS/CTS scheme, the improvement throughput of high speed networks caused by capture effect is more than that of low speed networks.

Edge detection based on fractal coding

We propose a novel edge detection method based on fractal coding. We point out that the mean-square-error distance (MSED) of fractal coding can be used to extract edges of a fractal image effectively. The algorithm for edge detection based on fractal coding MSED is given and its improvement is discussed. Results indicate that since the new algorithm for edge detection avoids the gradient operation, it is insensitive to noise and suitable for object detection in natural scenes based on edges.

A statistical inversion algorithm for aperture synthesis radiometers

In order to deal with the inverse problem in aperture synthesis radiometers (ASRs) imaging, some deterministic inversion algorithms are proposed. However, these inversion algorithms are deficient in utilizing the statistical properties of visibility samples and reconstructed image. In this paper, the probability density functions of visibility samples and pixels of reconstructed image are investigated. A statistical inversion algorithm is presented, in which the statistical properties are introduced to constrain solution of the inverse problem. Simulation and experiment results show the statistical inversion algorithm can greatly improve the image quality of ASRs.

Near-field imaging of one-dimensional aperture synthesis radiometers

For synthetic aperture radiometers under far-field (FF) condition, the relationship between the visibility and the brightness temperature is a Fourier Transform. However, it is no longer valid when synthetic aperture radiometers are applied at short distances. A novel method based on a reference position for near-field (NF) imaging of one-dimensional aperture synthesis radiometers (ASR) is proposed. By subtracting the phase of NF visibility samples of a point source at the reference position from the phase of NF visibility samples of the imaged scene, the relation between the brightness temperature and the NF visibility can be represented by another form of Fourier Transform. Then direct DFT inversion algorithm is applied. Simulations and NF experimental results demonstrate the validity of the method for both point and extended sources. The method can be used not only in those applications at NF region of ASR, but also indoor performances test of spaceborne ASR.

The Effect of the Signal Correlation on the Array of Synthetic Aperture Microwave Radiometer

The signal correlation, the key problem in the technology of Synthetic Aperture Microwave Radiometer (SAMR), is analyzed in detail. Firstly, the expression of the microwave signal passing through the front of radiometer is deduced. Secondly, the signal correlation of SAMR is analyzed, with the conclusion that the signal correlation has a strong effect on the array.