Mohsen Ashourian

A new masking method for spatial domain watermarking of three-dimensional triangle meshes

We examine a new masking scheme for three-dimensional mesh watermarking in the spatial domain. The masking factor at each point is defined based an estimate of the average difference between the position of connected vertices to a vertex. We test the proposed watermarking scheme by embedding a random binary sequence and applying different attacks, such as additive random noise, compression by MPEG-4 SNHC, and mesh simplification, which shows that the proposed masking scheme can improve the robustness of the spatial domain watermarking scheme.

Improved Dynamic Range Microwave Photonic Instantaneous Frequency Measurement Based on Four-Wave Mixing

An improved dynamic range instantaneous frequency measurement system based on four-wave mixing effect in a highly nonlinear fiber was practically demonstrated. A closed-form model was developed to predict the behavior of the system. The model predicted that the system output would have a low frequency voltage which was a function of RF input frequency. The system performance was also practically demonstrated. The system characterization showed a 0.04-40-GHz frequency measurement range with 51-dB dynamic range for 100-MHz measurement error at the end of the band. A maximum relative measurement error of 0.35% was achieved over the entire frequency range. This dynamic range was achieved by employing the lock-in amplification technique.

Digital watermarking of three-dimensional polygonal models in the spherical coordinate system

In this paper, we propose a new digital watermarking scheme for the three-dimensional (3D) mesh model in the spatial domain. In order to insert and extract watermark signals, we generate triangle strips by traversing the 3D mesh model. We embed the watermark signal into vertex positions of the 3D model in the spherical coordinate representation. We define a new masking operation for the watermark signal according to the variation of vertex positions along the traversed strips so that we can change the embedding strength adoptively and reduce the visibility distortion of the data embedding. We test the proposed watermarking scheme by embedding a random binary sequence and applying different attacks, such as additive random noise, compression by MPEG-4 SNHC, and mesh simplification, which shows the robustness of the watermarking scheme

A Low Complexity Resource Allocation Method for OFDMA System Based on Channel Gain

In orthogonal frequency division with multiple access (OFDMA) systems dynamic radio resource allocation improves overall performance by exploiting the multiuser diversity gains. A key issue in OFDMA is the allocation of the OFDM subcarriers and power among users sharing the channel. This paper proposes a new rate adaptive resource allocation scheme in the OFDMA downlink transmission system. Our proposed algorithm is based on the users’ sensitivity to the subcarrier allocation which means how frequency selective is the channel from the user’s perspective. As a result of frequency selectivity of the channel, different subchannels of the same user experience different levels of fade. However, how different they undergo fading could be measured by difference between maximum and minimum channel gain of that user. Our proposed method is based on difference between maximum channel gain and minimum channel gain for each user and uniform distribution of power among subcarriers. Simulation results show that the proposed algorithm achieves higher capacity over fixed TDMA method, and reported suboptimal methods with acceptable rate proportionality.

Dynamically Reconfigurable All Optical Frequency Measurement System

A microwave photonic frequency measurement system is demonstrated practically. The system employs the four-wave mixing effect in a highly nonlinear fiber to produce a low-frequency output voltage, which is a function of input RF frequency. Using an algorithm that allows dynamic reconfiguration, the system is able to instantaneously monitor a broad frequency range for threat signals and to provide fast yet accurate frequency measurement. An operating frequency range of 0.04-40 GHz with at most 0.016% error is achieved.

A review on online quality measures for videos

A growing concern of video researchers and broadcasters is the assurance and maintenance of an acceptable service quality level for the distribution of video signal. Subjective tests are the most reliable but they are too time-consuming for wide application. To overcome this problem many objective quality metrics have been proposed. In this paper we review some of the main proposed schemes and standards. Also we provide the potentials of new techniques for online visual quality evaluation systems.

Multiple Description Coding for Image Data Hiding in the Spatial Domain

In this paper, we develop a robust image data hiding scheme based on multiple description coding of the signature image. At the transmitter, the signature image is encoded by balanced two-description scalar quantizers in the wavelet transform domain. The information of the two descriptions are embedded in the host image in the spatial domain with a masking factor derived from the gradient of the image intensity values. At the receiver, the multiple description decoder combines the information of each description and reconstructs the original signature image. We experiment the proposed scheme for embedding a gray-scale signature image of 128×128 pixels size in the spatial domain of the gray-scale host image of 512×512 pixels. Simulation results show that data embedding based on multiple description coding has low visible distortions in the host image and robustness to various signal processing and geometrical attacks, such as addition of noise, quantization, cropping and down-sampling.

Carrier Frequency Independent RF Photonic QPSK Modulator

An RF photonic quadrature phase-shift keying (QPSK) modulator is conceived and demonstrated practically. The modulator has the ability to operate with any RF carrier frequency within an ultra-broad frequency range. This is achieved via utilization of a broadband Hilbert transformer. The transformer enables wideband 90 ° phase shifts required for QPSK to be realized. The carrier frequency independent operation of this modulator makes it a perfect candidate for many applications such as electronic warfare transmitters operating based on frequency hopping. An operational frequency range of 9.8-30.2 GHz was achieved.

Reconfigurable photonic radar warning receiver based on cascaded grating

A photonic radar warning receiver was conceived and practically demonstrated. The system was very flexible in terms of frequency measurement range and resolution. This was achieved using a cascaded grating which provided different time delays for different wavelengths. The system was thus able to become reconfigured to operate at both broadband, low resolution and narrow band, high resolution modes.

ROBUST AND FAST TRACKING ALGORITHM IN VIDEO SEQUENCES BY ADAPTIVE WINDOW SIZING USING A NOVEL ANALYSIS ON SPATIOTEMPORAL GRADIENT POWERS

Success of a tracking method depends largely on choosing the suitable window size as soon as the target size changes in image sequences. To achieve this goal, we propose a fast tracking algorithm based on adaptively adjusting tracking window. Firstly, tracking window is divided into four edge subwindows, and a background subwindow around it. Then, by calculating the spatiotemporal gradient power ratios of the target in each subwindow, four proper expansion vectors are associated with any tracking window sides such that the occupancy rate of the target in tracking window should be maintained within a specified range. In addition, since temporal changing of target is evaluated in calculating these vectors, we estimate overall target displacement by sum of expansion vectors. Experimental results using various real video sequences show that the proposed algorithm successfully track an unknown textured target in real time, and is robust to dynamic occlusions in complex noisy backgrounds.