A. Zolghadrasli; S. Rezazadeh
Volume 5, Issue 2 , July 2007, , Pages 123-139
Abstract
In this paper, we introduce a multiresolution watermarking method for copyright protection of digital images. The method is based on the discrete wavelet transform. A noise type Gaussian sequence is used as watermark. To embed the watermark robustly and imperceptibly, watermark components are added ...
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In this paper, we introduce a multiresolution watermarking method for copyright protection of digital images. The method is based on the discrete wavelet transform. A noise type Gaussian sequence is used as watermark. To embed the watermark robustly and imperceptibly, watermark components are added to the significant coefficients of each selected subband by considering the human visual system (HVS) characteristics. Some small modifications are performed to improve the HVS model. The host image is needed in watermark extraction procedure, and Normalized Correlation Function (NCF) is used to measure similarities of extracted watermarks. It is shown that this method is robust against wide variety of attacks. Comparison with the existing methods shows the better performance of this suggested method.
A. R. ZOLGHADR ASLI; B. AMIN SHAH; M. A. MASNADI SHIRAZI; M. H. GHAMAT
Volume 4, Issue 2 , July 2006, , Pages 1-14
Abstract
One of the limitations of orthogonal frequency division Multiplexing (OFDM) in many applications is its sensitivity to frequency shifts, errors normally referred to as carrier frequency offset (CFO). Although, this small offset is negligible in conventional single carrier communication systems, it ...
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One of the limitations of orthogonal frequency division Multiplexing (OFDM) in many applications is its sensitivity to frequency shifts, errors normally referred to as carrier frequency offset (CFO). Although, this small offset is negligible in conventional single carrier communication systems, it is a severe problem in the OFDM systems. Because, the carriers in OFDM are inherently closely spaced in frequency, the tolerable frequency offset becomes a very small fraction of the channel bandwidth. Besides, for OFDM communication systems, the frequency offset in mobile radio channels distorts the orthogonality between subcarriers, resulting in intercarrier interference (ICI). In this paper, we analyze and compare the performance of some already existing methods for reducing ICI with new ICI cancellation schemes by simulation. Also the advantage of using a coding scheme is shown.
A. R. Zolghadre Asli; D. Bakhshi
Volume 4, Issue 1 , July 2006, , Pages 23-37
Abstract
One of the most effective techniques to mitigate multipath fading and inter-cell interference at a downlink wireless channel in WCDMA systems for achieving high capacity is transmitter power control. In this case, system increases the power of the subscriber when its interference increases in order ...
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One of the most effective techniques to mitigate multipath fading and inter-cell interference at a downlink wireless channel in WCDMA systems for achieving high capacity is transmitter power control. In this case, system increases the power of the subscriber when its interference increases in order to satisfy the requested signal qualities. However, when the requested signal qualities are infeasible, the power control algorithms might diverge as a result of power limitation. Another way to mitigate multipath problems is using diversity techniques. Space-time diversity offers an advantage in the forward link of the WCDMA system. In this paper, three environments for forward link power control, together with space-time diversity, are examined. These are indoor office, indoor-outdoor pedestrian and vehicular environments. The simulator takes into account 19 hexagonal cells with spatially uniform user distribution and a propagation channel characterized by distance attenuation, fast Rayleigh fading and inter-cell interference. Computer simulations are given to evaluate the effect of space-time diversity on convergence of downlink power control algorithms. Simulation results show that space-time diversity together with downlink power control have very good performance, especially in the vehicular environments with high mobile speed.
A. Zolghadrasli
Volume 3, Issue 1 , July 2005, , Pages 47-56
Abstract
In this paper the author considers a general method, based on time domain samples for spectral manipulation of time limited signals. First, the original signal is divided into some frames in the time domain. Then, by presenting a suitable theoretical and computational algorithm, and using a method ...
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In this paper the author considers a general method, based on time domain samples for spectral manipulation of time limited signals. First, the original signal is divided into some frames in the time domain. Then, by presenting a suitable theoretical and computational algorithm, and using a method for improving the speed of convergence, we find the local bandwidth of each frame; thereby, each frame is sampled with a new rate, so the amount of data per frame is decreased. Finally, by storing suitable information at the beginning of each frame, the original signal could be reconstructed. Therefore, by this method some redundant data is removed and the net volume of data is reduced. The reconstruction of original signal is achieved by using periodic interpolation. In this technique, a method for reduction of error (due to false interpolation) at the end of any frame is examined carefully.
A. R. Zolghadr Asli; E. Goodarzi; M. Moosavinezhad
Volume 2, Issue 1 , July 2004, , Pages 3-12
Abstract
This paper presents a full duplex, real time implementation of ITU-T G.723.1 [7,8] speech coder using the TMS320C5402 DSP chip which is based on a 16 bit fixed-point architecture. An optimization method is proposed in order to reduce the total necessary cycle time consumed in real-time implementation. ...
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This paper presents a full duplex, real time implementation of ITU-T G.723.1 [7,8] speech coder using the TMS320C5402 DSP chip which is based on a 16 bit fixed-point architecture. An optimization method is proposed in order to reduce the total necessary cycle time consumed in real-time implementation. The Multi-Pulse Maximum Likelihood Quantization (MP-MLQ) excitation search block which is the most computation-intensive block in the coder is restructured to reduce the algorithmic redundancy. In addition, efficient filtering methods and memory management are used for further optimization. The bit-exact verification with the ITU test vectors and performance evaluation aspects are also discussed in this paper.
