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Mohammadzadeh Qaratlu M.,Iran Telecom Research Center | Ghanbari M.,University of Essex
Signal Processing: Image Communication | Year: 2011

A spatial loss concealment algorithm for reconstruction of the lost blocks in the I-frames of a video sequence is proposed. The algorithm is carried out in three steps. In the first step an edge directional analysis on the boundaries of the lost blocks is carried out. In the second step, the lost pixels are approximated from the available neighboring blocks of that boundary. In the third step, the derived approximations of all available boundaries are combined for final reconstruction of the lost pixels. Experimental results over an H.264/AVC codec show an improvement of about 0.51 dB over a similar spatial loss concealment algorithm. The subjective quality of loss concealed pictures is also evaluated through SSIM measure. © 2011 Elsevier B.V. All rights reserved. Source


Goudarzi P.,Iran Telecom Research Center
Journal of Information Science and Engineering | Year: 2014

Due to the proliferation of the diversity in user behaviors and traffic demands, traffic engineering mechanisms have become an inevitable task in data networks. Nowadays, most commonly used algorithm in end hosts is the popular TCP and its variants (such as MulTCP). These are loss based schemes therefore exhibit oscillatory behavior which reduces network performance. Moreover, since the price for all sessions is normally based on the aggregate throughput, losses that are caused by TCP may affect other sessions as well and aggressively reduce their throughput and also have a drastic effect on the overall throughput/goodput of the network. In this paper a novel traffic engineering mechanism in the form of the selective pricing is proposed in which different prices are imposed on the network resources for different users. The proposed mechanism not only reduces the packet loss ratio, but also increases the goodput performance of the non-TCP elastic sessions such as Proportional or Minimum Potential Delay schemes. Stability property of the algorithms are investigated and some numerical analysis is presented to validate the results. Source


Samimi H.,Iran Telecom Research Center | Azmi P.,Tarbiat Modares University
Journal of Optical Communications and Networking | Year: 2010

In this paper, the bit error rate (BER) performance of a subcarrier intensity-modulated (SIM) free-space optical (FSO) communications system using binary phase shift keying (BPSK) is investigated over a K-distributed turbulence channel. First, the performance is analyzed employing a negative exponential turbulence model, and an exact closed-form expression is derived for the BER. Then, it is shown that the probability density function (PDF) of the K distribution can be approximated accurately by a finite sum of weighted negative exponential PDFs. Based on this interesting result and by using the closed-form expression, which is derived for the case of a negative exponential model, an approximate, closed-form expression for the BER of the BPSK-based SIM FSO over a K channel is derived. Moreover, to improve the BER performance, spatial diversity using selection combining (SC) is considered. It is shown that the PDF of the resulting channel irradiance corresponding to the SC diversity scheme over a K channel can be approximated accurately by a finite linear combination of negative exponential functions. The derived approximate PDF accurately estimates the PDF of the channel irradiance for arbitrary values of diversity order and is valid for a wide range of channel parameters. Then, an approximate, closed-form expression is derived for the average BER of the BPSK-based SIM FSO system employing the SC diversity technique over a K channel. Numerical results presented in this paper show that the derived approximate expressions are very accurate and can be used as efficient tools for performance analysis of the system. © 2009 OSA. Source


Samimi H.,Iran Telecom Research Center
International Journal of Communication Systems | Year: 2011

A new composite channel model is proposed for the performance analysis of shadowed fading channels. This model is represented as a mixture of generalized Gamma (GG) multipath fading and lognormal shadowing. GG distribution includes the Rayleigh, Nakagami, and Weibull as special cases; hence the presented model, which is referred to as GG-L, is a generic model that covers many well-known composite fading models, including the Rayleigh-lognormal (R-L), Nakagami-lognormal (N-L), and Weibull-lognormal (W-L). The main drawback of the lognormal-based composite models is that the composite probability density function (PDF) is not in closed form, thereby making the performance evaluation of communication links in these channels cumbersome. To bypass this problem, an approximation method is developed which makes it possible to derive a closed-form, analytical expression for GG-L composite distribution. The proposed method only needs the mean and the variance of the underlying lognormal distribution, and hence, bypasses the required complicated integration needed to calculate the PDF of the received signal envelope in GG-L channel. Based on this method, the most statistical characteristics, such as cumulative density function (CDF) and moments of the GG-L composite distribution, are derived and used for the performance analysis of a single receiver operating over GG-L fading channel. Copyright © 2010 John Wiley & Sons, Ltd. Source


Goudarzi P.,Iran Telecom Research Center
Telecommunication Systems | Year: 2014

Video transmission over error-prone cognitive radio wireless networks is a challenging task. In much of the traditional tight admission control algorithms for video cognitive users (CUs) in cognitive networks, CUs are admitted sequentially based on the strict quality of service and interference constraints imposed on the cognitive and primary users respectively. The sequential admittance of CUs may impose some form of the queuing delay for time-sensitive CUs which may be unacceptable. On the other hand, traditional admission control schemes do not consider the quality of experience of video users for admitting newly incoming ones. For addressing these issues and obtaining a more flexible quality-centric admission control policy by which the admission system can admit eligible cognitive users in parallel, and to cope with uncertainties in the acceptable levels of the video quality for different CUs (which may use different softwares/hardwares with different capabilities) and interference levels imposed on the primary users, a soft admission control (SAC) technique (named FQAC) is proposed by which the admission probability level for the parallel CUs can intelligently be controlled based on some linguistic input variables. Numerical analysis has been performed to validate the efficiency of the proposed quality-centric SAC mechanism in sparse and dense networking scenarios. © 2014, Springer Science+Business Media New York. Source

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