Sharif Digital Repository

Multiple Description Coding (MDC) is a technique for video transmission over error prone networks where the descriptions are routed over multiple paths. Intra coding like MDC provides error resiliency but coding in this mode must be decided with care since it degrades the compression ratio. In this paper, we present our investigation results for a new intra coding approach in MDC. We have found that, in MDC streams, the best policy is to encode selective frames as I-frame instead of coding some macroblocks of frames in intra mode. In order to find the most suitable I-frame positions within a given video stream, we developed a cost function based on which intra/inter frame type is decided.... 

In this work, first, a Region of Interest (ROI)-based Unequal Loss Protection (ULP) scheme with no delay is proposed for High Definition (HD) interactive video applications such as video calls. The proposed scheme uses Data Partitioning and Flexible Macro block Ordering (FMO) tools of H.264/AVC and reduces error propagation. The obtained data demonstrates that this scheme achieves better ROI quality than others in high Packet Loss Rates (PLR). Second, it is also shown that the efficient scheme for protecting ROI-based interactive video applications in wide PLR ranges is switching both the Forward Error Correction (FEC) distribution pattern and the codec configuration between various... 

Background: The researches regarding the influence of microthread design variables on the stress distribution in bone and a biomechanically optimal design for implant neck are limited. The aim of the present study is to compare the effect of different microthread designs on crestal bone stress. Materials and Methods: Six implant models were constructed for three-dimensional finite element analysis including two thread profile (coarse and fine) with three different lengths of microthreaded neck (1 mm, 2 mm, and 3 mm). A load of 200 N was applied in two angulations (0° and 30°) relative to the long axis of the implant and the resultant maximum von Mises equivalent (EQV), compressive, tensile,... 

There has been an increasing demand for interactive video transmission over the Internet for applications such as video conferencing, video calls, and telepresence applications. These applications are increasingly moving towards providing High Definition (HD) video quality to users. A key challenge in these applications is to preserve the quality of video when it is transported over best-effort networks that do not guarantee lossless transport of video packets. In such conditions, it is important to protect the transmitted video by using intelligent and adaptive protection schemes. Applications such as HD video conferencing require live interaction among participants, which limits the... 

Massively multi-user virtual environments (MMVE) incorporate computer graphics, sound and haptics to simulate the experience of real-time interaction among multiple users in a shared three-dimensional virtual world. Such applications therefore deal with the distribution of updates among their users to provide them with a common sense of time and place while interacting in the virtual environment. As MMVEs grow larger in terms of size and numbers of users, they tend to rely on P2P architecture as a scalable way of exchanging the huge bulk of updates among their users without the need for the exponential increase in their central servers. While much work has been done on P2P architectures for... 

At a first glance, transmitting update information to a geographic region in the virtual space seems to be an attractive primitive in Massively Multiplayer Online Gaming (MMOG) applications where players are constantly moving and need to send updates to their neighbors who are in the same region of the virtual space. The system would become more scalable if entities did not need to keep track of each other or send messages directly to one another. Rather, an entity could just send a message to a specific region in the virtual space (its area of effect), as opposed to sending packets to specific IP addresses, significantly reducing tracking and routing overhead. Fundamentally speaking, update... 

Crosstalk faults occurring in wires of Networks on Chip (NoCs) can seriously threaten the reliability of data transfer. One efficient way to tackle crosstalk faults is numeral-based Crosstalk Avoidance Codes (CACs). Numeral-based CACs reduce crosstalk faults by preventing specific transition patterns to occur. One-Lambda Codes (OLCs) are the most efficient types of CACs. However, the codec of OLCs imposes overheads including power consumption, critical path and area occupation to the routers of NoCs. To find overhead-efficient OLCs, this paper proposes an Algorithm for Generating OLC Numeral systems (AGON). AGON provides a tradeoff for designers in selecting overhead-efficient OLCs. Using... 

As massively multiuser virtual environments (MMVEs) expand in terms of size and user population, they tend toward using P2P architectures as a way to provide scalability without the need for large centralized resources. Distributed hash table (DHT)-based networks have been introduced as a promising option for overlay-based distributed massively multiuser virtual environment applications. However, overlay latency stretch seriously affects MMVE performance where QoS is crucial for real-time user collaboration. This work includes a series of efforts in the alleviation of such undesired latency. Our approach to latency mitigation consists of two phases. First, we propose a position-based ID... 

Inter-wire coupling capacitance may lead to crosstalk faults that significantly limits the reliability of NoCs. In this paper, we propose a numerical-based crosstalk avoidance code that can omit the Triplet Opposite Direction (TOD) transitions produced by crosstalk faults. The proposed coding does not have ambiguity and uses all of the codeword space. Simulations using VHDL for different channel widths show that the proposed method can reduce crosstalk fault in the NoC links with negligible power and area overheads  

This paper proposes an efficient crosstalk mitigation method for Network-on-Chips. This method uses the binary-reflected Gray coding to send the proper code word into a channel. As the Gray code has reflective and unit distance properties, based on these facts, content of every flit is selected so that to minimize the number of forbidden transition patterns in the channel. A VHDL-based simulation is carried out for several channel widths. Simulation results show that the proposed method reduces the forbidden transitions up to 26% and can save power in NoC links  

Inter-wire coupling capacitances can lead to crosstalk fault that is strongly dependent on the transition patterns appearing on the wires. These transition patterns can cause mutual influences between adjacent wires of NoCs and as a result threaten the reliability of data transfer seriously. To increase the reliability of NoCs against the crosstalk fault, Forbidden Pattern Free (FPFs) codes are used. To generate FPF codes, numerical systems are among the overhead-efficient mechanisms. The algorithms of numerical systems have direct effect on the amounts of the codec overheads including power consumption, area occupation and performance of NoCs. To find an overhead-efficient numerical system,... 

Video activity analysis is used in various video applications such as human action recognition, video retrieval, video archiving. In this paper, we propose to apply 3D wavelet transform statistics to natural video signals and employ the resulting statistical attributes for video modeling and analysis. From the 3D wavelet transform, we investigate the marginal and joint statistics as well as the Mutual Information (MI) estimates. We show that marginal histograms are approximated quite well by Generalized Gaussian Density (GGD) functions; and the MI between coefficients decreases when the activity level increases in videos. Joint statistics attributes are applied to scene activity grouping,... 

Multiple Description Coding (MDC) is a technique where multiple streams from a source are generated, each individually decodable and mutually refinable. In this paper, a new Mixed Layer MDC (MLMDC) scheme is presented which achieves a higher side quality compared to conventional MDCs. The improved side performance leads to higher average video quality at the receiver in lossy networks. For each DCT coefficient, we generate two coefficients: Base Coefficient (BC) and Enhancement Coefficient (EC) which are combined together. When all descriptions are available, they are decomposed and decoded to achieve high quality video. When one description is not available, we use estimation to extract as... 

This paper addresses a new approach to the keyframe extraction problem employing generalized Gaussian density (GGD) parameters of wavelet transform subbands along with Kullback-Leibler distance (KLD) measurement. Shot and cluster boundaries are selected using KLDs between GGD feature vectors, and then keyframes are located based on similarity and dissimilarity criteria. Objective and subjective evaluations show the high accuracy of this new approach compared with traditional methods  

In this paper, we present a spatio-temporal event-based approach to video signal analysis and abstraction employing wavelet transform features. The video signal is assumed to be a sequence of overlapping independent visual components called events, which typically are temporally overlapping compact functions that describe temporal evolution of a given set of the spatial parameters of the video signal. We utilize event-based temporal decomposition technique to resolve the overlapping arrangement of the video signal that is known to be one of the main concerns in video analysis via conventional frame-based schemes. In our method, a set of spatial parameters, extracted from the video, is... 

We present an Autoregressive (AR) modeling method for video signal analysis based on 2D Wavelet Statistics. The video signal is assumed to be a combination of spatial feature time series that are temporally approximated by the AR model. The AR model yields a linear approximation to the temporal evolution of a stationary stochastic process. Generalized Gaussian Density (GGD) parameters, extracted from 2D wavelet transform subbands, are used as the spatial features. Wavelet transform efficiently resembles the Human Visual System (HVS) characteristics and captures more suitable features, as compared to color histogram features. The AR model describes each spatial feature vector as a linear... 

We propose an event based approach for locating keyframes in natural video through detection of locally correlated spectral targets. Temporal Decomposition (TD) is used to describe a set of spectral parameters of the video as a linear combination of a set of temporally overlapping event functions. This process provides preliminary information about keyframes, by selecting the frames located at event centroids as the keyframe candidates. No shot or shot cluster boundary detection is needed and keyframes are extracted directly from among event centroids that are much smaller in number than the number of frames. Generalized Gaussian Density (GGD) parameters, extracted from 2D wavelet transform...