Sharif Digital Repository

In this paper, the application of a well known mathematical theorem, Banach's fixed point theorem [1], is investigated in iterative signal processing in communications. In most practical communication systems some sort of a contraction mapping is used to enhance the operation of the system. Thus, using a suitable iterative approach, one can set the system in its fixed point and hence, the distortion produced in the transmitter, channel and the receiver can be compensated. In other words, a loosely designed transceiver can be enhanced by an iterative method. In order to verify the truth of the proposed iterative method, the distortion of A/D and D/A converters is compensated at the receiver.... 

Many forms of diversity have been exploited in communication systems to combat fading nature of wireless channels. Some examples are time diversity, frequency diversity, space diversity and multiuser diversity. However, another form of diversity inherent in any wireless network, which is usually not exploited, is the diversity due to the shared medium of propagation. When in a network one node transmits to the other node, all the other nodes may hear this transmission and some of them can decode the data as well. This data can be used later to enhance the end-to-end network reliability. Previous works mostly consider some special cases of relay nodes configurations, not the general case. In... 

In this paper we propose a new method for estimating the mixing matrix, A, in the linear model X = AS, for the problem of underdetermined Sparse Component Analysis (SCA). Contrary to most existing algorithms, in the proposed algorithm there may be more than one active source at each instant (i.e. in each column of the source matrix S), and the number of sources is not required to be known in advance. Since in the cases where more than one source is active at each instant, data samples concentrate around multidimensional subspaces, the idea of our method is to first estimate these subspaces and then estimate the mixing matrix from these estimated subspaces. ©2007 IEEE  

In this work, we have examined the distributed consensus averaging problem from a novel point of view considering the need for privacy and anonymity. We have proposed a method for incorporating security into the scalable average consensus mechanisms proposed in the literature. Random Offsets Method (ROM) is lightweight, transparent and flexible since it is not based on cryptography, does not require any change in the fusion system and can be used optionally by some nodes who care about their privacy. In this method, which is based on noisiflcation of nodes' information, we achieve robustness against n - 1 colluding adversaries in a network of n nodes, which is maximum level of robustness... 

In this paper, a new fixed structure learning automaton (FSSA), with a tuning parameter for amount of its rewards, is presented and its behavior in stationary environments will be studied. This new automaton is called TFSLA (Tunable Fixed Structured Learning Automata). The proposed automaton characterizes by star shaped transition diagram and each branch of the star contains N states associated with a particular action. TFSLA is tunable, so that the automaton can receive reward flexibly, even when it accepted penalty according to its previous action. Experiments show that TFSLA converges to the optimal action faster than some older FSSAs (e.g. Krinsky and Krylov) and the analytic examination... 

In this paper, we propose the first comprehensive mathematical performance model for product networks where fully adaptive routing is applied. Besides the generality of this model which makes it suitable to be used for any product graph, our analysis shows that the proposed model exhibits high accuracy. Simulation results show the validity and accuracy of the model even in heavy traffic and saturation region, where other models have severe problems for prediction. © 2007 IEEE  

In this paper, a new algorithm for Sparse Component Analysis (SCA) in the noisy underdetermined case (i.e., with more sources than sensors) is presented. The solution obtained by the proposed algorithm is compared to the minimum l1 -norm solution achieved by Linear Programming (LP). Simulation results show that the proposed algorithm is approximately 10 dB better than the LP method with respect to the quality of the estimated sources. It is due to optimality of our solution (in the MAP sense) for source recovery in noisy underdetermined sparse component analysis in the case of spiky model for sparse sources and Gaussian noise. © 2007 IEEE  

The most common technique for analysis and control of power electronics circuits is switch averaging. The model is not linear however, and often results in a multiplicative term in the state equations. Hence, it is common to perform a small signal linearization of the model about an operating point. Models obtained with such method involve considerable approximation, and produce results that are limited for higher performance designs. In this paper a Piecewise Affine Approximation (PWA) technique is introduced for modeling of switched circuits. Modeling of a DC-DC buck-boost converter is presented as an illustrative example to show the favorable properties and broad utility of this approach.... 

This paper introduces advanced SVC. Advanced SVC has been simulated with regard to reactive power and unbalancy compensation. Then, a new space has been chosen for state equation based on combination of d-q and real space to positive - negative. By decoupling of active, reactive powers and positive, negative sequences and using decoupling circuit, the facility of each sequence control, by control circuit will be provided independently. After advanced SVC modeling, the load - which is electrification railway system - will be simulated. So a sample of electric locomotive in Iran has been investigated and simulated. By using the load model, the advanced SVC has been used for compensation of... 

in this paper we present an integrated classifier that is used in mammogram MR-image for classification of breast cancers and abnormalities using a Multi-stage classifier, the method developed here first classifies mammograms into normal and abnormal and then for abnormal cases determines that if the case cancer is benign or malignant and also determine the type of breast cancer. In this paper there are two main topics that must be considered. First one is selection of good features and second is designing a good structure for classifier. In this study, the features are a combination of some features that are extracted from Spatial Grey Level Dependency matrix and some statistical descriptor... 

Voice activity detection is an important step in some speech processing systems, such as speech recognition, speech enhancement, noise estimation, speech compression ... etc. In this paper a new voice activity detection algorithm based on wavelet transform is proposed. In this algorithm we use the energy in each sub band, and by two methods we extract feature vector from these values. Experimental results demonstrate advantage over different VAD methods. ©2008 IEEE  

One of the most important parameters in evaluating a watermarking algorithm is its capacity. Of course capacity has a paradoxical relation with two other important parameters: image quality and robustness. Generally, watermarking capacity is expressed by bit per pixel (bpp) unit measure. This measure does not show what the side effects would be on image quality and capacity. Therefore, we proposed a two dimensional measure named capacity curve which shows the effects of capacity on visual quality. In this measure we can find the amount of degradation by a numerical value for each modification in pixels. Our experimental results are compatible with previous works in this field. © 2008... 

Watermarking is the process of hiding information in a media and usually used to for copyright protection. In software watermarking, the information is added to the source code of program and can be extracted from compiled executable code. In this paper, a new software watermarking algorithm is proposed by equation reordering. In this method, the order of operands in an equation is changed according to the information we want to hide in a way that the result of the equation is unchanged. One of the main advantages of this method is that no code added to the program, so the size and speed of the program not changed  

This paper proposes a new technique called CFEDC to detect and correct control flow errors (CFEs) without program interruption. The proposed technique is based on the modification of application software and minor changes in the underlying hardware. To demonstrate the effectiveness of CFEDC, it has been implemented on an OpenRISC 1200 as a case study. Analytical results for three workload programs show that this technique detects all CFEs and corrects on average about 81.6% of CFEs. These figures are achieved with zero error detection /correction latency. According to the experimental results, the overheads are generally low as compared to other techniques; the performance overhead and the... 

The rule based scheduling algorithms are a new trend in grid scheduling algorithms; the combination of rule based algorithms for resource selection with various dispatching rules for queuing of jobs can improve or deteriorate their performance. Thus, choosing a proper queuing strategy for each algorithm is a prominent issue in scheduling. In this paper, we introduce two new dispatching rules for resource selection and three new dispatching rules for queuing of jobs; we evaluate the performance of various combinations of these new rule based scheduling algorithms and queuing strategies. Also, we use some major combination of rule based scheduling algorithms with some important queuing... 

The IP Lookup Process is a key bottleneck in routing due to the increase in routing table size, increasing traffic and migration to IPv6 addresses. The IP routing lookup involves computation of the Longest Prefix Matching for which existing solutions, such as BSD Radix Tries, scale poorly when traffic in the router increases or when employed for IPv6 address lookups. In this paper, we describe a CREW PRAM multiprocessor organization lookup that uses P processor for solving LPM problem. By this technique P-1 IP addresses can be looked up simultaneously thus the performance of processors increase in linear manner. First we categorize all prefixes in some groups based on their first two bytes... 

A mobile ad hoc network (MANET) is a network without any predefined infrastructure in which every node not only enjoys the services from the network, but serves the network as a relaying router. Because of nodes mobility, these kinds of networks are highly dynamic. Therefore, link failure is so frequent. In this paper we propose a novel mobility management method which is independent of underlying routing protocol. Based on this mechanism, a node tries to keep an alternate node for its next hop and when a link breakage occurs, simply node uses its alternate node as next hop. Simulation results show that this mechanism can reduce average number of hop counts, number of selected routes and... 

Until now, many algorithms have been introduced for finding arbitrary shaped clusters, but none of these algorithms is able to identify all sorts of cluster shapes and structures that are encountered in practice. Furthermore, the time complexity of the existing algorithms is usually high and applying them on large dataseis is time-consuming. In this paper, a novel fast clustering algorithm is proposed. This algorithm distinguishes clusters of different shapes using a twostage clustering approach. In the first stage, the data points are grouped into a relatively large number of fuzzy ellipsoidal sub-clusters. Then, connections between sub-clusters are established according to the Bhatiacharya... 

Sudoku puzzle is a logical game which has recently got very popular. Every day various mass media print these puzzles. As a result these puzzles are a suitable alternative for hidden data transfer. SMS (short message service) is one of the popular mobile-phone services. In this service people can write short messages and send it to each other through mobile phones. In this paper a method has been presented for Steganography (hiding data) in Sudoku puzzles and through SMS. In this method after hiding data in a Sudoku puzzle, the puzzle is sent in a way that it does not attract any attention. Steganography algorithm is based on order of place of numbers 1 through 9 in one of the specified row... 

One of the major problems in liberalized power markets is loss allocation. In this paper, a new method for allocating transmission losses to pool market participants is proposed. The proposed method is fundamentally based on Bialek's "Tracing the flow of electricity" method. The losses is allocated to market participants using the loss weight factors (LWFs) which are obtained from the square current magnitude and Z-bus matrix. The LWF method is based on a solved load flow and strongly emphasizes on current magnitude while considers network topology. The method has been implemented and tested on several networks and one sample summarized in the paper. The results show that the method has an...