Sharif Digital Repository

In this paper, we study the downlink of cooperative Direct-Sequence Code Division Multiple Access (DS-CDMA) systems, where a set of Mobile Terminals (MT) cooperate with the purpose of improving their downlink communications reliability with Base Station (BS). For combating Multiple-Access Interference (MAI) as well as transferring complexity and spatial processing from the mobile terminals to the transmitter of BS, multiuser transmitter precoding is considered. In addition to multiuser precoding based on Minimum Mean-Square Error (MMSE) criterion for mitigating MAI, the proper transmission power control strategy under a fixed total power constraint is proposed and analyzed. Compared with... 

We study the problem of optimizing the symbol error probability (SEP) performance of cluster-based cooperative wireless sensor networks (WSNs). We propose that to achieve the minimum SEP at the destination, a joint optimization of power allocation and relay selection should be accomplished. To this aim, we reformulate the SEP performance of a simple cluster-based cooperative WSN in the general form and solve the joint optimization problem efficiently. Simulation results demonstrate that the proposed joint optimization can efficiently improve the SEP performance of the network in comparison with the previous disjoint optimal relay selection schemes  

We study the problem of power efficient tracking interval management for distributed target tracking wireless sensor networks (WSNs). We first analyze the performance of a distributed target tracking network with one moving object, using a quantitative mathematical analysis. We show that previously proposed algorithms are efficient only for constant average velocity objects; however, they do not ensure an optimal performance for moving objects with acceleration. Towards an optimal performance, first, we derive a closed-form mathematical expression for the estimation of the minimal achievable power consumption by an optimal adaptive tracking interval management algorithm. This can be used as... 

We study the problem of power optimization for object tracking using distributed Wireless Sensor Networks (WSNs). The accuracy of the object tracking is dependent on the tracking time interval. Smaller tracking time interval increases the accuracy of tracking a moving object. However, this increases the power consumption significantly. This paper proposes a modified adaptive sleep time management scheme called Modified Predict and Mesh (MPaM) to adapt tracking time interval such that it minimizes power consumption while keeping an acceptable tracking accuracy. Also a quantitative analysis to compare the performances of the conventional PaM and proposed Modified PaM (MPaM) schemes is... 

We consider the minimization of power consumption in target tracking wireless sensor networks (WSNs) using dynamic modification of tracking interval. In this context, we first analyze the performance of such networks, using a quantitative mathematical analysis. Then we calculate an upper bound for the achievable improvement in total power consumption, when using an adaptive time interval modification algorithm for tracking moving objects with acceleration. Towards this optimum functionality, we propose a novel adaptive algorithm (AHC) to adapt the tracking interval such that it minimizes power consumption while keeping an acceptable accuracy. Simulation results show that using the proposed... 

The accuracy of the object tracking is dependent on the tracking time interval. Smaller tracking time interval increases the accuracy of tracking a moving object. However, this increases the power consumption significantly. This paper proposes a new adaptive algorithm (AEC) to adapt tracking time interval such that it minimizes power consumption while keeping the required accuracy. Simulation results show that using the proposed algorithm, the tracking network has a good performance with the added advantage of reducing the power consumption significantly when compared with existing nonadaptive methods (like PATES). Moreover, simulation results show that the performance of the proposed... 

Reservoir topography has significant effects on mechanism of selective withdrawal. We study selective withdrawal of a linearly stratified fluid through a point sink in a long rectangular reservoir with a sill at the bed experimentally and analytically. Experiments were conducted for various flow rates and sill heights to evaluate their effects on withdrawal layer in the inertial-buoyancy regime. Transition to the steady state is discussed in terms of dynamics of shear waves over the sill. The results show that in presence of a sill the withdrawal layer is thicker and higher in elevation. For flows controlled at the sill crest, the withdrawal layer thickness in the point-sink flow is almost... 

This paper quantitatively investigates the role of flexibility of blade-like stems and, in particular, the occurrence of stem resonance on lateral dispersion in emergent aquatic canopies. Two sets of experiments are presented: single-stem and canopy tests. In the first set, the flow around single blade-like flexible model stems and the proximity to a resonant state are studied. Wake areas behind four model stems with distinct flexibilities are measured by particle image velocimetry for stem Reynolds numbers between 350 and 850. A single flexible emergent stem bends and oscillates in in-line and cross-flow directions due to periodic forcing associated with the vortex shedding. The plant... 

A social network is a set of people (or organizations or other social entities) connected by a set of social relationships, such as friendship, co-working or information exchange. Social network analysis focuses on the analysis of patterns of relationships among people, organizations, states and such social entities. Social network analysis provides both a visual and a mathematical analysis of human relationships. Web can also be considered as a social network. Social networks are formed between Web pages by hyperlinking to other Web pages. In this paper a state of the art survey of the works done on social network analysis ranging from pure mathematical analyses in graphs to analyzing the... 

Harmonic State Estimation (HSE) is a technique for identifying harmonic distributions in power systems with limited measurements. The main problem in HSE is the optimal placement of measurement meters such that the estimation error is minimized, while making the system fully observable. The second issue is the HSE method. This method must be accurate and fast enough in order to have an accurate HSE. This paper presents a new algorithm that uses minimum variance criterion (MVC) and a sequential method for optimal meters placement, SVD method for observability analysis and finally WLS method for harmonic estimation. The proposed method minimizes the number of measurement devices and the error... 

Harmonic state estimation (HSE) method has been used to locate harmonic sources and estimate harmonic distribution in power systems with limited number of harmonic meters. This paper focuses on a new technique for optimal placement of measurement devices and observability analysis for power systems harmonic state estimation. The proposed method optimizes the number of measurements and minimizes the error of estimation at the same time. The method is tested on the IEEE 14-bus power system to show its precision  

Understanding the mechanism of dispersion within plants is essential for proper operation of natural and constructed treatment wetlands. Plant deflection induced by the current drag modifies the flow and dispersion within an aquatic canopy. In this study, we look at the effect of the deflection angle of the plants on transverse dispersion. Experiments were carried out in a current flume on an array of inclined solid rods representing a deflected emergent canopy. The stem Reynolds number varied between 90 and 360, normalized stem densities between 0.011 and 0.033, and the inclination angles between 0° and 45°. The plume development was recorded using image processing technique. A special... 

Nowadays users of the Web are encouraged to generate content on the Web by themselves. Weblogs are the most popular tools to do this. In fact Weblogs are one kind of social networks and they are one of the most important components in Web 2.0. Blogs are often situated within a Blog community of similar interest. These communities can be a useful way for readers to access space slice of millions of Weblogs. In this paper we introduce a new algorithm to infer communities based on their link structure. This algorithm uses self organizing maps to identify communities among Weblogs. The link pattern of each Weblog is the input for SOM. © 2007 IADIS  

The rapid growth of the world-wide web poses unprecedented scaling challenges for general-purpose crawlers and search engines. A focused crawler aims at selectively seek out pages that are relevant to a pre-defined set of topics. Besides specifying topics by some keywords, it is customary also to use some exemplary documents to compute the similarity of a given web document to the topic. In this paper we Introduce a new hybride focused crawler, which uses link structure of documents as well as similarity of pages to the topic to crawl the web © 2006 HEE  

In quantum approaches to consciousness, the authors try to propose a model and mechanism for the mind-brain interaction using modern physics and some quantum concepts which do not exist in the classical physics. The independent effect of mind on the brain has been one of the challenging issues in the history of science and philosophy. In some recent mind-brain interaction models, the direct influence of mind on matter is either not accepted (as in Stapp's model) or not clear, and there have not been any clear mechanism for it (as in Penrose-Hameroff's model or in Eccles's model). In this manuscript we propose a model and mechanism for mind's effect on the matter using an extended Bohmian... 

In quantum approaches to consciousness, the authors try to propose a model and mechanism for the mind-brain interaction using modern physics and some quantum concepts which do not exist in the classical physics. The independent effect of mind on the brain has been one of the challenging issues in the history of science and philosophy. In some recent mind-brain interaction models, the direct influence of mind on matter is either not accepted (as in Stapp's model) or not clear, and there have not been any clear mechanism for it (as in Penrose-Hameroff's model or in Eccles's model). In this manuscript we propose a model and mechanism for mind's effect on the matter using an extended Bohmian... 

In this paper, collision of two balls in three dimensions with regard to energy loss and friction is studied. This investigation intends to propose the procedure which can determine the condition of pure sliding, sliding with rolling or sticking, and rolling or sticking at the beginning of contact. Furthermore, the other aim of this research is to suggest the closed-form relation for post-collision angular and linear velocities in which the possibility of three regimes of impact, pure sliding, sliding with rolling, and pure rolling, are considered. In this investigation, viscous Hertz contact force describes the normal interaction force. Moreover, stick regime is not taken into account and... 

Adaptive Model Predictive Transmission Control Protocol (AMP-TCP) as a new TCP delay-based congestion control algorithm is introduced. Both aspects of design and implementation of the algorithm are described using simulations on the ns-2 network simulator. The design stage is composed of two steps. First, a recursive system identification approach is proposed to capture the network delay dynamics from TCP source view. Second, the proposed modeling is employed to develop an adaptive model predictive TCP congestion control strategy in the absence of any explicit congestion notification. The characteristics and performance of AMP-TCP are investigated using several network simulations. Finally a... 

Transmission Control Protocol (TCP) uses multiple timers to do its work. The most important of these is the retransmission timer. In this paper, the TCP retransmission timer adjustment mechanism is approached from a system point of view and a new mechanism is proposed. A simple recursive system identification algorithm is used to capture both time variant and time invariant Internet behavior. Also a dynamic model-based Round-Trip Time (RTT) predictor was provided. Based on network simulation and real Internet data collection, it was observed that when the retransmission timer is adjusted by the proposed predictor instead of the traditional RTT estimator, performance increased significantly  

Power and bandwidth constraints are two major challenges in wireless sensor networks. Since a considerable amount of energy in sensor networks is consumed for data transmission, compression techniques may prolong the life of such networks. Moreover, with fewer bits to transmit, the network can cope better with the problem of inadequate bandwidth. In this paper, we consider an image sensor network and propose a paradigm based on the principles of Distributed Source Coding (DSC) for efficient compression. Our method relies on high correlation between the sensor nodes. The algorithm consists of two phases: the Training Phase and the Main Phase. In the Training Phase an aggregation node or a...