Sharif Digital Repository

Since interconnects are playing a very important role in today’s IC technology, introducing new models and approximations is vital to IC designers. In this dissertation, maxwell equations are introduced as they are the main equations governing transmission lines. Different methods to model interconnects are also presented. Moreover, because of the importance of the step response of a system, available methods for finding the step response of interconnects are briefly discussed. Some approximations are also described, which result in faster but not very accurate responses. Delay and noise in integrated circuit connections have been the subject of several investigations for a long time. Since... 

One of the frequent aspects of lawlessness at signalized intersections, is red-light violation (RLV). In addition to its adverse effect on intersection safety, RLV can cause delay in the startup of the vehicles in the next phase defined as “green flow”. In this research, in order to investigate the adverse effect of RLV, the required data were collected from two signalized intersections in the City of Esfahan, Iran using recording cameras. Then, using a cellular network in the intersections and the Aimsun traffic simulation software, the effects of RLV on the delay, capacity, and level of service of the intersections were evaluated. The results show that the behavior of the drivers in the... 

Distinguishing characteristic of wireless sensor network is limited resources such as processing power, bandwidth, memory. Restrictions of sensor networks is impressive on the transfer of multimedia data such as video requiring high bandwidth and low latency. In wireless multimedia sensor networks, the probability of packet loss is high due to the high volume of multimedia data and limited bandwidth. Many congestion control protocols for wireless sensor networks have presented. Most of these protocols did not consider the multimedia content. Even some wireless sensor network congestion control protocols have worse result than a network which has no congestion control protocol in case of... 

Recent advancements in wireless communications and also a tendency to use low cost, tiny, and autonomous high performance products have led to the emergence of wireless sensor networks (WSNs). As the main source of power in a sensor node is a limited and irreplaceable battery, energy is the main important issue. Data aggregation, as an in-network processing method, is a promised technique aiming to conserve energy by reducing the number of packet transmissions through the network. It is a key, yet time-consuming functionality in WSNS, where we hold packets in intermediate nodes to promote aggregation efficiency. However, the requirement of real-time communications is becoming more and more... 

In this thesis, we consider a neutral predator–prey model with the Beddington–DeAngelis functional response and impulsive effect. Sufficient conditions are obtained for the existence of positive periodic solutions by a systematic qualitative analysis. Some known results in the literature are generalized  

For any country, the road system is an important part of its infrastructure which can affect economic development. A good level of service for a road system requires implementation of work zone projects to maintain it which usually close one or more of the lanes available for traffic. Lane reductions could cause a disturbance to normal traffic flow and speed reductions, further resulting in a reduction of road capacity and an increase of traffic delay. In addition, work zone capacity and traffic delay are the two critical indices to determine whether the effectiveness of traffic control systems is acceptable or not. Hence, the accurate estimation of capacity and traffic delay in work zones is of... 

Considering energy efficiency ways a key role in designing future wireless networks( 5G mobile networks). Moreover Spectrum efficiency is another critical issues in designing wireless networks. Cognitive radios can improve the spectrum efficiency. On the other hand, radio frequency (RF) energy harvesting has emerged as a promising technique to supply energy for wireless networks and thereby increase their energy efficiency. In this thesis, we propose a new technique for the RF-powered CRNs.To this end,We consider a cognitive radio network comprised of a primary user and a secondary user. The primary user, uses a typical frequency band for transmit data in a time slot basis and both the... 

In this dissertation, we focus on two types of EH cooperative networks. In the first type, the source and relay nodes access a shared channel according to a random access protocol. Also, they harvest energy from non-RF environmental resources. The relay node has data and energy buffers to store the packets of the source and the harvested energy, respectively. Our main goal is to find the optimal relaying protocol at the relay node. In this regard, the first type of the EH cooperative networks are investigated in two different scenarios. In the first one, the MAC channels of the nodes are independent of the applied policy at the relay node, and thus the throughput of the network is fixed.... 

This thesis presents an investigation of the dynamics of two coupled non-identical FitzHugh–Nagumo neurons. It is known that signal transmission in coupled neurons is not instantaneous in general, and time delay is inevitable in signal transmission for real neurons. Therefore we consider the system of two coupled neurons with delayed synaptic connection. We consider coupling strength and time delay as bifurcation parameters, and try to classify all possible dynamics which is fairly rich and we will study the excitability of the neurons. By bifurcation study of the system the coupling strength and delay-dependent stability regions are illustrated in the parameter plane, to describe typical... 

This research discusses the delay in strengthening projects by shear wall and steel bracing. It studied importance of causes and effects of delay in such projects. Forty-four causes were identified and classified by source into nine groups. Eleven negative effects of delay were known in this research. A field survey was conducted through a structured questionnaire including 22 owners, 40 contractors, 40 university's professors who have a PhD degree in structural or earthquake engineering, 35 consultant engineers, and 37 supervisor engineers in Mazandaran and Tehran. Relative Importance Index technique ... 

According to the increasing amount of data exchanged among data centers, the need for speeding up and bandwidth and reduced power consumption has been increased. The information show that about 77% of the data is moved into the data centers. On the other hand, 10% of data center’s power consumption is used to data transmission. Improving the interconnection network of data centers can play an important role in reducing power consumption and speeding up. In recent years, optical interconnects have gained attention as a promising solution. Nevertheless, offering an all-optical and efficient architecture is an important issue. In this study, we intend to provide a multi-stage, all-optical... 

Today, the internal connections of the CPUs with a few billion wired transistors in 14 copper layers on the silicon wafer are possible. Recently, power dissipation has slowed the growth rate of clock growth in CPUs, and nowadays sometimes more than 60% power is lost in connections. In this situation, the increase in efficiency has been achieved in accordance with Moore's law with multi-core chips. This theme has made the connections between the cores much more important than before. Usually the information in the network structure on chip (NOC) is transmitted on these connections. Therefore, all three aspects of delay, power dissipation and bit rate are important for communication channels.... 

The residential construction projects are an important and extraordinary part of the economy of Iran. Due to their important role and lots of problems that these kinds of projects face, this research was conducted. Delay is one of the main problems in these projects. In order to identify the causes of delay and propose recommendations to minimize it in Mashhad, Iran, a comprehensive literature review and interview with experts were conducted. One hundred and eight factors were identified and categorized into nine main groups. Based on the identified factors, a questionnaire survey was prepared, developed and distributed among the people who were active in the residential construction... 

Wireless Sensor Networks (WSNs) have developed in recent years and are used in many different applications such as fire detection, military operations, and healthcare. Sensor nodes can sense an environment, sending and receiving information and forwarding packets from source nodes to a sink. These tasks consume large amounts of energy. In many WSN applications, delay and reliability of data delivery and the energy consumption of nodes are important design metrics. Network protocols such as medium access control (MAC) and routing should be designed to improve these metrics In this thesis, we propose a new cross layer algorithm that improves the performance of WSN networks based on these... 

If we consider a point set on the plane as the vertices and straight-line segments between them as the edges of a graph, and weight of each edge is equal to its Euclidean length, from this kind of graphs, triangulation is the graph with maximum number of the edges. In a triangulation, dilation of any two vertices is equal to the ratio of their shortest path length to their Euclidean distance, and dilation of the triangulation is defined as the maximum dilation of any pair of its vertices. Dilation is a characteristic that shows how much a triangulation approximates a complete graph. In the minimum dilation triangulation problem, the objective is to find a triangulation of a given set of... 

The use of wearable surveillance systems and wireless body sensor networks is an economical solution to medical care, which is capable of detecting abnormal conditions early, and by controlling the health status and enabling one to engage in normal and daily activities, improves the patient's quality of life. Information and communication security is very important in this area and its violation may even endanger the life of the patient. The selection and application of the appropriate security mechanism for a wireless body sensor network is subject to consider the requirements and limitations of the network. One of the most important security requirements in this area is the... 

Caching has been widely considered an efficient way of reducing and balancing the growing traffic in communications networks in recent years. In this thesis, for the first time, the stochastic requests traffic model in communication networks is considered and a performance analysis is provided based on such a realistic assumption. In addition, we introduce new comprehensive performance metrics which simultaneously take into account, the cache hit probability, load on the bottleneck links, and requests arrival rates. The main contribution of this thesis is to present a system model based on queuing theory and provide an analysis of the stability, maximum stable throughput, load on the... 

Caching is the process of storing part of popular contents near the users, which not only results in better traffic balance, but also reduces the delay of content delivery. Due to limited cache capacities and time-varying nature of contents popularity, using a proper replacement policy for cached contents during the heavy traffic hours is necessary. Many of the existing methods have ignored the dynamics of requests. Also, most of the previous works have focused on parameters other than QoS characteristics as the performance metric.We propose a cache updating policy for wireless networks considering dynamic popularity for file requests. Our model is a wireless heterogeneous network consisting... 

From the past, oil and gas industry has been among important industries in Iran and a major source of the government income. Hence achieving successful projects in the industry is of great importance for the country’s development and timely completion has always been considered as one of the characteristics of a successful project. Developing oil and gas fields, as it affect all of the other projects in this industry, is construed as crucial.In this regard, from the first oil exploration in Iran, authorities have signed different types of contracts with many contractors to develop oil and gas fields. Nonetheless projects in this industry, as of the projects in the construction industry in... 

Scheduling algorithms are responsible for allocation of various types of resources, interference management, and choosing the times and paths through which messages are to be delivered in a communication network. We consider certain fundamental problems in network scheduling. Any scheduling algorithm, to be practical, must have tractable computational complexity and tolerable delay. In the first part of the thesis, we address the following question: “for a given class of networks, does there exist a scheduling algorithm that performs polynomially many computations (in terms of the network dimensions), while keeping the expected delay of the network polynomially bounded (again in terms of the...