Sharif Digital Repository

Wireless networks with the shared media require Medium Access Control (MAC) protocol that provides contention resolution mechanism. The design of MAC protocol is a challenging issue because of limited energy source and high propagation delay in UnderWater Acoustic Sensor Networks (UWASNs). The most important goal of the MAC design for underwater sensor networks is to resolve data packet collision efficiently with respect to energy consumption. So, selection of MAC protocol is an important task because it has significant impact on the system efficiency. A suitable MAC protocol must consider some factors such as fairness, energy consumption, latency and throughput based on various... 

This project presents a routing algorithm to cope with the dynamic traffic pattern of network-on-chip (NoC) architectures aiming to distribute the on-chip traffic evenly across the network. In this algorithm, instead of relying solely on local congestion information, the routes are determined based on the global information about on-chip traffic. This is achieved by employing a light-weight and efficient control network which monitors the on-chip traffic and collects the required information for determining the appropriate path between any pairs of communicating nodes in such a way that the congestion is avoided and the NoC load is balanced. Our experiments show that the proposed method... 

Switching as one of important characteristics of on-chip network affects on power consumption and performance. In general there are two switching methods as circuit-switching and packet-switching. Hybrid switching includes both switching to have both resource utilization and scalability of packet switching and low power consumption and improved latency of circuit switching. Also topology is another network attribute that greatly affects the power, performance, cost, and design time/effort of NoCs. In this thesis, we propose a novel NoC architecture which holds both fixed connections between adjacent nodes and long connections virtually connecting non-adjacent nodes. Our proposed NoC... 

Highway work zone is one of the important factors that create long queues and Delays, increase air population, fuel consumption, and road accident. Since in this zones, one and two or sometimes three lanes may be closed, more careful evaluation of the causes of queue formation seems necessary. The purpose of this research was to develop a method to estimate queue length at work zone in rural freeways, based on its traffic flow characteristics. In this study, traffic data from three work zone locations in Karaj-Qazvin freeway was collected. Results of different modeling show that platooning arrival of vehicles at work zone, increase in percentage of heavy vehicles, high variation of speed and... 

In this article we investigate the strong convergence of the Euler-Maruyama method and stochastic theta method for stochastic differential delay equation with jump .Under a global lipschitts condition we not only prove the strong convergence but also obtain the rate of convergence.We show stronge convergence under a local lipschits condition and linear growth condition.Moreover it is the first time we obtain the rate of strong convergence under a local lipschits condition and a linear growth condition.i.e if the local lipschitsz constants for balls of radius R are supposed to grow not faster than logR  

Congestion is an important issue in the network environment. To keep stable the perfor-mance of the network, congestion control algorithms have been extensively studied. Queue management method employed by the routers is one of the important issues in the congestion control study. Active Queue Management (AQM) has been proposed for early detection of congestion inside the network. AQM mechanisms control the queue length in a router by dropping arriving packets. The Random Early Detection (RED) is the most popular AQM mechanism used in routers on the Intenet to allow network users to simultaneously achieve high throughput and low average delay. The RED algorithm may cause heavy oscillation of... 

Raising number of vehicles and increasing tendency of people to possess their own cars have posed a lot of expenses on users. One of the most significant of them is the time it takes to travel between origin and destination. Several researches have been conducted so far in order to evenly distribute travel times among transportation network users. A variable that has been neglected in many of these studies is travel time variability. Users, obviously, need to know not only the travel time, but also the probability of varying this time. In this research, an analytical model has been developed on a geometrical basis that includes both traffic conditions and intersection characteristics to... 

Frontage roads are widely used to separate the main and the local traffic flows in multilane highways. Based on the studies conducted by Texas Transportation Institute, the delay imposed by ramp junction is considered for calculating the average speed in frontage roads in addition to the control delay caused by traffic lights. This delay and the capacity of frontage roads are analysed using gap acceptance theory. In this study, two different sections consisting of a basic section and merge area are selected along Tehran-Karaj special road as case studies and the required data are collected by video recording. After classifying and analysing the data, a wide range of macro traffic-analyses... 

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... 

Cooperative control of autonomous multi-agent systems is one of the challenging problems in control theory. According to existing enhancements in communication networks and broad application of multi-agent systems in various engineering fields, coordinated motion control in multi-agent systems has been attracted the attention of researchers in control science. In this thesis, flocking algorithms in multi-agent systems with undirected interactions (bidirectional information flow) is considered and new convergence results and final characteristics are obtained. Also, geometric optimization methods are used to propose a new optimization problem to reduce the number of informed agents of 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...