Sharif Digital Repository

High peak to average power ratio (PAPR) is one major drawback of OFDM system which highly affects the performance if untreated. Several methods have been proposed to overcome this problem. In all these methods reduction in PAPR is gained through a tradeoff with another system figure such as mean transmit power, bandwidth or BER. In this thesis we investigate high PAPR problem in OFDM, and we will introduce some methods proposed to alleviate it. These methods are divided into two classes; methods in the first class are based on finding a peak cancelling signal and methods in second class rely on solving a discrete optimization problem. We give a general formulaion for the methods in second... 

In single service wireless cellular networks, two types of call are defined; new call and handoff call. New call blocking probability and handoff call dropping probability are two major parameters of QoS. Some call admission control schemes are proposed for handling new and handoff calls in the cell for keeping these QoS parameters under suitable values. In this work, we will introduce some call admission control schemes and will show performance analysis, advantages and disadvantages of them (under different channel holding times and same channel holding times for new calls and handoff calls). Then we will focus on two schemes and based on their ideas, we will propose a new call admission... 

Using field assisted dissociation model and with a classic view the dissociation probability is calculated when it a molecule is exposed with a Ti:sapphire laser with wavenumber of 800nm and the energy of . using gradient optimization method we find a tailored two rectangular laser pulse for controlling the dissociation of C-H bond of . Using classical method reduced the complicacy of solving schrodinger equation. In our optimization method in contrast with the usual controlling method experimental data is not needed and this reduced the controlling costs.

 

OFDMA multi-hop cellular network (MCN) is the topic of a wide range of research today. In this thesis, we analyse this type of networks, regarding shadowing status, mobility patterns and different service requirements. In the multi-hop (MH) scenario, six fixed relays are set up in each cell, which split the cell into seven subcells. For mobility modeling, each subcell is split into several sub-regions. Mobile nodes are able to maintain at each sub-region with a random time distribution and migrate from it to one of its neighboring sub-regions. We also consider three types of services requiring specific number of subcarriers with specific BERs. The set of subcarriers is distributed among... 

Vehicle headway distribution plays an important role in various traffic engineering aspects such as capacity and level of service analysis and simulation issues. Although many headway models have been developed over the past decades, few have investigated the effects of vehicle’s type and its position in the traffic lanes on headway distributions. In this research, time headway data were collected at three different freeways using video camera. The collected data were analyzed and modeled for four different categories (i.e., car-car, car-truck, truck-car, and truck-truck) and under two traffic conditions of platooning and non-platoonig. Four types of probability distribution functions of... 

In this study we investigate the performance of amplify-and-forward (AF) and beamforming schemes in wireless networks. In our study we consider a general cooperative network consisting one transmit-receive pair and an arbitrary number of relays in which each relay has a separate power constraint. A two-step master-slave protocol is deployed in which at the first stage, relays listen to the transmitter and at the second stage, relays forward the recently received signal coherently. Main contributions of this dissertation are providing the exact closed-form of bit error rate analysis in the case of general AF networks, providing an integral-form upper bound of error probability of network... 

In this thesis, we investigate the statistical performance of the array processing algorithms. Theoretical performance analysis leads to better methods that outperform the existing algorithms. Besides, analytical performance analysis, results in a more profound understanding of the nature of the considered problem. First of all, problem of covariance matrix estimation, in the non-Gaussian signal case will be investigated. We will focus on a nonparametric estimator which relies on the sign of the data to estimate the covariance matrix on an element-by-element basis. It was known that, sign estimator may give invalid covariance estimates in higher dimensions of the data. We prove this fact in... 

This thesis encompasses a number of issues in earthquake engineering which may appear quite diverse in nature. Several methodological aspects of both conventional and novel approaches to probabilistic seismic hazard assessment are discussed here along with subjects more strictly pertinent to structural and geotechnical engineering. This work, however, has a unique, ultimate goal: to provide procedures for an effective and practical probabilistic estimation of structural demand of offshore platforms due to seismic ground shaking. In modern multi-level design and rehabilitation procedures, structural performance is in fact quantified by deformation demand levels exceeded with a specified... 

In recent years, coded cooperation has been considered as one of the best methods to cope with fading and at the same time to achieve channel coding gain. On the other hand, the idea of network coding has been introduced for increasing the efficiency of cooperative networks. In addition, it has been shown that only by jointly designing of network coding and channel coding, the capacity will be achievable. Also, to adjust the rate to the channel capacity without requiring the channel state information at the transmitter, Rateless coding has been proposed. In this thesis above techniques are combined to gain their advantages and to improve system performance. To this end, first we consider a... 

Ground motions in close proximity to the causative fault of an earthquake can be significantly affected by the propagation of rupture. In particular, when the rupture and slip direction relative to a site coincide and a significant portion of the fault ruptures towards the site, the ground motion can exhibit the effects of Forward-Directivity (FD). Pulse-like near-fault ground motions resulting from directivity effects are a special class of ground motions that are challenging to characterize for seismic performance assessment. These motions contain a pulse in the velocity time history of the motion, often occurring in the direction perpendicular to the fault rupture at locations near the... 

This research has been worked out in two main parts and it is tried to reach a high level of Safety Integrity in Safety Instrumented Systems using in Oil, Gas and Petrochemical industries. The first part involves an overview of system risk analysis and initial investigation of Safety Integrity Level as a new parameter in safety instrumented systems which are very important section of Safety engineering during last couple of years. According to the fact that the available papers and articles in this area are very limit; we have faced a lot of problem in doing research and actually to be honest; all available resources have been focused plus the related standards. The second part is about... 

Cooperative communications have been introduced to combat degrading effects of fading in wireless networks and attracted much attention recently. This technique provides distributed spatial diversity that enables energy-efficient transmission of information from source nodes to destination nodes via intermediate relay nodes. Most existing protocols, detection techniques and optimization methods in cooperative networks assume that perfect channel state information is available. While in practical situations, the estimates of the channels may only be known and for acquiring such knowledge, a fraction of power and bandwidth have to be spent for channel estimation using pilot symbols. In this... 

In this thesis, we consider various Make-to-Order systems as a version of integrated production-inventory systems. Most Make-to-order systems can be sufficiently modeled by a queueing system with inventory in which completing each service in the queueing system requires an on-hand inventory. Unlike most researches in this field, we present an analytical approach. In all systems we embed a stochastic process with joint state space that can entirely describe the state of system. Then steady state distributions are derived. Those distributions are applied to compute performance measures and long-run average cost function which can be used for optimization. In our Make-to-Order models, demands... 

High construction and installation costs of offshore platforms, and also harsh environments in which they operate, make health monitoring of these structures more important. Conventional methods to solve the health monitoring problem are deterministic, whereas much uncertainties are imposed to the problem. In most methods of health monitoring methods we try to identify natural frequencies and mode shapes of structures by using its dynamic response. This set of data is then compared to results of modal analysis performed on a finite element model of structure in order to detect any possible damage. In deterministic methods each response of structure is pertained to one damage state, in a... 

Most of the researches on project planning and scheduling have supposed that there is a complete and fixed information about the activities duration and amount of resources needed for project, but in reality we face lots of uncertainty in activities duration and required resources. In previous researches there are some cases which lead to more than one schedule for project, but in most of them they offer no solution for choosing between the schedules. In this project we are trying to make a nonlinear model of project environment by using Weibull distribution as activities duration and then we determine the input information by using the methods of probability encoding in decision analysis.... 

In this thesis, a novel OFDMA-based cognitive cooperative relaying scheme is proposed in which cognitive users not only try not to interfere with primary users but also assist them by relaying their information. Both primary users (PU) and cognitive users (CR) communicate to a common base station (BS). Bit error probability (BEP) of primary users and outage probability of primary users are investigated to evaluate performance of the primary users. In all parts of this thesis, we assume that data of users is not jointly encoded across subcarriers. So, the outage probability and BEP are investigated for each subcarrier independently. In the last part of the thesis, it is assumed that data is... 

In recent years, there has been an increased interest on employing low-cost, high-speed, low-latency wireless links for short range communications (< 10m). Ultra-wideband (UWB) radio is a promising technology to meet this interest. However, due to the limitation on its transmitted power level, UWB system faces major challenges to achieve an adequate system performance. Therefore, it is greatly necessary to find some efficient methods to enhance the system performance. Recently, cooperative diversity has emerged as an effective scheme to overcome multipath fading and thus to improve the quality of service in the physical layer of wireless networks without increasing the transmission power of... 

Travel demand estimation is a complicated process as travel demand is highly influenced by uncertainties. These uncertainties can be analyzed in two levels: aggregate and disaggregate. Models in aggregate level are usually influenced by uncertainties in data insufficiency in some regions of data space because of non uniform distribution of input data. Uncertainties embedded in travelers’ perceptions of some influential variables on demand estimation (such as travel time) moreover affect these models. An expert-guided algorithm to incorporate expert knowledge into adaptive network-based fuzzy inference system for compensating data insufficiency and considering uncertainties inherent in... 

We can note to at least four very different interpretations of probability that have become popular in the twentieth century. These interpretations are as follows:1. Logical theory: According to this theory, the probability of each event will be equal to the degree of rational belief in that event. In addition, these rational beliefs are assumed to be equal for each individual in the same situation. This is the difference between logical theory and subjective theory.2. Subjective theory: as mentioned, in Subjective theory like Logical theory, probability of an event equals to degree of rational belief in that event, except that Subjective theory allows the differences between the beliefs...