Sharif Digital Repository

An Ad-Hoc wireless network consists of a collection of geographically distributed nodes that communicate with each other over a wireless medium. These networks don’t use any infrastructure or base station to channel allocation. The important difference between wireless networks and wired networks is the broadcast nature of wireless communications. In these networks, each node transmits data to all of the nodes in the transmission range which may cause an increase in interference and data loss. On the other hand, due to mobility of users, fading the channel between them and change of routing, the probability of data loss increases. The extensive and successful employment of TCP variants in... 

Mobile technology has become Ubiquitous and common in all over the world from the first years of 21st century. Mobile has been used as a strong media in marketing and specifically in advertising due to it’s unique features and various functions. Currently (2008) mobile media is not used very aggressively in Iran. Considering the quick expansions of mobile networks in Iran and growth of subscribers, it is anticipated that Mobile will affect many businesses and consumer market very soon in Iran. This study is the first academic research in the country on Mobile advertising via SMS. The purpose of this thesis is to provide the better understanding of the Mobile advertising via SMS in high... 

In this paper, the general research of impedance control is addressed for a robotic manipulator with a moving flexible base. Impedance control imposes a relation between force and displacement at the contact point with the environment. The concept of impedance control of flexible base moving manipulators (FBMM) is rather new and is being considered. The dynamic of manipulator is decomposed into slow and fast dynamics using singular perturbation method. New sliding mode impedance control method (SMIC), using an element on the end effector is proposed for high precision impedance control of FBMM. The sliding mode impedance control method as a robust impedance control law is derived for the... 

Temperature reduction from room temperature to liquid nitrogen temperature has a significant effect in improvement of semiconductor devices operation such as field effect transistors. Nowadays cryoelectronics as a considerable branch of electronics is concerned by several groups. In order to optimize the procedure of low temperature IC design and fabrication we investigated the temperature effects on different parameters of MOSFET in this thesis. Several transistors in a variety of channel lengths were fabricated in different technology files. Wide measurement experiments were done on these transistors in order to find their drain current vs. drain to source voltage characteristics. From... 

Phospholipid vesicles are able to carry drugs or DNA to infected or cancerous cells. The blood flow can carry them to their target positions but their performance will be enhanced if they complete their attack by swimming in final stages of their journey. Vesicles built only by lipid molecules have rotational symmetry and undergo a random motion in their solvents without having a preferred direction. In this project, we break the symmetrical shape of phospholipid vesicles by a cluster of transmembrane proteins. We use a triangulated model of the membrane, apply the method of multi-particle collision dynamics to the motion of solvent particles, and simulate the motility of vesicles for... 

Today, almost all the Iranian mobile telecommunication companies should rely heavily on customer loyalty and customer retention as essential and vital tools to provide a competitive advantage in this competitive telecommunication world by offering value and upper hand service with respect to the existing demand in the Iranian market, hence these determinants arise the need for studying eCRM, Loyalty and Retention in order to achieve customer satisfaction in the Iranian mobile telecommunication field. 400 customers who use the Iranian mobile telecom operators’ services (Hamrah-e Avval, Irancell, and Talia) have been asked as respondents in this research. The study is based mainly on primary... 

Delay Tolerant Networks are a variation of Mobile Ad Hoc Networks, in which low density of nodes in the network area results in global disconnectivity among the nodes. In these networks, communication of data throughout the networks takes place by the means of mobility; nodes store data packets and carry them around the network and forward them to other nodes they encounter along the way. In these situations, a proper selection of data to be exchanged between nodes has a great impact on the quality of data distribution in the whole networks. There is a common assumption among most of the techniques presented in category of Delay Tolerant Networks. They assume the probability of more than two... 

People often conduct extensive searches in Internet, when they are involved in purchasing process of digital products. One primary challenge with the method of such searches is this fact that they heavily rely on a wide variety of technical characteristics, while buyers not being well familiar with such attributes. As such, they frequently fail to identify and purchase the right product. To address this issue, value-based approach is proposed by which the decision process is expected to be facilitated and become more efficient since it is based upon direct comparison of values gained by each product. In this thesis, as a case study for digital products, value attributes of mobile products... 

Opportunistic spectrum access in cognitive radio networks has introduced multiple challenges in the realization of this technology. One of these key challenges is spectrum mobility, in which a secondary user (SU) must be able to vacate channels upon the appearance of a primary user (PU) and reestablish a communication link to avoid service termination, known as spectrum handoff. For a connection-based modeling, multiple interruptions can occur, which lead to multiple handoffs; hence, in a proactive approach, a sequence of target channels, rather than a single target channel must be determined. The first parts of this thesisis dedicated to the analysis of a time-slotted cognitive radio, in... 

In this thesis control of wheeled mobile manipulators for cooperative object transportation is investigated. Full dynamic model of a mobile manipulator with a three wheeled mobile base and a three DOF manipulator is derived using Gibbs-Appell method. Input-output linearization technique is used to control individual robots. Transporting the object is divided into two steps, first robots use a decentralized behavior-based method to approach and surround the object. Then virtual structure method is used to control the robots to transport the object cooperatively. Simulation results with three robots handling an object are presented to show the effectiveness of proposed method  

A Mobile Ad hoc NETwork (MANET) is a self-configuring network that is formed automatically by a collection of mobile nodes without the help of a fixed infrastructure or centralized management. In recent years, the use of MANETs has been widespread in many applications, including some mission critical applications, and as such security has become one of the major concerns in MANETs. Due to some unique characteristics of MANETs, prevention methods alone are not sufficient to make them secure; therefore, detection should be added as another defense before an attacker can breach the system. In this thesis, we have expressed some well-known and related intrusion detection systems. Besides we have... 

In recent decades, Securing mobile ad hoc networks has attracted much attention. Today, several security tools, such as intrusion detection systems are used in the network. Methods based IDS works on pattern recognition and anomaly detection are divided into two categories. Pattern recognition methods based on known attack patterns work with high detection rate, but do not have the ability to detect new attacks. Anomaly detection techniques have the ability to detect new attacks, but they have high false alarm rate.
In this thesis, an anomaly detection system based on artificial immune designed, implemented and evaluated.For example, an anomaly detection methods such cases, a variety of... 

Due to popularity of mobile wireless devices, security of mobile ad hoc networks (MANETs) being more important than before. Traditional key management schemes based on symmetric key cryptography are became ineffective because of dynamic and infrastructureless nature of these networks.Recent studies are mainly based on traditional public key cryptography schemes and ID-based cryptography schemes. On the other hand, Contributory schemes seem suitable for MANETs because of their inherent self-organize property. Key update and Key revocation are the fundamental issues of key management schemes in mobile ad hoc networks. Certificateless public key cryptography, in addition to solve those issues,... 

Mobile and wireless services industry has been among the most attractive businesses recently and is progressing at a fast pace. In this huge industry various organizations and entities cooperate to deliver value to the end user. The mobile operator plays the pivotal role in this chain. Hence mobile operator’s market was chosen in this study as the representative of the industry. Market segmentation and customer satisfaction are the main topics of this study.
Market segmentation for MCI was done using data mining with two-step algorithm. Input data included the consumer behavior extracted from mobile post-paid bills. The results indicated five distinctive clusters. The next part included... 

Our surrounding environment has valuable information about our life. We live in technological societies where we are leaving digital footprints in, continuously. Growing development and popularity of mobile phones, has turned them into the most important global sensors. Mobile phone tracking via GPS points is one of the data types which can be collected from these sensors and used for traffic monitoring, intelligence traffic control and travel time estimation.
In order to use these devices, we need to collect data, detect transportation mode and estimate travel time. By evaluation of previous works, we can feel the need to a comprehensive approach for detecting transportation mode of... 

In this thesis, the simulation of HEMT for high frequency applications has been explored. It has been tried to examine the changes such as: gate recess, T-shaped gate, changing the channel length and doping of buffer layer on the performance of the proposed device. Simulation results show that the best way to improve the device performance, in particular its cut-off frequency, is increase in buffer layer doping density. Because it significantly increase the saturation current, electron mobility inside the channel, the transconductance and the cut-off frequency. If we need to lower the noise, the T-shaped gate can also be used. Also, by change in doping of donor layer, amount of 1017 cm-3 is... 

Blackhole and grayhole attacks have been become two of the major security concerns in mobile ad hoc networks (MANET). To achieve security in MANETs, a lot of mechanisms had been proposed by now. Using intrusion detection systems(IDSs) is one of the important mechanism to reach this goal. Thus, a well-known IDS was chosen and analyzed in this thesis. Furthermore, a collaborative bayesian filter approach for this intrusion detection system was proposed to enhance its performance. Then the performance of this approach was considered. This intrusion detection system was analyzed using stochastic modeling like continuous time markov chain(CTMC), stochastic reward net(SRN) and stochastic... 

The intrinsic properties of Mobile Ad-hoc Networks (MANETs) caused many challenges for these networks. Among these challenges, security is the most important one. Cryptography has many applications as a network securing method. Limitations on memory and processing capability of nodes in an Ad-hoc network makes it almost impossible to use common cryptography algorithms for these networks. Key distribution is the main challenge of cryptography; therefore, it is reasonable to simply the problem of cryptography in an Ad-hoc network to the problem of key distribution. Up to now, different methods are proposed for key distribution in MANETs; each of which has their own weaknesses. For example some... 

Todays the use of microwave integrated circuits for military and commercial applications has gained much attention, especially with the advent of monolithic microwave integrated circuits, which provide the possibility of fabrication of amplifiers in large number, sufficient accuracy an affordable price.GaAs pHEMT process, because of good characteristics for noise and power in high frequencies, is a good choice for microwave and millimeter wave integrated circuits. A low noise amplifier is a key block in the receiver and, its noise figure and gain directly affects the sensitivity and dynamic range of the receiver. Hence, a low noise amplifier with low NF, high gain, good return loss, low... 

This paper proposes a globally and exponentially convergent predictor observer for attitude and position estimation based on landmark measurements and velocity (angular and linear) readings. It is assumed that landmark measurements are available with time delay. The maximum value of the sensor delay under which the estimation error converges to zero is calculated. Synthesis of the observer is based on representation of the rigid-body kinematics and the sensor delay by a combination of ordinary and partial differential equations (ODE-PDE). An observability condition specifies necessary and sufficient landmark configuration for convergence of attitude and position estimation error to zero....