Sharif Digital Repository

Digital Signal Processing (DSP) is used in a wide range of applications such as high-definition TV, digital audio, multimedia, digital cameras, radar, sonar detectors, biomedical imaging, global positioning, digital radio, speech recognition and etc. These applications can be implemented by either DSP processors or FPGA technology. Digital Signal Processors are microprocessors specifically designed to handle Digital Signal Processing tasks. These devices have seen a tremendous growth in the last decade, finding use in everything from cellular telephones to advanced scientific instruments. On the other hand, the rise of FPGA in the signal processing realm could be assigned to hardware to... 

In real-time packet-based communication systems one major problem is misrouted or delayed packets which result in degraded perceived voice quality. If some speech packets are not available on time, the packet is known as lost packet. The easiest task of a network terminal receiver is to replace silence for the duration of lost speech segments. In a high quality communication system in order to avoid quality reduction due to packet loss a suitable method and/or algorithm is needed to replace the missing segments of speech.There are several methods which have been proposed to reduce the effect of packet loss such as Waveform Substitution, High Order Autoregressive, Linear Prediction (LP),... 

Software Defined Networks provide programmability and centralized control for network’s administrator. Like other networks, security problems are important in these networks, but there is not enough research in this area. The problem being discussed here is to elevate the security level in software defined networks using centralized control and programmability of these networks. We will accomplish this purpose by using hosts and controller at the same time to prevent unwanted traffic from entering the network. By using this approach, we will be able to remove many short comings of these networks and implement security systems, like intrusion detection systems, more efficient. One of these... 

Despite having major advantages such as expert management, economy of scale and lower analysis costs for investors, the mutual funds may still underperform (at suboptimal levels) due to factors like information asymmetry between fund managers and unitholders along with the difficulties involving assessment of manager's performance by investors. So the conflict of interest between the manager and unitholders propels them towards deciding to manipulate the risk measure of the fund for reasons other than the maximization of profits for unitholders by shifting risk level of the portfolio. For instance, the promise of non-linear growth in attracting money by obtaining a considerable ranking... 

The conflict-free coloring is one of the computational geometry problems that has received attention in the last two decades. The root of this problem comes from the frequency allocation problem to telecommunications antennas, where we have several telecommunication antennas in two-dimensional space aiming to assign to each of them a frequency so that every point on the plane, which is at least inside one of the antenna ranges, stays in a range with a frequency different from the other antennas containing point.One of the generalizations of this problem is the k-strong case, where we have n regions (equivalent to the circular region of the antennas) that we want to color so that for each... 

In this research, we introduce the concept of local spanners for planar point sets with respect to a family of regions and prove the existence of local spanners of small size for some families. For a geometric graph $G$ on a point set $\points$ and a region $R$ belonging to a family $\Re$, we define $G \cap R$ to be the part of the graph $G$ that is inside $R$. An $\Re$-local $t$-spanner is a geometric graph $G$ on $\points$ such that for any region $R$ in $\Re$, the graph $G\cap R$ is a t-spanner with respect to $G_{c}(\points) \cap R$, where $G_{c}(\points)$ is the complete geometric graph on $P$.For any set P of n points and any constant $\eps > 0$, we prove that $P$ admits local $(1 +... 

A grid simulator is a system for testing various types of grid-connected devices, such as inverters of renewable energy sources, chargers, power supplies, etc. In this project, the design and implementation of a 3 KVA three-phase regenerative programmable AC current source is presented. In the future, this structure can be used as a grid simulator. The topology used for the current source is a two-level three-phase AC to DC converter. The current source can operate in constant current (CC), constant power (CP), constant impedance (CI), and constant voltage (CV) modes. In the constant current operating mode, the user sets the amplitude and phase of the 1st, 5th, 7th, 11th, and 13th harmonics... 

The primary objective of this research is the integrated guidance and control of a hexacopter system equipped with a robotic arm using deep reinforcement learning algorithms in an end-to-end and model-free framework. The hexacopter with a robotic arm system possesses 6 degrees of freedom for the hexacopter and 2 degrees of freedom for the robotic arm, which consists of rigid links attached to the underside of the hexacopter. The dynamic model of this system has been developed in an integrated manner to properly account for the coupling effects between the equations of the hexacopter and the arm in the analyses. After developing the equations describing the system's behavior, the goal is to... 

Flying has fascinated mankind for ages. Nowadays, planar actuators are performing the same task as that, once a dream, of a flying magic carpet found in Persian mythology. Magnetically levitated planar actuators (MLPAs) consist of two parts; a moving part, and a stationary part. In most applications the moving part which is an array of permanent magnets (PMs) produces a magnetic flux density in the air-gap, and the stationary part, an array of current carrying coils, produces force and torque when it is exposed to the magnetic flux of the PM array. These actuators have been utilized in industry in applications where precise positioning is important. In recent years however, they have found... 

The applications of science and technology of materials grows rapidly nowadays One of the major aspect of this science discuss about the growth of thin films via deposition of molecules and atoms. By this way we can diagnose physical and chemical properties of thin films whose applications in electronics, computer, microelectronic industry, material engineering telecommunications and so advances every day. In this way we smell out the process of the growth of diamond like carbon (DLC) thin films whose importance is extended nowadays. By acknowledgement of variables that influence the dynamics of film formation we make a big jump in attaining the optical, physical and electrical properties of... 

One of the most important problems in using wind energy is the estimation of wind energy potential of a region with acceptable accuracy. To use wind energy and convert it to electrical energy it is necessary to study the economical aspects of wind farm installation, and to choose an appropriate wind turbine to be installed in a region. To do such a study and to choose approperiate wind turbine, annual energy output of different wind turbines should be estimated in that region. The porpuse of this thesis is to develop new methods to estimate annual energy production of a wind turbine by using some of the parameters of wind speed pattern of a region such as wind speed average, wind speed... 

Speech enhancement in noisy environments improves the quality and intelligibility of speech and reduces communication fatigue. High performance speech enhancement models are based on Bayesian estimation models, requiring estimations of the parameters of the functions that describe the likelihood and the prior distributions of the signal and noise processes. Two Bayesian speech enhancement models which are used in this thesis are Bayesian-Kalman filter and Bayesian MAP estimation.In real time applications including VoIP, in addition to additive noise, packet loss or packet delays might also occur. In real time communications the receiver terminal replaces silence for the duration of lost... 

Traditional security approaches prevented participants of an environment from malicious behavior by closely monitoring every transaction of the network. Such approaches are very costly in modern autonomous systems, besides, they are also impossible to apply in many cases. Trust management mechanisms are developed in order to ensure safe interactions with unknown parties in such open environments. Most trust management mechanisms rely on testimonies of interaction participants as the source of information to estimate a peer’s reputation. The first challenge that arises here is the lack of incentives for providing such information. Even if interaction parties are encouraged to report the... 

The problem of restoring power systems after a complete or partial blackout is as old as the power industry itself. In recent years, due to economic competition and deregulation, power systems are operated closer and closer to their limits. At the same time, power systems have increased in size and complexity. Both factors increase the risk of major power outages. After a blackout, power needs to be restored as quickly and reliably as possible, and consequently, detailed restoration plants are necessary. This thesis concentrates on the initial stages of restoration where load pickup and frequency control problem is identified. The best sequence of load pickup for power plants during power... 

Motion dynamics of cat species has always been attractive to be studied. Flexibility in motion due to specific skeleton and complex muscle-skeleton mechanism, control concepts, special way of running, high speed direction change while moving, ability of twisting the body during free fall, and landing on four limbs were widely investigated in literature and the results have been used in different branches such as control, robotics and aerospace.In this project, kinematic and dynamic equations of cat species falling maneuver are derived using quaternions for a simple two-link robot, a three-link robot with tail, and a more complete eight-link model with the addition of legs which is designed... 

The effect of soil structure interaction, on displacement modification factor in constant reduction factors (CR) is evaluated, studied for SDOF structures placed on flexible base modeled by 3DOF system as the base foundation (a sway, a rocking and an internal degree of freedom to see the frequency dependency of dynamic stiffness of soil). 60 records of FEMA-440 for 3 types of soils (B, C and D) are analyzed for 28 different soil-structure conditions, 6 different level of reduction factors, and varied secondary hardening for 2 different hysteresis behavior to see the effect of stiffness hardening. Results are plotted in spectrums to see the role of Tn.
Final results show that effect of... 

Dynamic characteristics of structures—viz., natural frequencies, damping ratios, and mode shapes—are central to earthquake resistant design (model validation) and health monitoring. For civil structures like buildings and bridges, these characteristics can be highly influenced by surrounding soil in addition to the super-structure’s properties and cannot be correctly estimated using numerical modeling. For example, soil’s flexibility decreases the natural frequencies of the system; and in most cases, soil provides additional damping due to material hysteresis and radiation. On account of this fact, system identification techniques must be applied to extract such information from field data,... 

Liquefaction is one of the probable consequences of earthquake in soil layers of saturated loose sands. Various aspects of liquefaction have been investigated using different methods of field, laboratory, and numerical studies. Numerical simulation of liquefaction constitutes a major part of these researches. A proper constitutive law must be implemented in the numerical analysis for modeling the complicated behavior of saturated sands during dynamic loading. Simplicity of formulation, limited number of parameters and good performance are the main features of a proper constitutive law. In this study, Endochronic model for simulating liquefaction has been introduced. This model is implemented... 

In recent decades, the usage of robots in industrial applications increased dramatically. One group of robots are manipulators which they are used in production lines for moving parts, cutting, welding, …. In these applications, different control methods are used to control the end effector of manipulators precisely. From one aspect, control methods are divided to two parts: A) The methods that do not need to equation of motion of robot, such as proportional-integral-derivative method. B) The methods that are designed based on equation of motion of robot. To use these methods, first the equation of motion of manipulator should be calculated according to its structure. These equations are... 

It is several decades that the effect of soil-structure interaction (SSI) has been known to engineers. Many methods have been developed to estimate this effect, but modal analysis of soil-structure systems is one of the most popular techniques due to its simplicity and better insight. Due to this reasons, modal analysis found its place in codes and provisions such as NEHRP. Presence of soil beneath the structure not only would alter the natural periods and damping ratio of structure but also would impose some new vibration modes to the system due to soil’s degrees of freedom. Consequently, response of structure is a combination of the effects of all these modes. But, in practice,...