Sharif Digital Repository

There are a wide variety of radar systems that one of them is MIMO Radars. After a spark in communication in 1998 that developed MIMO communication, recently there has been a great attention towards MIMO radar systems. MIMO radars divided into co-located and widely separated branch. In this thesis, the spatial diversity and multiplexing gain and the tradeoff between them in MIMO communication and MIMO radar systems investigated. Diversity and multiplexing gains in communication defined analytically, so diversity and multiplexing gain presented as detection probability improvement and throughput or capacity improvement respectively. Also tradeoff between these two gains investigated... 

There are a wide variety of radar systems that one of them is MIMO Radars. After a spark in communication in 1998 that developed MIMO communication, recently there has been a great attention towards MIMO radar systems. Researchers have studied this topic from several points of view. Generally, MIMO radar systems are divided into two categories: MIMO radars widely separated antennas and MIMO radars with collocated antennas. One of the important issues of widely separated MIMO radars, is the placement manner of receivers in the geometrical area. This radar’s performance is very dependent to placement of the antennas, because the performance is dependent to relative position of... 

In this thesis, the challenges of the PHY and MAC layers in cognitive radio networks are discussed and a plan which considers the cross layer concept between them is presented.In the first part of the thesis, a brief survey on various spectrum sensing techniques is presented. A detector which can improve the network performance is introduced and based on this detector, the important problem of trade-off between spectrum sensing period and the network throughput is considered. For this purpose, first of all, the truncated SPRT detector is presented and for low SNRs the optimal truncation time which leads to maximum network throughput is obtained. In the second part of the thesis,the... 

Portfolio optimization is an most important field of study, affecting companies’ non-operating income, so companies try to achieve this beneficiary by incorporating it in market transactions. In this thesis, we propose some methods extending the Markowitz theory. We used the lagrangian method and other appropriate operations research techniques such as convex optimization in order to handle optimization process. Using these methods, we established portfolio optimization model for different corporation, i.e., banking industries and others, with different interest rate exposure for short and long conditions of risk free assets. We describe three risk criteria as possible alternatives to... 

Cooperative coexistence of two kinds of users with different priorities in random access wireless networks has been studied in this thesis. Source burstiness, a phenomenon in data communication networks, allows using silence periods of primary users (PUs) to have a better spectrum utilization. In this respect, new users, known as secondary users (SUs), are considered to exploit the resources opportunistically. In usual spectrum sharing systems, SUs have to act in a way to be transparent for the PUs. Therefore, they are allowed to access the common spectrum band only when PUs are silent. However, seeking such opportunities needs sensing capability of secondary nodes.In this thesis, sensing... 

There are a lot of methods for the settlement of the reserve power market which can ultimately lead to a pattern of consumption and generation for each of the participants of the power market. After this step, however, justified and logical methods should be utilized for paying the reserving costs to the participants as in a long-term it can optimize the economic conditions of the market which can result in getting more realistic bidding from the participants. The current methods used for paying the reserving costs are mostly locational marginal prices and pay-as bid approach. By the same token, for receiving the reserving costs from the customers, some consider the desired reliability level... 

Sparse representation and compressed sensing have been widely used in various fields, one of the most popular of which is ISAR imaging. Inverse Synthetic Aperture Radar (ISAR) provides an electromagnetic image of the target, which is mainly used to identify and classify targets. In some applications, recognizing targets from a 2D image can be difficult and error-prone. One idea to deal with this problem is 3D ISAR imaging. The most widely used method of ISAR imaging is direct method based on Fourier transform. This method requires the measurement of radar data with high measurement density in 3 directions, which increases the data collection time and volume, which is the main problem of... 

The primary objective of this research is probabilistic quantification of the fatigue life of tension-leg platforms (TLP) using reliability methods. The need for such methods stems from the significant uncertainty in the loads exerted on offshore structures. The scope of this paper is limited to the study of fatigue in TLP tendons. For this purpose, nonlinear force time history response of the TLP tendon under random wave loads is computed and the damage due to fatigue is estimated in accordance with the Palmgren-Miners rule. Assuming a Rayleigh distribution for stress variation and eight different sea states, the ultimate fatigue damage is computed by accumulating the damage over all... 

Developing of electric instruments with high performance needs high capacity heat transfer equipments. Pulsating heat pipes have better performance compared with normal heat pipes and can be used for cooling electronic instruments in near future. Also, one specific kind of heat pipes, which is called rotating pulsating heat pipe, can be used in cooling the turbine blades and every rotating device. Rotating pulsating heat pipe is a cooling device in which the pipes can rotate around the axis perpendicular to the plane of pipes. In this research one rotating heat pipe was built and the effects of heat input, filling ratio, working fluid and rotational acceleration were examined experimentally,... 

Nowadays, concrete is considered as one of the most important and useful engineering construction materials. Different concrete with diverse characteristics are used in various designs every day. One of the main considered parameters in concrete usage is its compressive strength. So far, many additives are used to increase the compressive strength of concrete most important of which are Nano-Silica and Micro-Silica. In addition, some of concrete characteristics such as water-to-cement ratio have significant effects on the concrete strength. Many experiments and investigations are conducted so far to study the effects of each of mentioned factors separately on the concrete strength. However... 

In this project Sharif Gas Turbine laboratory turbojet engine, and the turboshaft engine which is designed based on the turbojet gas generator are statically and dynamically modeled and required functions for turboshaft control are extracted. In static modeling a repetitive process is applied to reach static operation points. Static operation line and static characteristics of turbojet engine are extracted and compared to relevant sources. In dynamic modeling of turbojet engine a lumped volume is allocated to each component of engine and gas dynamic equations are solved in this volume along with individual performance map of engine components to acquire output characteristics in each time...