Sharif Digital Repository

Modeling languages are well-known mechanisms for describing the underlying structures in software and many other contexts. In order to use an information technology product to solve a specific problem, such as a modeling language, not only there is a need to cognize the problem and search for its solution, but also it’s necessary to have a correct perception of context and details of modeling language in first place. One of the setbacks that users encounter in perceiving the sense of diagrams and their details is cognitive complexity. Although lots of modeling languages are defined and introduced up to now, but there are no suitable yardsticks to evaluate the cognitive complexity of users... 

Frequency scarcity has emerged the necessity of opportunistic utilization of frequency bands, which can be realized through a cognitive radio system. During an agile communication between unlicensed users, a cognitive radio system must avoid collision with licensed users. Hence it should continuously observe the band of interest and report the presence of licensed user signals. This task is fulfilled by a vital part of a cognitive radio system, called the spectrum sensing core. Recently several techniques have been proposed for the spectrum sensing in literature. Some of them like matched filtering, cyclostationarity based detection are based on primary user signal features. However energy... 

Cognitive radio faces specific challenges due to its special spectrum access scheme. Providing required QoS and preventing irrecoverable interference on the primary users is among the crucial requirements. Beam forming is one of the interference avoidance schemes utilized in MIMO networks. Most of the studies on this scheme assume that each symbol is transmitted via vectors in order to grant desired beam forming and specific combinations in the receiver. Since transmitting multiple symbols at every transmission can provide higher data rates, it seems necessary to exploit beam forming through matrixes instead of vectors. In this thesis, by neglecting the interference of the secondary user,... 

In the present thesis we will design and study some rendezvous algorithms for cognitive radio networks. In cognitive radio networks, secondary users try to access the spectrum of primary users in an opportunistic manner. Each secondary user constructs a channel list of accessible resources by channel sensing. These resources are not necessarily the same for different users; therefore, in order to make a connection in absence of a fixed control channel, different secondary users should find each other properly and quickly after entering the network. This is known as the blind rendezvous problem. We will develop and examine a new sequence based algorithm for blind rendezvous. Moreover, some... 

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... 

Cognitive radio (CR) can successfully deal with the growing demand and scarcity of the wireless spectrum. To exploit limited spectrum efficiently, CR technology allows unlicensed users to access licensed spectrum bands. Since licensed users have priorities to use the bands, the unlicensed users need to continuously monitor the licensed users activities to avoid interference and collisions. How to obtain reliable results of the licensed users activities is the main task for spectrum sensing. Based on the sensing results, the unlicensed users should adapt their transmit powers and access strategies to protect the licensed communications. The requirement naturally presents challenges to the... 

Today, with the expanding usage of wireless communication systems, the need for system which uses the spectrum efficiently is inevitable. Therefore, Cognitive Radio structures have be the center of attention, recently. In cognitive radio structures, the system tries to use the empty spectrum efficientlyin time, frequency, and space domain. Autonomous Vehicular Networks are interesting application, in which cognitive radio can be used. In such networks, due to high speed, the channel state changes drastically which negatively affects the system.Hence, in this thesis, an OFDM-based multiuser structure is designed which work properly in such condition. For designing the structure, a doubly... 

Recommender Systems have become an attractive field within the recent decade since they facilitate users’ selection process in limited time. Conventional recommender systems have proposed numerous methods with a focus on recommending to individual users. Recently, due to a significant increase in the number of users, studies in this field have shifted to properly identify groups of people with similar preferences and provide a list of recommendations for each group. Because, offering a recommendations list to each individual undergoes computational cost and sometimes is not possible. So far, most of the previous studies requires the restrictive assumptions such as: (1) limited number of... 

The main purpose of this dissertation is to give an ethical evaluation of one of the consequences of ICT. Since these technologies are present in every corner of our personal and social life, recognizing their ethical and social consequences are of vital importance. The present dissertation, which is set up in 3 chapters, is allocated for evaluating one of these consequences. In the first chapter which is the first step of our overall argument indeed, one of recent theories in Cognitive Psychology and memory studies, namely Working Memory will be introduced. In the second chapter, introducing another theory in Cognitive Psychology namely Cognitive Load Theory, the role of Working Memory in... 

Increasing demand of bandwidth in wireless communications systems led to excessive congestion in frequency spectrum. Since radio spectrum is an expensive and rare source, its efcient use is an important challenge. These limitations as well as increasing number of communications service users,necessitate the use of newer technologies that work efciently with numerous users. Device-to-Device (D2D) communications, full-duplex capability and cognitive radio systems are introduced for this reason. In the previous technologies, due to excessive self-interference (SI), full-duplex transmission has not been implemented. However nowadays technology allows self-interference to be attenuated up to 100... 

Wireless Sensor Networks (WSNs) has been a research topic for more than a decade, and the range of potential applications has spanned beyond the military domain into commercial domains. A key feature of current WSN solutions is operation in unlicensed frequency bands, for instance, the worldwide available 2.4 GHz band. However, the same band is shared by other wireless applications, such as Wi-Fi and Bluetooth, as well as other proprietary technologies. There is evidence that unlicensed spectrum is becoming overcrowded, to solve this problem, concept of cognitive radio has been introduced.
A main challenge for routing in cognitive radio wireless sensor networks is the collaboration... 

Cognitive Radio (CR) technology enables dynamic spectrum access (DSA) to overcome the problems of unlicensed bands which is becoming overcrowded. However, providing an acceptable quality of service (QoS) for cognitive users requiresmore sophisticated approachesdut to the existence of primary users (PU) with their high priority over licensed bands. Additionally, reducing interference with primary users so that they can communicate without interruption is of extreme importance. In order to meet cognitive user’s quality of service as much as possible and reduce interference with PUs, a new class-based multipath on-demand routing protocol for cognitive radio networks (CMORC) is proposed. CMORC... 

Dynamic spectrum access with the aid of cognitive radio (CR) technology is a viable solution to spectrum scarcity. There are many military and emergency applications that require the use of cognitive radio ad-hoc networks (CRAHNs). In these net- works, nodes must first find each other in a wide spectrum and then exchange their desired data. The process of finding each other in a multichannel environment is a challenging task and is usually known as rendezvous. Since rendezvous is the first step in communication, disrupting will disable the nodes from establishing proper communication sessions. That results in a drastic degrade in the performance of the network. Therefore, it is important to... 

Due to both dynamic and opportunistic spectrum access, Cognitive radio networks is a promising solution for spectrum scarcity problem. In cognitive radio networks, users need to have a control channels in order to cooperate for sharing the sensing information, channel sharing and etc. In Ad-hoc cognitive radio networks because of the absence of infrastructure and central nodes, every user runs a distributed algorithm to create a common control channel. If the control channel gets jammed, network’s performance degrades dramatically, therefore the jammer’s target in cognitive radio networks is the control channels to disturb the networks’ performance. The traditional solution to confront... 

After three decades of research, the concept of emotion as an aspect of initelligence in artificial systems, is still unclear. Most of emotion models in AI are aimed to simulate the emotional states of human in differenct levels of abstraction and functionality. Therefore, the concept of emotions in artificial systems is completely dependent on human being’s emotional states and can not be used as a general tool for improving the intellingence of artificial systems. In this thesis, we have tried to show that defining emotion in a more abstract level can expand the domain of its appications in AI. According to some existing theories about emotions, we modeled emotions as local semi-soloutions... 

Deployment of demands, increase in users and new services highlight the necessity of effective frequency allocation i.e. dynamic allocation instead of fixed allocation. Cognitive radio is a proper solution for dynamic frequency allocation. Cognitive radio can scan the spectrum and use the idle bands for transmitting and receiving data. The main part of this radio which is responsible for the most pivotal task is spectrum sensing. Recently, varied methods have been proposed to sense the spectrum. The scope of this research is on designing a very high-speed spectrum sensing system. In this thesis, in order to meet the required scan rate, a tunable complex filter with 40MHz pass-band has... 

In economics, choice or behavior is considered as a result of utility optimization. However, there’s much theoretical and experimental evidence that shows human beings suffer from decision-making and judgment errors. This research aiming at examining the relationship between post-choice attitude changes and framing effects as the two instances of those errors designed and implemented a 2 by 2 between-subject lab experiment. The subjects were randomly assigned to one of these four groups. The two treatment groups made their decision after they rated the objects one time and the two control groups did this after they evaluated the objects two times. Another intervention was to manipulate... 

In recent years, demand for frequency spectrum has increased rapidly. Cognitive radio technology, as a tool for better access to the frequency spectrum, opportunistically uses the bandwidth of a licensed frequency band to solve the problem of congestion in unlicensed frequency bands. The spectrum allocation is one of the first steps in the implementation of cognitive radio networks. Many studies have been done to solve the problem of optimal spectrum allocation in such networks. One of the most commonly used methods to solve the optimization problem is using meta-heuristic algorithms. Harmony search and artificial bee colony algorithms are two of the most successful methods for this purpose.... 

The purpose of writing this thesis is to arrive at the concept of civilization. And in this process, using the constructive perception. My approach in constructive perception is different with approach of Allameh tabatabaei in constructive perception. In first chapter defining constructive perception as the perception that mind by analogy between two consepts makes the non-real relations and attributes it deliberated to the reality (the parties). Meanwhile, should have been constructive perception is the intermediary that stimulation our sense abut reality. These feelings can be tenderness or hatred or fear and hope and ... . In the second chapter we will show that the use of technology... 

The debate over the nature of perceptual states has been a significant part of the literature of philosophy of the mind during the past two decades. John Campbell's philosophical works on metaphysics and epistemology of sensory perception, according to many of his followers and critics, are among the most coherent contemporary philosophical works with recent advances in cognitive science. His research on the relationship between attention, reference, knowledge and spatial representations is to a large extent supported by scientific ideas in empirical psychology, and it can be said that most of his work is devoted to analyzing and solving the theoretical complexities deriving from empirical...