Sharif Digital Repository

My dissertation includes four chapters; three introductory chapters and a final conclusion. The first chpter is a comprehensive introduction to the problem of consciousness. The next chapter is allocated to representationalism, especially Michael Tye's PANIC theory, as a solution to the hard problem of consciousness and related phenomena. The third chapter is a brife look at causal theories of mental content. And the last chapter contains my arguments agaisnt Tye's theory. Apparently, mental states are of two categories; some mental states have representational content and some other have phenomenal aspect; there is something it is like to undergo latter states. Representationalism holds... 

In this research, two-layered sheets of copper and stainless steel 316 were produced by roll bonding. These sheets provide a combination of properties of copper and stainless steel; including high strength, thermal conductivity and corrosion resistance, as well as low weight and cost-efficient means of production. The effects of thickness reduction, different preheat temperatures and varying heating conditions after rolling on bond strength were studied. In some specimens, an aluminum sheet was used as a middle-layer, which significantly improved the bonding quality. In order to observe the interface of the bonded specimens, optical microscope images of the cross sections were studied.... 

The epistemic program in game theory uses formal models of interactive reasoning to provide foundations for various game-theoretic solution concepts. Much of this work is based on the (static) Aumann Partial models of interactive epistemology, but more recently dynamic models of interactive reasoning have been developed to analyse rational play in extensive form games. Here we surveyed (static) Aumman Partial models and (dynamic) Baltag and Smets plausibility models. compared these models, And investigated the backward induction problem by using these models  

In recent years applying solid state drives in data centers, cloud computing infrastructures and commercial servers have had a considerable growth. Low power consumption, high throughput and resistance to physical damages are some of the advantages of SSDs over HDDs. In recent works the necessity of using an interconnection network as a communication subcomponent between memory flash chips and disk controller is described. Disk mechanisms (mapping, wear-leveling and garbage collection) influence on throughput of the network. Based on this fact in this research an analytical model is provided considering disk mechanisms, flash chip structure and traffic characteristics. The error of the model... 

In the present research, a new material model utilizing anisotropic conduction and track-scale heat input model is used to predict the melt pool geometry, material state and thermal history during the selective laser melting process of SS316L in a large range of laser parameters. The model takes into account the phase transition of the material during the process. Furthermore, the phase transition problem in the track-scale model has been analyzed and a solution has been presented. The simulated melt pools in beam-scale and track-scale simulations are compared with experimental measurements in different laser parameters. It is found that the proposed material model is able to maintain... 

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... 

In this thesis, we evaluate the maximum stable throughput of a cognitive multi-hop IEEE 802.11-based WLAN overlaid on a cellular network. In the considered scenario, the secondary users operate in the downlink or uplink frequency band of primary network and transmit their data in free primary channels using OFDM technique. The activity of primary nodes is modeled independently by ON-OFF alternating states. To model the scenario, each secondary user is modeled with an open queueing network. The queueing network can model the transmission of data as well as the effect of primary users. By writing the traffic equations of the queueing network and applying the stability conditions, we are able... 

In this thesis the effect of frame aggregation mechanism in maximizing throughput in Wireless Local Area Networks (WLANs) have been investigated. Frame aggregation has become a part of the IEEE 802.11 standard as the amendment IEEE 802.11n. First, we have a quick review on access control layer in IEEE 802.11 standard then illustrate the necessity of frame aggregation. Afterwards, we propose an analytical model for the analysis of an IEEE 802.11n network comprised of an Access Point (AP) and several conventional nodes, all in the coverage area of each other. This analytical model focuses on downlink throughput; therefore only AP uses frame aggregation and the other nodes use basic IEEE 802.11... 

In this thesis, we propose two new network coding-based packet relaying schemes suitable for multiple unicast scenarios in a random access network. In such networks the channels may have memory dependent upon the random access scheme. Thus, the optimal scheme for memoryless channels reported recently in the literature is not necessarily optimal in random access networks. In our proposed schemes, we convert a multiple unicast scenario to a combination of multiple anycast and a few multicast scenarios. By such an approach, we exploit the channels between relay node and the other nodes, instead of using only one channel at each packet transmission, for as many as possible. By simple analytical... 

Car accident damages take about 7 percent of GPD of Iran every year. As a result of car accidents, the economy of the country is damaging irreparably. The amount of road casualties equals casualties in a complete war. Considering the aforementioned conditions, the researchers are thinking about new technologies to reduce the cost of the accidents. So the use of Vehicular ad-hoc Networks (VANET) is inevitable in the near future. Content distribution service is one of the emerging services of VANETs. This service is used in both safety and comfort related applications. Content distribution describes delivery of media content such as Video, Audio, Image, Text, Software, and Video Games over... 

In cognitive radio networks, secondary users try to use empty channels that primary users provide for transmitting data. First, the secondary users sense the target channels. If the selected channel is empty, they send their data. When the primary user returns, the secondary user has to find another empty channel for transmitting data. The process of changing channel is called hand off. In recent years, there are challenges in the spectrum mobility of for reducing delay time of secondary users packet. In this thesis, we assume that the secondary users network is an ad-hoc network. We use contestation based method for reducing collision between secondary users. In this thesis, we present an... 

In this dissertation, we focus on two types of EH cooperative networks. In the first type, the source and relay nodes access a shared channel according to a random access protocol. Also, they harvest energy from non-RF environmental resources. The relay node has data and energy buffers to store the packets of the source and the harvested energy, respectively. Our main goal is to find the optimal relaying protocol at the relay node. In this regard, the first type of the EH cooperative networks are investigated in two different scenarios. In the first one, the MAC channels of the nodes are independent of the applied policy at the relay node, and thus the throughput of the network is fixed.... 

In this thesis, we investigate the age of information in multisource networks. To this end, in the first phase of this thesis, we evaluate the Age of Information (AoI) in slotted ALOHA network. Regarding the interactions among the nodes in such a network, we model the memory of this network with a Trellis and find the peak Age of Information (PAoI) by using this Trellis. Then, we evaluate Age of Information-constrained regions and achievable throughput regions in the slotted ALOHA network and optimize Age of information in a symmetric case. In the second phase, we propose an efficient prioritizing scheme from AoI point of view and find the distribution of AoI and PAoI in such a scheme with... 

Cooperative networks have attracted much attention in the last decade. Being introduced to mitigate the inefficiencies in the physical layer, cooperation can also be beneficial in upper layers, such as MAC layer. Using cooperative communications is specifically more challenging in the random access networks, where collision is a main concern. Delay, as one of the main performance metrics in random access networks, can decrease significantly by using cooperative communications. Transmission delay, i.e., the required time for delivering one packet form its source to destination, is an important metric in many communication networks, such as the networks in which each node generates and... 

Today, with the proliferation of smart devices and the advent of various innovative applications, there has been an exponential surge in the number of users in telecommunication networks. Consequently, the data traffic rate is escalating considerably. This has created a major predicament for wireless networks due to the limited frequency spectrum. Therefore, the conventional centralized architecture makes it difficult for the network to address these numerous simultaneous requests. This issue can be solved by designing new architectures. In a way, network information is disseminated to the network's periphery and the contents of the primary data center are provided temporarily in closer... 

OFDMA modulation method is a multiple access technique that is resistant to fading effect in cellular communication systems. In OFDMA, multiple access is performed both in time and frequency, so more users can be served with less delay than other protocols. In this thesis, based on queuing theory, we seek to present a traffic model for OFDMA system traffic analysis in single-cell mode and in the next section in multi-cell mode. Then, by examining and comparing the analytical results and the simulation results, we show that our proposed model for traffic analysis of the OFDMA system is a suitable and effective model. Also, since users in the multimedia environment need different types of... 

In data transmission from a transmitter to a receiver, in some applications receiving updated data is crucial. To this end, a metric called Peak Age of Information has been introduced, the minimum of which is equivalent to having more updated packets. In this thesis, a method for calculating the probability distribution function of this random variable in a random access network with a transmitter, a relay, and a receiver in which the error probability of the channels between the transmitter and the relay and also the relay and the receiver is less than the error probability of the channel between the transmitter and the receiver, is proposed. The transmitter and the relay send their packets... 

In many communication scenarios, dependent requests are commonly observed, such as caching networks. In this thesis, we propose a new analytical model to examine the impact of dependent arrivals on the average response time in a simple queue with exponential service time. We examine two dependency scenarios: batch arrivals and the arrival of one customer after another with a random delay with a known distribution. To accurately model the effect of dependency between arrivals, we define redundant customers in our model to compensate for the existing dependency effects. We demonstrate the validity of our modeling approach analytically in the first scenario and through simulation in the second... 

Edge computing networks are ideal for emerging applications that require computation-intensive and timely processing, as they enable complex computation tasks to be offloaded and computed in parallel and distributed manner. However, for many applications that the calculations are of one type, such as determining the location of an object, it is crucial to insure the freshness of the information. Age of Information (AoI) metric is employed to measure freshness. This research focuses on identifying an appropriate model for calculating the average AoI in distributed computing systems and determining the optimal decision-making policy to enhance it. In essence, the primary objective is to... 

As the global demand for data has continued to increase exponentially, researchers have begun exploring the concept of semantic communication as an effective tool to meet this demand. Semantic communication transcends the boundaries of conventional telecommunication systems, focusing on the transmission as well as accurate retrieval of meaning at the source and destination, respectively, rather than transmitting and recovering merely symbols. One approach in semantic communication emphasizes the significance of information, rather than its meaning, to achieve efficient and goal-oriented communication. One key metric in goal-oriented communication is the Age of Information (AoI). AoI is a...