Sharif Digital Repository

With the growing deployment of host and network intrusion detection systems, analyzing generated alerts from these systems becomes critically important and challenging due to its complexity and high amount of data. Alert Correlation systems are a possible solution for deep analysis of incoming alerts in response to potential attacks against enterprise networks. Although several known alert correlation systems have been proposed for this purpose so far, most of them do not support high amount of input due to their centralized architecture. In this thesis, we propose a system architecture and approach for alert correlation to be extensible, flexible, and modular. The architecture encompasses... 

Ionizing radiation can modify physical, chemical and biological properties of the irradiated materials. At present, the principal industrial applications of radiation are sterilization of health care products including pharmaceuticals, irradiation of food and agriculture products and materials modification. In the above application the wide range of the required doses together with different product densities require spatial mechanical design of the irradiators to be able to properly handle the specified tasks. In the multipurpose irradiators the design of system and positioning of the source must be done in such a way that a nearly optimum dose distaition in the product boxes in... 

The epidemic of Covid 19 has killed millions of people worldwide. Despite the efforts of scientists around the world, there is still no cure for this disease. Approval of newly designed drugs due to clinical trial periods is time-consuming and costly. For this reason, in the current emergency situation, it is important to have a solution for screening available approved drugs in order to find effective substances for this disease.High-throughput assays are a good option for such problems. In this field of research, image-based high-throughput assays are amongst the most effective and cost-effective methods that help quantify the response of treated cells by measuring cell... 

The use of MANETs in many areas is rapidly spreading. Due to dynamic nature,and limited energy of this networks, they are vulnerable to some attacks including blackhole attack. Blackhole attack can disrupt the commiunication between hosts and cause denial of service. One of countermeasures to this attack which has been recently proposed is the ActiveTrust. ActiveTrust is a routing protocol which relys on malicious node detection using trust calculations; this scheme has been proposed for WSNs. In this work we adopt the ActiveTrust’s idea and try to apply it into MANETs. Then we simulate the resulting proposal in NS-3 and compare the results  

Distributed stream processing frameworks (DSPFs) are used for real-time processing of big data. Apache Storm is one of the most popular stream processing systems in industry today. By increasing data generation rate we need new methods to overcome processing requirements of DSPFs like Apache Storm. In this thesis we investigate the feasibility of incorporation FPGA acceleration into Apache Storm. Using FPGAs as co-processors in powerful servers can improve performance and accelerate processing of streaming data by increasing parallelism, decreasing processing time of each processing units and decreasing communication delay between these units. Our design includes a hardware part that... 

The importance of shared memory (scratchpad memory) in GPGPU programming, the memory size limits of GPGPUs and the influence of shared memory on overall performance of the GPGPU has led to its performance optimization. Moreover, the trend of new GPGPUs design shows that the ratio of shared memory to processing elements is going smaller. As a result, the limited capacity of shared memory becomes a bottleneck for a GPU to host a high number of thread blocks, limiting the otherwise available thread-level parallelism (TLP). In this thesis we introduced a reconfigurable and adaptive shared memory architecture for GPGPUs based on resource sharing which can be exploited for throughput improvement... 

Droplet microfluidic platform generates monodisperse droplets in a desired size through immiscible multiphase flows inside microchannels. Droplets are individual reactor and can be used for bio(chemical) analyses. Also, for materials fabrication, droplet microfluidics offers a versatile platform for generation of nano- or micro-sized particles and microcapsules that are widely used in drug delivery. In addition to the monodispersity, high-throughput generation is also necessary in many applications. Therefore, droplets must be formed in stable regimes (dripping and squeezing) in the highest possible frequency. In this study, the flow-focusing geometry, which is the most common geometry in... 

Designing a scalable protocol for the blockchain will reduce transaction fees and increase the use of cryptocurrencies for financial transactions. Increasing scalability means that if the investment of nodes increases or the number of network nodes increases, the security of the protocol and the decentralization of the network will be maintained and its throughput will increase. In this thesis, with the aim of increasing scalability, the scaling methods of layer one and layer two are examined and compared, and it is shown that sharding is a better method to achieve scalability. In sharding, nodes are divided into several shards (clusters) and each shard manages its own blockchain. The... 

In the future mobile network 5G will offer high speed and low delay but millimeter wave link are poor at penetrating into solid objects. Thus future network will be a hybrid of traditional sub-6GHz macrocells and denser 5G small cells. We develop a general analytical model to derive delay and throughput in this network. First we analyse the initial access delay which is very important in Internet of things and machine to machine communication. Then we go into data delay of network. With the foreseeable explosive growth of small cell deployment, backhaul has become the next big challenge in the next generation network. We analyse two option of fiber and millimeter wave. At the end we have end... 

Caching has been widely considered an efficient way of reducing and balancing the growing traffic in communications networks in recent years. In this thesis, for the first time, the stochastic requests traffic model in communication networks is considered and a performance analysis is provided based on such a realistic assumption. In addition, we introduce new comprehensive performance metrics which simultaneously take into account, the cache hit probability, load on the bottleneck links, and requests arrival rates. The main contribution of this thesis is to present a system model based on queuing theory and provide an analysis of the stability, maximum stable throughput, load on the... 

In this thesis, we propose a new resource allocation method for a heterogeneous cellular network comprised of a number of millimeter-wave-based microcells overlaid on a micro-wave-based macrocell. There are also different types of demanded file sizes for users in the network. Regarding the higher data rate in millimeter-wave coverage on the one hand, and the limited coverage of millimeter-wave microcells on the other hand, design of suitable resource allocation in both bands is of crucial importance. In our allocation proposal, we follow a hierarchical multi-object auction-based approach, where each user is able to use a number of frequency channels, i.e., different bandwidths, depending on... 

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.... 

Energy Harvesting has been appeared as an approach in order to make the green communications possible. In Energy Harvesting systems, nodes extract energy from the nature to extend their lifetimes. The harvested energy can also be used for the purpose of communication and specially for the transmission process. Compared to the conventional batterypowered systems, the Energy Harvesting systems have access to an unbounded source of energy (like vibration absorption devices, water mills, wind turbines, microbial fuel cells, solar cells, thermo-electric generators, piezoelectric cells, etc). However, the diffused nature of this energy makes it difficult to be used for communication. In this work,... 

Fair allocation of bandwidth between stations of a shared medium, is an important and challenging problem. It is even more challenging when there is no coordinator to arbitrate access to the medium and therefore, a distributed algorithm is needed to provide fairness. IEEE 802.11 DCF is the dominant distributed medium access control (MAC) protocol in a wireless LAN. However, DCF is not in general fair and suffers from short-term unfairness. In addition to that, it is desired to provide differentiated service for the stations of a LAN based on their demands. Since priority based protocols may lead to starvation of the low priority traffic, we are more interested in fair queuing. On the other... 

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 the recent years, the cooperative communications based on Network Coding have received significant attentions to simultaneously improve the diversity order and the network throughput. In this thesis, a new cooperative transmission scheme for the cooperative relay-based networks called “Convolutional Network-Coded Cooperation” (CNCC) is proposed, in which a systematic convolutional code is used in the network level. In this scheme, the systematic packets are directly transmitted by the sources, and the parity packets, calculated based on the received sources’ packets, are transmitted by the relays. The proposed CNCC scheme is considered in the cooperative networks including N sources, M... 

Increasing demand for higher data rates and more reliable communications along with growing applications of multimedia networks in everyday life on one hand, and limited resources on the other, have given rise to researches investigating spectrum efficiency enhancement techniques, among which multiuser diversity has always been of considerable importance. This thesis is a study on utilization of multiuser diversity in wireless LANs via scheduling. Where throughput and Quality of Service (QoS) in communication networks are being investigated, it is mostly advantageous to describe the traffic behavior of resources by greedy or non-greedy models. So far, there are plenty of investigations on... 

We analyze the fundamental communication limits and capabilities of random wireless networks. In order to achieve this goal, we investigate and analyze efficient communication strategies in such networks. The traffic model considered is unicasting. Also, we consider two different channel models, namely, the geometric channel model and the random connections model.
In networks with random connection model, channel powers between different nodes are drawn from a common distribution in an independent manner. We assume an on-off strategy for operation of transmitters, and show that finding the optimum transmission strategy problem is an NP-hard problem. Thus, we propose a heuristic algorithm... 

Optical Communication is a promising technology in access networks because of bandwidth hungry application like videos. So fiber Optic is an important candidate as a media in networks. There are different methods of modulation for transferring data through a channel. Among all, Orthogonal Frequency Division Multiplexing is a method which used in most wired and wireless systems. Recent researches show that OFDM is also a good approach for optical communication.
In this thesis we concentrate on hardware implementation of digital part of an Optical OFDM transceiver. In the first step we ignore the effect of optical channel and design and simulate the transmitter and receiver. After that we... 

In recent years, coded cooperation has been considered as one of the best methods to cope with fading and at the same time to achieve channel coding gain. There is a special case of cooperative networks that provide different level of user priority. Among all methods for creating user priority our motivation is to use of UEP codes for this propose. UEP codes are a special case of channel codes that provide different level of protection for message. It means that some part of message that has more protection it has less error. First we review all type of UEP codes and compare them in term of probability of bit error on the AWGN channel. And best code will be choosing for applying to this...