Sharif Digital Repository

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... 

The implementation of high-order multiple-input multiple-output (MIMO) detectors in complex domain, which finds applications in advanced wireless standards such as WiMAX and Long Term Evolution (LTE) systems, has always been a challenge in the literature. To address this challenge, two novel detection algorithms with their high-throughput VLSI architectures for a 4×4, 64-QAM complex MIMO detector are proposed in this thesis. The proposed architectures can easily be extended to high-order constellation schemes. For the first algorithm Complexity analysis and the synthesis results in a 0.13μm CMOS technology show that compared to the reported VLSI implementations in the complex domain, the... 

In this thesis, we propose an analytical model to evaluate the maximum stable throughput of a cognitive IEEE 802.11-based WLAN overlaid on a cellular network. In the considered scenario, the secondary nodes operate in uplink frequency band of primary network and transmit on their own idle detected primary channels using OFDM technique. The activity of primary nodes is modeled independently by ON-OFF alternating states with negative exponential distributed durations. The main feature of the proposed analytical model is to include different status of the secondary users, i.e., different spectrum opportunities for different cognitive users, as the result of dynamic nature of primary users as... 

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. On the other hand, the idea of network coding has been introduced for increasing the efficiency of cooperative networks. In addition, it has been shown that only by jointly designing of network coding and channel coding, the capacity will be achievable. Also, to adjust the rate to the channel capacity without requiring the channel state information at the transmitter, Rateless coding has been proposed. In this thesis above techniques are combined to gain their advantages and to improve system performance. To this end, first we consider a... 

Having special advantages over existing networks, mesh networks have attracted much attention. Proposing new MAC protocols which are in compliance with these networks is an interesting field in which many works have been done. Also, Task Group S of the IEEE802.11 is going to release a standard for the mesh networks. Analysis of a simplified version of IEEE802.11s is the first goal of this thesis. The standard is a spectrum sharing algorithm based on scheduling and contention. Although IEEE802.11e manages the contention for accessing the wireless medium in the standard, but for the sake of simplicity, in this thesis we used SlottedALOHA instead. Also, one gateway and six other nodes are... 

In this thesis we have studied slotted and unslotted ALOHA random access optical CDMA packet switching networks with a chip-level receiver structure. We used generalized optical orthogonal codes (GOOC) and Overlapping PPM (OPPM) signaling technique to improve system performance. The impact of physical layer parameters such as GOOC code cross correlation value and OPPM overlapping index on key performance benchmarks such as network throughput and delay are analyzed. We have also studied the stability of the network based on the number of backlogged users, using expected state drift. It has been shown that using GOOC instead of strict OOC improves the network average delay and throughput.... 

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... 

Simulation optimization has been one of the most important topics in recent years. It is especially useful when the objective function cannot be computed directly or some of the parameters are stochastic. Buffer allocation problem is one of the important problems related to production lines. In this problem the objective is to determine the buffers between workstations so that the throughput is maximized. Non-linear and combinatorial nature of the problem, stochastic factors like machine breakdown or processing times and most importantly lack of a distinct relation for the objective function are the reasons of using simulation ... 

The activity status of primary users in a cognitive network scenario is a key parameter in saturation throughput of the secondary users. In this respect, usually a simple on-off traffic model with exponentially distributed intervals is exploited. For time-scheduled users in modern common standards like WiMAX or LTE this traffic model is not valid anymore. In this thesis, we focus on the saturation throughput analysis of a cognitive network scenario, comprised of a WLAN overlaid on a network with time-scheduled primary users like WiMAX. In this scenario, the cognitive nodes (CNs) hear downlink map (DL-MAP) and thus, know the frequency and time locations of all allocated slots at each downlink... 

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... 

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... 

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... 

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... 

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... 

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 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 propose an analytical model in order to evaluate the maximum stable throughput for unicast services in Vehicular Ad hoc NETworks (VANETs). In this respect, we employ two queueing networks in order to model the mobility patterns of the vehicles as well as the multi-hop packet transmission scenario. In the proposed model, we map the features of IEEE 802.11, as well as the details of multi-hop packet transmission, regarding the dynamic status of vehicles, onto suitable parameters of the queueing networks. In our modeling approach, we take the details of MAC and routing schemes into account by classifying the vehicles based on their mobility patterns and considering... 

In recent years, the possibility of building large systems on chip, called SoC is provided. By scaling the technology, designing Socs will face numerous challenges. The Noc paradigm, has resolved many of the SoC’s problems, by deploying network properties in the structures of on chip interconnections. Today, with advances in the semiconductor industry, we can implement broadband wireless antennas, which are integrated on chip. Such NoCs are called WNoC. Due to immaturity of WNoCs, there still exist big challenges, providing routing algorithm and controlling shared medium via MAV layers, for them. In this project, we will provide a routing algorithm based on tag switching, and then, after... 

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... 

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...