Sharif Digital Repository

Recently studies have shown that about 50% to 70% of voice calls and other traffics are used in indoors by users. Due to the growing need to increase the rate of communication networks and macrocells resource constraints in providing this need, the idea of using femtocells was proposed. These cells transmite traffics via IP network to the operator. This would reduce the load of macrocells and thereby increase the rate of network users. So the idea of using femtocells inside macrocells was introduced. In addition to increasing the rate of network, the other advantages of using femtocells are lower cost, lower power consumption and better user channel condition. The important challenge of... 

Considering the advantages of optical communications and code division multiple access technique, Optical Code Division Multiple Access Networks (OCDMANs) was introduced. Thence, many researchers have suggested methods for creating Quality of Service (QoS) differentiated classes in OCDMANs. In this thesis, we have comprehensive review on the QoS assignment methods and enhance them by offering new techniques. In physical layer, we concentrate on variable chip rate OCDMANs and in MAC sub-layer, a new algorithm named Adaptive Level Control (ALC) is introduced. Then, we focus on the physical design of OCDMANs. Firstly, we solve the problem of one-class OCDMAN and introduce few simple and... 

Wireless technology is growing rapidly. We have seen the evolution of these networks from first to fourth generation. Along with this growth, number of users needing wireless data services supporting real-time multimedia applications with high quality of service is growing annually. The challenge is to have the best connection anytime anywhere. Radio access technologies (RATs) consist of different types. Each RAT has its own technological characteristics. Operators constantly are seeking to increase their subscribers by providing high quality services so they can earn more profit. On the other hand users try to have a better experience from provided data services according to their... 

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.... 

Data traffic in communication network has increased steadily in recent years. Service requirements have also changed to become more complex. Moreover decrease in relative prices of computation and storage against communication encourages using more caching in these networks . Meanwhile increased use of encryption in internet has forced service providers who were willing to enter content distribution market to cooperate with content providers. But the cooperation is discouraged by willingness of both parties to hide their internal information. There are solutions proposed for interaction and information exchange between ISPs and CPs which are based on game theory. However, these solutions... 

In this thesis, our aim was to assess the resource allocation problem in wireless sensor netowroks and to optimize network utility and lifetime. To achieve these aims, it is nesseccary to solve resource allocation problem through optimization methods. Since the central methods need a central node to manage resource allocation, they can not be implemented in sensor networks because the nodes neighbors to this central node drain energy very quickly. Also, since central methods require transmission of all information about network topology to this central node, every change in network topology result in transmission of new network topology informations and therefore, overload for frequent... 

Recently, cooperative communications have gained much interest due to its ability to mitigate fading in wireless networks through achieving spatial diversity while resolving the difficulties of installing multiple antennas on small communication terminals. There have been considerable research efforts on the performance analysis of cooperative diversity. This is while most of the current works assume that perfect knowledge of the channel information is available at the destination and/or relay terminals. However, in many practical scenarios, due to the errors caused by Doppler shift or noise on the pilot signals the perfect estimation of channel coefficients is not possible. In this thesis,... 

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... 

Ever growing users’ demand for higher mobile data traffic and a rise in the number of communicating devices in the network oblige operators to design novel schemes in order to respond to users’ requirements. The limited available frequency spectrum cannot handle this increased data traffic demand in cellular networks. It is estimated that by 2020 the amount of traffic in mobile networks, grows ten times more than mobile traffic in 2014. Data offloading is an existing approach that enables operators to support users’ demands. In this approach, in addition to utilizing Wi-Fi technology as a means to transfer data as well as conventional cellular communications, opportunistic communications... 

Software-Defined Networking is a new approach in networking which provides a great opportunity to improve network management. Network policy decisions and reachability policies are one of the main concerns of the network administrators. These policies are traditionally configured in different network devices. The configurations are manually implemented using ACLs in routers, firewalls, VLANs, etc. Network engineers configure every single device on the network with its vendor-specific low level language. As a result, access control policies of the network lie in the configuration files of the network devices or even only in the minds of the network engineers. Moreover, access control policies... 

There is an increasing demand from mobile users for higher bandwidth, lower latency, longer battery life and better quality of service. It is expected that the next generation of mobile networks standards which is called 5G meets most of these demands. It is expected that the enhanced features of the mobile networks can be achieved within the limited bandwidth which is offered by the regulators and therefore, one of the key challenges in the development of these new technologies would be the issue of resource allocation. Efficient allocation of frequency, time and power to different users is an important issue and therefore, one of the important areas of development in these standards has... 

Delay Tolerant Networks (DTNs) are sparse networks in which intermittent connectivity happens due to energy shortage or high mobility and long latency is unavoidable.These networks have a wide range of applications in our daily life such as internet of moving things. In delay tolerant networks, finding an end to end path between source and destination is almost impossible. Therefore, routing can’t be done based on finding an end to end path but it has to be done based on hop by hop sessions. In this thesis, we aim to represent an efficient routing algorithm for delay tolerant networks that can improve delivery probability, delivery cost and delivery latency.Our proposed routing algorithm is... 

Consistent growth in volume and dynamic behavior of traffic mandates new requirements for fast and adaptive resource allocation in modern optical networks.Elastic optical networks have been proposed to provide a competitive and scalable solution by creating tunable high-capacity optical communication networks in which network elements are configured according to the actual need to minimize resource usage for the specified service requirements. Resource allocation with quality of service constraints is one of the most challenging problems in elastic optical networks which is conventionally formulated as a complex mixed-integer nonlinear optimization program.In this research work, we focus on... 

There has been a rapidly growing interest in deployment of Wireless LAN Networks (WLANs) in the past decade. The cost of WLAN devices has steadily decreased while their performance has increased. As a result, a wide range of new connectivity services are using WLAN standards for data exchange between nodes and networks through WLAN access points. Deployment of many WLAN access points in enterprise applications causes severe degradation of performance due to interference between access point channels. Therefore, it is wise to control the access point channel assignment procedure to reduce interference and improve network performance. This process can be done in using centralized or... 

In recent years, Internet traffic has nearly doubled in the core network every two years, and it is expected to continue to grow in the future. With this growth, there is a need for very high capacity and economically efficient transmission systems, which optical communication is the best choice. Elastic optical network (EON) is one of the best options for achieving this goal in the future. Unlike existing networks, the transmission parameters of EON will be customizable, which will have an essential role in optimizing bandwidth assignment. The problem facing scientists today is to approach the final physical capacity of current optical fibers. The solution proposed for this challenge is... 

Telecommunications operators look forward to network virtualization to reduce capital and operational expenditures. Optimal performance of the virtualized networks requires efficient resource allocation. On the other hand, in recent years, traffic growth and its dynamic behavior are two main drivers for the development of elastic optical networks. In this research, the problem of resource allocation for virtualized network function requests over an elastic optical network is investigated. Due to the high cost of energy consumption, energy efficiency is considered as the objective of the resource allocation problem. Conventional pure static and dynamic solutions are not suitable for efficient... 

Secure routing is a major key to service maintenance in wireless ad hoc networks. Ad hoc nature exposes the network to several types of node misbehavior or attacks. Wormhole attack is one of the most severe active attacks to mobile ad hoc networks. Noting the resource limitations in such networks, nodes may have a tendency to behave selfishly. Selfish behavior can have drastic impacts on network performance. We have proposed a Misbehavior-Tolerant Multipath Routing protocol (MTMR) which detects and punishes all types of misbehavior such as selfish behavior, wormhole, sinkhole and grey-hole attacks. The protocol utilizes a proactive approach to enforce cooperation. In addition, it uses a... 

Providing high bandwidth network infrastructures for ever increasing need of data transport is of great importance. The underling infrastructure for many communication services such as GSM/3G/4G mobile networks and Internet services is Synchronous Digital Hierarchy (SDH) optical transport systems. SDH are standardized protocols that multiplex multiple lower rate digital bit streams, such as E1 and Ethernet, and transfer them synchronously over optical fiber using lasers or LEDs. In addition to high data transfer rates, flexible network management and protection mechanisms have great importance, hence are part of SDH standards. In order to obtain flexible network architecture and protected... 

Development of Smart Grid and deployment of smart meters in large scale has raised a lot of concerns regarding customers’ privacy. Consequently, several schemes have been proposed to overcome the above mentioned issue. These schemes mainly rely on data aggregation as a method of protecting users’ privacy from the grid operators. However, the main problem with most of these schemes is the fact that they require a large amount of processing power at the meter side. This, together with the fact that smart meters don’t usually have a powerful processor, can cause the unavailability of smart meter data at the required time for operators of the grid, and at the same time disables smart meters from...