Sharif Digital Repository

This thesis investigates methods to improve the utility of cellular spectrum to secondary users. Here, secondary users exploit the spectrum by hierarchical spectrum access. Since the information of the channels is available at the central controller, cellular networks can play an active role in spectrum use of the secondary users and increase their utility in this way. Transmitting the information available at the central controller to the secondary users and ordering the channels in use by primaries can help improve spectrum sensing. First, we consider the schemes which maximize secondary users’ utility by ordering the channel allocation process to primary users. We model the secondary... 

Network coding as an efficient approach for performance improvement of communication networks has been introduced by Ahlswede et al. Despite simple forwarding schemes, in network coding scenarios, intermediate nodes forward the encoded version of their received packets. In wireless Networks, resource allocation includes routing, network coding, flow control, scheduling and power control.In this dissertation a joint scheduling, routing, flow control and Inter-session NC formulation based on a convex optimization problem is studied. Our formulation integrates the optimal scheduling, flow control and Inter-session network coding with a modified version of minimum delay routing. We propose a way... 

In a data network, expressing an appropriate model for traffic and service is necessary for the guarantee of quality of service (QoS) parameters, e.g. delay and backlogged traffic. There are four main approaches for modeling the traffic and service. First approach is classic queuing theory. It is a useful tool for analyzing the networks with memory less input traffic. Second approach is deterministic network calculus. In this approach some deterministic bounds on delay and backlogged traffic can be derived. However, it is not accurate for analyzing the bursty traffic and wireless networks, because only trivial bounds can be derived in these scenarios. Third approach is effective bandwidth... 

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... 

Constructed wetlands are natural systems for wastewater treatment that Proper functionality of these systems to remove organic matter, pathogens, micro pollutants and etc., Are considered as environmental friendly systems. Proper capabilities of pollution removal and inexpensive cost of construction, commissioning and maintenance of these systems compared to engineering WWTPs in the world is leading to growing constructed wetlands. Due to the increasing use of artificial wetlands in the world for post treatment wastewater, because of right capabilities of this systems, and the absence of any natural wastewater treatment systems on Kish Island, this study investigates the possibility of... 

Generally to deal with errors in communication systems, two methods have been proposed: FEC and ARQ. In FEC, redundancy bits are added to the data that causes detection and correction of certain error patterns. ARQ method is based on retransmission of information if there is an error in the information. Another method, which is called Hybrid-ARQ, is the combination of these two methods; there are two types of TypeI and TypeII for this category. In typeI, number of redundancy bits in consecutive transmissions of one codeword is constant but in typeII, number of redundancy bits of a codeword increases in subsequent retransmissions.
To deal with burst errors, we can use interleaving along... 

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... 

Environmental pollution and depleting the resources of energy are two significant crises which has been caused by excessive Energy consumption in all over the world. One of the most appropriate and reproducible energies is the Biogas energy. Huge amount of sewages and dry wastes are produced in cities every day can causes devastated damages to environment. All types organic matter extracted from different processes of treating sewages are influenced by germ activities and will be transformed to mineral structures and the final product of these reactions would be gases which can be used as enormous sources of fuel and energy. There are different devices made all over the world to be utilized... 

Non-deterministic finite automata (NFA) are an elementary type of Turing machines with very high processing power. NFA processors provide parallelism at the data and task level because they can be in several different output states in one clock cycle. Implementing such machines with memory is a good strategy because if we consider each of the memory columns as a state, by selecting a row of the memory, we can activate several states at the same time, which is an implementation of NFA. NFA-based automata processors were first introduced by Micron and were very powerful for issues such as pattern matching, DNA sequencing, or regular expressions and, in general, for machine learning topics.... 

In contrast to traditional Networks where a designer can specify an action plan for each agent, in a network with strategic agents, every agent acts selfishly and chooses his strategy privately so as to maximize his own objective. In this dissertation, we study problems arising in the design of static and dynamic networks with strategic agents. We consider two classes of design problems. In the first class, the designer utilizes her control over decisions and resources in the system to incentivize the agents via monetary incentive mechanisms to reveal their private information that is crucial for the efficient operation of the system. In this class of problems, we address two main challenges... 

Deficiency of water leads to extensive researches on alternative water resources. recycling of wastewater for non-drinking purposes such as irrigation, industrial, green belts, forestry and streets and drainage channels washing is One of the existing methods. Therefore, sewage treatment with the purpose of reducing its electrical conductivity has been done in the current research using a real scale vermifilter. Hence, the effluent from a septic tank with a daily loading of 2 (m3/day) was pumped into the vermifilter during 45 days through a pumping system.Then, the effluent from the vermifilter by another pump entered on the surface of the substrate. The results showed that electrical... 

There has been a sudden emergence of next generation networks in the past decade where the primary purposes are data ggregation/mining, distributed information and signal processing, and environmental control and monitoring. The distributed algorithms operating in such networks, should have simple structure and be robust against node failures or network dynamics.Extensive studies on designing and analyzing these algorithms have resulted in introducing different models of distributed systems with similar properties such as gossip algorithms, population protocols, and cellular automata-based systems. In this dissertation, we take first steps toward understanding the computational power of... 

There are some important technologies for the 5th generation of wireless communication (or 5G) and one of them is transmitting signals by millimeter waves or mmWave. Since mmWave antennas are so small and they have high frequencies, mmWave signals are highly directable. MmWave antennas can generate transmission patterns that have a number of beams directed in different directions with small beam width.In this thesis, we propose a scheduling scheme for the mmWave networks with directional antennas.Since using millimeter waves is one of the most important choices for 5G, designing an efficient transmission scheduling algorithm in these networks have been a quite big challenge. As there are... 

Scheduling algorithms are responsible for allocation of various types of resources, interference management, and choosing the times and paths through which messages are to be delivered in a communication network. We consider certain fundamental problems in network scheduling. Any scheduling algorithm, to be practical, must have tractable computational complexity and tolerable delay. In the first part of the thesis, we address the following question: “for a given class of networks, does there exist a scheduling algorithm that performs polynomially many computations (in terms of the network dimensions), while keeping the expected delay of the network polynomially bounded (again in terms of the...