Sharif Digital Repository

Nowadays, H.264 is a popular format to data transfer. The growing use of video signals and importance of its ownership in the digital world, requires careful study of robust video watermarking. Distorting the watermark through recompression is a common attack to robust video watermarking schemes. It is aimed in this thesis to design a recompression resistant watermarking scheme and to address real-time extraction of the watermark from both compressed video bitstream and decoded video. In this thesis, we employ an objective quality metric, which is highly correlated with human perception, as a cost function in image/video watermarking optimization. We show that by embedding in the selected... 

In the modern world today, the increasing need for transfering data in high speeds and long distances has encouraged the investors of this area to use more efficient technologies of this field. With regard to the need for extensive and scalable communication networks, reusing the bandwidth in closer distances seems to be inevitable. Hence, finding an optimal way of using resources like bandwidth and power is necessary. In OFDMA-based networks there is no intra-cell interference due to using orthogonal subbands and the most important limiting factor in designing these networks is inter-cell interference. Therefore in this thesis we are gonig to analyase the partial frequency reuse method... 

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... 

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... 

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...