Sharif Digital Repository

In this study, the effect of submerged vanes on the bed scouring and deposition pattern at a 90̊ open-channel junction was investigated. First, the bed formation without submerged vanes were studied under the effect of hydraulic variables like the discharge ratio of tributary to main channel and the ratio of mean approach velocity to the threshold velocity. The results show that scour holes enlarge with time while they move towards the downstream and the outer wall in the main channel. Also, by increasing the ratio of mean approach velocity to the threshold velocity about 0.5, the maximum scour depth occurred at the downstream junction corner with time. In the second stage, the proper vane... 

Abstract: In this dissertation, the problem of tracking and stabilization of nonlinear dynamic systems over the packet erasure channel is addressed. Using the idea of linearization of nonlinear system around current working point, and by the design of an encoder, decoder, and controller for the linearized system, state tracking and reference tracking of the nonlinear system are addressed. To prove the traking and stability of the system, the strong law of large numbers and the dwell time approach are used. By computer simulations, the theoretical development is applied on the nonlinear dynamic of the unicycle model, which is a suitable model for autonomous vehicles, such as drones, unmanned... 

One of the main tools of the developing quantum technology is making the desired quantum gates and processes in the presence of the environmental noises. In this thesis, we first derive a Markovian master equation which defines purely the time evolution of the dynamics (process matrix) of the open system rather than its state (density matrix). This master equation indeed describes the time evolution of the Choi-Jamiolkowsli matrix which is independent of the state of the system at all times including the initial state. The n, by using this master equation we provide a scheme to manipulate optimally and locally the dynamics of the open system by external coherent agents. Such scheme... 

In this dissertation, different information networks such as Multiple-Access-Relay Network (MARN) and Broadcast-Relay Network (BRN) are introduced. MARN has one receiver, many relays and many senders. An achievable rate region is obtained for the MARN, using Partial Decode-and-Forward (PDF) strategy. In the case of semi-deterministic MARN, an outer bound and an inner bound to the capacity region are derived. BRN is a model with one sender, two relays and two receivers. Two different types of cooperation are considered for BRN: full cooperation and partial cooperation between relays. Inner bounds on the capacity region of BRN are obtained and compared with previous works. The main idea of the... 

In the signal transmission cycle in a telecommunication network, there are two coding blocks, which can be realized in two ways. In the traditional way, source coding is first used to remove redundancies and compress information. Then, channel coding is used to transmit on the telecommunication channel and deal with noise and other destructive factors of the channel. In other words, source coding and channel coding are done separately. In contrast, signal transmission can be done by joint source¬channel coding. According to Shannon separation theorem and with the fulfillment of the conditions mentioned in the theorem, the method of separation of source and channel coding in a point to point... 

In this thesis we consider transmitting an analog Gaussian source over an AWGN channel in the presence of an interference completely known at the transmitter intwo cases: 1) Compression bandwidth with interference uncorrelated with the sourceand 2) Matched bandwidth channel in the presence of interference correlated withthe source to be transmitted. We study joint source-channel coding schemes basedon hybrid digital-analog (HDA) codes. After providng a brief review, we will proposetwo new schemes for the ?rst case and one novel scheme for the second case. Aswe will see both schemes for the ?rst case achieve the optimal mean-squared error(MSE) distortion. The proposed HDA schemes can... 

CDMA is one of the main multiple access techniques. In this thesis, we study the channel capacity and the optimum codes for CDMA systems under different conditions. The optimality has different meaning for each studied scenario. The discussed scenarios differ from the aspects of the alphabet of the system, the ability of getting active or inactive for users, and the random fluctuation of the user powers. The first scenario is the systems with real input alphabet. In this case, by optimum codes, we mean a code that maximizes the sum channel capacity of the system. The second scenario is the systems with binary input alphabets and binary signatures. In this section, optimum codes are the codes... 

CDMA is one of the main multiple access techniques. The aim of this work is to propose optimum signature codes to improve the performance of such systems. First, we introduce criteria such as Sum Channel Capacity and Bit Error Rate (BER) to measure the performance of a CDMA system. Also a set of measures named as Distance criteria are proposed to reduce the computational complexity. Various optimization methods are used to optimize these criteria such as Genetic Algorithms and the Particle Swarm Optimization techniques. Then, several sub-optimum signature matrices are derived based on different factors and criteria to improve the performance of Overloaded CDMA systems in terms of the sum... 

In this thesis, some algorithms for PAPR reduction of OFDM systems are investigated and some of these methods are extended to MIMO-OFDM systems. Two types of multiple antenna OFDM systems are considered; OFDM systems with spatial multiplexing for increasing the data rate and OFDM systems with spatial diversity for improvement of the symbol error rate. For the systems of the first type we have proposed two PAPR reduction algorithms. In the first method, the signals of transmitter antennas are clipped and filtered independently. Then, at the receiver side an iterative algorithm is proposed to compensate for the clipping noise. In the second method, we have extended TR method to spatial... 

IPTV is one of the developing technologies in recent years. This technology is used to broadcast TV programs over IP protocol stack. Video quality improvement is the most important advantage of this technology. Users can watch programs anytime they want in opposition to the traditional TV channels in which programs cast at certain times. One of the challenges in IPTV is high latency for channel switching. This latency is caused by different sources, including network delay. The delay between sending the channel switch request and receiving the first packet of the new channel is called network delay. In this thesis a new approach is proposed to decrease network delay. The proposed approach... 

NOCs contribute to a large portion of a many-core SOC power consumption. A significant fraction of the mentioned power consumption is due to the buffers, crossbar and the links. Thus, in this thesis, a new method would be introduced which reduces the power consumption of the NOCs in large scale. This method utilizes the latency asymmetry of router pipeline stages for dynamic power reduction and uses different voltage swings for buffers, links and the crossbar in order to decrease the dynamic power consumption while maintaining the performance. Moreover, since the static power consumption has gained a noticeable importance in recent years, a method for degrading this power component is also... 

The interest in the Landau-Streater channel has been mainly due to its abstract mathematical properties. We show that in three dimensions and with a slight modification, this channel can be realized as a rotation of qutrit states in random directions by random angles. Therefore and because of the potential use of qutrits in quan- tum processing tasks and their realization in many different platforms, the modified Landau-Streater channel can be used as a very simple and realistic noise model, in the same way that the depolarizing channel is for qubits. We will make a detailed study of this channel and derive its various properties. In particular, we will use the recently proposed flag... 

In this thesis after the study of the reported works on butterfly network, we improve the rate region of full duplex butterfly network. We use a simple specification of lattice codes to break code book into two code books. By selection of the coded message of the two transmitters in symetric butterfly channel from these two code books, we can decode the sum of the two messages and recover each messages by simple mod operation. The simulation shows that the rate region is improved  

Information Theory, as an important part of communication theory, tries to find inner and outer bounds for reliable rate of information transmission in communication networks. In Network Information Theory, It is usually assumed that the channel statistics is known to everyone. However, in some practical situations, we might not know the statistics. The compound channel and the arbitrarily varying channel (AVC) are two categories of models which have considered this problem. In this thesis, in order to have a more general model regarding information transfer in the presence of channel uncertainty, we propose a model which is essentially a combination of compound channel and AVC. In our... 

In recent years, there has been an increased interest on employing low-cost, high-speed, low-latency wireless links for short range communications (< 10m). Ultra-wideband (UWB) radio is a promising technology to meet this interest. However, due to the limitation on its transmitted power level, UWB system faces major challenges to achieve an adequate system performance. Therefore, it is greatly necessary to find some efficient methods to enhance the system performance. Recently, cooperative diversity has emerged as an effective scheme to overcome multipath fading and thus to improve the quality of service in the physical layer of wireless networks without increasing the transmission power of... 

Public key encryption (PKE) cryptography plays a big role in securing communication channels of internet. The security of every PKE scheme is usually based on a hard problem that has no polynomial time solution using any computational structure. However, widely used classic PKE schemes such as RSA or ECC, are based on hard problems that have polynomial solutions using a quantum computer. Therefore, such PKE schemes will not be secure in post-quantum era. Among quantum-resistant schemes, lattice-based cryptography and especially learning with errors (LWE) problem have gained high attention due to their low computational complexity. In this thesis, different LWE-based cryptosystems are... 

Security of cryptographic devices lies amongst the most important issues in the field of hardware security. It is frequently seen that in the process of designing cryptographic systems insufficient attention is paid to the physical implementation details. This is happening while a lot of secret information is known to be leaked through side-channels such as power consumption, electromagnetic emission and execution time. Side-channel attacks are able to reveal secret keys by using these side-channel leakages. Additionally, side-channel attacks are one of the most powerful but low-cost attacks that put the security of cryptographic systems in vain. It can be claimed that the most dangerous... 

Electromagnetic wave scattering from objects is one of the most important problems in applied electromagnetics. Usually the electromagnetic scattering characteristic from an object is analyzed with the assumption that the object is in free space. If the object is not near other objects or surfaces this is acceptable. However if the object is near other objects or surfaces then the interactions between the scattered wave from the object and surroundings can significantly alter the scattering characteristic from the object.In this thesis we have proposed a method for the analysis of electromagnetic scattering from an object in the presence of rough surfaces. This method is based on the... 

In this thesis, we study the observability and stability problems of networked control systems (the control systems which communicate through communication channels) to answer two important questions about different system models. The first is that what is the constraints implied by the stability or observability of systems? (necessary condition on the observability and stability). The second is that under which constraints can we present a design for system to guarantee the observability or stability of systems? (sufficient condition on the observability and stability). Clearly, an efficient design is the one that presents a tight sufficient condition.One of system models addressed in this... 

In this thesis, we derive an achievable Degrees of Freedom (DoF) region for a MIMO channel that models uplink transmission in a cellular network of two interfering cells with two users in each cell, under two different genie-aided cognitive scenarios; a cognitive cell together with a primary cell, and a cognitive transmitter with a primary transmitter in each cell. Most of the previous works dealt with networks with only two transmitters. Here, we study the effect of increase in the number of transmitters on nullifying and aligning the interference. In each scenario, an outer bound on the DoF region is derived. Then, we evaluate how cognition can improve the maximum achievable DoF by...