Sharif Digital Repository

This research aims to establish a novel approach to meet the capacity utilization challenge of the freight forwarders in order to maximize the expected revenue in a cargo network. The two-dimensional cargo capacities are assumed to be stochastic and limited in each leg. A stochastic dynamic programming model is developed to demonstrate the maximization of expected revenue over a finite planning horizon, in which each fare class request is to be either accepted or rejected. Although the main problem is computationally intractable due to multidimensional state variable, it can be decomposed into one-dimensional capacity control sub-problems for each leg. A heuristic algorithm is developed to... 

Particuale matters, as a criterion for evaluationg the air quality, have been one of the most important air pollutants through the last decade. Considering the adverse health effects of particulate matters, the importance of monitoring pollutant’s concentration is inevitable. While there are monitoring stations for evaluating the air quality, our knowledge is so limtted since there are few stations working, so there is a spatial and temporal gap. On the other hand, chemical transport models and remote sensing provide us a better chance to track the air quality thoroughly. Since chemical transport models are our only way of filling the gaps, they should be rigorous and accurate. In this study... 

In the oil and gas industry, in different stages of exploration and production of oil from hydrocarbon reservoirs, there are several challenges, most of which are due to unbalanced physical-mechanical conditions of the formations. Today, geomechanics of reservoirs is recognized as a key to analyze and solve such problems.Activities such as drilling, perforation, fracturing, production and fluid injection into the reservoir can alter the reservoir stress field and can cause rock deformation. Excessive compaction of reservoir rock can cause surface or seabed subsidence and damage to surface facilities and subsurface tubular. In general, rock compaction can cause many problems if not predicted... 

In  this  dissertation,  we  investigate  the  frequency  hopped  spread  spectrum  systems  which are extensively used in many communication systems. We derive the capacity region  of  Synchronous  Frequency  Hopped  Multiple  Access  (FHMA)  channels  (for  any  kind of noisy or nonselective fading environment) by using the side information which exists in the multi‐user detection. We assume that random hopping patterns are used by all the transmitters, and the common receiver knows the hopping patterns. We also compute  the  capacities  of  FHMA  with  and  without  power  control  for  AWGN  and  noiseless MFSK (in particular BFSK) modulated systems and compare the ... 

Regarding to the emergence of quantum computers and advances in the large scale implementation of them, exploiting hard problems of coding theory is of great importance.This family of problems, like those of lattices, has an acceptable resistance against classic and quantum attacks. Thus, they can be replaced with hard problems in number theory and algebra. Increasing dominance of cyberspace made us highly dependent to it. Consequently, preparing tools and methods to mitigate future threats is necessary. Digital signatures constitute an important family of cryptographic primitives. Code-based digital signatures are mostly suffering from two main drawbacks: large public key and long time of... 

“Decode and Forward” is one of coding strategies used in relay channel and networks in which each relay in the network decodes the transmitted message by the sender and other relays in the network and then re-encode and transmit it to the other relays and the receiver in the network. This process results in the cooperation between the relays and the sender to remove the uncertainty of the receiver about the transmitted message. “irregular encoding-successive decoding”, “regular encoding-backward decoding” and “regular encoding-sliding window decoding” are different methods usually used in “Decode and Forward” strategy. “partial decode and forward” is a generalized form of “decode and... 

In this thesis the problem of simultaneously generating multiple keys among multiple terminals is investigated. After providing a survey on the related works and exploiting the problem of sharing a common secret key and a private key among three terminals, we introduce a new source model which we call it the Four-Terminal model. We consider the problem of generating three kinds of keys among legitimate terminals and investigate the problem under two different scenarios, Backward and Forward scenarios, which depend on the kind of restrictions imposed on the usage of the public channel. We derive an achievable region for the backward scenario, using the combination of superposition coding and... 

In order to utilize cooperative resources of a network, we have to investigate cooperative networks and strategies. Information theory, by introducing different concepts such as coordination and common information, gives us a suitable tool to study cooperative networks and using their resources. In this thesis, we investigate coordination and secret key agreement in cooperative networks. Our study consists of two parts. In the first part, we consider coordination and its applications in cooperative networks. For this purpose, we introduce the triangular multiterminal network as a proper model for studying empirical coordination in multiterminal networks and establish an inner and outer... 

In this thesis, the problem of secret key agreement in the channel model with side information is studiedx. In order to investigate the problem, we consider three models according to the different ways of side information availability which are the state-dependent broadcast channel; the state-dependent broadcast channel in presence of public channel and the state-dependent wiretap channel with degraded versions of the channel state information.For the problem of secret key agreement in broadcast channels, two models, the state-dependent wiretap channel and state-dependent three receivers broadcast channel, are considered. We obtain inner and outer bounds of the secret key capacity region for... 

Interference management is one of the key issues in wireless networks wherein multiple source-destination pairs share the same medium and frequency band and interfere with each other. The exponentially growth in the number of wireless systems and services results in the spectrum shortage which has emerged the technologies that increase the spectral efficiency. Providing the users with cognition equipments in these networks enables them to sense the medium and use the obtained data to adapt their transmissions to cooperate with other users and improve their own rates as well as the others which results in the cognitive radio technology. In order to access the full potential of this technology,... 

Due to the remarkable growth in using communication networks such as ad-hoc, wireless and sensor networks, studying the building blocks of these networks (e.g., relay channel and interference channel) from information theoretic viewpoint and investigating cooperative strategies have recently received considerable attention. Also, owing to wide range of applications, state-dependent channels have been widely studied. In this dissertation, at first, we consider a state-dependent relay channel (SD-RC). For the cases wherein channel states are available causally or non-causally at different nodes, we propose new achievable rates for this channel using compress-and-forward strategy. Also we... 

Energy Harvesting has been appeared as an approach in order to make the green communications possible. In Energy Harvesting systems, nodes extract energy from the nature to extend their lifetimes. The harvested energy can also be used for the purpose of communication and specially for the transmission process. Compared to the conventional batterypowered systems, the Energy Harvesting systems have access to an unbounded source of energy (like vibration absorption devices, water mills, wind turbines, microbial fuel cells, solar cells, thermo-electric generators, piezoelectric cells, etc). However, the diffused nature of this energy makes it difficult to be used for communication. In this work,...