Sharif Digital Repository

With high growth rate of demand for energy in different societies, the need for energy resources has been increased significantly. This has resulted in introduction of new energy resources, i. e. renewable energy resources in generation sector of energy systems. However, the intrinsic features of these energy resources call for higher flexibility in different sectors of energy systems. Flexibility in a comprehensive sense tries to cover the amount of imbalance between production and demand in energy systems. This paper has attempted to introduce the concept of operational flexibility in microgrids and it also has presented a step-by-step algorithm to assess this operational index based on a... 

Dynamic Index coding as a generalization of the traditional index coding problem, deals with transmission of some dynamic data flows in the presence of side information. For a dynamic index coding system, the set of average flow rates for which the system can be stable is named Code-Constraint Capacity region. In this paper, we identify the code-constraint capacity region for a dynamic index coding problem with complete bi-directional side information graph. Furthermore, we introduce the concept of Dynamic Index Coding Gain to quantify the improvement resulted from the dynamic index coding with respect to uncoded transmissions. We also provide some corollaries about system performance... 

We define a new feature called Teager Energy to Energy and mathematically show that it provides distinguished values for pure tone and white noise signals. We then employ the Teager Energy to Energy feature to propose an efficient procedure for voice activity detection and use simulation results to evaluate its performance in different noisy environments. Furthermore, we experimentally demonstrate the performance of the proposed voice activity detection technique in a real-time voice processing embedded system. Experimental and simulation results show that the introduced procedure provides more reliable results with a reasonable amount of computational complexity in comparison with its... 

In this paper, we propose a new method for creating more distinguishable QoS levels in OCDMA networks. The key idea behind the proposed scheme is to adaptively control the transmit power level in each chip based on OCDMA channel state. The structure of the transmitter and receiver are proposed. We provide performance analysis of the recommended scheme and show that it can reduce the system BER and provide better QoS differentiation in a multiclass network. We provide simulation results and demonstrate that they have a good match with the results obtained from mathematical analysis  

In this letter, we use stochastic optimization to schedule data transmissions in an adaptive optical code division multiple-access (OCDMA) system to maximize transmission rate. We employ Lyapunov drift theory to formulate a general optimization problem for rate-maximized scheduling in which user codes are adaptively assigned such that time-averaged transmission rate is maximized and important system parameters such as stability and BER performance are maintained. Simulation results show that the overall transmission rate in a rate-maximized scheduled OCDMA system can be up to 3 (1.2) times better than the transmission rate in its counterpart OCDMA system with fixed code assignment scheme... 

Efficient resource allocation in OFDM-based optical networks is directly affected by definition and formulations of Routing and Spectrum Assignment (RSA) problem. In this paper, we propose new Binary Linear Programming (BLP) formulations for the RSA problem that provide more efficient resource allocation in comparison with previous formulations. Unlike the conventional formulations that mainly aim at minimizing used spectrum slots, our formulations simultaneously aim at defragmentation and minimization of the assigned spectrum slots. We show contiguity constraint of the conventional formulations may incorrectly make a feasible solution unattainable. To solve this problem, we remove the... 

We propose an energy-efficient procedure for transponder configuration in few-mode fiber-based elastic optical networks in which bit error rate and physical constraints are guaranteed and joint optimization of temporal, spectral, and spatial resources are addressed. We use geometric convexification techniques to provide convex formulations for the signal-to-interference plus noise ratio, transponder power consumption, and transponder configuration problem. Simulation results demonstrate that the proposed convex formulation for the transponder configuration problem is considerably faster than its mixed-integer nonlinear counterpart. We consider transmit optical power as a configurable... 

Optical code division multiple access (OCDMA) systems can support multiple classes of service by differentiating code parameters, power level, and diversity order. In this paper, we analyze bit error rate (BER) performance of a multiclass 1-D/2-D OCDMA system and propose a new approximation method that can be used to generate accurate estimation of system BER using a simple mathematical form. The proposed approximation provides insight into proper system level analysis, system level design and sensitivity of system performance to the factors such as code parameters, power level, and diversity order. Considering code design, code cardinality, and system performance constraints, two design... 

We investigate the problem of energy-efficient transponder configuration constrained to quality of service and physical requirements in orthogonal frequency division multiplexing-based software-defined inter-data center elastic optical networks. We consider two types of services which are called delay-sensitive and delay-Tolerant. A deterministic and a stochastic mixed-integer nonlinear program with a target of minimizing the total transponder power consumption are formulated which their solutions provide a long-Term and a short-Term configuration for delay-sensitive service and delay-Tolerant service transponders, respectively. We use geometric and stochastic Lyapunov optimization... 

Resource allocation with quality of service constraints is one of the most challenging problems in elastic optical networks that is normally formulated as a mixed-integer nonlinear optimization program. In this paper, we focus on novel properties of geometric optimization and provide a heuristic approach for resource allocation that is much faster than its mixed-integer nonlinear counterpart. Our heuristic consists of two main parts for routing/traffic ordering and power/spectrum assignment. It aims at minimization of the transmit optical power and spectrum usage constrained to the quality of service and physical requirements. We consider three routing and three traffic ordering procedures... 

Spectrum conversion can improve the performance of orthogonal frequency division multiplexing (OFDM)-based elastic optical networks (EONs) by relaxing the continuity constraint and consequently reducing connection request blocking probability during routing and spectrum assignment process. We propose three different architectures for including spectrum conversion capability in bandwidth-variable wavelength cross-connects (BVWXCs). To compare the capability of the introduced architectures, we develop an analytical method for computing average connection request blocking probability in a spectrum-convertible OFDM-based EON in which all, part, or none of the BVWXCs can convert the spectrum. An... 

We investigate the problem of energy-efficient resource allocation constrained to quality of service and physical requirements in orthogonal frequency division multiplexing (OFDM)-based elastic optical networks and propose a fast two-stage algorithm to solve it. The first stage of the proposed algorithm deals with routing, traffic grooming, and traffic ordering and mainly aims at minimization of the number of deployed optical amplifiers and transponders. We provide an integer linear program for routing and traffic grooming and propose a heuristic procedure, which yields its near-optimum solution in a shorter runtime. In the second stage, we optimize transponder parameters to minimize total... 

In this paper, we propose an optimized parameter selection procedure for rainbow table Time Memory Trade-Off (TMTO) attack with sequential online search. Unlike previous works that mainly deal with minimizing required memory in the rainbow table TMTO attack we simultaneously focus on the required memory and online search time. Our parameter selection technique is optimized regarding the minimization of the required memory subject to a certain success probability and a maximum online search time. Obtained results are two compact mathematical expressions for determining rainbow table TMTO attack parameters, number and length of chains. The application of our optimized parameter selection... 

Smart grids help local distribution companies (LDCs) facilitate the communication between grid operators and residential prosumers. While the prosumers are striving to optimize their daily load profile by home energy management systems (HEMSs) deployment, the LDCs attempt to enhance the operation of the grid in an efficient way and decrease network losses. This paper attempts to develop a new bi-level probabilistic optimization framework wherein an HEMS optimizes its respective daily load profile, and determines its flexibility provision, which is communicated to an LDC. In the proposed framework, a decentralized approach is used to achieve the flexibility product, which is the modulation of... 

With the high penetration of Renewable Energy Resources (RERs) into power systems, distribution systems are facing various challenges due to their intermittency and uncertainty. One of the ways to cope with uncertainty and variability of the RERs is utilizing flexibility by market tools to enable active system management. Local Flexibility Markets (LFMs) provide opportunities to trade flexibility among distribution system operators and other participants (e.g., aggregators) in an economically efficient way. This research proposes an interactive framework for prosumers by a market-based platform to utilize and trade flexibility. The suggested framework comprises a novel flexibility allocation... 

In this paper, we show how time-sharing method may reduce transmission delay in the dynamic index coding scenario. We propose a novel time-shared dynamic index coding transmission scheme that achieves the maximum index coding gain for a complete bi-directional side information graph and formulate a constrained optimization problem to tune the transmission scheme for the minimum transmission delay. A closed-form solution is presented for the special case of two-user. We also use analytical and simulation results to provide graphical intuition for the obtained results  

Dynamic index coding is a practical generalization of conventional index coding that deals with real dynamic traffic streams. We identify the code-constrained capacity region of a dynamic index coding problem with a complete bi-directional side information graph and introduce the performance metric of dynamic index coding gain to measure how dynamic index coding reduces the required data transmissions. A greedy dynamic index coding scheme is proposed that achieves the maximum coding gain almost everywhere in the identified capacity region. Although the greedy scheme attains the maximum coding gain, its selfish nature may unacceptably increase transmission delay. To address this issue, a... 

The key element of a spoken dialogue system is a spoken language understanding (SLU) unit. Hidden Vector State (HVS) is one of the most popular statistical approaches employed to implement the SLU unit. This paper presents a two-step approach for Persian language understanding. First, a goal detector is used to identify the main goal of the input utterance. Second, after restricting the search space for semantic tagging, an extended hidden vector state (EHVS) parser is used to extract the remaining semantics in each subspace. This will mainly improve the performance of semantic tagger, while reducing the model complexity and training time. Moreover, the need for large amount of data will be... 

The common and traditional method for optical dispersion compensation is concatenating the transmitting optical fiber by a compensating optical fiber having a high-negative dispersion coefficient. In this Letter, we take the opposite direction and show how an optical fiber with a high-positive dispersion coefficient is used for dispersion compensation. Our optical dispersion compensating structure is the optical implementation of an iterative algorithm in signal processing. The proposed dispersion compensating system is constructed by cascading a number of compensating sub-systems, and its compensation capability is improved by increasing the number of embedded sub-systems. We also show that... 

When cells exposed to an electric field, localized changes in the distribution of the electric field will be induced and these changes in turn lead to electrical stresses on cell surface. The electrical stresses play a key role in the cell membrane structural changes which leads to important phenomena like hydrophilic pores formation on the cell membrane resulting in the cell permeability. In this work, protoplast cell interaction with direct current (DC) electric field is investigated. The electrical stresses acted on the cell membrane in the presence of electric field are investigated numerically by a modified finite difference method, fast Immersed Interface Method (IIM). Exact solution...