Sharif Digital Repository

Group-testing refers to the problem of identifying (with high probability) a (small) subset of D defectives from a (large) set of N items via a 'small' number of 'pooled' tests (i.e., tests have a positive outcome if even one of the items being tested in the pool is defective, else they have a negative outcome). For ease of presentation in this work we focus the regime when the number of defectives is sublinear, i.e., D = O (N1-δ) for some δ > 0. The tests may be noiseless or noisy, and the testing procedure may be adaptive (the pool defining a test may depend on the outcome of a previous test), or non-Adaptive (each test is performed independent of the outcome of other tests). A rich body... 

In this paper, random access procedure in terrestrial trunked radio (TETRA) networks is described and modeled. Then, the impact of different random access parameters on performance metrics such as "delay" and "throughput" is evaluated. Moreover, in order to have a fast "call setup" which is one of the most important features of TETRA, it is shown that random access delay can be minimized, while maintaining peak throughput. by adaptively adjusting the random access parameters according to the backlogged traffic. The performance improvement of the proposed adaptive parameter adjustment is proved via extensive simulation results  

Mobile networks have been growing rapidly, where it is of paramount importance to evaluate the performance of any protocol designed for such networks before deployment. Mobility is one of the main mobile network issues that directly affects performance metrics. Since mobile nodes are often carried by their owners, nodes movement should be modeled according to humans movement. In this paper, we extend our previously published human mobility model based on real collected data. The real human movement is traced, cleaned up and analyzed. To the best of our knowledge, our collected data set is the only one that contains the detail of both walking and driving nodes. The analysis shows several... 

In this paper, a 2D shuffle-exchange based mesh topology, or 2D shuffle-exchange mesh (SEM) for short, is presented for network-on-chips. The proposed 2D topology applies the conventional well-known shuffle-exchange structure in each row and each column of the network. Compared to an equal sized mesh which is the most common topology in on-chip networks, the proposed shuffle-exchange based mesh network has smaller diameter but for an equal cost. Finally for better performance cross-shuffle is proposed. Simulation results show that the 2D SEM and 2D cross-shuffle effectively reduce the power consumption and improve performance metrics of the on-chip networks compared to the conventional mesh... 

The authors propose a novel solution for decorrelating closely spaced antennas with identical radiation patterns. By proper steering of the directional elements' patterns, the decorrelation distance is reduced to 0.25λ in comparison with the well-established 0.4λ result based on the Bessel-shaped correlation expression. In addition, by proposing the definition of Decorrelation Factor of an antenna pattern, a framework for comparison of correlation behaviour of different antennas is provided. Subsequently, a performance metric characterised by the Jensen upper bound for the capacity of closely spaced antennas is proposed. Finally, we apply our results to two practical directional antennas,... 

In this paper, we propose a general delay and stability performance analysis in Heterogeneous Cellular Caching Networks (HCCNs), based on queuing theory. We introduce new performance metrics in HCCNs and propose an optimization problem which minimizes the average experienced delay for users by ensuring the stability of the network. In addition, from the design perspective, we address the problem of finding the minimum cache size for the small cell base stations (SBSs) for having a tolerable average delay and also a stable network. Finally, the analytic expressions derived in this paper are validated through real trace-driven experiments on traffic of YouTube video requests  

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... 

It is well known that load balancing and low delivery communication cost are two critical issues in mapping requests to servers in Content Delivery Networks (CDNs). However, the trade-off between these two performance metrics has not been yet quantitatively investigated in designing efficient request mapping schemes. In this work, we formalize this trade-off through a stochastic optimization problem. While the solutions to the problem in the extreme cases of minimum communication cost and optimum load balancing can be derived in closed form, finding the general solution is hard to derive. Thus we propose three heuristic mapping schemes and compare the trade-off performance of them through... 

Next generation wireless networks will consist of different types of radio access technologies. Emerging diverse applications have attracted a lot of users. Therefore, having the best connectivity anytime anywhere has become an important issue. Users would like to have continuous high quality network connection even when they handover from one network type to the other. Each access technology has its own features and service quality. In this regard, when there is a handover, it is important to choose the most suitable network based on user needs. Different algorithms have been proposed for network selection. Multi Attribute Decision Making (MADM) methods are widely used due to their... 

In this paper, we develop and analyze a novel performance metric, called interference efficiency (IE), that shows the number of transmitted bits per unit of interference energy imposed on the primary users (PUs) in an underlay cognitive radio network (CRN). Specifically, we develop a framework to maximize the IE of a CRN with multiple secondary users (SUs) while satisfying target constraints on the average interference power on PU receiver, total SUs transmit power and minimum ergodic rate for the SUs. In doing so, we formulate a multiobjective optimization problem (MOP), that aims to achieve the maximum ergodic sum rate of multiple SUs and the minimum average interference power on the... 

Recently, caching of the popularity video files in the caches near to the users has been proposed as a promising way to reduce data traffic. These caches can be considered as the nodes which their transmission ranges are limited but have significant storage capacity and are known as the helper nodes. To evaluate the performance and efficiency of the caches, a suitable model for their distributions should be taken into account. Stochastic geometry is a useful tool for modeling these nodes. In this paper, the helper nodes and users are distributed according to the Poisson point process distribution. However, to manage the interferences and their access to a distributed cache, the helper nodes... 

Vehicular ad hoc networks have attracted the attention of many researchers during the last years due to the emergence of autonomous vehicles and safety concerns. Most of the frameworks which are proposed for the modeling and analysis VANET applications make use of simulation techniques. Due to the high level of concurrency in these applications, simulation results do not guarantee the correct behavior of the system and more accurate analysis techniques are required. In this paper, we have developed a framework to provide model checking facilities for the analysis of VANET applications. To this end, an actor-based modeling language, Rebeca, is used which is equipped with a variety of model... 

New Advances in mobile computer technology, along with rapid growth of quality and quantity of wireless networks, introduce new capabilities, applications, and concerns to computer science and industry. Unique requirements and constraints of mobile systems bring new challenges to software development for such environments. It demands reconsidering the traditional approaches of information access, software design, and performance evaluation. Despite the various constraints and problems, research endeavors aimed at ameliorating the status quo through enhancing/devising software design and performance evaluation techniques for mobile software systems have been relatively few and far in between.... 

In this paper, a cross-layer approach introducing new design parameters is developed for multi-rate wireless links. The novel design jointly exploits the finite-length queuing at the data link layer and the adaptation capability of the adaptive modulation and coding (AMC) scheme at the physical layer to optimize system performance for a wireless link. The analytical framework is based on discrete time Markov Chain. The performance metrics such as packet drop probability, channel packet error rate and packet loss rate are derived. Using these metrics, a constrained optimization problem is solved numerically to maximize the overall system throughput  

As multi-hop wireless networks are attracting more attention, the need to evaluate their performance becomes essential. In order to evaluate the performance metrics of multi-hop wireless networks, including sending and receiving rates of a node as well as the collision probability, a model based on Stochastic Reward Nets (SRNs) is proposed. The proposed SRN models a typical node in such networks, considered as a general template to be applied to any wireless node. The SRN model of a single node is designed to take transmission effects of all neighboring nodes into account, while ignoring the ones whose transmission has no effect on the node under-study. Applying the proposed SRN to each node... 

In this study, four new indirect heat pump assisted mechanical vapor compression humidification-dehumidification (HDH) systems are proposed and their superiorities over the reference system are demonstrated from thermodynamics and thermoeconomics viewpoints. The proposed models are configured based on an HDH unit and a simple cascade heat pump, an HDH unit and a heat pump with an ejector, an HDH unit and a cascade heat pump with an ejector, and an HDH unit and a vapor injection heat pump. Although employing a heat pump with cascade and ejector configurations improved gain-output-ratio (GOR) and specific power consumption (SPC) values in comparison with the base system, the performance... 

A wide range of scheduling algorithms used in the data centers have traditionally concentrated on enhancement of performance metrics. Recently, with the rapid growth of data centers in terms of both size and number, the power consumption has become a major challenge for both industry and society. At the software level, energy-aware task scheduling is an effective technique for power reduction in the data centers. However, most of the currently proposed energy-aware scheduling approaches are only paying attention to computation cost. In the other words, they ignore the energy consumed by the network equipment, namely communication cost. In this paper, the problem of scheduling... 

A new hybrid approach for dynamic optimization problems with continuous search spaces is presented. The proposed approach hybridizes efficient features of the particle swarm optimization in tracking dynamic changes with a new evolutionary procedure. In the proposed dynamic hybrid PSO (DHPSO) algorithm, the swarm size is varied in a self-regulatory manner. Inspired from the microbial life, the particles can reproduce infants and the old ones die. The infants are especially reproduced by high potential particles and located near the local optimum points, using the quadratic interpolation method. The algorithm is adapted to perform in continuous search spaces, utilizing continuous movement of... 

In this paper, a method of determining physical dimension of Double Barrier Quantum Well (DBQW) of Resonance Tunneling Diodes (RTDs) is presented by using I-V characteristic governing on them. In this procedure, first we have used performance metrics related to RTDs I-V characteristic such as Peak to Valley Current Ratio (PVCR), peak current density (JP), valley current density (JV) and Voltage Swing (VS), and by some other arbitrary points, we have fitted a curve to the RTD current-voltage equation by MATLAB software. Then we have obtained the physical parameter of I-V equation and adjusted some of them with modification coefficients. Next, by choosing the material of barriers and the well...