Loading...
Search for: computer-applications
0.008 seconds
Total 34 records

    On the coding advantages of the quasi-orthogonal space-frequency block codes

    , Article IET Communications ; Vol. 8, Issue. 4 , 2014 , Pages 525-529 ; ISSN: 17518628 Shahabinejad, M ; Morsali, A ; Talebi, S ; Shahabinejad, M ; Sharif University of Technology
    Abstract
    In this study, the authors show that the coding advantage (CA) of quasi-orthogonal space-frequency block codes (QOSFBCs) could be decomposed into two parts, namely intrinsic CA (ICA) and extrinsic CA (ECA). Then, by using the ICA, the authors demonstrate that the optimum precoder of the QOSFBCs could be analytically derived without any requirement of the exhaustive search. Then, by improving the ECA, the authors enhance performances of the QOSFBCs efficiently - up to 4dB. Finally, the authors show that a very fast optimisation process for the QOSFBCs is viable over any arbitrary frequency-selective channel  

    On ideal homomorphic secret sharing schemes and their decomposition

    , Article Designs, Codes, and Cryptography ; Volume 89, Issue 9 , 2021 , Pages 2079-2096 ; 09251022 (ISSN) Ghasemi, F ; Kaboli, R ; Khazaei, S ; Parviz, M ; Rafiei, M. M ; Sharif University of Technology
    Springer  2021
    Abstract
    In 1992, Frankel and Desmedt introduced a technique that enables one to reduce the secret space of an ideal homomorphic secret sharing scheme (IHSSS) into any of its characteristic subgroups. In this paper, we propose a similar technique to reduce the secret space of IHSSSs called the quotient technique. By using the quotient technique, we show that it is possible to yield an ideal linear scheme from an IHSSS for the same access structure, providing an alternative proof of a recent result by Jafari and Khazaei. Moreover, we introduce the concept of decomposition of secret sharing schemes. We give a decomposition for IHSSSs, and as an application, we present a necessary and sufficient... 

    Kinetic collision detection for balls

    , Article Information Processing Letters ; Volume 171 , 2021 ; 00200190 (ISSN) Abam, M. A ; Sharif University of Technology
    Elsevier B.V  2021
    Abstract
    We study the collision detection of n moving balls of arbitrary sizes in 3-dimensional space. We improve both the storage and the event-handling time of the best existing KDS [1] by several logarithmic factors. Precisely, our KDS maintains O(n) certificates at the current time, uses O(nlog2⁡n) storage, handles each event in O(log3⁡n) time, and processes O(n2) events in the worst case, assuming that the balls follow constant-degree algebraic trajectories. © 2021 Elsevier B.V  

    Kinetic collision detection for balls

    , Article Information Processing Letters ; Volume 171 , 2021 ; 00200190 (ISSN) Abam, M. A ; Sharif University of Technology
    Elsevier B.V  2021
    Abstract
    We study the collision detection of n moving balls of arbitrary sizes in 3-dimensional space. We improve both the storage and the event-handling time of the best existing KDS [1] by several logarithmic factors. Precisely, our KDS maintains O(n) certificates at the current time, uses O(nlog2⁡n) storage, handles each event in O(log3⁡n) time, and processes O(n2) events in the worst case, assuming that the balls follow constant-degree algebraic trajectories. © 2021 Elsevier B.V  

    Multiple-access channel with correlated states and cooperating encoders

    , Article IET Communications ; Volume 6, Issue 13 , 2012 , Pages 1857-1867 ; 17518628 (ISSN) Emadi, M. J ; Zamanighomi, M ; Aref, M. R ; Sharif University of Technology
    IET  2012
    Abstract
    In this study, a two-user discrete memoryless multiple-access channel with two correlated states known non-causally at the corresponding encoder is considered. Each encoder transmits a message independent of the other encoder's and tries to cooperate with it. To consider cooperative encoders, it is assumed that each encoder strictly-causally receives and finds out the other encoder's transmitted signals and tries to cooperate with the other encoder by transmitting its message. A special case is also studied in which the common part of the states is known at the both encoders, resulting in a larger rate region. For these two scenarios, achievable rate regions are derived using a combination... 

    Comments on 'Information-Theoretic Key Agreement of Multiple Terminals - Part I'

    , Article IEEE Transactions on Information Theory ; Volume 63, Issue 8 , 2017 , Pages 5440-5442 ; 00189448 (ISSN) Gohari, A ; Anantharam, V ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Abstract
    Theorem 5 of A. Gohari, V. Anantharam, IEEE Transactions on Information Theory, vol. 56, no. 8, pp. 3973-3996, 2010, states an upper bound on the secrecy capacity for the source model problem. It has a three page proof given in Appendix B of the paper. Unfortunately, we show that this bound does not provide any improvement over the simpler bound given in Corollary 1 of the paper. We also provide an example of a family of two agent source model problems where the one-way secrecy rate in each direction is zero, but the secrecy rate is nonzero and can be determined exactly as a conditional mutual information. © 1963-2012 IEEE  

    A framework for estimation of complexity in agent oriented methodologies

    , Article 7th IEEE/ACS International Conference on Computer Systems and Applications, AICCSA-2009, Rabat, 10 May 2009 through 13 May 2009 ; 2009 , Pages 645-652 ; 9781424438068 (ISBN) Basseda, R ; Taghiyareh, F ; Alinaghi, T ; Ghoroghi, C ; Moallem, A ; Sharif University of Technology
    2009
    Abstract
    Agent-oriented software methodologies have found their way to become one of the most important issues of software development. The diversity of existing methodologies and the variety of newly arriving ones have arisen the question of which methodology is best in the context of a special problem, so the need for evaluating and comparing methodologies is becoming more important everyday. On the other hand evaluating methodologies can reveal their strengths and shortcomings which lead to an improvement in development of the next generation of agent-oriented methodologies. In this paper, we are going to introduce an approach for evaluating methodologies via the evaluation of their lifecycle... 

    Fair allocation of indivisible goods: Improvement

    , Article Mathematics of Operations Research ; Volume 46, Issue 3 , 2021 , Pages 1038-1053 ; 0364765X (ISSN) Ghodsi, M ; Hajiaghayi, M. T ; Seddighin, M ; Seddighin, S ; Yami, H ; Sharif University of Technology
    INFORMS Inst.for Operations Res.and the Management Sciences  2021
    Abstract
    We study the problem of fair allocation for indivisible goods. We use the maximin share paradigm introduced by Budish [Budish E (2011) The combinatorial assignment problem: Approximate competitive equilibrium from equal incomes. J. Political Econom. 119(6):1061-1103.] as a measure of fairness. Kurokawa et al. [Kurokawa D, Procaccia AD, Wang J (2018) Fair enough: Guaranteeing approximate maximin shares. J. ACM 65(2):8.] were the first to investigate this fundamental problem in the additive setting. They showed that in delicately constructed examples, not everyone can obtain a utility of at least her maximin value. They mitigated this impossibility result with a beautiful observation: no... 

    Extending a hybrid finite-volume-element method to solve laminar diffusive flame

    , Article Numerical Heat Transfer, Part B: Fundamentals ; Vol. 66, issue. 2 , August , 2014 , pp. 181-210 ; ISSN: 10407790 Darbandi, M ; Ghafourizadeh, M ; Sharif University of Technology
    Abstract
    We extend a hybrid finite-volume-element (FVE) method to treat the laminar reacting flow in cylindrical coordinates considering the collocation of all chosen primitive variables. To approximate the advection fluxes at the cell faces, we use the upwind-biased physical influence scheme PIS and derive a few new extended expressions applicable in the cylindrical frame. These expressions are derived for both the Navier-Stokes and reactive flow governing equations, of which the latter expressions are considered novel in the finite-volume formulation. To validate our derived expressions, the current results are compared with the experimental data and other available numerical solutions. The results... 

    Coding advantage decomposition inequality for the space-frequency block codes

    , Article IET Communications ; Vol. 8, Issue. 4 , 2014 , Pages 500-507 ; ISSN: 17518628 Morsali, A ; Tofigh, S ; Mohammadian, Z ; Talebi, S ; Sharif University of Technology
    Abstract
    In this study, the authors present a new criterion which can be used to decompose the coding advantage (CA) of space-frequency block codes (SFBCs). The proposed decomposition separates the CA into two parts, called precoder-CA and channel-CA. The precoder-CA represents the effects of the precoder and the signal constellation, and can be used in the design of the precoder of SFBCs. The channel-CA, on the other hand, gives an indication of the effects of the channel characteristics, and can be utilised for optimising the permutation parameter. The authors have shown that the proposed decomposition method leads to a lower computational complexity for the optimisation procedure compared with the... 

    Smith normal form using scaled extended integer ABS algorithms

    , Article Advances in Intelligent and Soft Computing ; Volume 145 AISC, Issue VOL. 2 , 2012 , Pages 367-372 ; 18675662 (ISSN) Golpar Raboky, E ; Mahdavi Amiri, N ; Sharif University of Technology
    2012
    Abstract
    Classes of integer ABS methods have recently been introduced for solving linear systems of Diophantine equations. The Smith normal form of a general integermatrix is a diagonal integer matrix, obtained by elementary nonsingular (unimodular) operations. Such a form may conveniently be used in solving integer systems of equations and integer linear programming problems. Here, we present a class of algorithms for computing the Smith normal form of an integer matrix. In doing this, we propose new ideas to develop a new class of extended integer ABS algorithms generating an integer basis for the integer null space of the matrix. Finally, we test our algorithms and report the obtained numerical... 

    Face recognition across large pose variations via boosted tied factor analysis

    , Article 2011 IEEE Workshop on Applications of Computer Vision, WACV 2011, 5 January 2011 through 7 January 2011 ; January , 2011 , Pages 190-195 ; 9781424494965 (ISBN) Khaleghian, S ; Rabiee, H. R ; Rohban, M. H ; Sharif University of Technology
    2011
    Abstract
    In this paper, we propose an ensemble-based approach to boost performance of Tied Factor Analysis(TFA) to overcome some of the challenges in face recognition across large pose variations. We use Adaboost.m1 to boost TFA which has shown to possess state-of-the-art face recognition performance under large pose variations. To this end, we have employed boosting as a discriminative training in the TFA as a generative model. In this model, TFA is used as a base classiœr for the boosting algorithm and a weighted likelihood model for TFA is proposed to adjust the importance of each training data. Moreover, a modiÔd weighting and a diversity criterion are used to generate more diverse classiœrs in... 

    A distributed truthful routing protocol for mobile ad hoc networks

    , Article Proceedings of ICCIA 2010 - 2010 International Conference on Computer and Information Application, 2 November 2010 through 4 November 2010, Tianjin ; 2010 , Pages 133-140 ; 9781424485963 (ISBN) Shirzad, F ; Movaghar, A ; Shirzadeh, E ; Sharif University of Technology
    2010
    Abstract
    In Mobile Ad hoc Networks (MANETs), nodes depend on each other for routing and forwarding their packets. However, to save power and other resources, nodes belonging to independent authorities may behave selfishly, and not cooperate in network activities. Such selfish behaviour poses a real threat to the proper functioning of MANETs. To cope with this situation, a motivation stimulation mechanism is required to provide sufficient incentives for nodes to forward other nodes' packets. One appropriate approach is to have network nodes pay in order to motivate them to cooperate with the protocol. To achieve truthfulness, the payment should be based on the cost of transmission of packets. Since... 

    Multiple access channel with common message and secrecy constraint

    , Article IET Communications ; Volume 10, Issue 1 , 2016 , Pages 98-110 ; 17518628 (ISSN) Zivari Fard, H ; Akhbari, B ; Ahmadian Attari, M ; Aref, M. R ; Sharif University of Technology
    Institution of Engineering and Technology 
    Abstract
    The authors study the problem of secret communication over a multiple-access channel with a common message. Here, the authors assume that two transmitters have confidential messages, which must be kept secret from the wiretapper (the second receiver), and both of them have access to a common message which can be decoded by the two receivers. The authors call this setting as multiple-access wiretap channel with common message (MAWC-CM). For this setting, the authors derive general inner and outer bounds on the secrecy capacity region for the discrete memoryless case and show that these bounds meet each other for a special case called the switch channel. As well, for a Gaussian version of... 

    A computationally efficient algorithm to find time-optimal trajectory of redundantly actuated robots moving on a specified path

    , Article Robotica ; 2018 ; 02635747 (ISSN) Mansouri, S ; Sadigh, M. J ; Fazeli, M ; Sharif University of Technology
    Cambridge University Press  2018
    Abstract
    time-optimal problem for redundantly actuated robots moving on a specified path is a challenging problem. Although the problem is well explored and there are proposed solutions based on phase plane analysis, there are still several unresolved issues regarding calculation of solution curves. In this paper, we explore the characteristics of the maximum velocity curve and propose an efficient algorithm to establish the solution curve. Then we propose a straightforward method to calculate the maximum or minimum possible acceleration on the path based on the pattern of saturated actuators, which substantially reduces the computational cost. Two numerical examples are provided to illustrate the... 

    Collective knowledge construction: a socio-cognitive approach

    , Article VINE Journal of Information and Knowledge Management Systems ; 2020 Farzaneh, M ; Mehralian, G ; Isaai, M. T ; Sharif University of Technology
    Emerald Group Publishing Ltd  2020
    Abstract
    Purpose: The purpose of this study is to use correlation analysis to understand how knowledge structure, task structure and collaboration affect collective knowledge (CK) by the mediating mechanism of communication. Design/methodology/approach: Drawing on an existing gap in the literature related to CK, a research model with five hypotheses is proposed. The hypotheses were analyzed based on data collected from 114 work-team practitioners using structural equation modeling. Findings: The results indicate that communication, knowledge structure, task structure and collaboration significantly contribute to CK and that communication partially mediates the impact of these constructs on CK.... 

    Pseudo-space Persian/Arabic text steganography

    , Article 13th IEEE Symposium on Computers and Communications, ISCC 2008, Marrakech, 6 July 2008 through 9 July 2008 ; 2008 , Pages 864-868 ; 15301346 (ISSN) ; 9781424427031 (ISBN) Shirali Shahreza, M ; Sharif University of Technology
    2008
    Abstract
    In recent years by growing computer applications, new technologies are also invented. Meanwhile new issues are faced such as security. One of the security areas is hidden exchange of information which contains methods such as cryptography and steganography. Steganography is the art of hiding data in a cover media such as image or sound. In this paper a new method for Steganography in Persian and Arabic texts is presented. In this method pseudo-space character is used for hiding the data. This character prevents the Persian and Arabic letters from joining but without adding a space between the two and keeps the words closer together. Its code is 200C in Unicode hex notation. This character... 

    State masking over a two-state compound channel

    , Article IEEE Transactions on Information Theory ; Volume 67, Issue 9 , 2021 , Pages 5651-5673 ; 00189448 (ISSN) Salehkalaibar, S ; Yassaee, M. H ; Tan, V. Y. F ; Ahmadipour, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    We consider the fundamental limits of reliable communication over a two-state compound channel when the state of the channel needs to be masked. Our model is closely related to an area of study known as covert communication, a setting in which the transmitter wishes to communicate to legitimate receiver(s) while ensuring that the communication is not detected by an adversary. Our main contribution is the establishment of upper and lower bounds on the throughput-key length region when the constraint that quantifies how much the states are masked is defined to be the total variation distance between the channel output distributions of the two states. When length of the key is sufficiently... 

    Generalisation of code division multiple access systems and derivation of new bounds for the sum capacity

    , Article IET Communications ; Vol. 8, Issue. 2 , 2014 , Pages 153-162 ; ISSN: 17518628 Dashmiz, S ; Takapoui, M. R ; Moazeni, S ; Moharrami, M ; Abolhasani, M ; Marvasti, F ; Sharif University of Technology
    Abstract
    In this study, the authors explore a generalised scheme for the synchronous code division multiple access (CDMA). In this scheme, unlike the standard CDMA systems, each user has different codewords for communicating different messages. Two main problems are investigated. The first problem concerns whether uniquely detectable overloaded matrices (an injective matrix, i.e. the inputs and outputs are in one-to-one correspondence depending on the input alphabets) exist in the absence of additive noise, and if so, whether there are any practical optimum detectors for such input codewords. The second problem is about finding tight bounds for the sum channel capacity. In response to the first... 

    Bottleneck of using a single memristive device as a synapse

    , Article Neurocomputing ; Volume 115 , September , 2013 , Pages 166-168 ; 09252312 (ISSN) Merrikh Bayat, F ; Bagheri Shouraki, S ; Esmaili Paeen Afrakoti, I ; Sharif University of Technology
    2013
    Abstract
    In this study we will show that the variation rate of the memristance of the memristive device depends completely on its current memristance which means that it can change significantly with time during the learning phase. This phenomenon can degrade the performance of learning methods like Spike Timing-Dependent Plasticity (STDP) and cause the corresponding neuromorphic systems to become unstable