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Total 149 records

    Analytic modeling of channel traffic in n-cubes

    , Article 1st International Computer Science Symposium in Russia, CSR 2006, St. Petersburg, 8 June 2006 through 12 June 2006 ; Volume 3967 LNCS , 2006 , Pages 567-579 ; 03029743 (ISSN) Sarbazi Azad, H ; Mahini, H ; Patooghy, A ; Sharif University of Technology
    Springer Verlag  2006
    Abstract
    Many studies have shown that the imbalance of network channel traffic is of critical effect on the overall performance of multicomputer systems. In this paper, we analytically model the traffic rate crossing the network channels of a hypercube network under different working conditions. The effect of different parameters on the shaping of non-uniformity and traffic imbalance over network channels, are considered and analytical models for each case are proposed. © Springer-Verlag Berlin Heidelberg 2006  

    Adaptive online prediction of operator position in teleoperation with unknown time-varying delay: simulation and experiments

    , Article Neural Computing and Applications ; 2020 Nikpour, M ; Yazdankhoo, B ; Beigzadeh, B ; Meghdari, A ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2020
    Abstract
    One of the most important problems in teleoperation systems is time delay and packet loss in the communication channel, which can affect transparency and stability. One way to overcome the time delay effects in a teleoperation system is to predict the master-side motion. In this way, when data is received in the slave side, it will be considered as the current position of the master robot and, thus, complete transparency could be achieved. The majority of the previous works regarding operator position prediction have considered known and constant time delay in the system; however, in the real applications, time delay is unknown and variable. In this paper, an adaptive online prediction... 

    Adaptive online prediction of operator position in teleoperation with unknown time-varying delay: simulation and experiments

    , Article Neural Computing and Applications ; Volume 33, Issue 13 , 2021 , Pages 7575-7592 ; 09410643 (ISSN) Nikpour, M ; Yazdankhoo, B ; Beigzadeh, B ; Meghdari, A ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2021
    Abstract
    One of the most important problems in teleoperation systems is time delay and packet loss in the communication channel, which can affect transparency and stability. One way to overcome the time delay effects in a teleoperation system is to predict the master-side motion. In this way, when data is received in the slave side, it will be considered as the current position of the master robot and, thus, complete transparency could be achieved. The majority of the previous works regarding operator position prediction have considered known and constant time delay in the system; however, in the real applications, time delay is unknown and variable. In this paper, an adaptive online prediction... 

    Secret key cryptosystem based on non-systematic polar codes

    , Article Wireless Personal Communications ; Volume 84, Issue 2 , September , 2015 , Pages 1345-1373 ; 09296212 (ISSN) Hooshmand, R ; Aref, M. R ; Eghlidos, T ; Sharif University of Technology
    Springer New York LLC  2015
    Abstract
    Polar codes are a new class of error correcting linear block codes, whose generator matrix is specified by the knowledge of transmission channel parameters, code length and code dimension. Moreover, regarding computational security, it is assumed that an attacker with a restricted processing power has unlimited access to the transmission media. Therefore, the attacker can construct the generator matrix of polar codes, especially in the case of binary erasure channels, on which this matrix can be easily constructed. In this paper, we introduce a novel method to keep the generator matrix of polar codes in secret in a way that the attacker cannot access the required information to decode the... 

    A lightweight signcryption scheme for defense against fragment duplication attack in the 6LoWPAN networks

    , Article Peer-to-Peer Networking and Applications ; 2018 , Pages 1-18 ; 19366442 (ISSN) Nikravan, M ; Movaghar, A ; Hosseinzadeh, M ; Sharif University of Technology
    Springer New York LLC  2018
    Abstract
    The Internet of Things (IoT) presents a new paradigm of the future Internet that intends to provide interactive communication between various processing objects via heterogeneous networks. The IPv6 over Low power Wireless Personal Area Networks (6LoWPAN) is an IPv6 adaptation sub-layer and provides the requirements of IP connectivity between resource-constrained devices in lossy, low power networks. Since the size of a packet in the IPv6 is larger than the size of a frame in the IEEE 802.15.4, the 6LoWPAN adaptation layer performs packet fragmentation. In this paper, first, the 6LoWPAN fragmentation mechanism in terms of security issues is analyzed and then, fragment duplication attack which... 

    An adaptive secure channel coding scheme for data transmission over LEO satellite channels

    , Article Scientia Iranica ; Volume 13, Issue 4 , 2006 , Pages 373-378 ; 10263098 (ISSN) Payandeh, A ; Ahmadian, M ; Aref, M. R ; Sharif University of Technology
    Sharif University of Technology  2006
    Abstract
    Both secure and error control coding are very extensive subjects, each with a variety of subdisciplines. A secure channel coding (joint encryption-channel coding) scheme provides both data secrecy and data reliability in one process to combat problems in an insecure and unreliable channel. In this paper, a joint encryption-channel coding scheme is developed, based on concatenated turbo codes for more efficient and secure transmission of LEO satellite data. Reliability and security are achieved by adapting the pseudo-random puncturing strategy with a change of distance between satellites and ground stations in the communication séance, an issue further burdened by reducing energy consumption... 

    Performance evaluations and comparisons of several LDPC coded MC-FH-CDMA systems

    , Article Scientia Iranica ; Volume 13, Issue 4 , 2006 , Pages 337-347 ; 10263098 (ISSN) Behroozi, H ; Haghighat, J ; Nasiri Kenari, M ; Jamali, S. H ; Sharif University of Technology
    Sharif University of Technology  2006
    Abstract
    In this paper, the application of regular Low-Density Parity-Check (LDPC) codes in Multi-Carrier Frequency-Hopping (MC-FH) CDMA systems is studied. To this end, different well-known constructions of regular LDPC codes are considered and the performance of LDPC coded MC-FH-CDMA systems, based on these constructions, are evaluated and compared in a frequency-selective slowly Rayleigh fading channel. These results are compared with those previously reported for super-orthogonal convolutionally coded MC-FH-CDMA systems. The simulation results indicate that the LDPC coded MC-FH-CDMA system significantly outperforms the uncoded and super-orthogonal convolutionally coded schemes. To alleviate the... 

    Performance analysis of time-hopping ultra-wideband systems in multipath fading channels (Uncoded and coded schemes)

    , Article Scientia Iranica ; Volume 13, Issue 1 , 2006 , Pages 67-77 ; 10263098 (ISSN) Ahmadi, H. R ; Nasiri Kenari, M ; Shayesteh, M. G ; Sharif University of Technology
    Sharif University of Technology  2006
    Abstract
    In this paper, the performances of both uncoded and coded multiple access TH-UWB systems, introduced in [1-3] in multipath Rayleigh fading channels, are evaluated. The receiver is a selective diversity combining receiver, known as SRake. Based on a Gaussian distribution assumption for the multiple access interference at the output of the SRake receiver and by using a virtual branch technique, as introduced in [4,5], the bit error rates for uncoded and coded schemes are derived. The performance analysis shows that the effective order of diversity achieved by the coded scheme is the product of the number of branches of the SRake receiver and the Hamming distance of the code applied.... 

    Unified multiple-access performance analysis of several multirate multicarrier spread-spectrum systems

    , Article Scientia Iranica ; Volume 13, Issue 1 , 2006 , Pages 33-49 ; 10263098 (ISSN) Nikjah, R ; Nasiri Kenari, M ; Sharif University of Technology
    Sharif University of Technology  2006
    Abstract
    A unified multiple-access performance analysis and comparison of three multicarrier spread-spectrum multiple-access schemes, namely, MC-CDMA (Multicarrier Code-Division Multiple-Access), MC-FH (Multicarrier Frequency Hopping) and a hybrid of the above systems, called DS-MC-FH (Direct-Sequence MC-FH), in a multirate environment, where each user can have several multirate services, is provided. In MC-CDMA and MC-FH systems, users and their diverse services are differentiated by means of only one kind of signature code. However, in a DS-MCFH scheme, different users and different services of the same user are distinguished through the first and second signature codes, respectively. The... 

    Lossy transmission of correlated sources over multiple-access wiretap channels

    , Article IET Communications ; Volume 9, Issue 6 , 2015 , Pages 754-770 ; 17518628 (ISSN) Salehkalaibar, S ; Aref, M. R ; Sharif University of Technology
    Institution of Engineering and Technology  2015
    Abstract
    In this study, the authors study lossy communication of correlated sources over a multiple-access wiretap channel (MAC-WT). Consider a system with two transmitters, a receiver and an eavesdropper. There are two correlated sources where each of them is observed by the corresponding transmitter, separately. Each transmitter wishes to describe its source sequence to the receiver with a desired distortion. The sources need to be kept secret from the eavesdropper. They find an achievable region for the MAC-WT with correlated sources by separation. A joint source-channel coding scheme for the MAC-WT is also proposed. They consider lossy communication of a bivariate Gaussian source over Gaussian... 

    Compute-and-forward two-way relaying

    , Article IET Communications ; Volume 9, Issue 4 , 2015 , Pages 451-459 ; 17518628 (ISSN) Azimi Abarghouyi, S. M ; Hejazi, M ; Nasiri Kenari, M ; Sharif University of Technology
    Institution of Engineering and Technology  2015
    Abstract
    In this study, a new two-way relaying scheme based on compute-and-forward (CMF) framework and relay selection strategies is proposed, which provides a higher throughput than the conventional two-way relaying schemes. Two cases of relays with or without feedback transmission capability are considered. An upper bound on the computation rate of each relay is derived, and based on that, a lower bound on the outage probability of the system is presented assuming block Rayleigh fading channels. Numerical results show that while the average sum rate of the system without feedback, named as max-CMF (M-CMF), reaches the derived upper bound only in low SNRs, that of the system with feedback, named as... 

    Comprehensive study on a 2 × 2 full-rate and linear decoding complexity space-time block code

    , Article IET Communications ; Volume 9, Issue 1 , 2015 , Pages 122-132 ; 17518628 (ISSN) Hosseini, S. S ; Talebi, S ; Abouei, J ; Sharif University of Technology
    Institution of Engineering and Technology  2015
    Abstract
    This paper presents a comprehensive study on the Full-Rate and Linear-Receiver (FRLR) STBC proposed as a newly coding scheme with the low decoding complexity for a 2×2 MIMO system. It is shown that the FRLR code suffers from the lack of the non-vanishing determinant (NVD) property that is a key parameter in designing a full-rate STBC with a good performance in higher data rates, across QAM constellation. To overcome this drawback, we show that the existence of the NVD feature for the FRLR code depends on the type of the modulation. In particular, it is analytically proved that the FRLR code fulfills the NVD property across the PAM constellation but not for the QAM scheme. Simulation results... 

    Diversity-multiplexing tradeoff in MIMO radars

    , Article IET Radar, Sonar and Navigation ; Volume 11, Issue 4 , 2017 , Pages 691-700 ; 17518784 (ISSN) Nazari Majd, M ; Radmard, M ; Chitgarha, M. M ; Farina, A ; Nayebi, M. M ; Bastani, M. H ; Sharif University of Technology
    Institution of Engineering and Technology  2017
    Abstract
    Two gains play key roles in recently developed multiple-input-multiple-output (MIMO) wireless communication systems: 'spatial diversity' gain and 'spatial multiplexing' gain. The diversity gain (DG) refers to the capability to decrease the error rate of the MIMO channel, whereas the multiplexing gain (MG) implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the DG) and increasing data rate (via an increase in the MG). On the other hand, recently, MIMO radars have attracted much attention for their superior... 

    Spatial multiplexing gain in MIMO radars with widely separated antennas

    , Article IET Signal Processing ; Volume 12, Issue 2 , March , 2018 , Pages 207-213 ; 17519675 (ISSN) Nazari Majd, M ; Radmard, M ; Chitgarha, M. M ; Farina, A ; Bastani, M. H ; Nayebi, M. M ; Sharif University of Technology
    Institution of Engineering and Technology  2018
    Abstract
    Multiple-input multiple-output (MIMO) radars have attracted much attention for their superior ability to enhance a system's performance. In this study, the authors' goal was the study of the spatial multiplexing gain of MIMO radars with widely separated antennas (WS-MIMO), which the authors showed that is equal to the number of unambiguously detectable targets. They obtained this number from two different aspects: first, by defining the ambiguity function of a WS-MIMO radar in the case of multiple targets, suitable for such purpose; Second, by modelling the MIMO radar system with a MIMO wireless channel. They showed that a MIMO radar is indeed a MIMO wireless system communicating the... 

    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... 

    On optimum asymptotic multiuser efficiency of randomly spread CDMA

    , Article IEEE Transactions on Information Theory ; Volume 61, Issue 12 , 2015 , Pages 6635-6642 ; 00189448 (ISSN) Sedaghat, M. A ; Müller, R. R ; Marvasti, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    We extend the result by Tse and Verdú on the optimum asymptotic multiuser efficiency of randomly spread code division multiple access (CDMA) with binary phase shift keying input. Random Gaussian and random binary antipodal spreading are considered. We obtain the optimum asymptotic multiuser efficiency of a K-user system with spreading gain N when K and N → ∞ and the loading factor, (K/N) , grows logarithmically with K under some conditions. It is shown that the optimum detector in a Gaussian randomly spread CDMA system has a performance close to the single user system at high signal-to-noise ratio when K and N → ∞ and the loading factor, (K/N), is kept less than (log3 K/2). Random binary... 

    Image restoration using gaussian mixture models with spatially constrained patch clustering

    , Article IEEE Transactions on Image Processing ; Volume 24, Issue 11 , June , 2015 , Pages 3624-3636 ; 10577149 (ISSN) Niknejad, M ; Rabbani, H ; Babaie Zadeh, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    In this paper, we address the problem of recovering degraded images using multivariate Gaussian mixture model (GMM) as a prior. The GMM framework in our method for image restoration is based on the assumption that the accumulation of similar patches in a neighborhood are derived from a multivariate Gaussian probability distribution with a specific covariance and mean. Previous methods of image restoration with GMM have not considered spatial (geometric) distance between patches in clustering. Our conducted experiments show that in the case of constraining Gaussian estimates into a finite-sized windows, the patch clusters are more likely to be derived from the estimated multivariate Gaussian... 

    An efficient DVS scheme for on-chip networks using reconfigurable Virtual Channel allocators

    , Article Proceedings of the International Symposium on Low Power Electronics and Design, 22 July 2015 through 24 July 2015 ; Volume 2015-September , July , 2015 , Pages 249-254 ; 15334678 (ISSN) ; 9781467380096 (ISBN) Sadrosadati, M ; Mirhosseini, A ; Aghilinasab, H ; Sarbazi Azad, H ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    Network-on-Chip (NoC) is a key element in the total power consumption of a chip multiprocessor. Dynamic Voltage Scaling is a promising method for power saving in NoCs since it contributes to reduction in both static and dynamic power consumptions. In this paper, we propose a novel scheme to reduce on-chip network power consumption when the number of Virtual Channels (VCs) with active allocation requests per cycle is less than the number of total VCs. In our method, we introduce a reconfigurable arbitration logic which can be configured to have multiple latencies and hence, multiple slack times. The increased slack times are then used to reduce the supply voltage of the routers in order to... 

    On Körner-Marton's sum modulo two problem

    , Article IWCIT 2015 - Iran Workshop on Communication and Information Theory, 6 May 2015 through 7 May 2015 ; May , 2015 ; 9781479982356 (ISBN) Sefidgaran, M ; Gohari, A ; Aref, M. R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    In this paper we study the sum modulo two problem proposed by Körner and Marton. In this source coding problem, two transmitters who observe binary sources X and Y, send messages of limited rate to a receiver whose goal is to compute the sum modulo of X and Y. This problem has been solved for the two special cases of independent and symmetric sources. In both of these cases, the rate pair (H(X|Y), H(Y|X)) is achievable. The best known outer bound for this problem is a conventional cut-set bound, and the best known inner bound is derived by Ahlswede and Han using a combination of Slepian-Wolf and Körner-Marton's coding schemes. In this paper, we propose a new outer bound which is strictly... 

    Differentially encoded blind multicell multiuser massive MIMO

    , Article IEEE International Conference on Communication Workshop, ICCW 2015, 8 June 2015 through 12 June 2015 ; June , 2015 , Pages 1054-1059 ; 9781467363051 (ISBN) Fozi, M ; Khalaj, B. H ; Pesavento, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    In this paper, we consider the uplink of the narrowband multicell multiuser massive multiple-input multiple-output (MIMO) systems. In traditional approaches, orthogonal pilots among users of all (interfering) cells are utilized to estimate their channels assumed to be constant during channel coherence time. However, in multicell scenarios, such schemes suffer from pilot contamination. In order to address this issue, based on asymptotic pairwise orthogonality of the users' channels in massive regime, blind channel estimation schemes have been proposed. On the other hand, such schemes rely on low interference or high signal to noise ratio (SNR) levels, to achieve reliable performance. Inspired...