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**Search for:**communication-channels--information-theory

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Total 148 records

#### Virtual point-to-point links in packet-switched NoCs

, Article IEEE Computer Society Annual Symposium on VLSI: Trends in VLSI Technology and Design, ISVLSI 2008, Montpellier, 7 April 2008 through 9 April 2008 ; 2008 , Pages 433-436 ; 9780769531700 (ISBN) ; Sarbazi Azad, H ; Tavakkol, A ; Sharif University of Technology
2008

Abstract

A method to setup virtual point-to-point links between the cores of a packet-switched network-on-chip is presented in this paper which aims at reducing the NoC power consumption and delay. The router architecture proposed in this paper provides packet-switching, as well as a number of virtual point-to-point, or VIP (VIrtual Point-to-point) for short, connections. This is achieved by designating one virtual channel at each physical channel of a router to bypass the router pipeline. The mapping and routing algorithm exploits these virtual channels and tries to virtually connect the source and destination nodes of high-volume communication flows during task-graph mapping and route selection...

#### Using a diversity scheme to reduce energy consumption in wireless sensor networks

, Article 2nd International Conference on Broadband Networks, BROADNETS 2005, Boston, MA, 3 October 2005 through 7 October 2005 ; Volume 2005 , 2005 , Pages 17-20 ; Ghiassi Farrokhfal, Y ; Mohammadnia Avval, M ; Hossein Khalaj, B ; Sharif University of Technology
2005

Abstract

In this paper, a new method is proposed utilizing a diversity scheme to reduce power consumption in large scale sensor networks. Sensor networks are composed of large number of battery powered nodes. Energy consumption is the most important design objective in sensor networks while delay and throughput are taken less into account. Wireless transmission is the other important characteristic of these networks. Small-scale fading decreases wireless communication performance. In a fading channel higher SNRs is needed and consequently more energy is consumed in fading channels. Another important characteristic of sensor networks is the necessity of fault tolerant protocols. Node-to-node links are...

#### Universal bounds on the scaling behavior of polar codes

, Article IEEE International Symposium on Information Theory - Proceedings ; 2012 , Pages 1957-1961 ; 9781467325790 (ISBN) ; Hassani, S. H ; Urbanke, R ; Sharif University of Technology
IEEE
2012

Abstract

We consider the problem of determining the tradeoff between the rate and the block-length of polar codes for a given block error probability when we use the successive cancellation decoder. We take the sum of the Bhattacharyya parameters as a proxy for the block error probability, and show that there exists a universal parameter μ such that for any binary memoryless symmetric channel W with capacity I(W), reliable communication requires rates that satisfy R < I(W) - αN -1/μ, where α is a positive constant and N is the block-length. We provide lower bounds on μ, namely μ ≥ 3.553, and we conjecture that indeed μ = 3.627, the parameter for the binary erasure channel

#### 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) ; 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...

#### Unified approach to the capacity evaluation of the relay channel

, Article IET Communications ; Volume 3, Issue 7 , 2009 , Pages 1208-1215 ; 17518628 (ISSN) ; Aref, M. R ; Sharif University of Technology
2009

Abstract

The authors indicate the dependence between the inputs of the relay channel with one auxiliary random variable as Cover, El-Gamal and Salehi have done for the multiple access channel with arbitrarily correlated sources. Then, by considering broadcast and multiple access sub-channels in the relay channel, the authors describe the essential role of the relay with special Markovity conditions on the auxiliary random variable and channel input-outputs, and unify most of known capacity theorems into one capacity theorem. The capacity theorem potentially may be applicable to a more general class of relay channels including at least the relay channels with known capacity. © The Institution of...

#### Transmission-line model to design matching stage for light coupling into two-dimensional photonic crystals

, Article Optics Letters ; Volume 35, Issue 2 , 2010 , Pages 115-117 ; 01469592 (ISSN) ; Khavasi, A ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
Abstract

The transmission-line analogy of the planar electromagnetic reflection problem is exploited to obtain a transmission-line model that can be used to design effective, robust, and wideband interference-based matching stages. The proposed model based on a new definition for a scalar impedance is obtained by using the reflection coefficient of the zeroth-order diffracted plane wave outside the photonic crystal. It is shown to be accurate for in-band applications, where the normalized frequency is low enough to ensure that the zeroth-order diffracted plane wave is the most important factor in determining the overall reflection. The frequency limitation of employing the proposed approach is...

#### Transition of d -level quantum systems through quantum channels with correlated noise

, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 75, Issue 4 , 2007 ; 10502947 (ISSN) ; Golshani, M ; Sharif University of Technology
2007

Abstract

Entanglement and entanglement assisted are useful resources to enhance the mutual information of the Pauli channels, when the noise on consecutive uses of the channel has some partial correlations. In this paper, we study quantum-communication channels in d -dimensional systems and derive the mutual information of the quantum channels for maximally entangled states and product states coding with correlated noise. Then, we compare fidelity between these states. Our results show that there exists a certain fidelity memory threshold, which depends on the dimension of the Hilbert space (d) and the properties of noisy channels. We calculate the classical capacity of a particular correlated noisy...

#### Transition behavior in the capacity of correlated noisy channels in arbitrary dimensions

, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 74, Issue 3 , 2006 ; 10502947 (ISSN) ; Memarzadeh, L ; Sharif University of Technology
2006

Abstract

We construct a class of quantum channels in arbitrary dimensions for which entanglement improves the performance of the channel. The channels have correlated noise and when the level of correlation passes a critical value we see a sharp transition in the optimal input states (states which minimize the output entropy) from separable to maximally entangled states. We show that for a subclass of channels with some extra conditions, including the examples which we consider, the states which minimize the output entropy are the ones which maximize the mutual information. © 2006 The American Physical Society

#### Throughput modeling of distributed reservation protocol

, Article IEEE Transactions on Mobile Computing ; Volume 15, Issue 2 , 2016 , Pages 503-515 ; 15361233 (ISSN) ; Manzuri Shalmani, M. T ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc

Abstract

To evaluate the performance of distributed mediumaccess control (MAC) layer of emerging ultra wideband (UWB) and 60-GHz millimeter wave (mmWave) wireless personal area networks (WPANs) based on distributed reservation protocol (DRP) of ECMA-368 and ECMA-387 standards, we provide an analytical model for the probability distribution of steady state throughput as a function of the network dimensions size, number of devices, antenna beamwidth, transmission range, bit error rate (BER), antenna disturbance rate (ADR), aggregation length, payload size, and incoming frame rate. Using this model, the optimal payload size is computed as an example of optimization problem.We also propose a formula for...

#### The new scheme for data rate improvement in HF communication without using equalizer

, Article 2005 IEEE/ACES International Conference on Wireless Communications and Applied Computational Electromagnetics, Honolulu, HI, 3 April 2005 through 7 April 2005 ; Volume 2005 , 2005 , Pages 1050-1054 ; 0780390687 (ISBN); 9780780390683 (ISBN) ; Alavi, M. H ; Sharif University of Technology
IEEE Computer Society
2005

Abstract

In this paper the new and improvement approach is suggested for realization of a HF receiver without using equalizer. This approach is based on implementing considerations suggested by [1]. In our approach an HF modem without using equalizer implemented which can communicate over several hundred bits per second with very low bits error rate. This improvement was obtained by changing the framing and the coding structures which has been suggested by [1] and by using the symbol time recovery approach which is proposed by [2]. In this paper, the symbol time recovery approach generalized for multipath fading channels. We implemented our approach on Digital Signal Processor named TMS320F2811....

#### The impacts of timing constraints on virtual channels multiplexing in interconnect networks

, Article 25th IEEE International Performance, Computing, and Communications Conference, 2006, IPCCC 2006, Phoenix, AZ, 10 April 2006 through 12 April 2006 ; Volume 2006 , 2006 , Pages 55-62 ; 1424401976 (ISBN); 9781424401970 (ISBN) ; Ould Khaoua, M ; Nayebi, A ; Sarbazi azad, H ; Sharif University of Technology
2006

Abstract

Interconnect networks employing wormhole-switching play a critical role in shared memory multiprocessor systems-on-chip (MPSoC) designs, Multicomputer systems and System Area Networks. Virtual channels greatly improve the performance of wormhole-switched networks because they reduce blocking by acting as "bypass" lanes for non-blocked messages. Capturing the effects of virtual channel multiplexing has always been a crucial issue for any analytical model proposed for wormhole-switched networks. Dally [8] has developed a model to investigate the behaviour of this multiplexing which have been widely employed in the subsequent analytical models of most routing algorithms suggested in the...

#### The capacity region of p-transmitter/q-receiver multiple-access channels with common information

, Article IEEE Transactions on Information Theory ; Volume 57, Issue 11 , 2011 , Pages 7359-7376 ; 00189448 (ISSN) ; Khosravi Farsani, R ; Aref, M. R ; Marvasti, F ; Sharif University of Technology
Abstract

This paper investigates the capacity problem for some multiple-access scenarios with cooperative transmitters. First, a general Multiple-Access Channel (MAC) with common information, i.e., a scenario where p transmitters send private messages and also a common message to q receivers and each receiver decodes all of the messages, is considered. The capacity region of the discrete memoryless channel is characterized. Then, the general Gaussian fading MAC with common information wherein partial Channel State Information (CSI) is available at the transmitters (CSIT) and perfect CSI is available at the receivers (CSIR) is investigated. A coding theorem is proved for this model that yields an...

#### State-dependent multiple access relay channel with cooperating transmitters

, Article 2018 Iran Workshop on Communication and Information Theory, IWCIT 2018, 25 April 2018 through 26 April 2018 ; 2018 , Pages 1-6 ; 9781538641491 (ISBN) ; Mirmohseni, M ; Seyfe, B ; Aref, M. R ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018

Abstract

In this paper, we consider a state-dependent multiple access relay channel (MARC) with two-way cooperation at transmitters, in which the transmitters cooperate with each other over two limited-rate channels. We derive an achievable rate region for this channel by using block-Markov superposition coding, and double binning techniques. In our proposed scheme, the relay decodes only parts of the messages which are shared between the transmitters. © 2018 IEEE

#### 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) ; 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...

#### Space-query-time tradeoff for computing the visibility polygon

, Article 3rd International Frontiers of Algorithmics Workshop, FAW 2009, Hefei, 20 June 2009 through 23 June 2009 ; Volume 5598 LNCS , 2009 , Pages 120-131 ; 03029743 (ISSN); 3642022693 (ISBN); 9783642022692 (ISBN) ; Ghodsi, M ; Sharif University of Technology
2009

Abstract

Computing the visibility polygon, VP, of a point in a polygonal scene, is a classical problem that has been studied extensively. In this paper, we consider the problem of computing VP for any query point efficiently, with some additional preprocessing phase. The scene consists of a set of obstacles, of total complexity O(n). We show for a query point q, VP(q) can be computed in logarithmic time using O(n 4) space and O(n 4 logn) preprocessing time. Furthermore to decrease space usage and preprocessing time, we make a tradeoff between space usage and query time; so by spending O(m) space, we can achieve O(n 2 log √ m/n)/√ m)query time, where n 2≤m≤n 4. These results are also applied to...

#### Simultaneous partial and backward decoding approach for two-level relay networks

, Article 2009 IEEE International Symposium on Information Theory, ISIT 2009, Seoul, 28 June 2009 through 3 July 2009 ; 2009 , Pages 517-521 ; 21578102 (ISSN); 9781424443130 (ISBN) ; Aref, M. R ; Sharif University of Technology
2009

Abstract

In this paper, we propose a new achievable rate for two-level relay networks by introducing a new strategy named simultaneous partial and backward decoding. In the proposed method, benefitting from regular encoding/backward decoding strategy, different message parts transmitted in the network are simultaneously decoded at the relays and the receiver. The proposed strategy is shown to achieve better rates than the previously proposed methods based on decode-and-forward and partial decode-and-forward. © 2009 IEEE

#### Simulation of a channel with another channel

, Article IEEE Transactions on Information Theory ; Volume 63, Issue 5 , 2017 , Pages 2659-2677 ; 00189448 (ISSN) ; Yassaee, M. H ; Beigi, S ; Gohari, A ; Aref, M. R ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2017

Abstract

In this paper, we study the problem of simulating a discrete memoryless channel (DMC) from another DMC under an average-case and an exact model. We present several achievability and infeasibility results, with tight characterizations in special cases. In particular, for the exact model, we fully characterize when a binary symmetric channel can be simulated from a binary erasure channel when there is no shared randomness. We also provide infeasibility and achievability results for the simulation of a binary channel from another binary channel in the case of no shared randomness. To do this, we use the properties of Rényi capacity of a given order. We also introduce a notion of 'channel...

#### SER of M-PSK modulation in incremental-selective decode-and-forward cooperative communications over Rayleigh fading channels

, Article International Conference on Advanced Communication Technology, ICACT, 13 February 2011 through 16 February 2011 ; February , 2011 , Pages 432-437 ; 17389445 (ISSN) ; 9788955191554 (ISBN) ; Saadat, R ; Aref, M. R ; Mirjalily, G ; Sharif University of Technology
2011

Abstract

In this paper we consider a cooperative communication systems over Rayleigh fading channels. The system utilizes a combination of incremental and selective decode-and-forward (ISDF) relaying protocols. The symbol error rate (SER) of M-PSK modulation for the ISDF protocol is derived. Using an approximation of the SER expression, the optimal power allocation is investigated. In order to reduce the complexity of the receiver, we used a modified version of the ISDF protocol which does not use the storage or retransmission of the first phase signal. We also derived optimal power allocation coefficient for modified ISDF. It has been noted that for the optimal power allocation in the ISDF protocol,...

#### Sensitivity of the secrecy capacity of a wiretap channel to the channel gains with imperfect channel information

, Article IWCIT 2017 - Iran Workshop on Communication and Information Theory, 3 May 2017 through 4 May 2017 ; 2017 ; 9781509047833 (ISBN) ; Bafghi, H. G ; Seyfe, B ; Sharif University of Technology
Abstract

In this paper, the impact of a small variations in the channel gains on the secrecy rate of the wiretap channel is studied, in which it is assumed that the imperfect channel knowledge is available at the transmitter. First, we consider general additive noise model for both legitimate and eavesdropper channels in the wiretap channel, and compute the variation of the secrecy rate resulting from the small variations in the channel gains. Then, we focus on the Gaussian wiretap channel, as a special case and calculate the sensitivity of the secrecy capacity to the channel gains with imperfect channel knowledge. Interestingly, it is shown that in some situations the effect of the channel variation...

#### Secret key cryptosystem based on non-systematic polar codes

, Article Wireless Personal Communications ; Volume 84, Issue 2 , September , 2015 , Pages 1345-1373 ; 09296212 (ISSN) ; 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...