Loading...
Search for:
radio
0.008 seconds
Total 402 records
Preventing the transmission of harmful cognitive radio users in the presence of primary users
, Article Proceedings - 2009 1st UK-India International Workshop on Cognitive Wireless Systems, UKIWCWS 2009, 11 December 2009 through 12 December 2009, New Delhi ; 2009 ; 9781457701832 (ISBN) ; Soleimanipour, M ; Sharif University of Technology
Abstract
A cognitive radio provides access to a licensed spectrum for unlicensed users opportunistically provided that they are not harmful for licensed users (primary users). We call a cognitive radio user (CR user) harmful, when it generates interference for primary users (PU) or occupies spectrum holes excessively. This paper discusses the spectrum management policy against harmful CR users. For this, we design a jammer signal which ruins transmission of harmful CR users and forces them to leave the spectrum without damaging the communication of PUs. This signal is designed using group subspace technique for both synchronous and asynchronous channels. Our simulation results show that the designed...
Lofar: recent imaging results and future prospects
, Article Journal of Astrophysics and Astronomy ; Volume 32, Issue 4 , January , 2011 , Pages 589-598 ; 02506335 (ISSN) ; Bell, M. R ; Horneffer, A ; Offringa, A. R ; Pizzo, R ; van der Tol, S ; van Weeren, R. J ; van Zwieten, J. E ; Anderson, J. M ; Beck, R ; van Bemmel, I ; Bîrzan, L ; Bonafede, A ; Conway, J ; Ferrari, C ; De Gasperin, F ; Haverkorn, M ; Jackson, N ; Macario, G ; McKean, J ; Miraghaei, H ; Orrù, E ; Rafferty, D ; Röttgering, H ; Scaife, A ; Shulevski, A ; Sotomayor, C ; Tasse, C ; Trasatti, M ; Wucknitz, O ; Sharif University of Technology
2011
Abstract
The Low-Frequency Array (LOFAR) is under construction in the Netherlands and in several surrounding European countries. In this contribution, we describe the layout and design of the telescope, with particular emphasis on the imaging characteristics of the array when used in its 'standard imaging' mode. After briefly reviewing the calibration and imaging software used for LOFAR image processing, we show some recent results from the ongoing imaging commissioning efforts. We conclude by summarizing future prospects for the use of LOFAR in observing the little-explored low-frequency Universe
A location privacy-preserving method for spectrum sharing in database-driven cognitive radio networks
, Article Wireless Personal Communications ; Volume 95, Issue 4 , 2017 , Pages 3687-3711 ; 09296212 (ISSN) ; Ahmadian Attari, M ; Jannati, H ; Aref, M. R ; Sharif University of Technology
Springer New York LLC
2017
Abstract
The great attention to cognitive radio networks (CRNs) in recent years, as a revolutionary communication paradigm that aims to solve the problem of spectrum scarcity, prompts serious investigation on security issues of these networks. One important security concern in CRNs is the preservation of users location privacy, which is under the shadow of threat, especially in database-driven CRNs. To this end, in this paper, we propose a Location Privacy Preserving Database-Driven Spectrum-Sharing (L-PDS 2) protocol for sharing the spectrum between PUs and SUs in a database-driven CRN, while protecting location privacy of both primary and secondary users, simultaneously. We also present two...
The capacity region for broadcast channels with conditionally independent message sets
, Article 4th Advanced International Conference on Telecommunications, AICT 2008, Athens, 8 June 2008 through 13 June 2008 ; 2008 , Pages 283-286 ; 9780769531625 (ISBN) ; Sharif University of Technology
2008
Abstract
A more general class of broadcast channels with conditionally independent message sets is defined and its capacity region is determined using Marton's inner bound and the outer bound considered by Nair and El Gamal. The capacity region for this class of channels includes the capacity region for broadcast channels with degraded message sets, semi-deterministic broadcast channels, deterministic broadcast channels with and without common information, less noisy and (special) more capable broadcast channels. © 2008 IEEE
Compress-and-forward strategy for causal cognitive interference channel
, Article Proceedings 2010 IEEE International Conference on Information Theory and Information Security, ICITIS 2010, 17 December 2010 through 19 December 2010, Beijing ; 2010 , Pages 1088-1095 ; 9781424469406 (ISBN) ; Akhbari, B ; Aref, M. R ; Sharif University of Technology
2010
Abstract
In this paper, we consider Causal Cognitive Interference Channel (CC-IFC), wherein the cognitive user overhears the channel and exploits knowledge of the primary user's message from the causally received signals. We propose a coding scheme which combines Compress-and-Forward (CF) strategy with Marton coding with common information at the cognitive user. Rate splitting for messages at both transmitters is used to have a collaborative strategy. Moreover, the cognitive user compresses its channel observation using Wyner-Ziv coding and splits the index of its compressed signal. Then, the cognitive user having common information to both receivers and private information to each of them, jointly...
Modeling the behavior of contending opportunistic cognitive radios
, Article 2007 IEEE International Conference on Signal Processing and Communications, ICSPC 2007, Dubai, 14 November 2007 through 27 November 2007 ; 2007 , Pages 720-723 ; 9781424412365 (ISBN) ; Ashtiani, F ; Hassani, S. H ; Tootoonchi, P ; Sharif University of Technology
2007
Abstract
In this paper, we propose a new model to evaluate the behavior of cognitive radios (CRs). In this model, we consider a specific number of primary users having independent probabilistic on-off behavior. In addition, a specific number of opportunistic cognitive radios in saturation mode is assumed. We consider contention for CRs in order to occupy an inactive primary channel independently according to a simple MAC scheme. Our model is based on a closed BCMP state-dependent queueing network. We map contention of the CRs and the behavior of primary users on suitable parameters of the queueing network. By solving the network, we obtain the steady state behavior of CRs, then we find the efficient...
Opportunistic spectral access in cooperative cognitive radio networks
, Article IEEE Vehicular Technology Conference ; 14-17 September , 2014 ; ISSN: 15502252 ; ISBN: 9781479944491 ; Ng, S. X ; Bayat, S ; Li, Y ; Hanzo, L ; Sharif University of Technology
Abstract
A pragmatic distributed algorithm (PDA) is proposed for supporting the ef-cient spectral access of multiple Primary Users (PUs) and Cognitive Users (CUs) in cooperative Cognitive Radio (CR) networks. The CUs may serve as relay nodes for relaying the signal received from the PUs to their destinations, while both the PUs' and the CUs' minimum rate requirements are satis-ed. The key idea of our PDA is that the PUs negotiate with the CUs concerning the speci-c amount of relaying and transmission time, whilst reducing the required transmission power or increasing the transmission rate of the PU. Our results show that the cooperative spectral access based on our PDA reaches an equilibrium, when it...
IGM heating in fossil galaxy groups
, Article Monthly Notices of the Royal Astronomical Society ; Vol. 444, issue. 1 , Jul , 2014 , pp. 651-666 ; Khosroshahi, H. G ; Klockner, H. R ; Ponman, T. J ; Jetha, N. N ; Raychaudhury, S ; Sharif University of Technology
Abstract
We study intergalactic medium (IGM) heating in a sample of five fossil galaxy groups by using their radio properties at 610MHz and 1.4 GHz. The power by radio jets introducing mechanical heating for the sampled objects is not sufficient enough to suppress the cooling flow. Therefore, we discussed shock-, vortex heating, and conduction as alternative heating processes. Further, the 1.4 GHz and 610MHz radio luminosities of fossil groups are compared to a sample of normal galaxy groups of the same brightest group galaxies (BGGs), stellar mass, and total group stellar mass, quantified using the K-band luminosity. It appears that the fossil BGGs are under luminous at 1.4 GHz and 610MHz for a...
Cognitive radio networks spectrum allocation: An ACS perspective
, Article Scientia Iranica ; Volume 19, Issue 3 , 2012 , Pages 767-773 ; 10263098 (ISSN) ; Talebi, S ; Salehinejad, H ; Sharif University of Technology
2012
Abstract
Cognitive Radio (CR) is a promised solution to the lack of spectrum, as well as spectrum inefficiency, in current communication networks. A major demand of this technology is for fair spectrum assignment to unlicensed (secondary) users. This paper addresses a new approach to this challenge in CR networks, based on the Graph Coloring Problem (GCP) and the Ant Colony System (ACS). In addition, we compare the performance of the proposed algorithm with Color Sensitive Graph Coloring (CSGC) and Particle Swarm Optimization (PSO) based techniques
A new spectrum sensing circuit for cognitive radio applications
, Article Proceedings - CIMSim 2011: 3rd International Conference on Computational Intelligence, Modelling and Simulation, 20 September 2011 through 22 September 2011, Langkawi ; 2011 , Pages 404-407 ; 9780769545622 (ISBN) ; Forooraghi, K ; Atlasbaf, Z ; Ahmadi, A. F ; Sharif University of Technology
2011
Abstract
Fast, accurate and efficient sensing is of important aspects in cognitive radio technology. A new sensing circuit is proposed using a phase frequency detector for cognitive radio applications. Using this method, spectral sensing can be done in a very short time by a low cost, low power circuit, compared with available implemented methods. The PFD circuit resolves different frequencies without the need of variable filter bandwidth or the banks of filters. Also it accelerates sensing procedure because of short time needed to detect the signal. Simulations show the accurate operation of this method and comparison with other methods shows faster sweep rates
Cooperative spectrum sensing by algorithmic techniques using spatial information
, Article ; 2010 5th International ICST Conference on Communications and Networking in China, ChinaCom 2010, 25 August 2010 through 27 August 2010 , 2010 ; 9780984589333 (ISBN) ; Hemmatyar, M. A ; Fazli, M. A ; Izadi, M ; Sharif University of Technology
Abstract
Spectrum sensing is the basic step in cognitive radio networks. Its accuracy directly affects spectrum utilization. In this paper we propose a new method for blind cooperative spectrum sensing using spatial information. We model our sensing matrix as a graph, taking advantage of signal and spatial correlation of antennas. We prove that the general settings of the problem are hard to approximate. Taking spatial information into account, we propose a new scheme to find white space subregions. Cognitive radio users residing in the region may be able to transmit, but must keep their transmission power to the extent that no interference is caused to primary receivers out of the region
Resolving microlensing events with triggered vlbi
, Article Astrophysical Journal ; Volume 833, Issue 2 , 2016 ; 0004637X (ISSN) ; Broderick, A. E ; Rahvar, S ; Reid, M ; Sharif University of Technology
Institute of Physics Publishing
2016
Abstract
Microlensing events provide a unique capacity to study the stellar remnant population of the Galaxy. Optical microlensing suffers from a near-complete degeneracy between mass, velocity, and distance. However, a subpopulation of lensed stars, Mira variable stars, are also radio-bright, exhibiting strong SiO masers. These are sufficiently bright and compact to permit direct imaging using existing very long baseline interferometers such as the Very Long Baseline Array (VLBA). We show that these events are relatively common, occurring at a rate of ≈2 yr-1 of which 0.1 yr-1 are associated with Galactic black holes. Features in the associated images, e.g., the Einstein ring, are sufficiently well...
On the devroye-mitran-tarokh rate region for the cognitive radio channel
, Article IEEE Transactions on Wireless Communications ; Volume 8, Issue 7 , 2009 , Pages 3458-3461 ; 15361276 (ISSN) ; Aref, M. R ; Sharif University of Technology
2009
Abstract
An achievable rate region for the genie-aided cognitive radio channel is obtained using the celebrated HanKobayashi jointly decoding strategy for the interference channel and the Gel'fand-Pinsker coding scheme for channels with side information known at the transmitter. The achievable rate region is then simplified by Fourier-Motzkin elimination. The obtained achievable rate region (i) extends the Chong-Motani-Garg region for the interference channel to the cognitive channel and (ii) is a simplified description of the Devroye-Mitran-Tarokh rate region for the genie-aided cognitive radio channel. © 2009 IEEE
Simultaneous Block Iterative Method with Adaptive Thresholding for Cooperative Spectrum Sensing
, Article IEEE Transactions on Vehicular Technology ; Volume 68, Issue 6 , 2019 , Pages 5598-5605 ; 00189545 (ISSN) ; Abtahi, A ; Marvasti, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
The effective utilization of the spectrum has become an essential goal in the communications field, which is addressed by the Cognitive Radio (CR) systems. The primary task in a CR system is to sense the spectrum to identify its holes to be exploited by the secondary users. In this paper, we tackle the compressed spectrum sensing problem in a cooperative manner. The CRs distributed in an area take the samples of the signal that has been reached to them through a wireless fading channel. The spectrum has the block-sparse structure. Moreover, the spectrum observed by different CRs in an area share the same block-sparse support. Therefore, we suggest to exploit the joint block-sparsity...
Web graph compression by edge elimination
, Article Data Compression Conference, DCC 2006, Snowbird, UT, 28 March 2006 through 30 March 2006 ; 2006 , Pages 459- ; 10680314 (ISSN) ; Khalili, H ; Nourbakhsh, E ; Ghodsi, M ; Brandeis University ; Sharif University of Technology
2006
Transmission of multiband OFDM and impulse radio ultrawideband signals over single mode fiber[electronic resource]
, Article IEEE Journal of Lightwave Technology ; Vol. 26, No. 15, PP. 2594-2603, August 2008 ; Cabon, B ; Salehi, J. A ; Sharif University Of Technology
Abstract
In this paper we examine the transmission of two types of ultra-wideband (UWB) signals, multiband orthogonal frequency division multiplexing (MB-OFDM) and impulse radio ultra-wideband (IR-UWB), over single mode fiber at 1550 nm. In order to investigate the impact of optical components such as laser diode, external modulator and single mode fiber on UWB signals, we develop mathematical models for these components. These models are experimentally verified and corresponding numerical parameter values are obtained by experiment. Using these models we discuss the transmission of two types of UWB signals over single mode fiber. A new figure of merit namely distortion factor is defined. Using...
Efficient enhancement of the accuracy of ray tracing
, Article 2010 IEEE International Symposium on Antennas and Propagation and CNC-USNC/URSI Radio Science Meeting - Leading the Wave, AP-S/URSI 2010, 11 July 2010 through 17 July 2010 ; July , 2010 ; 9781424449682 (ISBN) ; Parsa, S ; Shishegar, A. A ; Sharif University of Technology
2010
Abstract
Proper design of wireless personal and local area networks requires accurate characterization of radio wave propagation in indoor environments. The Shooting-and-Bouncing-Ray tracing (SBR) method, which uses Geometrical Optics (GO) approximation, has been widely used for indoor propagation modeling [1-2]
Efficient cooperative spectrum sensing in cognitive radio networks
, Article 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC'07, Athens, 3 September 2007 through 7 September 2007 ; December , 2007 ; 1424411440 (ISBN); 9781424411443 (ISBN) ; Nasiri Kenari, M ; Jamshidi, A ; Sharif University of Technology
2007
Abstract
Rcent measurements suggest the possibility of sharing spectrum among different parties subject to interference-protection constraints. In order to enable access to an unused licensed spectrum, a secondary user has to monitor licensed bands and opportunistically transmit whenever no primary signal is detected. In this paper, we study spectrum-sharing between a primary licensee and a group of secondary users. The structure of an asymptotically optimum detector based on the measurements of all secondary users is derived and the effect of the quantization error in such a system is evaluated. The results show the superiority of the proposed detector to other schemes. © 2007 IEEE
Using game theory to battle jammer in control channels of cognitive radio ad hoc networks
, Article 2016 IEEE International Conference on Communications, ICC 2016, 22 May 2016 through 27 May 2016 ; 2016 ; 9781479966646 (ISBN) ; Khorramshahi, P ; Salehi, J. A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
Because of opportunistic spectrum access, cognitive radio networks is a promising solution for spectrum scarcity problem. In cognitive radio networks, users need to communicate through control channels in order to cooperate for sharing sensing information, channel sharing and spectrum management. As a result control channels security is of a great importance. If control channels get jammed, network's performance degrades dramatically; therefore, the jammers primary target in cognitive radio networks is to demolish control channels in order to disturb the network's performance. Traditionally hopping sequences were used to battle this problem but considering cognitive radio networks...
CMORC: class-based multipath on-demand routing protocol for cognitive radio networks
, Article Scientia Iranica ; Volume 24, Issue 6 , 2017 , Pages 3117-3131 ; 10263098 (ISSN) ; Afshin Hemmatyar, A. M ; Sharif University of Technology
Abstract
Cognitive radio (CR) technology enables dynamic spectrum access (DSA) to improve the efficiency of under-utilized licensed bands and overcrowded unlicensed bands. However, providing an acceptable service for cognitive users requires more sophisticated approaches due to the existence of Primary Users (PU) with high priority over licensed bands. Additionally, it is of paramount importance that interference with PUs be reduced so that they can communicate without interruption. In order to meet requirements of users as much as possible and reduce interference with PUs, a new Class-based Multi-path Ondemand Routing protocol for Cognitive radio networks (CMORC) is proposed. CMORC is a multipath...