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Keivan G Stassun - One of the best experts on this subject based on the ideXlab platform.
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high resolution spectroscopy during eclipse of the young substellar eclipsing binary 2mass 0535 0546 ii Secondary Spectrum no evidence that spots cause the temperature reversal
The Astrophysical Journal, 2012Co-Authors: Subhanjoy Mohanty, Keivan G StassunAbstract:We present high-resolution optical spectra of the young brown dwarf eclipsing binary 2M0535-05, obtained during eclipse of the higher-mass (primary) brown dwarf. Combined with our previous Spectrum of the primary alone (Paper I), the new observations yield the Spectrum of the Secondary alone. We investigate, through a differential analysis of the two binary components, whether cool surface spots are responsible for suppressing the temperature of the primary. In Paper I, we found a significant discrepancy between the empirical surface gravity of the primary and that inferred via fine analysis of its Spectrum. Here we find precisely the same discrepancy in surface gravity, both qualitatively and quantitatively. While this may again be ascribed to either cool spots or model opacity errors, it implies that cool spots cannot be responsible for preferentially lowering the temperature of the primary: if they were, spot effects on the primary Spectrum should be preferentially larger, and they are not. The T{sub eff}'s we infer for the primary and Secondary, from the TiO-{epsilon} bands alone, show the same reversal, in the same ratio, as is empirically observed, bolstering the validity of our analysis. In turn, this implies that if suppression of convection by magnetic fields on themore » primary is the fundamental cause of the T{sub eff} reversal, then it cannot be a local suppression yielding spots mainly on the primary (though both components may be equally spotted), but a global suppression in the interior of the primary. We briefly discuss current theories of how this might work.« less
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high resolution spectroscopy during eclipse of the young substellar eclipsing binary 2mass 0535 0546 ii Secondary Spectrum no evidence that spots cause the temperature reversal
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Subhanjoy Mohanty, Keivan G StassunAbstract:We present high-resolution optical spectra of the young brown-dwarf eclipsing binary 2M0535-05, obtained during eclipse of the higher-mass (primary) brown dwarf. Combined with our previous Spectrum of the primary alone (Paper I), the new observations yield the Spectrum of the Secondary alone. We investigate, through a differential analysis of the two binary components, whether cool surface spots are responsible for suppressing the temperature of the primary. In Paper I, we found a significant discrepancy between the empirical surface gravity of the primary and that inferred via fine analysis of its Spectrum. Here we find precisely the same discrepancy in surface gravity, both qualitatively and quantitatively. While this may again be ascribed to either cool spots or model opacity errors, it implies that cool spots cannot be responsible for preferentially lowering the temperature of the primary: if they were, spot effects on the primary Spectrum should be preferentially larger, and they are not. The Teff we infer for the primary and Secondary, from the TiO-epsilon bands alone, show the same reversal, in the same ratio, as is empirically observed, bolstering the validity of our analysis. In turn, this implies that if suppression of convection by magnetic fields on the primary is the fundamental cause of the Teff reversal, then it cannot be a local suppression yielding spots mainly on the primary (though both components may be equally spotted), but a global suppression in the interior of the primary. We briefly discuss current theories of how this might work.
Subhanjoy Mohanty - One of the best experts on this subject based on the ideXlab platform.
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high resolution spectroscopy during eclipse of the young substellar eclipsing binary 2mass 0535 0546 ii Secondary Spectrum no evidence that spots cause the temperature reversal
The Astrophysical Journal, 2012Co-Authors: Subhanjoy Mohanty, Keivan G StassunAbstract:We present high-resolution optical spectra of the young brown dwarf eclipsing binary 2M0535-05, obtained during eclipse of the higher-mass (primary) brown dwarf. Combined with our previous Spectrum of the primary alone (Paper I), the new observations yield the Spectrum of the Secondary alone. We investigate, through a differential analysis of the two binary components, whether cool surface spots are responsible for suppressing the temperature of the primary. In Paper I, we found a significant discrepancy between the empirical surface gravity of the primary and that inferred via fine analysis of its Spectrum. Here we find precisely the same discrepancy in surface gravity, both qualitatively and quantitatively. While this may again be ascribed to either cool spots or model opacity errors, it implies that cool spots cannot be responsible for preferentially lowering the temperature of the primary: if they were, spot effects on the primary Spectrum should be preferentially larger, and they are not. The T{sub eff}'s we infer for the primary and Secondary, from the TiO-{epsilon} bands alone, show the same reversal, in the same ratio, as is empirically observed, bolstering the validity of our analysis. In turn, this implies that if suppression of convection by magnetic fields on themore » primary is the fundamental cause of the T{sub eff} reversal, then it cannot be a local suppression yielding spots mainly on the primary (though both components may be equally spotted), but a global suppression in the interior of the primary. We briefly discuss current theories of how this might work.« less
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high resolution spectroscopy during eclipse of the young substellar eclipsing binary 2mass 0535 0546 ii Secondary Spectrum no evidence that spots cause the temperature reversal
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Subhanjoy Mohanty, Keivan G StassunAbstract:We present high-resolution optical spectra of the young brown-dwarf eclipsing binary 2M0535-05, obtained during eclipse of the higher-mass (primary) brown dwarf. Combined with our previous Spectrum of the primary alone (Paper I), the new observations yield the Spectrum of the Secondary alone. We investigate, through a differential analysis of the two binary components, whether cool surface spots are responsible for suppressing the temperature of the primary. In Paper I, we found a significant discrepancy between the empirical surface gravity of the primary and that inferred via fine analysis of its Spectrum. Here we find precisely the same discrepancy in surface gravity, both qualitatively and quantitatively. While this may again be ascribed to either cool spots or model opacity errors, it implies that cool spots cannot be responsible for preferentially lowering the temperature of the primary: if they were, spot effects on the primary Spectrum should be preferentially larger, and they are not. The Teff we infer for the primary and Secondary, from the TiO-epsilon bands alone, show the same reversal, in the same ratio, as is empirically observed, bolstering the validity of our analysis. In turn, this implies that if suppression of convection by magnetic fields on the primary is the fundamental cause of the Teff reversal, then it cannot be a local suppression yielding spots mainly on the primary (though both components may be equally spotted), but a global suppression in the interior of the primary. We briefly discuss current theories of how this might work.
David Grace - One of the best experts on this subject based on the ideXlab platform.
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cognitive Spectrum management in dynamic cellular environments
Engineering Applications of Artificial Intelligence, 2016Co-Authors: Nils Morozs, Tim Clarke, David GraceAbstract:This paper examines how novel cellular system architectures and intelligent Spectrum management techniques can be used to play a key role in accommodating the exponentially increasing demand for mobile data capacity in the near future. A significant challenge faced by the artificial intelligence methods applied to such flexible wireless communication systems is their dynamic nature, e.g. network topologies that change over time. This paper proposes an intelligent case-based Q-learning method for dynamic Spectrum access (DSA) which improves and stabilises the performance of cognitive cellular systems with dynamic topologies. The proposed approach is the combination of classical distributed Q-learning and a novel implementation of case-based reasoning which aims to facilitate a number of learning processes running in parallel. Large scale simulations of a stadium small cell network show that the proposed case-based Q-learning approach achieves a consistent improvement in the system quality of service (QoS) under dynamic and asymmetric network topology and traffic load conditions. Simulations of a Secondary Spectrum sharing scenario show that the cognitive cellular system that employs the proposed case-based Q-learning DSA scheme is able to accommodate a 28-fold increase in the total primary and Secondary system throughput, but with no need for additional Spectrum and with no degradation in the primary user QoS.
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Heuristically accelerated reinforcement learning for dynamic Secondary Spectrum sharing
IEEE Access, 2015Co-Authors: Nils Morozs, Tim Clarke, David GraceAbstract:This paper examines how flexible cellular system architectures and efficient Spectrum management techniques can be used to play a key role in accommodating the exponentially increasing demand for mobile data capacity in the near future. The efficiency of the use of radio Spectrum for wireless communications can be dramatically increased by dynamic Secondary Spectrum sharing; an intelligent approach that allows unlicensed devices access to those parts of the Spectrum that are otherwise underutilized by the incumbent users. In this paper, we propose a heuristically accelerated reinforcement learning (HARL)-based framework, designed for dynamic Secondary Spectrum sharing in Long Term Evolution cellular systems. It utilizes a radio environment map as external information for guiding the learning process of cognitive cellular systems. System level simulations of a stadium temporary event scenario show that the schemes based on the proposed HARL framework achieve high controllability of Spectrum sharing patterns in a fully autonomous way. This results in a significant decrease in the primary system quality of service degradation due to interference from the Secondary cognitive systems, compared with a state-of-the-art reinforcement learning solution and a purely heuristic typical LTE solution. The Spectrum sharing patterns that emerge by using the proposed schemes also result in remarkable reliability of the cognitive eNodeB on the aerial platform. Furthermore, the novel principle and the general structure of heuristic functions proposed in the context of HARL are applicable to a wide range of self-organization problems beyond the wireless communications domain.
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cognitive communications distributed artificial intelligence dai regulatory policy and economics implementation
Cognitive Communications: Distributed Artificial Intelligence (DAI) Regulatory Policy and Economics Implementation 1st, 2012Co-Authors: David Grace, Honggang ZhangAbstract:This book discusses in-depth the concept of distributed artificial intelligence (DAI) and its application to cognitive communicationsIn this book, the authors present an overview of cognitive communications, encompassing both cognitive radio and cognitive networks, and also other application areas such as cognitive acoustics. The book also explains the specific rationale for the integration of different forms of distributed artificial intelligence into cognitive communications, something which is often neglected in many forms of technical contributions available today. Furthermore, the chapters are divided into four disciplines: wireless communications, distributed artificial intelligence, regulatory policy and economics and implementation. The book contains contributions from leading experts (academia and industry) in the field.Key Features:Covers the broader field of cognitive communications as a whole, addressing application to communication systems in general (e.g. cognitive acoustics and Distributed Artificial Intelligence (DAI)Illustrates how different DAI based techniques can be used to self-organise the radio SpectrumExplores the regulatory, policy and economic issues of cognitive communications in the context of Secondary Spectrum accessDiscusses application and implementation of cognitive communications techniques in different application areas (e.g. Cognitive Femtocell Networks (CFN)Written by experts in the field from both academia and industryCognitive Communications will be an invaluable guide for research community (PhD students, researchers) in the areas of wireless communications, and development engineers involved in the design and development of mobile, portable and fixed wireless systems., wireless network design engineer. Undergraduate and postgraduate students on elective courses in electronic engineering or computer science, and the research and engineering community will also find this book of interest.
Zhiyong Feng - One of the best experts on this subject based on the ideXlab platform.
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Priority-Based Dynamic Spectrum Management in a Smart Grid Network Environment
IEEE Journal on Selected Areas in Communications, 2015Co-Authors: Zhiyong Feng, T. Aaron Gulliver, Ping ZhangAbstract:The heterogeneous smart grid (SG) poses two major challenges for wireless networks, namely, providing sufficient bandwidth for a wide variety of applications and high reliability for critical real-time applications. To address these challenges, the impact of communication outage on the demand response management as a typical SG application is analyzed in this paper. A dynamic Spectrum management (DSM) technique is proposed to allocate resources, considering the QoS and application priorities. Vacant digital TV frequency bands are utilized to support SG applications. An algorithm to estimate the SG capacity is introduced, which can be applied to various user distributions and SG environments. This is used in conjunction with a low-complexity coloring theory algorithm to allocate the Spectrum. The results presented show that DSM provides better performance than traditional fixed Spectrum management, in terms of QoS and Secondary Spectrum utilization.
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a novel approach to reduce the storage amount and load of geolocation database
Vehicular Technology Conference, 2013Co-Authors: Xiao Jin, Zhiyong Feng, Qixun Zhang, Yifan Zhang, Yinghua LiuAbstract:The Secondary usage of TV white spaces by cognitive devices is a widely concerned topic in recent years. Both the Federal Communications Commission (FCC) in USA and the Electronic Communications Committee (ECC) in Europe have proposed rules to enable the Secondary Spectrum access in TV white spaces by geolocation database method. Geolocation database in cognitive network maintains records of all authorized services in the TV frequency bands and has the capability of providing a list of available frequencies and power levels for each geographical pixel based on the interference protection requirements. Since the data in geolocation database are defined for each geographical pixel, the complexity and cost of the database is highly correlate with the size of the pixel. In this paper, a novel method to reduce the complexity and cost is proposed and explained, which compress some compressible geographic pixels and use non-uniform dimensions of pixels in populating the database. With simulation and performance evaluations, we concluded that this method can significantly reduce the computational complexity and implement cost of geolocation database.
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dynamic Spectrum management for wcdma dvb heterogeneous systems
IEEE Transactions on Wireless Communications, 2011Co-Authors: Zhiyong Feng, T.a. GulliverAbstract:This paper proposes a novel Dynamic Spectrum Management (DSM) scheme for Wideband Code Division Multiple Access (WCDMA) / Digital Video Broadcasting (DVB) heterogeneous systems. Capacity estimation algorithms for both WCDMA and DVB are developed which consider both the user distribution and characteristics of the hybrid services. Based on these algorithms, a new dynamic Spectrum allocation scheme is presented which allows for optimum allocation of resources and maximum Secondary Spectrum usage. Coloring theory is used to significantly reduce DSM complexity while providing near-optimal performance. Numerical results are given which show that the proposed DSM scheme has better performance than Fixed Spectrum Management (FSM).
R Chandramouli - One of the best experts on this subject based on the ideXlab platform.
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reliable multimedia transmission over cognitive radio networks using fountain codes
Proceedings of the IEEE, 2008Co-Authors: Harikeshwar Kushwaha, Yiping Xing, R Chandramouli, H HeffesAbstract:With the explosive growth of wireless multimedia applications over the wireless Internet in recent years, the demand for radio spectral resources has increased significantly. In order to meet the quality of service, delay, and large bandwidth requirements, various techniques such as source and channel coding, distributed streaming, multicast etc. have been considered. In this paper, we propose a technique for distributed multimedia transmission over the Secondary user network, which makes use of opportunistic Spectrum access with the help of cognitive radios. We use digital fountain codes to distribute the multimedia content over unused Spectrum and also to compensate for the loss incurred due to primary user interference. Primary user traffic is modelled as a Poisson process. We develop the techniques to select appropriate channels and study the trade-offs between link reliability, spectral efficiency and coding overhead. Simulation results are presented for the Secondary Spectrum access model.
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dynamic Spectrum access with qos and interference temperature constraints
IEEE Transactions on Mobile Computing, 2007Co-Authors: Yiping Xing, R Chandramouli, Chetan Nanjunda Mathur, M A Haleem, K P SubbalakshmiAbstract:Spectrum is one of the most precious radio resources. With the increasing demand for wireless communication, efficiently using the Spectrum resource has become an essential issue. With the Federal Communications Commission's (FCC) Spectrum policy reform, Secondary Spectrum sharing has gained increasing interest. One of the policy reforms introduces the concept of an interference temperature - the total allowable interference in a spectral band. This means that Secondary users can use different transmit powers as long as the sum of these power is less than the interference threshold. In this paper, we study two problems in Secondary Spectrum access with minimum signal to interference noise ratio (quality of service (QoS)) guarantee under an interference temperature constraint. First, when all the Secondary links can be supported, a nonlinear optimization problem with the objective to maximize the total transmitting rate of the Secondary users is formulated. The nonlinear optimization is solved efficiently using geometric programming techniques. The second problem we address is, when not all the Secondary links can be supported with their QoS requirement, it is desirable to have the Spectrum access opportunity proportional to the user priority if they belong to different priority classes. In this context, we formulate an operator problem which takes the priority issues into consideration. To solve this problem, first, we propose a centralized reduced complexity search algorithm to find the optimal solution. Then, in order to solve this problem distributively, we define a Secondary Spectrum sharing potential game. The Nash equilibria of this potential game are investigated. The efficiency of the Nash equilibria solutions are characterized. It is shown that distributed sequential play and an algorithm based on stochastic learning attain the equilibrium solutions. Finally, the performances are examined through simulations
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priority based dynamic Spectrum access with qos and interference temperature constraints
International Conference on Communications, 2006Co-Authors: Yiping Xing, R Chandramouli, Chetan Nanjunda Mathur, M A Haleem, K P SubbalakshmiAbstract:We study the problem of dynamic Spectrum access by Secondary users with minimum signal to interference noise ratio (quality of service (QoS)) and interference temperature constraints. A non-linear optimization problem with the objective to maximize the total transmitting rate of the Secondary users is formulated. The non-linear optimization is solved efficiently using geometric programming techniques. When not all the Secondary links can be supported with their QoS requirement, a reduced complexity search algorithm is introduced to find the optimal subset of allowable links. Secondary users may belong to different priority classes. Accessing opportunities should be proportional to priorities. Therefore, we defined a Secondary Spectrum sharing potential game which takes these priority classes into consideration. The Nash equilibria of this potential game are reached by distributed sequential play. The efficiency of the Nash equilibria solutions are characterized. Finally, the performances of both the reduced complexity algorithm and the sequential play are examined through simulations.
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qos constrained Secondary Spectrum sharing
First IEEE International Symposium on New Frontiers in Dynamic Spectrum Access Networks 2005. DySPAN 2005., 2005Co-Authors: Y Xing, R ChandramouliAbstract:Spectrum is one of the most precious radio resource. With the increasing demand for wireless communication, efficiently using the Spectrum resource has become an essential issue. With the Federal Communications Commission's (FCC) Spectrum policy reform, Secondary Spectrum sharing has become a viable option. One of the policy reforms introduces the concept of an interference temperature-the total allowable interference in a spectral band. This means that Secondary users can use different transmit powers as long as the sum of these power is less than the interference threshold. In this paper, we study the quality of service (QoS) issue in Secondary Spectrum sharing subject to an interference temperature constraint. A non-linear optimization problem with the objective to maximize the total transmitting rate of the Secondary users is formulated. The non-linear optimization is solved efficiently using geometric programming techniques. We also propose a joint coordination and power control (JCPC) algorithm with the objective to maximize the Secondary system capacity. JCPC is a distributed algorithm and requires only local feedback information. This algorithm is proved to converge to the Nash equilibrium solution
