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[우수논문] Queuing Analysis for Overlay/Underlay Spectrum Access in Cognitive Radio Networks
Cuong T. Do,Choong Seon Hong 한국정보과학회 2012 한국정보과학회 학술발표논문집 Vol.39 No.1D
In this paper, we present theoretical queuing analysis for hybrid overlay/underlay Cognitive Radio (CR) system by applying M/M/1 queuing model where the rate of arrival and the service capacity are subject to Poisson alterations. Numerical results are used to prove a high degree of accuracy for the derived expressions. The result can be used as a benchmark to evaluate the performance of a hybrid overlay/underlay CR system.
Optimal Pricing for Duopoly in Cognitive Radio Networks: Cooperate or not Cooperate?
Do, Cuong T.,Tran, Nguyen H.,Zhu Han,Long Bao Le,Sungwon Lee,Choong Seon Hong IEEE 2014 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.13 No.5
<P>Pricing is an effective approach for spectrum access control in cognitive radio (CR) networks. In this paper, we study the pricing effect on the equilibrium behaviors of selfish secondary users' (SUs') data packets which are served by a CR base station (BS). From the SUs' point of view, a spectrum access decision on whether to join the queue of the BS or not is characterized through an individual optimal strategy that is joining the queue with a joining probability. This strategy also requires each SU to know the average queueing delay, which is a non-trivial problem. Toward this end, we provide queueing delay analysis by using the M/G/1 queue with breakdown. From the BS's point of view, we consider a duopoly market based on the two paradigms: the opportunistic dynamic spectrum access (O-DSA) and the mixed O-DSA & dedicated dynamic spectrum access (D-DSA). In the first paradigm, two co-located opportunistic-spectrum BSs utilize freely spectrum-holes to serve SUs. Then, we show the advantages of the cooperative scenario due to the unique solution that can be obtained in a distributed manner by using the dual decomposition algorithms. For the second paradigm, there are one opportunistic-spectrum BS and one dedicated-spectrum BS. We study a price competition between two BSs as a Stackelberg game. The cooperative behavior between two BSs is modeled as a bargaining game. In both paradigms, bargain revenues of the cooperation are always higher than those due to competition in both cases. Extensive numerical analysis is used to validate our derivation.</P>
T. Thuy Hoang,Minkyu Park,Do Duc Cuong,S. H. Rhim,S. C. Hong 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
Recently, a combined experimental and theoretical study has shown that anomalous Hall conductivity (AHC) can be tailored via tuning Berry curvature regardless of magnetization, which may pave a new way to achieve large AHC without net magnetic moment. For instance, non-negligible AHC of 330(133) Ω<SUP>-1</SUP>cm<SUP>-1</SUP> and 300 Ω<SUP>-1</SUP>cm<SUP>-1</SUP> were predicted in non-collinear antiferromagnetic and compensated ferrimagnetic Heusler compounds Mn₃Ge (Sn) and Ti₂MnAl. In this work, using the PAW and FLAPW methods implemented in VASP and Fleur codes, AHC of a ferrimagnet quaternary Heusler compounds TiZrMnAl (F43m) is studied. Among three possible structural phases (Fig. 1), α-phase is energetically most stable, by energy differences of 0.34 eV/fu and 0.03 eV/fu compared to β- and γ-phase. The local magnetic moment of Mn is antialigned with those of Ti and Zr. As a result, total magnetic moment is fully compensated (mt = 0.0 μB) in α- and β-phase, and nearly compensated (mt = 0.1 μB) in γ-phase. Interestingly, α-phase possesses a large AHC of 1470 Ω<SUP>-1</SUP>cm<SUP>-1</SUP>, while β- and γ-phase show moderate AHC of 200 and 100 Ω<SUP>-1</SUP>cm<SUP>-1</SUP>, consistently in both the PAW and FLAPW methods. The large AHC in α-phase stems from the direct gapless band along the symmetry line LM, which shows a gigantic Berry curvature and nontrivial topology with non-zero Chern number x = ±1. 〈그림 본문참조〉