• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.11
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• pp.5370-5393
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• 2019

In this paper, we consider a two-way relay non-orthogonal multiple access (TWR-NOMA) system with residual hardware impairments (RHIs) and channel estimation errors (CEEs), where two group users exchange their information via the decode-and-forward (DF) relay by using NOMA protocol. To evaluate the performance of the considered system, exact analytical expressions for the outage probability of the two groups users are derived in closed-form. Moreover, the asymptotic outage behavior in the high signal-to-noise ratio (SNR) regime is examined and the diversity order is derived and discussed. Numerical simulation results verify the accuracy of theoretical analyses, and show that: i) RHIs and CEEs have a deleterious effects on the outage probabilities; ii) CEEs have significant effects on the performance of the near user; iii) Due to the RHIs, CEEs, inter-group interference and intra-group interference, there exists error floors for the outage probability.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.3
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• pp.1363-1376
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• 2020

An improved clustering scheme based on user group is proposed. Every two users are grouped among N-users in the allowed system according to their link gain from large to small. Each user group is numbered sequentially. Two user clusters are obtained according to the principle of maximizing link gain difference for the users in the first and last user groups. The remaining user groups are added to the two existing user clusters according to the parity of the group number. The clustering should be clustered again among the users in either user cluster if the throughput summation of a user cluster in NOMA is less than that of these users in orthogonal multiple access. The simulation results show that the proposed clustering scheme can increase the system throughput by about 8% compared with the hybrid clustering scheme when the number of users requiring service is 12.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.9
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• pp.4295-4316
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• 2018

In this paper, the performance of non-orthogonal multiple access (NOMA) dual-hop (DH) amplify-and-forward (AF) relaying networks is investigated, where Nakagami-m fading channel is considered. In order to cover more details, in our analysis, the transceiver hardware impairments at source, relay and destination nodes are comprehensively considered. To characterize the effects of hardware impairments brought in NOMA DH AF relaying networks, the analytical closed-form expressions for the exact outage probability and approximate ergodic sum rate are derived. In addition, the asymptotic analysis of the outage probability and ergodic sum rate at high signal-to-noise ratio (SNR) regime are carried out in order to further reveal the insights of the parameters for hardware impairments on the network performance. Simulation results indicate the performance of asymptotic ergodic sum rate are limited by levels of distortion noise.

• ETRI Journal
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• v.41 no.5
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• pp.626-636
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• 2019

A novel algorithm for joint user selection and optimal power allocation for Stackelberg game-based revenue maximization in a downlink non-orthogonal multiple access (NOMA) network is proposed in this study. The condition for the existence of optimal solution is derived by assuming perfect channel state information (CSI) at the transmitter. The Lagrange multiplier method is used to convert the revenue maximization problem into a set of quadratic equations that are reduced to a regular chain of expressions. The optimal solution is obtained via a univariate iterative procedure. A simple algorithm for joint optimal user selection and power calculation is presented and exhibits extremely low complexity. Furthermore, an outage analysis is presented to evaluate the performance degradation when perfect CSI is not available. The simulation results indicate that at 5-dB signal-to-noise ratio (SNR), revenue of the base station improves by at least 15.2% for the proposed algorithm when compared to suboptimal schemes. Other performance metrics of NOMA, such as individual user-rates, fairness index, and outage probability, approach near-optimal values at moderate to high SNRs.

• ETRI Journal
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• v.45 no.5
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• pp.874-886
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• 2023

A joint resource-optimization scheme is investigated for nonorthogonal multiple access (NOMA)-enhanced scalable video coding (SVC) multicast in unmanned aerial vehicle (UAV)-assisted radio-access networks (RANs). This scheme allows a ground base station and UAVs to simultaneously multicast successive video layers in SVC with successive interference cancellation in NOMA. A video quality-maximization problem is formulated as a mixed-integer nonlinear programming problem to determine the UAV deployment and association, RAN spectrum allocation for multicast groups, and UAV transmit power. The optimization problem is decoupled into the UAV deployment-association, spectrum-partition, and UAV transmit-power-control subproblems. A heuristic strategy is designed to determine the UAV deployment and association patterns. An upgraded knapsack algorithm is developed to solve spectrum partition, followed by fast UAV power fine-tuning to further boost the performance. The simulation results confirm that the proposed scheme improves the average peak signal-to-noise ratio, aggregate videoreception rate, and spectrum utilization over various baselines.

• The Magazine of the IEIE
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• v.41 no.12
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• pp.24-32
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• 2014

• 순환기질환의공학회:학술대회논문집
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• 2003.11a
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• pp.10-11
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• 2003

• 순환기질환의공학회:학술대회논문집
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• 2003.11a
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• pp.12-13
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• 2003

• Journal of Chest Surgery
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• v.37 no.12
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• pp.1036-1039
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• 2004

Most tumors of the tracheobronchial tree are malignant, and benign tumors are less than 10%. Especially, the incidence of primary neurogenic tumors of the lung has been estimated to be less than 2 percent of primary lung cancer, and majority of these tumors are originated from Schwann cells. These tumors can be presented either as a solitary benign neoplasm or as a malignant form, which is rare. We present two cases of bronchial Schwan noma managed by means of lobectomy.

• Bulletin of the Korean Mathematical Society
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• v.54 no.4
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• pp.1323-1330
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• 2017

For a nondegenerate projective irreducible variety $X{\subset}{\mathbb{P}}^r$, it is a natural problem to find an upper bound for the value of $${\ell}_{\beta}(X)=max\{length(X{\cap}L){\mid}L={\mathbb{P}}^{\beta}{\subset}{\mathbb{P}}^r,\;{\dim}(X{\cap}L)=0\}$$ for each $1{\leq}{\beta}{\leq}e$. When X is locally Cohen-Macaulay, A. Noma in [10] proves that ${\ell}_{\beta}(X)$ is at most $d-e+{\beta}$ where d and e are respectively the degree and the codimension of X. In this paper, we construct some surfaces $S{\subset}{\mathbb{P}}^5$ of degree $d{\in}\{7,{\ldots},12\}$ which satisfies the inequality $${\ell}_2(S){\geq}d-3+{\lfloor}{\frac{d}{2}}{\rfloor}$$. This shows that Noma's bound is no more valid for locally non-Cohen-Macaulay varieties.