• Journal of Communications and Networks
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• v.11 no.5
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• pp.489-499
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• 2009

We describe the fundamental issue of scheduling the allocation of wireless network resources and provide several formulations of the associated problems. The emphasis is on scheduling transmission attempts. We place this problem in the context of existing approaches, like information theoretic and traditional network theoretic ones, as well as novel avenues that open up the possibility of addressing this issue for non-stationary and non-ergodic environments. We summarize concrete recent results for specific special cases that include unicast and multicast traffic, different objective functions, and reduced complexity versions of the problem. We conclude with some thoughts for future work. We identify and single out the cross-layer nature of the problem and include a simple physical-layer criterion in what is mostly a medium access control (MAC) problem.

• Journal of Communications and Networks
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• v.11 no.4
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• pp.384-389
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• 2009

Optical wireless communication (OWC) systems are rapidly gaining popularity as effective means of transferring data at high rates over short distances. OWC facilitates rapidly deployable, lightweight, high-capacity communication without licensing fees and tariffs. Nevertheless, the performance of this new technology depends strongly on the atmospheric conditions and the characteristics of the link. In this work, we study the influence of these parameters on both the average (ergodic) capacity and the outage capacity of an OWC system over moderate to strong turbulence channels modeled by gamma-gamma distribution. Moreover, we compare the results that we obtain estimating the average and outage capacities.

• Journal of Communications and Networks
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• v.15 no.4
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• pp.398-406
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• 2013

In this paper, we investigate two types of in-phase and quadrature-phase (IQ) data transfer methods for cloud multiple-input multiple-output (MIMO) network operation. They are termed "after-precoding" and "before-precoding". We formulate a cloud massive MIMO operation problem that aims at selecting the best IQ data transfer method and transmission strategy (beamforming technique, the number of concurrently receiving users, the number of used antennas for transmission) to maximize the ergodic sum-rate under a limited capacity of the digital unit-radio unit link. Based on our proposed solution, the optimal numbers of users and antennas are simultaneously chosen. Numerical results confirm that the sum-rate gain is greater when adaptive "after/before-precoding" method is available than when only conventional "after-precoding" IQ-data transfer is available.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.10
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• pp.901-913
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• 1991

Data compression has important application in the areas of file storage and distributed computer systems. The universal data compression achieves asymptotically optimum cimpression ratio for strings generated by any stationary ergodic source without a priori source probabilities.The paper describes the principle and the recent research trends on universal data compression. And its applications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.6
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• pp.2893-2907
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• 2019

Wireless mobile communication systems in subway tunnels have been widely researched these years, due to increased demand for the communication applications. As a result, an accurate model is essential to effectively evaluate the communication system performance. Thus, a neoteric three-dimensional (3D) geometry-based stochastic model (GBSM) is proposed for the massive multiple-input multiple-output (MIMO) fading channels in tunnel environment. Furthermore, the statistical properties of the channel such as space-time correlation, amplitude and phase probability density are analyzed and compared with those of the traditional two-dimensional (2D) model by numerical simulations. Finally, the ergodic capacity is investigated based on the proposed model. Numerical results show that the proposed model can describe the channel in tunnels more practically.

• ETRI Journal
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• v.43 no.4
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• pp.758-768
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• 2021

In this work, the secrecy of a typical wireless cooperative dual-hop non-orthogonal multiple access (NOMA)-enabled decode-and-forward (DF) relay network is investigated with the impact of collaborative and non-collaborative eavesdropping. The system model consists of a source that broadcasts the multiplexed signal to two NOMA users via a DF relay, and information security against the eavesdropper nodes is provided by a helpful jammer. The performance metric is secrecy rate and ergodic secrecy capacity is approximated analytically. In addition, a differential evolution algorithm-based power allocation scheme is proposed to find the optimal power allocation factors for relay, jammer, and NOMA users by employing different jamming schemes. Furthermore, the secrecy rate analysis is validated at the NOMA users by adopting different jamming schemes such as without jamming (WJ) or conventional relaying, jamming (J), and with control jamming (CJ). Simulation results demonstrate the superiority of CJ over the J and WJ schemes. Finally, the proposed power allocation outperforms the fixed power allocation under all conditions considered in this work.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.1
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• pp.365-382
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• 2021

This paper proposes a novel two-way relaying (TWR) approach for a two-relay wireless network based on non-orthogonal multiple access (NOMA), where two terminals exchange messages with a cellular base station (BS) via two intermediate relay stations (RSs). We propose a NOMA-based TWR approach with two relaying schemes, i.e., amplify-and-forward (AF) and decode-and-forward (DF), referred to as NOMA-AF and NOMA-DF. The sum-rate performance of our proposed NOMA-AF and NOMA-DF is analyzed. A closed-form sum-rate upper bound for the NOMA-AF is obtained, and the exact ergodic sum-rate of NOMA-DF is also derived. The asymptotic sum-rate of NOMA-AF and NOMA-DF is also analyzed. Simulation results show that the proposed scheme outperforms conventional orthogonal multiple access based transmission schemes. It is also shown that increasing the transmit power budget of the relays only cannot always improve the sum-rates.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.8 no.3
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• pp.105-114
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• 1998

Maurer가 제안한 유니버설 통계적 검정을 소개하고 검정에 사용된 통계량의 의미를 분석한다. 기존 검정법을 포괄하는 이 검정법은 보다 넓은 의미의 통계적 결점들을 탐지해낼 수 있다. 또한, 검정에 사용되는 통계량은 엔트로피와 밀접한 연관이 있으며 암호학적 응용에서 시스템의 안전성에 영향을 키치는 요소들을 탐지해 낸다. 이러한 특징과 함께 기존 검정법 보다 상당히 긴 표본 수열을 필요로 한다는 사실이 유니버설 검정의 단점으로 지적되어 왔다. 그러나 본 논문에서는 빈도(freequency) 검정법과의 비교를 통해서 미세한 편의(bias)를 탐지해내기 위한 도구로서는 유니버설 검정이 오히려 더 효율적이라는 사실을 보였다.

• Journal of the Korean Mathematical Society
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• v.60 no.2
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• pp.255-271
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• 2023

In this paper, we deal with random attractors for dynamical systems forced by a deterministic noise. These kind of systems are modeled as skew products where the dynamics of the forcing process are described by the base transformation. Here, we consider skew products over the Bernoulli shift with the unit interval fiber. We study the geometric structure of maximal attractors, the orbit stability and stability of mixing of these skew products under random perturbations of the fiber maps. We show that there exists an open set U in the space of such skew products so that any skew product belonging to this set admits an attractor which is either a continuous invariant graph or a bony graph attractor. These skew products have negative fiber Lyapunov exponents and their fiber maps are non-uniformly contracting, hence the non-uniform contraction rates are measured by Lyapnnov exponents. Furthermore, each skew product of U admits an invariant ergodic measure whose support is contained in that attractor. Additionally, we show that the invariant measure for the perturbed system is continuous in the Hutchinson metric.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.10a
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• pp.536-538
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• 2022

Since the invention of a novel diversity technique, namely a space-time line code (STLC), though the previous studies have theoretically analyzed the error rate and ergodic capacity, the outage probability has not been revealed yet. In this paper, we characterize the probability density function of the instantaneous signal-to-noise ratio, and mathematically derive the closed-form expression of the outage probability. Based on numerical simulations, furthermore, we validate the accuracy of the mathematical analysis, and present the insight into the system design and implementation.