• Journal of Communications and Networks
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• v.18 no.1
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• pp.95-104
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• 2016

Massive multiple-input multiple-output (MIMO) is a promising approach for cellular communication due to its energy efficiency and high achievable data rate. These advantages, however, can be realized only when channel state information (CSI) is available at the transmitter. Since there are many antennas, CSI is too large to feed back without compression. To compress CSI, prior work has applied compressive sensing (CS) techniques and the fact that CSI can be sparsified. The adopted sparsifying bases fail, however, to reflect the spatial correlation and channel conditions or to be feasible in practice. In this paper, we propose a new sparsifying basis that reflects the long-term characteristics of the channel, and needs no change as long as the spatial correlation model does not change. We propose a new reconstruction algorithm for CS, and also suggest dimensionality reduction as a compression method. To feed back compressed CSI in practice, we propose a new codebook for the compressed channel quantization assuming no other-cell interference. Numerical results confirm that the proposed channel feedback mechanisms show better performance in point-to-point (single-user) and point-to-multi-point (multi-user) scenarios.

• Industrial Engineering and Management Systems
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• v.9 no.2
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• pp.97-106
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• 2010

Can eBay.com's fee structure coordinate the channel? It's a critical strategic problem in e-commerce operations and an interesting research hypothesis as well. eBay's fees include three parts: monthly subscription fee, insertion fee, and final value fee (i.e., a revenue sharing portion), which represent a generic form of revenue sharing fee structure between the retailer and the vendor in a supply chain. This research deals with such a channel consisting of a price-setting vendor who sells products through eBay's marketplace exclusively to the end customers. The up- and down-stream channel relationship is consignment-based revenue sharing. We use a game-theoretic approach with assumption of the retailer (i.e., eBay.com) being a Stackelberg-leader and the vendor being a follower. The Stackelberg-leader decides on the terms of revenue sharing contract (i.e., fee structure), and the follower (vendor) decides on how many units to sell and the items' selling price. This study formulates several profit-maximization models by considering the effects of the retail price on the demand function. Under such settings, we show that eBay's fee structure can improve the channel efficiency; yet it cannot coordinate the channel optimally.

• Journal of information and communication convergence engineering
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• v.16 no.2
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• pp.72-77
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• 2018

This paper presents a novel channel capacity maximization method for a distorted $2{\times}2$ line-of-sight (LOS) multiple-input multiple-output (MIMO) link. A LOS MIMO link may be distorted by the influence of environmental factors such that the channel capacity of the LOS MIMO link may be degraded. By using the proposed method, the channel capacity of a distorted $2{\times}2$ LOS MIMO link can be the same as that of the ideal $2{\times}2$ LOS MIMO link. The proposed method employs an additional receiver antenna to maximize the channel capacity. In contrast to a $3{\times}2$ LOS MIMO link, a receiver circuit for a third receiving antenna is not necessary. Hence, the receiver for the proposed method is much simpler than that for a $3{\times}2$ LOS MIMO link. We determine the optimal position of the additional receiver antenna analytically. Simulation results show that the channel capacity can approach the ideal using the proposed method.

• Journal of Distribution Science
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• v.20 no.2
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• pp.19-29
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• 2022

Purpose: Understanding the distribution channel is a foundational element of successful hotel revenue management. This study aims to assess hotel distribution network partnerships and develops a model that can be utilized to ensure hoteliers are not becoming increasingly reliant on a single channel, optimize their market exposure, and maximize their portion of the overall worth of the network. Research design, data and methodology: This study utilizes a grounded theory approach to form a theoretical model by analyzing and examining the current practice of hotel distribution management through interviews with 15 stakeholders in Indonesia, such as hoteliers, online travel agents, wholesalers, and connectivity managers. Results: Based on data analysis, we describe hotel distribution elements, revenue team, managed channels, and channel prioritization for a different type of hotel. Finally, we propose a distribution channel model that comprises hotel teams, customer types, indirect channels, and direct channels. Conclusions: The model contributes to the literature by exploring the options of distribution channels for various hotel types to support hotel revenue management practice. By utilizing our model, practitioners can have a complete picture regarding the strategic choice of the channel by considering their hotel capacity and market target.

• ETRI Journal
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• v.45 no.6
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• pp.952-962
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• 2023

In this study, a space-time transmission scheme is proposed to tackle the limitations of channel estimation with orthogonal pilot information in colocated multiple-input multiple-output systems with several transmitting and receiving antennas. Channel information is obtained using orthogonal pilots. Channel estimation introduces pilot heads required to estimate a channel. This leads to bandwidth insufficiency. As a result, trade-offs exist between the number of pilots required to estimate a channel versus spectral efficiency. The detection of data symbols is performed using the maximum likelihood decoding method as it provides a consistent approach to parameter estimation problems. The moment-generating function of the instantaneous signal-to-noise ratio is used to drive an approximate expression of the symbol error rate for the proposed scheme. Furthermore, the order of diversity is less by one than the number of receiver antennas used in the proposed scheme. The effect of the length of a pilot sequence on the proposed scheme's performance is also investigated.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.5
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• pp.8-14
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• 2008

There are two a approaches for the Cognitive Radio(CR) development. One is 'Full CR', which Joseph Mitola III proposed, and another is 'Spectrum CR', which is currently being standardized. The target approach of this paper is the latter and we develop a Cognitive Engine(CE) and simulated a channel set management(CSM), which is a core function of CE. The Channel set management evaluates channel quality and Incumbent User(IU) vacancy possibility and classifies the channel set, which is performed by using channel state history. Especially, a very important function for the channel set management is a channel state prediction and this paper proposed a Hidden Markov Model(HMM) based channel state prediction and a method for increasing performance. Also, we applied the proposed method into our simulator and simulated channel state prediction. Through the simulation, we verified as we applied our proposed scheme, the performance of channel state prediction gets better and through comparing with RS and SS, we verified the HMM based Channel state prediction is better.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.45-54
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• 2010

This paper studies the design of a multiuser multiple-input multiple-output (MIMO) system, where a base station (BS) transmits independent messages to multiple users. The remarkable "dirty paper coding (DPC)" result was first presented by Costa that the capacity does not change if the Gaussian interference is known at the transmitter noncausally. While several implementable DPC schemes have been proposed recently for single-user dirty-paper channels, DPC is still difficult to implement directly in practical multiuser MIMO channels. In this paper, we propose a network channel matrix triangulation (NMT) algorithm for utilizing interference known at the transmitter. The NMT algorithm decomposes a multiuser MIMO channel into a set of parallel, single-input single-output dirty-paper subchannels and then successively employs the DPC to each subchannel. This approach allows us to extend practical single-user DPC techniques to multiuser MIMO downlink cases. We present the sum rate analysis for the proposed scheme. Simulation results show that the proposed schemes approach the sum rate capacity of the multiuser MIMO downlink at moderate signal-to-noise ratio (SNR) values.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.12
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• pp.5820-5834
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• 2017

This paper investigates the channel selection problem with dynamic users and the asymmetric interference relation in distributed opportunistic spectrum access systems. Since users transmitting data are based on their traffic demands, they dynamically compete for the channel occupation. Moreover, the heterogeneous interference range leads to asymmetric interference relation. The dynamic users and asymmetric interference relation bring about new challenges such as dynamic random systems and poor fairness. In this article, we will focus on maximizing the tradeoff between the achievable utility and access cost of each user, formulate the channel selection problem as a directional graphical game and prove it as an exact potential game presenting at least one pure Nash equilibrium point. We show that the best NE point maximizes both the personal and system utility, and employ the stochastic learning approach algorithm for achieving the best NE point. Simulation results show that the algorithm converges, presents near-optimal performance and good fairness, and the directional graphical model improves the systems throughput performance in different asymmetric level systems.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.625-630
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• 2000

Numerical and experimental investigations are peformed for the rarefied gas flows in pumping channels of a helical-type drag pump. Modern turbomolecular pumps include a drag stage in the discharge side, operating roughly in $10^{-2}{\sim}10Torr$. The flow occurring in the pumping channel develops from the molecular transition to slip flow traveling downstream. Two different numerical methods are used in this analysis: the first one is a continuum approach in solving the Navier-Stokes equations with slip boundary conditions, and the second one is a stochastic particle approach through the use of the direct simulation Monte Carlo(DSMC) method. The flow in a pumping channel is three-dimensional(3D), and the main difficulty in modeling a 3D case comes from the rotating frame of reference. Thus, trajectories of particles are no longer straight lines. In the Present DSMC method, trajectories of particles are calculated by integrating a system of differential equations including the Coriolis and centrifugal forces. Our study is the first instance to analyze the rarefied gas flows in rotating frame in the presence of noninertial effects.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.5
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• pp.1976-1997
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• 2016

This paper investigates the problem of co-tier interference mitigation for dynamic small- cell networks, in which the load of each small-cell varies with the number of active associated small-cell users (SUs). Due to the fact that most small-cell base stations (SBSs) are deployed in an ad-hoc manner, the problem of reducing co-tier interference caused by dynamic loads in a distributed fashion is quite challenging. First, we propose a new distributed channel allocation method for small-cells with dynamic loads and define a dynamic interference graph. Based on this approach, we formulate the problem as a dynamic interference graph game and prove that the game is a potential game and has at least one pure strategy Nash equilibrium (NE) point. Moreover, we show that the best pure strategy NE point minimizes the expectation of the aggregate dynamic co-tier interference in the small-cell network. A distributed dynamic learning algorithm is then designed to achieve NE of the game, in which each SBS is unaware of the probability distributions of its own and other SBSs' dynamic loads. Simulation results show that the proposed approach can mitigate dynamic co-tier interference effectively and significantly outperform random channel selection.