• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.5A
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• pp.450-456
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• 2011

In this paper, idle channel search schemes based on spectrum sensing are proposed for cognitive radio systems with multiple channels. Specifically, we propose a scheme for determining the order of sensing for multiple channels, for which the probability of each channel being idle is estimated every search interval. By performing sensing in the descending order of the probabilities, the time required for searching idle channels is expected to decrease. In addition, we combine the proposed scheme with a user grouping scheme to further improve the sensing performance. Simulation results show that the user grouping reduces the search time, although it degrades the reliability of detection. The proposed search scheme based on probability estimation of channel idleness is found to reduce the search time significantly as compared to the conventional random search scheme. We apply both the proposed search scheme and user grouping scheme to a cognitive radio system to validate the overall performance.

• Journal of Distribution Science
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• v.19 no.9
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• pp.19-27
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• 2021

Purpose: Purchasing food via online shopping channels is booming during Covid-19 Pandemic in Vietnam. However, the perceived risks of food bought via online shopping channels may discourage consumers. Hence, this study assesses the effects of perceived risks on food purchase intention via online shopping channels in Vietnam. Research design, data and methodology: This study applied the multiple regression analysis with 253 samples collected from consumers who frequently purchase food via online shopping channels in Vietnam. The questionnaire is provided to respondents via Google Form. The sample collection method is convenience sampling. Three hundred samples were collected, but 253 samples are used after filtering the responses with missing data. The Exploratory Factor Analysis (EFA) and regression analysis are used for data analysis on SPSS software version 20. Results: The results show that product risk, security risk, time risk, and fraud risk of the seller negatively affect the intention to buy food via online shopping channels in Vietnam. Conclusions: The study provides several implications and recommendations for food companies and online food sellers. Reducing customers' perceived risks online food makes customers more willing to buy food online during Covid-19 Pandemic. Limitations and suggestions for further research are also discussed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2C
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• pp.187-198
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• 2004

In this paper, we analyze the performance of BPM (Bi-Phase Modulation) UWB (Ultra Wide Band) multiple access system using PN (Pseudo Noise) code based time hopping sequence in indoor wireless channels. In particular, we compare BPM UWB multiple access system with PPM (Pulse Position Modulation) UWB multiple access system in terms of signalling and demodulation schemes. Moreover, we analytically evaluate the performance of these UWB systems by deriving the bit error rate expressions under the assumption that pulse energy and data transmission rate are identical for both systems. Simulation results in additive white Gaussian noise and realistic indoor multipath wireless channels show that the performance of BPM scheme is approximately 1 dB better than that of PPM scheme. However, the performance discrepancy becomes negligible as the number of users increases.

• The Research Journal of the Costume Culture
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• v.31 no.3
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• pp.361-378
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• 2023

This research not only determined the preference of fashion brand distribution channels of active Korean and Chinese seniors who became major consumers in the fashion industry, but also analyzed the effect on these preferences and choices of distribution channels depending on personal consumption characteristics and differences between the two groups. Data was collected by a professional survey firm. SPSS 24.0 and AMOS 24.0 were used for empirical analysis, and frequency analysis, multiple response analysis, EFA, reliability analysis, CFA, SEM, and multiple-group comparison analysis were performed. As a result of multiple response analysis, the offline channel was revealed as the preferred fashion distribution channel for active Korean and Chinese seniors; the second most popular was the online channel. The results of multiple-group comparison analysis reveal differences between two groups in seeking emotional consumption via the offline channel; the effect was only evident for active Korean seniors. A difference in seeking emotional consumption via preference for online channel also existed, but only for active Chinese seniors. For these reasons, marketers targeting active Korean seniors will be effective to not only offer brand information by fashion display to let seniors understand the fashion brand, but also to have brand events to form positive emotions toward the fashion brand. Moreover, targeting active Chinese seniors will be necessary to transmit brand sensibility by utilizing metaverse marketing comprising various factors, so that consumers can enjoy the fashion brand.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7B
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• pp.695-705
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• 2002

In this paper, we propose a simple open loop transmit diversity (TD) scheme for the wideband code division multiple access (W-CDMA) systems in Rician multipath fading channels such as rural area or satellite channels where line-of-sight (LOS) paths are in presence. The proposed scheme does not require any pre-processing of transmit data, resulting in simpler structure as compared to conventional closed loop transmit adaptive array (TxAA) and open loop space-time transmit diversity (STTD). We analytically derive the probability density function of signal-to-noise ratio at the Rake receiver output and the uncoded bit error rate performance of the proposed scheme. Extensive simulation is Performed to verify the analytical performance of the proposed scheme under typical Rician multipath fading channel environments. Moreover, comparative results with the conventional TxAA and STTD are also provided. Simulation results show that the proposed scheme shows slightly better performance than the conventional open loop STTD under the channels with very weak LOS components, however, it significantly outperforms the STTD under the channels with dominant LOS components, and achieves a close performance of ideal closed loop TxAA.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.1
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• pp.331-343
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• 2015

We propose a distributed medium access control protocol for cognitive radio networks to opportunistically utilize multiple channels. Under the proposed protocol, cognitive radio nodes forecast and rank channel availability observing primary users' activities on the channels for a period of time by time series analyzing using smoothing models for seasonal data by Winters' method. The proposed approach protects primary users, mitigates channel access delay, and increases network performance. We analyze the optimal time to sense channels to avoid conflict with the primary users. We simulate and compare the proposed protocol with the existing protocol. The results show that the proposed approach utilizes channels more efficiently.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5A
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• pp.651-659
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• 2000

In this paper, a computer simulation approach is proposed to analyze the performance of reverse traffic channels in a base station serving voice and data calls in CDMA cellular systems. It is assumed that multiple traffic channels simultaneously serve a data call and a voice call is served by one traffic channel in a base station. The numerical examples will be presented to derive the capacity of traffic channels from the parameters such as the arrival rates and mean durations of voice and data calls, the soft handoff area ratio, etc..

• Journal of Communications and Networks
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• v.11 no.5
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• pp.473-479
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• 2009

Conventional frequency domain equalization (FDE) schemes were originally devised for quasi-static channels. Thus, such equalization schemes could suffer from significant performance degradation in fast-fading channels. This paper proposes a frequency domain equalization algorithm to mitigate the effect of fast time-varying fading. First, a mathematical expression is derived to quantify the total interference resulting from the time variation of the channel. Then, the proposed approach attempts to eliminate the effect of time-variations of the channel. This cancellation allows efficient use of the classical FDE structures in fast time-varying fading environments, although they are built upon the quasi-static channel model. Simulation results of bit-error-rate performance are provided to demonstrate the effectiveness of the proposed algorithm.

• ETRI Journal
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• v.37 no.5
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• pp.906-916
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• 2015

High-speed I/O channels require adaptive techniques to optimize the settings for filter tap weights at decision feedback equalization (DFE) read channels to compensate for channel inter-symbol interference (ISI) and crosstalk from multiple adjacent channels. Both ISI and crosstalk tend to vary with channel length, process, and temperature variations. Individually optimizing parameters such as those just mentioned leads to suboptimal solutions. We propose a joint optimization technique for crosstalk cancellation (XTC) at DFE to compensate for both ISI and XTC in high-speed I/O channels. The technique is used to compensate for between 15.7 dB and 19.7 dB of channel loss combined with a variety of crosstalk strengths from $60mV_{p-p}$ to $180mV_{p-p}$ adaptively, where the transmit non-return-to-zero signal amplitude is a constant $500mV_{p-p}$.

• Asia pacific journal of information systems
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• v.29 no.2
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• pp.248-267
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• 2019

As merging online and offline channels into one single platform, individuals could easily and frequently switch between online and offline channels. In order for understanding such unique behaviors, this study attempts to explore why and how consumers choose their channels to search and purchase a product. We have drawn on multiple theories that have been used to explain individuals' judgment and decision making (i.e., construal level theory and regula-tory focus theory) in order to develop and tested two-way ANOVA based models of how both regulatory focus (e.g., promotion vs. prevention) and product types (e.g., experience goods vs. searching goods) including the psychological distance cue separately and jointly affect individuals' channel selection behavior (e.g., intention to use single channel vs. intention to use cross-channels). Our results have indicated that consumers with promotion-focus are more likely to use a single channel in experience goods rather than in searching goods when there exists the psychological cue. Based on our findings, the implication for both research and practice are discussed.