• Journal of Korea Society of Digital Industry and Information Management
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• v.8 no.4
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• pp.129-133
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• 2012

Coordinated multi-point transmission (CoMP) is a candidate technique for next generation cellular communications systems. One of the primary elements discussed in LTE-Advanced technology is CoMP, which can improve cell edge user data rate as well as spectral efficiency due to multiple input multiple output - orthogonal frequency division multiplex (MIMO-OFDM). We consider a system with multiple cells in which base stations coordinate with each other by sharing user channel state information (CSI), which mitigates inter cell interference (ICI), especially for users located at the cell edge. We introduce a new user scheduling method of ICI cancellation and the loss reduction of effective channel gain during the beamforming process, the proposed method improves the system sum rate, when compared to the conventional method by an average of 0.55bps/Hz in different number of total users per cell. It also outperforms the conventional method by approximately 0.38bps/Hz using different SNRs.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2008.10b
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• pp.634-642
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• 2008

Radio wave is the valuable resources in $21^{st}$ century. It will be widely used in various applications such as DMB, USN, telematics, and home network as well as mobile and wireless communications. Cognitive Radio technology is devised to maximize the utilization of radio resources by sensing near-by spectrum and dynamic and allocating free resources dynamically and adaptively. Wireless links for the secondary user need to be frequently switched to idle frequencies during the transmission of multimedia data in the cognitive radio based system. This may cause delay and information loss, and QoS degradations occur inevitably. The efficient frequency allocation scheme is necessary to support the seamless multimedia service to the secondary user while maintaining QoS of the primary user. This paper suggests a frequency selection scheme which considers other parameters such as cell load, data rate, and available bandwidth than just received signal strength during the frequency selection process. The performance of our proposed scheme is analyzed by simulation.

• The Journal of Information Systems
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• v.16 no.3
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• pp.133-159
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• 2007

The primary purpose of this study is to examine the effects of perceived characteristics on user satisfaction and continuous usage intention in personal communities. We developed a research model based on the literature reviews of personal communities, TAM, perceived risks, and satisfaction. The research model includes perceived playfulness, perceived ease of use, perceived usefulness, and perceived risk as perceived characteristics in personal communities. For validation of this theoretical model, we survey the users of 'Mini-hompy', one of the most popular personal communities in Korea. The research model was empirically verified by structural equation model analysis with data collected from 407 samples. Analysis of the results indicates that perceived ease of use is positively related perceived playfulness and perceived usefulness. Perceived playfulness, perceived ease of use, and perceived risks are significantly related to satisfaction. User's satisfaction has positive relationship with continuous usage intention in personal communities.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1B
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• pp.8-15
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• 2008

Cognitive radio technology enables to share the spectrum dedicated to primary users. In CR network, it is of primary concern to protect the primary users. Thus, it is required to periodically sense the spectrums occupied by primary users and adapt the communication parameters used by CR users to protect the primary users. However, it is inevitable to experience the hidden node problem due to the primary users, that are not detected by spectrum sensing. To perfectly protect the primary users, it is essential to address the hidden node problem in CR network. In this paper, we propose a new approach to handle the hidden node problem and evaluate the performance of proposed scheme.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.1
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• pp.145-150
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• 2010

In this paper, the performance of cognitive radio network is analyzed in terms of Erlang capacity. To improve the Erlang capacity with respect to primary user (PU) and secondary user (SU) traffic, we propose an efficient radio resource management scheme utilizing the buffer for new SUs and interrupted SUs. Markov model is developed, and analyzed to derive the performances of the proposed spectrum sharing scheme in both primary system and secondary system. To determine the Erlang capacity region, the blocking probability, the forced termination probability and the non-completion probability are calculated. Simulation results provide insight into the advantages of the buffer utilization. It is observed that the supportable traffic loads of PU and SU can be increased significantly according to the buffer length.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.2
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• pp.104-109
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• 2016

In this paper, a localization method for multiple robots based on Bayesian inference is proposed when multiple robots adopting multi-RAT (Radio Access Technology) communications exist in cognitive radio networks. Multiple robots are separately defined by primary and secondary users as in conventional mobile communications system. In addition, the heterogeneous spectrum environment is considered in this paper. To improve the performance of localization for multiple robots, a realistic multiple primary user distribution is explained by using the probabilistic graphical model, and then we introduce the Gibbs sampler strategy based on Bayesian inference. In addition, the secondary user selection minimizing the value of GDOP (Geometric Dilution of Precision) is also proposed in order to overcome the limitations of localization accuracy with Gibbs sampling. Via the simulation results, we can show that the proposed localization method based on GDOP enhances the accuracy of localization for multiple robots. Furthermore, it can also be verified from the simulation results that localization performance is significantly improved with increasing number of observation samples when the GDOP is considered.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.1
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• pp.37-44
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• 2016

It is important that using of efficient radio resource because of deficiency spectrum problem, so that related to this problem many researches are have proceeded. To solve this problem, Cognitive Radio(CR) was suggested. The channels are allocated to the secondary users when the primary users don't use the channels, and unfairness of secondary users can be serious problem and channel quality of multichannel can be different due to the different traffic pattern of primary users. In this paper, we propose MAC prtocol both of the user's fairness and channel quality in CR networks. Simulation results show the comparison with CR MAC protocols.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.6
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• pp.87-92
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• 2013

This paper focuses on analyzing the effects of primary user (PU) signal arrival on the local spectrum sensing performance. The probability for signal arrival at a sample in the sensing time is uniformly distributed in the sensing time. We first analyze the main factor that causes the degradation in the detection results in the conventional energy detection (CED) under the uniformly random arrival of the PU-signal. Thus we propose an approach in order to enhance the detection performance, in which an estimator which detects the arrival of the PU signal cooperates with a composite energy detection. The mathematical analysis and numerical simulation has validated the outperformance of the proposed approach compared to the CED.

• Journal of Information Technology Services
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• v.11 no.1
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• pp.15-37
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• 2012

This study is progressed for understanding of the acceptance intention differentiated through the view of smart phone non-user's adopting plan. And the research model is proposed in the view of new technology adopting, Innovation Diffusion Theory, Rogers 1995, and Technology Acceptance Model, Davis 1989. In the survey, SPSS 18.0 and AMOS 18.0 are used to analyze the 685 smart phone non-users data. The results of the feasibility analysis and the factor analysis show the measured variables determined in the statistical significant range. Also, 11 hypotheses, among the 16 hypotheses, are adopted by the hypothesis tests through the path analysis, one-way-ANOVA and hierarchial regression analysis. The results indicate variables affect on the non-smart phone user's adopting intention. The primary factor is the perceived usefulness, secondary factor is the social property, and the rest is the playfulness. And, the primary adoption factor is affected to early majority and late majority among each innovation adopters.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.206-209
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• 2014

Control message exchange is major job for cognitive radio to exist and use spectrum opportunistically. For this control message exchange they need a common control channel (CCC). Once this channel is affected by a primary user, communication stops until new CCC is setup. This takes substantial time and if they could not get free channel, this halt continues for long time. To prevent such cease of communication, we propose a combination of two networks, namely WLAN and UWB, to let the communication continue. In our proposed idea if the CCC of a certain CR in WLAN is affected, the CR changes its network from WLAN to UWB and keeps the communication because UWB cannot be affected by PU. In the proposed idea every cognitive radio has two transceivers; one for the overlay network (WLAN) and another UWB network. If a primary user is detected in the spectrum of a cognitive radio, it continues exchanging control messages under the UWB network and in parallel negotiates for a new CCC using the WLAN network. This idea solves the communication interruption until new CCC is setup.