• Journal of Broadcast Engineering
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• v.23 no.1
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• pp.154-161
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• 2018

As the number of smartphone users increases, research on indoor location recognition service is necessary. Access to indoor locations is predominantly WiFi, Bluetooth, etc., but in most quarters, WiFi is equipped with WiFi functionality, which uses WiFi features to provide WiFi functionality. The study uses the random forest algorithm, which employs the fingerprint index of the acquired WiFi and the use of the multI-value classification method, which employs the receiver signal strength of the acquired WiFi. As the data of the fingerprint, a total of 4 radio maps using the Mac address together with the received signal strength were used. The experiment was conducted in a limited indoor space and compared to an indoor location recognition system using an existing random forest, similar to the method proposed in this study for experimental analysis. Experiments have shown that the system's positioning accuracy as suggested by this study is approximately 5.8 % higher than that of a conventional indoor location recognition system using a random forest, and that its location recognition speed is consistent and faster than that of a study.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.153-155
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• 2010

Internet phone (VoIP) services in Korea have achieved noticeable growth year after year since the service launching, and the growth still coninues. The market of mobile internet phone also expands sharply. Therefore, it is crucial to deploy networks which can support mobile internet phone services with excellent quality. For mobile internet phone services, it will be necessary to build and use networks with good mobility and high transmission rate. Current wireless networks for Internet services include 3G, Wi-Fi, and mobile WiMAX networks. 3G provides good mobility but lower transmission rate, whereas Wi-Fi exhibits excellent transmission rate but less mobility. Mobile WiMAX networks taking the merits of both, high mobility and transmission rate, are being deployed widely in recent years. This article examines the recent standardization efforts of WiMAX Forum for VoIP service in WiMAX networks.

• Investigative Magnetic Resonance Imaging
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• v.25 no.2
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• pp.118-128
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• 2021

Purpose: To investigate the value of MR textural analysis, including use of diffusion-weighted imaging (DWI) to differentiate malignant from benign soft-tissue tumors on 3T MRI. Materials and Methods: We enrolled 69 patients (25 men, 44 women, ages 18 to 84 years) with pathologically confirmed soft-tissue tumors (29 benign, 40 malignant) who underwent pre-treatment 3T-MRI. We calculated MR texture, including mean, standard deviation (SD), skewness, kurtosis, mean of positive pixels (MPP), and entropy, according to different spatial-scale factors (SSF, 0, 2, 4, 6) on axial T1- and T2-weighted images (T1WI, T2WI), contrast-enhanced T1WI (CE-T1WI), high b-value DWI (800 sec/mm²), and apparent diffusion coefficient (ADC) map. We used the Mann-Whitney U test, logistic regression, and area under the receiver operating characteristic curve (AUC) for statistical analysis. Results: Malignant soft-tissue tumors had significantly lower mean values of DWI, ADC, T2WI and CE-T1WI, MPP of ADC, and CE-T1WI, but significantly higher kurtosis of DWI, T1WI, and CE-T1WI, and entropy of DWI, ADC, and T2WI than did benign tumors (P < 0.050). In multivariate logistic regression, the mean ADC value (SSF, 6) and kurtosis of CE-T1WI (SSF, 4) were independently associated with malignancy (P ≤ 0.009). A multivariate model of MR features worked well for diagnosis of malignant soft-tissue tumors (AUC, 0.909). Conclusion: Accurate diagnosis could be obtained using MR textural analysis with DWI and CE-T1WI in differentiating benign from malignant soft-tissue tumors.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6B
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• pp.334-341
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• 2007

A Mobile IP is considered for the efficient mobility function in IEEE 802.16/WiBro environment. However, during the deployment of WiBro, only some of the ACRs(Access Control Router) can support the Mobile IP function. Therefore, a WiBro network can not support the mobility function for the mobile node. In this paper, we implement an overlay-based Mobile IP function and measure the performance through a field trial. Moreover, we evaluate the possibility of commercial deployment and suggest areas that need to be improved.

• 전자공학회논문지 IE
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• v.47 no.4
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• pp.48-52
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• 2010

Recently, WiBro service as a mobile internet has been being extended. The market of wireless data communication has been being extended rapidly due to the increase of mobile data communication service supply such as smart-phone, WiBro service and so on. As the result, security is also emphasized in the mobile Internet In this paper, we propose the methods that tighten up security in the upcoming Enterprise Mobile-VPN service on WiBro network.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.51-56
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• 2011

WiBro network technologies developed mainly by Korea are one of very promising 4G technologies. WiBro has been standardized as international standard called Mobile WiMAX, and has been deployed in many countries. Emergency Services in WiBro networks are infrastructure services and will be very essential to induce subscribers from other types of networks. This paper proposes a network architecture for supporting emergency services for WiBro mobile VoIP networks. The proposed architecture is based on WMF's architecture for international compatibilities, and reflects national considerations on interfacing PSAP for domestic compatibilities.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.341-349
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• 2010

In this paper, we studied on the optimization of the output power of Mobile WiMAX (IEEE 802.16) base station considering the technical condition of base station and wireless channel condition. The optimum power of base station can be estimated based on the link budget calculation of downlink and uplink in the Mobile WiMAX communication system. We investigated the optimum output power of base station in the case of 2Tx-2Rx base station with $2{\times}2$ MIMO(multiple input multiple output) technology, 2Tx-4Rx base station with improved receiver sensitivity, and 4Tx-4Rx base station with beamforming technology.

• Journal of the Korea Society of Computer and Information
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• v.14 no.11
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• pp.233-245
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• 2009

The number of subscribers and the level of service usage are moderately low though WiBro service, as a new mobile Internet service, has been provided to mobile Internet users since June 2006. Considering this situation, the study was to identify, in exploratory point of view, which critical success factors are considered by mobile Internet users as the most important one to facilitate WiBro service, and to examine the perception of critical success factors of WiBro service varies according to their demographic characteristics. The study also was to suggest a few of research propositions on the relationships between critical success factors of WiBro service and characteristics of mobile Internet users, based on various statistical analyses. To accomplish these research purposes, the study defined research variables such as demographic characteristic of mobile Internet users, types of user, and critical success factors of WiBro service based on the review of mobile Internet service related studies. And then, the study performed various statistical analyses using survey questionnaires on mobile Internet users. The analyses show that there are little differences in perception on critical success factors of WiBro service among the mobile Internet users grouped by job and residential region, and that only the relationship between occupation of mobile Internet users and critical success factors of WiBro service is moderated by the types of user. Finally, the study proposed some research propositions, based on these analysis results, that could be used in the future studies.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.233-236
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• 2008

There are several kinds of service standards for 3G($3^{rd}$-Generation) wireless communication as WCDMA, CDMA2000 and WiBro(Wireless Broadband Internet). Especially WiBro Wave2 system is a marked currnt issue. In this paper, we describe on the cell plan tool to desgin WiBro Wave2 network. For this, we treat from basic theory to practical substance to produce new(or modified) path loss prediction model for 2.3GHz. And we explain the method how to implement new technology MIMO(Multiple Input Multiple Output) deployed in Wave2 system. Also we emphasize on the importance of LOS(Line Of Sight) analysis in WiBro network design.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.11
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• pp.2218-2229
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• 2015

Recently Wi-Fi Alliance defined Wi-Fi direct, which can communicate through a direct connection between the mobile device anytime, anywhere. In Wi-Fi direct, all devices are categorized by group of owner (GO) and client. Since portability is emphasized in Wi-Fi direct devices, it is essential to control the energy consumption of a device very efficiently. In order to avoid unnecessary power consumed by GO, Wi-Fi direct standard defines two power management schemes: Opportunistic power saving scheme and Notice Of Absence (NOA) scheme. But, these two schemes do not consider the traffic pattern, so we cannot expect high energy efficiency. In this paper, we suggest an algorithm to enhance the energy efficiency of Wi-Fi direct power saving, considering the characteristics of multimedia video traffic. Proposed algorithm utilizes the statistical distribution for the size of video frames and adjusts the length of awake interval dynamically. Also, considering the inter-dependency among video frames, the proposed algorithm assigns priorities to video frames and ensures that a video frame with high priority is transmitted with higher probability than other frames with low priority. Simulation results shows that the proposed method outperforms the traditional NOA in terms with average delay and energy efficiency.