• KIPS Transactions on Computer and Communication Systems
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• v.3 no.1
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• pp.7-14
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• 2014

The rapid increase of mobile devices such as smart phone and smart pad have raised the needs for seamless multimedia services during moving at anytime and anywhere. Current 4G mobile devices are equipped with both 4G (LTE) and WLAN (WiFi) interfaces, and mobile services operators provide wireless Internet services using 4G network with a wider coverage and WiFi zone. Generally users prefer to use the Internet services through WLAN rather than LTE in the coverage of WLAN. However, since WLAN has a long L2 handover latency, it is difficult to support seamless services during a handover. In this paper, we proposed an efficient handover scheme based on flow mobility for WLANs to support a seamless service during handovers by using the overlaid 4G network with a wider coverage. Also, we showed the outperformance of the proposed scheme on a testbed.

• 한국정보통신설비학회:학술대회논문집
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• 2009.08a
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• pp.99-103
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• 2009

Recently, as wired and wireless communication services have rapidly developed and multimodal mobile devices which have various characteristics have widely spread, the need for new convergence services increases. The growing population of VoIP technologies and the high communication expense yield that the market of IP based telephony such as WiFi phone and IP phone is substituted for one of the conventional PSTN telephony. With the help of this trend, the wireline network operators desire to find a market in mobile networks. Therefore, they focus on Fixed Mobile Convergence (FMC) service as one of the key factors to accomplish this goal. FMC services are able to provide the mobility of voice services between circuit switched and packet switched networks. IP Multimedia Subsystem (IMS) based Voice Call Continuity (VCC) is one of the schemes to embody FMC services. As Application Server (AS) which has this VCC function provides seamless handover of services between heterogeneous networks, FMC subscribers can communicate seamlessly with others m WiFi domain and COMA domain using WiFi-COMA dual phone. Most of enterprises have already introduced IP network infrastructure and IP-PBX (Private Branch eXchange) for telephony. However, the problems of high communication cost and work inefficiency due to frequent outside jobs or business trips have remained. In order to solve these problems, demands for enterprise FMC services increase. In this paper, we introduce a new IP-PBX based VCC model that can provide seamless handover of voice services between WiFi and COMA networks for enterprise users and we investigate some interworking and security issues between Soft Switch (SSW) and IMS, or between IMSs. In addition, we introduce a new service that can provide the continuity of voice sessions as well as video sessions using Multimedia Session Continuity (MMSC) technology which has evolved from VCC. This service is expected to be one of the next-generation personalized services based on user's context.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.6
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• pp.1-16
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• 2013

Smartphones and tablets including phone, calendar are the necessities of modern man. They are one of the MN(Mobile Node), each with wireless network capabilities. Necessities of modern human MNs are almost included cellular module available in LTE/3G and Wi-Fi module for high-speed Internet. Until now, MN mobility management is handled, but using network-based mobility management in this paper. Then, carriers can manage and maintain the network for low-cost. In addition, it was considered that use a lot of modern people with Wi-Fi and LTE/3G, and using Cross-Layer-Based handoff.

• Journal of Advanced Navigation Technology
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• v.15 no.2
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• pp.197-203
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• 2011

A triple-band antenna which can be used at GSM900, PCS1900 and Bluetooth(or Wi-Fi) frequency band is proposed. The proposed antenna is designed based upon switching between IFA(Inverted F Antenna) that has a resonant length of ${\lambda}/4$ and loop antenna that has a resonant length of ${\lambda}/2$. It can be applied to triple-band only by use of single printed pattern due to the switching characteristic. It is designed by use of the IFA for the application to the GSM900, while it is designed by use of the loop antenna for the application to the PCS1900 and by use of additional pattern of IFA for the application to the Bluetooth(or Wi-Fi) respectively. As a result, it has been observed that the proposed antenna satisfies the required return loss(${\leq}10dB$) and also has efficiency(${\geq}80%$) over the whole band. Moreover the proposed antenna has omni-directional radiation pattern which is suitable to apply to the mobile phone.

• Journal of Korean Society of Transportation
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• v.29 no.5
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• pp.33-42
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• 2011

As the scale of transfer center becomes gradually large, transfer information service considering convenience of users in motion in a large transfer center is required. This service provides moving users with information through individual portable terminals such as mobile phone or, smart phone which are capable of wireless communication. In particular, technology of measuring indoor location using Wi-Fi is in a stage of commercial practice and indoor/outdoor location-base transfer information service is possible through smart phones with built-in GPS and Wi-Fi. In this study, we suggest information services that support transfer activities based on the locations of visitors inside transfer centers. This study also suggests the logical and physical architectures, and physical components required for the flow of information as well as the target connected standardized information for connecting destinations of each proposed draft standards.

• Journal of Internet Computing and Services
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• v.17 no.3
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• pp.11-18
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• 2016

Accessing unauthorized rogue APs in WiFi environments is a very dangerous behavior which may lead WiFi users to be exposed to the various cyber attacks such as sniffing, phishing, and pharming attacks. Therefore, prompt and precise detection of rogue APs and properly alarming to the corresponding users has become one of most essential requirements for the WiFi security. This paper proposes a new rogue AP detection method which is mainly using the installation information of authorized APs and the DHCP snooping information of the corresponding switches. The proposed method detects rogue APs promptly and precisely, and notify in realtime to the corresponding users. Since the proposed method is simple and does not require any special devices, it is very cost-effective comparing to the wireless intrusion prevention systems which are normally based on a number of detection sensors and servers. And it is highly precise and prompt in rogue AP detection and flexible in deployment comparing to the existing rogue AP detection methods based on the timing information, location information, and white list information.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.4
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• pp.424-430
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• 2012

A ground radiation antenna is designed using a capacitor connected between two ground points by a strip line. This paper analyzes the variations of radiation performance when changing the capacitor position. The surface current distribution of the ground antenna was investigated as the capacitor position is changed, in order to demonstrate the effects on the impedance bandwidth and antenna efficiency. Our antenna is for the Wi-Fi application. It is verified that the capacitor at the end of the strip line provides a wide impedance bandwidth(7.2 % at the 2.45 GHz frequency) and good antenna efficiency(measured as 66 % averaged over the overall Wi-Fi frequency band).

• Journal of KIISE
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• v.42 no.2
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• pp.272-279
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• 2015

Concurrent with the more widespread usage of smart devices, mobile users' desires are becoming much more complex. Most IT experts insist that smart devices should have additional functions to satisfy these requirements. In particular, research has concentrated on LBS (Locationbased Service), because it is considered one of the most common mobile service types. Generally, Wi-Fi has a critical limitation for use for LBS services, because it requires new network connection points whenever its location (Network Zone) changes. Unfortunately, GPS also has a systematic problem in providing LBS service in the indoor environment, because of its inaccuracy in processing data. So, to redress these limitations, iBeacon technology has been designed, and is currently used for LBS service instead of Wi-Fi or GPS. By using iBeacon, which is based on Bluetooth 4.0 LE technology, we propose a M-SAS (Mobile-Subway-Alarm-Service System) that could accurately and timely provide its users with various mLBS (micro LBS) services, such as current user location, and subway arrival time.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.12
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• pp.1044-1049
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• 2015

In this paper, isolation enhanced antenna using isolating resonator was proposed. Two loop type antennas were designed to operate at Wi-Fi band(2.4~2.5 GHz), in symmetry to the center, and are closely located to each other. In order to enhance isolation characteristics at Wi-Fi bands, isolating resonator was designed between the two loop type antennas. The proposed isolating resonator is a slot type antenna that enhances isolation with the control of the size, and by adjusting the value of capacitor($C_D$) the resonant frequency of the isolating resonator can easily be adjusted to enhance isolation characteristic at the target frequency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.4
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• pp.374-380
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• 2015

With explosion of wireless traffic it is required to further investigate the technologies on acquiring available spectrum resources and on sharing frequency with existing users. In 3GPP, it is started to study on feasibility and functional requirement of LTE standard in order to extend cellular services offered on only licensed band to 5 GHz unlicensed band. Operating scenario on LTE in unlicensed band is focused on carrier aggregation with licensed band, and the coexistence with Wi-Fi services in 5 GHz band is concerned as a major requirement. For a single global solution framework for licensed assisted access to unlicensed spectrum, listen-before-talk(LBT) mechanism of European regulation for fair access to channel under the coexistence environments is currently examined in 3GPP. In this paper, we evaluate two types of LBT, frame based equipment and load based equipment, with considering LTE carrier aggregation feature and performances of file transferred time and throughput.