• The Journal of Korean Institute of Communications and Information Sciences
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• 제37권6B호
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• pp.474-482
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• 2012

Mobile Gateway(MG) is a wireless LAN device to provide internet services to a passenger on vehicles like a bus. For using internet services, MG connects the Road Side Unit AP(RSU AP) based on WLAN .To provide a stable communication service on the moving vehicle, handoff changing MG's RSU must be handled fast and stably. However, it has a physical limits to remove a disconnection time of handoff process by reason of its technological features. In this paper, we suggest a MIMG(Multi-Interface Mobile Gateway) executing seamless handoff by using multiple wireless LAN interfaces for connecting RSU. In the detailed way to do stable handoff, we suggest the "Link Sharing Technique" to disconnection time of packet transmission for RSU to MIMG and the "Path Sharing Technique" to remove disconnection time of packet transmission for MIMG to RSU. we implemented the MIMG which performs the suggested handoff technique. We confirmed the superiority of our system by remove of the disconnection time(0 ms), and improved over 50 % of the communication bandwidth.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• 제10권6호
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• pp.98-107
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• 2011

In this paper, we propose the location determination system of an agent mobile device using the information provided by the WLAN(Wireless LAN) infrastructure. This system is configured as a typical ESS(Extended Service Set)-type WLAN structure with real-time location positioning engine and thru AP(Access Point) controller. The positioning engine collects the information of agent devices using SNMP(Small Network Management Protocol) thru AP controller and utilize those information as Cell ID. for LBS(Location Based Service). In the result of a real office environment implementation, the average success rate of inter-AP roaming is measured to 62.5% and the duration time of the device information update within the AP is average of 11 second of time, which means this system is adaptable to the location based service of above average accuracy but somewhat less urgency.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제15권10호
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• pp.2143-2148
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• 2011

In general, existed kiosk using touch-screen based kiosk system has been used by only single user, so that multiple users to access this kiosk need to provide a lot of waiting time and maintenance costs. To solve this problem, the framework design based on Bluetooth profile for kiosk servers is presented. The proposed kiosk system can be more efficiently used in theater, train station, bank, government, and public offices by using Bluetooth module and AP in mobile system such as smart phone.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제41권1호
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• pp.107-109
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• 2016

In this paper, we address the TCP-over-WLAN performance problem that occurs during periodic active background scanning with which mobile devices discover available APs in the vicinity. We measure the impact of the scanning period on the TCP throughput and observe a significant performance degradation when the scan operation period is shortened. Our experimental analysis has identified the main cause of the problem, that is, the associated AP continues to send packets to the mobile device even when the device is not able to receive due to the scanning operation.

• Smart Media Journal
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• 제9권3호
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• pp.71-79
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• 2020

Mobile network is used by many users worldwide for diverse services, including phone-call, messaging and data transfer over the Internet. However, this network may experience massive damage if it is exposed to cyber-attacks or denial-of-service attacks via wireless communication interference. Because the mobile network is also used as an emergency network in cases of disaster, evaluation or verification for security and safety is necessary as an important nation-wide asset. However, it is not easy to analyze the mobile core network because it's built and serviced by private service providers, exclusively operated, and there is even no separate network for testing. Thus, in this paper, a virtual mobile network is built using OpenAirInterface, which is implemented based on 3GPP standards and provided as an open source software, and the structure and protocols of the core network are analyzed. In particular, the S1AP protocol messages captured on S1-MME, the interface between the base station eNodeB and the mobility manager MME, are analyzed to identify potential security threats by evaluating the effect of the messages sent from the user terminal UE to the mobile core network.

• The Journal of the Korea institute of electronic communication sciences
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• 제14권5호
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• pp.927-934
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• 2019

Recently, mobile devices have evolved into small computers with various functions according to user requirements. Careful attention must be paid to the design of the power supply network for the stable operation of the application processor (AP), the wireless communication modem, the high performance camera, and the various interfaces of the mobile device to implement various functions of the mobile device. In this paper, we analyzed and verified the method of optimizing the design parameters such as the position, capacity, and number of decoupling capacitors to meet the target impedance required by the driver IC chip to ensure the stability of the power supply network of mobile devices that should be designed as wiring type due to mounting density limitation. The proposed wired power supply network design method can be applied to various applications including high-speed signal transmission line in addition to mobile applications.

• KIPS Transactions on Computer and Communication Systems
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• 제3권11호
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• pp.393-402
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• 2014

We have experienced an explosive increase of the IoT(Internet of Things) technology based devices including smart phones and the wireless communications. Also the growing power consumption in IEEE 802.11 WLANs(Wireless LANs) driven by these dramatic increases in not only mobile users and but also wireless APs(Access Points). To reduce the power consumption, this paper proposes a wireless AP power saving algorithm, which minimizes the transmission power without decrease the transmission and carrier sense ranges. A wireless AP which is use in our algorithm checks its own original coverage periodically for whether there is a new STA(Station) or not when its transmission power is decreased. Moreover, if there are no signaling message to connect the wireless AP, it changes its operation mode Wake-up to sleep. A Result shows that the proposed AP algorithm can reduce the total power consumption of the wireless AP approximated 18% and 35% compared to the conventional wireless AP with and without the existing power saving algorithm, respectively.

• Journal of Environmental Science International
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• 제23권9호
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• pp.1643-1654
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• 2014

The university is one of the main energy consumption facilities and thereby releases a large amount of greenhouse gas (GHG). Accordingly, efforts for reducing energy consumption and GHG have been established in many local as well as international universities. However, it has been limited to energy consumption and GHG, and has not included air pollution (AP). Therefore, we estimated GHG and AP integrated emissions from the energy consumed by Seoul National University of Science and Technology during the years between 2010 and 2012. In addition, the effect of alternative energy use scenario was analysed. We estimated GHG using IPCC guideline and Guidelines for Local Government Greenhouse Inventories, and AP using APEMEP/EEA Emission Inventory Guidebook 2013 and Air Pollutants Calculation Manual. The estimated annual average GHG emission was $11,420tonCO_{2eq}$, of which 27% was direct emissions from fuel combustion sectors, including stationary and mobile source, and the remaining 73% was indirect emissions from purchased electricity and purchased water supply. The estimated annual average AP emission was 7,757 kgAP, of which the total amount was from direct emissions only. The annual GHG emissions from city gas and purchased electricity usage per unit area ($m^2$) of the university buildings were estimated as $15.4kgCO_{2eq}/m^2$ and $42.4tonCO_{2eq}/m^2$ and those per person enrolled in the university were $210kgCO_{2eq}$/capita and $577kgCO_{2eq}$/capita. Alternative energy use scenarios revealed that the use of all alternative energy sources including solar energy, electric car and rain water reuse applicable to the university could reduce as much as 9.4% of the annual GHG and 34% of AP integrated emissions, saving approximately 400 million won per year, corresponding to 14% of the university energy budget.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권5호
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• pp.888-908
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• 2011

The increasing demand from passengers in vehicles to improve safety, traffic efficiency, and comfort has lead to the growing interest of Wi-Fi based vehicle-to-infrastructure (V2I) communications. Although the V2I system provides fast and cost-effective Internet connectivity to vehicles via roadside Wi-Fi access points (APs), it suffers from frequent handoffs due to the high mobility of vehicles and the limited coverage of Wi-Fi APs. Recently, the Mobile AP (MAP) platform has emerged as a promising solution that overcomes the problem in the V2I systems. The main advantage is that MAPs may yield longer service duration to the nearby vehicles that have similar mobility patterns, yet they provide smaller link capacities than the roadside APs. In this paper, we present a new association control technique that harnesses available connection duration as well as achievable link bandwidth in high-speed vehicular network environments. We also analyze the tradeoff between two association metrics, namely, available connection duration and achievable link bandwidth. Extensive simulation studies based on real traces demonstrate that our scheme significantly outperforms the previous methods.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 한국해양정보통신학회 2003년도 추계종합학술대회
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• pp.141-144
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• 2003

The mobile radio networks can be divided into networks that has the base station or the infrastructures like AP(Access Point) and Ad Hoc network that hasn't any infrastructures. As there aren't any fixed infrastructures in Ad Hoc Networks, mobile nodes should transmit the data only among mobile nodes themselves. To supplement these weakpoints of the two networks, many studies about Ad Hocs based on the 802.11 are in progress. In this thesis, we try to propose the efficiency of the suggested protocols by comparing and analyzing power saving protocols according to the Beacon intervals in multi hop Ad Hoc Networks based on IEEE 802.11.