• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.21-34
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• 2000

Millimeter wave is expected as the unlimited useful frequency resources for the next generation wireless communication services. In the past, its usage was limited to the military warfare due to lack of millimeter devices. The development of GaAs pHEMT in 1980 and the progress in the processing technologies made the new consumer wireless services possible utilizing millimeter waves. Specially, most of passive components necessary for circuit design can be integrated with GaAs pHEMTs and this removes the difficulty in assembly unavoidable in hybrid design. InP based pHEMTs developed later possess all the properties of GaAs and it shows many advantages in higher frequency applications. In this paper, the status and trends of those devices and MMICs are presented and the future developing trends is also described.

• Journal of KIISE:Information Networking
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• v.30 no.5
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• pp.631-640
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• 2003

Because of multi-hop wireless communication, P2P applications in ad hoc networks suffer poor performance. We Propose neighbor caching strategy to overcome this shortcoming and show it is more efficient than self caching that nodes store data in theirs own cache individually. A node can extend its caching storage instantaneously with neighbor caching by borrowing the storage from idle neighbors, so overcome multi-hop wireless communications with data source long distance away from itself. We also present the ranking based prediction that selects the most appropriate neighbor which data can be stored in. The node that uses the ranking based prediction can select the neighbor that has high possibility to keep data for a long time and avoid caching the low ranked data. Therefore the ranking based prediction improves the throughput of neighbor caching. In the simulation results, we observe that neighbor caching has better performance, as large as network size, as long as idle time, and as small as cache size. We also show the ranking based prediction is an adaptive algorithm that adjusts times of data movement into the neighbor, so makes neighbor caching flexible according to the idleness of nodes

• Asian-Australasian Journal of Animal Sciences
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• v.29 no.1
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• pp.149-156
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• 2016

In this experiment, we proposed and implemented a disease forecasting system using a received signal strength indication ZigBee-based wireless network with a 3-axis acceleration sensor to detect illness at an early stage by monitoring movement of experimentally infected weaned piglets. Twenty seven piglets were divided into control, Salmonella enteritidis (SE) infection, and Escherichia coli (EC) infection group, and their movements were monitored for five days using wireless sensor nodes on their backs. Data generated showed the 3-axis movement of piglets (X-axis: left and right direction, Y-axis: anteroposterior direction, and Z-axis: up and down direction) at five different time periods. Piglets in both infected groups had lower weight gain and feed intake, as well as higher feed conversion ratios than the control group (p<0.05). Infection with SE and EC resulted in reduced body temperature of the piglets at day 2, 4, and 5 (p<0.05). The early morning X-axis movement did not differ between groups; however, the Y-axis movement was higher in the EC group (day 1 and 2), and the Z-axis movement was higher in the EC (day 1) and SE group (day 4) during different experimental periods (p<0.05). The morning X and Y-axis movement did not differ between treatment groups. However, the Z-axis movement was higher in both infected groups at day 1 and lower at day 4 compared to the control (p<0.05). The midday X-axis movement was significantly lower in both infected groups (day 4 and 5) compared to the control (p<0.05), whereas the Y-axis movement did not differ. The Z-axis movement was highest in the SE group at day 1 and 2 and lower at day 4 and 5 (p<0.05). Evening X-axis movement was highest in the control group throughout the experimental period. During day 1 and 2, the Z-axis movement was higher in both of the infected groups; whereas it was lower in the SE group during day 3 and 4 (p<0.05). During day 1 and 2, the night X-axis movement was lower and the Z-axis movement was higher in the infected piglets (p<0.05). Overall, the movement of infected piglets was altered, and the acceleration sensor could be successfully employed for monitoring pig activity.

• Journal of the Korea Society of Computer and Information
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• v.14 no.4
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• pp.111-117
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• 2009

Improvement of Wireless internet and handheld devices makes it possible that users can use various multimedia services. But, access point devices are needed while using handheld devices, and those devices use virtual network address for networking. For that reason, end-users hardly use the 1:1 voice or video chat, and messenger service that require direct communications between devices. Also, service providers need central server for relaying packets from terminals to others, the traffic and costs of relaying go high, so real-time massive data transmission services are restrictively provided. In this study, we apply TCP/UDP hole punching technique to those applications. And we implement service that supports real-time multimedia direct transmission between equipments that use virtual network addresses.

• Journal of Electrical Engineering and Technology
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• v.2 no.1
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• pp.123-128
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• 2007

SPWPM traditional software development is surveyed and essential problems are investigated on the basis of system wireless link considerations. This paper presents the current state software planning tools for wireless LAN link optimization. The software directory is based on combination of MatLab and MapInfo software and measurement which gives the best grouping parameters to build up the software development. Among the requirements assumed, the WLAN site selections must be Line-of-sight (LOS) or near line of sight (NLOS) field strength prediction for either point to point or point to multi points. The results obtainable the out put of the program include two-dimensional (2D) and three dimensional (3D) plots for creating the link; design parameters through GUI representing the height and location for each antenna is depending on K-factor of the area and transmit antenna location.

• Journal of the Korea Society of Computer and Information
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• v.17 no.2
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• pp.95-103
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• 2012

In this paper, we propose an efficient mobile P2P streaming architecture to minimize playback jitters in P2P overlay networks based on wired/wireless networks even though mobile peers experience the handover. In this architecture, mobile peers receive data in a push manner to maximize the data receiving speed before and after the handover. In addition, they can maintain the buffering above a specific level through handover prediction and re-selection of neighbor peers. By simulation experiments, we show that our proposed architecture can improve the performance significantly when the handover occurs compared to the existing mesh structure.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.6
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• pp.111-116
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• 2012

Vehicular communication is one of main convergence technologies which combines information and communication technology (ICT) with vehicle and road industries. In general, vehicular communication adopts IEEE 802.11p standard which is commonly referred as wireless access in vehicular environments (WAVE). In this paper, we investigate a multi-hop communication scheme for IEEE 802.11p based communication systems which support both vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communications. First, we briefly overview the performance of IEEE 802.11p based communication systems. Then, a multi-hop communication scheme is introduced for both broadcast and unicast. The performance of proposed scheme is presented via experimental measurements.

• Journal of information and communication convergence engineering
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• v.18 no.2
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• pp.88-93
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• 2020

The IEEE 802.11p-based wireless access in vehicular environments (WAVE) [1] communication is a method used exclusively for wireless communication on the road. This technique enables information sharing not only among moving vehicles but also between vehicles and infrastructure [2]. As part of WAVE communication, data is transmitted to and from vehicles in motion; in this case, it is difficult to determine the channel accurately in an outdoor environment owing to the Doppler shift [3]. This paper proposes a new channel estimation scheme for enhancing the reception performance of the IEEE 802.11p-based WAVE system. The proposed technique obtains the initial channel value by estimating the least square in the time domain by inserting a pilot signal for channel estimation into the IEEE 802.11p virtual subcarrier. Subsequently, a least mean square algorithm is applied to the initial channel value to update the estimated channel value. The simulation results obtained using the proposed channel estimation technique confirm its remarkable efficiency.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.566-568
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• 2003

본 논문은 급속히 추진되는 유무선망 통합에 따른 P2P 서비스의 효과적인 제공을 위한 새로운 아키텍쳐를 개발하고, 이를 바탕으로 다양한 응용들을 개발한다. 제안하는 P2P 플랫폼은 무선환경의 채널의 불안정성과 모바일 디바이스의 열악한 자원 및 컴퓨팅 성능 둥을 고려한 개념이 도입되어 모바일 사용자의 비접속상태에서도 지속적인 P2P 연결성을 제공할 수 있도록 설계되었다. 플랫폼의 실용성을 높이기 위하여 방화벽이나 NAT 같은 침투성을 막는 장치에 대해 http 전송방식을 대행하는 Relay server의 기능을 강화시켜 모바일 단말의 Prexy server 기능을 추가하여 통신 효율을 높인다. 응용으로는 인스턴트 메시징과 파일 공유 서비스를 구현하여 그 성능을 검증한다.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06d
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• pp.280-282
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• 2012

Wi-Fi P2P는 Wi-Fi Alliance에 의해 제정된 표준 규격으로 근접 거리에 위치한 장치들간의 효율적이고 빠른 데이터 송수신을 위해 IEEE 802.11n을 이용하고 있다. 근접거리 통신을 위한 기존 블루투스 등의 규격이 갖는 단점을 보완했다는 점에 있어 높은 평가를 받고 있으며, 모바일 디바이스용 플랫폼인 Android ICS 버전부터 공식적으로 지원됨에 따라 널리 사용될 것으로 전망된다. 한편, 한국전자통신연구원(ETRI)에서는 오랫동안 PAN 수준의 네트워킹을 연구해왔으며 그 일환으로 PAN 및 M2M에 적합한 통신 수단으로 여겨지는 Wi-Fi P2P에 대한 연구도 진행 중에 있다. 이에 본 논문에서는 ETRI가 과제를 수행하면서 부수적으로 연구한 Wi-Fi P2P를 위한 Linux용 플랫폼 구조를 공유하고자 한다. 특히 Linux Wireless 프로젝트인 hostap에 속한 wpa_supplicant를 이용해 실제로 동작하는 Wi-Fi P2P 커넥션 매니저를 설계하고 구현하는 방법을 설명함으로써 Android 플랫폼이 아닌 일반적인 Linux 장치에서 Wi-Fi P2P를 사용할 수 있는 방법에 대해 논한다.