• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.110-115
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• 1999

The emergence of portable information terminals in work and living environments is accelerating introduction of wireless digital links and local-area networks(LANs). Transmission using infrared radiation recently become a viable option. As a transmission medium, infrared offers several advantage over radio. The infrared spectral region offers a virtually unlimited bandwidth that is unregulated worldwide. In this paper we examine the performance of several modulation schemes on the wireless infraredcommunication system. We compare the power and bandwidth efficiency of several schemes.

• Journal of Information Technology Services
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• v.9 no.3
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• pp.145-161
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• 2010

Recently, identifying user locations is becoming important as the society evolves into an ubiquitous society with the innovation of information technology. Particularly, many researches on identifying user locations are headed in direction to identify locations of users in the indoors, because a GPS that is widely used to identify the locations of users in the outdoors is inapplicable in the indoors. However, those researches are mostly not useful to general indoor environment because they are performed in a specific environment with specialized or customized devices such as UWB, RFID. Therefore, in this paper we propose a effective method to identify user locations in general indoor environments with wireless local network access points. Our approach enables to identify user location efficiently by measuring signal power of access points around the user and using the FRIIS formula which is used to calculate the distance among the things.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.6
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• pp.1016-1021
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• 2008

A number of wireless technologies have been implemented, but each technology has its limitation in terms of coverage and bandwidth. WLAN and 3G cellular network has emerged to be a complementary platform for wireless data communications. However, the mobility of roaming terminals in heterogeneous networks poses several risks. To maintain secure communications in universal roaming, the effective authentication must be implemented. The focus of this paper is on analysis of authentication architecture involved in integrated WLAN/3G networks.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.4
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• pp.29-36
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• 2003

In this paper, we propose a new Two-factor Authentication and Key Exchange(TAKE) protocol that can be applied to low-power PDAs in Public Wireless LAMs using two factor authentication and precomputation. This protocol provides mutual authentication session key establishment, identity privacy, and practical half forward-secrecy. The only computational complexity that the client must perform is one symmetric key encryption and five hash functions during the runtime of the protocol.

• Journal of information and communication convergence engineering
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• v.19 no.1
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• pp.1-7
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• 2021

Reinforcement learning is an area of machine learning that studies how an intelligent agent takes actions in a given environment to maximize the cumulative reward. In this paper, we propose a new MAC protocol based on the Q-learning technique of reinforcement learning to improve the performance of the IEEE 802.11 wireless LAN CSMA/CA MAC protocol. Furthermore, the operation of each access point (AP) and station is proposed. The AP adjusts the value of the contention window (CW), which is the range for determining the backoff number of the station, according to the wireless traffic load. The station improves the performance by selecting an optimal backoff number with the lowest packet collision rate and the highest transmission success rate through Q-learning within the CW value transmitted from the AP. The result of the performance evaluation through computer simulations showed that the proposed scheme has a higher throughput than that of the existing CSMA/CA scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3A
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• pp.293-302
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• 2004

Wireless LAN is a rather mature communication technology that connects mobile terminals. A typical wireless LAN system is composed of one AP and more than one terminals, which is called a BSS. Terminals near to an AP can receive high rate data but terminals far from an AP may not receive data with guaranteed high speed rate because received signal strength is weakened. This paper proposes a method to allow high speed data transmission by grouping terminals and using part of wireless terminals as repeaters. We compare and analyze proposed grouping algorithms based on Depth First Search and Breadth First Search via simulations. A grouping algorithm based on Breadth First Search is shown to be more effective in term of efficiency and coverage.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.225-225
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• 2006

• Proceedings of the Korean Information Science Society Conference
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• 2003.10c
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• pp.34-36
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• 2003

본 논문은 무선 LAN 상에서 단말간에 전송되는 트래픽의 서비스 품질을 차별화하고, 처리율 관점에서 기존의 IEEE 802.11e 프로토콜보다 향상된 서비스 품질을 제공하기 위한 새로운 백오프 방식을 제안한다. 제안된 백오프 방식은 단말의 수나 트래픽 손실률과 같은 서비스 영역의 정보를 분석하여 그 정보를 바탕으로 트래픽 특성에 따라 경쟁 윈도우를 동적으로 변화시켜 백오프 절차를 수행한다. 본 논문에서는 제안된 백오프 방식을 분석하기 위해 마코프 모델을 이용한 수학적 분석으로 기존의 IEEE 802.11e 백오프 방식과 비교 분석한다.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.21-22
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• 2007

The reference scheduler presented by IEEE 802.11e standard is inefficient because it polls all admitted stations in the same interval. It increases poll overheads and waste time. In this paper we proposed an efficient scheduling algorithm to improve the aggregate throughput and the number of admitted stations.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.584-586
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• 2003

무선 통신은 유선 통신과 달리 사용되는 단말기들이 배터리를 주 전원 공급으로 사용되고 있으므로 통신 기법의 전력 소모량에 따라 단말기의 전체적인 사용시간이 결정된다. 이에 본 논문에서는 802.11 무선 LAN상에서 전력 절약모드를 이용한 전력 효율적인 오류제어 기법을 제안한다.