• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.1
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• pp.38-40
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• 2014

In this paper, proposed method achieves delay reduction and throughput improvement by utilizing token-ring method in infrastructure network. Access Point gives token passing effect by successively transmitting ACK frame including a node's Association ID. Not only can this method considerably reduce time for medium access, but also improve throughput. Furthermore, AP offers more frequent medium access opportunity to node having highest data queue among nodes associated by AP. these method can evenly offer medium access opportunity according to Queue's volumes.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.13 no.4
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• pp.57-62
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• 2014

Recently, research activities to develop services for providing safety information to the drivers in fast moving vehicles based on various wireless network technologies such as DSRC (Dedicated Short Range Communication), IEEE 802.11p WAVE (Wireless Access for Vehicular Environment) are widely being carried out. This paper presents a proof-of-concept model based on a robot-car for Dilemma Zone Decision Assistant Service using the wireless LAN technology. The proposed model system consists of a robot-car based on an embedded Linux OS equipped with a WiFi interface and an on-board unit emulator, an Android-based remote controller to model a human driver interface, a laptop computer to run a model traffic signal controller and signal lights, and a WiFi access point to model a road-side unit.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.8
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• pp.1741-1748
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• 2005

In this paper, we describe VLSI design and performance evaluation of OCB-AES crytographic algorithm that simulataneously provides privacy and authenticity. The OCB-AES crytographic algorithm sovles the problems such as long operation time and large hardware of conventional crytographic system, because the conventional system must implement the privancy and authenticity sequentially with seqarated algorithms and hardware. The OCB-AES processor with area-efficient modular offset generator and tag generator is designed using IDEC Samsung 0.35um standard cell library and consists of about 55,700 gates. Its cipher rate is about 930Mbps and the number of clock cycles needed to generate the 128-bit tags for authenticity and integrity is (m+2)${\times}$(Nr+1), where m and Nr represent the number of block for message and number of rounds for AES encryption, respectively. The OCB-AES processor can be applicable to soft cryptographic IP of IEEE 802.11i wireless LAN and Mobile SoC.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9C
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• pp.905-912
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• 2007

This paper proposes an efficient estimation and compensation scheme of IQ imbalance for OFDM-based WLAN systems in the presence of symbol timing error. Since the conventional scheme assumes perfect time synchronization, the criterion of the scheme used to derive the estimation of IQ imbalance is inadequate in the presence of the symbol timing error and the system performance is seriously degraded. New criterion and compensation scheme considering the effect of symbol timing error are proposed. With the proposed scheme, the IQ imbalance can be almost perfectly eliminated in the presence of symbol timing error. The bit error rate performance of the proposed scheme is evaluated by the simulation. In case of 54 Mbps transmission mode in IEEE 802.11a system, the proposed scheme achieves a SNR gain of 4.3dB at $BER=2{\cdot}10^{-3}$. The proposed compensation algorithm of IQ imbalance is implemented using Verilog HDL and verified. The proposed IQ imbalance compensator is composed of 74K logic gates and 6K bits memory from the synthesis result using 0.18um CMOS technology.

• Journal of Advanced Navigation Technology
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• v.23 no.6
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• pp.542-547
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• 2019

Autonomous train is investigated to increase the capacity of railroad, and the reliability of wireless communication plays a critical role in terms of decreasing the inter-train distance. In this paper, we propose a transmission scheme for autonomous train communication in highly congested environment. The proposed scheme, namely distributed uplink orthogonal frequency division multiple access (OFDMA) random access (UORA), applies the triggered uplink access (TUA) and the UORA, introduced in the sixth generation WLAN standard, IEEE 802.11ax, for communication devices on vehicle and platform in a distributed manner. The simulation results show that the proposed scheme efficiently improves the packet transmission success rate in highly congested channel conditions compared to the conventional enhanced distributed channel access (EDCA) transmission scheme.

• Proceedings of the Korean Society of Computational and Applied Mathematics Conference
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• 2003.09a
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• pp.2.2-2
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• 2003

PRF(Pseudo Random Function)에 대한 랜덤성 검증은 pre-computation공격에 대해 알고리즘이 특별한 통계적 약점이 없이 적절하게 개발되었는지를 평가할 수 있다. 이 논문에서는 NIST에서 실시한 AES 후보 알고리즘 랜덤성 평가 기준을 적용하여 IEEE의 802.11i Draft에서 인증자와 요청자가 비밀키(PTK, GTK)를 생성하는데 사용되는 PRF의 랜덤성을 검증하였다. 랜덤성 테스트를 위해 표본 수는 300개, 표본 길이는 2$^{20}$ (= 1,048,576)으로 검정 표본을 생성하고, 유의 수준은 0.01로 선택하였다. 랜덤성 검증 방법으로는 NIST의 16가지 통계 테스트를 사용하였다.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.40 no.5
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• pp.397-409
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• 2003

This paper describes an implementation of radix-4 trellis parallel architecture and backward state transition control trace back Viterbi decoder, and presents the application results to high speed wireless LAN. The radix-4 parallelized architecture Vietrbi decoder can not only improve the throughput with simple structure, but also have small processing delay time and overhead circuit compared to M-step trellis architecture one. Based on these features, this paper addresses a novel Viterbi decoder which is composed of branch metric computation, architecture of ACS and trace back decoding by sequential control of backward state transition for the implementation of radix-4 trellis parallelized structure. With the proposed architecture, the decoding of variable code rate due to puncturing the base code can easily be implemented by the unified Viterbi decoder. Moreover, any additional circuit and/or peripheral control logic are not required in the proposed decoder architecture. The trace back decoding scheme with backward state transition control can carry out the sequential decoding according to ACS cycle clock without additional circuit for survivor memory control. In order to evaluate the usefulness, the proposed method is applied to channel CODEC of the IEEE 802.11a high speed wireless LAN, and HDL coding simulation results are presented.

• Journal of Internet Computing and Services
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• v.5 no.3
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• pp.99-108
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• 2004

We have designed and implemented a Voice Messenger System(VMS) for sending and receiving voice data in order to measure and analyze the performance of a multimedia data transfer system using PDAs(Personal Digital Assistants) in a fast wireless LAN environment. The VMS has been configured as an infrastructure network by integrating a wireless intra-network based on IEEE 802,11 b standard with a wired network based on Ethernet. A sending time, a receiving time and a round-trip time(RTT) have been measured by varying its pecket size from 256 to 6656 bytes, Besides, we have performed the experiments to see which NIC is more stable between CF and PCMCIA type in such a wireless LAN environment, The results of such experiments show that the NIC with PCMClA type is better than that with CF type from the points of both efficiency and stability. The performance of a notebook computer with the attachment of a wireless NIC that is used as a VMS client is almost constant by varying its packet size when transferring voice data. However, with PDA client, in the case of receiving packets from the VMS server, the performance is the best when the pecket size is 6656 bytes, In addition, in the case of sending packets from PDA client to the VMS server, the performance is the best when the packet size is 4096 bytes. Even with the same pecket size, the time of receiving packets from the VMS server to PDA is longer than the time of sending packets from PDA to the VMS Server, Thus, we conclude that when PDA is used as a client by applying different pecket size when sending and receiving packets should be achieved a better performance over a wireless LAN environment.

• Proceedings of the Korean Information Science Society Conference
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• 2007.06d
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• pp.273-278
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• 2007

Snoop 프로토콜은 유 무선 혼합망에서 무선 링크에서 발생하는 TCP 패킷 손실을 효과적으로 보상하여 TCP 전송률을 향상시킬 수 있는 효율적인 프로토콜이다. 하지만, 무선 링크에서 연집한 패킷 손실이 발생하는 경우에는 지역 재전송을 효과적으로 수행하지 못하여 전송 효율이 떨어진다는 문제점이 있다. 본 논문에서는 Snoop 프로토콜의 이러한 문제점을 개선하기위해 MAC 계층의 재전송 메커니즘인 Stop &Wait ARQ 기법을 기반으로 하는 $A^2Snoop$ (ARQ Assistance Snoop) 프로토콜을 제안한다. $A^2Snoop$ 프로토콜은 현재 유 무선 혼합망에서 가장 널리 사용되는 IEEE 802.11 MAC 프로토콜 기반의 지역 재전송 메커니즘으로서, MAC 계층의 ARQ 기법과 TCP의 혼잡제어 메커니즘의 연동을 통해 효율적인 재전송을 수행한다. ns-2 시뮬레이터를 이용한 실험을 통해 $A^2Snoop$의 지역 재전송 기법은 무선 구간의 연집적인 패킷 손실에 대해 효율적인 보상을 수행하며, 전송률을 유지하는 것을 확인할 수 있었다.

• Proceedings of the Korean Information Science Society Conference
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• 2008.06d
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• pp.230-235
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• 2008

현재 대부분의 무선랜은 유선 분산 시스템을 통하여 백본에 연결되어 있다. 그러나 지역회담이나 재해재난 지역 그리고 군사용등은 유선 백본을 사용할 수 없다. 따라서 무선으로 액세스 포인트를 연결하여 일시적으로 네트워크 서비스를 원하는 곳이나 케이블을 연결하기 힘든 지역에서 빠르고 쉽게 네트워크 구성을 제공하기 위한 무선 메쉬 네트워크의 요구가 늘어나고 있다. 본 논문에서는 이러한 무선 메쉬 네트워크의 기반 기술인 무선 분산 시스템 환경에서 TCP와 UDP 프로토콜의 성능에 대하여 연구하였다. 시스템 성능 측정은 IEEE 802.11g 인터페이스를 가지고 있는 액세스 포인트에서 체인 토폴로지를 기본으로 측정되어졌고, 홉수와 트래픽 종류 그리고 트래픽 흐름의 방향에 따라 수율(throughput)과 전송시간(transaction time) 그리고 전송실패율(loss rate) 등을 비교 분석하였다.