• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.13 no.9
• /
• pp.1819-1828
• /
• 2009

Until now, much research on cooperative communications to increase system throughput at Ad Hoc networks has been provided. In this paper, in order to enhance system throughput much more at Ad Hoc networks, a network coding-enabled new MAC protocol, called NC-MAC protocol, is proposed and its performance is evaluated with a mathematical approach. Numerical results show that this scheme provides conspicuously enhanced system throughput compared to DCF scheme, and more increased system throughput by 48% than rDCF and CO-MAC schemes.

• Proceedings of the Korean Information Science Society Conference
• /
• 2006.06d
• /
• pp.115-117
• /
• 2006

IEEE 802.11 표준은 채널 상태에 따라 다양한 전송 속도를 지원하며, 무선랜 환경에서 이러한 특성을 활용하는 연구들이 진행되어 왔다. 그러나, 모바일 애드 혹 네트워크 환경에서 다중전송속도를 활용하는 연구는 거의 이루어지지 않았다. 본 논문은 모바일 애드 혹 네트워크에서 동적으로 다중전송속도를 활용하여 채널 효율을 높이는 알고리즘을 제안한다. 제안 기법은 MAC 계층과 네트워크 계층 중간에 위치하며 각 계층에 독립적으로 동작한다. 라우팅 프로토콜에서 결정한 다음 홉에 더불어, 제안 기법은 더 빠른 전송 속도를 갖는 중계 경로를 탐색한다. 또한, 패킷의 크기에 따라 경쟁 부하를 고려하여 선택적으로 전송 경로를 변경한다. 모의 실험을 통한 성능 평가는 제안 기법의 우수한 성능을 입증한다.

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

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.14 no.3
• /
• pp.24-30
• /
• 2015

Wi-Fi STAs in power saving mode described in the Wi-Fi specification can deteriorate the system performance such as throughput, time delay when they receive data frames from a Wi-Fi AP. This problem is caused by data frame reception failure due to the channel state, and it increases re-transmissions. In this paper, we propose a modified power saving mode considering fairness of Wi-Fi system in order to solve the problem. By simulation, we showed that data throughput can be increased without time delay degradation if the proposed method restricting the number of packet transmission attempts and HARQ are used.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.13 no.3
• /
• pp.38-46
• /
• 2014

Wi-Fi STAs in power saving mode described in the Wi-Fi specification can deteriorate the system performance such as throughput, time delay when they receive data frames from a Wi-Fi AP. This problem is caused by data frame reception failure due to the channel state, and it increases re-transmissions. In this paper, we propose a modified power saving mode of Wi-Fi system in order to solve the problem. Also, we evaluate its performance in terms of throughput and time delay by simulation.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2002.04b
• /
• pp.1365-1368
• /
• 2002

OFDM은 제4세대 변조기술로 일컬어지는 방식이다. 이는 최근 유럽에서 디지털 오디오 방송(DAB)과 디지털 비디오 방송(DVB)에 표준이 되었으며, IEEE 802.11a 무선 LAN 에서도 이 방식을 채택했고, ADSL, VDSL 등에서도 사용되어지고 있다. 본 논문에서는 이러한 OFDM 방식의 핵심이라고 할 수 있는 64포인트 FFT(Fast Fourier Transform)하드웨어 프로세서의 여러 가지의 구현된 예를 비교 분석하고, 가장 효율적인 방법인 Radix-2 SDF(Singlepath Delay Feedback)[1] 방법을 개선하여 새로운 구조를 제안하였다. 동일한 속도 성능을 가지는 여러구조 중에서 적은 수의 지연소자를 활용하여 FFT 크기를 작게 한 것이 SDF 방식으로 가장 널리 사용되고 있다. 본 논문에서는 SDF 방식이 내부적으로 4개의 복소곱셈기를 필요로 하는데 비해 2개의 복소곱셈기만을 사용하는 구조로 변형하고 컨트롤을 조절하여 새로운 구조를 설계하였다. 구현한 결과, FFT에서 전체 구조의 약 80%를 차지하는 복소곱셈기의 수를 절반으로 줄여 FFT 하드웨어 크기를 SDF 방식의 60% 정도로 줄일 수 있게 되었고, 이러한 구현방식은 64포인트 FFT만이 아닌 더 큰 크기의 FFT를 구현함에 있어서도 동일하게 적용할 수 있으며 현재 국내외에 발표된 논문 중 성능 대 면적비가 가장 우수한 구조이다.

• Journal of Internet Computing and Services
• /
• v.14 no.1
• /
• pp.15-22
• /
• 2013

WAVE(Wireless Access for Vehicular Environment) is new concepts and Vehicles communications technology using for ITS(Intelligent Transportation Systems) service by IEEE standard 802.11p. Also it increases the efficiency and safety of the traffic on the road. However, the efficiency of Scrambler bit computational algorithms of OFDM modulation in WAVE systems will fall as it is not able to process in parallel in terms of hardware and software. This paper proposes an algorithm to configure 64-bits matrix table in scambler bit computation as well as an algorithm to compute 64-bits matrix table and input data in parallel. The proposed algorithm on this thesis is executed using 64-bits matrix table. In the result, the processing speed for 1 and 1000 times is improved about 40.08% ~ 40.27% and processing rate per sec is performed more than 468.35 compared to bit operation scramble. And processing speed for 1 and 1000 times is improved about 7.53% ~ 7.84% and processing rate per sec is performed more than 91.44 compared to 32-bits operation scramble. Therefore, if the 64 bit-CPU is used for 64-bits executable scramble algorithm, it is improved more than 40% compare to 32-bits scrambler.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.22 no.1
• /
• pp.12-21
• /
• 2012

IEEE 802.11 MAC protocol standard, DCF(CSMA/CA), is originally designed to ensure the fair channel access between mobile nodes sharing the local wireless channel. It has been, however, revealed that some misbehavior nodes transmit more data than other nodes through artificial means in hot spot area spreaded rapidly. The misbehavior nodes may modify the internal process of their MAC protocol or interrupt the MAC procedure of normal nodes to achieve more data transmission. This problem has been referred to as a selfish node problem and almost literatures has proposed methods of analyzing the MAC procedures of all mobile nodes to detect the selfish nodes. However, these kinds of protocol analysis methods is not effective at detecting all kinds of selfish nodes enough. This paper address this problem of detecting selfish node using Tsallis-Entropy which is a kind of statistical method. Tsallis-Entropy is a criteria which can show how much is the density or deviation of a probability distribution. The proposed algorithm which operates at a AP node of wireless LAN extracts the probability distribution of data interval time for each node, then compares the one with a threshold value to detect the selfish nodes. To evaluate the performance of proposed algorithm, simulation experiments are performed in various wireless LAN environments (congestion level, how selfish node behaviors, threshold level) using ns2. The simulation results show that the proposed algorithm achieves higher successful detection rate.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.46 no.4
• /
• pp.53-63
• /
• 2009

This work proposes a 10b 100MS/s 27.2mW $0.8mm^2$ 0.18um CMOS ADC for WLAN such as an IEEE 802.11n standard. The proposed ADC employs a three-stage pipeline architecture and minimizes power consumption and chip area by sharing as many circuits as possible. Two multiplying DACs share a single amplifier without MOS switches connected in series while the shared amplifier does not show a conventional memory effect. All three flash ADCs use only one resistor ladder while the second and third flash ADCs share all pre-amps to further reduce power consumption and chip area. The interpolation circuit employed in the flash ADCs halves the required number of pre-amps and an input-output isolated dynamic latch reduces the increased kickback noise caused by the pre-amp sharing. The prototype ADC implemented in a 0.18um n-well 1P6M CMOS process shows the DNL and INL within 0.83LSB and 1.52LSB at 10b, respectively. The ADC measures an SNDR of 52.1dB and an SFDR of 67.6dB at a sampling rate of 100MS/s. The ADC with an active die area of $0.8mm^2$ consumes 27.2mW at 1.8V and 100MS/s.

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