• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.3
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• pp.570-576
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• 2004

In this paper, we design the IFFT/FFT (Inverse fast Fourier Transform/Fast Fourier Transform) modules for IEEE 802.11a-1999, which is a standard of the High-speed Wireless LAN using the OFDM (Orthogonal Frequency Division Multiplexing). The designed IFFT/FFT is the 64-point FFT to be compatible with IEEE 802.11a and the pipelined architecture which needs neither serial-to-parallel nor parallel-to-serial converter. We compare four types of IFFT/FFT modules for the hardware complexity and operation : R22SDF (Radix-2 Single-path Delay feedback), the R2SDF (Radix-2 Single-path Delay feedback), R2SDF (Radix-4 Single-path Delay Feedback), and R4SDC (Radix-4 Single-path Delay Commutator). In order to minimize the error, we design the IFFT/FFT module to operate with additional decimal parts after butterfly operation. In case of the R22SDF, the IFFT/FFT module has 44,747 gate counts excluding RAMs and the minimized error rate as compared with other types. And we know that the R22SDF has a small hardware structure as compared with other types.

• Electronics and Telecommunications Trends
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• v.31 no.5
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• pp.21-30
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• 2016

현재 이동/무선통신 환경은 사람과 사람 간의 통신 서비스 형태뿐만 아니라 IoT 통신 서비스로 점차 확대되어가고 있으며, Wi-Fi, Bluetooth 중심의 근거리 무선통신뿐만 아니라 더욱 통신영역이 좁아진 근접통신의 필요성이 대두되고 있다. 이에 따라 근접통신 기술 개발이 지속적으로 이루어지고 있으며, 특히 기기 간의 대용량 데이터 교환이 증가함에 따라 기가급의 속도를 제공하는 초고속 근접통신 기술들이 활발하게 개발되고 있다. IEEE 802에서는 주변 기기들간의 직접(Point-to-Point: P2P) 통신을 지원하는 802.15.3e 초고속 근접통신 기술을 개발하고 있으며, 또한, 802.11ad의 후속 표준으로 개발이 시작된 802.11ay의 Usage Model에도 근접통신이 포함되어 있다. 본고에서는 이러한 초고속 근접통신 기술동향에 대해 기술하고자 한다.

• Information and Communications Magazine
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• v.22 no.9
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• pp.175-186
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• 2005

향후 수년 내에 흠, 오피스 및 핫스팟 영역에서 초고속 멀티미디어의 서비스 수요가 폭발적으로 증가할 것으로 전망됨에 따라 IEEE 802.11에서는 200-500Mbps급의 차세대 초고속 무선랜 표준으로서 IEEE 802.11n의 표준안을 제정하는 작업을 진행하고 있다. 새로운 표준에는 무선통신의 다양한 기술들이 표준으로 채택될 전망이다. 논의되고 있는 기술들로는 물리계층에서의 다중 안테나의 사용, 송신 빔 형성, 듀얼 밴드 그리고 LDPC (Low Density Parity Check) 등의 기술과 MAC (Media Access Control) 계층에서의 집합 전송, 블록 전송, 링크 적응 기법 등의 채택이 논의되고 있다. 기존의 무선랜 시스템에서 널리 사용되어온 IEEE 802.11a/b/g와의 호환성을 보장한다. 또한 차세대 무선랜은 차량용 통신 장치를 위한 고속 이동성을 보장하는 표준인 IEEE 802.11p에 대한 논의도 함께 이루어지고 있다. 본 고에서는 표준회의에서 논의되고 있는 후보 기술들과 차세대 무선랜의 기술동향을 살펴본다.

• Journal of Information Processing Systems
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• v.8 no.1
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• pp.1-20
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• 2012

The most important criterion for achieving the maximum performance in a wireless mesh network (WMN) is to limit the interference within the network. For this purpose, especially in a multi-radio network, the best option is to use non-overlapping channels among different radios within the same interference range. Previous works that have considered non-overlapping channels in IEEE 802.11a as the basis for performance optimization, have considered the link quality across all channels to be uniform. In this paper, we present a measurement-based study of link quality across all channels in an IEEE 802.11a-based indoor WMN test bed. Our results show that the generalized assumption of uniform performance across all channels does not hold good in practice for an indoor environment and signal quality depends on the geometry around the mesh routers.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.2
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• pp.7-16
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• 2000

In this paper, IEEE 802.11 MAC layer protocol is modeled by p-persistent CSMA method. And We introduce performance analysis model based on Basic CSMA/CA protocol, CTS/RTS protocol and hidden node effect reflected Basic CSMA/CA Protocol, Which is mathematically assayed by renewal theory. In this throughput, the result shown that Basic CSMA/CA protocol is profitable when the number of active node is smaller, or the length of packet is shorter, and CTS/RTS protocol is lucrative when the number of active node is larger, or the length of packet is longer. Also the result shown that hidden node less affected when the active node has small one, rather than when the active node has larger one.

• Journal of Digital Contents Society
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• v.14 no.1
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• pp.25-33
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• 2013

P2P(Peer-to-Peer) architecture can reduce the network bandwidth and resource on the server since peers exchange data chunks with each other, while server-client architecture causes a lot of traffic on the server. Peers receive a data more reliably when the number of participating peer increases. Currently, P2P traffic has accounted for about 65% of the world's Internet traffic and diverse P2P streaming services have launched combining to video streaming technology. However, the requirements and data chunk delivery algorithms for mobile P2P streaming service should be investigated, since the existing P2P technologies have been developed and designed for the wired network. In particular, the bandwidth fluctuation caused by user mobility, wireless packet collisions, and packet losses brings about different problems on the mobile P2P streaming service compared to existing P2P streaming service. In this paper, we analyzed the problem of mobile P2P streaming services in the 802.11n wireless LAN environment through experiments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3C
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• pp.248-255
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• 2002

An RF module in compliance with the IEEE 802.11a standard has been designed and its performance has been measured. Conventional heterodyne architecture with 580MHz intermediate frequency has been realized. Measurement results show that the receiver has a low Noise Figure of 5dB, the maximum gain of 70dB, and dynamic range as wide as 61dB. Also, the SAW filter used for channel selection in the IF section allowed minimum inter-channel interference. in addition to satisfying the RF output power requirement, the transmitter features its output P1dB as high as 34dBm so that the high peak-to-average ratio of the Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme can be handled with minimum nonlinear distortion. The output P1dB of 34dBm of the transmitter corresponds to back-off powers of 18dB and 11dB with respect to the output power for the low and the middle frequency bands, respectively.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.15 no.1
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• pp.95-101
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• 2016

Vehicular communications is system which can be applied for transmission of various safety messages or Intelligent Transportation Systems(ITS) applications by combining vehicle/road technology with Information and Communication Technology(ICT). In recent years, a variety of ITS services are available such as driving information, road conditions, V2X messages as well as navigation and traffic jams notification. In general, vehicular communications can be used for vehicle-to-vehicle and vehicle-to-infrastructure communication by adopting IEEE802.11p/1609 standard which is commonly known as wireless access in vehicular environments. In this paper, WAVE communication standard based on the IEEE802.11p is explained and signal characteristics in WAVE communication is introduced. Also, The H/W and S/W characteristics in Road Side Station and On Board Equipment for the Vehicle to Everything communication are analyzed. Received Signal Strength which is power of receiving signal of communication equipment is measured in test road to estimate the real WAVE communication's performance. It is shown that the implemented WAVE communication technology is satisfactory to provide ITS services.

• Journal of the Korea Society for Simulation
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• v.20 no.1
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• pp.19-28
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• 2011

The safety applications based on the IEEE 802.11p, periodically transmit the safety-related information to all surrounding vehicles with high reliability and a strict timeline. However, due to the high vehicle mobility, dynamic network topology and limited network resource, the fixed beacon scheduling scheme excess delay and packet loss due to the channel contention and network congestion. With this motivation, we propose a novel beacon scheduling algorithm referred to as spatial-aware(SA) beacon scheduling based on the spatial context information, dynamically rescheduling the beaconing rate like a TDMA channel access scheme. The proposed SA beacon scheduling algorithm was evaluated using different highway traffic scenarios with both a realistic channel model and 802.11p model in our simulation. The simulation results showed that the performance of our proposed algorithm was better than the fixed scheduling in terms of throughput, channel access delay, and channel load. Also, our proposed algorithm is satisfy the requirements of vehicular safety application.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7A
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• pp.702-709
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• 2008

This paper presents a frequency offset estimation scheme which can be used for packet based OFDM communication systems. The proposed scheme detects the failure of performing coarse frequency offset estimation and compensates the error of estimated coarse frequency offset. The preamble structure considered in this paper is based on the preamble specified in IEEE802.11a and IEEE802.11p standards. We performed simulation to compare the performance according to the different number of reference packets used to detect the failure of performing coarse frequency offset estimation. The simulation results show that the proposed scheme has better performance than the conventional scheme in the low SNR(below 2dB) environment.