• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.8A
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• pp.745-751
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• 2006

The transmitter requires knowledge of the channel status information in order to adopt the adaptive modulation and coding scheme(AMC) for OFDM system. But in the outdoor environment which the users have high mobility, the channel status information from the users is outdated, so that it induces the degradation of system throughput and packet error rate(PER) performance. To solve this problem, researches about applying channel prediction technique to the AMC scheme have been proceeded. Most channel prediction techniques assume that there is no channel variation in the predefined time duration, e.g., a slot. As a result, those techniques cannot compensate the degradation of PER performance resulting from the rapid variation of channel during the slot duration. This paper introduces a novel channel prediction technique for OFDM/FDD system to support adaptive modulation and coding scheme over rapidly time-varying multipath fading channel. The proposed channel prediction technique considers the time-varying nature of channel during the slot duration. Simulation results show that the AMC scheme of OFDM/FDD system utilizing the proposed channel prediction technique can guarantee the target PER of 1% without any loss of system throughput compared with the case supported by the conventional channel prediction under ITU-R Veh A 30km/h.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5A
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• pp.381-390
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• 2009

In this paper, we propose a seamless intra MR-BS handover scheme based on IEEE802.16j transparent. The proposed scheme estimates the outage probability of mobile stations at a base station, finds the optimum relay user, and provides low handover latency for seamless data transmission. The simulation results show that the proposed scheme outperforms the conventional handover schemes in terms of the handover latency by 65% of conventional scheme. Moreover, the proposed scheme exhibits lower packet error rate compared with the conventional handover scheme when a mobile station moves to outside of the cell coverage and reduce both outage probability and the number of handover about 50% from setting forgetting factor and redundant threshold.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.9
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• pp.1057-1062
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• 2014

Vehicular communications 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 this paper, we represent measurement results of radio characteristics of vehicular communications using IEEE 802.11p based system in urban environments. Radio characteristics are based on the packet error rate (PER) and received spectrum mask. Using measurement results, we discuss implementation issues of vehicular communication systems for supporting reliable services.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2002.11a
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• pp.201-206
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• 2002

패킷 기반 통신 시스템에서는 비트오율 보다는 패킷오율이 시스템 파라미터 설계에 보다 중요한 역할을 한다. 패킷오율을 분석하기 위해서는 대부분의 접근이 패킷을 이루고 있는 비트열의 오류 발생 사건을 독립이라고 가정한다. 그러나 실제의 통신 시스템에서는 오류 발생 형태가 버스트 형태로 그룹을 이루고 있다[1]. 본 논문은 비터비 디코더를 포함하는 통신시스템에 있어서의 버스트의 확률 분포를 기반으로 한 PER 모델을 제안하고, Eureka-147 방식의 디지털 오디오 방송 시스템의 시뮬레이션을 통하여 얻은 비트열에 대한 패킷오율과 제안한 패킷오율 모델과의 비교를 통하여 제안한 모델을 검증하였다.

• Journal of the Optical Society of Korea
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• v.11 no.3
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• pp.93-96
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• 2007

We demonstrate a 240 km reach DWDM-PON at 8-Gb/s capacity based on wavelength-locked Fabry-Perot laser diodes and a bidirectional EDFA. We achieve a packet-error-free transmission in both the 64 upstream and 64 downstream channels, guaranteeing a 125 Mb/s symmetric data rate per user. There is no noticeable dispersion penalty. The power penalty due to the crosstalk induced by the DWDM transmission and detuning between AWGs is less than 1.2 dB, when the detuning is within ${\pm}0.12 nm$.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.1027-1029
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• 2012

최근 IEEE 802.11(Wi-Fi), IEEE 802.15.1(Bluetooth), IEEE 802.15.4(ZigBee) 등 2.4GHz 대역의 비허가 주파수 대역의 사용이 늘어나고 있다. 통신 방식은 다르지만 사용 주파수 대역이 동일하다는 관점에서 간섭의 영향을 피할 수 없기 때문에 각 기술간 간섭의 영향을 완화하고 간섭 상황에서 각 기술의 성능을 향상하기 위해 각 기술에 대한 상호 작용하는 것에 대한 연구가 진행 되어야 한다. 본 논문에서는 IEEE 802.11b/g, IEEE 802.15.1, IEEE 802.15.4가 2.4GHz 대역에서 상호간에 미치는 영향을 분석하기 위해 PER(Packet Error Rate) 분석을 수행하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1613-1621
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• 2015

This paper analyzes the rate adaptation scheme and suggests applicable strategy of the MCS(Modulation and Coding Scheme) for improving DCF throughput in the IEEE 802.11ad and 802.11ad wireless LAN. IEEE 802.11ac and 802.11ad wireless LAN provide MCS technique that dynamically adjusts modulation level and code rate to the time-varying channel conditions in order to obtain considerably high data rates. But these standards did not provide rate adaptation algorithm, so this paper surveyes rate adaptation algorithm and suggests MCS scheme applied to IEEE 802.11ac and 802.11ad wireless LAN. Specially A MAC(Medium Access Control) layer throughput is evaluated over error-prone channel in the IEEE 802.11ac-based wireless LAN. In this evaluation, DCF (Distributed Coordination Function) protocol and A-MPDU (MAC Protocol Data Unit Aggregation) scheme are used. Using theoretical analysis method, the MAC saturation throughput is evaluated with the PER (Packet Error Rate) on the condition that the number of station, transmission probability, the number of parallel beams and the number of frames in each A-MPDU are variables.

• 전자공학회논문지 IE
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• v.48 no.1
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• pp.30-35
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• 2011

In this paper, we propose a method to improve the performance of initial channel estimation (CE) for the multiband-OFDM (MB-OFDM) UWB. The performance of the initial CE can be generally improved as increasing the number of the used preamble symbols. The MB-OFDM specification presents two CE symbols per band in preamble format. The performance of CE estimation with two CE symbols may be satisfied in relatively high sensitivity -77.5 and -72.5 dBm for 200 Mbps and 480 Mbps data rate, respectively, but can not be enough in the degraded 55 Mbps and 110 Mbps sensitivities such as -83.5 and -80.5 dBm, respectively. A method proposed in this paper achieves the performance improvement by extending CE estimation region to packet synchronization (PS) symbols and frame synchronization (FS) symbols including two CE symbols. This can improve the CE performance in the degraded SNR and increase the link-margin by reducing the error rate in physical-layer header. The link-margin improvement obtained by the proposed CE preamble can induce the decrease of error-rate in physical-layer header and increase of communication throughput. Simulation results for the proposed initial method show that the performance is improved by about 0.7 dB at 10-4 bit-error-rate using '4' symbols than initial method using only two CE symbols.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.5
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• pp.1608-1615
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• 2010

In this paper, we proposed the method called "DoublePico"(Double Piconet) forovercoming low data transmission rate in a scatternet. This needs a new Ad-hoc network topology to transmit with high rate. Every node performs the function of the relay station. DoublePico has two bluetooth devices that should form two different poconets; every node can make a link between two different piconets. Two different piconets are linked in one node by the link with two bluetooth divices thereby forming the Ad-Hoc network. In this paper, we shows the method of DoublePico which supports about 457kbps of the maximum data transmission rate. This method supports a higher data transmission rate than the traditional bluetooth's Ad-Hoc topology by using analysis and comparison of existing algorithm of bluetooth specification and simulation results. Specifically, this paper focuses on the impact of intererence on the PER (Packet Error Rate), throughput performance, and the throughput improvement with SAW(Stop and Wait)-ARQ scheme in DoublePico.

• ETRI Journal
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• v.26 no.5
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• pp.375-383
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• 2004

This paper proposes a common interleaving method associated with independent channel-encoding among transmitter antenna branches in orthogonal frequency and code division multiplexing based on multiple-input multiple-output (MIMO) multiplexing to achieve an extremely high throughput such as 1 Gbps using a 100 MHz bandwidth. This paper also investigates the average packet error rate performance as a function of the average received signal energy per bit-to-background noise power spectrum density ratio $(E_b/N_0)$. We found that the loss in the required average received $E_b/N_0$ of the proposed method is only within approximately 0.3 dB in up to a 12-path Rayleigh fading channel, using 16QAM and Turbo coding with a coding rate of 5/6. We also clarify that even for a large fading correlation among antenna branches, 1 Gbps is still possible by increasing the transmission power. Therefore, the proposed method reduces the processing rate to 1/4 in the turbo decoder with only a slight loss in the required average received $E_b/N_0$.