• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1383-1390
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• 2000

Pilot symbol-based coherent detection is used to increase the link capacity in CDMA systems. In order to detect data efficiently, data signals must be compensated with channel estimation values obtained by using pilot symbols. Many channel estimation schemes were published in previous literatures. However, most of these schemes have performance deterioration in fast fading because of using average vaules of several timeslots. In this paper, we propose an improved channel estimation scheme which is efficient in fast fading and also operates in slow fading satisfactorily. Through computer simulation we show that the proposed scheme has better performance than other schemes in terms of both MSE and BER in fast fading and show robustness for variation in Doppler frequencies.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.4
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• pp.861-868
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• 2000

This paper discusses the development of an acoustic vector channel simulator for the performance analysis of an acoustic digital communication system. The channel simulator consists of transmission module, acoustic channel model, receiver, beamformer, and adaptive equalizer. QPSK source signal is generated by the parameters specified by a user. The transmitted signal generates multipath signals which have a different delay, amplitude, and dopper frequency. The multipath singnals with the acoustic noises are the received signal. This paper presents the performance analysis of an acoustic digital communication system according to the antenna structure and the various baseband signal processing techniques.

• The Journal of the Acoustical Society of Korea
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• v.17 no.5
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• pp.35-41
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• 1998

본 논문에서는 다중 빔을 사용한 저궤도 위성 이동 통신시스템 환경에서 부호 분할 다중접속 및 주파수 분할 다중접속 방식의 채널 용량을 비교 분석하였다. 위성 중계기의 출 력의 효율성, 주파수 효율성, 부호화 방식 및 안테나의 EIRP나 G/T형태 등과 같은 파라미 터들을 순방향 링크와 역방향 링크에서 채널 용량을 결정하는 시스템 파라미터로서 고려하 였고, 피더 링크(feeder link)는 Ku-band를, 사용자는 링크는 L-band를 사용한 다중 스팟빔 (spot beam) 시스템을 채널 용량 분석의 모델로 적용하였다. 분석결과 도플러 현상 및 다중 경로에 강한 부호 분할 다중접속 방식이 용량면에서 주파수 분할 다중접속 방식에 비해 성 능이 우수함을 알 수 있었다.

• Journal of Advanced Navigation Technology
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• v.13 no.4
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• pp.544-550
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• 2009

In this paper, we proposed the radio wave propagation characteristics of the next-generation ultrafast wireless communication system in millimeter-wave fading channel. For considering doppler shift and Rayleigh fading simultaneously, the fading simulator of Jakes model implemented and analyzed the performance of the next-generation wireless communication system. In addition, the error rate characteristics of DS-CDMA system analyzed in the millimeter-wave fading channel and the system performance improved by coding technique and diversity technique.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2001.06a
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• pp.33-36
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• 2001

In MC-CDMA systems effects of delay spread of the channel are reduced with increased symbol duration by simultaneously transmitting data symbols on the parallel subcarriers. However, the increased symbol duration causes the system to be more vulnerable to time selective fading. In this paper, we investigate the effects of time selective fading characteristics of the mobile channel from the viewpoint of desired signal power to inter-carrier interference power ratio at the combiner output of the MC-CDMA receiver.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2005.11a
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• pp.87-90
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• 2005

이 연구는 DVB에서 제안한 휴대형 디지털 TV 전송시스템인 DVB-H 시스템의 이동수신 성능을 분석하였다. DVB-H 시스템은 DVB-T 시스템을 휴대용으로 보완한 것으로 4K 모드, MPE-FEC 및 In-depth Interleaver 등이 추가되었으며, 이 연구는 각 추가 기능에 대하여 이동수신 성능향상 정도를 분석하였다. 이동수신 환경을 제공하기 위하여 COST 207을 적용하였다. 4K 모드는 최대지연시간이 긴 다중경로채널에서 8K 모드와 유사하고 2K 모드보다 훨씬 우수한 수신성능을 보였으며 도플러에 대해서는 2K와 8K 모드의 중간정도의 수신성능을 보여 주었다. MPE-FEC와 In-depth Interleaver는 이동수신채널에서 약간의 수신성능 향상을 보여 주었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.5
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• pp.798-805
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• 2006

I evaluate the BER performance of downlink OFDMA systems in time variant Rayleigh Doppler fading channel, considering the carrier frequency offset and the nonlinear high power amplifier. I obtain the required output back-off of the nonlinear amplifier and value of frequency offset for good BER performance. And I also analyze the BER degradation upon Doppler fading channel.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.12
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• pp.2391-2397
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• 2007

I evaluate the BER performance of uplink OFDMA systems in time variant Rayleigh Doppler fading channel, considering the carrier frequency offset and the nonlinear high power amplifier. I obtain the required output back-off of the nonlinear amplifier and value of frequency offset for good BER performance. And I also analyze the BER degradation upon Doppler fading channel.

• Journal of KIISE:Information Networking
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• v.37 no.2
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• pp.85-93
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• 2010

WLAN virtualization can make multiple simultaneous experiments, each of which is conducted by a separate researcher, share scarce wireless resources in an IEEE 802.11 WLAN. The experiment performed in a virtualized WLAN should be consistent with that in a non-virtualized WLAN. The more similar these two experimental results, the better the consistency. To this end, we propose a novel virtualization scheme that has good consistency by preventing multiple simultaneous experiments from interacting with one another, without any modifications to the IEEE 802.11 standard. Through an intensive simulation study, we confirm that the consistency depends not only on the number of simultaneous experiments but also on wireless channel characteristics such as Doppler frequency and Ricean factor. According to such dependencies, the proposed scheme is optimized, so that it supports good consistency.

• Journal of Advanced Navigation Technology
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• v.8 no.2
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• pp.120-128
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• 2004

Although conventional OFDM/QAM modulation scheme using guard interval is robust to channel induced ISI (Inter-Symbol Interference) in time-domain, it is very sensitive to ICI (Inter-Carrier Interference) due to doppler effect in frequency domain. OFDM/OQAM-IOTA modulation scheme utilizes IOTA (Isotropic Orthogonal Transform Algorithm) filter that has orthogonality in time and frequency domain so that it is robust to delay spread and doppler effect. OFDM/OQAM-IOTA system can increase bandwidth effeciency since it does not use guard interval. In this paper, we show the structure of OFDM/OQAM-IOTA and perfect channel estimation scheme for OFDM/OQAM-IOTA system. We also compare OFDM/OQAM-IOTA system and OFDM/QAM system in AWGN and 1-path Rayleigh fading channel. Simulation results show that OFDM/OQAM system outperforms OFDM/QAM system.