• Journal of Advanced Navigation Technology
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• v.18 no.4
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• pp.260-267
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• 2014

For the purpose of improving the accuracy of Wide Area Differential GNSS (WA-DGNSS), estimation performance of ionospheric delay error which has a great impact on GPS error sources should be enhanced. This paper applied multi-constellation GNSS which represents GPS in USA, GLONASS in Russia, and Galileo in Europe to WA-DGNSS algorithm in order to improve performance of ionospheric delay estimation. Furthermore, we conducted simulation to analyze ionospheric delay estimation performance in Korean region by increasing the number of reference stations. Consequently, using multi-constellation GNSS to improve performance of ionospheric delay estimation is more effective than increasing the number of reference stations in spite of similar number of measurements which are in use for estimation. We expect this result can contribute to improvement for ionospheric delay estimation performance of single-frequency SBAS (Satellite Based Augmentation System) user.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1998.05a
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• pp.150-154
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• 1998

CDMAPCS 시스템은 Rake 수신기를 이용만 경로 다이버시티를 채택하여 우수한 시스템 향상을 얻을 수 있어 주로 TDMA 시스템에서 적용하고 있는 등화기를 사용할 필요가 없다. 그러나 CDMA PCS 시스템의 역방향 링크에서는 순방향과는 달리 채널의 크기 및 위상 추정에 필요한 파이롯 채널이 없어 성능의 저하를 가져오게 된다. 따라서 역방향 링크에서 채널환경에 따라 Rake 수신기의 성능에 미치는 영향을 분석하는 것은 중요하다. 본 논문에서는 시스템 성능 및 광대역 채널 파라미터 분석을 위해 광범위한 라이브러리와 시스템 구성의 유연성을 가지고 있는 Ptolemy [1] 플랫폼에서 CDMA PCS 시스템의 역방향 링크 규격에 따라 각 블록을 사용자 정의로 구현하였다. Ptolemy 시뮬레이터를 이용하여 CDMA PCS 시스템의 역방향 링크 비트오율 성능을 채널의 특성과 연관지어 분석하였다. 그리고 가상할 수 있는 각 채널 모델을 이용하여 CDMA PCS 시스템의 성능과 광대역 채널 파라미터 (예: 지연확산)와의 상관 관계를 파악하였다. 본 연구에서 CDMA PCS 시스템에서는 일반적으로 알려져 있는 지연확산보다 평균지연 파라미터가 더 높은 상관 관계가 있음을 발견하였다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.11a
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• pp.349-352
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• 2011

모바일 IPTV는 이동통신망을 이용하여 방송서비스를 제공한다. 이동통신망을 통해 원활하게 방송서비스를 제공하기 위해서는 극복해야 할 기술적인 장벽이 몇 가지 존재한다. 그 중 하나로, 사용자가 기지국과 기지국 사이를 이동하는 경우 통신망은 연속적으로 서비스를 제공하기 위해 상대 기지국에 사용자의 정보를 전달하는 핸드오버 절차가 수행된다. 핸드오버 절차가 수행되면 시간의 지연이 발생하는데, 시간 지연은 방송 품질에 영향을 미칠 수 있다. 따라서 핸드오버의 발생에 따른 성능 분석은 원활한 방송 서비스를 제공하는데 있어 필수적인 과정으로 볼 수 있다. 본 논문은 핸드오버 성능을 분석하기 위하여 기본적인 무선 액세스 네트워크의 기능이 이미 구현되어 있는 NLS(Network-level Simulator)를 이용한 모의실험 방법을 제시한다. 하지만, 성능 분석에 필요한 기능이 모두 NLS에 포함되어 있지는 않다. 따라서 본 논문에서는 NLS 중 하나인 QualNet을 이용하여 핸드오버 성능 분석에 필요한 기능을 구현하는 방법을 예로 설명한다. 성능은 핸드오버 지연시간과 지연시간의 CDF(Cumulative Distribution Function) 로서 나타낸다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.1
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• pp.91-102
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• 1996

The multicast routing algorithm is necessary to transmit multimedia traffic efficiently in ATM (asynchronous transfer mode) networks. In this paper, we propose the multicast routing algorithm which is based on VP/VC characteristic. The proposed algorithm is based on VP tree concept and using cost function which is based on VP/VC switching. The cost funication is composed of link cost, delay and weighting factor on delay and the weighting factor is calculated by delay sensitivity of the traffic. The proposed algorithm can choose delay bounded path which satisfies delay constraint, moreover it can choose optimal path among VPs which has the same link cost and satisfying delay constraint. With controlling weighting factor, proposed algorithm can set-up efficient path. When the weighting factor sets to be between 0.8 and 1, experimental results show that the perforance of proposed scheme is approximated to that of cost optimal algorithm and strongly delay optimized algorithm.

• The Journal of the Acoustical Society of Korea
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• v.34 no.6
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• pp.463-469
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• 2015

In this paper, we propose an underwater propagation delay-aware medium access control protocol and evaluate the performance of the proposed protocol. In the proposed propagation delay-aware medium access control protocol, a sink node can restore the received RTS frames that are not piled up in a slot time. We analyze and compare the performance of the proposed underwater propagation delay-aware medium access control protocol with that of the conventional medium access control protocol in various environments.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.5
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• pp.17-23
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• 2012

Recently, for spectral efficiency and power saving, an incremental best relay selection of a cooperative diversity scheme is proposed. However during the best relay selection process, there may exist a delay between channel estimation and actual data transmission. Consequently, this delay causes outdated channel state information (CSI). We analytically derive the effect of the outdated CSI to an incremental best relay selection diversity scheme. It is noted that the system performance deteriorates with decreasing the value of the correlation coefficient sensitively. When the correlation coefficient reduces from 1 to 0.9, the most performance degradation is denoted. However, the performance degradation is diminished with decreasing the correlation coefficient.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6B
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• pp.579-585
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• 2002

The investigation into the effect of various feedback errors on system performance can help the robust feedback channel design and transmission of exact feedback channel information as well. In this paper, we address the algorithm that determines space combining weight vector maximizing received signal power at mobile on frequency flat fading channel and investigate the performance degradation by feedback channel delay in the FDD/CDMA systems employing transmit beamforming. We observe the effect of feedback channel delay corresponding to the number of transmit antennas and the temporal/spatial correlation of channel. The results show that performance is more sensitive to feedback delay with the larger number of antennas when fadings at transmit antennas are not spatially correlated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1079-1086
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• 2008

During transfer alignment navigation information transferred MINS(master inertial navigation system) to SINS(slave inertial navigation system) has a changed time delay. The changed time delay degrades the performance of transfer alignment. This paper proposes an adaptive filter that estimates covariance of a time delay in real-time using residual of measurements. The performance of the adaptive filter is compared with that of the EKF(extended Kalman filter) in case of transfer alignment for vertical launcher in the ship. The results show that proposed method is more effective than EKF in estimating attitude errors.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.4
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• pp.600-610
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• 2001

The effects of group delay and non-linear characteristics on high data rate(HDR) satellite channel are presented in this paper Based on the modeling of group delay and non-linear characteristics the system performances which provide various data rate services were analyzed in Ka-band satellite channel. As the transmission data rate is increased, the degradation due to these channel characteristics is severely increased. The linear component of group delay and the AM-AM component of non-linear characteristics severely affect the system performance. To efficiently provide the various service via the same transmission system it is necessary to equalize the primary impairment factors. The optimum operating points of HDR satellite transmission system are implemented by considering the analyzed results on channel characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.4
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• pp.310-317
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• 2013

In this paper an ESPRIT-based super-resolution time delay estimation algorithm is developed for real-time locating system (RTLS) and its performance is analyzed in various multipath environments. The performance of the existing correlation method for time delay estimation seriously degrades in multipath environments where the relative time delays of multipath signals are less than a PN chip. To solve the problem we shall develop a frequency domain super-resolution time delay estimation algorithm using the ESPRIT, the most representative super-resolution direction-of-arrival (DOA) estimation algorithm, and analyze its performance in various multipath environments.