• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.11
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• pp.21-27
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• 2002

When decision-directed channel estimation is used for QAM-OFDM systems, the optimal shape of the two-dimensional filter depends on the amplitudes of the modulated symbols as well as the channel characteristics such as delay spread, Doppler frequency, and signal-to-noise ratio. While most conventional channel estimation methods did not consider the amplitudes of the modulated symbols because of the large computational complexity, we propose a simple channel estimation method for multi-level-amplitude-modulated systems. The proposed method can effectively reduce the noise variance of the estimates with small-sized filtering and there is a possibility of reducing the implementation cost and producing better results by avoiding the bias due to large filter sizes.

• Journal of Biomedical Engineering Research
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• v.23 no.2
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• pp.87-99
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• 2002

This paper describes a method for overcoming the motion artifacts inherent in synthetic aperture(SA) imaging. based on the investigation results as to the influence of a target motion on synthetic aperture techniques. This method uses a region-based motion compensation approach in which only the axial motion is estimated and compensated for a given region of interest(ROI) under the assumption that the whole ROI moves uniformly The estimated axial motion is calculated with a crosscorrelation(CC) method at the Point where the focused signal has the maximum energy within the ROI. We also presents a method for estimating the axial motion using the autocorrelation(AC) method that is widely used to estimate average Doppler frequency Both computer simulations and in vivo experiments show that the proposed methods can improve greatly the spatial resolution and SNR of ultrasound imaging by implementing the SA techniques for two-way dynamic focusing without motion artifacts. In addition the AC-barred motion compensation method provides almost the same results as the CC-based one, but with a dramatically reduced computational complexity.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.10
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• pp.28-33
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• 2009

In this paper, we propose the receiver algorithms suitable for the VHF (Very High Frequency) digital link mode-2(VDL Mode-2) system. Unlike conventional digital communication systems using the root raised cosine filter as a transmit and receive filter, raised cosine filter is used as a transmit filter in the VDL Mode-2 system. Hence, it is crucial to design and implement the optimum lowpass receive filter by considering inter-symbol interference and noise performance. On the other hand, due to the short preamble pattern, it is crucial to develop an efficient packet detection algorithm for reliable communication link for the VDL Mode-2 system. Also, frequency offset due to the carrier frequency difference between transmitter and receiver and doppler frequency shift must be estimated and compensated for reliable communication. In this paper, the optimum receive filter, packet detection and frequency offset compensation algorithms are proposed and the performance of the VDL system employing the proposed algorithms are evaluated.

• Journal of Satellite, Information and Communications
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• v.10 no.4
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• pp.146-150
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• 2015

The COSPAS-SARSAT committee decides MEOSAR (Medium-Earth Orbit for search and rescue) service development for installing 406MHz SAR instruments on their respective MEO navigation satellite system of the United States, EU, and Russia, since 2000. The transmitted beacon signal is separately arrived by satellites with different FOA (Frequency of Arrival) and TOA (Time of Arrival). It is directly transferred to MEOLUT. In MEOLUT, a LUT track at least 3 or 4 satellites simultaneously and estimate location of beacon using time difference of arrival (TDOA) and frequency difference arrival (FDOA). But the transmitted distress signals may be overlapped each other because the distress beacons transmit signal on mean interval of 50 seconds in arbitrary time. It's difficult that simultaneously estimate location of beacon by current scheme for several overlapped distress signal. So we use cross ambiguity function (CAF) Map algorithm and present Multi-CAF MAP scheme in order to satisfy performance requirement of system. The performance is analyzed for COSAPS-SARSAT MEOSAR.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.2
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• pp.54-61
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• 2000

This paper presents the performance evaluation of channel estimation algorithm using RLS algorithm lot W-CDMA reverse link over Rayleigh fading channels. By obtaining BER(Bit Error Rate) performance through computer simulations, the RLS(Recursive Least Square) algorithm is compared with the existing WMSA(Weighted Averaging)(K=1,3) and constant gain algorithm. The channel structure, modulation and pilot patterns are applied to the ARIB (Association of Radio Industries and Business) and 3GPP (3rd Generation Partnership Project) ITU-R proposal for the IMT-2000. The BER performance of RLS algorithm with linear interpolation is similar to that of WMSA(K=1) and slightly superior to that of constant gain algorithm at low Doppler frequencies. Also, RLS algorithm performance is better than that of the WMSA(K=1,3) and constant gain algorithms about 4dB at BER=2.0$\times$$10^{-2}$ and Doppler frequencies $F_D$=320Hz. With increasing Doppler frequency, therefore, the BER performance of RLS algorithm with linear interpolation is superior to WMSA(K=L.3) and constant rain algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2A
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• pp.91-99
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• 2011

Several repeater systems are used to enhance the cell coverage to location such as shadow and rural areas in mobile systems. But the general RF repeater solutions are not suitable for high power outdoor environment because it has the weakness such as self oscillation problem With adoption of a adaptive digital filter technology, feedback interference cancellation repeater prevents oscillation by detecting and canceling the unwanted feedback signal between transmission and receiver antenna. In this paper, dual NLMS based interference cancellation method is proposed and the step size adaptation can be implemented by the estimation of the feedback channel Doppler frequency characteristics. The performance of the proposed algorithm is quantified via analysis and simulation for the static and multipath fading feedback channels.

• Proceedings of the KSRS Conference
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• 2009.03a
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• pp.147-150
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• 2009

본 논문에서는 해상 클러터를 고려하여 움직이는 물체의 SAR 원시 데이터를 생성하고, SAR 원시 데이터 중간 처리 결과인 range 압축 데이터의 azimuth 차분 신호로부터 물체의 속도를 측정하는 방법을 여러 가지 환경에 적용하여 그 정확도 및 적용 가능한 경우를 분석하였다. 움직이는 물체에 의한 도플러 중심 주파수의 변이가 azimuth 차분 신호에서 위상의 변화를 가져오므로, 이를 이용하여 움직이는 물체의 속도를 측정하는 알고리듬을 정리하였다. 이 알고리듬을 위에서 생성한 range 압축 데이터에 적용하여, 타깃이 되는 물체가 독립적으로 존재하는 경우, azimuth 상에 또 다른 속도를 가지는 산란체가 존재하는 경우, 그리고 높은 후방산란계수를 가지는 육지에 타깃이 되는 물체가 인접해 있는 경우를 가정하여 속도를 측정하였다. 그 결과, 타깃이 되는 물체가 SAR 영상에서 256 픽셀 범위 내에서 독립적으로 존재할 경우에는 높은 정확도로 물체의 속도를 측정할 수 있었으나, 128 픽셀 범위에 다른 움직이는 물체가 존재하거나, 높은 후방산란 계수를 갖는 육지와 인접해 있을 경우에는 최대 1m/s 의 오차를 나타냈다. 이는 주변 산란체의 영향에 의해 신호가 교란되어 목표물의 위치를 추정하는 과정에서 오차가 발생했기 때문이다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.132-139
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• 2016

This study was carried out near the waters of Jango port, Dangjin-gun, Chungcheongnam-do by utilizing 10kHz carrier frequency, for the purpose of measurement and analysis of underwater channel environment of the Western sea. For the measurement of horizontal channel environment, the separation distance between transmitter and receiver is made differently in the range between 10m and 4000m. Meanwhile, for the measurement of vertical channel environment, transmission and receiving side ships are fixed as contacted each other and measured differently depending on their depth of submergence. In this study, the Coherence Bandwidth and the Coherence Time were estimated by analyzing the Power delay profile of the real sea based on the measured data, and analyzing the doppler frequency through frequency conversion of received tone-signal, respectively. This study is expected to become a base study in carrying out the frame design for underwater communication to improve the communication and secure the reliability of communication in future underwater channel environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.7
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• pp.1128-1138
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• 2000

This paper presents two different approaches for channel estimation of IMT-2000 pilot symbol-assisted W-CDMA reverse link over Rayleigh fading channels of one and two paths. By obtaining BER performance through computer simulations, the proposed algorithms of 2-point second-order interpolation and IDD BWMA are compared with the performance of existing interpolation and adaptive algorithms. The BER performance of the proposed algorithms is superior to WMSA, linear and second-order Gaussian interpolation, LMS, and RLS algorithm in fast fading channels. In particular, the BER performance of the IDD BWMA algorithm is nearly insensitive for Doppler frequency within simulation range $E_b/N_0$ = 28 dB. The two proposed algorithms also have relatively simple structure and similar processing delay in comparison to the existing algorithms. Therefore, these algorithms are more suitable for high-speed mobile communication environments.

• The Journal of the Acoustical Society of Korea
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• v.38 no.3
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• pp.290-301
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• 2019

The proposed algorithm deals with a detection problem of target echo for narrow-band continuous-wave active sonar in the underwater environment in this paper. In the active sonar systems, ping signal emitted for target detection produces a signal that consists of multiple reflections by many scatterers around, which is called reverberation. The proposed algorithm aims to detect the low-Doppler target echo in the reverberant environment. The proposed algorithm estimates the bearing, frequency, and temporal bases based on beamspace-domain multichannel nonnegative matrix factorization. In particular, the bases are divided into two basis groups - the reverberation group and the echo group, then the basis groups are estimated independently. In order to evaluate the proposed algorithm, a simulation with synthesized reverberation was performed. The results show that the proposed algorithm has enhanced performance than the conventional algorithms.