• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.11a
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• pp.344-344
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• 2004

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.2
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• pp.131-140
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• 1998

MAI(Multi-Access Interference) and fast channel variation due to the fading environment are the major problems in the mobile CDMA communication systems. Recently, interest has been increasing in applying the Adaptive Linear MMSE Detector to MAI cancellation in the CDMA reverse link. In this paper, we propose a modified Adaptive Linear MMSE Detector structure which can be used in Long-duration code CDMA system in the presence of independent Rayleigh fading. We use independent multiple tap-weight vector structure to cope with the variation of spreading sequence pattern between neighbor symbols because of the Long-duration code. In this case, more exact channel parameter estimation is required. To solve this problem, we use coherent CDMA structure which can track the channel parameters like amplitude and phase by employing the low power pilot channel in the CDMA reverse link.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.20-23
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• 2003

A reduced-state sequence estimation(RSSE) for trellis-coded (TC) 8PSK/cyclic prefixed single carrier(CPSC) with minimum mean-square error-liner equalization(MMSE-LE) on frequency-selective Rayleigh fading channels is proposed. The Viterbi algorithm (VA) is used to search for the best path through the reduced-state trellis combined equalization and TCM decoding. The symbol error probability of the proposed scheme is confirmed by computer simulation.

• Journal of Digital Convergence
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• v.16 no.5
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• pp.231-237
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• 2018

This paper investigates the impact of the channel variations and channel estimation errors on the error performance of convolutional coded STBC systems. We consider the orthogonal Almouti STBC and the quasi-orthogonal Jafarkhani STBC, and the error performance of the convolutional coded STBC system is investigated according to the channel variation and channel estimation error via numerical simulations. Simulation results show that, if the channel variation speed is slow, time diversity effects improve the error performance compared to the static-channel cases. However, if the channel variation speed is fast, unlike ZF or MMSE detection, the conventional STBC detection has the significant performance degradation especially with the quasi-orthogonal Jafarkhani STBC. Further, the error performance of the system is significantly degraded as the channel estimation errors become stronger, regardless of the detection scheme and channel variation speed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8A
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• pp.813-819
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• 2007

In this paper, the effect of a propagation delay resulting from the use of an OFDM-based cellular system with a transparent mobile multi-hop relay(MMR) is initially analyzed. Then, channel estimation techniques, a least square(LS) method and a minimum mean square error(MMSE) method, for the OFDM systems with throughput enhancement(TE) MMR or cooperative MMR are proposed. The proposed channel estimation techniques can overcome the performance degradation caused by the propagation delay in TE MMR or cooperative MMR systems. It is demonstrated by computer simulation that the proposed channel estimation techniques for OFDM systems with transparent MMR are superior to the conventional techniques in terms of mean square error(MSE) and bit error rate(BER).

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.3
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• pp.11-20
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• 2016

In this paper, we propose the channel estimation scheme for Long Term Evolution-Advanced (LTE-A) downlink system. The proposed scheme uses the fast fourier transform (FFT) interpolation scheme for the user moving at a high speed. The FFT interpolation scheme converts the channel frequency response obtained from least square (LS) or minimum mean square error (MMSE) channel estimation scheme to time domain channel impulse response by taking the inverse FFT (IFFT). After windowing the channel response in the time domain, we can obtain the channel frequency response by taking the FFT. We perform the system level simulation based on 20MHz bandwidth of 3GPP LTE-A downlink system. Simulation results show that the proposed channel estimation scheme can improve signal-to-noise-plus-interference ratio (SINR), throughput, and spectral efficiency of conventional system.

• The Journal of the Acoustical Society of Korea
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• v.32 no.1
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• pp.22-31
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• 2013

In this paper, we propose a method that estimates the channel response from underwater communication signals with MMSE (Minimun Mean Squared Error) and detects dominant components automatically based on power of response components using CFAR (Constant False Alarm Rate). Statistical characteristics are analyzed with variation of magnitude and phase and time coherence via experimental data obtained by drifting transmitter and receiver. We show that bit error rate has small difference, 1.2 times, compared with the case using every channel information estimated within data period when estimation and equalization is performed with extracted characteristic obtained by the proposed method.

• The Journal of the Acoustical Society of Korea
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• v.29 no.2E
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• pp.86-99
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• 2010

This paper analyzes the performance of various single channel speech enhancement algorithms when they are applied to automatic speech recognition (ASR) systems as a preprocessor. The functional modules of speech enhancement systems are first divided into four major modules such as a gain estimator, a noise power spectrum estimator, a priori signal to noise ratio (SNR) estimator, and a speech absence probability (SAP) estimator. We investigate the relationship between speech recognition accuracy and the roles of each module. Simulation results show that the Wiener filter outperforms other gain functions such as minimum mean square error-short time spectral amplitude (MMSE-STSA) and minimum mean square error-log spectral amplitude (MMSE-LSA) estimators when a perfect noise estimator is applied. When the performance of the noise estimator degrades, however, MMSE methods including the decision directed module to estimate a priori SNR and the SAP estimation module helps to improve the performance of the enhancement algorithm for speech recognition systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1499-1509
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• 2000

In this paper, we propose an efficient channel estimation technique for space-time coded orthogonal frequency-division multiplexing (OFDM) systems with transmitter and receiver diversity. The proposed technique estimates uniquely all channel frequency responses needed in a decoder of space-time coded OFDM systems using "comb-type" raining symbols. The computational complexity of the proposed technique is reduced dramatically, compared with the previous minimum mean-squared error (MMSE) technique, due to the processing is made all in the frequency-domain. Also, several other techniques for mitigating random noise effect and tracking channel variation are discussed to further improve the performance of the proposed approach. The performances of the proposed approach are demonstrated by computer simulation for mobile wireless channels. channels.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.7
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• pp.1277-1282
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• 2016

In the next generation wireless communication systems, an energy harvesting from radio frequency signals is considered as a method to solve the lack of power supply problem for sensors. In this paper, we try to propose an efficient algorithm for simultaneous wireless information and power transfer in energy harvesting networks with channel estimation error. At first, we find an optimal channel training interval using one-dimensional exhaustive search, and estimate a channel using MMSE channel estimator. Based on the estimated channel, we propose a power allocation and splitting algorithm for maximizing the data rate while guaranteeing the minimum required harvested energy constraint, The simulation results confirm that the proposed algorithm has an insignificant performance degradation less than 10%, compared with the optimal scheme which assumes a perfect channel estimation, but it can improve the data rate by more than 20%, compared to the conventional scheme.