• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.4
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• pp.332-341
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• 1997

In this paper, we propose an adaptive trellis-coded Multipe Quadrature Amplitude Modulation (ATCMQAM) for slowly varying Rayleigh fading channels. The proposed system adaptively controls the coding rate combined with modulation level of pargmatic approach to trellis-coded modulation according to the instantaneous fading channel conditions, and employs MQAM as modulation scheme. Results by computer simulation show that the proposed adaptive model using MQAM can realize higher quality transmission with the improvement more than 0.5~1 bit in average bit rate, and there is a coding gain of 2~5 dB, depending on the high SNR value, compared with the conventional adaptive model employing MPSK.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1A
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• pp.38-47
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• 2006

In this paper, we propose a velocity-adaptive channel estimation scheme using the simple zero-forcing technique in the frequency domain. Channel estimation is performed by removing frequency components that are higher than the maximum Doppler frequency in the received signal. The proposed scheme can be extended to the combined estimation scheme for channel coefficients and mobile velocity using one FFT/IFFT module. Simulation results show that the proposed scheme outperforms conventional schemes for a wide range of mobile velocities($3{\sim}300\;Km/h$). Finally, the MSE for the proposed channel estimation scheme is analyzed.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.533-536
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• 2000

We consider the design of quadrature amplitude modulation (QAM) transceivers f3r fixed wireless communications. The use of adaptive power control in the transmitter (Tx) can provide BER performance robust to fading and improved BER performance. The BER performance is evaluated by analytical and simulation results when multi-level QAM transceiver employing power control in the Tx is applied to fixed wireless channel with flat fading and frequency selective fading. The effect of power control parameters such as power control range and power control step size is investigated

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.285-286
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• 2008

In this paper, we propose adaptive search channel estimate algorithm. The proposed algorithm is modified LMS algorithm which has a variable step size and parallel convolution. In simulation result, a error estimate accuracy of the proposed algorithm is about -20 dB and general LMS algorithm is about 10 dB. The proposed algorithm is better error estimate accuracy than general LMS algorithm.

• Proceedings of the IEEK Conference
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• 2002.06e
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• pp.39-42
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• 2002

A new adaptive PRML architecture, considered not only DVD-ROM but also DVD-Multi including DVD-RAM as well, is presented to demonstrate its superiority over the conventional analog channel in a DVD system. For this new architecture, channel adaptation algorithm using gain controlled type of FIR filter, and asymmetry compensation algorithm using expected level adaptation of viterbi decoder are presented. In addition, a method of modelling the disk tilt and asymmetrical read-back signal are discussed.

• The Magazine of the IEIE
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• v.12 no.5
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• pp.23-35
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• 1985

본 논문은 디지털 음성통신에서 사용되는 예측부호화(predictive coding) 방식에 관하여 기술하고 있다. 특히 전송속도가 16∼48kbit/s 대역에서 많이 사용하고 있는 adaptive differential pulse code modulation(ADPCM)과 adaptive delta modulation(ADM)에 관하여 중점적으로 토의한다. 또한 variable-rate ADPCM과 ADM에 관해서 기술하고, 이들 시스템의 noisy channel에서의 효과 및 성능개선방법, 그리고 PCM과의 transcoding에서의 문제점 등을 통의한다. ADPCM은 최근 CCITT에서의 표준화 결과로 앞으로 PCM과 함께 많이 쓰여질 전망이며, ADM은 시스템이 간단하고 또한 channel error에 강한 이유로 특수통신에 많이 쓰여질 것이다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1995.06a
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• pp.59-61
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• 1995

An adaptive code rate change scheme in DS-SSMA systems is proposed. In the proposed scheme, the error correcting code rate is changed according to the channel state, the effective number of users. The channel state is estimated based on retransmission requests. The criterion for the change of the code rate is to maximize the throughput under given error bound.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.213-214
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• 2006

To reduce the feedback overhead of predicted CSI (channel status information) of adaptive OFDM (orthogonal frequency division multiplexing), we use partial data of CSI and employ linear interpolation. Simulation results show estimated CSI and its MSE.

• Journal of Korea Society of Digital Industry and Information Management
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• v.5 no.3
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• pp.99-105
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• 2009

This paper suggests novel signal processing methods for optimal beamforming of smart antenna system in CDMA2000 mobile communication environments. This method utilize characteristics of the reverse pilot channel of CDMA2000 mobile communication systems, and applies them to improve the performance of an adaptive algorithm, which is used to a smart antenna system for beamforming. To perform the best beamforming, it is important to get an exact beamforming algorithm. This paper proposed an algorithm based on Laglange multiplier which has such an adaptive process, and also proposed the method to demodulate the received signal through array antenna using pilot channel in CDMA2000 environment. This paper analysed the enhanced performance of proposed algorithm in various signal environment through signal modeling of physical layer in CDMA2000 reverse link.

• Journal of Korea Multimedia Society
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• v.6 no.1
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• pp.114-120
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• 2003

Blind channel estimation of communication channels is a problem of important current theoretical concerns. Recently proposed solutions for this problem exploit the diversity induced by antenna array or time oversampling, leading to the so-called, second order statistics techniques. This paper proposes the blind adaptive channel estimation using multichannel linear prediction method. Computer simulations are presented to compare the proposed algorithm with the existing ones.