• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.8A
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• pp.745-751
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• 2006

The transmitter requires knowledge of the channel status information in order to adopt the adaptive modulation and coding scheme(AMC) for OFDM system. But in the outdoor environment which the users have high mobility, the channel status information from the users is outdated, so that it induces the degradation of system throughput and packet error rate(PER) performance. To solve this problem, researches about applying channel prediction technique to the AMC scheme have been proceeded. Most channel prediction techniques assume that there is no channel variation in the predefined time duration, e.g., a slot. As a result, those techniques cannot compensate the degradation of PER performance resulting from the rapid variation of channel during the slot duration. This paper introduces a novel channel prediction technique for OFDM/FDD system to support adaptive modulation and coding scheme over rapidly time-varying multipath fading channel. The proposed channel prediction technique considers the time-varying nature of channel during the slot duration. Simulation results show that the AMC scheme of OFDM/FDD system utilizing the proposed channel prediction technique can guarantee the target PER of 1% without any loss of system throughput compared with the case supported by the conventional channel prediction under ITU-R Veh A 30km/h.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.83-85
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• 2016

The OFDM with LS signal detection performs worse in fast time varying channels as the channel matrix has higher chance of becoming ill-conditioned. Various regularization methods are applied to avoid performance degradation in LS signal detection. In this paper, we proposed a CGLS method with the stopping criteria imposed by the characteristics of the modulation method, which shows performance comparable to that of the optimal LMMSE.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.10
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• pp.53-59
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• 2004

A new downlink beamforming method is proposed for coherent detection of Cellular systems with BPSK modulation where there exists only common pilot channel. To solve phase mismatch between traffic and pilot signals at desired mobile and to reduce interference to other mobiles, the proposed downlink beamforming method considers a cost function of signal to interference ratio criteria and gives a solution for the cost function. The computer simulation showed that the proposed method can solve the phase mismatch problem and give improved BER performance in time-varying channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.6B
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• pp.1127-1135
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• 2000

The beamforming procedure in Adaptive Array Antenna System is affected by signal degradation and data rate due to DS-CDMA characteristics. Until this time, a lot of techniques are suggested to overcome this problems. This paper shows the simulation result about the beamforming performance of symbol level system that process slow data rate, compensated signal by despreading procedure in front of beamformer, and that of chip level system that process chip level signal without it. we analysis the performance using MSE, beam pattern, scattering points of beamformer output. chip level system is superior to symbol level system in time varying channel, while the performance of them didn't have difference in static channel.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.4
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• pp.826-832
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• 2007

A recurrent neural network has been frequently used in equalizing the channel for fast communication systems. The existing techniques, however, have mainly dealt with time-invariant chamois. The modern environments of communication systems such as mobile ones have the time-varying feature due to fading. In this paper, powerful decision feedback - recurrent neural network is used as channel equalizer for nonlinear and time-varying system, and two kinds of algorithms, such as extended Kalman filter (EKF) and sigma-point Kalman filter (SPKF), are proposed; EKF is for fast convergence and good tracing function, and SPKF for overcoming the problems which can be developed during the process of first linearization for nonlinear system EKF.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2000.12a
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• pp.25-28
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• 2000

시변 특성을 갖는 무선 채널 환경에서 UEP(Unequal Error Protection) 채널 부호화 방법은 효율적인 정보 전송을 가능케 한다. 본 논문에서는 IP-SCCC (Interleaved Puncturing Serially Concatenated Convolutional Codes)로 CSI(Channel State Information)와 SSI(Source Significance Information)를 이용한 두가지 UEP 채널 부호화 방법을 제안한다. 또한 AWGN(Additive White Gaussian Noise)과 Rayleigh 페이딩이 존재하는 채널을 가정하고 모의 실험을 통해 알고리즘의 우수성을 검증한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5C
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• pp.556-564
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• 2007

This paper proposes an efficient scheme to track a time variant channel induced by multi-path Rayleigh fading in mobile MIMO-OFDM systems with null sub-carriers. The proposed adaptive channel tracking scheme removes in the frequency domain the interfering signals of the other transmit (Tx) antennas by using a predicted channel frequency response before starting the channel estimation. Time domain channel estimation is then performed to reduce the additive white Gaussian noise (AWGN). The simulation results show that the proposed method is better than the conventional channel tracking method [3] in time varying channel environments. At a Doppler frequency of 300 Hz and bit error rates (BER) of 10-3, signal-to-noise power ratio (Eb/N0) gains of about 2.5 dB are achieved relative to the conventional channel tracking method [3]. At a Doppler frequency of 600 Hz, the performance difference between the proposed method and conventional one becomes much larger.

• The Journal of the Acoustical Society of Korea
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• v.41 no.4
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• pp.410-418
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• 2022

Channel reliability estimation for iterative codes such as turbo codes is very important factor in time varying underwater acoustic channel, an incorrect estimation of channel reliability induced performance degradation. Therefore, this paper presents an optimal channel reliability estimation method for turbo coded FSK signal with rate of 1/3. The estimated BER algorithm is a method that can estimate the reliability of received data by comparing received data and decoded data, and we determine optimal channel reliability by using the method. In order to analyze the performance, the experiment was conducted on a lake in Munkyeong city by moving in the range of 300 m to 500 m. At the result of applying presented method to failed decoding packets, we confirm all packets are decoded successfully.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1996.10a
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• pp.27-30
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• 1996

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.256-268
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• 2008

This paper proposes an efficient scheme to track the time variant channel induced by multi-path Rayleigh fading in mobile wireless Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems with null sub-carriers. In the proposed method, a blind channel response predictor is designed to cope with the time variant channel. The proposed channel tracking scheme consists of a frequency domain estimation approach that is coupled with a Minimum Mean Square Error (MMSE) time domain estimation method, and does not require any matrix inverse calculation during each OFDM symbol. The main attributes of the proposed scheme are its reduced computational complexity and good tracking performance of channel variations. The simulation results show that the proposed method exhibits superior performance than the conventional channel tracking method [4] in time varying channel environments. At a Doppler frequency of 100Hz and bit error rates (BER) of 10-4, signal-to-noise power ratio (Eb/N0) gains of about 2.5dB are achieved relative to the conventional channel tracking method [4]. At a Doppler frequency of 200Hz, the performance difference between the proposed method and conventional one becomes much larger.