• Journal of Korea Society of Industrial Information Systems
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• v.16 no.4
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• pp.19-26
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• 2011

Relay-assisted multiple input multiple output (MIMO) technique has become a promising candidate for next generation broadband wireless communications. In this paper, we propose maximum ratio combining (MRC) minimum mean-square-error (MMSE) equalization for single carrier-frequency domain equalizer (SC-FDE) in amplify-and-forward (AF) relaying networks. The performance of SC-FDE system can be improved considerably by achieving both the diversity gain and the MMSE equalization gain when the signals from source-destination (S->D) and source-relay-destination (S->R->D) are combined and equalized by means of the MMSE criteria. We find the weighting coefficients of MRC combining and the tap coefficients of MMSE equalizer for SC-FDE in AF relaying networks. Simulation results show that the proposed relay-based system considerably outperforms the conventional SC-FDE system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.1
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• pp.76-82
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• 2010

In this paper, we analyze the performance of the block linear MMSE equalization for OFDM systems in doubly selective channels by computer simulations. The block linear MMSE equalization shows somewhat unusual BER characteristics in that the BER curve drops at first as SNR increases but then rises up as SNR increases further beyond some point. In this paper, we investigate the BER characteristics of the block linear MMSE equalization by analyzing the condition number of the coefficient matrix in the linear system involved in the equalization process, and propose a new method to avoid the BER performance degradation at high SNR.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7A
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• pp.743-750
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• 2008

Orthogonal frequency division multiplexing (OFDM) is a attractive modulation scheme for high data rate transmission in frequency-selective channels. However, the time selectivity of wireless channel introduces intercarrier interference (ICI), and consequently degrades system performance. In this paper, we first propose a novel recursive algorithm for minimum mean squared error (MMSE) with successive interference cancellation (SIC). The proposed algorithm can significantly reduce the complexity of the MMSE-SIC scheme and achieve the same performance when optimal ordering is known. Also, the further reduced scheme of the proposed algorithm can be developed based on ICI properties, while preserving performance.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.486-492
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• 2002

In this paper. we presented 1 & 2 dimensional minimum mean-squared-error (MMSE) equalization scheme in a digital holographic data storage system to improve bit-error-rate (BER) and to mitigate inter-symbol interference (ISI) which were generated during the data storage and retrieval processes. We showed experimentally for ten data pages retrieved from the holographic storage system that BER and signal-to-noise ratio (SNR) were improved by adopting MMSE equalization.

• Journal of the Korea Society for Simulation
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• v.20 no.4
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• pp.91-96
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• 2011

As the user's demand for ultra high-speed wireless internet has increased, the standardization, research and development of future mobile communication systems have been done for several years. IMT-Advanced system which is called fourth generation mobile communication should support the data rate of 1 Gbps for nomadic users and 100 Mbps for mobile users. Also, the system should hold call connection at the mobile speed of 350 km/h. Meanwhile, since Doppler spread is linearly proportional to mobile speed, high mobility leads to the increase of interference between subcarriers and the deterioration of detection performance consequently. In this paper, we evaluate and analyze detection probability with respect to equalization methods in time-varying channels under system parameters complying with IMT-Advanced requirements. According to computer simulation conducted by varying mobile speed and code rate, MMSE based equalization can mitigate performance degradation of IMT-Advanced system considerably in time-varying channels.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.560-562
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• 2011

본 논문에서는 송신단에서의 shifted TR 기법과, 이 것에 수신단에서의 선택적 MMSE 등화기를 추가한 통신시스템을 주파수 선택적 채널에서 실험해보고 이것이 shifted TR 기법만 사용했을 때와 비교하여 수신단의 선택적 MMSE 등화기가 성능에 어떤 영향을 끼치는지 관찰하였다. 이를 보호 구간 별로 실험 결과를 비교하였으며 수신단에 선택적 MMSE 등화기를 추가시켰을 경우, shifted TR 기법만을 사용했을 경우보다 비트 오차율 측면에서 성능의 이득이 있음을 확인하였다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.219-222
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• 2010

OFDM시스템의 대안으로, SC-FDE시스템은 주파수 선택적 페이딩 환경에서 구현상의 복잡도가 크지 않으면서 낮은 PAPR로 다중 경로 지연에 의한 영향을 완화시키기 위한 기술로 연구되어 왔다. SC-FDE시스템에서 보호 구간으로 PN신호를 훈련 심볼(Training Sequence)로 둠으로써 CP에 비해 빠른 동기화와 채널 추정에 사용될 수 있는 장점이 있으며, 채널 추정을 위해 Correlation과 LMS기법을 동시에 적용함으로써 에러가 최소가 되기까지 수렴 시간을 줄일 수 있다. 본 논문에서는 PN시퀀스를 기반으로 추정한 채널 값으로, ISI를 효과적으로 제거할 수 있는 MMSE-FDE 등화 기법을 제안한다. SFN 채널 환경과 같이 스펙트럼 널이 강한 다중 경로 페이딩환경에서 ISI를 선 제거 하는 ISI cancellation 기법을 통해 정확한 SNR추정을 할 수 있고, 이를 통해 MMSE-FDE 등화 성능을 향상 시킬 수 있다.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.597-600
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• 2001

본 논문에서는 비선형 왜곡이 있는 환경에서 QAM 신호의 수신 성능을 개선시키기 위한 비선형 왜곡 제거 알고리즘을 제안한다. 비선형 왜곡의 효과를 줄이기 위하여 MMSE-DFE 수신기의 역방향 필터에 비선형 탭을 포함시키고 등화기 출력에서 추가적인 처리를 통해 남아 있는 잔여 비선형 왜곡을 제거한다. 비선형 왜곡이 있는 환경에서 MMSE-DFE 수신기와 제안된 수신기의 성능을 분석하고 전산 모의 실험을 통해 검증한다. MMSE-DFE 수신기와 비교한 제안된 수신기의 SNR 이득은 QAM 신호의 신호점 수가 커지고 비선형 왜곡이 커질수록 증가한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12A
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• pp.1978-1982
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• 2001

In a Multi-carrier modulation system, CP (Cyclic prefix) is inserted in the transmit tame in order to eliminate the ISI (Intersymbol Interference) and ICI (Interchannel Interference) caused by delay spread of a received signal, which in rum degrades the throughput of the system. TEQ (Time-domain equalizer) improves the system throughput by shortening the CIR (Channel Impulse Response) time and maintaining the CP length to the minimum regardless of the channel condition. In this paper, a new MMSE (Minimum Mean Square Error) TEQ algorithm is proposed and its performance is analyzed in order to speed up computing the optimum tap coefficients of the equalizer by employing Newton method.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.1
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• pp.29-34
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• 2011

In this paper, we propose and analyze the equalizer schemes, zero-forcing (ZF) and minimum mean square error (MMSE) in power line communication (PLC) system for automatic meter reading (AMR). For efficient implementation of AMR system with PLC, effects of impulsive noise and multipath channel should be mitigated. To overcome these effects, the above equalizer schemes are employed. System performance is evaluated in term of bit error rate. From simulation results, it is confirmed that the equalizer can significantly improve bit error rate (BER) performance in PLC system, and MMSE equalizer provides better performance than ZF scheme. The results of this paper can be applied to AMR system as well as various smart grid services using PLC.