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Near-Optimal Decoding Algorithm for Alamouti Transmit Diversity over Time-Selective Fading Channels
Hoojin Lee 한국정보기술학회 2011 한국정보기술학회논문지 Vol.9 No.6
In this paper, we propose a low-complexity but efficient symbol decoding algorithm for an Alamouti transmit diversity system, especially in order to overcome the adverse effect of time-selective fading channels. By exploiting symbols initially detected by existing simple detectors, the proposed detection algorithm for Alamouti's scheme iteratively searches for a better estimate in the signal constellation. Hence, over time-selective fading channels, the proposed algorithm exhibits comparable performance to the existing optimal maximum-likelihood(ML) decoder, while maintaining much lower complexity than the ML decoder.
Low-Complexity Equalizer for OFDM Systems in Doubly-Selective Fading Channels
LEE, Namjeong,LEE, Hoojin,KANG, Joonhyuk,GIL, Gye-Tae The Institute of Electronics, Information and Comm 2009 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.92 No.3
<P>In this letter, we propose a computationally effient equalization technique that employs block minimum mean squared error (MMSE) depending on LDL<SUP>H</SUP> factorization. Parallel interference cancellation (PIC) is executed with pre- obtained output to provide more reliable symbol detection. In particular, the band structure of the frequency domain channel matrix is exploited to reduce the implementation complexity. It is shown through computer simulation that the proposed technique requires lower complexity than the conventional algorithm to obtain the same performance, and that it exhibits better performance than the conventional counterpart when the same complexity is assumed.</P>
Hoojin Lee 보안공학연구지원센터 2015 International Journal of Software Engineering and Vol.9 No.12
This paper addresses the asymptotic diversity performance of Alamouti transmit diversity technique especially in time-selective fading channels. In particular, a linear quasi-maximum-likelihood (QML) decoding method is employed for the Alamouti transmit diversity system to solve the error floor problem induced by the conventional linear ML decoding method. By judiciously utilizing the derived asymptotic closed-form formula of symbol pairwise error rate (SPER), it is theoretically verified that the asymptotic diversity orders achieved by the QML decoding algorithm become 2 and 1 in quasi-static and time-selective fading channels, respectively.
Hoojin Lee(이후진) 대한전자공학회 2018 전자공학회논문지 Vol.55 No.3
본 논문에서는 Hoyt 페이딩 채널에서 MRC 다이버시티 및 저복잡도 Greedy 신호 검출 기법이 적용된 MCIK-OFDM 시스템의 평균 쌍 오류 확률 (pairwise error probability)의 상한 (upper bound)에 대한 효율적인 닫힌 형태의 새로운 수식을 유도한다. 또한, 이를 이용하여 주어진 시스템 및 채널 환경에서 대표적인 시스템 점근 성능 지표들 (점근적 평균 쌍 오류 확률 상한, 부호 이득, 다이버시티 계수 등)의 수식을 유도 및 분석하였으며, 이로부터 높은 신호 대 잡음비 (SNR) 영역에서 Hoyt 페이딩 채널이 MCIK-OFDM 시스템의 오류 확률 성능에 미치는 영향을 보다 명확하게 예측할 수 있게 된다. 유도되고 분석된 결과들의 타당성을 입증하기 위한 다양한 수치 결과들을 제시한다. In this paper, a novel and effective closed-form formula is derived for the upper bound on the overall average pairwise error probability (PEP) of a multi-carrier index keying orthogonal frequency division multiplexing (MCIK-OFDM) system employing maximal ratio combining (MRC) diversity and low-complexity greedy detection techniques over Hoyt fading channels. Based on the derived formula, asymptotic analyses (e.g., asymptotic upper bound, achievable coding gain, diversity gain, etc.) are also performed, which enable us to more explicitly evaluate the achievable error probability performance in the high signal-to-noise ratio (SNR) regime especially under Hoyt fading. Some numerical results are demonstrated to verify our analytical results.
Asymptotic Error Probability Analysis of M-ary Modulation Schemes in Hoyt Fading Channels
Hoojin Lee 한국정보기술학회 2014 한국정보기술학회논문지 Vol.12 No.9
This paper derives simple asymptotic closed-form formulas for the average error probabilities of various M-ary modulation schemes (i.e., M-ary differentially coherent phase shift-keying (DPSK) signals, noncoherent correlated binary (NCB) signals, M-ary coherent phase shift-keying (PSK) signals, and M-ary square quadrature amplitude modulation (QAM)), especially in Hoyt (or Nakagami-q) fading channels, since the formula can be effectively used to study the asymptotically achievable error performance. The derived expressions for the representative modulation schemes are much more concise than the existing conventional formulas, showing the very tightness to the error probability results from the existing exact formulas in the high signal-to-noise ratio (SNR) region. Through the rigorous numerical results, we clearly justify the validity of our derivations and analyses.
Hoojin Lee(이후진) 대한전기학회 2016 전기학회논문지 Vol.65 No.12
Using the existing exact but quite complicated symbol error rate (SER) expressions for M-ary phase shift keying (M-PSK) and M-ary differential phase shift keying (M-DPSK), we derive effective and concise closed-form asymptotic SER formulas especially in Rician-Nakagami fading channels. The derived formulas can be utilized to efficiently verify the achievable error rate performances of M-PSK and M-DPSK systems for the Rician-Nakagami fading environments. In addition, by exploiting the modulation gains directly obtained from the asymptotic SER formulas, we also theoretically demonstrate that M-DPSK suffers an asymptotic SER performance loss of 3.01dB with respect to M-PSK for a given M in Rician-Nakagami fading channels at high signal-to-noise ratio (SNR).
Hoojin Lee(이후진) 대한전자공학회 2018 전자공학회논문지 Vol.55 No.6
Rayleigh, Rician, Nakagami-m 등과 같은 기존의 일반적인 페이딩 채널 모델과 비교하여 double Nakagami-m 페이딩 채널은 dual-hop amplify-and-forward relay networks, satellite mobile communications, mobile-to-mobile (M2M) communications 등과 같은 통신 시스템 환경에 보다 적절한 페이딩 채널 모델로 알려져 있다. 따라서 본 논문에서는 double Nakagami-m 페이딩 채널에서 MRC 다이버시티 기법을 채택한 시스템의 다양한 변조기법에 대한 평균 비트 오류율 (bit error rate)의 상한(upper bound)에 대한 간결하면서도 닫힌 형태의 수식을 유도한다. 구해진 수식을 효과적으로 활용하면 다양한 시스템 및 채널 환경에서의 오류율 성능을 보다 간편하게 예측하고 분석할 수 있을 것으로 판단된다. 본 논문의 후반부에서는 다양한 시스템 및 채널 조건에서의 수치해석 결과를 제시하여 유도된 수식의 효율성을 입증하고자 한다. Comparing with the conventional fading channel models (e.g., Rayleigh, Rician, Nakagami-m, etc.), double Nakagami-m fading channels are well-known to be more suitable for dual-hop amplify-and-forward relay networks, satellite mobile communications, mobile-to-mobile (M2M) communications, etc. Thus, considering M-ary signals employing maximal ratio combining (MRC) diversity technique, this paper derives a simple closed-form upper bound formula of the average bit error rate (BER) especially in double Nakagami-m fading channels. Exploiting the derived simple formula enables us to more efficiently evaluate the achievable error rate performance for various system and channel environments. Finally, we provide several numerical results to verify the effectiveness of our derivations.