Chonghan Song

Sungkyunkwan University, Sŏul, Seoul, South Korea

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Publications (12)0 Total impact

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    ABSTRACT: This paper proposes a novel asynchronous transmission scheme for cooperative wireless networks using Alamouti coded orthogonal frequency division multiplexing (OFDM) modulation. The proposed scheme obviates the need for the timing synchronization at the relay nodes through a renewal of the cyclic prefix (CP) of the OFDM symbol, and achieves a cooperative diversity gain through some simple complex-valued operations at the relay node. Numerical results demonstrate that the bit error rate (BER) performance of the proposed scheme, unlike that of the conventional scheme, does not degrade even when there exists a timing synchronization error at the relay nodes, and also, that the proposed scheme obtains two times higher cooperative diversity gain compared with that of the conventional scheme at the cost of the symbol transmission rate being reduced by half.
    Local Computer Networks (LCN), 2010 IEEE 35th Conference on; 11/2010
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    ABSTRACT: The conventional ultra-wideband (UWB) synchronization schemes could cause poor performance in receiver operations such as demodulation after the synchronization, since unreliable timing information corresponding to low-power multipath components might be transferred to the next stage. To solve this problem, in this paper, we propose novel synchronization schemes for UWB systems. We first derive an optimal scheme based on the maximum likelihood (ML) criterion and then develop a simpler suboptimal scheme. Simulation results show that both proposed schemes provide a better synchronization performance over the conventional scheme.
    Computational Science and Its Applications - ICCSA 2010, International Conference, Fukuoka, Japan, March 23-26, 2010, Proceedings, Part III; 01/2010
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    ABSTRACT: In this paper, we propose a novel maximum-likelihood (ML) decoding scheme based on the combination of depth- and breadth-first search methods on a partitioned tree for multiple input multiple output systems. The proposed scheme first partitions the searching tree into several stages, each of which is then searched by a depth- or breadth-first search method, possibly exploiting the advantages of both the depth- and breadth-first search methods in an organized way. Numerical results indicate that, when the depth- and breadth-first search algorithms are adopted appropriately, the proposed scheme exhibits substantially lower computational complexity than conventional ML decoders while maintaining the ML bit error performance.
    Seventh International Conference on Information Technology: New Generations, ITNG 2010, Las Vegas, Nevada, USA, 12-14 April 2010; 01/2010
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    ABSTRACT: This paper deals with the integer frequency offset (IFO) estimation issue for reliable transmission in orthogonal frequency division multiplexing (OFDM)-based digital video broadcasting-terrestrial (DVB-T) systems. To estimate the IFO the conventional scheme uses only partial information of combinations that pilots provide. However, since the conventional scheme exploits a small number of correlations, it does not use sufficient signal energy for the IFO estimation. Thus, in this paper, we propose novel IFO estimation schemes efficiently using the additional correlations between pilots. The simulation results show that the proposed schemes are highly accurate in terms of the IFO detection probability.
    The 35th Annual IEEE Conference on Local Computer Networks, LCN 2010, 10-14 October 2010, Denver, Colorado, USA, Proceedings; 01/2010
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    ABSTRACT: In this paper, we propose a novel code acquisition scheme called modified multiple-shift (MMS) for optical code division multiple access (CDMA) systems. By using the modified local code whose sign is positive or negative, the proposed MMS scheme provides a shorter mean acquisition time (MAT) than the conventional multiple-shift (MS) scheme. The simulation results demonstrate that the MAT of the MMS scheme is shorter than that of the MS scheme in both single-user and multi-user environments.
    Computational Science and Its Applications - ICCSA 2010, International Conference, Fukuoka, Japan, March 23-26, 2010, Proceedings, Part III; 01/2010
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    ABSTRACT: This paper proposes two novel schemes for pilot-aided integer frequency offset (IFO) estimation in orthogonal frequency division multiplexing (OFDM)-based digital video broadcasting-terrestrial (DVB-T) systems. The conventional scheme proposed for estimating the IFO uses only partial information of combinations that pilots can provide, which stems from a rigorous assumption that the channel responses of pilots used for estimating the IFO change very rapidly. Thus, in this paper, we propose the novel IFO estimation schemes exploiting additional information of combinations that pilots can provide to improve the performance of the IFO estimation. The simulation results show that the proposed schemes are highly accurate in terms of the IFO detection probability.
    Proceedings of the 6th International Wireless Communications and Mobile Computing Conference, IWCMC 2010, Caen, France, June 28 - July 2, 2010; 01/2010
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    ABSTRACT: This paper proposes a novel detection scheme based on multiple correlator outputs to enhance the detection performance in ultra-wideband (UWB) signal acquisition. Due to the rich multipath of UWB channels, the signal energy spreads over multiple correlator outputs, which makes each correlator output have only a portion of the signal energy, and thus, degrades the detection performance of the conventional scheme where a single correlator output is used as the decision variable for detection. In the proposed two-stage detection scheme, the decision variable is formed by combining multiple correlator outputs, making it possible to collect the signal energy spread by the multipath. Simulation results show that the proposed scheme can provide a better detection performance over the conventional scheme in various UWB channel environments.
    Seventh International Conference on Information Technology: New Generations, ITNG 2010, Las Vegas, Nevada, USA, 12-14 April 2010; 01/2010
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    ABSTRACT: Binary offset carrier (BOC) signal synchronization is based on the correlation between the received and locally generated BOC signals. Thus, the multiple side-peaks in BOC autocorrelation are one of the main error sources in synchronizing BOC signals. Recently, new correlation functions with no side-peak were proposed for sine and cosine phased BOC signal synchronization, respectively, by the authors [3]. In this paper, we propose new correlation functions with no side-peak for alternative BOC (AltBOC) and composite BOC (CBOC) signals by using the similar approach to the previous work.
    Computational Science and Its Applications - ICCSA 2009, International Conference, Seoul, Korea, June 29-July 2, 2009, Proceedings, Part II; 01/2009
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    ABSTRACT: 요 약 처프 확산 대역 (chirp spread spectrum: CSS) 기술은 방해전파 신호에 강인한 특성으로 인하여 무선 통신 분 야에서 크게 주목받고 있다. 하지만 방해전파 신호에 따른 CSS 시스템의 성능에 대한 구체적인 연구는 아직 부 족한 실정이다. 따라서 본 논문에서는 광대역 및 톤 (tone) 방해전파 신호에 따른 CSS 시스템의 성능을 분석한다. 구체적으로는 CSS 기반  진 위상 편이 방식 (-ary phase shift keying: MPSK) 시스템의 심볼 오류율 수식을 유도하고 Monte Carlo 방법에 기반한 모의실험 결과와 비교한다. 이를 통하여, 본 논문에서 유도한 심볼 오류율 수식이 모의실험 결과와 일치함을 확인한다. ABSTRACT Due to its capability to resist jamming signals, chirp spread spectrum (CSS) technique has attracted much attention in the field of wireless communications. However, there has been little rigorous analysis for the performance of CSS systems in the presence of jamming signals. In this paper, thus, we present analytic results on the performance of a CSS system: specifically, symbol error rate (SER) expressions are derived for a CSS -ary phase shift keying (MPSK) system in the presence of broadband and tone jamming signals, respectively. The numerical results show that the empirical SER closely agree with the analytic result.
    The Journal of Korea Information and Communications Society. 01/2009; 34(4C).
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    ABSTRACT: In this paper, we propose a novel code acquisition scheme called enhanced multiple-shift (EMS) for optical code division multi- ple access (CDMA) systems. By using multiple thresholds, the proposed EMS scheme provides a shorter mean acquisition time (MAT) than that of the conventional mutiple-shift (MS) scheme. The simulation results demonstrate that the MAT of EMS scheme is shorter than that of MS scheme in both single-user and multi-user environments.
    Computational Science and Its Applications - ICCSA 2009, International Conference, Seoul, Korea, June 29-July 2, 2009, Proceedings, Part II; 01/2009
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    ABSTRACT: Ren et al. presented an efficient carrier frequency offset (CFO) estimation method for orthogonal frequency division multi-plexing (OFDM), which has an estimation range as large as the bandwidth of the OFDM signal and achieves high accuracy without any constraint on the structure of the training sequence. However, its detection probability of the integer frequency offset (IFO) rapidly varies according to the fractional frequency offset (FFO) change. In this paper, we first analyze the Ren's method and define two criteria suitable for detection of IFO. Then, we propose a novel method for the IFO estimation based on the maximum-likelihood (ML) principle and the detection criteria defined in this paper. The simulation results demonstrate that the proposed method outperforms the Ren's method in terms of the IFO detection probability irrespective of a value of the FFO.
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    ABSTRACT: This paper proposes a novel spectrum sensing technique for the digital video broadcasting-terrestrial (DVB-T) systems, which utilizes the periodicity of pilot signals in the orthogonal frequency division multiplexing (OFDM) symbols. The proposed scheme can overcome the effect of the timing synchronization error by re-correlating the correlation values in the same sample distances. The numerical results demonstrate that the detection probability perfor-mance of the proposed scheme outperforms that of the conventional scheme when there exists a timing synchronization error.