• Journal of Communications and Networks
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• 제11권1호
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• pp.42-46
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• 2009

Superimposed training (SIT) design for estimating of time-varying multipath channels is investigated for mobile orthogonal frequency division multiplexing (OFDM) systems. The design of optimum SIT consists of two parts: The optimal SIT sequence is derived by minimizing the channel estimates' mean square error (MSE); the optimal power allocation between training and information data is developed by maximizing the averaged signal to interference plus noise ratio (SINR) under the condition of equal powered paths. The theoretical analysis is verified by simulations. For the metric of the averaged SINR against signal to noise ratio (SNR), the theoretical result matches the simulation result perfectly. In contrast to an interpolated frequency-multiplexing training (FMT) scheme or an SIT scheme with random pilot sequence, the SIT scheme with proposed optimal sequence achieves higher SINR. The analytical solution of the optimal power allocation is demonstrated by the simulation as well.

• Journal of the Optical Society of Korea
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• 제20권5호
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• pp.557-562
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• 2016

In this paper, for the first time, the transmission performances of long-haul 100-Gb/s direct detection optical OFDM (DDO-OFDM) and coherent optical OFDM (CO-OFDM) wavelength division multiplexing (WDM) systems are compared by simulation. It provides specific guides for system parameter selection to get a high-performance and cost-effective OFDM WDM system. Specifically, the comparison involves three aspects: launched power is investigated to achieve better system performance; laser linewidth is numerically investigated to choose cost-effective laser; system dispersion tolerances with different laser linewidths are analyzed to further reveal the advantages and disadvantages of these two detecting methods, direct detection and coherent detection, in long-haul OFDM WDM system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 학술대회 논문집 정보 및 제어부문
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• pp.277-279
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• 2004

In this paper, we propose an channel estimation method for Multi-Input Multi-Output-Orthogonal frequency Division Multiplexing (MIMO-OFDM). The proposed method estimates uniquely all channel frequency responses needed in space-frequency block coded OFDM systems using "comb-type" pilot symbols. To reduce the computational complexity of the proposed method, least square(LS) and linear minimum mean square error(LMMSE) are used in the frequency-domain. The performance of the proposed approach is evaluated by computer simulation for rayleigh fading channel.

• 한국통신학회논문지
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• 제33권8C호
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• pp.613-616
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• 2008

In this paper, a fine residual frequency offset estimation scheme is proposed for multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols carry the identical information in the MB-OFDM UWB system, thus removing the need of pilot symbols. The mean square error of the synchronization scheme is evaluated and simulation results are used to verify the effectiveness of the proposed estimator. When compared to the pilot-aided conventional estimator, the proposed estimator has a lower estimation error.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.201-202
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• 2008

In this paper, an efficient frequency offset compensation design for OFDM(Orthogonal Frequency Division Multiplexing) is proposed. The conventional CORDIC(COordinate Rotation Digital Computer) algorithm for frequency offset compensation utilizes CORDIC hardware and complex multiplier. But, proposed structure utilizes only one CORDIC hardware.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 심포지엄 논문집 정보 및 제어부문
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• pp.60-62
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• 2006

This paper presents an efficient frequency offset (FO) estimation algorithm for the orthogonal frequency division multiplexing (OFDM) based wireless local area networks (WLANS). The packet preamble imformation is utilized on the high rate WLAN standards adopted by the IEEE 802.11a. We present FO estimation schemes using diversity. In the simulation results, we prove that the presented schemes can improve the estimation performance compared with the convolutional scheme.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2006년도 학술대회
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• pp.175-177
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• 2006

This letter deals with non-pilot-aided symbol timing estimation methods in an orthogonal frequency division multiplexing (OFDM) system. To do this, OFDM system uses a frequency diversity scheme over two consecutive data symbols. Our approach can be viewed as an expansion of Schmidl's and Minn's correlation methods. Using the OFDM signal equipped with frequency diversity, however, symbol timing is accurately estimated without additional training symbol and a second-order diversity gain is achieved.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권2호
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• pp.583-599
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• 2015

We apply the Bayesian matching pursuit (BMP) algorithm to the estimation of time-frequency selective channels in orthogonal frequency division multiplexing (OFDM) systems. By exploiting prior statistics and sparse characteristics of propagation channels, the Bayesian method provides a more accurate and efficient detection of the channel status information (CSI) than do conventional sparse channel estimation methods that are based on compressive sensing (CS) technologies. Using a reasonable approximation of the system model and a skillfully designed pilot arrangement, the proposed estimation scheme is able to address the Doppler-induced inter-carrier interference (ICI) with a relatively low complexity. Moreover, to further reduce the computational cost of the channel estimation, we make some modifications to the BMP algorithm. The modified algorithm can make good use of the group-sparse structure of doubly selective channels and thus reconstruct the CSI more efficiently than does the original BMP algorithm, which treats the sparse signals in the conventional manner and ignores the specific structure of their sparsity patterns. Numerical results demonstrate that the proposed Bayesian estimation has a good performance over rapidly time-varying channels.

• 한국전자통신학회논문지
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• 제7권5호
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• pp.1229-1234
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• 2012

차량통신은 통신시스템과 차량산업을 융합하여 ITS (Intelligent Transport Systems)분야에서 다양한 서비스 제공을 위해 고려되어져 왔다. 일반적으로 차량통신은 WAVE (Wireless Access in Vehicular Environments)라고 알려져 있는 IEEE 802.11p/1609표준을 채택하여 차량간 통신 및 차량-노변기지국간 통신에 이용된다. WAVE 시스템은 OFDM (Orthogonal Frequency Division Multiplexing) 신호를 5.9GHz대의 주파수를 사용하여 신호를 전송하는 시스템이다. 본 논문에서는 차량통신 영역 중 물리계층의 이슈들에 관하여 논의한다. 먼저 WAVE 표준의 물리계층과 5.9GHz대의 신호의 특성에 대해 살펴본 후 신뢰성 있는 통신링크 제공을 위해 물리계층에서 개선되어야할 점에 대해 논의한다.

• 방송공학회논문지
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• 제11권2호
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• pp.222-228
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• 2006

이 논문에서는 동일채널 간섭이 존재하는 채널 환경에서 OFDM(Orthogonal Frequency Division Multiplexing) 시스템의 수신 다이버시티 결합 방법을 제시한다. 제시한 방법에서 각 수신 안테나로부터의 수신 신호는 주파수 영역에서 부반송파 단위로 결합하며, 잡음과 간섭 전력을 고려한 MRC(Maximum Ratio Combining)를 적용한다. 잡음과 간섭 전력은 채널의 제한된 지연 확산에 기인하는 주파수 대역에서의 상관특성(coherency)을 이용하여 상관성이 큰 일정구간 이내의 부채널에 대해 잡음과 간섭 전력의 평균을 취함으로써 더 정확한 추정치를 얻는다. IEEE 802.11a 무선 LAN 규격에서 모의실험한 결과 제안방법은 간섭전력을 이용하지 않는 방식에 비해 신호대잡음비를 2-3.5dB 개선하였으며, 정확하게 잡음 및 간섭 전력을 추정한 경우에 대해 1dB 이내로 접근하는 결과를 나타내었다.