• 한국산업정보학회논문지
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• 제20권6호
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• pp.1-10
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• 2015

본 논문에서는 음영 지역을 위한 다중 중계기 기반의 주파수 효율적인 OFDMA(orthogonal frequency division multiple access) 전송 시스템을 제안한다. 본 논문에서는 다중 중계기를 통해 확보된 다중 경로에 주파수 공간 블록 부호를 적용하여 음영 지역의 시스템 성능을 향상시킨다. 또한, 주기적 프리픽스 부족으로 인해 발생하는 채널 주기성 손실을 복원하는 과정이 포함된 주기적 프리픽스를 사용하지 않는 OFDMA 시스템을 제안한다. 본 논문에서 제안된 주기적 프리픽스를 사용하지 않는 OFDMA 시스템의 성능이 충분한 주기적 프리픽스를 사용하는 기존 OFDMA 시스템의 성능과 거의 동일하여, 기존 시스템 대비 주파수 효율이 향상되는 것을 실험을 통해서 확인할 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권6호
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• pp.1914-1925
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• 2014

Inter-symbol interference (ISI) problem is inevitable when the guard interval (GI) is shorter than the delay spread (DS) for an orthogonal frequency division multiplexing (OFDM) system. Iterative techniques have been proposed to overcome such a problem. However, most of existing algorithms are not efficient for an OFDM system with a small GI working under the channel with a large DS. Especially in the case of the DS spans a longer time than the half of the OFDM symbol duration. On the other hand, conventional algorithms, which can reduce the effects of the severe ISI, often employ several impractical assumptions to support the conclusions. In this paper, we present a robust decision feedback equalizer (DFE) for the OFDM system to overcome the severe ISI problem. The proposed DFE removes the ISI in a same manner as the residual inter-symbol interference cancellation (RISIC) algorithm. However, the inter-carrier interference (ICI) is reduced via cyclicity removal instead of the cyclicity restoration used in the conventional algorithms. The link-level simulation (LLS) results indicate that our proposed DFE scheme can dramatically improve the BER performance when the DS spans longer than the half of ODFM symbol duration.

• 한국통신학회논문지
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• 제37A권12호
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• pp.1106-1114
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• 2012

In order to provide high data rate and real time services under maritime environment, link-level performance of ship ad-hoc network (SANET) based on 3GPP LTE and IEEE 802.11p (WAVE) specifications are investigated and discussed in this paper. The measured maritime channel, whose delay spread is longer than the length of guard interval (GI) of both 3GPP LTE and IEEE 802.11p specifications, is adopted for the link-level simulations. For the purpose of eliminating inter-symbol interference (ISI) due to insufficient GI length, double antenna pattern (DAP) scheme and advanced time-domain decision-feedback equalizer (DFE) are proposed for LTE and WAVE systems, respectively. The proposed DFE removes the ISI in a same manner as the residual inter-symbol interference cancellation (RISIC) algorithm, but the inter-carrier interference (ICI) is reduced via cyclicity removal instead of cyclicity restoration used in the RISIC algorithm. Compared with existing schemes, our proposed DFE is a robust technique to overcome the severe ISI channel which has a comparatively large delay spread. Based on simulation results, not only comparisons between systems are discussed, but also some reformative suggestions are given.

• Journal of Communications and Networks
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• 제10권3호
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• pp.239-252
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• 2008

For orthogonal frequency division multiplexing (OFDM), cyclic prefix (CP) should be longer than the length of channel impulse response, resulting in a loss of bandwidth efficiency. In this paper, we describe a new technique to restore the cyclicity of the received signal when the CP is not sufficient for OFDM systems. The proposed technique efficiently restores the cyclicity of the current received symbol by adding the weighted next received symbol to the current received symbol. Iterative CP reconstruction (CPR) procedure, based on the residual intersymbol interference cancellation (RISIC) algorithm, is analyzed and compared to the RISIC. In addition, we apply the CPR method to Alamouti space-time block coded (STBC) OFDM system. It is shown that in the STBC OFDM, tail cancellation as well as cyclic reconstruction of the CPR procedure should be repeated. The computational complexities of the RISIC, the proposed CPR, the RISIC with STBC, and the proposed CPR with STBC are analyzed and their performances are evaluated in multipath fading environments. We also propose an iterative channel estimation (CE) method for OFDM with insufficient CP. Further, we discuss the CE method for the STBC OFDM system with the CPR. It is shown that the CPR technique with the proposed CE method minimizes the loss of bandwidth efficiency due to the use of CP, without sacrificing the diversity gain of the STBC OFDM system.

• 한국산학기술학회논문지
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• 제16권11호
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• pp.7456-7462
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• 2015

본 논문에서는 중계기를 통해 다중 경로가 확보된 음영 지역에서 주파수 공간 블록 부호를 적용한 주파수 효율적인 SC-FDMA(Single Carrier-Frequency Division Multiple Access) 전송 시스템을 제안한다. 본 논문에서 제안된 시스템은 주기적 프리픽스 사용에 따른 주파수 효율 감소를 방지하기 위하여 주기적 프리픽스를 사용하지 않는다. 주기적 프리픽스를 사용하지 않음에 따라 훼손되는 채널 주기성을 중계기와 수신국의 수신기에서 복원함으로써, 주기적 프리픽스를 사용하지 않는 제안된 시스템의 성능이 충분한 주기적 프리픽스를 사용하는 기존 시스템의 성능과 거의 동일하여 시스템의 주파수 효율이 향상되는 것을 실험을 통해 확인할 수 있다.