고속 레일레이 페이딩 채널에서 STBC-OFDM의 간섭 분석 및 보상
The Analysis and Compensation of Interferences for STBC-OFDM in a Fast Rayleigh Fading Channel
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초록
MRC(Maximal Ratio Combining) 기반의 복호 방식을 사용하는 STBC-OFDM(Space-Time Block Coded Orthogonal Frequency-Division Multiplexing)에서는 시변 채널에 의해 채널간 간섭(ICI: Inter-Channel Interference)과 함께 자기 채널 간섭(SCI: Self-Channel Interference)이 발생한다. 본 논문에서는 STBC-OFDM 에서 발생되는 SCI의 특성을 분석하고, SCI의 전력을 채널의 시간 영역 자기 상관 함수를 이용하여 유도한다. SCI의 전력이 채널의 시간 변화율에 비례하며, 그 크기가 ICI의 전력보다 크게 나타남을 보인다. 고속 시변 채널에서 STBC-OFDM의 성능을 향상시키기 위해 수신단에서의 SCI 발생을 근원적으로 방지할 수 있는 간단한 사전제거 (pre-canceling) 기법을 제안한다. 또한 수신단에서 최대비율 기준에 의해 결합된 OFDM 심볼의 SCI 영향을 SCI 구 조를 이용하여 보상할 수 있는 사후제거(post-canceling) 기법을 제안한다. 제안된 보상 기법을 두 개의 송신 안테나 와 두 개의 수신 안테나를 사용하는 STBC-OFDM에 적용할 경우 0.0889의 채널 변화율과 2bps/Hz의 대역폭 효율 에서 10-4 이하의 BER을 얻을 수 있다.
Abstract
Self-channel interference (SCI) as well as inter-channel interference (ICI) is occurred by time-varying channels in space-time block coded orthogonal frequency-division multiplexing (STBC-OFDM) using conventional maximal ratio combining (MRC) based decoding scheme. In this paper, we analyze the characteristic of the SCI and derive SCI power by using a time-domain correlation function of Rayleigh fading channel. We show that the SCI power is proportional to rate of channel variation and higher than the ICI. A simple pre-canceling technique is proposed to prevent the SCI and is shown to improve the performance of the STBC-OFDM. A post-canceling technique that can compensate the effect of the SCI after the MRC is also proposed by considering the structure of the SCI. The proposed techniques can provide a bit error rate (BER) lower than 10-4 for the STBC-OFDM using two transmit and two receive antennas, under the rate of channel variation of 0.0889 and a bandwidth efficiency of 2bit/s/Hz.
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