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양흥, 김익상 배재대학교 공학연구소 2011 공학논문집 Vol.13 No.1
Specially, in an OFDMA uplink, CFO(Carrier Frequency Offset), STO(Symbol Timing Offset), and CIR(Channel Impulse Response) cause degraded BER performance by distorting original transmitted symbols, which come from the frequency difference of local oscillators between mobile and base stations, different arrivals at base station of OFDMA symbol from each mobile station, and multi-path fading of different paths form mobile station to base station, respectively. In order to compensate the distorted symbol, CFO, STO, and CIR characteristics have to be known at first. In this paper, the estimate of CFO, STO, and CIR parameters is presented by using AP(Alternating Projection) method, where likelihood function is introduced so as to make it maximized by estimating CFO factors of mobile stations. Specially, the estimation error is reduced by considering the noise effect of likelihood function.
고정이득 L-band EDFA에서 발진 파장 및 방향에 따른 과도응답 특성
김익상,김창봉,양흥,손영호,Kim Ik sang,Kim Chang bong,Yang Heng,Sohn Young ho 한국통신학회 2005 韓國通信學會論文誌 Vol.30 No.3a
WDM(Wavelength Division Multiplexing) 광통신망의 노드에서 신호채널들이 분기 결합될 때 잔류채널들의 이득을 일정하게 제어해 주기 위해 고정이득 EDFA를 사용한다. 본 논문에서는 양방향 펌프에 의해 고이득을 가지는 L-band EDFA에서 발진광에 의해 입력변화를 보상해주는 방식으로 고정이득 EDFA를 구현하였다. 여기서 발진방향 및 파장에 따른 잔류채널의 과도응답 특성에 있어서 단파장 후방발진의 경우가 최적임을 확인할 수 있었다. The gain-clamped EDFA has been developed to eliminate the output power change of WDM surviving channels to occur with added or dropped channels, which degrades the performance of WDM optical network. It maintains the constant gain of surviving channels when WDM channels are added or dropped in a network amplifying node. In this paper, the hi-directionally pumped gain-clamped EDFA is implemented to compensate the change of the input power by a lasing. The results show that the lasing of a short wavelength and backward propagation is the optimal condition to minimize the transient response of surviving channels in terms of the overshoot and gain saturation due to the inhomogeneous broadening effect.