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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.
OFDMA 상향링크에서 반송주파수 차이, 채널, 시간지연의 복합추정에 대한 특성 분석
양흥(Heng Yang),김익상(Ik-Sang Kim) 한국정보기술학회 2012 한국정보기술학회논문지 Vol.10 No.12
In OFDMA uplink transmissions, the received signal in a base station is composed of signals from several mobile stations, which are distorted by carrier frequency offset, symbol timing offset, and multipath fading in a different degree for each mobile station. The received signals from mobile stations can be reliably recovered by estimating these three factors using AP(Alternating Projection) algorithm. However, it is found that AP cannot be adopted in the case of sub-band carrier allocation or a large number of mobile stations having a long CP(Cyclic Prefix) because of its singularity. CRB(Cramer Rao Bound) is a very useful tool measuring estimation errors theoretically. Errors estimated by CRB demonstrate that CFO estimation error does not depend on the CFO bias and increases as the number of mobile stations becomes large.
OFDMA 상향전송에서 반송주파수 오프셋 잔여오차 보정
양흥(Heng Yang),김익상(Ik-Sang Kim) 한국정보기술학회 2011 한국정보기술학회논문지 Vol.9 No.12
CFO(Carrier Frequency Offset) causes degraded BER performance in OFDMA(Orthogonal Frequency Division Multiple Access) system, which comes from the frequency difference of local oscillators between a mobile station and a base station. CLJL and HL algorithms have been presented for compensation of CFO problem. However, they have their own intrinsic residue error. In this paper, the method to compensate such a residue error according to interleave, local, and random CAS(Carrier Allocation Scheme) is shown. When the HL algorithm is applied to compensate CFO, interleave CAS is the weakest against CFO problem because of the severe ICI(Inter Carrier Interference) between subcarriers. It is shown that the BER performances are improved almost the same for all the CASs after HL and residue error compensation.
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.
FSR(Force Sensitive Resistors) 센서를 사용한 압력분포 측정 단말기의 구현
이범준(Beom-Joon Lee),양흥(Heng Yang),김익상(Ik-Sang Kim) 한국정보기술학회 2010 한국정보기술학회논문지 Vol.8 No.11
FSR(Force Sensitive Resistor) sensor used in this research consists of 256 resistors varying to the pressure, which are connected to 16 row and 16 column conductor lines. The analog voltages of 16 row and 16 column conductor lines are acquired 16 times by micro-processor, as one column conductor line is supplied by the bias voltage and the others are electrically open. The 16 equations whose coefficients are acquired as voltages of one row and 16 column conductor lines and unknown variables are resistances of 16 resistors connected to them, are established by applying KCL(Kirchhoff Current Law) at one row conductor line. We can get the pressure distribution by solving these equations. We implemented a handy equipment measuring the pressure distribution of a degree of palm, which is processed and displayed on color TFT-LCD by micro-processor with FSR sensor.