• 전자공학회논문지A
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• 제31A권7호
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• pp.29-35
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• 1994

The performance of continuous phase modulation signals is well known for the coherent demodulation. But the carrier recovery circuits of the coherent receiver have long acquisition time and the receiver experiences high error floors for fading channels. In this paper, we propose the differential demodulation of 2-h continuous phase modulation signals. The sets of modulation indices of 2-h phase codes adequate to the differential demodulation for differentially encoded input are obtained and the average bit error probability in Additive White Gaussian Noise environments is derived and analyzed.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 I
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• pp.182-185
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• 2003

Error performance of two modulation schemes of millimeter-wave over fiber (MMoF) system i.e., optical double side band (ODSB) and optical single side band (OSSB) modulations is analyzed under Rician fading. Bit error rates (BER) of two detection techniques i.e., coherent and noncoherent detection are also compared in Rician fading. In aspect of error performance, ODSB modulation scheme has better BER than OSSB modulation scheme has under Rician fading. On the other hand, OSSB modulation scheme is advantageous in case of considering high bandwidth efficiency and small power degradation. Coherent detection technique is proper in Rician fading, because coherent detection provides more SNR gain whether fading is serious or not. Noncoherent detection can be applied when we need a simple receiver structure.

• ETRI Journal
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• 제34권6호
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• pp.800-806
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• 2012

Transmission performances of direct detection-based 100-Gb/s modulation formats are investigated and compared for metro area optical networks. The effects of optical signal-to-noise ratio sensitivity, chromatic dispersion, cross-channel nonlinearity, and transmission distance on the performance of differential 8-ary phase-shift keying (D8PSK), differential phase-shift keying plus three-level amplitude-shift keying (DPSK+3ASK), and dual-carrier differential quaternary phase-shift keying (DC-DQPSK) are evaluated. The performance of coherent dual-polarization quadrature phase-shift keying (DP-QPSK) with block phase estimation and coherent DP-QPSK with digital differential detection are also presented for reference. According to our analysis, all three direct detection modulation formats could transmit a 100-Gb/s signal over several hundred kilometers of a single-mode fiber link. The results also show that DC-DQPSK outperforms D8PSK and DPSK+3ASK, and the performance of DC-DQPSK is comparable to that of coherent DP-QPSK with digital differential detection. The maximum transmission distance of DC-DQPSK is over 1,000 km, which is enough distance for metro applications.

• 한국광학회:학술대회논문집
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• 한국광학회 1991년도 제6회 파동 및 레이저 학술발표회 Prodeedings of 6th Conference on Waves and Lasers
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• pp.121-125
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• 1991

A basic coherent optical transmission was demonstrated using FSK modulation and heterodyne detection scheme. Optical frequency of DFB LD light source at the transmitter side was stabilized with Fabry Perot etalon and bias feedback circuit. A tunable external cavity LD was used as a local oscillator at the receiver. Heterodyned output signal at IF frequency of 2GHz was measured and discussed.

• 한국광학회:학술대회논문집
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• 한국광학회 1989년도 제4회 파동 및 레이저 학술발표회 4th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.214-217
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• 1989

The most attractive feature of semiconductor lasers as sources for coherent optical communication system is the ability to produce frequency modulation by modulation of the bias current. The frequency deviation of semiconductor lasers under direct modulation depends on the laser structure and modulation frequency. This paper describes a circuit modeling techniques for the directly frequency modulated CSP (Channeled Substrated Planner) semiconductor laser. Predictions from this model are compared with the other published results of sinusoidal frequency modulation below than 1 GHz.

• 한국전자통신학회논문지
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• 제11권1호
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• pp.17-22
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• 2016

중계 네트워크에서는 중계기를 이용하여 송신기로 수신된 신호를 증폭 혹은 복조 후 재변조하여 수신기로 전송하는 역할을 수행한다. 수신기에서는 여러 중계기로부터 수신된 신호를 결합하여 신호를 복조함으로써 통신 성능을 향상 시킬 수 있다. 본 논문에서는 철도환경에서 에너지 할당에 따른 중계 네트워크의 성능을 분석한다. 변조방식은 중계기에서는 동기방식을 사용하고 수신기에서는 비동기 방식을 사용하는 부분차등변조 방식을 적용한다. 중계 네트워크에서 주어진 전체 에너지에 대해 수신기와 중계기의 다양한 에너지 할당에 따른 성능을 분석한다.

• Journal of the Optical Society of Korea
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• 제17권1호
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• pp.57-62
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• 2013

We have numerically implemented a receiver side all-optical signal processing method, i.e. optical backward propagation (OBP), by dispersion compensating fiber (DCF) and non-linear compensator (NLC) devised by effective negative Kerr non-linear coefficient using two highly non-linear fibers (HNLFs). The method is implemented for the post-processing of fiber transmission impairments, i.e. chromatic dispersion (CD) and non-linearities (NL). The OBP module is evaluated for dual-polarization (DP) m-ary (m=4,16,32,64,256) quadrature amplitude modulation (QAM) in 112 Gbit/s coherent transmission over 1200 km standard single mode fiber (SMF). We have also investigated an intensity limited optical backward propagation module (IL-OBP) by using a self-phase modulation-based optical limiter with an appropriate pre-chirping to compensate for the intensity fluctuations in the transmission link. Our results show that in highly non-linear sensitive 256QAM transmission, we have observed a 66% increase in the transmission distance by implementing IL-OBP as compared to conventional OBP.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(II)
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• pp.833-836
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• 1987

The error probability for coherent frequency-hopped spread-spectrum multiple-access communications is computed. We employ PSK as a modulation scheme. The channel capacity is performance measure and the minimum bit signal-to-noise ratio for reliable communications is obtained.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2007년도 하계종합학술대회 논문집
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• pp.91-92
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• 2007

LR-UWB utilizes BPSK and PPM for the transmission, which embeds the information in the transmitted pulse position. Meanwhile, by using coherent method, there is approximately 3dB enhancement on the BER performance over that using non-coherent method. However, due to the variable channel conditions, conventional system which uses fixed modulation is not efficient. To maximize the efficient and performance, in this paper, we propose an adaptive method including 4PPM+BPSK mode and 2PPM mode, in which the modulation method is dynamically changed depending on the channel condition which is determined according to the preamble correlation output.

• 한국ITS학회 논문지
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• 제5권2호
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• pp.19-28
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• 2006

IEEE 802.15.4a에서는 거리/위치 인식과 저속 데이터 송수신을 위해 간단하고 경제적이며 전력 소모가 적은 송수신기의 구현을 요구하며, 이를 위해 LR-WPAN 시스템은 간단한 변복조 방법을 사용하는 송수신기를 필요로 하게 된다. 본 논문에서는 무선 다중 경로 채널 상황을 다소 극복하기 위해 PPM+BPSK 방식의 변복조 방식과 채널에 의해 왜곡된 신호를 windowing을 통해 신호를 보상해주는 방식을 UWB 대역에서 동작하는 LR-WPAN(Low-Rate Wireless Personal Area Network) 시스템에 적용시킨 후 수신기의 방식에 따른 성능을 비교, 분석해 본다. 신호 보상을 위한 수신기는 Preamble을 사용하여 채널 특성을 파악한 후, 채널 파라미터를 사용하여 다중 경로 채널의 영향에 의해 지연/간섭 및 왜곡되어 수신되는 데이터신호를 수신단의 채널 왜곡 보상기에서 windowing를 사용하여 보상해 줌으로써 복조기에서 신호 검출이 용이하도록 채널왜곡 보상기가 신호를 전처리 해주는 방식을 사용하였다. 수신기는 Coherent 방식과 Non-Coherent 방식으로 동작되며, 모의 실험 결과 수신기의 방식에 관계없이 LOS(Line-of-Sight) 채널보다 NLOS(Non-Line-of-Sight) 채널에서의 성능 향상이 상대적으로 좋아진다는 특징이 있다는 것을 확인하였고, Coherent/Non-Coherent 방식에 상관없이 모든 채널 환경에서 성능 향상을 보이는 것을 확인하였다.