• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권12호
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• pp.3237-3256
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• 2012

In the context of effective usage of a scarce spectrum resource, emerging wireless communication standards will demand spectrum sharing with existing systems as well as multiple access with higher spectral efficiency. We mathematically analyze the sum throughput of a spectrum sharing space-division multiple access (SDMA) system, which forms a transmit null in the direction of other coexisting systems while satisfying orthogonal beamforming constraints. For a large number of users N, the SDMA throughput scales as log N at high signal-to-noise ratio (SNR) ((J-1) loglog N at normal SNR), where J is the number of transmit antennas. This indicates that multiplexing gain of the spectrum sharing SDMA is $\frac{J-1}{J}$ times less than that of the non-spectrum sharing SDMA only using orthogonal beamforming, whereas no loss in multiuser diversity gain. Although the spectrum sharing SDMA always has lower throughput compared to the non-spectrum sharing SDMA in the non-coexistence scenario, it offers an intriguing opportunity to reuse spectrum already allocated to other coexisting systems.

• 전자공학회논문지A
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• 제33A권7호
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• pp.205-215
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• 1996

We derive the analytic equations for the transmission gain spectrum of a phase shift controlled (PSC) DFB filters with complexed coupled gratings considering both facet reflections and the phase of gratings using the transfer matrix method. The number of parameters of the equations is reduced by using the parameter of effective phase shift defined by the sum of the phase shift in a PSC region the effect of both facets reflections and the effective phase shift on the transmission gain spectrum and verify the validity of those equations from the computer simulation results. Computer simulation results show the PSC DFB filter with a pure index coupled grating has the widest tunable range and that with a pure gain grating has the largest side mode suppression ratio.

• Journal of Communications and Networks
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• 제18권3호
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• pp.311-319
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• 2016

In this paper, we analyze the spectrum-sensing performance of a cooperative cognitive radio (CR) network consisting of a number of CR nodes and a fusion center (FC). We introduce the "log-average-SNR ratio" that relates the average SNR of the CR-node-FC link and that of the primary-user-CR-node link. Assuming that the FC utilizes the K-out-of-N rule as its decision rule, we derive exact expressions for the sensing gain and the coding gain - parameters used to characterize the CR network performance at the high SNR region. Based on these results, we determine ways to optimize the performance of the CR network.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 춘계학술대회
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• pp.240-242
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• 1996

In this paper, we proposed a method of a hearing aid suitable for the sensorineural hearing impaired. Generally as the sensorineural hearing impaired have narrow audible ranges between threshold and discomfortable level, the speech spectrum may easily go beyond their audible range. Therefore speech spectrum must be optimally amplified and compressed into the impaired's audible range. The level and frequency of input speech signal are varied continuously. So we have to make compensation input signal for frequency-gain loss of the impaired, specially in the frequency band which includes much information. The input sigaal is divided into short time block and spectrum within the block is calculated. The frequency-gain characteristic is determined using the calculated spectrum. The number of frequency band and the target gain which will be added input signal are estimated. The input signal within the block is processed by a single digital filter with the calculated frequency-gain characteristics. From the results of monosyllabic speech tests to evaluate the performance of the proposed algorithm, the scores of test were improved.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2000년도 하계종합학술대회논문집
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• pp.13-16
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• 2000

Since stimulated Brillouin scattering (SBS) impact wavelength division multiplexing (WDM) optical transmission systems, it is important to understand the implication of SBS in the design of such lightwave systems. Therefore, Brillouin gain spectrum (BGS) is measured to characterize the effect of SBS in optical fiber. The Brillouin gain coefficient is found to vary as the wavelength and linewidth of source. Theoretically measurement of BGS shows a dependence on wavelength(λ) and on linewidth(Δν), respectively.

• Journal of the Optical Society of Korea
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• 제14권4호
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• pp.342-350
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• 2010

An optimal wideband gain flattened hybrid erbium-doped fiber amplifier/fiber Raman amplifier (EDFA/FRA) has been introduced. A new and effective optimization method called particle swarm optimization (PSO) is employed to find the optimized parameters of the EDFA/FRA. Numerous parameters which are the parameters of the erbium-doped fiber amplifier (EDFA) and the fiber Raman amplifier (FRA) define the gain spectrum of a hybrid EDFA/FRA. Here, we optimize the length, $Er^{3+}$ concentration, and pump power and wavelength of the EDFA and also pump powers and wavelengths of the FRA to obtain the flattest operating gain spectrum. Hybrid EDFA/FRA with 6-pumped- and 10-pumped-FRAs have been studied. Gain spectrum variations are 1.392 and 1.043 dB for the 6-pumped- and 10-pumped-FRAs, respectively, in the 108.5 km hybrid EDFA/FRAs, with 1 mW of input signal powers. Dense wavelength division multiplexing (DWDM) system with 60 signal channels in the wavelength range of 1529.2-1627.1 nm, i.e. the wide bandwidth of 98 nm, is studied. In this work, we have added FRA's pump wavelengths to the optimization parameters to obtain better results in comparison with the results presented in our previous works.

• 한국위성정보통신학회논문지
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• 제7권2호
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• pp.30-35
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• 2012

본 논문에서는 인지무선 통신의 스펙트럼 센싱을 위해 PU와 CR 사용자의 수신단 사이에 릴레이를 적용하여 가상의 공간 다이버시티이득(Spatial Diversity Gain)을 얻는 협력 릴레이 센싱 모델 중 여러개의 single hop AF 릴레이를 사용하는 기존 시스템 모델의 센싱 성능을 올리고자, 릴레이의 채널 상태에 따라 릴레이의 사용 유무를 선택함으로써 신뢰도 높은 다이버시티 이득을 얻는 모델을 제안하였다. 이는 Hidden terminal 환경이나, 또는 음영지역에 위치한 릴레이의 불분명한 정보를 줄임으로써 최적의 다이버시티를 얻을 수 있게 된다. 신호 검출 확률을 보임으로써 센싱 성능 향상을 보인다.

• 한국광학회지
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• 제14권3호
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• pp.286-291
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• 2003

광대역 이득 특성을 얻기 위한 InGaAsP-InP 응력보상 비대칭 다중 양자우물(Asymmetric Multiple Quantum Well, AMQW) 구조를 성장하고, Ridge Waveguide Laser Diodes(RWG-LDs)를 제작하였다. 제작 후 소자의 동작변수와 모드 이득을 측정하였으며, 얻어진 결과를 비교, 분석하였다. 외부 공진기형 구조에서 넓고 평탄한 이득특성을 얻기 위해 한쪽 단면에 Anti-Reflection(AR) 코팅을 수행하여 AR coated AMQW RWG LD의 이득특성을 분석하였다.

• 한국광학회지
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• 제6권4호
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• pp.302-309
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• 1995

상온에서 $1.55{\mu}m$ 를 발진하는 격자 정합된 InGaAs/InGaAsP 양자우물 레이저를 설계하여 주입 운반자 밀도와 온도의 함수로 이득 곡선을 계산하였다. 밴드 구조와 운동량 행력 요소의 계산에는 블록대각화된 8*8 이차 k.p 해밀토니안에 근거한 변환행렬법을 사용하였다. 이 격자정합된 양자우물은 TE 모우드로 발진하였다. 온도가 증가함에 따라 발진파장이 길어졌고, 투명 운반자 밀도는 증가하였으며 미분이득은 감소하였다. 이득 곡선의 온도의존도는 밴드 구조의 온도의존성과 페르미 함수의 온도의존성에 기인하는데 이중 후자의 효과가 주도적인 것이었다.

• 한국광학회지
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• 제17권2호
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• pp.143-148
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• 2006

광섬유 내 브릴루앙 산란의 이득 스펙트럼을 측정하는 새로운 방법을 제안하고 실험하였다. 기존의 측정 방식과는 달리, 주입전류를 직접 변조하여 광주파수 변조된 하나의 레이저 다이오드로부터 펌프광과 프로브광을 발생시키고, 주입전류를 사각파로 변조할 때 나타나는 광주파수 처핑을 이용하여 펌프/프로브간 광주파수 차이를 연속적으로 변화시키는 방법으로 브릴루앙 이득 스펙트럼을 측정하였다. 통신용 단일모드 광섬유의 브릴루앙 이득 스펙트럼을 측정하여 기존 문헌의 결과와 거의 일치하는 결과를 얻었다.