• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.12
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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.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.7
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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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• v.18 no.3
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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.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.05
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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.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2000.08a
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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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• v.14 no.4
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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.

• Journal of Satellite, Information and Communications
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• v.7 no.2
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• pp.30-35
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• 2012

In this paper, we proposed spectrum sensing using cooperative relay to solve problem of sensing performance degradation due to CPE (Customer-Primise equipments) which causes low SNR (signal-to-noise ratio) problem. This system model is expected that cooperative relay scheme guarantees the high sensing performance by its diversity gain. Based on these backgrounds, in this paper, we apply to cooperative relay scheme to the CR (cognitive radio) system, and simulation results show comparison of the sensing performance combining method EGC and MRC.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.286-291
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• 2003

Asymmetric multiple quantum well ridge waveguide laser diodes (AMQW RWG LDs) with a wide and flat gain spectrum were designed and fabricated. The operating parameters and gain spectra were measured and analyzed for uncoated and anti-reflection (AR) coated LDs. For AR coated 500 mm-long RWG LOs, the extremely flat gain spectrum over a spectral range of 90 nm was obtained at the current 75 ㎃.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.302-309
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• 1995

We desinged a lattice-matched InGaAs/lnGaAsP quantum well laser that lases at $1.55{\mu}m$ at room temperature, and calculated the gain spectrum as a function of injected carrier density and temperature. For the calculation of band structures and momentum matrix elements, we used a transfer JIlatrix method based on a block-diagonalized 8x8 second-order Ii$.$ P Hamiltonian. This lattice-matched quantum well lases in transverse electric mode. As the temperature increases, the lasing wavelength gets longer, the transparency carrier density increases, and the differential gain is reduced. The temperature dependence of the gain spectrum comes from the temperature dependence of the band structure and that of the Fermi function, and the latter contributes dominantly.nantly.

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.143-148
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• 2006

A new method of measuring the Brillouin gain spectrum of optical fiber is proposed and demonstrated. Unlike existing methods, both the pump light and the counter-propagating probe light are generated from a single laser diode whose optical frequency is directly modulated by injection current modulation. The frequency difference between the pump and the probe is scanned continuously through optical frequency chirp occurring when the injection current is modulated with a square wave. The measured Brillouin gain spectrum of telecom single-mode fiber agrees well with that shown in other literature.