• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.237-243
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• 2002

This paper studies the channel estimation schemes of Time Division Duplex (TDD) Code Division Multiple Access (CDMA) system with a parallel interference canceller (PIC) in multi-path fading channels. furthermore, the effective interpolation method which maintains the flexibility of UTRA TDD mode is proposed. By Monte Carlo simulations, it is verified that the proposed interpolation method can be used in order to obtain the proper performance of a multi-stage PIC and in order to reduce the required Eb/No for a given bit error rate (BER).

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.479-485
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• 2002

We propose a vector analysis for designing multimode-interference power splitters, which can show an arbitrary splitting ratio. Power splitting is a fundamental characteristic in integrated optical circuits and its value would be multiplied for many applications if the splitting ratio could be selected freely. Since the vector analysis utilizes a graphical method based on the previously-reported mathematical results of multimode interference, it shows an excellent advantage especially for designing power splitters with an arbitrary splitting ratio.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6B
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• pp.403-410
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• 2008

In this paper, we investigate the performance of MMR system in Non-transparent mode. The IEEE 802.16j MMR system has two node of operation, Single-frame (in band) and Multi-frame (out band) mode. In the analysis, we assume that channel interference between MR-BS and RS, or between RSs anywhere in the given area is ignored. The performance is presented in terms of the delay and the frame efficiency by varying number of RS and BS coverage to RS coverage ratio and the maximum coverage area of a BS by varying traffic density. Analytical results show that the Single-frame is more efficient than Multi-frame in frame efficiency and coverage extension.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.53.2-53.2
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• 2015

Fiber Bragg gratings (FBGs) are the most compact and reliable method of suppressing atmospheric emission lines in the infrared for ground-based telescopes. It has been proved that real FBGs based filters were able to eliminate 63 bright sky lines with minimal interline losses in 2011 (GNOSIS). Inscribing FBGs on multi-core fibers offers advantages. Compared to arrays of individual SMFs, the multi-core fiber Bragg grating (MCFBG) is greatly reduced in size, resistant to damage, simple to fabricate, and easy to taper into a photonics lantern (PRAXIS). Multi-mode fibers should be used and the number of modes has to be large enough to capture a sufficient amount of light from the telescope. However, the fiber Bragg gratings can only be inscribed in the single-mode fiber. A photonic lantern bi-directionally converts multi-mode to single-mode. The number of cores in MCFBGs corresponds to the mode. For a writing system consisting of a single ultra-violet (UV) laser and phase mask, the standard writing method is insufficient to produce uniform MCFBGs due to the spatial variations of the field at each core within the fiber. Most significant technical challenges are consequences of the side-on illumination of the fiber. Firstly, the fiber cladding acts as a cylindrical lens, narrowing the incident beam as it passes through the air-cladding interface. Consequently, cores receive reduced or zero illumination, while the focusing induces variations in the power at those that are exposed. The second effect is the shadowing of the furthest cores by the cores nearest to the light source. Due to a higher refractive index of cores than the cladding, diffraction occurs at each core-cladding interface as well as cores absorb the light. As a result, any core that is located directly behind another in the beam path is underexposed or exposed to a distorted interference pattern from what phase mask originally generates. Technologies are discussed to overcome the problems and recent experimental results are presented as well as simulation results.

• Journal of KIISE:Information Networking
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• v.37 no.4
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• pp.294-300
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• 2010

In this paper, We analysis of effective coverage extension for Tri-sector cellular systems using Multi-hop Relay based on IEEE802.16j system. In the proposed international standard of IEEE 802.16j MMR (Mobile Multi-hop Relay) use of the omni-directional antenna, 3-sector and 6-sector antenna is considered to Base Station and Relay Station. Omni-directional antenna service can offer as all directions but a throughput decreases due to the signal interference of near Relay Stations. In the directional antenna, cause of an interference with the base station which it arranges an antenna so that a beam can have the direct and does with neighbor Base Station and Relay Station can be reduced interference, therefore the effective throughput is higher than the omni-directional antenna system. But, In case of Base Station and Relay Station use the directional antenna, the efficiency which the directional antenna has the Co-channel interference due to in the different cell by the channel reuse is decreased. In this study, we propose the structure of arranging the Base Station and Relay Station having the directional antenna in the NBTC, WBTC antenna in a multi-tier. It compared and analyzed with the mode that the multi-hop Relay Station has the omni-directional antenna, Relay Station are used the NBTC antenna and the WBTC antenna system also, We analyze a relation between the performance degradation and the cell coverage extension which it follows because the number of hop in the multi-hop Relay Station.

• Journal of the Optical Society of Korea
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• v.16 no.2
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• pp.157-161
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• 2012

This work reports the stability of the resonant characteristics in multimode interferometer coupled square ring semiconductor cavities. Based on the analysis of single square ring cavities, the single mode operations in the multimode interferometer coupled ring cavities are analyzed and the devices are demonstrated on the semiconductor multiple quantum well epitaxial structure. By varying the lasing conditions such as substrate temperature and input pump power, single resonant mode operations are also observed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.4
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• pp.363-368
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• 2003

In this paper, the characteristics of the horn antenna for the high power transfertation system is stuided and several kinds of a horn antenna are compared and finally a conical hem antenna using multi-mode is proposed. In the high power system, the efficiency of power transfer is very important. Therefore the feeding hem of a reflector must have a circular symmetric radiation pattern. And the side lobe must be suppressed to reduce a spillover power loss and interference. By using multi-mode in a circular hem antenna, the whole length can be shorter and the radiation pattern can be adjusted according to the shape and direction of a reflector. This is confirmed by the experiments.

• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.418-422
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• 2000

In this paper, we have modeled and fabricated a mutimode interference (MMI) $1\times4$ optical power splitter using finite-difference beam propagation method and $Ag^+-Na^+$ ion-exchanged method in BK7 glass. The power splitting ratio of the fabricated MMI $1\times4$ optical power splitter shows 0.46 dB..46 dB.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.11
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• pp.85-90
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• 1998

A 1 4 polymeric optical power divider based on the multimode interference effect is designed and fabricated. The two dimensional finite difference beam propagation method has been utilized in designing the device. Polymers used for the core layer and the cladding layer are Cyclotene-3022 and UV-15, respectively. The device is fabricated by the reactive ion etching method. The splitting ratio of the fabricated device is 0.93 : 1.00 : 0.93 : 0.90 for TE mode and 0.84 : 0.94 : 1.00 : 0.83 for TM mode. The advantages of this device are small size and low polarization-dependence.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.394-400
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• 2010

Mobile Multi-hop Relaying (MMR) system can provide increased system capacity of wireless access network by coverage extension and enhanced transmission rate within the Base Station (BS) coverage area. The previous researches for the MMR system with a non-transparent mode Relay Station (RS) do not consider channel selection procedure of Mobile Station (MS), co-channel interference and Multi-hop Relay Base Station (MR-BS) coverage and RS coverage ratio in MMR system. In this paper, we investigate the performance of MMR uplink system in multicell environments with various topologies. The performance is presented in terms of call blocking probability, channel utilization, outage probability and system throughput by varying offered load. It is found that, for certain system parameters, the MMR uplink system achieve the maximum system throughput when MR-BS coverage to RS coverage ratio is 7.