• Korean Journal of Materials Research
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• v.9 no.9
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• pp.861-864
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• 1999

A new plasma source using the multi-cathode electron beam has been designed and manufactured. A multi-cathode was adopted to produce bulk plasmas in a large volume. Multi-cathode electron beam plasma source(MCEBPS) was found to generate stable plasmas over the wafer diameter of 300 mm or above. W(tungsten) filament was used as a cathode. Over a 320 mm diameter, both the plasma potential $V_p$ and floating potential $V_f$ were uniformly maintained and the difference between $V_p and V_f$ was measured to be small. The plasma density was around $10^{10} cm^{-3}$ and its variation along the radial distance was small.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.360-370
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• 2010

In this paper, a distributed beamforming problem is considered in an amplify-and-forward (AF) wireless relay network consist of multiple source-destination pairs and relaying nodes. To exploit degree of freedom of the number of beamformers, in the first step, we proposed that the sources transmit their signals through orthogonal channels. During the second step, the relays transmit their received signals multiplied by complex weights to amplify and compensate for phase changes introduced by the backward channels through one common channel. The optimal beamforming vectors are obtained through minimization of the total relay transmit power while the signal-to-interference-plus-noise ratios (SINRs) at the destinations are above certain thresholds to meet a quality of services (QoSs) level. In the numerical example, it is shown that the proposed scheme needs less transmit power for moderate network data rates than other schemes, such as space division multiplexing or time-division multiplexing scheme.

• Korean Journal of Optics and Photonics
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• v.31 no.2
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• pp.105-110
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• 2020

A compact beam combiner based on two-mode interference (TMI) in multimode waveguides is proposed, and its feasibility is shown through simulation with the three-dimensional beam propagation method. The input waveguides are separated by about 1 ㎛ at the interface with the multimode waveguide, so that the fabricated waveguide pattern is well repeated. The power transmission to the output port from the red, green, and blue input port is 93.5%, 94%, and 93%, respectively. When the wavelength deviation from a center wavelength is 10 nm, the power transmission is maintained to be greater than 90%. When the waveguide width error is 40 nm, the power transmission is maintained to be greater than 85% for all the three colors. The polarization dependence of the beam combiner is almost negligible, and its size is as tiny as 0.02 × 4 ㎟.

• The Journal of the Acoustical Society of Korea
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• v.16 no.6
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• pp.100-105
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• 1997

To analyze the multipath propagation effects on the source bearing detection of HLA(Horizontal Line Array), the conversion mechanism of the multipath into the bearing is described, and the bearing is estimated from the multipath modeled with typical sound velocity structures of the East and the South Sea of Korea. The erroneous bearing is observed from the beamforming outputs simulated with the modeled multipath, and the erroneous phenomena are analyzed. In case of the East Sea, since the multipath propagation with a high receiving angle occurs due to strong inverse slope of the sound velocity structure, it is possible that the estimated source bearing is different from the real source bearing, and that the number of the source is misrecognized.

• Journal of Satellite, Information and Communications
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• v.5 no.2
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• pp.97-103
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• 2010

In this paper, we present an efficient design scheme based on analysis of design requirements and considerations of baseband packet switch for S-band satellite/terrestrial hybrid multi-beam satellite communication systems. To establish design requirements and considerations, we analyze required functions of baseband packet switch, specifications of multi-beam satellite communications, communication services and performance requirements. And also we analyze and compare conventional layer-2 and layer-3 satellite baseband packet switching techniques, packet switching protocols and packet switch architectures, to apply from analyzed results. Finally, we propose a hardware design scheme of MPEG based layer-2 baseband packet switch using analyzed results.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.1
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• pp.59-69
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• 2018

In this paper, we present a robust beamforming design to tackle the weighted sum-rate maximization (WSRM) problem in a multicell multiple-input multiple-output (MIMO) - non-orthogonal multipleaccess (NOMA) downlink system for 5G wireless communications. This work consider the imperfectchannel state information (CSI) at the base station (BS) by adding uncertainties to channel estimation matrices as the worst-case model i.e., singular value uncertainty model (SVUM). With this observation, the WSRM problem is formulated subject to the transmit power constraints at the BS. The objective problem is known as on-deterministic polynomial (NP) problem which is difficult to solve. We propose an robust beam forming design which establishes on majorization minimization (MM) technique to find the optimal transmit beam forming matrix, as well as efficiently solve the objective problem. In addition, we also propose a joint user clustering and power allocation (JUCPA) algorithm in which the best user pair is selected as a cluster to attain a higher sum-rate. Extensive numerical results are provided to show that the proposed robust beamforming design together with the proposed JUCPA algorithm significantly increases the performance in term of sum-rate as compared with the existing NOMA schemes and the conventional orthogonal multiple access (OMA) scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11A
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• pp.861-869
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• 2011

In this paper, we propose coordinated scheduling and beamforming based on limited feedback to overcome the effects of inter-cell interference in multi-cell environment. The goal of this study is to improve a performance of cell-edge area significantly affected by the inter-cell interference and also to guarantee a performance of the entire system. Existing coordinated scheduling and beamforming based on the perfect channel state information generates an overhead for the channel state information feedback and exchange at the users and base stations, respectively. In this study, first we propose a novel codebook to obtain a null space of an interference channel efficiently which can be used to reduce the inter-cell interference. Using the proposed codebook, we propose coordinated scheduling and beamforming to improve the performance of cell-edge area and the entire system. Through the proportional fair scheduling, the performance of the proposed technique is shown as improvement of channel capacity for users located cell-edge area and entire system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.3
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• pp.491-498
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• 2017

GPS (global positioning system) is a popular system that provides location information by measuring arrival time difference at the receiver between several GPS satellite signals. GPS is widely used in commercial area as well as military systems. Reliable GPS signal reception is more important in the military applications such as guided missiles. However, since the carrier frequencies of the GPS signals are well known and the received power is extremely low, the GPS systems are vulnerable to intentional jamming attacks. To remove jammers while maintaining GPS signals at the received signals, a popular technique is an adaptive beam steering method based on array antenna. Among adaptive beam steering techniques, this paper considers MVDR (minimum variance distortionless response) algorithm, and proposes a new adaptive technique that preserves the received signals at desired directions, but removes the unknown jamming signals adaptively. The performance of the proposed method is verified through computer simulation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.8
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• pp.665-675
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• 2016

With the development of active phased array radar technology in recent years, active phased array antennas, which digitally combine signals received from subarray units using dozens of digital receiver, have been developed. The beam characteristics are greatly affected by the shape of the subarray structure as well as the weight of subarray in digital beamforming. So in this paper, the method to generate subarray structures by using recursive element exchanging method and the method to optimize subarray structures that can minimize sidelobes of operating beams are proposed. Additionally it presents the result to find the optimized subarray structure to minimize the maximum sidelobe of monopulse beam and pencil multi-beam respectively or simultaneously which are commonly used for digital beamforming by applying the algorithm propsed in this paper.

• Korean Journal of Optics and Photonics
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• v.14 no.1
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• pp.65-71
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• 2003

To maximize the storage density in a localized hologram recording method, each hologram should be recorded as close as possible to its neighboring holograms. In this case, the reference beams used to record two adjacent holograms may overlap in spatial multiplexing. Through simulations and experiments, we show that there exists an optimal reference beam size to minimize the overlap for a given shifting distance of the reference beams in spatial multiplexing. Thus the advantages of the localized hologram recording method can be minimally sacrificed while the storage density is increased.