• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.268-272
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• 2012

A propulsion controller for vehicles should be designed to overcome a sensor failure during a flight, and it is necessary to control the system properly at any circumstances. Therefore, the vehicles need to retain reliability on the sensor measurements by implementing extra sensors to replace the original control sensors in case of their failure. This paper presents the MIMO NARX model by simulation which substitutes measured values with estimated ones by the state estimation technique in case of a sensor failure in a turbojet engine. It is also presented that the NARX model can be adapted as an engine model in HILS equipments.

• ETRI Journal
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• v.45 no.3
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• pp.418-432
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• 2023

In this work, we proposed a low-complexity hybrid layered tabu-likelihood ascent search (LTLAS) algorithm for large multiple-input multiple-output (MIMO) system. The conventional layered tabu search (LTS) approach involves many partial reactive tabu searches (RTSs), and each RTS requires an initialization and searching phase. In the proposed algorithm, we restricted the upper limit of the number of RTS operations. Once RTS operations exceed the limit, RTS will be replaced by low-complexity likelihood ascent search (LAS) operations. The block-based detection approach is considered to maintain a higher signal-to-noise ratio (SNR) detection performance. An efficient precomputation technique is derived, which can suppress redundant computations. The simulation results show that the bit error rate (BER) performance of the proposed detection method is close to the conventional LTS method. The complexity analysis shows that the proposed method has significantly lower computational complexity than conventional methods. Also, the proposed method can reduce almost 50% of real operations to achieve a BER of 10^-3.

• ETRI Journal
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• v.37 no.6
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• pp.1055-1064
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• 2015

We demonstrate a next-generation high-capacity mobile fronthaul based on radio over fiber (RoF) technology, which links between a digital unit and a radio unit supporting two frequency assignments and $2{\times}2$ multiple input, multiple output antennas. To confirm the technical feasibility of a mobile fronthaul, we experimentally investigate its down- and uplink end-to-end performances including the optical and radio frequency (RF) signal path. Frequency-dependent performance deviations, error vector magnitude variations, overall system performance variations caused by optical to electrical conversion, and intermediate frequency to RF conversions are examined. Experimental verifications on multiple LTE uplink signals are performed for the first time. We also demonstrate several commercial mobile Internet services, YouTube video streaming, and file transfers using off-the-shelf mobile devices, through a mobile fronthaul based on RoF.

• ETRI Journal
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• v.35 no.1
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• pp.51-57
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• 2013

In this paper, a small internal antenna for a mobile handset is presented using multiband, wideband, and high-isolation multiple-input multiple-output techniques. The proposed antenna consists of three planar inverted-F antennas (PIFAs) that operate in the global system for mobile communication (GSM900), the digital communication system (DCS), the personal communication system (PCS), the universal mobile telecommunication system (UMTS), and wireless local area network (WLAN) bands with a physical size of $40mm{\times}10mm{\times}10mm$. A resonator attached to the folded PIFA creates dual resonances, achieving a wide bandwidth of approximately 460 MHz, covering the DCS, PCS, and UMTS bands; a meander shorting line is used to improve impedance matching. Additionally, a modified neutralization link is embedded between diversity antennas to enhance isolation, which results in a 6-dB improvement in the isolation and less than 0.1 in the envelope correlation coefficient evaluated from the far-field radiation patterns. Simulation and measurements demonstrate very similar results for S-parameters and radiation patterns. Peak gains show 3.73 dBi, 3.77 dBi, 3.28 dBi, 2.15 dBi, and 5.86 dBi, and antenna efficiencies show 56.15%, 72.15%, 68.59%, 52.92%, and 82.93% for GSM900, DCS, PCS, UMTS, and WLAN bands, respectively.

• The Journal of the Korea Contents Association
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• v.9 no.7
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• pp.67-75
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• 2009

IEEE 802.11 WLAN(Wireless Local Area Network) standard is currently developing with increased wireless internet demand. Study trends of IEEE 802.11n for high throughput show two aspects, enhanced system throughput using aggregation among packets in MAC(Medium Access Control) layer, and better data rates adapting MIMO(Multiple-Input Multiple-Output) in PRY(Physical) layer. But, no one demonstrates IEEE 802.11n system performance results considering MAC and PRY connection. This paper adapts A-MPDU(Aggregation-MAC Protocol Data Unit) method in MAC layer and MIMO in PRY layer for IEEE 802.11n system. Consequently, Simulation results show enhanced throughput and data rates compared to existing system. Also, We use NS-2(Network Simulator-2) considering MAC and PRY connection for reality.

• Journal of Communications and Networks
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• v.12 no.1
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• pp.11-18
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• 2010

Diversity-multiplexing tradeoff (DMT) is an efficient tool to measure the performance of multiple-input and multiple-output (MIMO) systems and cooperative systems. Recently, cooperative multicast system with wireless network coding stretched tremendous interesting due to that it can drastically enhance the throughput of the wireless networks. It is desirable to apply DMT to the performance analysis on the multicast system with wireless network coding. In this paper, DMT is performed at the three proposed wireless network coding protocols, i.e., non-regenerative network coding (NRNC), regenerative complex field network coding (RCNC) and regenerative Galois field network coding (RGNC). The DMT analysis shows that under the same system performance, i.e., the same diversity gain, all the three network coding protocols outperform the traditional transmission scheme without network coding in terms of multiplexing gain. Our DMT analysis also exhibits the trends of the three network coding protocols' performance when multiplexing gain is changing from the lower region to the higher region. Monte-Carlo simulations verify the prediction of DMT.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.98-102
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• 2005

In the QR Decomposition-based (QRD) decoding class, the system performance is sensitive to the error propagation. Thus, it is critical to correctly decode the previous layers. One approach to desensitize the error propagation is to propose the optimal decoding order of layers. In this work, we propose a new extended-list Sorted QRD-base (SQRD) decoding approach. In the proposed decoding scheme, the solution of the few first layers is extended as the list of promising possible solutions. By doing so, the diversity of the lowest layer is increased. As a result, the system performance is less sensitive to the error propagation than its counterparts. The proposed approach is verified by the computer simulation results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.8
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• pp.1773-1779
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• 2015

Shore-to-sea visible light communication using color clustered multiple-input and multiple-output (MIMO) is presented. The proposed maritime visible light communication (MVLC) offers a low-cost, high-speed wireless link for shore-to-sea maritime communications. Each color cluster is comprised of 50 red, green and blue (RGB) light emitting diodes (LEDs) and is modulated using on-off-keying (OOK). Selection combining is performed at the receiver, producing diversity effect within that color cluster. In this paper, we employ sea states (wave height, wind speed, etc.) data from both Pierson-Moskowitz and JONSWAP spectrum models under atmospheric turbulence conditions. Based on the simulation model, the maritime link quality is analysed in terms of coverage distance and bit error rate performance. The results show that the proposed system provides an efficient MVLC, while satisfying International Association of Lighthouse Authorities (IALA) requirements for maritime buoyage system and also offering sufficient illumination from high power LEDs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1833-1844
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• 2004

A controller is proposed for the robust backstepping control of a class of nonlinear multiple-input multiple-output (MIMO) systems which can be converted to a strict feedback form. The proposed robust backstepping control scheme follows a systematic procedure for the design of control laws and uses time delay estimation (TDE) to estimate the uncertainties such as parameter variations, unknown disturbances, and unmodeled dynamics, etc. The proposed controller can be also applied to nonlinear MIMO systems with unmatched uncertainties. Stability analysis of the closed-loop system which contains the plant and the proposed controller is also studied and hereby a sufficient stability condition for the closed-loop system is proposed. The simulation results show that the control scheme works well with uncertainties and the proposed stability condition is valid. The controller is experimentally verified on a single-link flexible arm to show the effectiveness of the proposed scheme in the complicated systems with uncertainties.

• Journal of Communications and Networks
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• v.18 no.5
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• pp.688-698
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• 2016

In this paper, we investigate the achievable sum rate and energy efficiency of downlink massive multiple-input multiple-output antenna systems with zero-forcing precoding, by taking into account the randomness of user locations. Specifically, we propose two types of non-uniform user distributions, namely, center-intensive user distribution and edge-intensive user distribution. Based on these user distributions, we derive novel tight lower and upper bounds on the average sum rate. In addition, the impact of user distributions on the optimal number of users maximizing the sum rate is characterized. Moreover, by adopting a realistic power consumption model which accounts for the transmit power, circuit power and signal processing power, the energy efficiency of the system is studied. In particular, closed-form solutions for the key system parameters, such as the number of antennas and the optimal transmit signal-to-noise ratio maximizing the energy efficiency, are obtained. The findings of the paper suggest that user distribution has a significant impact on the system performance: for instance, the highest average sum rate is achieved with the center-intensive user distribution, while the lowest average sum rate is obtained with the edge-intensive user distribution. Also, more users can be served with the center-intensive user distribution.