• 한국통신학회논문지
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• 제31권6A호
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• pp.563-574
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• 2006

본 논문에서는 OFDM(Orthogonal Frequency Division Multiplexing) 기반 다중 안테나 시스템의 링크레벨 성능 분석을 위하여 실제 전파 환경과 유사한 특성을 갖는 Ray-tracing 방식 채널의 하나인 SCM(Spatial Channel Model) 채널을 구현한다. 3GPP & 3GPP2 Spatial Channel AHG(Ad-hoc Group)에서 시스템레벨 성능 비교용으로 제안한 SCM 채널을 링크레벨 성능의 비교 분석을 위하여, 본 논문에서는 시스템레벨 채널에 대한 채널 계수 및 파라메터들을 링크레벨 성능 비교용으로 변환하여 구현한다. 모의실험을 통하여 구현한 SCM 채널의 특성을 검증하고, 이를 이용하여 기존의 OFDM 기반 MIMO (Multiple Input Multiple Output) 적용 시스템 및 스마트 안테나 적용 시스템에서의 실제적인 링크레벨 성능을 분석하고, 정확한 비교 검증을 위하여 SCM 채널과 동일한 파라메터를 적용한 I-METRA 채널 및 독립 채널 상황에서의 링크 레벨 성능을 함께 비교 분석한다. MIMO 및 스마트 안테나 적용 시스템에 대하여 여러 채널 환경에서 채널 상관도에 따른 링크레벨 성능을 분석함으로써, 채널 상관도의 영향에 따라 주어진 환경에 적합한 다중 안테나 시스템을 제안한다.

• Journal of Communications and Networks
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• 제7권3호
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• pp.284-293
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• 2005

A critical issue in applications involving networks of wireless sensors is their ability to synchronize, and mitigate the fading propagation channel effects. Especially when distributed 'slave' sensors (nodes) reach-back to communicate with the 'master' sensor (gateway), low power cooperative schemes are well motivated. Viewing each node as an antenna element in a multi-input multi-output (MIMO) multi-antenna system, we design pilot patterns to estimate the multiple carrier frequency offsets (CFO), and the multiple channels corresponding to each node-gateway link. Our novel pilot scheme consists of non-zero pilot symbols along with zeros, which separate nodes in a time division multiple access (TDMA) fashion, and lead to low complexity schemes because CFO and channel estimators per node are decoupled. The resulting training algorithm is not only suitable for wireless sensor networks, but also for synchronization and channel estimation of single- and multi-carrier MIMO systems. We investigate the performance of our estimators analytically, and with simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권12호
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• pp.5898-5916
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• 2018

In this paper, the downlink performance of multi-cell distributed antenna systems (DAS) with a single user in each cell is investigated. Assuming the channel state information is available at the transmitter, four transmission modes are formulated as combinations of remote antenna units (RAUs) selection and cooperative transmission, namely, non-cooperative transmission without RAU selection (NCT), cooperative transmission without RAU selection (CT), non-cooperative transmission with RAU selection (NCT_RAUS), and cooperative transmission with RAU selection (CT_RAUS). By using probability theory, the cumulative distribution function (CDF) of a user's signal to interference plus noise ratio (SINR) and the system ergodic capacity under the above four modes are determined, and their closed-form expressions are obtained. Furthermore, the system energy efficiency (EE) is studied by introducing a realistic power consumption model of DAS. An expression for determining EE is formulated, and the closed-form tradeoff relationship between spectral efficiency (SE) and EE is derived as well. Simulation results demonstrate their consistency with the theoretical analysis and reveal the factors constraining system EE, which provide a scientific basis for future design and optimization of DAS.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.186-186
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• 2000

In the GPS/DR integrated system, the GPS position(or velocity) is used to compensate the DR output and to calibrate errors in the DR sensor. This synergistic relationship ensures that the calibrated DR accuracy can be maintained even when the GPS signal is blocked. Because of the observability problem, however, the DR sensors are not sufficiently calibrated when the vehicle speed is low. This problem can be solved if we use a multi-antenna GPS receiver for attitude determination instead of conventional one. This paper designs a two-antenna GPS receiver integrated with DR sensors. The proposed integration system has three remarkable features. First, the DR sensor can be calibrated regardless of the vehicle speed with the aid of two-antenna GPS receiver. Secondly, the search space of integer ambiguities in GPS carrier-phase measurements is reduced to a part of the surface of the sphere using DR heading. Thirdly, the detection resolution of cycle-slips in GPS carrier-phase measurements is improved with the aid of DR heading. From the experimental result, it is shown that the search grace is drastically reduced to about 3120 of the non-aided case and the cycle-slips of 1 or half cycle can be detected.

• Journal of Communications and Networks
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• 제15권4호
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• pp.370-382
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• 2013

Distributed massive MIMO systems, which have high bandwidth efficiency and can accommodate a tremendous amount of traffic using algorithms such as zero-forcing beam forming (ZFBF), may be deployed in large public venues with the antennas mounted under-floor. In this case the channel gain matrix H can be modeled as a multi-banded matrix, in which off-diagonal entries decay both exponentially due to heavy human penetration loss and polynomially due to free space propagation loss. To enable practical implementation of such systems, we present a multi-banded matrix inversion algorithm that substantially reduces the complexity of ZFBF by keeping the most significant entries in H and the precoding matrix W. We introduce a parameter p to control the sparsity of H and W and thus achieve the tradeoff between the computational complexity and the system throughput. The proposed algorithm includes dense and sparse precoding versions, providing quadratic and linear complexity, respectively, relative to the number of antennas. We present analysis and numerical evaluations to show that the signal-to-interference ratio (SIR) increases linearly with p in dense precoding. In sparse precoding, we demonstrate the necessity of using directional antennas by both analysis and simulations. When the directional antenna gain increases, the resulting SIR increment in sparse precoding increases linearly with p, while the SIR of dense precoding is much less sensitive to changes in p.

• Journal of Communications and Networks
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• 제7권2호
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• pp.157-170
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• 2005

The combination of multiple antennas and multi-carrier code division multiple-access (MC-CDMA) is a strong candidate for the downlink of the next generation mobile communications. The study of such systems in scenarios that model real-life trans-missions is an additional step towards an optimized achievement. We consider a realistic MIMO channel with two or four transmit antennas and up to two receive antennas, and channel state information (CSI) mismatches. Depending on the mobile terminal (MT) class, its number of antennas or complexity allowed, different data-rates are proposed with turbo-coding and asymptotic spectral efficiencies from 1 to 4.5 bit/s/Hz, using three algorithms developed within the European IST-MATRICE project. These algorithms can be classified according to the degree of CSI at base-station (BS): i) Transmit space-frequency prefiltering based on constrained zero-forcing algorithm with complete CSI at BS; ii) transmit beamforming based on spatial correlation matrix estimation from partial CSI at BS; iii) orthogonal space-time block coding based on Alamouti scheme without CSI at BS. All presented schemes require a reasonable complexity at MT, and are compatible with a single-antenna receiver. A choice between these algorithms is proposed in order to significantly improve the performance of MC-CDMA and to cover the different environments considered for the next generation cellular systems. For beyond-3G, we propose prefiltering for indoor and pedestrian microcell environments, beamforming for suburban macrocells including high-speed train, and space-time coding for urban conditions with moderate to high speeds.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(1)
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• pp.139-142
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• 2004

X-band Waveguide slot way antenna is developed for heliborne MTD radar applications. The antenna is composed of multi-layer waveguide structures. Each of them has it's own functions, such as, radiation, power/phase distribution, coupling, etc. Broad-wall offset slots are used for radiators, inclined slots on broad-wall for power distribution to radiating(branch) waveguide, some kind of coaxial probe structures for in-phase coupling and H-plane T-junction power dividers. Antenna is realized by precision machining and careful assembly. It is tested and measured by 3m${\times}$l.7m planar near-field probe, which is set-up in MTG. Far-field calculations have good agreement in tolerable bounds. Special but necessary process such as brazing, will increase the accuracy and performance. Results show promising possibilities of future applications for real systems.

• 한국ITS학회 논문지
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• 제6권3호
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• pp.101-110
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• 2007

본 논문에서는 UHF대역의 RFID 리더기용 원형편파 안테나를 설계 제작하였다. 그리고 설계 제작된 안테나의 성능분석을 통하여 Return Loss (S11)는 914 MHz에서 약 -45.529 dB로 상당히 적었으며, 안테나 이득은 약 6.09 dBi값을 얻었다. 또한 임피던스 매칭은 약 $50.48\;{\Omega}$이고, 사용 대역 중심 주파수인 911 MHz에서 축비는 1.2 dB로 설계되어 모든 RFID 리더기에 적용 가능함을 확인하였다. 따라서 RFID 리더기의 파라미터에서 가장 중요한 것 중 하나는 수신감도를 향상시켜서 원거리에서도 멀티태그를 인식하는데 있어서 원형편파 안테나의 이득을 높게 설계 제작함으로써 감도를 향상 시킬 것으로 기대 된다.

• 대한전자공학회논문지TC
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• 제46권12호
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• pp.52-58
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• 2009

본 논문에서는 부하 저항을 갖는 접힌 구조의 모노폴 안테나를 제안 하였고, 설계 변수들이 안테나의 반사손실 특성에 미치는 영향에 대해 분석 했다. 제안한 안테나의 임피던스 대역폭(VSWR < 3)은 30 ~ 2000 MHz이고, 이는 HF/VHF/UHF 대역을 모두 포함한다. 진행파 안테나로 동작하게 하기 위해 안테나에 여섯 개의 부하 저항을 이용하여 안테나의 끝에서 발생하는 반사파를 많이 줄일 수 있었다. 부하 저항에 의해서 감소되는 방사 효율 감소를 줄이기 위해 안테나의 끝부분에 부하 저항을 달았고, 부하 저항들의 저항 값은 반사 손실 특성이 좋은 Klopfenstein taper를 이용하였다. 제안한 안테나는 모노폴 안테나와 같이 전방향성 방사패턴을 갖는다. 급전부분과 제안한 안테나의 입력단 부분에서의 광대역 임피던스 변환을 위해 급전 부분과 안테나의 입력단 사이에 10 ~ 1900 MHz에서 동작하는 발룬(Balun)을 이용하였다. 제안한 안테나의 광대역 특실과 방사패턴은 다대역 다기능 통신기에 이용될 수 있을 것으로 예상한다.

• 한국정보통신학회논문지
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• 제8권8호
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• pp.1626-1631
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• 2004

OFDM 전송 방식에서는 데이터 전송 시, 서로 직교성이 있는 여러 개의 부반송파들을 사용한다. 그러므로 주파수 다이버시티 효과를 얻을 수 있어서 성능이 우수한 전송이 가능하다. 본 논문에서는 여러 가지 종류의 안테나를 사용했을 때의 OFDM 전송 시스템 성능을 분석한다. 이러한 여러 가지 시스템들에서 데이터가 다중 경로 Rayleigh 페이딩 환경 하에서 전송될 때의 데이터 비트 에러율을 분석한다.