• Journal of Communications and Networks
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• 제13권1호
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• pp.63-69
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• 2011

In this paper, we propose a fixed-complexity sphere encoder (FSE) for multi-user multi-input multi-output (MU-MIMO) systems. The proposed FSE accomplishes a scalable tradeoff between performance and complexity. Also, because it has a parallel tree-search structure, the proposed encoder can be easily pipelined, leading to a tremendous reduction in the precoding latency. The complexity of the proposed encoder is also analyzed, and we propose two techniques that reduce it. Simulation and analytical results demonstrate that in a $4{\times}4$ MU-MIMO system, the proposed FSE requires only 11.5% of the computational complexity needed by the conventional QR decomposition with M-algorithm encoder (QRDM-E). Also, the encoding throughput of the proposed encoder is 7.5 times that of the QRDM-E with tolerable degradation in the BER performance, while achieving the optimum diversity order.

• 제어로봇시스템학회논문지
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• 제18권5호
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• pp.419-425
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• 2012

This paper presents an approach to implement the behaviors of multi-robots responding to user's input characters. The robots are appropriately displaced to express any input characters. Using our method, any user can easily and friendly control multirobots. The responses of the robots to the user's input are intuitive. We utilize the centroidal Voronoi algorithm and the continuoustime Lloyd algorithm, which have popularly been used for the optimal sensing coverage problems. Collision protection is considered to be applied for real robots. LED sensors are used to identify positions of multi-robots. Our approach is evaluated through experiments with five mobile robots. When a user draw alphabets, the robots are deployed correspondingly. By checking position errors, the feasibility of our method is validated.

• 대한전자공학회논문지TC
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• 제46권4호
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• pp.1-7
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• 2009

본 논문에서는 다중안테나 OFDM(Orthogonal Frequency Division Multiplexing) 시스템에서의 인접 셀 혹은 인접 섹터 간섭제거 능력을 갖는 MIMO(Multi-Input Multi-Output) 수신 알고리즘을 제안하였다. 제안된 알고리즘은 시간축에서의 Filtering 기법에 관한 기존의 연구와는 다르게 주파수 영역에 적용이 가능한 Pre-filtering 기법을 채널 추정을 위한 파일럿 심벌만을 이용하여 구현하였다. 또한 제안된 기법은 간섭성분이 MIMO(C-SM(Collaborative-Spatial Multiplexing)) 뿐만이 아니라 SIMO(Single-Input Multi-Out)이더라도 적용이 가능함을 이론적으로 검증하였다. 그리고 제안된 수신 알고리즘을 검증하기 위하여 IEEE 802.16e 표준의 UL-PUSC SR off에서의 모의실험을 수행하였다. 이를 통하여 제안된 알고리즘이 간섭 성분의 종류에 관계없이 적용이 가능함을 확인하였다. 또한 간섭 성분의 영향이 큰 경우에 대해서도 우수한 성능을 보장하여 시스템 Throughput 향상을 보장할 수 있음을 확인하였다.

• 융합신호처리학회논문지
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• 제14권1호
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• pp.39-44
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• 2013

본 논문에서는 멀티암(multi-arm) 스파이럴 안테나용 디지털 위상천이기(digital phase-shifter)를 힐버트 변환(Hillbert transform)을 이용하여 설계하였다. 힐버트 변환은 입력신호에 포함된 모든 주파수 성분을 $90^{\circ}$ 위상천이 시키며, 퓨리에 변환(Fourier transform)과 역퓨리에 변환(Inverse FIT)을 통해 구현된다. 디지털 위상천이기는 ADC(Analog-digital converter)로 샘플링된 입력신호에 힐버트 변환을 적용하여 위상차가 $90^{\circ}$인 두 신호를 생성하고, 이 두 신호를 이용하여 입력신호의 위상을 천이위상만큼 천이시키게 한다. 힐버트 변환 기반의 디지털 위상천이기는 Xilinx사의 System generator로 설계되었고, 입력 잡음, FFT 포인트 수, 샘플링 주기, 입력신호의 초기위상 및 천이 위상각 등에 따른 위상천이 성능을 시뮬레이션 하였으며, Matlab 결과와 비교하여 일치함을 확인하였다.

• 한국소음진동공학회논문집
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• 제15권9호
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• pp.1070-1076
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• 2005

Vibration test using the MAST(multi axial simulation table) provide a more reliable testing environment than any conventional one. The multi axial simulation could be possible with a advanced control algorithm and hardware supports so that most of the operation is automatically conducted by MAST system itself except the input information that is synthesized by the measured response signals. That means the reliability of the vibration test is highly depended on the quality of the input profile. In this paper, the optimal algorithm based on the energy method is introduced to construct a best combination of candidated input PSD data could be constructed. Since the optimal algorithm renders time information, the nitration fatigue test is completely possible for any measured signals one wants. The proposed method is explained with representing acquired road signals from the candidate input PSD obtained from a proving ground.

• 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.

• Journal of Communications and Networks
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• 제14권4호
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• pp.443-450
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• 2012

As for cluster-based wireless sensor networks (WSNs), cluster lifetime is one of the most important subjects in recent researches. Besides reducing the energy consumptions of the clusters, it is necessary to make the clusters achieve equal lifetimes so that the whole network can survive longer. In this paper, we focus on the cluster lifetimes in multi-hop WSNs with cooperative multi-input single-output scheme. With a simplified model of multi-hop WSNs, we change the transmission schemes, the sizes and transmission distances of clusters to investigate their effects on the cluster lifetimes. Furthermore, linear and uniform data aggregations are considered in our model. As a result, we analyze the cluster lifetimes in different situations and discuss the requirements on the sizes and transmission distances of clusters for equal lifetimes.

• Journal of information and communication convergence engineering
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• 제8권4호
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• pp.393-398
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• 2010

For multi-cell environments, coordinated random beamforming technique in multiuser MIMO(multiple-input multiple-output) broadcast channel is considered. In order to mitigate severe interference at receivers, the multi-cell environments might require complex transmitter and receiver design because the scheduler decision based on full channel state information (CSI) in one cell must be intertwined with decision made by other cells' CSI. With limited CSI, however, this paper considers a scheme of randomizing transmitters' beamforming but being coordinated with other cell transmitters. The transmitters in each cell share random beamforming patterns and schedule data transmission within coherent scheduling period. The corandomized beams allow the users to be selected with the highest SINRs even in multi-cell environments. We analyze the performance of the proposed scheme. And numerical results show that the scheme achieves better performance than the conventional random beamforming when applying to multi-cell environments.

• 한국군사과학기술학회지
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• 제13권4호
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• pp.673-682
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• 2010

This paper describes and analyzes a various generation methods of the mutually orthogonal polyphase sequences with low cross-correlation peak sidelobe and low autocorrelation peak sidelobe levels. The mutual orthogonality is the key requirement of multi-static or MIMO(Multi-Input Multi-Output) radar systems which provides the good target detection and tracking performance. The polyphase sequences, which are generated by SA(Simulated Annealing) and GA(Genetic Algorithm), have been analyzed with ACF(Autocorrelation Function) PSL(Peak Sidelobe Level) and CCF(Crosscorrelation Function) level at the matched filter output. Also, the ambiguity function has been introduced and simulated for comparing Doppler properties of each sequence. We have suggested the phase selection rule for applying multi-static or MIMO systems.

• 대한기계학회논문집
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• 제9권6호
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• pp.691-698
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• 1985

본 논문에서는 종래의 FRF법을 이용하였을때의 문제점을 보완하고 계의 정확 한 진동원을 파악하기 위하여 진동원 간에 강한 상관관계가 존재하는 경우에 사용되는 다차원 스펙트럼해석(Multi-Dimensional Spectral Analysis` MDSA)법을 가솔린엔진에 적용 검토하였다.