• 한국전자파학회논문지
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• 제19권4호
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• pp.461-469
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• 2008

본 논문은 MIMO OFDM 시스템에 적용 가능한 하이브리드 심볼 옵셋 추정 알고리즘을 제안한다. MIMO OFDM 시스템은 다중 송수신 안테나 시스템이므로 종래의 단일 송수신 안테나 시스템에 적용되는 알고리즘과는 다르게 다중 수신 안테나 시스템에서 사용하는 결합 기법을 고려하여 사용할 수 있다. 따라서 본 논문에서는 MIMO OFDM 시스템과 같은 다중 수신 안테나 시스템에서 적용 가능한 심볼 옵셋 추정 알고리즘을 제안하고, MIMO 시스템 환경에서 모의 실험하였으며, ISI가 심한 채널의 경우에는 제안하는 동일 이득 결합 상관 관계 알고리즘이 종래의 이른 심볼 옵셋 추정 알고리즘보다 이상적인 샘플 위치를 찾는 성능이 1.8배 우수함을 제시하였다.

• Journal of Communications and Networks
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• 제14권3호
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• pp.273-279
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• 2012

In this paper, we propose an iterative interstream interference cancellation technique for system with frequency selective multiple-input multiple-output (MIMO) channel. Our method is inspired by the fact that the cancellation of the interstream interference can be regarded as a reduction in the magnitude of the interfering channel. We show that, as iteration goes on, the channel experienced by the equalizer gets close to the single input multiple output (SIMO) channel and, therefore, the proposed SIMO-like equalizer achieves improved equalization performance in terms of normalized mean square error. From simulations on downlink communications of $2{\times}2$ MIMO systems in high speed packet access universal mobile telecommunications system standard, we show that the proposed method provides substantial performance gain over the conventional receiver algorithms.

• Journal of Communications and Networks
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• 제8권3호
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• pp.290-296
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• 2006

In this paper, a generalized blind adaptive algorithm is introduced for multi-user detection of direct sequence code division multiple access (OS-COMA) wireless communication systems. The main property of the proposed algorithm is its ability to resolve the multipath fading channel resulting in inter symbol interference (ISI) as well as multiple access interference (MAI). Other remarkable properties are its low complexity and mitigation to the near-far problem as well as its insensitivity to asynchronous transmission. The proposed system is based on the minimization of the output energy and convergence to the minimum mean square error (MMSE) detector. It is blind in the sense that it needs no knowledge of the other users' signatures, only the intended user signature and timing are required. Furthermore, the convergence of the minimum output energy (MOE) detector to the MMSE detector is analytically proven in case of M-ary PSK. Depicted results show that the performance of the generalized system dominates those previously considered. Further improvements are obtained when multiple input multiple output (MIMO) technique is employed.

• Journal of Communications and Networks
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• 제14권2호
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• pp.199-205
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• 2012

This work investigates the progressive linear precoder design for packet retransmissions in multi-input multi-output (MIMO) systems with multiple codewords and automatic repeat request (ARQ) bundling feedback. Assuming perfect channel state information, a novel progressive linear ARQ precoder is proposed in the perspective of minimizing the packet error rate. We devise the ARQ precoder by combining power loading and sub channel pairing between current retransmission and previous transmissions. Furthermore, we extend the design to the case that the channel estimation error exists. Numerical results show that the proposed scheme can improve the performance of MIMO ARQ systems significantly regardless of the channel estimation error.

• Journal of Communications and Networks
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• 제17권6호
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• pp.634-646
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• 2015

Assuming perfect channel state information (CSI) at the transmitter and receiver, the optimization problem of maximizing the minimum Euclidean distance between two received signals by a linear precoder is considered for multiple-input multiple-output (MIMO) systems with arbitrary dimensions and arbitraryary quadrature amplitude modulation (QAM) input. A general precoding framework is first presented based on the Gram matrix, which is shown for 2-dimensional (2-D) and 3-dimensional (3-D) MIMO systems when employing the ellipse expanding method (EEM). An extended precoder for high-dimensional MIMO system is proposed following the precoding framework, where the Gram matrix for high-dimensional precoding matrix can be generated through those chosen from 2-D and 3-D results in association with a permutation matrix. A complexity-reduced maximum likelihood detector is also obtained according to the special structure of the proposed precoder. The analytical and numerical results indicate that the proposed precoder outperforms the other precoding schemes in terms of both minimum distance and bit error rate (BER).

• Journal of Power Electronics
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• 제3권4호
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• pp.230-238
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• 2003

Electric vehicles (EV) demands for greater acceleration, performance and vehicle range in pure electric vehicles plus mandated requirements to further reduce emissions in hybrid electric vehicles (HEV) increase the appeal for combined on-board energy storage systems and generators. And the power electronics plays an important role in providing an interface between fuel cells (FC) and loads. This paper deals with a multiple input DC-DC power converter devoted to combine the power flowing of multi-source on energy systems. The multi-source is composed of (i) FC system as a prime power demands, (ii) super capacitor banks as energy storage devices for high and intense power demands, (iii) superconducting magnetic energy storage system (SMES), (iv) multiple input DC-DC power converter and (v) a three phase inverter-fed permanent magnet synchronous motor as a drive. In this system, It is used super capacitor banks and superconducting magnetic energy replaces from the battery system. The modeling and transient performance simulation is effective for reducing transient influence caused by sudden charge of effective load. The main purpose of power electronic converters is to convert the DC power output from the fuel cell and other to a suitable AC voltage, which can be connected to electric loads directly (PMSM). The fuel cell and other output is connected to the DC-DC converter, which regulates the DC link voltage.

• 한국통신학회논문지
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• 제40권11호
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• pp.2298-2304
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• 2015

본 논문은 다중 셀 다중입력 단일 출력 (MISO : multiple-input single-output) 하향링크 능동 안테나 시스템 (AAS : active antenna systems)에서 기지국의 수직 각도를 최적화하는 새로운 기법을 제시한다. 본 연구에서는 기존의 전역 탐색 방식 대신 간단하면서 최적의 값에 근사한 알고리듬들을 제안한다. 먼저, random matrix theory의 특성을 반영하여 평균 전송용량에 large system approximation이 적용된 수직적 빔포밍 알고리듬을 소개한다. 다음으로, signal-to-leakage-and-noise ratio (SLNR)을 기반으로 최적화 문제를 간단하게 만드는 수직적 빔포밍 알고리듬을 제안한다. 실험 결과를 통해 제안된 알고리듬들의 성능이 기존의 전역 탐색 알고리듬에 비해 복잡도가 매우 감소됨에도 불구하고 거의 비슷한 성능을 보임을 증명하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권7호
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• pp.2614-2632
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• 2015

A multiple symbol detection (MSD) algorithm is proposed relying on soft information for ultra-wideband systems, where differential space-time block code is employed. The proposed algorithm aims to calculate a posteriori probabilities (APP) of information symbols, where a forward and backward message passing mechanism is implemented based on the BCJR algorithm. Specifically, an MSD metric is analyzed and performed for serving the APP model. Furthermore, an autocorrelation sampling is employed to exploit signals dependencies among different symbols, where the observation window slides one symbol each time. With the aid of the bidirectional message passing mechanism and the proposed sampling approach, the proposed MSD algorithm achieves a better detection performance as compared with the existing MSD. In addition, when the proposed MSD is exploited in conjunction with channel decoding, an iterative soft-input soft-output MSD approach is obtained. Finally, simulations demonstrate that the proposed approaches improve detection performance significantly.

• Journal of Communications and Networks
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• 제9권4호
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• pp.473-481
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• 2007

Energy efficiency is one of the most critical concerns for wireless sensor networks. By allowing sensor nodes in close proximity to cooperate in transmission to form a virtual multiple-input multiple-output(MIMO) system, recent progress in wireless MIMO communications can be exploited to boost the system throughput, or equivalently reduce the energy consumption for the same throughput and BER target. However, these cooperative transmission strategies may incur additional energy cost and system overhead. In this paper, assuming that data collectors are equipped with antenna arrays and superior processing capability, energy efficiency of relevant traditional and cooperative transmission strategies: Single-input-multiple-output(SIMO), space-time block coding(STBC), and spatial multiplexing(SM) are studied. Analysis in the wideband regime reveals that, while receive diversity introduces significant improvement in both energy efficiency and spectral efficiency, further improvement due to the transmit diversity of STBC is limited, as opposed to the superiority of the SM scheme especially for non-trivial spectral efficiency. These observations are further confirmed in our analysis of more realistic systems with limited bandwidth, finite constellation sizes, and a target error rate. Based on this analysis, general guidelines are presented for optimal transmission strategy selection in system level and link level, aiming at minimum energy consumption while meeting different requirements. The proposed selection rules, especially those based on system-level metrics, are easy to implement for sensor applications. The framework provided here may also be readily extended to other scenarios or applications.

• 대한전자공학회논문지TC
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• 제48권6호
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• pp.6-13
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• 2011

시공간 부호화기법을 가진 MIMO(Multiple-input multiple-output)-OFDM(Orthogonal frequency division multiplexing)은 미래의 무선통신 시스템에서 성능향상을 위한 약속된 기술이다. 그러나 다중 송신기를 가진 다른 사용자에 따른 간섭과 다중경로의 지연신호에 따른 영향으로 성능이 크게 감소된다. 이 논문에서는 MIMO-OFDM 시스템에서 시공간 다이버스티를 유지하면서 이와 같은 간섭신호와 다중경로 지연신호를 효율적으로 제거하기 위하여 MMSE(minimizing the mean squared error) 기반의 pre-FFT 다중 빔형성기법을 제안한다. MIMO-OFDM 시스템에 제안된 다중 빔형성기법을 적용할 경우 성능 개선 효과를 CCI(Cochannel interference)를 가진 다중경로 채널환경에서 모의실험을 통하여 확인한다.