• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.9
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• pp.566-568
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• 2014

In this letter, an MMSE based iterative soft decision interference cancellation scheme for massive MIMO systems is proposed. To reduce the complexity, the proposed scheme uses the Sherman-Morrison-Woodbury formula to compute the entire MMSE filtering vectors in one iteration by one matrix inverse operation. Simulation results show that the proposed scheme also has a comparable BER to the conventional scheme for massive MIMO systems.

• The Journal of the Acoustical Society of Korea
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• v.40 no.5
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• pp.417-427
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• 2021

Long-range communication in deep waters must overcome the low data rate due to limited bandwidth. This paper presents the performance of Multiple-Input-Multiple-Output (MIMO) system to increase the data rate. In MIMO system, communication performance is degraded by crosstalk between users and an adaptive passive Time Reversal Processing (TRP) is widely used to eliminate this. In October 2018, long-range underwater acoustic communication experiment was conducted in deep water (1,000 m ~) off the east of Pohang, South Korea. During the experiment, a vertical line array was utilized and communication signals modulated by binary phase shift keying and quadrature phase shift keying with a symbol rate of 512 sps were transmitted. To generate MIMO communication signals, received signals from ranges of 26 km and 30 km is synthesized. Compared to the conventional passive TRP, the adaptive passive TRP eliminates the crosstalk between users and achieves error-free performance with an increase of output signal-to-noise ratio. Therefore, two users separated by 4 km in range achieves an aggregate data rate of 1,024 symbols/s.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.4
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• pp.17-25
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• 2013

In this paper, a coding algorithm is proposed for multi-user multi-input multi-output (MU-MIMO) systems to improve the reception performance in fading conditions without reducing the bandwidth efficiency. The space division multiple access (SDMA) scheme that is one of the commonly used for MU-MIMO systems is vulnerable to the fading. The space time block code (STBC) scheme that is used to overcome the fading has a disadvantage of reduced throughput. The proposed MU-MIMO system first encodes transmitted symbols by linear dispersion code (LDC) which is less vulnerable to the fading and increases the throughput in proportional to the number of transmit antennas. Then, the LDC coded symbols are pre-coded by the result of singular value decomposition (SVD) of the estimated channel gain. We evaluate the performance of the proposed scheme compared with the conventional algorithms by computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.8
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• pp.896-902
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• 2016

In this paper, we investigate a minimum mean-squared error based nonlinear successive precoding method as a practical solution of dirty paper coding for multiuser downlink channels where each user has more than one antenna in the presence of other cell interference (OCI). Unlike conventional zero-forcing (ZF) based methods, the proposed scheme takes the OCI plus noise into account when suppressing the inter-cell multiuser interference, which results in improvement of the received signal-to-interference-plus-noise ratio. Simulation results show that the proposed scheme outperforms conventional methods in terms of sum rate for various OCI configurations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.6
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• pp.635-641
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• 2010

Time-varying channel characteristics in OFDM systems over doubly selective channels cause inter-carrier interferences(ICI) in the frequency domain. Time domain windowing gives rise to restriction on the bandwidth of the frequency domain channel matrix and makes it possible to approximate the OFDM system as a simplified linear input-output model. When successive interference cancellation based on linear MMSE estimation is employed for channel equalization in OFDM systems, symbol detection ordering produces considerable effects on overall system performances. In this paper, we show the reduction of the residual ICI by time domain windowing and the resultant performance improvements, and investigate the effects of SINR- and CSEP-based symbol detection ordering on the performance of successive interference cancellation.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.3
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• pp.58-69
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• 2003

위성 통신의 수요가 증가하고 있고, 무궁화 위성 등 우리 위성이 발사되면서 위성 탑재체의 국내 개발이 꾸준히 진행되고 있다. 위성 탑재체의 채널 성능은 채널 필터와 입출력 멀티플렉서의 주파수 특성에 의해 크게 좌우된다. 이 글에서는 채널 필터와 멀티플렉서의 구성과 설계에서의 고려 사항에 대해 검토하겠다. 채널 필터를 포함하는 멀티플렉서는 전기적 설계뿐만 아니라 기계적, 열적 설계에서도 까다로운 사양을 요구하고 있다. 채널필터는 소형 경량화의 요구에 따라 주로 이중 모드(dual mode) 필터로 설계되고 있고, 최근에는 HTS 필터에 의한 설계도 시도되고 있다. 입력 멀티플렉서는 채널 사이의 간섭을 방지하기 위해 써큘레이터를 이용하여 구성하고, 출력 멀티플렉서는 손실을 최소화하기 위하여 매니폴드(manifold)를 이용하여 채널필터를 결합한다. 이 글은 Kunes와 Kudsia의 논문을 주로 참조하였다.

• Proceedings of the KIEE Conference
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• 2002.07d
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• pp.2188-2191
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• 2002

MIMO 비최소위상 시스템에 대한 입출력 선형화 제어에 대해서 새로운 접근 방식을 제안한다. 처음에 몇가지 조건 하에서 비선형 궤환과 상태 변환을 하고 또한 magnitude & time scaling을 해서 일반적인 비선형 시스템을 특이 섭동 시스템으로 변환할 수 있다는 것을 보였다. 특히 제안된 방법에 의하여 변환된 특이 섭동 시스템에서 숨겨진 동적 특성이 fast subsystem의 역할을 하게 된다. 그 다음에는 잘 알려진 composite control 기법을 적용하여 시스템이 거의 선형적이고 비간섭적인 I/O 동적 특성을 갖게 하고 내부 상태가 안정화되도록 한다. 기존의 방식 보다 제안된 제어 방법의 가장 큰 이점은 적용될 수 있는 비최소위상 시스템의 범위를 보다 넓히게 되었다는 것이다. 게다가 특이 섭동 방법은 제어기 설계 과정을 단순화시켜 제어기 구현에 있어서 계산 시간을 단축시킨다.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.1
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• pp.75-84
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• 2017

It becomes more and more more important for the storage that supports high speed recording and stable access from network environment. As one field of basic science which produces massive astronomical data, VLBI(: Very Long Baseline Interferometer) is now demanding more data writing performance and which is directly related to astronomical observation with high resolution and sensitivity. But most of existing storage are cloud model based for the high throughput of general IT, finance, and administrative service, and therefore it not the best choice for recording of big stream data. Therefore, in this study, we design storage system optimized for high performance of I/O and concurrency. To solve this problem, we implement packet read and writing module through the use of libpcap and pf_ring API on the multi core CPU environment, and build a scalable storage based on software RAID(: Redundant Array of Inexpensive Disks) for the efficient process of incoming data from external network.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.4 no.3
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• pp.189-196
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• 2011

In this paper, we analyze the error performance of SIC-based signal detection methods in MIMO systems. Considered detection methods are SIC signal detection and LR-SIC signal detection. We derive BLER performance of the methods and the performance is confirmed by computer simulations.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.1976-1981
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• 2013

In this paper, we propose a frequency-domain interference cancellation algorithm for direct-sequence spread spectrum systems. In the previously proposed frequency-domain interference cancellation algorithms that protocol defines the rules concerning the collection of means of Transmission Control Protocol (TCP: Transmission Control Protocol) is the most widely used in the transport layer. Two-way traffic through the network path to the same end-to-end transfer of data in the opposite direction between pairs of nodes are infused with two or more TCP connection using the network traffic patterns from the exchanger and routers share results of approval. Per-flow input/output structure of matter using the LTS online reaction when evaluated as this is the most important factor. TCP-MT when the connection duration is one of the largest performance gains.