• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.2
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• pp.27-34
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• 2013

We propose a simple power allocation scheme for an amplify-and-forward multiple relay system with multiple-input multiple-output antennas. Unlike the existing relay precoding matrix with full elements, proposed precoder is a diagonal matrix whose diagonal element is the relay gain for each stream. Furthermore, a weight vector is applied to streams, such that the mutual information of the system approaches that of the exhaustive search scheme, regardless of the number of antennas. Numerical results show that proposed scheme outperforms the conventional schemes with respect to mutual information.

• Journal of Korea Society of Industrial Information Systems
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• v.11 no.3
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• pp.69-81
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• 2006

In this paper, an adaptive algorithm is proposed in streaming MPEG-4 contents with fluctuating resource amount such as throughput of network conditions. In the area of adaptive streaming issue, a lot of researches have been made on how to represent encoded media(such as video) bitstream in scalable way. By contrast, MPEG-4 supports object-based multimedia content which is composed of various types of media streams such as audio, video, image and other graphical elements. Thus, it can be more effective to provide individual media streams in scalable way for streaming object-based content to heterogeneous environment. The proposed method provides the multiple media streams corresponding to an object with different qualities and bit rate in order to support object based scalability to the MPEG-4 content. In addition, an optimal selection of the multiple streams for each object to meet a given constraint is proposed. The selection process is adopted a multiple choice knapsack problem with multi-step selection for the MPEG-4 objects with different scalability levels. The proposed algorithm enforces the optimal selection process to maintain the perceptual qualities of more important objects at the best effort. The experimental results show that the set of selected media stream for presenting objects meets a current transmission condition with more high perceptual quality.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.1
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• pp.280-294
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• 2023

Unmanned aerial vehicles (UAVs) and millimeter-wave frequencies play key roles in supporting 5G wireless communication systems. They expand the field of wireless communication by increasing the data capacities of communication systems and supporting high data rates. However, short wavelengths, owing to the high millimeter-wave frequencies can cause problems, such as signal attenuation and path loss. To address these limitations, research on high directional beamforming technologies continue to garner interest. Furthermore, owing to the mobility of the UAVs, it is essential to track the beam angle accurately to obtain full beamforming gain. This study presents a beam tracking method based on the unscented Kalman filter using hybrid beamforming. The simulation results reveal that the proposed beam tracking scheme improves the overall performance in terms of the mean-squared error and spectral efficiency. In addition, by expanding analog beamforming to hybrid beamforming, the proposed algorithm can be used even in multi-user and multi-stream environments to increase data capacity, thereby increasing utilization in new-radio multiple-input multiple-output orthogonal frequency-division multiplexing systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.6
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• pp.444-451
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• 2017

In this paper, we have evaluated and analyzed OTFS(Orthogonal Time Frequency Space) modulation and OTFS-MIMO(Multiple Input Multiple Output) system. OTFS modulation can concisely compensate delay-Doppler spreading effect by using 2D(2-Dimension) iDFT (inverse Discrete Fourier Transform) and DFT(Discrete Fourier Transform) operation. It enables OTFS system to transmit high-speed data. Especially, OTFS-MIMO system can transmit all data streams without performance degradation on high Doppler frequency channel. As simulation results, we have confirmed that $1{\times}1$ OTFS system's achievable rate is a similar to each stream of $2{\times}2$ OTFS-MIMO system. That is, we have also confirmed that $2{\times}2$ MIMO system can completely achieve double achievable rate in comparison with OTFS system on high Doppler frequency channel.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.178-180
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• 2004

인터넷에서 전 세계에 분포되어 있는 수많은 노드로 파일을 전송하는 경우 어떻게 하면 빨리, 효율적으로 전송할 것인가가 큰 문제가 된다. 전송을 순차적으로 할 경우, 수행시간이 길어지고 되고, parallel stream으로 전송하여 수행시간을 줄인 경우에도 송신자 링크의 병목현상이라는 문제가 발생한다. 본 연구에서는 토폴로지 정보를 이용하여 지역적으로 가까운 노드들은 그룹으로 만들고, 각 그룹 간의 한 번의 전송을 통해, 전송 시간을 줄이고, 송신자 링크의 병목 현상을 해결하기 위한 방법을 제안한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.5
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• pp.531-538
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• 2016

In this paper, we have proposed MIMO-IBFD system that can transmit and receive multiple data stream at the same time in the single band, and analyze the system. We have confirmed that MIMO-IBFD system requires multiple RF cancellation and multiple Digital cancellation techniques. In simulation, we have analyzed characteristic of received signal on MIMO-IBFD system, and evaluate system performance of conventional $2{\times}2$ MIMO system and MIMO-IBFD system. As simulation results, we have confirmed that MIMO-IBFD system can transmit and receive multiple data stream at the same time in the single band by using multiple RF and digital cancellation techniques. Additionally, we have confirmed that BER performance of $2{\times}2$ MIMO-IBFD system with low-level QAM modulation is similar to performance of $2{\times}2$ MIMO system, and BER performance of $2{\times}2$ MIMO-IBFD system with high-level QAM modulation is degraded in comparison with $2{\times}2$ MIMO system with high-level QAM modulation. We can confirm that MIMO-IBFD system requires high level self-interference cancellation technique in order to use high level modulation.

• Journal of KIISE:Databases
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• v.35 no.6
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• pp.459-468
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• 2008

A data stream which is a massive unbounded sequence of data elements continuously generated at a rapid rate. Many recent research activities for emerging applications often need to deal with the data stream. Such applications can be web click monitoring, sensor data processing, network traffic analysis. telephone records and multi-media data. For this. data processing over a data stream are not performed on the stored data but performed the newly updated data with pre-registered queries, and then return a result immediately or periodically. Recently, many studies are focused on dealing with a data stream more than a stored data set. Especially. there are many researches to optimize continuous queries in order to perform them efficiently. This paper proposes a query optimization algorithm to manage continuous query which has multiple join operators(Multi-way join) over data streams. It is called by an Extended Greedy query optimization based on a greedy algorithm. It defines a join cost by a required operation to compute a join and an operation to process a result and then stores all information for computing join cost and join cost in the statistics catalog. To overcome a weak point of greedy algorithm which has poor performance, the algorithm selects the set of operators with a small lay, instead of operator with the smallest cost. The set is influenced the accuracy and execution time of the algorithm and can be controlled adaptively by two user-defined values. Experiment results illustrate the performance of the EGA algorithm in various stream environments.

• ETRI Journal
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• v.27 no.3
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• pp.326-329
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• 2005

The MPEG-4 multiple auxiliary component (MAC) is a good mechanism to achieve one-stream stereoscopic video coding. However, there is no syntax or semantics for the residual texture data of the disparity-compensated image in the current MAC. Therefore, we propose a novel disparity-compensated coding method using the MAC for stereoscopic video. We also define a novel MAC semantics in MPEG-4 so as to support the proposed coding algorithm. The major difference between the existing and proposed coding methods using the MAC is the addition of the residual texture coding.

• ETRI Journal
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• v.29 no.2
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• pp.240-242
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• 2007

This letter proposes a simplified maximum likelihood detection (SMLD) scheme to improve the detection performance of multiple-input multiple-output receivers. The SMLD detects V streams according to the first detected V sub-streams. Through an ML test, the most probable stream is selected. Moreover, to detect the layer with the worst post-detection SNR accurately, reverse ordering is applied to the SMLD. Simulation results show that the performance of the Vertical Bell Laboratories layered space-time (V-BLAST) system can be improved by adopting the SMLD technique. In the case of reverse ordering, the SMLD can achieve a similar ML performance with significant reduction in computational complexity.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2017.06a
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• pp.49-51
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• 2017

본 논문에서는 ATSC 3.0 시스템의 2x2 MIMO (multiple input multiple output) 방식을 적용한 송수신기 구조에 대해서 살펴본다. ATSC 3.0 시스템의 MIMO 에서 적용된 프리코더 (precoder)는 스트림 결합기(stream combining), IQ 편파 인터리빙 (I/Q polarization interleaving), 위상 홉핑부 (phase hopping)로 구성된다. 또한, ATSC 3.0 의 2x2 MIMO 방식을 사용함으로써 공간 다중화 (spatial multiplexing) 이득과 공간 다이버시티 (spatial diversity) 이득을 얻을 수 있다.