• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.46-49
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• 2007

Multiple Antenna Technologies such as Multiple-Input Multiple-Output (MIMO) and Beamforming provide the increase of channel capacity and the reliability of wireless link. To obtain these advantages, WiBro, Mobile WiMAX and $4^{th}$ Generation System are employing multiple antenna technologies. There exist, however, many technical issues in considering the application of the technologies or the providing of services using them. In this paper, various technical topics are discussed and simple solutions are proposed. Beamforming has several technical issues which include coverage imbalance, difficulties in providing Multicast-Broadcast Service (MBS). In Addition, network planning is a critical point from a cell extension and initial network entry point of view. In case of MIMO, network deployment is discussed in that cellular data network such as WiBro has many repeaters. MIMO mode selection for maximizing the cell capacity is also covered.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.12
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• pp.2331-2342
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• 2015

In this paper, we design non-linear transmitter and receiver using a uniform channel decomposition (UCD) to take account of inter-cell interference in multi-cell downlink systems. The designed UCD scheme brings forth the same SINR for all sub-channels in each cell. It provides great convenience to modulation/coding process and achieves the maximum diversity gain. The simulation results confirm that it exhibits a lower BER than the conventional method.

• ETRI Journal
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• v.31 no.5
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• pp.481-488
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• 2009

This paper proposes a new multiuser scheduling algorithm that can simultaneously support a variety of different quality-of-service (QoS) user groups while satisfying fairness among users in the same QoS group in MIMO broadcast channels. Toward this goal, the proposed algorithm consists of two parts: a QoS-aware fair (QF) scheduling within a QoS group and an antenna trade-off scheme between different QoS groups. The proposed QF scheduling algorithm finds a user set from a certain QoS group which can satisfy the fairness among users in terms of throughput or delay. The antenna trade-off scheme can minimize the QoS violations of a higher priority user group by trading off the number of transmit antennas allocated to different QoS groups. Numerical results demonstrate that the proposed QF scheduling method satisfies different types of fairness among users and can adjust the degree of fairness among them. The antenna trade-off scheme combined with QF scheduling can improve the probability of QoS-guaranteed transmission when supporting different QoS groups.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.186-193
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• 2008

A two-hop multiple-input multiple-output (MIMO) relay network which comprises a multiple antenna source, an amplify-and-forward MIMO relay and many potential users are studied in this paper. Consider the achievable sum rate as the performance metric, a joint design method for the processing units of the BS and relay node is proposed. The optimal structures are given, which decompose the multiuser MIMO relay channel into several parallel single-input single-output relay channels. With these structures, the signal-to-noise ratio at the destination users is derived; and the power allocation is proved to be a convex problem. We also show that high sum rate can be achieved by pairing each link according to its magnitude. The sum rate of three broadcast strategies, time division multiple access (TDMA) to the strongest user, dirty paper coding (DPC), and beamforming (BF) are investigated. The sum rate bounds of these strategies and the sum capacity (achieved by DPC) gain over TDMA and BF are given. With these results, it can be easily obtained that how far away TDMA and BF are from being optimal in terms of the achievable sum rate.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2015.07a
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• pp.17-18
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• 2015

다중 안테나(MIMO, multi-input multi-output) 기법은 채널 용량을 증가시키기 위한 기술로써 최근 많이 연구되어 지고 있으며, DVB-T2, LTE 기술 및 802.11ac 등 방송, 이동통신 및 Wi-Fi 등 여러 분야에서 다양하게 쓰이고 있다. 그러나 다중 안테나 전송 기법은 송 수신 안테나 개수에 비례하여 채널 용량이 증가되므로, 채널 용량을 중가시키기 위해서는 많은 송 수신 안테나가 필요하다는 단점을 가지고 있다. 최근 다중 안테나 전송 기술과는 다른 방법으로 전송량을 증가시키는 기술인 FTN(faster than Nyquist) 전송 기법이 연구되고 있다. FTN 전송 기법은 동일한 대역폭에서 비트 오류 없이 정보를 전송할 수 있는 나이퀴스트(Nyquist) 심벌율보다 빠르게 심벌을 전송하는 기법으로 이론적으로 최대 20%까지 채널 용량을 증가시킬 수 있다. 그러므로 본 논문에서는 채널 용량을 증가시키기 위하여 다중 안테나 기법과 FTN 송신 기법을 연동하여 기존 다중 안테나 전송 기법의 단점을 보완하는 MIMO-FTN 전송 기법의 성능을 분석한다.

• Journal of Communications and Networks
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• v.18 no.6
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• pp.892-901
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• 2016

In the multi-user multiple-input multiple-output (MIMO) system, orthogonal random beamforming (ORBF) scheme is proposed to serve multiple users simultaneously in order to achieve the multi-user diversity gain. The opportunistic space-division multiple access system (OSDMA-S) scheme performs multiple weighting matrices during the training phase and chooses the best weighting matrix to be used to broadcast data during the transmitting phase. The OSDMA-S scheme works better than the original ORBF by decreasing the inter-user interference during the transmitting phase. To save more time in the training phase, a partly random multiple weighting matrices selection scheme is proposed in this paper. In our proposed scheme, the Base Station does not need to use several unitary matrices to broadcast pilot symbol. Actually, only one broadcasting operation is needed. Each subscriber generates several virtual equivalent channels with a set of pre-saved unitary matrices and the channel status information gained from the broadcasting operation. The signal-to-interference and noise ratio (SINR) of each beam in each virtual equivalent channel is calculated and fed back to the base station for the weighting matrix selection and multi-user scheduling. According to the theoretical analysis, the proposed scheme relatively expands the transmitting phase and reduces the interactive complexity between the Base Station and subscribers. The asymptotic analysis and the simulation results show that the proposed scheme improves the throughput performance of the multi-user MIMO system.

• Journal of Broadcast Engineering
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• v.20 no.1
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• pp.3-15
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• 2015

Recently terrestrial digital broadcasting systems have experienced a growth with the demand of high data rate. In order to meet such demand, the MIMO technology has received a wide attention. This paper proposes a pre-coding method, which provides high space channel correlation for the improved performance over terrestrial broadcasting channels when the polarized $2{\times}2$ MIMO SM is adopted for DVB-NGH systems. When signals with two different modulation orders are transmitted through two antennas, a method that is based on non-uniform power is also proposed for improved reception performance. To optimize the proposed method, phase shifting values for the pre-coding method and appropriate unequal power ratio are obtained. These obtained parameters are applied to a terrestrial broadcasting system, and then the performance improvement over the conventional SM is shown through computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1C
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• pp.79-85
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• 2008

Dirty Paper Coding(DPC) can achieve the sum capacity of a multiuser multiple-input multiple-output(MU MIMO) broadcast channels. However, due to the high computational complexity of the successive encoding and decoding, deploying DPC in real systems is impractical. As one of practical alternatives to DPC, Block Diagonalization(BD) was researched. BD is an extension of the zero-forcing preceding technique that eliminates interuser interference(IUI) in downlink MIMO systems. Though BD has lower complexity than DPC, BD shows poor sum capacity performance. We show that sum capacity performance of BD is degraded due to no IUI constraint. Then, we modify BD to improve its sum capacity performance with relaxing the constraint and sub optimal channel set searching. With simulation results, it can be verified that our modification in BD induces some improvement in sum capacity performance.

• Journal of Broadcast Engineering
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• v.28 no.1
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• pp.141-144
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• 2023

Recently, a joint channel estimation, channel quantization, feedback, and precoding system based on deep-neural network (DNN) was proposed. The corresponding system achieved a joint optimization based on deep learning such that it achieved a higher sum rate than the existing codebook-based precoding systems. However, this DNN-based procoding system is not directly applicable for the environments with many users such that a specific user selection can potentially increase the sum rate of the system. Thus, in this letter, we study an appropriate user selection method suitable for DNN-based precoding.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.11a
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• pp.318-320
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• 2011

본 논문은 다중경로 페이딩 채널에서 폐루프 MIMO-OFDM 시스템을 구현할 때 효율적인 피드백 정보를 제공하기 위한 채널 품질 지시자(Channel Quality Indicator, CQI)를 결정하는 방법에 관한 것이다. 다중경로 페이딩에서 OFDM심볼의 부반송파들이 주파수영역에서 서로 다른 채널이득을 경험할 수 있고 여러 채널행렬 중에서 어느 채널행렬에 기반해서 채널 상태를 반영하는 채널대표값을 계산해야 하는지 분명하지 않다. 따라서 수신측에서 송신측으로 피드백하기 위해서 하나의 CQI정보를 생성하는데 필요한 채널 대표값이 필요하다. 채널 대표값을 구할 때 쉽게 생각 할 수 있는 방법인 기준신호의 평균 채널행렬을 이용하는 경우에는 채널상태를 정확히 반영하지 못하고 기준신호의 MMSE검출 후 SNR을 검출하는 방식은 채널상태를 정확히 반영해서 성능을 향상시키지만 많은 연산량을 필요로 한다. 이러한 문제를 해결하기 위해 허미시안 연산된 값을 채널 행렬 평균화해서 채널상태를 정확하게 반영하고 연산량을 줄이는 것에 중점을 두고 있다.