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Orthogonalized Spatial Multiplexing for Rank-3 Transmission in Closed-Loop MIMO Systems
송창익,이인규 에스케이텔레콤 (주) 2011 Telecommunications Review Vol.21 No.4
Orthogonalized Spatial Multiplexing (OSM) scheme for Multiple-Input Multiple-Output (MIMO) channels has been originally developed for transmitting two data streams, which allows simple maximum ikelihood decoding at the receiver with small feedback information. In this paper, by extending the existing OSM scheme, we propose a new Spatial Multiplexing (SM) system which supports a larger number of data streams. To this end, we adopt three successive rotation precoding with four phase angles, so that we can decompose the MIMO channel into two identical subchannels. Moreover, it is shown that we can further improve the performance by applying multidimensional constellation rotation. Through the numerical results, we show that the proposed scheme outperforms the Singular Value Decomposition (SVD) based scheme while the computational complexity and the feedback overhead are reduced.
송창익,이경재 한국통신학회 2022 ICT Express Vol.8 No.4
In this paper, we investigate a regularized artificial fast fading (AFF) design for multi-user multi-input multi-output (MIMO) wiretap channels. To solve the effective channel gain reduction issue in conventional zero-forcing (ZF) based approaches, we propose a regularized AFF beamforming method by applying the minimum mean squared error (MMSE) problem and Lagrangian dual analysis. Finally, simulation results show that the proposed MMSE based AFF scheme improves the error performance of the legitimate user compared to the conventional ZF AFF method while achieving the same low probability of interception at the eavesdropper for multi-user MIMO secure transmission systems.
Beyond 4G 시스템을 위한 다중안테나 무선 릴레이 시스템의 기술 동향 및 전망
송창익,이인규 한국통신학회 2012 정보와 통신 Vol.29 No.8
스마트폰의 대중화에 따라 요구되는 데이터 전송 속도와 품질이 증가하면서 4세대 이후의 차세대 통신 (Beyond 4G) 시스템은 기존의 셀 기반의 통신 방식에서 벗어나 협력통신이라는 새로운 패러다임으로의 전환을 요구받고 있다. 본고에서는 협력 통신 기법들 중에서 차세대 통신의 핵심 기술로써 주목받고 있는 무선 릴레이 시스템에 대하여 소개하고 현재까지의 학계와 산업계의 기술동향과 앞으로의 전망을 알아본다.
정규화된 결합 공간 분할 다중화 기법의 제한된 피드백 환경에서 성능 분석
송창익(Changick Song) 한국전기전자학회 2021 전기전자학회논문지 Vol.25 No.3
5G통신의 핵심 기술인 거대다중안테나 시스템은 송신단에서 많은 양의 채널정보가 필요하기 때문에 제한된 채널 피드백을 사용하는 주파수 분할 이중 시스템에서 구현이 어려운 문제점이 있었다. 이러한 문제점을 해결하기 위해 장시간 변하지 않는 채널 상관도 정보를 이용하여 단말 그룹 간 간섭을 제거함으로써 채널정보 요구량을 비약적으로 감소시키는 Joint Spatial Division and Multiplexing(JSDM)기법이 제안되었고, 최근에는 그룹 간 잔여 간섭을 허용함으로써 성능을 더욱 향상시키는 정규화된 JSDM기법이 제안된 바 있다. 하지만 기존 JSDM관련 연구들은 주로 그룹 간 간섭제거에 초점을 두고 설계되었기 때문에, 그룹 내 간섭 제거 단계에서 제한적인 피드백을 가정한 보다 실제적인 환경에서 성능분석이 이루어지지 못하였다. 본 논문에서는 JSDM기법과 정규화된 JSDM기법을 제한된 피드백 환경에서 그룹 수와 그룹 내 사용자 수에 따른 성능을 분석하고 시뮬레이션 결과를 통해 정규화된 JSDM기법이 제한된 피드백 환경에서 기존 JSDM대비 더욱 두드러지는 이득을 보임을 입증한다. The massive MIMO system, which is a core technology of 5G communication systems, has a problem that it is difficult to implement in a frequency division duplex system based on limited channel feedback because a large amount of channel information is required at the transmitting end. In order to solve this problem, the Joint Spatial Division and Multiplexing (JSDM) technique that dramatically reduces the channel information requirement by removing interference between the user groups using channel correlation information that does not change for a long time has been proposed. Recently, a regularized JSDM technique has been proposed to further improve performance by allowing residual interference between the user groups. However, such JSDM-related studies were mainly designed to focus on inter-group interference cancellation, and thus performance analysis was not performed in a more realistic environment assuming limited feedback in the intra-group interference cancellation phase. In this paper, we analyze the performance of the JSDM and regularized JSDM techniques according to the number of groups and users in a limited feedback environment, and through the simulation results, demonstrate that the regularized JSDM technique shows a more remarkable advantage compared to the existing JSDM in a limited feedback environments.
송창익(Song, Chang-Ik) 한국체육과학회 2017 한국체육과학회지 Vol.26 No.3
This research aimed to examine the effects of western grip and semi-western grip on muscle coordination change among the members of the Korean tennis national team. Conclusions are as follows. First, there were differences in muscle coordination sequences between western grip and semi-western grip across P1, P2, and P3 periods. For the P1 period, the same muscle manifestation sequence was observed with right-sided latissimus dorsi muscle. For the P2 period, the same muscle manifestation sequence was observed with backbone erector. For the P3 period, however, the same muscle manifestation sequence was not observed. Second, although changing from western grip to semi-western grip for forehand strokes resulted in different muscle manifestation sequences, it did not affect motor actions because of balances among agonistic muscle, antagonist muscle, and synergic muscle when doing a same action. In conclusion, this research shows that it is not easy to obtain deep understanding about muscle coordination and generalize the results. But an important point is that this research provides basic data for clarifying the coordination relationship between agonistic muscle and antagonist muscle. Based on this set of data, it is hoped that future research can examine what happens before and after athletes’ injuries more in depth.