• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.6-12
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• 2009

In this paper, we propose the opportunistic channel state information feedback scheme for eigen based scheduling in multiuser MIMO systems. According to 3GPP SMC channel model, the system capacity of MU-MIMO systems is severly degraded, since the antennas are highly correlated in urban macro cell. Although the eigen based scheduling scheme mitigates the adverse effect of the antenna correlation, it achieves only small amount of the multiuser diversity gain. Since the opportunistic channel state information scheme can achieve sufficient multiuser diversity gain, the system capacity of MU-MIMO systems can be improved. The system capacity improvement is verified by the computer simulation results.

• Journal of Korea Game Society
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• v.7 no.2
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• pp.101-112
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• 2007

Along with the development of mobile technology, mobile game has undergone a change from downloadable game to network game, where a large number of users connect to server and play real-time game with a mobile phone. In order to develop these mobile network games economically, a proper, suitable game engine is needed. This study proposes the result of design and implementation of RWMMO-GE(Realtime Wireless Massively Multiplayer Online RPG Game Engine) that is used to develop a mobile network game. The structure of RWMMO-GE, which is the research result of this study, consists of major components such as Network/Client Module, Object Module, Map Tool, Script Editor, and Character Editor. The characteristics of the multiplayer mobile game developed by this engine is that a large number of players can play real-time game in a single map, which implies a possibility of a new business model in this area. This research is a result of the RWMMO-GE supported by 2006 IT Excellent Technology Support Project(No:A1300-0601-0125) of IITA(Institute Information Technology Advancement).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.188-195
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• 2002

In this paper, we consider efficient multiuser receiver structures using Hopfield neural network algorithm focused to construct a synchronous multi-rate code division multiple access (CDMA) system. Although the optimum receiver for multiuser detection can be realized attaining the best BER performance, it is too complex for practical implementation. Therefore, we propose near-optimal receivers of relatively low computationally complex multiuser detection structures for realizing multi-rate CDMA system and their performances are compared with conventional matched filter and other prominent multi-rate multiuser detectors, Computer simulations show that the Hopfield neural network based multiuser receiver achieves substantially better BER performance in Rayleigh fading environments.

• Information and Communications Magazine
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• v.25 no.5
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• pp.23-29
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• 2008

기지국이 셀 내에 있는 여러 사용자에게 신호를 전송하는 하향링크에서 셀 전체 채널 용량을 달성하기 위해서는 채널상태가 가장 좋은 사용자에게만 전송해야 한다. 무선 페이딩 채널에서 여러 사용자 중에 채널이 좋은 사용자를 선택하면, 다중 사용자 다이버시티 이득을 얻을 수 있다. 본 고에서는 이런 다중 사용자 다이버시티를 얻으면서도 사용자 간에 공평하게 자원을 할당하는 여러 방식에 대해서 알아본다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.1
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• pp.77-82
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• 2015

Recently, multi-user massive MIMO (MU-Massive MIMO) network has attracted a lot of attention as a technology to accommodate explosively increasing mobile data traffic. However, the MU-Massive MIMO network causes a tremendous hardware complexity in a base station and computational complexity to select optimal set of users. In this paper, we thus propose a simple algorithm for selecting antennas and users while reducing the hardware and computational complexities simultaneously. The proposed scheme has a computational complexity of $O((N-S_a+1){\times}min(S_a,K))$, which is significantly reduced compared to the complexity of optimal scheme based on Brute-Force searching, $$O\left({_N}C_S_a\sum_{i=1}^{min(S_a,K)}_KC_i\right)$$, where N, $S_a$, and K denote the number of total transmit antennas, the number of selected antennas, and the number of all users, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.11
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• pp.1-7
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• 2004

We propose multistage parallel nulling (MPN) partial parallel interference cancellation (PPIC) receiver for downlink multiple-input multiple-output (MIMO) multicarrier (MC)-code division multiple access (CDMA) systems. Though the V-BLAST is a popular MIMO receiver, it shows error floor for multiuser downlink MIMO MC-CDMA systems. The proposed MPN-PPIC receiver does not produce error floor for multiuser case, and achieves substantial performance gains with multistage processing. For single user case, the proposed method also surpasses the V-BLAST receiver with multistage processing for MIMO MC-CDMA systems with chip level interleaving. The system performance of the proposed MPN-PPIC receiver is evaluated through computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.286-295
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• 2008

In this paper, we consider the use of orthogonal multiple beams (OMBs) to simultaneously achieve multi-user diversity and multiplexing gain in a packet-based wireless system. Previous OMB scheme considers the use of a fixed number of multiple beams equal to the number of transmit antennas. However, unless the number of active users is sufficiently large, the use of a fixed number of multiple beams may not provide desired performance due to the interference signal transmitted through other beams, being even worse than the use of a single beam. To alleviate this problem, we consider the adjustment of the number of beams in use to maximize the spectral efficiency according to the operating condition. Simulation results show the validity of the proposed scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1A
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• pp.64-72
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• 2012

We consider multiuser multiple antenna two-way relaying systems in which all users exchange their data with their counterparts with the help of a relay. The systems complete all data exchanges in two time phases called multiple access phase and broadcasting phase for spectral efficiency and therby require an effective scheme reducing self-interference (SI) and multiuser interference (MUI). Different from the conventional scheme suppressing both SI and MUI at the relay, the proposed scheme adopts SI cancelation (SIC) at the users and renders the relay to suppress the MUI mainly considering the SIC output. We analyze the symbol error rate (SER) and the achievable diversity order of the proposed scheme when the multiple access phase is dominant in the performance and obtain simulation results on the SER and the sum rate under various conditions. The results show that the proposed scheme improves the symbol error rate and the sum rate remarkably at the cost of complexity increase.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 1997.11a
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• pp.123-128
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• 1997

가상현실(Virtual Reality)의 응용분야는 지금까지의 연구성과로 인하여 연구와 활용분야가 다양해지고 있을 뿐만 아니라 지금도 많은 연구가 활발히 진행 중에 있다. 그러나 통신의 발달로 인해 네트워크 사용이 생활화됨으로써 더이상 VRML(Virtual Reality Modeling Language) 이 Netscape Navigator Microsoft Internet Explorer같은 웹 브라우져상에서 단순한 3차원 오브젝트만을 보여주는 시기는 지났다. 사용자들은 3차원 오브젝트를 사용해서 공간적, 지역적으로 멀리 떨어져있는 상대방과의 실시간 대화는 물론 상대방의 행위를 보고 그에 대한 자신의 행위를 보여중으로써 현실감을 느끼고 싶어한다. 더욱이 가까운 미래에 수많은 사용자들은 3D를 기반으로 자신을 분신인 아바타를 사용하여 하나의 가상세계를 공유하고 가상 이벤트를 사용하여 하나의 가상세계를 공유하고 가상 이벤트에 참석을 하게 될 것이다. 이러한 종류의 어플리케이션을 제공하기 위해서는 3D그래픽스처리와 사용자 인터페이스 및 네트워크 환경을 제공해야만 한다. 이에 본 논문에서는 기존의 다중사용자용 VRML브라우저중의 하나인 OZ Virtual의 여러가지 비능에 대해서 살펴보고, VRML이 어떻게 대화식, 분산, 다중사용자 가상 세계에 적합하게 확장될 수 있는지를 두중사용자용 VRML시스템의 구조를 통해서 증명해 본다.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.94-96
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• 2003

맡은 사용자 영역의 프로그램들이 확장성과 성능 향상을 목적으로 다중 프로세스 모델에서 다중 스레드 모델로 바뀌고 있다. 웹 서버도 폭발적으로 증가하는 사용자 요청을 수용할 수 있도록 확장성과 성능 향상을 위해서 다중 스레드 모델을 적용하였다. 본 논문에서는 다중 프로세스 모델을 적용한 웹 서버와 다중 프로세스/다중 스레드 모델을 적용한 웹 서버에 대한 성능을 여러 운영체제 환경에서 평가하였다. 실험 결과 전체적으로 다중 프로세스 모델이 다중 스레드 모델보다 더 좋은 성능과 안정성을 보였다.