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Woohyun Seo,Hyungjoon Song,Jemin Lee,Daesik Hong IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.1
<P>This letter presents our study of throughput enhancement achieved by multiuser diversity (MUDiv) in a multiuser system using a new asymptotic approach. The MUDiv gain is evaluated by deriving a new asymptotic formula with a closed form, which is flexible to the number of MUDiv orders. To do this, we simplify a Puiseux series instead of a extreme value theory used in the previous researches. The formula shows that the MUDiv gain is independent of the signal-to-noise ratio, and it is applied to analyze proportional fair scheduling. Finally, this analysis is verified using Monte-Carlo simulations of scheduling algorithms.</P>
A New Full-band Feedback Scheme Using the Adaptive Grouping Method in OFDMA Systems
Woohyun Seo,Myeon-gyun Cho,Yu, T.,Daesik Hong IEEE 2008 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.7 No.6
<P>Opportunistic scheduling algorithms with link adaptation can increase system throughput, but have the drawback of requiring the channel quality information (CQI) to be transmitted from all the candidate users. In order to alleviate this problem, we propose a new feedback reduction scheme that preserves CQIs over all channels. The proposed scheme binds similar CQIs in groups to represent them more effectively, and uses a simple method for fast grouping. Simulation results show that the proposed scheme with this simple grouping achieves close to perfect feedback performance with respect to the original CQIs under reasonable feedback loads.</P>
사용자 제한을 이용한 양자화된 채널 상태 정보를 갖는 공간 분할 다중 접속 방식의 되먹임 감소 기법
서우현(Woohyun Seo),박성수(Sungsoo Park),민현기(Hyunkee Min),홍대식(Deasik Hong) 대한전자공학회 2010 電子工學會論文誌-TC (Telecommunications) Vol.47 No.2
양자화된 채널 상태 정보를 이용하는 공간 분할 다중 접속 방식은 제한된 되먹임 정보로도 다중 송신의 이득을 가질 수 있다. 그러나 되먹임 정보의 양은 사용자에 따라 선형적으로 증가하기 때문에, 공간 분할 다중 접속 방식은 제한된 되먹임 방식을 사용하더라도 여전히 높은 신호처리 부담을 갖게 된다. 그러므로 본 논문에서는 대상이 되는 사용자 수를 효과적으로 제어할 수 있는 새로운 되먹임 방식을 제안한다. 제안하는 방식에서는 성능 열화 없이 되먹임 정보량을 줄이기 위해, 되먹임 요청기준 조건을 제시하고 이에 미치지 못하는 열악한 통신 환경의 사용자들을 제한한다. 본 논문의 모의 실험에서는 제안하는 방식이 전송 효율 이득을 높일 뿐만 아니라 되먹임 정보를 합리적으로 감소시킬 수 있음을 보여준다. Introducing the quantized channel state information (CSI), space division multiple access (SDMA) can extract the multiplexing gain with the limited feedback burden. However, huge signaling burden of feedback can still suffer SDMA system because the total feedback data of SDMA is linearly dependent on the number of users. Hence, we propose a new feedback scheme to control the feedback load decided by the number of users. In this scheme, the cut-off level, which restricts the feedbacks of poor conditioned users, is suggested for the reduction of the feedback burden without the performance loss. From simulation results, then, we show that the proposed feedback scheme can achieve not only the sum-rate gain but also the reasonable feedback reduction.
다중 사용자 다이버시티로부터 얻게 되는 처리율 증가에 대한 새로운 근사적 분석
서우현(Woohyun Seo),김성태(Sungtea Kim),곽경철(Kyungchul Kwak),홍대식(Daesik Hong) 한국통신학회 2007 韓國通信學會論文誌 Vol.32 No.11C
본 논문은 다중 사용자 시스템에서 좋은 채널을 가진 사용자를 선택함으로써 얻을 수 있는 다이버시티, 즉 다중 사용자 다이버시티로부터 증대되는 처리율 (throughput)에 대해 새로운 접근 방식을 이용하여 분석하였다. 이와같은 다중 사용자 다이버시티 이득으로부터 도출되는 처리율의 증가를 근사적 형태의 식으로 유도하기 위하여, 본논문에서는 Puiseux 급수를 이용하였고 이를 통해 단순화된 맺음식 (closed form)의 결과를 얻을 수 있었다. 이 결과식은 다중 사용자 다이버시티 이득이 신호 대 잡음비 (SNR)에 독립적이라는 것을 보여주고 있다. 또한 본 논문에서는 위의 결과를 Max C/I과 proportional fair scheduling과 같은 스케쥴링 알고리즘에 확대 적용하였다. 그리고 제시한 결과식을 모의실험과 비교하여 검증하였다. This paper presents our study of throughput enhancement achieved by selection diversity in a multiuser system, called multiuser diversity (MUDiv), using a new asymptotic approach. The MUDiv gain is evaluated by deriving an asymptotic formula for the throughput enhancement from the MUDiv gain as a simple closed form introducing a Puiseux series. The formula shows that the MUDiv gain is independent of the signal-to-noise ratio (SNR). This concept can be extended to analysis applicable to scheduling algorithms, such as Max C/I and proportional fair scheduling. The MUDiv gain throughput analysis is verified using Monte-Carlo simulations.
Low-Cost Software-Defined GPS Simulator with the Capability of Time Synchronization
Woohyun Kim,Jiwon Seo 제어로봇시스템학회 2018 제어로봇시스템학회 국제학술대회 논문집 Vol.2018 No.10
In this paper, a low-cost software-defined Global Positioning System (GPS) simulator for indoor positioning is proposed. The purpose of the proposed GPS simulator is to generate GPS signals so that the users can obtain the desired positions in an indoor environment with conventional GPS receivers. Since some commercial GPS receivers cannot properly provide position solutions if the calculated time based on the simulated signals is earlier than the last measured time based on the actual signals, the proposed GPS simulator generates GPS signals that do not cause this problem. In order to achieve this, an outdoor receiver was utilized to retrieve live ephemeris data, and the proposed GPS simulator generated baseband GPS signals that can provide a desired indoor position and time based on the ephemeris data. During the process of baseband GPS signal generation, time delay in the simulation process was compensated. Then, the baseband signals were modulated to GPS L1 frequency and were broadcast as radio frequency (RF) signals using a software-defined radio platform. The proposed GPS simulator was implemented using a u-blox M8T as an outdoor receiver and a USRP N210 as a software-defined radio platform. The performance of the proposed simulator was validated with another u-blox receiver as a user. The u-blox receiver successfully acquired the desired position with the simulated RF signals that were transmitted via a coaxial cable to the receiver.
Development of Record and Management Software for GPS/Loran Measurements
Woohyun Kim,Pyo-Woong Son,Joon Hyo Rhee,Jiwon Seo 제어로봇시스템학회 2020 제어로봇시스템학회 국제학술대회 논문집 Vol.2020 No.10
In this paper, a software implementation that records Global Positioning System (GPS) and long-range navigation (Loran) measurement data output from an integrated GPS/Loran receiver and organizes them based on time is proposed. The purpose of the developed software is to collect measurements from multiple Loran transmitter chains for performance analysis of navigation methods using Loran, and to organize the data based on time to make it easy to use them. In addition, GPS measurements are also collected and managed as ground truth data for performance analysis. The implemented software consists of three modules: recording, classification, and conversion. The recording module records raw text data streamed from the receiver, and the classification module classifies the recorded text data according to the message format. The conversion module parses the classified text data, sorts GPS and Loran measurements based on timestamp, and outputs them according to the software platform of the user to analyze the measurements. Each module of the software runs automatically without user intervention. The functionality of the implemented software was verified using GPS and Loran measurements collected over 24 h from an actual integrated GPS/Loran receiver.