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Modified Power Control Algorithms for Mobile Satellite Communication Systems with ATCs
YOU, Cheolwoo,KIM, Byounggi,RYOO, Sangjin,HWANG, Intae The Institute of Electronics, Information and Comm 2009 IEICE transactions on fundamentals of electronics, Vol.92 No.3
<P>In this paper, in order to increase system capacity and reduce the transmitting power of the user's equipment, we propose a modified power control scheme consisting of a modified closed-loop power control (CLPC) and open-loop power control (OLPC). The modified CLPC algorithm, combining delay compensation algorithms and pilot diversity, is mainly applied to the ancillary terrestrial component (ATC) link in urban areas, because it is more suitable to the short round-trip delay (RTD). In the case of rural areas, where ATCs are not deployed or where a signal is not received from ATCs, transmit power monitoring equipment and OLPC algorithms using efficient pilot diversity are combined and applied to the link between the user's equipment and the satellite. Two power control algorithms are applied equally to the boundary areas where two kinds of signals are received in order to ensure coverage continuity. Simulation results show that the modified power control scheme has good performance compared to conventional power control schemes in a geostationary earth orbit (GEO) satellite system utilizing ATCs.</P>
Nonlinear Blind Equalization Schemes Using Complex-Valued Multilayer Feedforward Neural Networks
You, Cheolwoo,Hong, Daesik 연세대학교 전자정보통신연구소 1998 전자 정보 통신 논문집 Vol.3 No.1
Among the useful blind equalization algorithms, stochastic-gradient iterative equalization schemes are based on minimizing a nonconvex and nonlinear cost function. However, as they use a linear FIR filter with a convex decision region, their residual estimation error is high. In this paper, four nonlinear blind equalization schemes that employ a complex-valued multilayer perceptron instead of the linear filter are proposed and their learning algorithms are derived. After the important properties that a suitable complex-valued activation function must possess are discussed, a new complex-valued activation function is developed for the proposed schemes to deal with QAM signals of any constellation sizes. It has been further proven that by the nonlinear transformation of the proposed function, the correlation coefficient between the real and imaginary parts of input data decreases when they are jointly Gaussian random variables. Lastly, the effectiveness of the proposed schemes is verified in terms of initial convergence speed and MSE in the steady state. In particular, even without carrier phase tracking procedure, the proposed schemes correct an arbitrary phase rotation caused by channel distortion.
Neural Convolutional Decoders in the Satellite Channel
You,Cheolwoo,Hong,Daesik 연세대학교 전자정보통신연구소 1995 전자 정보 통신 논문집 Vol.2 No.1
The Neural Convolutional Decoders(NCD) has been used as an alternative for decoding convolutional codes〔1〕. The motivation of the NCD is to maintain the performance and to reduce the hardware complexity of the conventional convolutional decoders. In order to show that the nonlinearity of the neural networks is important, simulations are performed under the satellite channel that has the nonlinear distortion. We restrict our attention to the case of coherent QPSK modulation. In this case, the neural networks can learn the nonlinear distortion caused by the characteristics of the satellite channel including the filtering effects and the nonlinear effects of the traveling-wave tube(TWT) amplifiers. In result, the performance of the NCD with a simple structure is almost equal to that of the soft decision Viterbi decoder for the systematic code with 32-bit paths which need 128-bit memory storage. And, the performance difference between the NCD for the systematic code and the soft decision Viterbi decoder for the nonsystematic code is about 1.0 dB and nearly identical to that caused by the dissimilarity of the error-correcting ability in two codes. Therefore, if we could efficiently train the NCD for the nonsystematic codes, the NCD would perform as well as the soft decision Viterbi decoder for the nonsystematic code.
Adaptive Modulation and Coding Scheme with Independent MCS Level Selection in MIMO Systems
CHOI, Kwangwook,YOU, Cheolwoo,HWANG, Intae,RYOO, Sangjin,LEE, Kyunghwan,JUNG, Taejin,KIM, Cheolsung The Institute of Electronics, Information and Comm 2008 IEICE transactions on fundamentals of electronics, Vol.91 No.4
<P>In this paper, we propose a system that adopts the independent MCS (modulation and coding scheme) level for each layer in the AMC (adaptive modulation and coding) scheme combined with the V-BLAST (vertical Bell lab layered space time) system. From the simulation results, we observe that since the independent MCS level case adapts modulation and coding rate for maximum throughput to each channel condition in separate layers, the combined AMC-V-BLAST system with the independent MCS level selection results in improved throughput compared to the combined AMC-V-BLAST system with the common MCS level selection and the conventional AMC system based on the 1x EV-DO standard. Especially, the combined AMC-V-BLAST system with the independent MCS level achieves a gain of 700kbps in 7-9dB SNR (signal-to-noise ratio) range.</P>
다중 사용자 다중 안테나 시스템을 위한 두 단계 결합 프리코딩 방안
박상우(Sangwoo Park),유철우(Cheolwoo You) 한국통신학회 2022 한국통신학회 학술대회논문집 Vol.2022 No.2
본 논문에서는 다중 사용자 다중 입력 다중 출력(Multiuser multiple-input multiple-output: MU-MIMO) 시스템에서 사용자 당 다중 스트림을 지원하기 위한 새로운 프리코더(Precoder) 및 포스트코더(Postcoder)의 결합된 설계 방안을 제안한다. 이 방식은 송신기에서 등채널 이득 분해(Equal channel gain decomposition)와 블록 대각화 (Block diagonalization: BD)을 사용하는 2 단계 프리코딩으로 구성된다. 제안된 알고리즘은 Full diversity order 를 유지하면서 다중 안테나 방송 채널(MIMO Broadcast channel)의 Sum-rate capacity 에 점근적으로 접근 가능하다.