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Hybrid combiner design for downlink massive MIMO systems
Seo, Bangwon Electronics and Telecommunications Research Instit 2020 ETRI Journal Vol.42 No.3
We consider a hybrid combiner design for downlink massive multiple-input multiple-output systems when there is residual inter-user interference and each user is equipped with a limited number of radio frequency (RF) chains (less than the number of receive antennas). We propose a hybrid combiner that minimizes the mean-squared error (MSE) between the information symbols and the ones estimated with a constant amplitude constraint on the RF combiner. In the proposed scheme, an iterative alternating optimization method is utilized. At each iteration, one of the analog RF and digital baseband combining matrices is updated to minimize the MSE by fixing the other matrix without considering the constant amplitude constraint. Then, the other matrix is updated by changing the roles of the two matrices. Each element in the RF combining matrix is obtained from the phase component of the solution matrix of the optimization problem for the RF combining matrix. Simulation results show that the proposed scheme performs better than conventional matrix-decomposition schemes.
Fast Convergent LMS Adaptive Receiver for MC-CDMA Systems with Space-Time Block Coding
Bangwon Seo,Woo-Geun Ahn,Cheol Jeong,Hyung-Myung Kim IEEE 2010 IEEE communications letters Vol.14 No.8
<P>For multicarrier code-division multiple access (MC-CDMA) systems employing Alamouti's simple space-time block coding (STBC), a special relationship between two minimum mean-square error (MMSE) filter weight vectors is derived in which one filter is for detecting odd-indexed symbols and the other for even-indexed symbols. Using this relationship, a modified MSE cost function is presented and an improved least mean-square (LMS) adaptive receiver is proposed. Since the number of filter taps independently updated in the proposed adaptive receiver is only half that of the conventional LMS adaptive receiver, the proposed adaptive receiver has a faster convergence rate than the conventional LMS adaptive receiver while keeping the same steady-state MSE performance. This is verified through the simulation.</P>
SLNR-based Precoder Design in Multiuser Interference Channel with Channel Estimation Error
( Bangwon Seo ) 한국인터넷정보학회 2020 KSII Transactions on Internet and Information Syst Vol.14 No.1
In this paper, we consider a precoder design problem for multiuser interference channel. Most of the conventional schemes for precoder design utilize a signal-to-interference-plus-noise ratio (SINR) as a cost function. However, since the SINR metric of a desired transmitter-receiver pair is a function of precoding vectors of all transmitters in the multiuser interference channel, an analytic closed-form solution is not available for the precoding vector of a desired transmitter that maximizes the SINR metric. To eliminate coupling between the precoding vectors of all transmitters and to find a closed-form solution for the precoding vector of the desired transmitter, we use a signal-to-leakage-plus-noise ratio (SLNR) instead as a cost function because the SLNR at a transmitter is a function of the precoding vector of the desired transmitter only. In addition, channel estimation errors for undesired links are considered when designing the precoding vector because they are inevitable in a multiuser interference channel. In this case, we propose a design scheme for the precoding vector that is robust to the channel estimation error. In the proposed scheme, the precoding vector is designed to maximize the worst-case SLNR. Through computer simulation, we show that the proposed scheme has better performance than the conventional scheme in terms of SLNR, SINR, and sum rate of all users.
직교 주파수 분할 다중화 시스템을 위한 채널 추정 방법
서방원(Bangwon Seo) 한국정보기술학회 2014 Proceedings of KIIT Conference Vol.2014 No.5
직교 주파수 분할 다중화 시스템에서 기존의 이산 푸리에 변환 기반의 채널추정 방법들은 시간 영역으로 변환된 채널 계수들 중에서 순환전치(cyclic prefix: CP) 길이에 해당하는 채널 계수들을 이용하여 채널추정 성능을 향상시켰다. 그러나 실제 채널 탭의 길이가 순환전치의 길이보다 매우 작은 경우에는 기존 방법들로는 성능 개선에 한계가 있었다. 본 논문에서는 채널 탭의 길이가 CP 길이보다 훨씬 작은 경우에 우수한 성능을 나타내는 채널 추정 방법을 제안한다. 제안하는 방법에서는 먼저 시간 영역 채널 탭의 길이와 채널 탭 중에서 값이 0인 탭들을 추정하고 이 정보를 이용하여 향상된 이산 푸리에 변환 기반의 채널추정 방법을 제안한다. In Orthogonal frequency division multiplexing (OFDM) systems, conventional DFT-based channel estimation schemes have improved the channel estimation performance using the time-domain channel coefficients with the tap length equal to the cyclic prefix (CP) length. However, in case channel tap length is too short compared with the CP length, the performance improvement of the conventional schemes is very limited. In this case, we propose an improved channel estimation scheme. We first propose an estimation scheme for the channel tap length and the channel taps with the value of 0. Using this information, we propose an improved DFT-based channel estimation scheme.
서방원(Bangwon Seo) 한국정보기술학회 2014 Proceedings of KIIT Conference Vol.2014 No.5
본 논문은 다중 송신 안테나를 이용하여 시공간 부호화를 적용한 직교 주파수 분할 다중화 시스템에 대해서 다룬다 이 시스템에서는 시공간 부호화를 위해서 복수의 송신 안테나에 대한 파일럿 심볼들을 동시에 전송하기 때문에 파일럿 심볼들 간에 서로 간섭을 주게 된다 따라서 기존 논문은 채널 추정 성능을 향상시키기 위하여 파일럿 심볼들 간의 간섭을 줄이는 방법을 제안하였지만 배경 잡음을 줄이는 방법에 대해서는 다루지 않았다. 본 논문에서는 파일럿 심볼들 간의 간섭 뿐만 아니라 배경 잡음도 줄이는 채널 추정 방법을 제안하며 모의 실험을 통해서 제안하는 방법이 기존 방법보다 더 우수한 성능을 나타낸다는 것을 보인다. In this paper, we consider space-time block coded (STBC) orthogonal frequency division multiplexing (OFDM) system with multiple transmit antennas. Since pilot symbols for multiple transmit antennas are simultaneously transmitted in this system, there is an interference between received pilot symbols at the received signal. Conventional channel estimation schemes have been proposed to reduce the interference, but they did not consider to reduce additive white Gaussian noise (AWGN). In this paper, we propose a new channel estimation scheme for STBC-OFDM system taking account of both the interference between pilot symbols and AWGN, and show that the proposed scheme has better performance than the conventional scheme.