SVM의 분류성능을 향상시키기 위한 방법에 관한 비교연구

학위논문(석사)--서울대학교 대학원 :통계학과,2006.Maste

OFDM 시스템을 위한 저 복잡도를 가지는 LMMSE 채널 추정방식

학위논문(석사) - 한국정보통신대학원대학교 : 공학부, 2005, [ 49 p. ]In general, coherent orthogonal frequency division multiplexing (OFDM) detection requires knowledge about the reference amplitudes and phases of the constellation on each subcarrier. To achieve this, several channel estimation schemes have been investigated. In this thesis, we briefly introduce some techniques to estimate the channel in OFDM system. The least square (LS) algorithm is simple and has low complexity but the performance is not suitable for practical case. The linear minimum mean square error (LMMSE) channel estimator which makes full use of the correlation of the channel frequency response has good performance but it requires knowledge of the channel frequency correlation and the operating SNR. Also the complexity is so high due to the fact that it needs matrix inversion of autocorrelation matrix and the large number of complex multiplications. Although the computational complexity of the LMMSE estimator can be reduced by using singular value decomposition (SVD), LMMSE estimate is not acceptable because the complexity by the SVD cannot be negligible. Therefore, we propose a low complexity LMMSE channel estimator for OFDM system. We partition channel correlation matrix in frequency domain into small sub-matrices by using non-overlap and overlap techniques. The size of sub-matrix is determined by channel coherence bandwidth which defines a range of highly correlated channel frequency response. In case of non-overlap, we observe that mean square error (MSE) is higher at edge subcarriers of partitioned sub-matrix than other subcarriers. To compensate such a high MSE at edge subcarrier, we propose the overlap method. By utilizing overlap technique, we show that the MSE of the estimator can be reduced as compared with that using non-overlap method. Also the characteristic that the channel impulse response is independent for different paths in time domain is employed for diminishing both computational complexity and memory size of proposed estimators. F...한국정보통신대학원대학교 : 공학부

Low Complexity OFDM Channel Estimation Algorithm on Fading Channels

LS(Least Square)을 이용한 채널 추정방법은 낮은 복잡도를 가지지만 성능이 좋지 않고 LMMSE(Linear Minimum Mean Square Error)를 이용한 채널 추정방법은 성능은 좋지만 매우 높은 복잡도와 채널의 통계적 특성을 알 고 있어야 하는 단점이 있다. 제안한 채널 추정 방법은 채널의 주파수 응답이 구분적으로 선형화 할 수 있을 경우, 일정한 길이의 연속된LS 채널 추정 값에 대해 시간 영역으로 이동 평균을 취하는 방법이다. 이동 환경에서도 LS와 비슷한 복잡도를 가지면서 LS와 LMMSE방법의 중간 성능을 가진다. 또한 제안한 채널 추정 방법은 LS와 같이 채널의 통계적 특성에 무관하게 일정한 성능을 가진다