LTE 시스템 채널 추정치의 후처리 기법 연구

다국어 초록 (Multilingual Abstract)

The Long Term Evolution (LTE) system is designed to provide a high quality data service for fast moving mobile users. It is based on the Orthogonal Frequency Division Multiplexing (OFDM) and relies its channel estimation on the training samples which are systematically built within the transmitting data. Either a preamble or a lattice type is used for the distribution of training samples and the latter suits better for the multipath fading channel environment whose channel frequency response (CFR) fluctuates rapidly with time. In the lattice-type structure, the estimation of the CFR makes use of the least squares estimate (LSE) for each pilot samples, followed by an interpolation both in timeand in frequency-domain to fill up the channel estimates for subcarriers corresponding to data samples. All interpolation schemes should rely on the pilot estimates only, and thus, their performances are bounded by the quality of pilot estimates. However, the additive noise give rise to high fluctuation on the pilot estimates, especially in a communication environment with low signal-to-noise ratio. These high fluctuations could be monitored in the alternating high values of the first forward differences (FFD) between pilot estimates. In this paper, we analyzed statistically those FFD values and propose a postprocessing algorithm to suppress high fluctuations in the noisy pilot estimates. The proposed method is based on a localized adaptive moving-average filtering. The performance of the proposed technique is verified on a multipath environment suggested on a 3GPP LTE specification. It is shown that the mean-squared error (MSE) between the actual CFR and pilot estimates could be reduced up to 68% from the noisy pilot estimates.

목차 (Table of Contents)

• Abstract
• 1. 서론
• 2. 시스템 모델
• 3. CFR-LSE의 통계적 분석
• 4. 국지적 MA 필터링 기법을 이용한 LSE 향상 기법
• 5. 결론
• 참고문헌
• 저자소개

참고문헌 (Reference)

1 H. Hsu, "Windowed DFT-based OFDM channel estimation by adding virtual channel frequency response" 1-5, 2009

2 B. Yang, "Windowed DFT based pilot-symbol-aided channel estimation for OFDM systems in multipath fading channels" 1480-1484, 2000

3 F. Fontan, "Modeling the wireless propagation channel: A simulation approach with MATLAB" Wiley 2008

4 R. Becker, "LTE and the evolution to 4G wireless: Design and measurement challenges" Agilent Technologies Publication 2009

5 X. Cai, "Error probability minimizing pilots for OFDM with M-PSK modulation over Rayleigh-fading channels" 53 (53): 146-155, 2004

6 박현철, "Efficient DFT-based channel estimation for OFDM systems on multipath channels" INST ENGINEERING TECHNOLOGY-IET 1 (1): 197-202, 200704

7 M. Morelli, "Comparison of pilot-aided channel estimation methods for OFDM systems" 49 (49): 3065-3073, 2001

8 S. Coleri, "Channel estimation techniques based on pilot arrangement in OFDM systems" 48 (48): 223-229, 2002

9 S. Kang, "A comparative investigation on channel estimation algorithms for OFDM in mobile communications" 49 (49): 142-149, 2003

10 3GPP TS 36.211, "3GPP TS 36.211, Evolved universal terrestrial radio access (E-UTRA): Physical channels and modulation (Release 9), Technical Specification Group Radio Access Network"