高行動性OFDM系統之聯合時域與頻遇通道估計

Abstract

在時變的OFDM系統下，通道估計通常倚賴著響導訊號。然而，嚮導訊號的數目是有限的。因此在接收機設計上，通道估計即為一項關鍵性的工作。在本篇論文中，我們首先針對IEEE802.16e系統提出一個二維滑行視窗通道估測器。在性能上不僅勝過傳統的方法，並且能有低複雜度。為了更近一步的提升系統效能，我們提出了一個結合了時域與頻域的高效能最小平方估測器。主要的概念是利用頻域上通道估計的結果，來求得時域上通道響應的位置。接著利用最小平方演算法來估計這些位置上的通道響應。並且利用遞迴演算法，我們能進一步得到更精準的通道估計。在運算複雜度上，也比傳統時域上的最小平方估測器來的小。

In time-variant OFDM systems, channel estimation usually relies on pilot subcarriers. However, the number of pilot subcarriers is usually limited. Channel estimation is then a critical task for receiver design. In this thesis, we first propose a two-dimension slide-window channel estimator for IEEE802.16e systems. The estimator can outperform conventional approaches and requires low-complexity. To further improve the performance, we then propose a high-performance least-squares (LS) channel estimator, joint operated in the time and frequency domains. The main idea is use the channel response, estimated in the frequency domain, to locate significant time-domain channel taps, and then use the LS method to estimate the responses in those taps. With an iterative algorithm, we can then obtain accurate channel estimate with computational complexity much lower than the conventional time domain LS estimator.