應用於時變與非時變OFDM系統之新通道估測法

Abstract

通道估測(channel estimation)通常是依靠系統中的領航訊號(pilot)來完成。當通道的時間延遲較長時，估測效能可能會因為受限於有限的領航訊號而下降。最近有研究者在DVB-T系統下提出的聯合時域和頻域通道估測法，比舊有頻域通道估測法的效能好很多。然而，因為這個估測方法需要四個OFDM訊號的資訊來完成，所以對於記憶體的使用量大，在時變通道中也不適用。在本篇論文中，我們提出了一個新的通道估測法來解決此問題。在本篇論文的第一部分，我們提出適用於非時變通道的新通道估測法，而在本篇論文的第二部分，我們延伸此新通道估測法，使它適用於時變通道的估測。我們所提出的通道估測法，最主要的特色是即使在領航訊號(pilot)密度很低時，也只需要一個OFDM訊號就可以完成。而從模擬結果也可以看出，我們所提出的通道估測法有很好的效能。

In pilots-aided OFDM systems, the channel estimation relies on the pilots inserted in the systems. Since the number of pilots is usually limited, the performance of the channel estimate may not be satisfactory when the delay spreard of the channel is large. Recently, a joint time and frequency domain estimator, which can grealty outperform the conventional frequency domain channel estimator, has been proposed for DVB-T systems. However, this method need to collect four OFDM symbols in order to conduct the estimation. This will significantly increase the memory size and cause problems in time-variant channels. In this thesis, we propose new joint time and frequency domain methods to solve the problem. In the first part of this thesis, we propose new methods for the time-invariant channel estimation. In the second part of this thesis, we extend the proposed methods to accommodate time-variant channels. The distinct feature of the proposed methods is that only one OFDM symbol is required even when the pilot density is very low. Simulations show that the performance of the proposed methods can approach the optimum.