臺灣博碩士論文加值系統

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.

Chapter 1 Introduction 1
Chapter 2 OFDM System and Channel Estimation 3
2.1 Introduction to OFDM System 3
2.1.1 Basic Principle of OFDM System 5
2.1.2 Cyclic Prefix 8
2.1.3 Discrete-Time Equivalent System Model 9
2.2 Introduction to IEEE 802.16e 11
2.2.1 Generic OFDMA Symbol Description 12
2.2.1.1 Time Domain Description 12
2.2.1.2 Frequency Domain Description 12
2.2.1.3 Primitive Parameters 12
2.2.1.4 Derived Parameters 13
2.2.2 DL Preamble Structure and Modulation 13
2.2.3 DL Carrier Allocation 15
2.2.3.1 DL PUSC 15
2.2.3.2 DL FUSC 17
2.2.4 DL Carrier Modulation 18
2.2.4.1 DL Pilot Modulation 18
2.2.4.2 DL Data Modulation 19
2.3 Conventional Time-Invariant Channel Estimator 20
2.3.1 LS Channel Estimator 20
2.3.2 MMSE Channel Estimator 22
2.3.3 Frequency Domain Interpolation Methods23
Chapter 3 Proposed Channel Estimator 29
3.1 Sliding-Windowed LAQ Channel Estimator 31
3.2 Low-Complexity Time Domain Channel Estimator 32
3.3 Channel Tap Search Algorithm 34
3.3.1 Preliminary Channel Estimation with Preamble 34
3.3.2 Preliminary Channel Estimation with Pilots 35
3.3.3 Channel Tap Search Method 36
3.4 Joint Time and Freq Domain Channel Estimator 38
3.5 Time-Variant Channel Estimation 41
Chapter 4 Simulation Results 44
4.1 Channel Model 45
4.2 Sliding-Windowed LAQ Results 46
4.3 Low-Complexity Time Domain Channel Estimation Results 49
4.4 Joint Time and Freq Domain Channel Estimation Results 51
4.5 Time-Variant Channel Estimation Results 53
Chapter 5 Conclusion and Future Works 57

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