臺灣博碩士論文加值系統

本篇論文介紹LTE-like環境下關於通道估計的問題，包括背景概念介紹、問題陳述、演算法推導、以及程式模擬。有別於傳統上使用單一通道狀態資訊來做估計，我們發展了一套基於多個通道狀態資訊的通道估計演算法。首先，我們從預先設計好的探測預編碼矩陣群中選出一個接一個來編碼及傳送資料串流，然後我們會接收到多個對應不同預編碼矩陣的通道狀態資訊回授。最後，我們使用這些通道資訊狀態回授來做通道估計。在演算法的推導中，我們推導對於通道不隨時間改變的通道估計方法，接著我們將這個方法使用在通道隨時間改變上的情況，我們也嘗試合併使用LTE編碼簿裡面的預編碼，用於通道估計。
在模擬的部分，我們建立一個合理的LTE下行多用戶多輸出入傳輸的系統模型，並使用我們的演算法在訊號傳輸端進行通道估計，在單路徑瑞利衰減(Rayleigh fading)通道下得到的數據來驗證此演算法，接著我們測試此演算法在多路徑通道不同車速下的完美通道及估計通道之間均方差比較，以及使用估計通道用於預編碼產生觀察總傳輸量(sum rate)在各個訊雜比(SNR)下的表現。

This thesis introduces the topic about channel estimation, including background introduction, problem formulation, algorithm derivation and simulation in LTE-like scenario. We develop a channel estimation algorithm based on multiple CSI feedbacks other than one CSI feedback in convention. We first transmit data streams with our sounding precoding matrices one after another, and then receive CSI feedbacks corresponding to different precoding matrices. Finally, we use these CSI feedbacks to perform channel estimation. In algorithm derivation, we derive a channel estimation method in time-invariant channel and then use it to be in time-variant channel. We also try combining the codebook precoding matrices with our sounding precoding matrices to estimate channel information.
In simulation, we establish a reasonable downlink MU-MIMO system model in LTE specification and estimate channels with our proposed method in the transmitter-side. We simulate our proposed estimation method under single-path Rayleigh fading channel to verify its derivation. Moreover, we test our method at different mobile speeds in multi-path channels, and analyze MSE between perfect channel and estimated channel. We also observe the sum rate with SLNR precoding scheme based on our estimated method at different SNR.

1 Introduction 1
1.1 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Thesis Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Overview of LTE and LTE-A Downlink Specifications 4
2.1 LTE and LTE-A Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 OFDM and OFDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.2 OFDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3 LTE Frame Structure and Physical Resources . . . . . . . . . . . . . . . . . 10
2.3.1 Transmission Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.2 Frame Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.3 Slot Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.4 Physical Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 Downlink MIMO Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4.1 Channel Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4.2 Scrambling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4.3 Layer Mapper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4.4 MIMO Precoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.5 Downlink MU-MIMO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.5.1 MU-MIMO in LTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.5.2 MU-MIMO in LTE-A . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.6 Precoding and User Feedback Schemes . . . . . . . . . . . . . . . . . . . . . 22
2.6.1 Beamforming and Precoding . . . . . . . . . . . . . . . . . . . . . . . 22
2.6.2 Precoding Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.6.3 User Feedback Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.7 Reference Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.7.1 Channel State Information Reference Signals (CSI-RSs) . . . . . . . . 34
3 Channel Estimation Based on Implicit Feedbacks 37
3.1 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2 CSI Feedbacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3 Channel Estimation with Multiple CSI Feedbacks . . . . . . . . . . . . . . . 42
3.3.1 Fading Gain Estimation . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3.2 Phase Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.3.3 Channel Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.4 Channel Estimation with Other Sounding Precoding Matrices . . . . . . . . 54
4 Simulation Results and Analysis 56
4.1 Channel Estimation Results for Single-Path Channels . . . . . . . . . . . . . 58
4.2 Channel Estimation Results for Multi-path Channels . . . . . . . . . . . . . 60
4.2.1 Simulation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.2.2 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5 Conclusion and Future Work 81
5.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
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