臺灣博碩士論文加值系統

本論文旨在探討，通道估測研究於多細胞下鏈(Downlink, DL)傳輸頻分雙工(Frequency Duplex Division, FDD)巨量(Massive)天線多輸出多輸入(Multi-Input Multi-Output, MIMO)正交分頻多工(Orthogonal Frequency Division Multiplexing, OFDM)系統。
傳統領航序列擺放在不同的正交分頻多工符元上，利用時間做領航序列的正交。傳送端給定資料傳輸能量下，為了達成最佳化的通道估測效能，會加大擺放領航序列正交分頻多工符元的傳輸能量。當傳輸能量越大時，傳統領航序列擺放方法，能量集中於擺放領航序列的符元上，產生高峰均功率比(Peak to Average Power Ratio, PAPR)問題；本論文使用札德奧夫-朱(Zadoff and Chu, ZC)序列為領航序列，將領航序列利用不同頻帶與時間擺放，在同調時間與同調頻寬內傳輸領航序列，能量會平均分配在不同的OFDM符元上，OFDM符元彼此能量差異不大，相較傳統擺放方式，有較小的PAPR。
接下來推導該系統下LS估測器與估測效能，發現估測效能受領航汙染主導，其受到領航序列交相關值加總影響。我們利用互熵(Cross Entropy, CE)演算法選出最佳領航序列組合分配給基地的天線傳輸，使得接收端接收到的最大交相關值加總最小，降低領航汙染，提升通道估測的效能。
由模擬的結果觀察到，由CE演算法挑選出來的最佳領航序列組合，相較隨機挑選的領航序列組合，具有較小的最大交相關加總值。將最佳領航序列組合代入最小平方估測器中，領航汙染降低，具有較佳的通道估測效能。在巨量天線數的情況下，為了達到相同的效能，本論文提出的方法相較傳統擺放方式，更適用於巨量天線系統。

In this paper, we consider a channel estimation problem which based on a multi-
cell with downlink (DL) training framework for frequency duplex division (FDD) massive multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems.
In traditional MIMO-OFDM systems, transmitter transmits pilot sequences with different OFDM symbols which utilize time to satisfy orthogonality. In order to improve the performance of channel estimation, transmitter distributes larger power to OFDM symbol with pilot sequences in frequency domain. This procedure could cause the high peak-to-average power ratio (PAPR) effect in time domain. Using Zadoff and Chu (ZC) sequences as our pilot sequences which arrange them to both coherence bandwidth and coherence time interval to prevent high PAPR effect. According to the deviation of estimation performance, the MSE of LS estimator is dominated by pilot contamination which is proportional to the sum of cross-correlation of pilot sequences from inter-cell. We appropriately select pilot sequences with Cross Entropy (CE) algorithm could mitigate pilot contamination. According to the simulations, our scheme can mitigate the pilot contamination that further improve the estimation performance.

論文審定書 i
誌謝 ii
中文摘要 iii
Abstract iv
目錄 v
圖次 vii
表次 ix
Chapter 1 介紹 1
1.1 論文架構 3
Chapter 2 系統介紹 5
2.1 正交分頻多工系統 5
2.1.1 正交分頻多工背景 5
2.1.2 OFDM架構 6
2.1.3 同調時間與同調頻寬 9
2.1.4 領航序列排列與設計 12
2.2 多輸入多輸出系統 14
2.2.1 空間多樣技術 14
2.2.2 空間多工技術 15
2.3 MIMO-OFDM傳接收架構 18
2.3.1 MIMO-OFDM系統 18
2.3.2 領航序列擺放 19
2.3.3 系統架構 19
2.3.4 傳統MIMO-OFDM傳接收架構 20
Chapter 3 提出的MIMO-OFDM系統領航序列設計 23
3.1 單細胞巨量天線MIMO-OFDM架構 23
3.1.1 提出的領航序列擺放方式 23
3.1.2 系統架構 24
3.1.3 提出的MIMO-OFDM傳接收架構 25
3.2 單細胞巨量天線MIMO-OFDM系統通道估測 28
3.3 多細胞巨量天線MIMO-OFDM架構 29
3.3.1 系統架構 29
3.3.2 提出的MIMO-OFDM傳接收架構 29
3.4 多細胞巨量天線MIMO-OFDM系統通道估測 33
3.5 最佳化問題 35
Chapter 4 Cross Entropy演算法 38
Chapter 5 模擬分析與討論 43
Chapter 6 結論 54
參考文獻 55
中英對照表 61
縮寫對照表 66

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