長期演進(Long Term Evolution, 簡稱LTE) 是由第三代合作夥伴計畫(Third Generation Partnership Project, 簡稱3GPP) 所提出的標準, 預計將成為第四代 (4G) 行動通訊標準的主流技術。LTE分為分頻雙工(Frequency Division Duplex, 簡稱FDD) 和分時雙工 (Time Division Duplex, 簡稱TDD) 兩種模式, 在下行鏈路(Downlink) 都是使用正交分頻多工(Orthogonal Frequency Division Multiplexing, 簡稱OFDM) 系統為架構, 然而OFDM 系統具有對時間與頻率偏移敏感的缺點, 因此同步是OFDM 系統很重要的工作。

本論文設計一個LTE FDD 模式的基頻接收機來處理同步問題, 利用循環字首與符元尾端重複的特性, 對時間偏移以及載波頻率偏移做估測和補償, 同時偵測系統所使用的循環字首類型。接收機在達成同步後會繼續進行基地台搜尋的動作, 利用LTE 所
提供的同步訊號, 經過快速傅立葉轉換得到通道能量來判斷基地台識別碼(Cell Identity, 簡稱Cell ID) 。從模擬結果可以看出本論文設計的接收機能夠達成時間和頻率同步,並且完成基地台搜尋的工作。

Long Term Evolution (LTE) developed by Third Generation Partnership Project (3GPP) is expected to be the standard of the Fourth-Generation (4G) of wireless communication system. LTE supports Frequency Division Duplex (FDD) and Time Division Duplex (TDD), and both of them are based on Orthogonal Frequency Division Multiplexing (OFDM) system in downlink. OFDM systems are sensitive to timing and frequency offset. Therefore, synchronization plays an important role in OFDM systems.

In this thesis, we study synchronization problems of a LTE FDD baseband receiver. Particularly, we develop a complete procedure to deal with the synchronization problems. The basic design concept and procedure are as follows: The receiver estimates and compensates the timing and frequency offset by using the repetition property of the cyclic prefix. In the meanwhile, the receiver also detects cyclic prefix mode (or the length of the cyclic prefix). After the frequency offset has been compensated, the receiver then processes cell search. To this end, we multiply each subcarrier by the synchronization sequence provided by LTE specification and transform them into time domain. We then estimate the channel energy in time domain to detect the Cell Identity (Cell ID). Using computer simulations, we verify that the designed receiver performs well.

摘要i
Abstract ii
目錄iii
圖次v
表次vii
1 緒論1
11 研究背景與動機 1
12 論文架構 2
2 正交分頻多工技術與3GPP LTE 標準介紹3
21 正交分頻多工系統簡介 3
22 串列與並列轉換 6
23 反離散傅立葉轉換和離散傅立葉轉換 6
24 循環字首 7
25 LTE 訊框結構 7
26 LTE 同步訊號 8
261 主要同步訊號 10
262 次要同步訊號 11
iii
3 通道模型13
31 多重路徑與瑞雷衰減通道 13
32 時間與載波頻率偏移 14
4 同步與基地台搜尋演算法18
41 符元時序同步 18
42 循環字首類型偵測 21
43 小數部分載波頻率偏移偵測 22
44 主要同步訊號偵測 23
441 整數部分載波頻率偏移估測 23
442 判斷主要同步訊號 24
45 次要同步訊號偵測 27
5 模擬結果28
51 載波頻率偏移估測與補償模擬結果 29
52 次要同步訊號多符元累積效能比較 32
53 基地台搜尋效能模擬 34
6 結論36
參考文獻37

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