臺灣博碩士論文加值系統

多天線傳接之正交分頻多工(Multi-Input Multi-Output-Orthogonal Frequency Division Multiplexing, MIMO-OFDM)結合了MIMO與OFDM的系統架構，可達到更高品質的傳輸效益，其中OFDM在有限的頻寬中利用各個正交的次載波來傳送資料，具備了對抗頻率選擇衰減通道特性，使得每個次載波視為平坦衰減通道，並可個別調變。而MIMO系統利用其多樣性來增加其傳輸的效能，有效的應用在平坦衰減通道上，正交載波多工視每個次載波為平坦衰減通道，多天線傳接有其多樣性，因此MIMO-OFDM結合了這兩項系統各自的優點所建立出的架構。但正交分頻多工對其次載波的干擾( Inter-Carrier Interference, ICI )非常敏感，而在高速移動下都卜勒效應會使得次載波間失去正交性，本篇論文利用階層式調變技術作用在多天線傳接下，估計在通道衰減與都卜勒情況下的載波頻率飄移( Carrier Frequency Offset, CFO)
階層式調變其目的是為了不同重要性資料有不同的錯誤率保護程度，因此每個階層都有各自對於通道的敏感程度而有不同的錯誤率，並在多天線傳接底下使其敏感程度更加明顯，利用其多天線傳接之階層式調變，對於不同階級，不同維度下的位元錯誤率來估計都卜勒效應的程度。
本篇論文提出領航訊號( pilot signal )做階層式的調變，因為在高速移動下其通道衰減與都卜勒效應導致其錯誤率集中在某個範圍之內，也就是本篇論文定義的錯誤相鄰情況，所以無法準確利用不同的錯誤地限情況，進而偵測目前載波頻率飄移，因此在高維度天線傳接情況下，會使其錯誤率變動範圍增加，拉開其錯誤相鄰的影響，因而更精準的估計都卜勒飄移，因此我們建立出表格與一套規則來判定目前載波頻率飄移的情況，以達到補償回正交分頻多工因次載波間干擾而破壞的正交性，並且進而使系統符合目前所對應的服務品質之要求，來選擇其傳輸訊號之天線維度。

In this thesis, we address the estimation of carrier frequency offset (CFO) in the orthogonal frequency division multiplexing (OFDM) based on multiple input multiple output (MIMO) communication system. The basic principle of OFDM is to convert a wideband frequency-selective channel into numerous narrow-band flat-fading subchannels. On the other hand, MIMO techniques boost the performance under flat-fading channels for wireless communications significantly. By combining the features of OFDM and MIMO, the MIMO-OFDM techniques can achieve better performance in high data rate wireless communication systems. However, OFDM is sensitive to inter carrier interference (ICI) which destroys the subcarriers’ orthogonality. In addition, the Doppler effect will make ICI more severe in high mobility communication. Therefore, we apply the hierarchical modulation to estimate CFO in MIMO-OFDM system for high mobility communication.
Hierarchical constellations offer a different degree of protection to the transmitted messages according to their relative importance. In this thesis, it is observed that the bit error rate and error floor of each level caused by additive white Gaussian noise (AWGN), ICI, and Rayleigh fading are different. In the single-input single-output (SISO) system, the error floor will be very close in some range and it is difficult to estimate CFO. On the other hand, the MIMO system can not only separate the error floors of different levels but also can estimate CFO more accurately in high mobility systems.
In this thesis, we proposed the hierarchical 64-QAM to modulate the pilot signals at the transmitter in the MIMO-OFDM system. Based on the factor of different error floor level at different CFO among each level bit, and MIMO gain (diversity), the CFO resulting from the Doppler effect can be estimated more exactly at the receiver. Moreover, we establish two constrains (error floor and error close) in different MIMO domains (antennas), and find more MIMO domains which can estimate CFO more accurately. In the proposed system, we can estimate the CFO by lookup table to the subcarriers’ orthogonality caused by ICI. In addition, considering the tradeoff between the error degree of data signals and different MIMO domains of estimation CFO, we can construct an adaptive system to fulfill quality of service (QoS) of data by utilizing the number of the antennas.

口試委員會審定書 #
中文摘要 i
ABSTRACT ii
目錄 iv
圖目錄 vi
表目錄 ix
第 1 章 緒論 1
1.1 前言 1
1.2 研究動機 1
1.3 正交分頻多工系統 2
1.3.1 正交分頻多工系統優缺點[2] 4
1.4 多天線傳接系統 5
1.4.1 MIMO-OFDM複合技術 7
1.5 高速傳輸系統之通道問題探討 7
1.5.1 都卜勒效應 8
1.5.2 同調頻寬 9
1.5.3 同調時間 10
1.6 章節介紹 12
第 2 章 多天線之階層式調變 14
2.1 MIMO 系統 16
2.1.1 空間區塊碼( Space Block Code ) 17
2.1.2 空域多工( Spatial Multiplexing ) 19
2.1.3 空域解相關( Spatial De-correlation ) 21
2.2 階層式 M-QAM調變 22
2.2.1 各階層位元在AWGN通道錯誤率分析 24
2.2.2 階層式64-QAM訊號在AWGN及都卜勒效應下錯誤率分析 26
2.2.3 階層式64-QAM訊號在多傳接天線下AWGN，雷利通道及都卜勒效應下錯誤率分析 29
第 3 章 多天線傳接正交分頻多工系統以及無線通道設計 36
3.1 多天線傳接正交分頻多工系統簡介 36
3.1.1 階層式調變 36
3.1.2 多天線傳接 37
3.1.3 串列和並行的概念 37
3.1.4 載波配置 38
3.1.5 資源區塊 39
3.1.6 反快速傅立葉轉換和快速傅立葉轉換 40
3.1.7 保護區間和循環字首 40
3.2 無線通道設計 42
3.2.1 都卜勒效應 42
3.2.2 MIMO 通道模型 45
第 4 章 多維度天線下之階層式領航訊號應用於載波頻率飄移估計 47
4.1 系統簡介 47
4.1.1 傳輸端模型 49
4.1.2 接收端模型 56
4.2 載波頻率飄移評估 58
4.2.1 載波頻率飄移分析與估計 59
4.2.2 不同天線維度之查表內容 62
4.2.3 系統誤差與天線維度選擇 65
4.3 模擬結果分析 70
第 5 章 結論與未來展望 77
5.1 結論 77
5.2 未來展望 78
參考文獻 81

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