多用戶正交分頻多工(Orthogonal Frequency Division Multiple Access, OFDMA)上傳系統中的一個困難點，即是因為頻率偏差(Carrier Frequency Offset, CFO)所產生的多用戶干擾(Multi-user Interference, MUI)。在子頻帶形式的OFDMA系統中，各個上傳資訊的用戶都會分配到一小段連續的載波頻帶，並且相互間頻帶不存在重疊的情況，因此，一般系統習慣上將領航訊號(Pilot)設定在用戶所屬頻帶的兩邊邊緣，藉以處理同步和通到估測。然而，由於鄰近頻帶用戶因頻率偏差而產生的干擾，將會使得系統在同步處理以及通道估測上的效能大大的受到影響。當然系統上也可以在用戶頻帶間設置一個不傳送任何資訊的空載波，以阻隔鄰近用戶的干擾。本篇碩士論文主要是提出一種新穎的領航訊號設置方式，在維持系統頻寬使用效率等同於上述利用空載波方式的前提下，除此之外，其額外具有使系統在同步和通道估測時，可以有更好的系統效能：更甚地，此領航訊號還可降低用戶相互的干擾。

In this thesis, One of the difficulties in the orthogonal frequency division multiple access (OFDMA) systems is the multi-user interference (MUI) induced by the carrier frequency offset (CFO). In sub-band OFDMA systems, each user occupies a consecutive and non-overlapping frequency sub-band. The pilots are usually placed at the edges of a sub-band for frequency synchronization and channel estimation. However, the both frequency synchronization and channel estimation performance are influenced seriously by the multi-user interference (MUI) induced by CFO of other users. The MUI can be reduced by inserting the guard sub-carrier between adjacent users. In this paper, a novel pilot architecture is investigated, which has the same bandwidth efficiency as the conventional guard sub-carrier insertion scheme. In addition, the proposed pilot architecture provides better carrier frequency synchronization and channel estimation performance than conventional pilot assignment. Moreover, this new pilot architecture also has MUI reduction utility.

Chapter1 Introduction ……………………………………1
1.1 The MUI Effect of OFDMA Systems………………1
1.2 CFO and Channel Estimations in Several Kinds of OFDMA Systems ……………………………………… 2
1.3 Content about this Thesis ………………………… 3
Chapter 2 System Model ………………………………6
2.1 OFDM System Description …………………………6
2.2 Signal Model……………………………………… 12
2.2.1 Signal Model in Timing Offset …………………12
2.3 MUI Effect on Estimation…………………… ……15
Chapter 3 Pilot Design……………………………… 18
3.1 Basic Criterions…………………………………… 18
3.2 CFO Estimation……………………………………19
3.3 Channel Estimation………………………………22
Chapter 4 Interference Analysis ……………………24
4.1 MUI Reduction Analysis …………………………24
Chapter 5 Simulation …………………………………27
5.1Cannel Models …………………………………… 27
5.2 Simulation Results ……………………………… 27
5.2.1 Sub-band OFDMA System Channel Estimator with CFO Compensated Perfectly ………………… 28
5.2.2 Sub-band OFDMA System Channel Estimator with CFO Compensated Imperfectly …………………31
5.2.3 The CFO Estimator and Channel Estimator Performance in Sub-band OFDMA System…………33
Chapter 6 Conclusion…………………………………36
Appendix…………………………………………………37
References ……………………………………………43

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