臺灣博碩士論文加值系統

正交分頻多工(orthogonal frequency division multiplexing；OFDM)傳輸技術具有高頻譜效率以及穩健對抗多重路徑衰減效應的優勢，但OFDM訊號的高峰均功率比(peak-to-average power ratio ; PAPR)特點可能會在訊號通過功率放大器時造成非線性失真。子載波預留(tone reservation)是一種可有效降低OFDM系統之PAPR的技術，其中傳統作法採用預先選定且固定不變的子載波預留方式；此一方法的缺點為，有些通道狀況良好的子載波會被強制保留作為降低PAPR之用，而不被用於資料傳輸，這將不利於系統之位元錯誤率(bit error rate；BER)效能。在本論文中，我們提出一個基於預留子載波與通道狀態資訊(channel state information；CSI)的混合式PAPR降低技術，其中預留的子載波包含預先決定的固定部分以及根據CSI決定的動態部分；電腦模擬結果顯示，在使用相同數量的預留子載波情況下，所提方法比傳統作法具有較佳的BER效能和稍微高一點的PAPR；在使用較少預留子載波的情況下，所提方法亦可達到與傳統作法相近的BER效能。

Orthogonal frequency division multiplexing (OFDM) transmission has advantages of high spectral efficiency and robustness against multipath fading, but the high peak-to-average power ratio (PAPR) feature of an OFDM signal may cause nonlinear distortion when the signal passes through a power amplifier. Tone reservation (TR) is an effective technique for PAPR reduction in OFDM systems, where a fixed arrangement of reserved tones or subcarriers is predetermined appropriately in the conventional method. For such a TR-based method, some tones with good channel conditions would be forcibly reserved for the purpose of PAPR reduction, rather than used for data transmission, and this is adverse to the system bit-error-rate (BER) performance. In this thesis, we propose a hybrid TR-based PAPR reduction scheme with assistance of channel state information (CSI), where the reserved tones consist of a predetermined fixed part and a dynamic part selected based on CSI. Computer simulation results show that, as compared with the conventional TR-based method, the proposed one provides better BER performance with a slightly higher PAPR under the same number of reserved tones. It can also achieve similar BER performance to the conventional approach by using a smaller number of reserved tones.

Abstract------------------------------------------------i
Contents-----------------------------------------------ii
List of Figures---------------------------------------iii
List of Tables-----------------------------------------iv
I.Introduction------------------------------------------1
II.Background-------------------------------------------4
A.Definition of PAPR in OFDM Systems-------------------4
B.Review of the Conventional TR-Based Method-----------5
C.A Model of the Power Amplifier-----------------------8
III.TR-Based PAPR Reduction with CSI Assistance--------10
A.Concept of CSI-Assisted Tone Reservation------------10
B.A Hybrid TR-Based PAPR Reduction Algorithm----------11
IV.Simulation Results----------------------------------14
V.Conclusion-------------------------------------------20
References---------------------------------------------21

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