Improved Reception for Orthogonal Frequency-Division Multiplexing Systems with Phase Noise

具相位雜訊正交分頻多工系統之改良接受技術研究

陳曉旻(Hsiao-Min Chen)

指導教授 ： 趙啟超

國立清華大學/電機資訊學院/通訊工程研究所/碩士(2008年)

摘要

近年來為了因應高速傳輸的需求，多載波系統的應用已經大量增加。正交分頻多工(Orthogonal Frequency-Division Multiplexing)是一種調變技術，因為具有以下幾個優點，例如：高頻譜效益，對於訊符間干擾和多路徑干擾有很強的對抗性等，所以已經被廣泛運用於無線傳輸系統上。然而，正交分頻多工技術卻對一些隨著時間而改變的效應非常地敏感。特別是，來自於不可避免的振盪器抖動造成的相位雜訊(Phase Noise)，是一種隨機的擾動且會造成兩個效應:共同相位誤差(Common Phase Error)和載波間干擾(Inter-carrier Interference)。
已經有很多學術上的文獻提出了解決這個問題的方法；但是，這些方法的假設在某些情況之下可能有不合理的地方，例如：必須完全知道通道的訊息和(或)傳送訊號的訊息，或是系統必須有前置序列。在傳輸通道是會變化的環境之下，倘若沒有追蹤通道變化量，效能還是會衰減。
因此，這篇論文的目的在於提出一個可以只用前導訊號就能同時做到補償共同相位誤差和估計出未知通道響應的演算法。達到這個目標的關鍵步驟在於，考慮一段合理時間內的通道穩定性和利用多個正交分頻多工訊符一起作估計。此外，在逆映射階段考慮具有頻率選擇特性的載波間干擾加上通道雜訊能量變化，在加碼系統上的效能會帶來增益。有關於在演算法實現上的一些實際考量也在內文裡有所討論。最後，我們也提供了模擬的結果來驗證提出的演算法的效能。

關鍵字

正交分頻多工系統 ； 相位雜訊

並列摘要

Applications of multi-carrier systems have increased extensively in recent years to cope with the need of high-data-rate transmissions. Orthogonal frequency-division multiplexing (OFDM) is a modulation technique wildly employed in wireless communication systems due to its advantages such as high spectra efficiency, robustness against inter-symbol interference (ISI) and multipath interference, etc. However, OFDM is extremely sensitive
to time-varying effects. In particular, phase noise, coming from unavoidable oscillator jitters, is a random perturbation that would result in two unwanted effects: common phase error (CPE) and inter-carrier interference (ICI). There were quite a number of research works in the literature that have been proposed to deal with the problem; yet, the assumptions of those methods, such as
the requirement of full knowledge on the channel and/or the
transmitted signals or the need of preambles, may be impractical for certain situations. Therefore, the purpose of this thesis is to propose an algorithm that can compensate the CPE caused by phase noise and estimate the unknown channel response jointly by using pilots only. The key step toward this feature is to exploit the channel stationarity within a reasonable time duration and to
perform joint estimation over several OFDM symbols. Improvements on the coded performance can be realized by incorporating the frequency-selective ICI-plus-noise energy profile in de-mapping. Several practical considerations of algorithm implementation are also addressed. Finally, simulation results are provided to demonstrate the performance of the proposed algorithm.

並列關鍵字

Orthogonal Frequency-Division Multiplexing ； Phase Noise

參考文獻

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[3] L. Piazzo and P. Mandarini, Analysis of phase noise e®ects in OFDM modems," IEEE

Trans. Commun., vol. 50, pp. 1696{1705, Oct. 2002.

[4] S. Wu and Y. Bar-Ness, OFDM systems in the presence of phase noise: Consequences