正交分頻多工系統中非資料輔助型頻率偏移估計之研究

正交分頻多工(Orthogonal Frequency Division Multiplexing OFDM)傳輸技術以高傳輸資料量與抵抗衰減通道的優異性能，使其在近幾年的通訊系統發展中，已被廣泛應用在各無線通訊系統、數位電視、數位廣播與無線網路等領域。正交分頻多工系統比一般的多載波傳輸系統更能有效的提高頻譜的使用率、解決通訊系統中的字符(Symbol)干擾現象和對抗多重路徑衰減等問題。但在正交分頻多工系統的通訊過程中，對於頻率偏移有很高的敏感度，容易造成正交分頻多工系統中各個子載波失去正交性，而喪失了原有的優異通訊性能。有鑑於頻率偏移問題對正交分頻多工系統的重要性，本篇論文比較及討論數種不同的非資料輔助型正交分頻多工系統之頻率偏移估計方法，所謂非資料輔助型即是不使用週期性導引信號或其他週期性的訓練信號來協助估計之方法。此外，我們也提出一個以虛擬子載波為基礎的ML估計方法。經由電腦模擬的結果可知，此方法在合理的訊雜比之情形下，得到令人滿意的結果。最後，提出對於正交分頻多工系統所使用之頻率偏移估計方法的建議。期望能對於將來想研究此一領域的同好有所助益。

關鍵字

載波間干擾；多路徑衰減效應；正交分頻多工

並列摘要

Orthogonal Frequency Division Multiplexing (OFDM) has been widely applied to several mobile radio communication systems, DVB, DAB, and Wireless LAN recently during the development of communication system. OFDM technique is an effective transmission scheme to cope with many channel impairments compared to other multi-carrier communication systems. For example, it offers better performance under multi-path fading channels, yielding higher spectral efficiency and may reduce the effects of inter-symbol interference (ISI). However, OFDM is highly sensitive to carrier frequency offset, which may easily cause each sub-carrier in the system to lose orthogonality and therefore lose its original outstanding performance. Owing to the importance of carrier frequency offset to OFDM, this paper, several non-data-aided frequency synchronization algorithms are compared. In addition , we propose a maximum likelihood (ML) estimation of the CFO in the presence of virtual carriers. Simulation results show that the proposed algorithm performs well for reasonable SNR values. This paper will be ended in the suggestion of frequency offset estimation of OFDM. This research is done under the expectation to be beneficial to future studies for the researchers who have the same interests in this field.

並列關鍵字

Inter-Carrier-Interference (ICI) ； Orthogonal Frequency Division Multiplexing (OFDM) ； Multipath Fading Channel

參考文獻

[1] Draft prETS 300401:1994, “Radio broadcast system: Digital Audio Broadcasting (DAB) to mobile, portable and fixed receivers”. 1994.

[4] B. Sklar, “Rayleigh Fading Channels in Mobile Digital Communication Systems Part 1: Characterization”, IEEE Communication Magazine, pp. 90-100, July. 1997.

[6] Kuchen,F.; Didascalou, D.L.; Wiesbeck, W. “Terrestrial network planning for digital vedio broadcasting to mobile receivers’,Vehicular Technology Conference, VTC98. 48th IEEE Vol.3, pp.1889-1893. 1998.

[7] Reimers, U. “DVB-T: The COFDM-Based System for Terrestrial Television,” Electronics and Communication Engineering Journal, Vol.9, No. 1, pp.28-32, Feb. 1997.

[10] IEEE 802.16ab-01/01r2. Air Interface for fixed broadband wireless access systems part A: Systems between 2 and 11 GHz.

國際替代計量

正交分頻多工系統中非資料輔助型頻率偏移估計之研究

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