應用剪枝快速傅利葉協助降低峰均值計算之研究

STUDIES OF REDUCTION OF COMPUTATIONAL COMPLEXITY FOR THE REDUCTION OF PAPR BY USING PRUNING FFT

葉晉廷(Chin-Ting Yeh)

指導教授 ： 許超雲

大同大學/電機資訊學院/通訊工程研究所/碩士(2012年)

摘要

正交分頻多工系統，為多載波調變通訊系統，擁有高傳輸效率、抗多重路徑和窄頻信號干擾等等的優點，經常被運用在各種通訊系統上面。OFDM最大的缺點是會產生高峰均值比。當N個調變載波在相同相位相加，會產生N倍峰值的OFDM訊號，而產生較高的「峰值對均值比」。高峰均值比會造成放大器產生非線性反應，需要花費高成本解決。
為了解決這個問題，有許多的方法被提出來解決，其中由許超雲教授團隊研究所提出DFT整形方法[1]，在降低PAPR有顯著的效果。其方法需要加入一組較短點數DFT矩陣，打散資料，降低資料相關性[2]。這個過程會附帶著高複雜度的計算。本論文以802.11a為例，藉由使用剪枝法及基數為4之快速傅利葉和反快速傅利葉之間的共軛關係，去降低其運算的複雜度。在運算量方面，複數乘法降低10%及複數加法降低28%

關鍵字

峰均值功率比 ； 剪枝 ； IEEE 802.11a ； DFT整形法

並列摘要

Orthogonal frequency division multiplexing (OFDM) is multicarrier modulation technique. It has many advantages like high-speed data transmission and combat the frequency selective fading channel, usually used in many communication systems. One major drawback of OFDM is the high peak-to-average power ration. When N modulated subcarriers are added with the same phase, the peak power is N times the average power of the OFDM signal. The high PAPR will cause the power amplifier operated in the nonlinearity region. It need cost a large amount of money.
Many ways are proposed to solve the problem of PAPR. Chau Yun Hsu’s group on Tatung University, Jan 20008 presented the DFT-Shaping Scheme[1]，used for reduction of PAPR . The simulations results show that DFT-Shaping scheme have significant reduction of PAPR. It required a shorter bank of DFT-shaping matrices to generate low-correlation constellation sequences to let data relationship lower. [2]This process will need high computational complexity. In this thesis, we take 802.11a as an example, using pruning and the relationship between FFT and IFFF to reduce the computational complexity. The results of analysis show that proposed scheme could reduce 10% in the number of complex addition and 28% in the number of complex multiply.

並列關鍵字

DFT-Shaping Scheme ； PAPR ； IEEE 802.11a

參考文獻

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[5] Hsinying Liang, Zhe Lin , Houshou Chen, and Cheng-Ying Yang, " A modified genetic algorithm PTS technique with error correction for PAPR reduction in OFDM system," International Symposium on Information Theory and its Applications (ISITA), pp. 1050-1053, Oct. 2010.

[6] Jyh-Horng Wen, Gwo-Ruey Lee, Chih-Chung Kung ,and Cheng-YingYang" Coding Schemes Applied to Peak-to-Average Power Ratio (PAPR) Reduction in OFDM Systems," International Conference on Wireless Communications and Mobile Computing 2008. pp. 807-812, Aug. 2008.

[7] A. Mobasher , and A.K. Khandani, "Integer-based constellation-shaping method for PAPR reduction in OFDM systems," Communications, IEEE Transactions on. pp. 119-127, Jan. 2006.