使用頻帶保留法降低正交分頻多工訊號功率峰均比之性能評估

Performance Evaluation of Tone Reservation Technique in PAPR Reduction of OFDM Signals

曾奎皓(KUEI HAO TSENG)

指導教授 ： 李穎

元智大學/工程學院/通訊工程學系/碩士(2004年)

摘要

使用頻帶保留法降低正交分頻多工訊號功率峰均比之性能評估
學生: 曾奎皓 指導教授:李 穎 博士
元智大學通訊工程研究所
摘要
OFDM訊號具有高功率峰均比的特性，造成訊號對功率放大器非線性的容忍度低，降低放大器的功率效率。將部份頻帶保留不傳送資料訊號，且於保留頻帶傳送可降低峰值功率的訊號，可達到降低功率峰均比¬¬¬¬¬而不會造成訊號失真的效能。本論文探討以頻帶保留法降低功率峰均比的技術。因保留頻帶訊號不用符合資料頻帶訊號的調變格式，可傳送任意可降低峰值功率的訊號，若保留頻帶訊號功率佔OFDM訊號總平均功率百分比太高時，會影響功率峰均比作為性能指標的客觀性。本論文提出較合理的性能指標:peak to average data power Ratio(PADPR)，和訊號經放大器後之功率頻譜符合頻譜遮罩所需之功率反減值（Backoff）。功率反減值較能直接反應降峰均比方法成效。本論文並提出一種演算法求出保留頻帶訊號，稱為Sinc Reduction。以電腦模擬，將論文提出的演算法和文獻中的梯度演算法[Tel95]，實現在IEEE 802.11a的規格中，探討這兩種演算法在新的性能指標下產生的增益。結果顯示:sinc reduction法降低峰值功率略有成效。梯度法可能會因發散而使保留頻帶功率過高，訊號峰值與均值功率均上升，PAPR雖下降並無降峰值功率成效。新指標（PADPR及Backoff）較原本指標更能確實評估保留頻帶法的性能。

關鍵字

正交分頻多工訊號 ； 頻帶保留法 ； 功率峰均比

並列摘要

Performance Evaluation of Tone Reservation Technique in PAPR Reduction of OFDM Signals
Abstract
The high peak-to-average power ratios (PAPR) of OFDM signals lead to sensitivity of power amplifier nonlinearities and decreased amplifier power efficiency.This thesis studies the tone reservation technique, where some subcarriers are reserved to transmit symbols for peak power reduction. The reserved subcarriers can transmit any symbols, and are not limited by data’s modulating format. When the percentage of the reserved tone power in OFDM signals’ average power is too high, PAPR will no longer be a faithful performance index. We employ two performance index that are more reasonable. One is the Peak-to-Average Data Power Ratio(PADPR). The other is the backoff required to satisfy the spectrum mask after the signal is passed through the amplifier. This backoff can reflect the performance of tone reservation technique more directly. A simple method called sinc reduction algorithm is proposed to calculate the reserved tone symbols in this thesis. We perform computer simulations with the sinc reduction algorithm and existing gradient algorithm for IEEE 802.11a OFDM signals, and discuss these two algorithm’s gain using the proposed performance index. The results show limited effect of sinc reduction algorithm in reducing peak power is not very good. The gradient algorithm may diverge to make the power of reserved tone too large, and both the peak and the average power become large even though the PAPR is reduced. There is no effect in terms of peak power reduction. The PADPR and the required backoff can better reflect tone reservation technique’s performance compare to the original index, PAPR.

並列關鍵字

HASH(0x96396b4)

參考文獻

[Che03]程國祥,”以編碼降低正交分頻多工訊號之功率峰均比,”元智大學碩士論文,2003

[Chi03]Chin-Liang Wang ,Yuan Ouyang , Hsien-Chih Chen,”A Peak-to —Average Power Ratio Reduction Technique for the IEEE 802.11a Wireless Lan” , Institute of Communications Engineering, National Tsing Hua University Hsinchu , Taiwan 300 , Republic of China.

[Chy03]陳意婷,”以相位變化降低正交分頻多工訊號峰均比,”元智大學碩士論文,2003

[Law99] Lawrey, E.; Kikkert, C.J.,” Peak to average power ratio reduction of OFDM signals using peak reduction carriers” Signal Processing and Its Applications, 1999. ISSPA '99. Proceedings of the Fifth International Symposium on , Volume: 2 , 1999

[She02]申家玲,”802.11a傳輸端減少非線性效應之訊號預先處理,” 元智大學碩士論文,2002