標題: 無合成器之 LINC-OFDM系統最大似然偵測
Maximum Likelihood Detection for Combinerless LINC-OFDM Systems
作者: 許愷珊
Hsu, Kai-Shan
吳文榕
Wu, Wen-Rong
電信工程研究所
關鍵字: 無合成器;最大似然偵測;LINC;OFDM;ML
公開日期: 2010
摘要: 眾所周知,OFDM(Orthogonal Frequency Division Multiplexing; OFDM)系統的傳送訊號有很高的PAPR(peak-to-average power ratio; PAPR)值,因此其功率放大器(power amplifier; PA)需有較大的線性放大區使系統能正常操作,這造成PA為射頻(radiofrequency; RF)電路中最消耗功率的元件。LINC(Linear amplification with nonlinear component; LINC)技術為降低高PAPR系統功率消耗的方法之一,LINC系統可將輸入訊號利用效率較好的非線性放大器進行線性放大。然而,在LINC系統中有一關鍵的元件即功率合成器(power combiner),其設計及實現有最高的難度,為了避免使用合成器,有研究者提出了無合成器之LINC系統,但在非理想的通道條件下,無合成器之LINC系統效能很不理想。在本篇論文中,我們研究提出無合成器之LINC-OFDM系統,並提出一最大似然(maximum likelihood; ML)偵測演算法以改善其效能,使用我們的方法可以非理想的通道條件能有效地操作。模擬結果顯示,出我們所提出的演算法能有效的提升無合成器之LINC-OFDM的效能,在很多情況下甚至比傳統OFDM系統的效能表現更好。此外,我們也提出了數種降低ML運算複雜度的方法。
The transmit signal in Orthogonal Frequency Division Multiplexing (OFDM) systems is known to have high peak-to-average power ratio (PAPR). Due to this property, the power amplifier (PA) of the system must operate in a wide linear region, making it the most power-hungry device in the RF circuit. The linear-amplification-with-nonlinear-component (LINC) technique has been developed to reduce the power consumption in high-PAPR systems. By using the LINC architecture, nonlinear PAs with high power efficiency can be used to linearly amplify the input signal. However, a critical component in LINC transmitter, named power combiner, is difficult to design and implementation. To avoid the use of the combiner, a combinerless LINC system is later proposed. Unfortunately, the performance of the system is poor in some non-ideal channel conditions. In this thesis, we study the combinerless LINC-OFDM system and propose a new maximum likelihood (ML) detection algorithm to improve its performance. With the proposed algorithm, the LINC-OFDM system can be effectively operated in non-ideal channel environments. Simulations show the proposed algorithm can significantly enhance the performance of the combinerless LINC-OFDM systems. In most cases, the proposed algorithm can even outperform the conventional OFDM systems. We also propose several methods to reduce the computational complexity of the ML algorithm.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079813529
http://hdl.handle.net/11536/47015
Appears in Collections:Thesis