編碼無合成器之LINC-OFDM系統最大似然偵測

Abstract

正交多頻分工(OFDM)為一高效能的調變技術已廣泛的使用在各種通訊系統中。然而OFDM有一個主要缺點即傳送訊號有很高的峰值與平均功率比( peak-to-average power ratio, PAPR)，因此需要高線性度的功率放大器才能使系統正常操作，造成傳送機需要很高的功率。使用非線性元件之線性放大(Linear amplification with nonlinear component, LINC)技術為一降低PAPR的有效方法，LINC系統將訊號拆解成兩路並各經由非線性放大器後，再藉由功率合成器將兩路訊號合併，但功率合成器的在實現上有很高的難度，為了克服此問題有研究者提出無合成器之LINC系統，但是在非理想的通道條件下，無合成器之LINC系統效能會受到很大的影響。本篇論文旨在研究無合成器之LINC-OFDM系統，我們使用一編碼之無合成器之LINC-OFDM系統，並提出新的接收端等化與解碼的演算法，使用所提的方法此系統可以在非理想通道條件下可以有效的運作。模擬結果顯示，我們所提出的編碼無合成器之LINC-OFDM系可以與傳統OFDM系統有相同的效能表現，在某些情況甚至可以超越傳統OFDM。

Orthogonal frequency division multiplexing (OFDM), an efficient modulation technique, has been widely used in many wireless systems. One of the drawbacks of OFDM systems is its high peak to average power ratio (PAPR). Thus, the power amplifier used in the system requires high linearity, making its power consumption large. Linear-amplification-with-nonlinear-component (LINC) has been developed to solve the problem. LINC decomposes the signal into two components, amplifies the decomposed signals with nonlinear power amplifiers, and then combines them with a power combiner. However, the power combiner is known to be difficult to implement. To avoid the problem, the combinerless LINC system is proposed. Unfortunately, the performance of this system is seriously degraded in non-ideal channel conditionals. In this thesis, we study a coded combinerless LINC-OFDM system. We propose new equalization and decoding schemes for the coded system such that it can be effectively operated in non-ideal channel environments. Simulation results show the proposed system can have the same performance as the conventional OFDM system. In some cases, it can even outperform the conventional OFDM system.