利用適應性降峰值載波減小正交分頻多工之峰值對平均功率比

Abstract

由於正交分頻多工訊號的振幅會產生極大的動態範圍變化，導致訊號的峰值對平均功率比很大，而此比值若愈大會使傳輸訊號對於非線性失真愈敏感，造成功率放大器的效能降低與ADC及DAC的複雜度增加。為了解決峰值對平均功率比的問題，學者專家提出了很多不同種方法，其中Tone Reservation是一個用來降低峰值對平均功率比而不會破壞訊號本身的方法。 本篇論文採取Tone Reservation的概念並考慮了通道狀況的因素，以適應性的方式找出通道狀況最差的子載波作為降峰值載波來有效降低傳送訊號之峰值對平均功率比並使載波傳輸效率提升。 而在搜尋降峰值載波適當參數方面，我們主要是修改王的演算法以遞迴式的調整欲降低峰值的倍率β，使得每一個適應性降峰值載波都可以有效降低訊號的峰值對平均功率比而避免降峰值載波因無法降低PAPR而被捨棄浪費的情形發生。

Due to the large dynamic range of the OFDM signal, the peak-to- average power ratio (PAPR) can be very high. This large PAPR value will lead to severe nonlinear distortion, resulting in reduced efficiency of the RF power amplifier and increased complexity of the analog-to-digital and digital-to-analog converters. To reduce the PAPR, several techniques have been proposed, among them Tone Reservation is a technique which lowers the PAPR without distorting the signal. In this thesis, we investigate the technique of Tone Reservation and consider the effect of channel condition. Base on the channel condition, we adaptively choose the subcarrier with the worst channel condition to be our peak reduction carrier to effectively lower the signal PAPR and increase the efficiency of subcarrier transmission. In searching the proper value of the peak reduction carriers, we modified Wang’s algorithm to recursively adjust the percentage (β) we wanted to lower the peak value, so that each of the adaptive peak reduction carriers can effectively reduce the signal PAPR while avoiding the circumstance of wasting them if failed to reduce signal PAPR.