正交頻率多工訊號之低複雜度峰均值降低方法

Abstract

由於正交頻率多工(OFDM) 信號會使傳送時間訊號產生高峰均值 (PAPR)，讓系統的傳輸功率效能打了不少折扣。在許多種解決方案中，選擇性 映射(Selective Mapping) 及部分傳輸序列(Partial Transmit Sequences)算是比較 簡易可行的。然而，此兩種方法需要作多次的IDFT，其運算複雜度仍高，為提 升其可行性，簡化運算複雜度是必要的。現有大多數的簡化複雜度的方法似乎都 沒有考慮到快速傅立葉轉換(FFT)或反轉換（IFFT）的代數與硬體結構性質。我 們認為上述兩種降低峰均值方法若能一併考慮快速傅立葉轉換的結構將有助於 簡化其實現複雜度，提高其實用性。 在這篇論文中，我們依前述理念，提出新型的架構概念可以達到上述的目 的。目前現有的選擇性映射及部分傳輸序列均可藉由我們提出的兩種方法，達到 降低複雜度的目的。我們提的方法，除可降低運算複雜度之外，也能在相同複雜 度的前提之下，降低更多的峰均值。此外，我們又提出了一個可以提早結束計算 的機制，根據這個機制，可以節省更多的運算量。

One major problem with an orthogonal frequency division multiplexing (OFDM)system is high peak-to-average power ratio (PAPR) of the transmitter's output signals. To deal with it, several reduction scheme have been proposed and selective mapping (SLM) and partial transmit sequence (PTS) are two of them. Nevertheless, both two schemes incur high computational complexity and simplification is required. Although there are several works are devoted to the simplification, we find that most of them are designed without considering the structure of fast Fourier transform (FFT). It motives us to jointly design the PAPR reduction scheme and FFT.

In this thesis, we propose a concept to achieve this goal and several existed PAPR reduction schemes can be simplified with this concept. Here, two variant PAPR reduction schemes are considered and we will show that either the computational complexity can be reduced or we can get lower PAPR compared to the conventional schemes. In addition, a early stopping criterion is proposed to further reduce the computational complexity.