在正交分頻多工系統中，高峰均功率比實為一大問題，由於比平均訊號準位高的瞬間尖峰訊號產生的高峰均功率比效應，會降低高功率放大器的效能。現今有許多技術已被發展用來抑制產生高峰均功率比的機率，其中一種方法即為頻道預留技術。頻道預留技術是利用預留部份的子載波通道，載送消減峰值訊號降低其傳送訊號的峰值，改善傳送端峰均值功率比。
一般而言，當頻道預留技術的裁剪臨界值設定愈低，峰值消除的效果愈高，抑制高峰均功率比效應愈好。可是，臨界值一旦設定過低，卻可能導致其它新的峰值訊號產生，反而無法達到降低高峰均功率比的預期效果。由此可知訊號的振幅臨界值設定對其峰均功率比也會有所影響；因此，我們利用頻道預留技術提出改良的裁剪方法，降低其高峰均功率比的產生。
在本論文中，基於最小平方近似法提出兩段式截波技術，改善因低裁剪臨界值造成峰值訊號重生，無法有效消減峰值訊號的問題。最後的模擬結果顯示出兩段式截波之頻道預留技術不但改善了訊號裁剪雜訊比與傳統單一裁剪技術兩種方法的峰均功率比，而且在比較相同的降低峰均功率比效能下，本論文提出的兩段式截波比單一裁剪的最小平方近似法的疊代次數少，因此兩段式截波大約只需單一裁剪整體運算量的54 %。

Orthogonal frequency division multiplexing (OFDM) system suffers from high peak to average power ratio (PAPR). The high PAPR lead to low power efficiency at the high power amplifier. Several techniques have been devised to reduce PAPR. One popular technique is Tone Reservation (TR) where PAPR is reduced by using reserved tones to generate a peak-canceling signal. In general, the lower PAPR is expected when the clipping level is set as lower as possible. However, the existing TR scheme has an associated the new peak re-growth which prevents achieving maximum PAPR reduction. This newly generated peak is due to the severely low clipping level used in TR.
In this paper, we propose a two-level clipping approach based on least square approximation (LSA) algorithm to combat the new peak re-growth. The simulation results show that our modified technique achieves a better PAPR reduction than signal to clipping noise power ratio (SCR) and LSA algorithm. In addition, the computational complexity of our proposed scheme does not increase owing to adjusted clipping threshold. To achieve the same PAPR reduction, it requires almost 54% computation of LSA-TR scheme due to less iterations used in our scheme.

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