正交分頻多工(Orthogonal frequency-division multiplexing,OFDM)系統中，在傳送端有嚴重的高峰均值比(Peak-to-Average Power Ratio,PAPR)的問題，因此對如何改善PAPR是個必須面對的議題。過去幾年，已經有很多技術被提出來降低OFDM訊號的PAPR問題，其中壓縮轉換(companding transform)也是常被拿來使用的技術之ㄧ，它的主要優點是計算複雜度低。在傳送端，壓縮轉換技術能有效的降低PAPR，但在接收端會因為訊號的還原，使得雜訊跟著一起被放大，導致符元錯誤率(Symbol Error Rate ,SER)提升。\\n本論文，我們研究一個可變的hyperbolic tangent companding，以PAPR與SER的表現做為性能的評估。透過OFDM系統結合M-QAM調變進行模擬分析，我們設計了一個以PAPR與SER性能為指標的判斷式，以探討hyperbolic tangent companding的適當參數。利用這個參數來進行模擬結果，在PAPR與SER表現衡量下會有較佳的性能表現。 ;One drawback of orthogonal frequency-division multiplexing (OFDM) is high peak-to-average power ratio (PAPR) at the transmit terminal, which leads to an important issue to study how to reduce high PAPR for OFDM. There have been many PAPR reduction approaches proposed to reduce the PAPR of OFDM signals in the past decade. The companding transform method is one of attractive methods because of the advantage of low computational complexity. Although the companding approach can effectively reduce PAPR with a proper nonlinear compression function at the tramitter, the symbol error rate (SER) perfomance is seriously degraded because of noise amplification due to the expanding characteristics of the inverse of the compression function at the receiver.\\ In this thesis, a variable hyperbolic tangent companding function is studied to take PAPR and SER into joint consideration for a practical performance tradeoff. Through theroretical anlaysis of the PAPR and SER performances of M-QAM for OFDM with the inverse hyperbolic tangent function for the expander, we design an index for joint consideration of PAPR and SER performances to explore a proper parameter for guiding the hyperbolic tangent companding function. Simulation results show that with the index, the proposed PAPR reduction method has a well tradeoff of the PAPR and SER performances.
