正交分頻多工系統(OFDM)是一種新的調變技術，專門用在高速率的資料傳輸上，特別是在頻率非選擇性通道(Frequency-Selective Channel)下，可以克服碼際干擾(Inter-Symbol Interference, ISI)的影響，然而這種新的傳輸技術尚存在一些關鍵問題必須克服，平均功率峰值比(PAPR)過高是其中一項很嚴重的缺失，這主要是由於放大器線性區域有限，使得訊號在放大後的失真。平行組合正交分頻多工系統(Parallel Combinatory OFDM Signaling, PC-OFDM)是一種可以同時提高頻譜效益、降低錯誤率(BEP)又達到降低平均功率峰值比的新方法。它是根據資料的型式，決定那些子載波振幅為零那些不為零以達到降低PAPR的目地。但此種方法最大的缺點是會因封包偵測(Envelope Detection)錯誤而影響錯誤率的效能。我針對這項缺點提出有效的改善方法，稱之為編碼平行組合正交分頻多工系統(Coded Parallel Combinatory OFDM Signaling, CPC-OFDM)，此種方法是以二階段的調變方式來達成；第一階段是針對決定載波型式的位元加以編碼以降低封包偵測錯誤的機率，到了第二階段則是將碼字打散到各個載波上結合資料位元一起傳送。這個方法不但能有效的降低平行組合正交分頻多工系統的錯誤率同時提供了更佳的頻譜效益。 The OFDM system is a new modulation scheme. It usually use for high speed data transmission, especially on Ricean fading channel, to overcome intersymbol interference. However, this new transmission scheme has a large peak-to-average power ratio (PAPR), which can result in significant distortion when transmission through a nonlinear power amplifier. Parallel Combinatory OFDM system (PC-OFDM) is a new scheme which has lower peak-to-average power ratio, higher bandwidth efficiency, and lower bit error probability. Although, the PC-OFDM system can effectively lower PAPR, the bit errors mainly result from erroneously selected subcarriers. This paper proposed a new scheme, which can effectively improve the performance of PC-OFDM, called CPC-OFDM. The CPC-OFDM system uses two stage modulations to achieve the goal of decreasing BEP. In the first stage, CPC-OFDM system use block coding on the PC-bits which decide the type of subcarriers. In the second stage, it uses ordinary PC-OFDM for transmission. The scheme improves not only bandwidth efficiency but also power efficiency.
