在MIMO-OFDM系統中於時域上峰均值功率比之降低方法

Abstract

在多輸入多輸出正交分頻多工系統中，空頻碼已經有廣泛的研究與討論。在這篇報告中，在兩根傳送天線的情形下，我們討論的空頻碼是把低密度同位檢查碼與阿拉姆提碼串連連結而成。也基於此種空頻碼，我們提出一種如何簡單的降低峰均值功率比之技術。因為這個技術只需在時域上做運算，而不須要在頻域上來做運算，因此傳統上使用選擇性對應技術時，會有反向離散快速傅立葉轉換計算量很大的缺點，但在此技術下會大量的減低到只需要兩個。此提出的技術用在較少的候選數目時會比較優良，不但可以簡化系統而且也不會犧牲掉錯誤率，這些結果最後都會用電腦把它模擬出來。

We consider the problem of space-frequency (SF) codes design for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) modulation in frequency-selective Rayleigh fading channel. To combat frequency-selective channel and to provide a channel coding gain, we combine low-density-parity-check (LDPC) codes and Alamouti scheme. The resulting codes are shown to be capable of achieving the diversity and coding gain in multi-path fading channel. Also, a new method is proposed for the peak-to-average power ratio (PAPR) reduction of OFDM signals. Compared with the scheme of cross-antenna rotation and inversion (CARI), which utilizes additional degrees of freedom by employing multiple antennas. However, CARI requires invoking the IFFT process several times per transmitted OFDM symbol. The proposed method requires only two IFFT operations by using time domain modification. In case the number of candidates is not great (no more than 16), the proposed technique can significantly reduce the complexity without sacrificing the PAPR reduction capability and error performance. Simulation results verify the advantage of the proposed PAPR reduction technique.