減少正交分頻多工系統之循環字首冗餘與消除衍生之符際干擾之研究

Abstract

正交分頻多工（OFDM）技術已經成為目前最流行的傳輸技術之一。使用 OFDM 的主要的原因是，在每個OFDM 符號的最前面加上循環字首（CP）可有效地處理出現在多路徑通道的符際干擾（ISI）。然而，CP 降低了帶寬效率和分散發射的能量。我們稱這種情況為「CP 的冗餘」。它是一種不被期望的現象，我們應該想辦法把傷害降到最低。 本篇論文探討了減少CP 冗餘的方案：透過在一個時隙中留下部分的CP， 除去其餘的，並且修改所述一般傳輸過程。並提出演算法於接收機端如何消除ISI和同等化。我們亦建議類似的傳輸結構，以利於減少等待時間。應用於LTE 系統的模擬顯示在符號錯誤率方面有優異的結果。

Orthogonal frequency division multiple (OFDM) technique has become the a most popular transmission technique. The main reason to use OFDM is that the method of including a cyclic prefix (CP) at the beginning of each OFDM symbol can effectively deal with inter-symbol interference (ISI) appearing in multipath channels. However, CP reduces the bandwidth efficiency and disperses the transmitter energy. This situation is called "CP overhead." It is an undesirable feasure which should be minimized. This thesis explores a scheme that achieves CP overhead reduction by leaving the portion of CPs and removing the remaining ones in a time slot, while modifying the general transmission procedure. The algorithms are proposed at the receiver for ISI cancellation and equalization. We also propose the resemble transmitted structure in order to reduce latency. Simulations show excellent results in terms of symbol error rate when applied to an LTE system.