序列之轉換域產生法及其在多輸入多輸出正交分頻多工系統之應用

Abstract

多輸入多輸出系統(MIMO)搭配正交分頻多工(OFDM)技術具有相當大的潛力可以達到更高的傳輸容量，在實際系統方面已有相當多的研究成果，但仍有一些關鍵性的議題待克服。本論文重點在於MIMO-OFDM系統所需的前置訊號設計。

在本論文中，我們提出一系統化的轉換域序列產生法；此方法可以產生一組具有良好自相關(autocorrelation)與互相關(cross-correlation)性質的序列。這些序列也可由有限訊號群集點(finite constellation points)經由反向離散傅利葉轉換來產生。一些已有的序列可以用我們所提出的方式產生，然而我們提出的序列較舊有者受較少的限制。基於我們所提出的概念，這些建立一維序列的方法可以輕易地延伸到多維陣列序列(multi-dimensional array sequences)的建構。

利用本文所介紹的新序列，我們提出了可用於MIMO-OFDM系統的前置信號結構；我們也討論了基於此結構對應的頻率漂移估測以及通道估測演算法。由電腦模擬的結果可知我們所提出的作法的確達到了最佳的效能表現。

Multiple antenna based Multiple-Input Multiple-Output (MIMO) systems employing Orthogonal Frequency Division Multiplexing (OFDM) have the potential of achieving the capacity promised by information theoretical prediction. Though much progress toward a practical high rate MIMO-OFDM system has been made, many related system design issues remain to be settled. This thesis sets forth to solve the critical issue of the preamble design for MIMO-OFDM systems.

We present a systematic method based on the frequency (transform) domain characterization to generate a new family of sequences with the desired autocorrelation and cross-correlation properties. Sequences having the desired properties can then be generated by taking inverse transform of some finite constellation points (BPSK, QPSK, ... etc.). We also demonstrate that some existing sequences can easily be generated by our approach but our new family of sequences renders less constraints. The proposed approach can easily be extended to synthesize two dimensional arrays or even higher dimensions waveforms that possess the desired multi-dimensional correlation properties.

A preamble structure based on our new sequence family is suggested and algorithms for frequency offset and channel estimations in MIMO-OFDM systems are developed. Both theoretical analysis and computer simulation show that these algorithms yield optimal performance.