最近，正交分頻多工調變-分碼多重存取系統(OFDM-CDMA)在無線通訊廣範地被研究。在這篇論文裡，我們主要研究在瑞雷衰減通道下[1]，OFDM-CDMA系統使用MMSE等化器的偵測技術。我們提出了結合時間和頻率展頻方案：在時間和頻率領域二維的交錯展頻碼。這個方案得到時間分集(diversity)和頻率分集增益。我們比較未使用與使用二維交錯展頻碼系統的位元錯誤率的效能。我們也觀察了不同frame長度所能得到的效能；利用兩個複數高斯建立完全無相關性的通道，在相應CDMA系統的位元錯誤率下做為最低界限(lower bound) 。

　Recently, the combination of orthogonal frequency division multiplexing (OFDM) with code division multiple access (CDMA) is investigated widely in mobile radio communications. In this thesis, we study OFDM-CDMA detection techniques based on the minimum mean-square error (MMSE) equalization in modified Rayleigh fading model [1]. We propose a joint time-frequency spreading scheme: 2-D interleaved spreading sequences in both time and frequency domains. This scheme achieves both time diversity and frequency diversity gains. We compare the bit-error rate (BER) with and without 2-D interleaved spreading sequences. We also observe the BER performance of different frame lengths and use an independent complex Gauss process to model the fully uncorrelated fading, over which the corresponding BER of CDMA system can be served as a lower bound.

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