本論文中將以正交分頻多工為基礎,我們在這裡使用的預先編碼都為正交碼, 例如哈達碼,而我們把正交碼分別使用在時域上和頻域上來做展頻,而我們稱之為二維展頻,而我們本篇論文把時間的展頻碼的維度固定為 ,而頻率展頻碼的維度是不固定的,如果頻率展頻碼的維度越大的話,那麼頻率分集增益就越強,所以這就是近幾年來展頻通訊為什麼如此的發達,而本篇論文最主要的主題是探討在接收機在做解碼,如何去降低複雜度,並且又能達到最好的效能,又不會比傳統最大事後機率還來的差,這就是我們所想要的結果。
而我們這裡所使用的通道環境是用雷利衰減通道,並且接收端是已知通道的情況下,而我們在接收端也把迴旋碼和渦輪碼的編碼技術加了進去,利用偵測器和解碼器來做軟資訊的交換,以達到最佳解。
而我們在這裡所提出的新式演算法,它的複雜度為 ,而我們所提出的演算法,最主要的特性都是降低傳統演算法所需要的高複雜度,和提高效能,並且我們也做了不同的調變,測試不同的負載,來觀察出展頻和非展頻的最佳化。

In this paper ,we based on OFDM for studying. And we used Hadamard code as precoder to increased frequency diversity ,then we employed the orthogonal code to use on both frequency domain and time domain to do spread ,so we call this process as two-dimentional spreading .In this article we fixed the time spreading factor ,then the frequency spreading factor is variable ,the diversity gain is very strong if the frequency spreading factor is vary larger .Because this reason ,then the spreading communication is so popular. We will explore the decoder how to decode in the receiver in this article, how to lower the complexity ,and must achieving the best performance ,such that the performance was not poor than MAP ,this result we want。
The channel model used in this research is a Rayleigh Fading channel, and then the channel model parameter is known on the receiver. We also added the Turbo code and convolution code in this technology, utilizing the soft extrinsic information to do exchange between detection and coder to achieve the optimum performance.
In this article, we proposed the novel algorithm, the complexity of the novel algorithm is , its major feature is to decrease complexity of conventional algorithms ,and enhanced the performance. In this process ,we also adjusted modulation level to test the system load ,and observed the optimal performance both spreading and non-spreading。

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