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Performance Analysis of Asynchronous Multi-carrier DS-CDMA System Using Different 2-D Spreading Codes in Fading Channels
|關鍵字:||MC DS-CDMA;多載波直接序列展頻分碼多工;2D OVSF code;二維正交可變長度展頻碼||出版社:||電機工程學系||摘要:||
近年來由於消費者對於無線傳輸服務之需求快速的增加，使得無線通訊產品製造商不得不提供更新更好的產品來滿足消費大眾，因此第二代行動通訊IMT-2000應運而生，在眾多的提案中，WCDMA被認為是最有希望成為第三代行動通訊的提案之一，而未來下一代則是預計採用多載波調變技術。在本篇論文當中，一種新的二維展頻碼的架構被提出來應用在多載波直接序列展頻分碼多工的系統上，我們稱之為二維正交可變長度展頻碼2D OVSF code，展頻碼的正交性被應用來提高頻寬的效率以及直接序列展頻分碼多工系統上抑制干擾的能力。在本文中我們探討二維正交可變長度展頻碼與其他的展頻碼在不同的通道中使用MRC或EGC接收端的表現。
In this thesis, a multi-carrier direct-sequence code-division multiple-access (MC DS-CDMA) system is studied, in which each user is assigned a set of mutually orthogonal multiple spreading-factor code sequences. The code set is here designated as two-dimensional orthogonal variable spreading factor (2-D OVSF) codes because the codes can be generated by the tree structure commonly used by VSF codes and preserve orthogonality among code sequences with different spreading factors in the code tree. Our analysis shows that interference created by our OVSF codes is minimal and our system has better performance than that of the multi-carrier system using single spreading sequence in non-fading channels. On the opposite, the system performance is identical to multi-carrier systems employing a single spreading sequence per user because orthogonality of the OVSF codes is destroyed in Rayleigh fading channels. We also analyze the system performance under the Rician fading assumption when the fading effect is relative small and the phase distribution in each frequency band is no longer uniformly distributed over . Finally, the performances of three different kinds of code sets─ one-dimensional (1-D) Gold codes, 2-D random codes, and 2-D OVSF codes─ in receivers employing the equal-gain combining (EGC) and maximal-ratio combining (MRC) methods (commonly used in wireless RAKE receptions) are compared.
|Appears in Collections:||電機工程學系所|
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