Study on Code Selection Methods of MC-CDMA System under Carrier Frequency Offset and Multipath Fading Channel

[[abstract]]本論文探討MC-CDMA系統在載波頻率偏移與多路徑衰減通道環境下的一致序列選碼方法。研究發現展頻碼選擇方法會直接影響到系統的通訊性能，因為載波頻率偏移以及多路徑衰減通道造成展頻碼的正交性被破壞造成MAI。因此找出有效的選碼方法抑制載波頻率偏移以及多路徑衰減通道干擾產生的MAI為本論文主要的研究方向。本論文提出對展頻碼分組的方式使展頻碼在載波頻率偏移與多路徑衰減通道環境下依然可以維持展頻碼之間的正交性，並且提出先選組後選碼的新方法套用在MC-CDMA系統的選碼上，使用本論文提出的方法可以得到好的一致序列選碼結果並得到好的系統性能而且不必增加系統的硬體複雜度。[[abstract]]This paper illustrates that the multiple access interference (MAI) effect produced by carrier frequency offset (CFO) and multipath interference can be reduced, and performance can be heighten by consistent sequence code selection under the multi-carrier code division multiple access (MC-CDMA) system. Studies found that spreading code selection method will affect the system performance, because CFO and multipath interference destroy the orthogonal characteristic of spreading code. In this thesis, I propose a grouping method for spreading code which can still keep the orthogonal characteristic of spreading code under the CFO and multipath fading channel. And this research presents a new method which does the group selection first and then the code selection. The method can get a good result of code selection of consistent sequence. It can also get a good MC-CDMA system performance without increasing complexity of hardware.[[note]]碩