訊框展頻分碼多工在多使用者同時且同步傳收系統中，用以解決 傳統分碼多工系統無法克服的使用者間干擾與接收器硬體複雜度過 高的問題。在本篇論文，先對舊有的訊框展頻系統接收器做些微的修 正，再將主題延伸至現實情況中會遇到的多使用者同時但非同步傳輸 造成的多使用者間干擾，我們提出了三種方法來解決：第一種為展 頻、解展頻碼的設計，方法二為利用循環字首與字尾的插入，第三為 序列式多使用者間干擾消除法，這三種方法都能有完美消除干擾的能 力。另外，在頻域等化通道時須得知通道脈衝響應參數，故在最後我 們針對訊框展頻系統設計一個簡易通道估計法則。 Using mutually shift orthogonal spreading codes, block spread code division multiple access (BS-CDMA) systems have been developed to perform multiuser interference (MUI) free reception in order to reduce the complexity of a receiver assuming the signals of all users arrive at the base station synchronously. In practice, imperfect synchronization destroys the orthogonality among users and causes MUI. In this paper, we present three methods to reduce the MUI due to quasi-synchronous reception. At first, we introduce the design of spreading and despreading codes. Second one is using cyclic prefix and cyclic suffix to maintain orthogonality of spreading and dispreading codes. The last one is the successive MUI cancellation (SMC) method. All of them can be shown to achieve the performance close to that of a synchronous system, while maintaining a low receiver complexity. In addition, we also explore a method to estimate channel impulse response.
