多重接取系統中某些使用者採用相同簽記之設計

Abstract

在本篇論文中，我們處理在多重接取系統下，某些使用者使用相同簽記(signature)時，會造成接收端無法正確得解出使用者的訊息，直接地影響系統下整體的吞吐量之問題，我們稱之為碰撞。首先，會回顧兩種多重接取系統的技術，分別為分碼多重接取系統(CDMA)以及交織多重接取系統(IDMA)，在分碼多重接取系統下使用者使用專屬的展頻碼做為簽記，而在交織多重接取系統下使用者是採用不同的交織器為簽記。接著我們會回顧前一屆的碩士論文中將交織多工接取系統的接收端結合廣義信道解碼聯合實體層網路編碼技術，來處裡碰撞的問題，雖然能有效的解決問題，但是實現的複雜度太高，因此我們提出一個新的方法稱做多點偵測法，計算碰撞用戶可能傳送訊息之組合的機率，並推導出新的接收端演算法，我們將新提出的方法應用在分碼多重接取系統以和交織多重接取系統下的碰撞問題，皆能夠得到效能的改善，而且大幅減少系統的複雜度。

In this thesis, we deal with the problem in the multiple access system that when many users transmit messages simultaneously, there are possibilities that some users use the same signatures. We call this condition as collision in this thesis. While the collision occurs, the system cannot successfully decode the users' messages and the performance is severely affected. We fist review two multiple access systems, Code Division Multiple Access(CDMA) and Interleave Division Multiple Access(IDMA). In a CDMA system, each user use a unique spreading code for signature. In a IDMA system, the signature is a user-specific interleaver. For improving the performance when collision occurring, the scheme in the senior thesis employs physical layer network coding(PLNC) technique in the IDMA system. This scheme not only decode the collision users' messages successfully but also improve the overall performance. However, IDMA system using PLNC is high complexity. Thus, we propose a new algorithm in the ESE function. This scheme allows lower complexity and solves the collision cases. The proposed scheme is called Multi-level detection(MLDT). Finally, We apply MLDT in a CDMA system when more than one user uses the same signature and it also obtains the improving performance.