以快速富立葉轉換為基礎之DS-CDMA多用戶偵測接收機架構之設計與模擬

Abstract

多重進接干擾(Multiple access interference，MAI)是影響直接序列展頻多重進接(DS-CDMA)系統容量與效能的重要因素，多重進接干擾是指直接序列用戶之間的干擾。這種干擾源於用戶之間的展頻碼無法達到完全的正交性。任何單一位用戶所造成的多重進接干擾通常很小但隨著用戶訊號功率增加或是用戶的人數增加，多重進接干擾是相當可觀的。傳統的DS-CDMA接收機沒有考慮多重進接干擾的問題。由於用戶之間存在多重進接干擾，所以一個較為適當的接收機是加入多用戶偵測或稱多用戶干擾消除機制的接收機。 本論文中提出一以快速富立葉轉換為基礎之DS-CDMA多用戶偵測接收機架構。在此架構中，我們將通道量測接收機，領航訊號干擾消除，展頻碼匹配濾波器，通道匹配濾波器，以及多用戶干擾消除機制整合於同一接收機系統中。因為在頻域上實現匹配濾波器，所以接收機不需要做通道路徑搜尋(Path searching)和展頻碼相位追蹤(Code phase tracking)，但接收機需要知道正確的資料位元時間(Symbol timing)。我們將於分別在靜態通道(Static channel)和動態通道(Mobile radio channel)中模擬多用戶環境下接收機的效能。

Multiple access interference (MAI) is a factor which limits the capacity and the performance of DS-CDMA systems. MAI refers to the interference between direct-sequence users. This interference is the result of the random time offsets between signals, which make it impossible to design the code waveforms to be completely orthogonal. While the MAI caused by any one user is generally small, as the number of interferers or their power increases, MAI becomes substantial. The conventional receiver does not take into account the existence of MAI. Because of the interference among users, a better receiver is one of multi-user detection (or multi-user interference cancellation) receiver. In this article, we propose an FFT-based DS-CDMA multi-user detection receiver architecture. In this architecture, we integrate channel estimation, pilot signal cancellation, code match filter, channel match filter, and multi-user interference cancellation in a single receiver system. Moreover, due to FFT-based matched filtering, no path searching and code phase tracking are needed. Only correct received timing is required by the receiver. Monte Carlo simulation is used to evaluate the receiver performance in both a static channel and a mobile radio channel under multi-user environment.