非線性衛星CDMA接收器之系統設計與分析

Abstract

為了得到最大輸出功率，衛星上的高功率放大器（ＨＰＡ）通常運作在接近飽和點。 HPA非線性放大的特性會使輸入的訊號遭受扭曲而產生失真，由輸出訊號來看，有以下 兩種失真：輸出訊號振幅調變（ＡＭ╱ＡＭ）的失真，以及輸出訊號相位調變 （ＡＭ╱ＰＭ）的失真，尤其是後者對於相位調變的訊號造成的系統性能損失更為嚴重。 在本論文中，我們在以下三種情況中討論接收器的設計並分析模擬其性能表現。 （1）使用BPSK或QPSK調變的用戶環境。 （2）使用BPSK調變的直接序列展頻信號的多用戶環境。 （3）在BPSK調變的直接序列展頻信號在單一或多重用戶，且有窄頻干擾的環境。 由於介於傳送訊號的地面站與接收訊號的地面站之間的衛星通道為一個具有記憶性的非 線性通道，所以我們使用Volterra模型來描述這個衛星的通道特性，並分析在這樣的非線性 失真下不同的接收機架構之位元錯誤率來比較接收機的性能。

In order to attain maximum output power, the high power amplifie (HPA) on board a satellite usually operates near the saturation point. It is well-known that the nonlinear characteristic of an HPA will induce the so-called AM/AM and AM/PM effects. AM/PM introduces nonlinear phase rotation that is especially harmful to phase-modulated signals. The "satellite channel" between the input of the uplink transmitter filter and the transponder output constitutes a nonlinear channel with memory that must be dealt with by the downlink receiver. This thesis intends to provide receiver solutions for the following three operation scenarios: (i) single BPSK/QPSK user, (ii) multiple BPSK/QPSK-modulated direct sequence spread spectrum (DS/SS) users, (iii) multiple BPSK/QPSK DS/SS users in the presence of narrow-band interference(NBI). We use a Volterra model to identify the above-mentioned nonlinear channel and analyze the impacts of such nonlinear distortions on the performances of various receiver structures. We also analyzed and simulated the corresponding mean-squared error (MSE) and bit error probability (BEP) performances.