多項式系統的鑑別與等化

Abstract

在許多通訊系統中，由於使用高功率放大器(HPA)之類的非線性元件而有著非線性的特性。非線性通道和它的預、後處理濾波器的組合有時可以模組化成一個多項式的濾波器，就像是一個Volterra型式的濾波器。這篇論文探討一些Volterra系統的鑑別和等化。 我們的第一個主旨就是衛星TDMA系統。如同我們所知，由於在衛星轉頻器上的高功率放大器有著非線性的特性，所以要有一個適當的輸入退據(input backoff)來保證系統在線性的操作下。而頻寬需求的日漸增加和節省輸出功率的要求導致高功率放大器必須得操作在飽和區，這引起頻寬限制信號的失真。我們建議有通道編碼和沒有通道編碼的解決方案圴利用非線性的特性來增進地面接收器的效能。之後，我們考慮一個衛星CDMA系統，並採用與之前相同的理論來做接收器的設計。我們發現我們的方法能有效的消除非線性的失真並同時壓低多重接進干擾和窄頻干擾。 我們的最後一個應用例子就是一個正交分頻多工技術(OFDM)。在OFDM系統中的一個主要設計上的困擾就是它有著高的尖峰對平均功率比和非線性的失真。我們分別提出了在時域和頻域上的補償方法。最後有等化器的系統和沒有等化器的系統相比較，前者的確提供了顯著的改善。

Many communication systems exhibit nonlinear behavior due to the presence of nonlinear devices such as high power amplifiers (HPA) in the system. The combination of a nonlinear and its pre-processing and post-processing filters can sometimes be modeled as a polynomial filter, in particular a Voterra-type filter. This thesis investigates the identification and equalization of some Voterra systems. Our first topic has to do with satellite TDMA systems. As is well-known, due to the nonlinear characteristic of the HPA onboard a satellite transponder, an appropriate input backoff (IBO) is often needed to guarantee a linear operation. Increasing demand for bandwidth and the desire to conserve energy lead to the HPA being driven at or near saturation, resulting in distortion of the band-limited signals. We suggest both coded and uncoded solutions that make use of the nonlinearity to improve the ground receiver performance. We then consider a code division multiple access (CDMA) satellite system and apply the same principle to ground receiver design. We find that our approach is effective in eliminating nonlinear distortion and suppressing both multiple access interference (MAI) and narrowband interference (NBI). Our last application example is a wireless orthogonal frequency division multiplexing (OFDM) system. One of the major design problems of an OFDM system is its large peakto- average ratio and the associated nonlinear distortion. We present both time-domain and frequency-domain compensation approaches. The resulting equalizers do provide significant improvement over unequalized systems.