多輸入多輸出OFDM與無合成器LINC-OFDM系統之遞迴偵測與解碼

Abstract

在多輸入多輸出的系統中，軟性映射器渦輪等化接收器設計上的一個重要運算。但很不幸的是最佳的軟性映射需要很高的複雜度，因此具備低複雜度又效能不錯的最小均方誤差軟性映射器便成了一個替代方案。在這篇論文中，我們首先考慮傳統多輸入多輸出OFDM系統的渦輪等化接收器，我們提出兩個方最小均方誤差軟性映射器兩個改進方案，其主要的做法是在將連續干擾消除的概念置入軟性映射當中。接著，為了降低等化的複雜度，我們提出一個最大比率合成的軟性映射器。模擬結果顯示我們所提出的最小均方誤差軟性映射器可以在與傳統最小均方誤差軟性映射器相同的複雜度下達到更好的錯誤率，而最大比率合成器也可以在低一個階數複雜度的情況下達到與傳統最小均方誤差軟性映射器類似的錯誤率。接著，我們探討無合成器之使用非線性元件線性放大OFDM系統。我們提出一個方法把BCJR解碼器解出的軟性位元放入遞迴干擾消除，透過模擬發現這樣的遞迴解碼方式在錯誤率上會遠比傳統OFDM系統表現得好。

A key operation in turbo equalization (TEQ) of MIMO systems is the soft-input-soft-output demapping. Unfortunately, optimum demapping requires a prohibitively high complexity. The MMSE demapper, with good performance and lower complexity, is known to be an effective remedy. In this thesis, we first consider the turbo equalization in MIMO-OFDM systems. We propose two methods to improve the performance of the MMSE demapper. The main idea is including ordered-successive-interference-cancellation (OSIC) in the demapping process. To further reduce the complexity, we also propose a maximum-ratio-combining (MRC) demapper. Simulation results show that the proposed MMSE demapper achieves much better performance while the complexity is the same and the proposed MRC demapper have a complexity an order less than that of the MMSE demapper while the performance remains similar. We then consider the iterative decoding of combinerless (CL) linear-amplification-with-nonlinear-component (LINC) OFDM systems. Taking the soft decoding result of the BCJR algorithm, we include a partial interference- cancellation (IC) scheme in the iteration. Simulations show that the proposed CL-LINC-OFDM receiver significantly outperforms the conventional one.