基於隱含式通道狀態資訊回授以強化LTE下行多用戶多輸出入傳輸之通道估計

Abstract

本篇論文介紹LTE系統裡關於通道估計的問題，包括背景概念介紹、問題陳 述、演算法推導、以及程式模擬。有別於傳統上使用單一通道狀態資訊來做估計， 我們發展了一套基於多個通道狀態資訊的通道估計演算法。首先，我們從預先設 計好的預編碼矩陣群中選出一個接一個來編碼及傳送資料串流，然後我們會接收 到多個對應不同預編碼矩陣的通道狀態資訊回授。最後，我們使用這些通道資訊 狀態回授來做通道估計。在演算法的推導中，我們先推導對於通道不隨時間改變 的通道估計方法，接著我們將這個方法擴展到適合通道隨時間改變的情況。由於 在我們的方法中有最佳化的問題，所以計算的複雜度較高但估計的結果較準確。 在模擬的部分，我們建立一個合理的LTE下行多用戶多輸出入傳輸的系統模型， 在瑞利衰減(Rayleigh fading)通道下得到的數據來驗證此演算法，接著我們討 論此演算法中的參數設定以及測試此演算法在不同預編碼方法與車速下的表現。

This thesis introduces the topic about channel estimation, including background introduction, problem formulation, algorithm derivation and simulation, in LTE system. We develop an channel estimation algorithm based on multiple CSI feedbacks other than one CSI feedback in convention. We first transmit data streams with our pre-designed precoding matrices one after another, and then receive CSI feedbacks corresponding to different precoding matrices. Finally, we use these CSI feedbacks to perform channel estimation. In algorithm derivation, we derive a channel estimation method for time-invariant channel and then extend it to be suitable for time-variant channel. Because of the optimization problem in our method, the computation complexity is higher but the estimation result is more accurate. In simulation, we establish a reasonable downlink MU-MIMO system model in LTE specification and then simulate our proposed estimation method under Rayleigh fading channel to verify its performance. Moreover, we discuss parameters setting in our method and test it with different precoding schemes at different mobile speed.