LTE-Advanced之下行多輸出入通道估計

Abstract

正交分頻多重進接(OFDMA)技術近年來在行動環境中頗受歡迎，並且已經廣泛地運用在許多數位通訊應用中。而採用OFDMA一個最主要的因素是其有優異的抗頻率選擇性衰減能力。在此篇論文中，我們主要探討長期演進技術升級版(LTE-Advanced)運用正交頻分多址的下行通道估計，並且介紹在多輸出入下的通道估計問題、演算法、分析及模擬等議題。 在通道估計中，首先我們在四傳一收的環境下利用參考訊號(reference signal)並使用最小平方差(least square)估計器來估計出其通道頻率響應，接著再用兩種方法來估計出整個通道的響應。第一種方法是利用線性內插來求得解。而第二種方法是用線性最小均方根誤差(LMMSE)，由於做線性最小均方根誤差通道估計需要知道通道相關矩陣，而其可以由兩個通道參數定義，分別為初始延遲參數及均方根延遲擴展參數，所以我們介紹了兩種方法來解出這些參數。 最後在程式模擬部分，我們在加成性白色高斯雜訊(AWGN)通道下驗證全部通道估計方法所得的結果，然後在數種不同的多路徑衰減通道中來測試其結果。

Orthogonal frequency division multiple access (OFDMA) technique is popular in recent years in the mobile transmission environment and has been generally applied to a wide variety of digital communications applications over the past several years. One of the main reasons to use OFDMA is its robustness against frequency selective fading. In this thesis, we focus on the OFDMA downlink (DL) channel estimation based on LTE-Advanced. We will introduce the subjects of channel estimation problems, algorithms, analysis of multi-path transmission in OFDMA with multi-input multi-output (MIMO) channel. In channel estimation, first we use least-squares (LS) estimator to estimate the channel frequency response by the reference signal (RS) in four Tx and one Rx transmission. Then we use two methods to estimate the overall channel response. The first method is linear interpolation. And the second method is linear minimum-mean square error (LMMSE). The LMMSE channel estimation needs to know the channel correlation function which can be described in two channel delay parameters, the initial delay and the root-mean-square (RMS) delay spread. We introduce two techniques to estimate these parameters. In simulation, we simulate all estimation methods under AWGN channel to verify its performance and then test them under different multipath fading channels.