運用功率延遲輪廓近似之線性最小均方差通道估計於LTE下行時變通道傳輸

Abstract

正交分頻多重進接(OFDMA)技術近年來在行動環境中廣受注目，而且已經應用在許多數位通訊應用中。採用OFDMA一個最主要的原因是其抗頻率選擇性衰變的能力。在此篇論文中，我們聚焦於LTE與 LTE-A OFDMA下行通道估測部分。 本篇論文最主要採用的通道估測方法為線性最小均方差(LMMSE)通道估測法。在使用LMMSE通道估測法於多載波傳輸系統中，我們需要知道通道相關性函數。 這在參考訊號(RS)較少的傳輸系統中帶來了問題。為了解決這個問題，我們將通道的功率延遲輪廓做近似，使其可以完全被兩個通道延遲參數所定義，這兩個參數為初始延遲參數以及方均根延遲擴展參數。除此之外，我們發展了一個技術來估測這些參數。為了增進估測參數的準確度，我們引入了虛參考響應生成的概念來達成我們的目標。接著我們可以找到功率延輪廓遲近似所相對應的自相關矩陣。最後藉由這個自相關矩陣，使用LMMSE通道估測法來估計次載波上的資訊。我們藉由加成性白高斯雜訊通道來驗證我們的模擬程式以及通道估測方法，接著在幾個多路徑通道做模擬。 在本篇論文中，我們首先簡介LTE與LTE-A下行的標準機制。接著，我們依造兩種標準機制分別各傳輸情形下介紹所用的通道估測方法並探討其估測效能。

Orthogonal frequency division multiple access (OFDMA) technique has drawn much interest recently in the mobile transmission environment and been successfully applied to a wide variety of digital communications applications over the past several years. One of the main reason to use OFDMA is its robustness against frequency selective fading. We focus on the OFDMA downlink (DL) channel estimation based on LTE and LTE-A. The main channel estimation method is linear-minimum-mean-square-error (LMMSE) channel estimation in this thesis. In LMMSE channel estimation for multicarrier systems, one needs to know the channel correlation function. This brings up a problem for systems with a small number of reference signals (RSs). To solve this problem, we approximate the channel power-delay profile (PDP) that can completely be described in two channel delay parameters, i.e., the initial delay and the root-mean-square (RMS) delay. In addition, we develop a technique to estimate these delay parameters. For improving the accuracy of the estimated channel delay parameters, we employ an idea, producing pseudo RR, to meet our purpose. Then we find the autocorrelation function associated with the approximate PDP. Finally base on this autocorrelation function, do LMMSE filtering to estimate the data subcarrier response. We verify our simulation program and channel estimation methods on AWGN channel and then do the simulation on several multipath channels. In this thesis, we first introduce the standard of the LTE and LTE-A DL. Then we describe the channel estimation methods we use and discuss the performance in each transmission condition for LTE and LTE-A.