IEEE 802.16e 與 802.16m OFDMA 下行通道之線性最小均方差通到估計

Abstract

正交分頻多重進接(OFDMA)技術近來在行動環境中廣受注目且已經應用在 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 及窄頻干擾的能力。我們聚焦在IEEE 802.16e 與 802.16m OFDMA 下行傳輸的 通道估測部分。 本篇論文採用兩種通道估測方法。第一種為進階4 點群線性內插法，首先我 們使用最小平方差的估測器來估計在導訊上的通道頻率響應，這是為了硬體的計 算方便。最後我們在頻率域上使用線性內插法來得到在資料載波上的通道響應。 第二種為線性最小均方差通到估測法，首先我們使用線性內插法來估計在導訊上 的通道頻率響應，其次估計延遲參數，再利用指數函數的功率延遲曲線求出自相 關函數，最後根據自相關函數做線性最小均方差以估測出資料載坡上的通道響 應。我們先在AWGN 通道上驗證我們的模擬模型，然後分別在IEEE802.16e 與 802.16m 兩種標準下於多重路徑通道上模擬。 在本篇論文中，我們首先簡介IEEE 802.16e 與 802.16m OFDMA 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。

OFDMA (orthogonal frequency division multiple access) 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 and narrowband interference. We focus on the OFDMA downlink channel estimation based on IEEE 802.16e and 802.16m. We present two channel estimation methods. One is advanced 4-point linear interpolation. First, we use LS estimator on pilot subcarriers because of its low computational complexity. Second, we estimate the channel response in the middle of the pilot location in the time domain. Finally we estimate the channel response on data subcarriers using linear interpolation in the frequency domain. The other method is LMMSE channel estimation, First, we use LS estimator on pilot subcarriers, and do linear interpolation at the pilot location in time. Second, we estimate the delay parameters. Third, 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 model on AWGN channel and then do the simulation on multipath channels for IEEE 802.16e and 802.16m. In this thesis, we first introduce the standard of the IEEE 802.16e and 802.16m OFDMA downlink. Then we describe the channel estimation methods we use and discuss the performance in each transmission condition for IEEE 802.16e and 802.16m.