LTE上行通道估測技術之研究

Abstract

無線通訊在未來通訊的發展佔了很重要的地位，其中更以WiMAX(IEEE)跟 LTE(3GPP)這兩個分支為基礎個別發展；雖然大致上這兩個系統十分相似，但最 主要的差異就在於LTE在上傳採用的是單載波分頻多工存取(SC-FDMA)的技術。 有別於WiMAX 所使用的正交分頻多工存取(OFDMA)，其優點在於能降低峰均 值比(PAPR)而使手機端(MS)的電池壽命更久、更省電，因而延長使用時間。本 篇論文介紹LTE 單載波分頻多工存取(SC-FDMA)中，多通道傳輸通道估計的問 題、演算法、分析及模擬等議題。 在通道估測中，我們先採用最小平方差(least square)的估計器，然後再利用 兩種方法去估測出載波的頻率響應並比較其效能。第一種方法是多項式內插，利 用最小平方差估計器所求得的參考訊號(reference signal)上載波頻率響應，在時域 利用多項式內插的方式來得到資料載波上的頻率響應。第二種方法則是採用最小 均方根誤差(MMSE)估計器，一樣是先利用最小平方差估計器所求得的參考訊號 上載波頻率響應，更而推導出參考訊號間的互相關，利用所推導出的互相關，我 們採用多項式內插的方式去求得參考訊號載波跟資料載波間的相關性，最後再帶 入最小均方根估計器中求出參考訊號載波相對應的權重，使資料載波上的頻率響 應估測的更為精準。 在模擬當中，我們先在AWGN通道上驗證我們的模擬模型，然後在放置於多 重路徑的通道上模擬，首先結果發現在低訊號雜訊比(SNR)的情況下，最小均方 根估計器的效能不論是在錯誤率或是載波上頻率響應均方根誤差皆較多項式內 插好，再來我們觀察到參考訊號如果使用zadoff chu序列的模擬結果跟我們假設 的序列相比，在載波上頻率響應均方根誤差上效能表現差很多，可是在錯誤率的 表現卻比我們假設的序列好。

Wireless Communication will play an important role in the evolution of communication in the future, especially basing on WiMAX (IEEE) and LTE (3GPP) to develop individually. Although the two systems are very similar, the biggest difference of them is that LTE using SC-FDMA (single carrier frequency division multiple access) technique in uplink transmission. The advantage of LTE is to decrease peak-to-average power ratio (PAPR) which saves more power of the batteries of user equipments (UEs) and efficiently extends the using time, rather than using OFDMA (orthogonal frequency division multiple access) which is adopted by WiMAX. This thesis will introduce the subjects of channel estimation problems, algorithms, analysis of multi-path transmission in SC-FDMA. In channel estimation, first we use least square estimator, then use two different methods to estimate the channel response and compare the performance between them. The first method is polynomial interpolation. We use polynomial interpolation to interpolate the channel response of data carrier form reference signal channel response which estimates by least square estimator. The second method is using MMSE estimator. The same as method one, we get the channel response which estimates by least square estimator form reference signal, more than that we calculate the correlation between reference signals. By using the result, we use polynomial interpolation to interpolate the channel correlation of data carriers and reference signal carriers, then we substitute them into MMSE estimator to get the weighting of reference signal carriers to let channel response what we try to estimate be more accurate. In simulation, we test and verify the simulate model which we proposed, in AWGN. Then we simulate in multi-path channel. First we find that MMSE estimator has better performance than polynomial interpolation in SER and MSE; second we iv observe that if RS sequence use zadoff-chu sequence compare to the sequence which we supposed, the performance of channel response MSE is worse, but the performance of SER is better.