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標題: | 應用於正交分頻多工無線通訊系統之可適性通道估測器設計 Adaptive Channel Estimator Design for OFDM-Based Wireless Communication Systems |
作者: | Yen-Ming Huang 黃彥銘 |
指導教授: | 李學智(Hsueh-Jyh Li) |
關鍵字: | 正交分頻多工,通道估測,同步,線性內插,離散傅立葉內插,無線通道,多重路徑延遲效應,邊際效應,都普勒偏移,載波頻率偏移,長期演進技術, OFDM,Channel Estimation,Synchronization,Linear Interpolation,DFT-Based Interpolation,Wireless Channel,Multipath Propagation Delay,Edge Effect,Doppler Shift,Carrier Frequency Offset (CFO),Long Term Evolution (LTE), |
出版年 : | 2012 |
學位: | 碩士 |
摘要: | 在以正交分頻多工(OFDM)為基礎的無線通訊系統設計中,準確且穩固的通道估測來確保可靠的傳送資料回復是非常關鍵且重要的。在本篇論文中,不只假設接收端的符元時間已完美同步,並且採用已知的領航訊號來做通道估測,其目的是為了要根據無線通道的特性,開發出一個基於務實性考量的可適性通道估測器。因為在資料載波上的通道頻率響應可以經由對兩旁的領航訊號作內插,來得到估測結果,我們嘗試在沒有通道統計特性事先已知的狀況下,根據把多重路徑效應和都卜勒偏移列入考量,去找出適當的內插使用判斷基準。
對於以離散傅立葉轉換為基礎的內插而言,虛擬載波的使用被用來提供保護頻帶,這將導致在頻帶邊際處,其通道估測的效能大幅降低,在本論文中會給予此現象一個完整的討論並加以釐清。除此之外,相較於許多建立在通道長度資訊的時域處理方法,根據已知的雜訊能量來選擇一個適當的門檻值是更加合理的。在本研究中,以高斯雜訊的統計特性為出發點,提出了兩種門檻值選擇的機制。並呈現出兩種廣為人知的邊際效應消除方法在不同通道延遲擴展下的成效。 在轉向時域上內插的觀點時,時變通道的合理假設要先被正確地闡明,如此一來,儘管是在高速移動的情況下,藉由載波頻率偏移的補償技巧,時域上線性內插的限制會被大幅地放寬。 為了擴大簡單線性內插的適用性,提出了移動式平均和離散傅立葉轉換的技巧以用來消除領航訊號上的雜訊成分。同時,亦提出了應對嚴重通道延遲擴展和超高速通道衰落這兩種狀況的策略。 最後,為了去確認這篇論文所提出的想法在實際環境下的可行性,實驗模擬參數將會依照現行的LTE規格。根據對於通道狀況的瞭解,此篇論文所提及的可適性通道估測器演算法設計,可以達到有效地節省接收端功率上的消耗,且大幅降低計算時間量的目標。 In the design of OFDM-based wireless communication systems, accurate and robust channel estimation is very critical to ensure reliable data recovery. In this thesis, not only perfect timing synchronization is assumed but also pilot-aided for channel estimation is adopted. The objective is to develop an adaptive channel estimator in light of practical concerns according to wireless channel characteristics. Because the channel frequency response (CFR) on data subcarriers can be estimated via the interpolation between two adjacent pilots, we attempt to find the appropriate linear interpolation criteria with no prior channel statistic information on the grounds that the multipath propagation delay and the Doppler shift are taken into consideration. There is one thing that is important for DFT-based interpolation in frequency domain. The utilization of virtual subcarriers is provided as guard bands, but which results in the performance degradation of channel estimation for band edge spectrum. The clarification of this phenomenon is completely given in this thesis. Furthermore, compared with many proposed methods of time domain processing based on the information of channel delay length, the proper threshold selection according to the known noise power is more rational. In this study, inspired from the statistical characteristics of Gaussian noise, two schemes of threshold selection have been proposed. The use of two well-known methods of repetition and linear fashion under different channel delay spreads for edge effect mitigation has also been demonstrated. Turning to the aspect of time domain interpolation, the reasonable assumptions of time-varying channel are correctly clarified. Thus, in spite of the high-speed conditions which act on the Rician fading channel, the restriction of linear interpolation is remarkably loosened by the techniques of carrier frequency offset (CFO) compensation. For the sake of enlarging the usability of linear interpolation, two techniques of Moving Average and DFT-based transition for noise reduction on pilots have been proposed. The strategies for large delay spread channel and fast fading channel are also presented. To confirm the practicability proposed in this thesis in realistic environments, the simulation parameters will follow the specification of LTE. As a result, the power and the latency of computation can be saved effectively with this adaptive channel estimator algorithm design based on channel understanding. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/63795 |
全文授權: | 有償授權 |
顯示於系所單位: | 電信工程學研究所 |
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