適用於多路徑快速時變通道中多天線正交分頻多工系統的低延遲通道估測方法

Low-Latency Channel Estimation for MIMO-OFDM System in Multipath Fast Fading Channel

林律綺(Lu-Chi Lin)

指導教授 ： 林茂昭

共同指導教授 ： 李晃昌(Huang-Chang Li)

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101951

摘要

由於正交分頻多工可有效對抗多重路徑衰落通道，因而被廣泛地運用在許多無線通訊系統中。然而，快速衰落通道會對正交分頻多工系統產生載波間干擾。許多近期的研究顯示，在多路徑快衰落通道下的通道估測，為降低載波間干擾的影響，需要成群的引導信號和跨多個符元的長時間觀測以達到較好的準確率。
根據先前研究中提出針對有嚴重都普勒效應之多路徑快速時變通道，結合錯誤更正碼使得接收端能將解碼資訊和對數概似比迭代傳回以協助估測的方法，本篇論文改良並考慮相鄰子載波間頻率通道響應的連續性，用以在一個正交分頻多工符元時間長度下僅利用多個孤立引導信號得到更準確的估測結果。由於多路徑快速衰落通道的通道估測可在一個符元時間利用多個孤立的引導信號完成，我們將此方法靈活延伸至各種多樣性中。論文中介紹可達到空間多樣性的多天線無線通訊系統，結合前述通道估測方法，以降低通道估測所需的遞迴次數並達到較好的準確率。最後，在單天線系統中若允許較長的偵測延遲，我們加入跨多個符元長度的低密度奇偶檢查碼作為內碼，達到時間多樣性並得到較佳的錯誤率表現。

關鍵字

多重路徑快速衰落通道 ； 正交頻分多工 ； 低密度奇偶檢查碼 ； 通道估測 ； 多輸入多輸出系統

並列摘要

Orthogonal frequency division multiplexing (OFDM) is widely used in the wireless communication system due to its robustness against frequency selective channel. However, OFDM suffers from inter-carrier interference (ICI) introduced by fast fading channel. Most of the recent researches show that, in order to mitigate ICI, grouped pilots and long-duration observation across multiple symbols are required for the accurate estimation to multipath fast-fading channel.
In previous study, an iterative channel estimation for OFDM system in multipath fast-fading channel was proposed by utilizing error correcting code, where the receiver exploits the decoding information and log-likelihood ratios (LLRs). Based on the assistance of iterative decision feedback, the correlation among neighboring channel impulse responses is considered to provide accurate estimation results in this thesis which aims at completing the estimation scheme in one OFDM symbol period by using stand-alone pilots. Since the estimation to multipath fast-fading channel can be accomplished using stand-alone pilots within single OFDM symbol, variety of diversity can be flexibly explored. Multi-input-multi-output (MIMO) system is introduced in this thesis for space diversity so as to reduce the iteration times and improve the accuracy of channel estimation. Finally, if long detection latency is allowed, long LDPC code crossing multiple OFDM symbols can be introduced as an inner code for time diversity with better error rate performance for single-input-single-output (SISO) system.

並列關鍵字

Multipath fast-fading channel ； OFDM systems ； LDPC codes ； channel estimation ； MIMO systems

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