應用於多路徑快速衰退通道中空頻區塊碼之正交分頻多工系統上的通道估測指標設計方法

Pilot Design for Channel Estimation in SFBC-OFDM Systems over Multipath Fast-Fading Channels

王京騰(Jing-Teng Wang)

指導教授 ： 林茂昭

共同指導教授 ： 李晃昌(Huang-Chang Lee)

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202202125

摘要

正交分頻多工系統廣泛被用於無線通訊系統，於多路徑通道中仍能維持好的傳輸率。然而，系統面對快速衰落通道，都卜勒效應產生的載波間干擾，會嚴重影響到通道估測的精確性，使傳送出去的信號無法成功解調、錯誤率表現不佳。在之前的研究，低延遲的迭代通道估測模型被提出，應用多個使用錯誤更正碼的編碼器，使解碼的結果能反饋的利用於更新通道資訊，因而能用較高的有效訊息比例達到精準的通道估測。也能進一步延伸至多天線系統，並加入空頻區塊碼，來達到更好的錯誤率表現。

而這篇論文在先前研究基礎上，延伸與作近一步研究。首先，改良考慮相鄰子載波間的連續性以應用孤立引導信號之演算法，使之應用於變化之通道。再者，討論使用重複碼輔助之多天線系統在我們估測模型的可行度與提出的空頻區塊碼之解碼器對於由快速衰退通道的優勢探討。論文中也進一步討論引導信號的挑選方式，在我們提出遞迴架構之上，確保估測不會錯誤辨認通道，進而應用於更多傳送天線的系統之上，藉此得到更多的通道多樣性。最後，嘗試獨立使用空頻區塊碼必要的成對引導信號，並研究提高的已知信號群數與孤立引導信號對於通道估測的影響。

關鍵字

正交分頻多工系統 ； 多輸入多數出系統 ； 空頻區塊碼 ； 多重路徑快速衰落通道 ； 低密度奇偶檢查碼 ； 通道估測

並列摘要

Orthogonal frequency division multiplexing (OFDM) is widely used in wireless communication systems for its advantages in high bit rate transmissions over multipath channel. However, the inter-carrier interference (ICI) caused by Doppler effect in fast fading channels can seriously affect the accuracy of channel estimation, making the transmitted signals unsuccessful in demodulation and poor error rate performance. In previous studies, the low-latency iterative channel estimation model was proposed. With the assistance of multiple error-correcting encoders, the feedback decoding results are utilized to update channel information, and accurate channel estimation can be achieved with lower overhead ratio. It can also be further extended to multi-input multi-output (MIMO) systems and combined with space-frequency block code (SFBC) to achieve better error rate performance.

Based on previous studies, the technique of iterative channel estimation has been refined in this thesis. First, we modify the algorithm of considering the continuity of channel frequency responses between neighboring subcarriers to assign pseudo pilots for adopting to changing environments. In addition, the feasibility of repetition-coded MIMO systems in our estimation model is evaluate, and the advantage of proposed SFBC decoder in high-speed scenario is viewed. In this thesis, the selection of the pilot signals is revised, based on our iterative structure, to ensure the estimations do not misidentify channels. This can then be applied to systems with more transmission antennas to obtain more channel diversity. Finally, an attempt of isolation of paired pilot tones required for SFBC is presented, and the effect of increasing number of pilot group and stand-alone pilots on the channel estimation is also discussed.

並列關鍵字

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

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