快速衰減多輸入多輸出廣播通道與有限的回授：自由度的分析

Fast Fading MIMO Broadcast Channel with Rate Limited Feedback: Degrees of Freedom Analysis

蕭博修(Po-Hsiu Hsiao)

指導教授 ： 王奕翔

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201602969

摘要

在這篇論文當中，我們探討多輸入多輸出廣播通道與資源有限的回授。在快衰減多輸入多輸出廣播通道中，接收端的通道資訊不足以對下行網路的傳輸速率（自由度）有顯著的提升是廣為人知的，傳送端需要知道下行網路的通道資訊才有辦法進行比較複雜的編碼技術來進行干擾管理進而提升下行網路的傳輸速率。傳送端的通道資訊是透過回授獲得的， 有限的回授造成延遲與不準確的通道資訊，我們想探討究竟這個經過延遲與不準確的通道資訊究竟能給予我們的傳輸速率有多少的增益。

首先，我們考慮無時間相關性的快速衰減通道(i.i.d. fast fading channel)。 傳統的回授方法是接收端將通道資訊量化後回授給傳送端，然而隨著接收端的增加回授需求也跟著增加，這個方法並沒有辦法很有效率地使用回授。我們提出了一種新的回授方法，接收端會直接把干擾量化過後回授給傳送端而不是回授通道資訊，這樣的方法會讓接收端更有效率地使用回授資源，我們可以證明我們提出的干擾回授方法可以給予下行網路的傳輸速率有更顯著的增益。

在分析完無時間相關性的快速衰減通道之後，我們想把我們的回授方法套用在有時間相關性的通道中。在有時間相關性的通道裡，傳送端可以由回授偵測當下的通道資訊。我們對此提出了一種新的傳輸方式，並可以與我們干擾回授的方法並行。我們的傳輸與回授方法在有時間相關性的通道中仍然有比較好的表現。

關鍵字

有限的回授 ； 自由度 ； 多輸入多輸出

並列摘要

In this thesis, we study MIMO broadcast channel with rate limited feedback. For fast fading MIMO broadcast channel, it is well known that channel state information at receiver (CSIR) is not sufficient to provide significant increase of the throughput, namely, degrees of freedom gain. The transmitter needs the channel state information to carry out interference mitigation techniques such as beamforming to improve capacity. Typically, channel state state information at transmitter (CSIT) is obtained from feedback. Since rate-limited feedback creates delay and inaccuracy in CSIT, it is of fundamental interest to understand how such delayed imperfect CSIT can improve system performance.

First, we consider independent and identically distributed (i.i.d.) fast fading channel. A scheme based on network coding ideas, where the receivers feedback quantized channel gains through rate-limited feedback links and the transmitter uses these channel gains to reconstruct interference and sends the combined interference to create network coding opportunities. However, the feedback requirement of this scheme grows very large as the number of users increases, and hence it does not utilize feedback efficiently. We propose a novel scheme in which the receivers feedback quantized interference through rate-limited feedback links instead of channel gains. This method can utilize the feedback resource more efficiently. We show that our proposed scheme and feedback method can provide more degrees of freedom gain than baseline scheme.

After the analysis in i.i.d. fast fading channel, we extend our scheme to temporally correlated channel. Transmitter can estimate current CSIT from the feedback. We propose our transmission scheme which is suitable for our feedback-interference method. Our proposed feedback method and transmission scheme still has better performance than the best-known schemes in the literature.

並列關鍵字

rate-limited feedback ； degrees of freedom ； MIMO

參考文獻

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