快速衰減通道下多天線廣播通道與有限回授和區域通道資訊影響之自由度分析

在本篇論文當中，我們探討在多輸入單輸出廣播通道情境下，在執行一種可以達到最佳總和自由度的機制時，考慮真實情境下，額外的成本帶來的影響。這個機制是由Maddah-Ali and Tse所提出可以最佳化利用過去的通道資訊，來達到最佳的總和自由度，我們稱呼這個機制為MAT scheme。第一個所需的成本是散播接收端通道資訊的成本，我們提出一個數學模型來計量這樣的成本。我們發現在一系列的線性傳輸方法下，過去的通道資訊沒有辦法提升在同質性傳輸端延遲通道資訊假設的自由度區域，但是可以提升異質性傳輸端通道資訊假設的自由度區域。第二個所需的成本是回授成本。我們證明了兩種回授方法下，最佳的回授策略：回授干擾以及回授通道係數。我們分析了這兩種策略的最佳化問題並且找到最佳的解法。一般傳統通訊系統使用回授通道係數，我們透過兩種方法的最佳解，證明了回授干擾優於回授通道資訊。因此在有限的回授下，回授干擾可以提供較多的總和自由度增益。最後我們考慮在雙基地台干擾通道情境下，發現我們可以透過通道資訊的多樣性來降低要執行MAT scheme所要讓基地台交換的資訊量。這方法可以降低所需要交換的資源，進而達到在廣播通道下的最佳總和自由度。

關鍵字

延遲通道資訊；廣播通道；區域通道資訊；有限回授

並列摘要

In this thesis, we cope with some extra cost when we want to implement an optimal DoF-achievable scheme of MISO broadcast channel through utilizing delayed channel state information (DCSIT). The seminal work by Maddah-Ali and Tse shows that DCSIT can increase the sum of degrees of freedom (DoF) in fast-fading MIMO BC regime. We call the optimal scheme ``MAT scheme". The first cost of disseminating CSIR is investigated and we propose a model to capture the cost. In a family of linear schemes, we find DCSIT is not useful to improve DoF region in a homogeneous DCSIT setting. However, DCSIT is still useful in heterogeneous CSIT setting to improve DoF region while considering the cost. The second cost is the CSI feedback. We propose optimal strategies of two methods: feedback interference and feedback channel coefficients. We characterize the mathematical optimization problem and solution. Moreover, we prove that the feedback-interference method outperforms the feedback-channel-coefficient method, which is a traditional method of feedback. The feedback-interference method can provide more DoF gain. Finally, we consider a two-cell interference channel and find a method which utilizes the channel diversity to reduce the exchanging quantity between two base station while implementing MAT scheme. This method can help the base stations cooperate and use less resource to achieve the optimal sum of DoF of the broadcast channel.

並列關鍵字

delayed CSIT ； Broadcast channel ； Local CSIR ； rate-limited feedback

參考文獻

[2] T. Gou and S. A. Jafar. Optimal use of current and outdated channel state information: Degrees of freedom of the MISO BC with mixed CSIT. IEEE Communications Letters, 16(7):1084–1087, July 2012.

[4] M. Kobayashi and G. Caire. On the net DoF comparison between ZF and MAT over time-varying MISO broadcast channels. In 2012 IEEE International Symposium on Information Theory Proceedings, pages 2286–2290, July 2012.

[5] S. Lashgari, R. Tandon, and S. Avestimehr. MISO broadcast channel with hybrid CSIT: Beyond two users. IEEE Transactions on Information Theory, 62(12):7056– 7077, December 2016.

[6] M. A. Maddah-Ali and D. Tse. Completely stale transmitter channel state information is still very useful. IEEE Transactions on Information Theory, 58(7):4418–4431, July 2012.

[7] M. Medard. The effect upon channel capacity in wireless communications of perfect and imperfect knowledge of the channel. IEEE Transactions on Information Theory, 46(3):933–946, May 2000.

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快速衰減通道下多天線廣播通道與有限回授和區域通道資訊影響之自由度分析

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