空間異質之多天線系統減少通道資訊回饋之效能分析

Performance Analysis of Feedback Reduction in MIMO System with Spatial Heterogeneity

汪煒翔(Wei-Hsiang Wang)

指導教授 ： 蘇炫榮

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201701165

摘要

在多用戶多輸入多輸出下行廣播系統中，基地台利用多天線系統提供的空間多工增益以空間多重存取技術來同時服務數個使用者，進而提升系統效能。透過使用者回傳各自的通道資訊給基地台進行有效排程，如最大傳輸率排程，能夠大量提升傳輸效率，然而在使用者數量龐大時，其所付出之代價為頻寬使用之負荷。因此有許多文獻透過設計閾值來減少通道數量回饋進而改善回傳數量龐大之負擔。然而這些文獻皆只在均質網路中進行探討且缺乏閉合解，因此本篇論文提出一個實際且通用的模型以考慮使用者在網路中的空間異質性。
在此模型且利用最大傳輸率排程以服務使用者下，我們推導了傳輸率的極限行為，其結果與均質網路相同。且在傳輸功率夠大時，我們推導了閉合解，其也適用於均質網路。然而利用最大傳輸率排程將造成嚴重的公平性問題，對於平均通道狀況較好的使用者將有較高的機率被服務，我們利用累積分佈函數排程之技術來達成使用者間的使用公平且有效的降低回傳數量，利用累積分佈函數排程，我們也求得系統效能之閉合解。最後，我們考慮了多媒體廣播多播業務，其為上述問題之對偶問題，透過排程最差通道之使用者進而達成可靠傳輸，我們將上述提出之模型用以該系統下，同時也在傳輸功率夠大時，推導了閉合解，其也適合於均質網路。

關鍵字

空間多重存取 ； 通道數量回饋 ； 多用戶多輸入多輸出 ； 空間異質性 ； 均質網路 ； 累積分佈函數排程 ； 多媒體廣播多播業務

並列摘要

In multiuser multiple-input multiple-output (MU-MIMO) downlink broad-cast channel, several users can be simultaneously served through space division multiple access (SDMA), which exploits the multiplexing gain of MIMO system. To improve the system sum rate, users feedback their channel state information (CSI) to help the base station (BS) to schedule those with the best channel conditions. This incurs a large aggregate feedback bandwidth growing linearly with the number of users. There are already several studies investigating the threshold-based feedback schemes to reduce the amount of feedback. However, they are limited to the homogeneous cases. In this thesis, we develop the realistic and general model for the MU-MIMO opportunistic feedback scheme, where users are uniformly distributed in the cell. With this model, we analyze the sum rate growth as the number of users is in nite and extend the feedback reduction method to the heterogeneous network considering the fairness problem with CDF scheduling. It provides the fair channel access time fraction and tractable analysis. For homogeneous network, the closed form expression of sum rate/rate loss(due to the outage event, i.e. no one feedback CSI), with nite users is obtained. Also, we analyze the dual problem, MU-MIMO opportunistic feedback scheme in multicast channel with the proposed model, and the closed form expression of homogeneous case is also derived.

並列關鍵字

SDMA ； Feedback reduction ； MU-MIMO ； Multicast

參考文獻

[1] T. Yoo and A. Goldsmith, “On the optimality of multiantanna broad-

with partial side information," IEEE Trans. on Inf. Theory, vol. 51,

[3] D. Gesbert and M. S. Alouini, “How much feedback is multi-user diver-

[4] T. Yoo, N. Jindal, and A. Goldsmith, “Multi-antenna downlink chan-

nels with limited feedback and user selection," IEEE J. Select. Areas