無線中繼網路分層視訊之合作式群播

Layer-Encoding Multicasts in Wireless Relay Networks Using Cooperative Communications

許芷榕(Tsu-Jung Hsu)

指導教授 ： 廖婉君

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.01897

摘要

在無線行動網路中，近年來視訊群播的需求急速增加。在資源有限的系統中，合作式通訊被視為重要的通訊技術，能夠改善群播的品質。分層視訊編碼則是另一個適用於視訊傳播的技術，可以依照不同通道狀況給予不同品質的群播內容。
在這篇論文中，我們首先研究一子問題，即如何針對合作式群播進行資源分配，以求能夠使用最少的資源去服務所有使用者。假設中繼站和使用者之間的通道狀況可以視為遞增、遞減或是先遞增再遞減，我們提出一個可以求得最佳解的演算法，證明其最佳性並推導出複雜度。此外我們也處理了不符合上述假設的例外狀況。
接著，我們探討分層式編碼應用在合作式群播中時，如何決定每個使用者可以接收的視訊分層；在有限的資源中將系統總裨益最大化，並同時考慮分層視訊編碼必須連續接收視訊分層的特性。我們設計的演算法根據一個新定義的指標來分配每層分層視訊中對基地台和中繼站的資源，並且藉由動態規劃來處理每層視訊之間對資源的競爭。接著，我們會運用前述可將所需資源最小化的演算法來調整每個使用者可接收的視訊分層。
針對上述處理的兩個問題，我們分別透過模擬來評估所提出的演算法。模擬結果顯示和貪婪式演算法(greedy algorithm)相比，我們所提出的兩個方法皆能夠改善系統表現。

關鍵字：合作式通訊、分層視訊編碼、中繼站網路

關鍵字

合作式通訊 ； 分層視訊編碼 ； 中繼站網路

並列摘要

Today, demands for video multicasts increase rapidly in wireless mobile networks. In such a resource-limiting system, cooperative communication is a promising technique to improve multicast performance. Scalable video coding (SVC) also suits for video delivery, such that it can differentiate users and send different video quality according to their channel quality. Hence in this thesis, we study the layered multicasts destination assignment problem with relay cooperation to maximize total utility.
First, we consider a subproblem of multicasts with relay cooperation and formulate the problem as minimizing required resource subject to the subscribed user set and the channel conditions of users. We propose an algorithm which can yield the optimal solution under the assumption that the user channel condition trend viewed from each RS is either in increasing order, decreasing order or the combination of the two. Then the optimality proof and complexity analysis are derived. Also, the method for exception handling is provided.
Afterwards, we go back to the original problem by incorporating the SVC and aim at finding destination assignment of each layer. The objective is to maximize the system utility under the resource constraint and the SVC rule that a layer is valid only if all layers lower than it has been received. The designed algorithm allocates resource to the BS and RSs in each layer according to a defined utility index and models the resource contention between layers through dynamic programming. Then we trim the destination assignment based on our previous devised algorithm that minimizes the total required resource.

For the two problems we tackled, we evaluate our proposed methods through simulation. The results show that the devised resource minimizing algorithm greatly outperformed the other two greedy methods and the devised utility maximizing achieves a high system utility in all settings, indicating our method can adjust assignment strategy according to the utility functions.

Index Terms – wireless relay networks, relay cooperation, layered multicast, scalable video coding, OFDMA

並列關鍵字

wireless relay networks ； relay cooperation ； layered multicast ； scalable video coding ； OFDMA

參考文獻

[1]J. N. Laneman, D. N. C. Tse, and G. W. Wornell, “Cooperative Diversity in Wireless Networks: Efficient Protocols and Outage behavior,” IEEE Transaction Information Theory, vol. 50, pp. 3062-3080, Dec. 2004.

[2]T. C. Y. Ng and W. Yu, “Joint Optimization of Relay Strategies and Resource Allocations in Cooperative Cellular Networks,” IEEE Journal on Selected Areas in Communications, vol. 25, pp. 328-339, Feb. 2007.

[3]G. Li and H. Liu, “Resource Allocation for OFDMA Relay Networks With Fairness Constraints,” IEEE Journal on Selected Areas in Communications, vol. 24, pp. 2061-2069, Nov. 2006.

[4]W. Dang, M. Tao, H. Mu, and J. Huang, “Subcarrier-Pair Based Resource Allocation for Cooperative Multi-Relay OFDM Systems,” IEEE Transactions on Wireless Communications, vol. 9, pp.1640-1649, May 2010.

[5]Z. Han, T. Himsoon, W. P. Siriwongpairat, and K. J. R. Liu, "Resource Allocation for Multiuser Cooperative OFDM Networks: Who Helps Whom and How to Cooperate", IEEE Transactions on Vehicular Technology, vol. 58, pp. 2378-2391, June 2009.