無線網路中機會主義群播排程的研究

Abstract

近年來，隨著人們無線上網型態的改變，發展更高效能無線存取技術的研究刻不容緩。特別是機會主義群播排程（OMS），它是一個利用多用戶分集提昇無線網路群播效能的技術。在本論文中，我們考慮在無線網路中群播一份資料給所有用戶的問題，並針對無線網路群播的兩個議題進行了研究和調查：i）減少機會主義群播排程所需的反饋，和ii）針對異構無線終端設備發展多媒體群播系統。 在減少機會主義群播排程所需的反饋方面，雖然反饋允許排程演算法能更有效利用多用戶分集，但這可能會干擾系統的上行流量。我們提出一個弱一致機會主義群播排程方法，它能夠降低系統反饋負載，同時保持系統能提供與全反饋情況下相當的群播效能。 另一方面，針對我們提出的弱一致機會主義群播排程方法，我們進一步提出一個公式讓網路運作商設定最佳的反饋間隔大小。我們的分析顯示，透過我們的公式設定的反饋間隔可以顯著減少系統中反饋的負載，同時提供媲美於全反饋的效能。

The ever-increasing demand for richer multimedia contents anytime, anywhere, on any devices, has driven the development of highly efficient content distribution technologies over wireless networks. In particular, opportunistic multicast scheduling (OMS) has recently emerged as one of the most promising techniques for content delivery, which effectively increases throughput with reduced delay by exploiting multiuser diversity inherent in wireless networks. In this dissertation, we consider the problem of multicasting a common set of data to all subscribers on the downlink of a wireless network. Two issues of wireless multicasting are studied and investigated: i) reducing feedback load of OMS, and ii) transmitting real-time multimedia over heterogeneous wireless terminal devices. For reducing feedback load of OMS, a Weakly Consistent OMS scheme for channel condition feedback reduction is presented. Channel condition feedbacks, although it allows the scheduler to exploit the multiuser diversity, it results in overhead which may interfere the uplink traffic in the system. Our proposed scheme is able to reduce the feedback load while maintaining the multicast throughput performance comparable with the case of full feedback. For our proposed OMS, we further propose an equation for system operators to determine the best size of feedback interval for the subscribers to update their channel conditions. Our analysis shows that the size of feedback interval determined through our equation can significantly reduce the feedback load in the system while providing comparable throughput performance to the subscribers. For real-time multimedia transmission over heterogeneous terminal devices, an effective layered video multicasting (LVM) algorithm is presented, and a prototyping system called WiMAX-LVM is developed. The WiMAX-LVM system is a working realization for LVM over mobile WiMAX, which can serve as a basis for future researches in creating video-related multicasting services over orthogonal frequency-division multiple access (OFDMA)-based fourth generation (4G) wireless networks. The research results presented in this dissertation provide some useful mechanisms and guidelines for broadband wireless operators to achieve high system performance in their networks.