IEEE 802.16 系統下針對變動位元速率影像傳輸之增進效率的上傳排班演算法

Abstract

在無線網路中，多媒體的應用越來越熱門和受歡迎，而變動位元速率(VBR)的多媒體影像傳輸是常見的應用之一，因此設計一個能針對變動位元速率影像傳輸之增進效率的上傳排班演算法是很重要的。然而，在IEEE 802.16寬頻無線接取(BWA)的系統之下，傳統定義的上傳排班演算法用在變動位元速率的影像傳輸上會有一些缺點，如額外的上傳頻寬浪費，或是造成較多的媒體存取控制(MAC)層負擔以及不必要的存取延遲等。因此我們提出一種在IEEE 802.16系統下，能針對變動位元速率影像傳輸增進效率的上傳排班演算法，我們的方法主要是利用BS根據傳輸的變動位元速率影像串流本身的狀態轉換特性，配置上傳的頻寬給使用者端，且將上傳頻寬等分成數個區間，因此只有當狀態有轉換時，才需要做頻寬請求的動作。而使用者端則是透過IEEE 802.16寬頻無線接取所定義的通用媒體存取控制頭(generic MAC header)內的兩個保留位元來通知BS目前影像串流的狀態。在本篇論文裡，我們也分析在變動位元速率影像傳輸的過程中，利用傳統定義的上傳排班演算法和我們所提出的上傳排班演算法，分別所造成的系統整體頻寬浪費率，最後我們利用QualNet 4.0進行模擬，結果顯示我們所提出的上傳排班演算法確實有較佳的效能。

Recently, the applications of real time multi-media for broadband wireless access (BWA) systems have become more and more popular. One of the major challenges in transmitting real time multi-media data in BWA systems is that the bit rate of the video traffic varies from time to time, and hence the bandwidth utilization is low. The conventional uplink scheduling algorithms for variable bit rate (VBR) video traffic transmission in IEEE 802.16 BWA systems have some disadvantages, including waste of uplink bandwidth, MAC overhead, and access delay. To cope with the difficulties, we propose an enhanced uplink scheduling algorithm for VBR video traffic transmission for IEEE 802.16 BWA systems. In our proposed algorithm, the base station (BS) assigns uplink bandwidth to the video user by considering the traffic state transitions. We equally divided the uplink bandwidth into several intervals and each interval represents a traffic state. Only when the traffic state is changed, the bandwidth request process is incurred. Also, by using two reserved bits in the generic MAC header of IEEE 802.16 BWA systems as piggyback bits, the information of video traffic state transition can be sent to the BS without extra overhead. With QualNet 4.0, simulation results show that the extra bandwidth consumption of our proposed algorithm is less than that of the conventional algorithms. That is, our proposed algorithm outperforms the conventional algorithms for VBR video traffic transmission in IEEE 802.16 BWA systems.