適應性編碼技術基於服務品質之丟棄封包機制於IEEE 802.16e網路之研究

Abstract

IEEE 802.16 is a new communication standard for supporting the Wireless Metropolitan Area Network. IEEE 802.16 replaces the last one mile by the way of wireless connects and fetches. Because it used high-efficiency wireless signal transmitting and treatment technology, it is farthest to 48km to transmit the distance, wide 300Kbps- 2Mbps bandwidth of end. Compared with the tradition wired network, IEEE 802.16 possesses the characteristics of the fast laying of hardware, being free from the effect of topography, and low cost. Multimedia applications over mobile wireless network are becoming popular in recent years. High video quality depends on the wide bandwidth but the wide bandwidth restricts the number of users in the network system. Effective bandwidth utilization is the major problem in wireless network because the bandwidth resource in wireless environment is limited and precious. For this reason, we propose an active dropping mechanism to deal with the effective bandwidth utilization problem. In the proposed mechanism, if the network loading exceeds the threshold, the dropping mechanism starts to drop the enhancement layer data for low level user and the dropping probability is varying with the different network loading. For the multimedia application, we use the characteristic of the Scalable Video Coding (SVC) extension of H.264/AVC standard to provide different video quality for different level user. By the dropping mechanism, base station increases the system capability and users can obtain better quality of service when the system is under heavy loading. In this research, we study the network of the 802.16e standard and add the QoS-based Active Dropping mechanism to the MAC layer. The dropping mechanism works when the base station loading is exceeding the bandwidth threshold. We adjust the threshold value dynamically to balance between the bandwidth utilization and video quality. By the dropping mechanism, network system can release bandwidth which is used to transmit the dropped data before and base station can support more users to access this network system. In the simulation results, we improve the bandwidth utilization and the network capability and achieve the QoS for each user.