應用於H.264/SVC之適應性正向錯誤修正與交錯式順序機制於無線網路之研究

Abstract

The main challenge of wireless video transmission originates from the error-prone nature caused by the time-varying channel itself. By complex calculation of preceding and succeeding frames, the H.264 video compression standard achieves high compression ratios. Packet loss degrades its quality and even affects the decoding of dependent frames. This means that the error spreads to the neighboring frames as well which depend on the several preceding differentially coded frames. The unavoidable wireless video transmission errors make it hard for the traditional error recovery techniques to recover the lost video packets timely. Many studies have tried to solve this problem and their major design consideration has been given to the total throughput. Such studies include Forward Error Correction (FEC) and Automatic Retransmission ReQuest (ARQ). In FEC approach, the source node transmits the parity packets along with the original data packets. The receiver can accurately recover any lost data packets less than the parity packets. The amount of the parity packet is determined at the time of FEC encoding. Although eliminating the need for time-consuming acknowledgement and retransmission operations of ARQ, FEC consumes more bandwidth. Recently, an intelligent FEC mechanism, Enhanced Adaptive FEC (EAFEC), has been proposed to provide improved video delivery over wireless networks. Based on both network traffic load and wireless channel state, the redundant FEC packets are dynamically added. Instead of adding unnecessary packets into the congested network, EAFEC algorithm tunes FEC packet numbers in such a way. In this research, we extend the EAFEC scheme to further propose and analyze the effeciency of using different FEC strength depending on H.264/SVC video stream priorities for wireless video transmission. In this scheme, we define different threshold groups to compute the FEC strength (the number of redundant packets) for the specified H.264/SVC video stream priorities with the EAFEC scheme. To protect data from the burst loss between the Access Point (AP) and the client nodes, the interleaving technique for each H.264/SVC FEC video data is also introduced. The adaptive FEC strength to different priority video frame under current rate of wireless channel loss is the objective of this research.