Transmission and transport broadband video services over wireless access networks.

摘要

In this dissertation, we initiated a research direction on the transmission and transport issues when providing MPEG-2 encoded broadband video services over wireless access networks, in particular the broadband fixed wireless access networks.; Most practical and marketable broadband video services, mobility is not considered to be a top-priority in the near future. Therefore, broadband wireless access networks (B-WANs), especially broadband fixed WANs (B-FWANs), have attracted significant attention recently.; Due to the competition among different broadband access technologies, there will exist heterogeneous access networks in the near future. To save network resources, FEC-based error control has to be applied locally. Since there exists unequal importance between MPEG-2 control information and MPEG-2 video information, we propose a header redundancy FEC (HRFEC) scheme to provide excess protection to priority MPEG-2 control headers. The HRFEC scheme can improve the overall performance by guaranteeing a larger number of decoded frames at the cost of a small amount in overhead. We also proposed and implemented an end-to-end transport protocol for MPEG-2 video broadcast service over heterogeneous access networks, based on ATM and wireless ATM (WATM) infrastructures, in which the HRFEC scheme is applied locally and transparently when necessary.; Secondly, we investigated the feasibility of applying ARQ-based error control schemes and the effectiveness of applying hybrid ARQ error control schemes, including type-I (ARQ/RS) and type-II (ARQ/RCPC) schemes, to the transmission of MPEG-2 encoded video streams over B-WANs for VoD services. A specific wireless channel model which combines the K-factor Rician fading model and an ad hoc finite hidden Markov model (HMM) was proposed to emulate the performance of the fixed wireless channel in B-FWANs. The results show that a hybrid ARQ scheme generally guarantees better video quality at the cost of a drop in the channel throughput, however, the drop in the throughput will be compensated for by the error correction capability associated with the hybrid ARQ scheme when the channel condition worsens, especially when the channel experiences long fades. When the channel condition is poor and experiences long fades, type-II hybrid ARQ schemes with RCPC codes can guarantee most consistent video quality, at the extra cost of computational complexity due to the Viterbi algorithm.; We also proposed and investigated several prediction algorithms for the excess bandwidth reservation needed for retransmissions, when using hybrid-ARQ schemes for pre-recorded VoD services over B-WANs. The choice of the excess reservation algorithm is a tradeoff between the requirement of the queue capacity and the tolerance of the wasted channel bandwidth due to underflow. Overall, dynamic or adaptive algorithms work effectively, as they take the short-term channel variance into consideration. (Abstract shortened by UMI.)