In this paper, we investigate the optimal streaming strat-egy for dynamic adaptive streaming over HTTP (DASH). Specifically, we focus on the rate adaptation algorithm for streaming scalable video (H.264/SVC) in wireless networks. We model the rate adaptation problem as a Markov Decision Process (MDP), aiming to find an optimal streaming strat-egy in terms of user-perceived quality of experience (QoE) such as playback interruption, average playback quality and playback smoothness. We then obtain the optimal MDP solution using dynamic programming. We further define a reward parameter in our proposed streaming strategy, which can be adjusted to make a good trade-off between the av-erage playback quality and playback smoothness. We also use a simple testbed to validate our solution. Experiment results show the feasibility of the proposed solution and its advantage over the existing work.

Abstract—Error control is critical for wireless networks to combat channel fading and ensure efficient resource utilization. Adaptive modulation and coding (AMC) in the physical (PHY) layer and packet fragmentation and automatic repeat request (ARQ) in the link layer are widely used error-control mechanisms. However, how to jointly optimize them in both layers for high-rate wireless networks is still open. In this paper, using the WiMedia ultrawideband (UWB) networks as an example, we first develop a general analytical framework to quantify the link delay and loss performance considering the channel fading, the joint errorcontrol mechanisms, and the arbitrary reservation-based media access control (MAC) protocol. Second, we introduce a cross-layer design to optimize the PHY-layer AMC and the link-layer packet fragmentation and propose a joint-adaptation mechanism that is simple to implement and has near-optimal performance. Numerical results reveal that fragmentation has a greater impact than AMC on the delay and loss performance for marginal links and that the proposed joint-adaptation strategy is efficient for high-rate wireless networks. Index Terms—Adaptive modulation and coding, automatic repeat request, error control, fading channels, packet fragmentation, queueing analysis, reservation-based medium access control. I.

permission of the author. ii

Abstract—Developing an accurate and mathematically tractable high-speed railway (HSR) channel model is a key issue to provide reliable, cost-effective wireless services for the HSR operators and users. Although finite-state Markov chain (FSMC) has been ex-tensively investigated to describe fading channels, most of FSMC channel models are designed based on the first-order Markov chain, which are no longer valid when the transceivers operate in high mobility scenarios, specially in HSR communications. In this letter, an advanced FSMC channel model for HSR is proposed, which incorporates the impacts of moving speed on the temporal channel statistical characteristic. The closed-form expressions of state transition probabilities between channel states are derived. The accuracy of the proposed FSMC channel model is validated via extensive measurements conducted on the Zhengzhou-Xi’an HSR line in China. Index Terms—Fast time-varying fading channels, finite-state Markov chain, high-speed railway communications. I.