Link Adaptation and Cross-Layer Signaling for Wireless Video-Streaming in a Shared Medium

Abstract — Changes in the quality of wireless links impose great demands on video codecs and underlying network layers when seamless video-streaming is to be achieved. Moreover, it is not enough that only the video codec or only the radio adapts to these changes; the efforts should be applied in both layers, and – if possible – synchronized. So, on the one hand, a responsive link adaptation method should be employed in the radio. And, on the other hand, the video codec should be able to follow the changes in the maximum throughput due to wireless link performance variations. In this paper we present the results of video-streaming over 802.11a link in the presence of background traffic, generated by other stations sharing the same medium. We show that great improvements in the quality of the video can be achieved by cross-layer signaling between the link layer and the video coder. However, we show that this is only realizable if a correct estimation can be made of the throughput decline due to the medium sharing

Automatic IEEE 802.11 rate control for streaming applications

Streaming multimedia content in real-time over a wireless link is a challenging task because of the rapid fluctuations in link conditions that can occur due to movement, interference, and so on. The popular IEEE 802.11 standard includes low-level tuning parameters like the transmission rate. Standard device drivers for today’s wireless products are based on gathering statistics, and consequently, adapt rather slowly to changes in conditions. To meet the strict latency requirements of streaming applications, we designed and implemented an advanced hybrid control algorithm that uses signal-strength (SNR) information to achieve fast responses. Since SNR readings are quite noisy we do not use that information to directly control the rate setting, but rather as a safeguard limiting the range of feasible settings to choose from. We report on real-time experiments involving two laptops equipped with IEEE 802.11a wireless interface cards. The results show that using SNR information greatly enhances responsiveness in comparison to statistics-based rate controllers. Finally, we will present the results of an experiment with realtime video streaming to a moving laptop in an office-like environment. Our hybrid control algorithm effectively prevented many packets losses, thereby achieving a much higher video quality than 1 the statistics based algorithm

Quality of Service Controlled Adaptive Video Coding over IEEE 802.11 Wireless Links

In this paper we present the initial results of experiments where encoded video data is transmitted over an IEEE 802.11a wireless link. The changing link state and the perhaps changing constraints imposed by mobile device or user, will move the optimal settings of both the video encoder and the IEEE 802.11 network layer. The video encoder and the network layer will negotiate their options facilitated by a Quality of Service negotiation scheme called "Adaptive Resource Contracts", thereby jointly optimizing their parameters. When time is a constraint, this optimization has to be fast and simple, maybe even at the cost of finding suboptimal solutions, as long as the found settings will give a better Quality of Service than fixed parameter settings