Crosslayer optimization for wireless video communication With the rapid growth of wireless networks and increasing popularity of portable video devices, wireless video communication is poised to become the enabling technology for many multimedia applications over wireless networks. Realtime wireless video transmission typically has requirements on quality of service (QoS). However, wireless channels are unreliable and the channel capacities are timevarying, which may cause severe degradation to video presentation quality. In addition, for portable devices, video compression and wireless transmission are tightly coupled through the constraints on data rate, power, and delay. These issues make it particularly challenging to design an efficient realtime video compression and wireless transmission system on a portable device. In this paper, we take a crosslayer approach to this problem; our objective is to maximize the video quality under the constraints of resource and delay. Specifically, we minimize the endtoend video distortion under the constraints of resource and delay, over the parameters in physical, link, and application (video) layers. This formulation is general and capable of capturing the fundamental aspects of the design of wireless video communication systems. Based on this formulation, we study how the resources could be intelligently allocated to maximize the video quality and analyze the performance limits of the wireless video communication system under resource constraints.

PowerEfficient Video Streaming on Mobile Devices Using Optimal Spatial Scaling This paper derives optimal spatial scaling and rate control parameters for powerefficient wireless video streaming on portable devices. A video streaming application is studied, which receives a highresolution and highquality video stream from a remote server and displays the content to the enduser. We show that the resolution of the input video can be adjusted such that the qualitypower tradeoff is optimized. Making use of a power model from the literature and subjective quality evaluation using a perceptual metric, we derive optimal combinations of the scaling factor and the ratecontrol parameter for encoding. For HD sequences, up to 10% of power can be saved at negligible quality losses and up to 15% of power can be saved at tolerable distortions. To show general validity, the method was tested for WiFi and a mobile network as well as for two different smartphones.