| Recent advances in media streaming and wireless networking are rapidly opening up opportunities for high-quality content streaming over wireless links. Supporting media applications over interference-limited, erratic wireless channels on battery-limited mobile devices introduces various technical challenges at multiple levels. We focus on cross-layer network control issues, addressing performance tradeoffs in wireless media streaming. In particular, we consider transmission power control (for wireless QoS support, interference mitigation, and battery power conservation) jointly with media playout buffer control (for delay/jitter cushioning) and frame selection control for bandwidth management.; We first investigate a special transmitter power control scheme for wireless multimedia traffic, where transmission power adapts to channel interference to provide QoS support at minimum battery drain and interference stress on the channel. We then consider frame-type selection control, where the streamed content frames are pre-encoded into multiple types or classes with different bandwidth requirements and corresponding viewing quality. Joint control of frame type and transmitter power is seen to achieve substantial performance gains. We also seek to improve the performance of media streaming by using appropriate joint transmission power and playout buffer control. Slowing down the video playout rate can prevent playout buffer underflow, thereby reducing video freezes. We further extend playout control to be content-aware, that is, take into account the motion intensity of different parts of the video sequence. We observe that combining content-aware playout at the receiver with selective frame dropping at the transmitter increases the wireless video quality substantially. |
