Radio Link Buffer Management and Scheduling for Video Streaming over Wireless Shared Channels

In this work we investigate strategies for joint radio link buffer management and scheduling for video streaming over wireless shared channels with focus on High–Speed Downlink Packet Access (HSDPA). The simulations have been carried out with the virtual mode of our wireless system emulator WiNe2. We compare different end–to–end streaming options including variations in the initial delay and timestamp–based streaming versus ahead–of–time streaming. It turns out that buffer management at the entrance to the wireless system has a similar effect as server–based rate control schemes, but avoids the need for frequent end-to-end link probing. In case of an overloaded system packets with the longest waiting time in the radio link buffer should be dropped, since most likely their presentation deadline has already expired anyway. We also conclude that hybrid scheduling strategies do not yield large gains for timestamp-based streaming, since the inherent coarse ”rate control” is sufficient to avoid extreme unfairness in the system. In this case the use of a simple maximum–throughput scheduling policy provides best results. However, if the streaming application does not behave fair as in case of ahead–of–time streaming, the maximum–throughput policy degrades the overall system, as users with bad channel conditions are blocked. Hence, a fair scheduling algorithm provides significantly better performance. Finally, it is shown that the exploitation of simple priority information in packet headers in the dropping strategy can only increase the quality for high initial delays.