Adaptive rate control for broadcasting multimedia streams in IEEE 802.11 networks

In IEEE 802.11 [1] standard, a variety of physical transmission rates are offered, how to use them is not regulated. In order to improve transmission quality and throughput against the packet loss due to unstable wireless environment, several mechanisms with adaptively transmission rate adjustment have been proposed. However, all of them are designed for unicast traffic and most of them exploit ACK frame as the feedback of signal quality. Thus, they are not suitable for broadcasting/multicasting services since no ACK frame will be generated after receiving broadcast frame in IEEE 802.11 protocol. In addition, especially for broadcast/multicast multimedia streaming services, it is possible that each subscriber will suffer from different degree of pack loss due to its distance to the access point and wireless interference. Thus, the subscribers with higher packet loss rate will experience bad playback quality while the others have good quality. In this paper, a novel adaptive rate control mechanism with packet loss rate tracing is proposed for broadcasting multimedia streams such that the subscribers will eventually get almost the same level of packet loss in short interval. The proposed mechanism is implemented on an access point (ADI Pronghorn Metro platform) with Atheros 802.11g interface card. Several experiments are performed and the results show the effectiveness of the proposed mechanism.