On the design of robust and adaptive IEEE 802.11 multicast services for video transmissions

Video communications require the use of networks capable of optimally allocating resources and adapting dynamically themselves to the changing operating conditions. When a video stream has to be delivered to various receivers, the appropriate service to accomplish the delivery process is the multicast communication service. In the particular case of the widely used IEEE 802.11 Wireless LANs (WLANs), the multicast service is simply specified as an unreliable broadcasting service, i.e., it does not include any error recovery mechanism. The absence of feedback from the receivers does not only prevent the sender from taking proper action to recover the corrupted packets, but it also makes unfeasible the implementation of a channel rate adaptation mechanism as the one used by the IEEE 802.11 unicast service. The absence of such mechanism may render the multicast service useless if the channel conditions are so that it makes unreliable the delivery process of the multicast traffic. Even though the IEEE has been working on an amendment to the standard specifying the operation of various error recovery mechanisms for the multicast service, these services have not been designed to support any rate adaptation mechanism. In this paper, we present a novel auto rate selection multicast mechanism, whose design is based on the collision prevention to increase the reliability. We have developed QoS and QoE evaluations via simulation, demonstrating that our proposal outperforms the video quality perceived by the end-user.