PROXY−BASED REFERENCE PICTURE SELECTION FOR REAL−TIME VIDEO TRANSMISSION OVER MOBILE NETWORKS (WedAmOR4)

We propose a framework for error robust real−time video telephony over wireless networks. In our approach we cope with packet loss on the downlink by retransmitting lost packets from the base station to the receiver terminal. The effect of lost packets is reduced using error concealment. Retransmitted packets are used for error recovery. In order to be able to use the retransmissions for error recovery, we signal the sender to use fixed−distance reference picture selection during encoding where the distance to be used corresponds to the round−trip−time measured between the base station and the receiver terminal. We deal with transmission errors on the uplink by sending acknowledgment information from the base station to the sender terminal. The video encoder uses this information to predict the next frame to be encoded from the most recent frame that has been positively acknowledged by the base station. The most recent frame that can be used for this is always earlier than the fixed distance reference picture that is adapted to the round−trip−time on the downlink. We show that these two separate approaches for uplink and downlink nicely fit together. We compare our approach to state−of−the art error resilience approaches that employ random Intra update of macroblocks and FEC across packets for error resilience. [continued in the next page]