Adaptive Delay and Synchronization Control for Wi-Fi Based Mobile AV Conferencing

The tremendous success of the IEEE 802.11b technology and the popularity of portable computing units (e.g., PDAs) have led to a surge of Wi-Fi based real-time multimedia applications. However, due to the unpredictable and often fluctuating channel behavior, it is rather difficult to configure an appropriate de-jitter buffer to maintain a satisfactory perceived quality for end users. Motivated by this problem, we propose in this paper an adaptive delay and synchronization control scheme for Wi-Fi based AV conferencing applications. We target at campus-wide IEEE802.11b WLANs that are generally capable of supporting low-latency multimedia applications. The proposed scheme employs a distributed timing mechanism and performs localized control at the receiver side. The scheme can also be configiured flexibly with either one of the two inter-stream synchronization control options. Based on real-time monitored synchronization errors, Media Data Unit (MDU) loss, and real-time statistical estimation of the delay jitter among adjacent MDUs, the scheme is able to piece-wisely adjust the equalization delay to compensate for the delay jitter and control the MDU loss effectively. We investigate the performance of the proposed scheme using trace-driven approach. Through simulations, we show that the proposed scheme is capable of dynamically balancing between synchronization and latency requirements and effectively control the MDU loss as well. In particular, compared to the solutions using a static setting, the proposed scheme is able to provide the same MDU loss performance with a significant reduction in resultant latency.