Effective capacity optimization with layered transmission for multicast in wireless networks

Effective capacity is an effective technique in devising and evaluating the capability of a time-varying wireless channel to support data transmissions with diverse statistical quality of service (QoS) guarantees. In this paper, we propose an efficient framework to optimize and analyze the effective capacity for mobile multicast over broadcast fading channels. Our analyses identify the fundamental tradeoffs among the system through-put, delay statistical QoS guarantees, and reliability in terms of the effective capacity, QoS exponent, and average loss-rate threshold, respectively. The QoS exponent specifies the exponentially decaying rate of the violation probability against the queue-length/delay bound, playing a key role in statistical QoS guarantees, while the average loss-rate threshold upper-bounds the tolerable loss level for all multicast receivers. The tradeoff is achieved by optimizing the effective capacity via channel-aware rate adaptation subject to the specified QoS exponent and average loss-rate threshold. For rate adaptation, we employ the layered multicast transmissions, implemented by either the time-sharing (TS) or superposition-coding (SPC) techniques, to handle the heterogeneous qualities over channels across multicast receivers, and develop a novel pre-drop scheme to implement the more flexible rate control. Our simulations demonstrate the tradeoff between the effective capacity and QoS metrics, and show the superiority of our derived optimal schemes as compared to the other suboptimal schemes.