Hierarchical queue-length-aware power control for delay-sensitive applications over wireless networks

We consider the problem of optimal power control for quality-of-service-assured wireless communication. The quality of service (QoS) measures of our consideration are a triplet of data rate, delay, and delay bound violation probability. Our target is to develop power control laws that can provide delay guarantees for real-time applications over wireless networks. The power control laws that aim at optimizing certain physical-layer performance measures, usually adapt the transmission power based on the channel gain; we call these ldquochannel-gain-basedrdquo (CGB) power control (PC). In this paper, we show that CGB-PC laws achieve poor link-layer delay performance. To improve the performance, we propose a novel scheme called hierarchical queue-length-aware (HQLA) power control. The key idea is to combine the best features of the two PC laws, i.e., a given CGB-PC law and the clear-queue PC law; here, the clear-queue PC is defined as a PC law that uses a transmission power just enough to empty the queue at the link layer. We analyze our proposed HQLA-PC scheme by the matrix-geometric method. The analysis agrees well with the simulation results. More importantly, our simulation results show that the proposed HQLA-PC achieves significant gain over the CGB-PC scheme, for tight delay requirements.