Scheduling in networks with time-varying channels and reconfiguration delay

Abstract

We consider the optimal control problem for networks subjected to time-varying channels, reconfiguration delays, and interference constraints. We model the network by a graph consisting of nodes, links, and a set of link interference constraints, where based on the current network state, the controller decides either to stay with the current link-service configuration or switch to another service configuration at the cost of idling during schedule reconfiguration. Reconfiguration delay occurs in many telecommunications applications and is a new modeling component of this problem that has not been previously addressed. We show that the simultaneous presence of time-varying channels and reconfiguration delays significantly reduces the system stability region and changes the structure of optimal policies. We first consider memoryless channel processes and characterize the stability region in closed form. We prove that a frame-based Max-Weight scheduling algorithm that sets frame durations dynamically, as a function of the current queue sizes and average channel gains is throughput-optimal. Next, we consider arbitrary Markov modulated channel processes and show that memory in the channel processes can be exploited to improve the stability region. We develop a novel approach to characterizing the stability region of such systems using state-action frequencies which are stationary solutions to a Markov Decision Process (MDP) formulation. Finally, we develop a frame-based dynamic control policy, based on the state-action frequencies, and show that it is throughput-optimal asymptotically in the frame length. The FBDC policy is applicable to a broad class of network control systems, with or without reconfiguration delays, and provides a new framework for developing throughput-optimal network control policies using state-action frequencies.