On the universality of age-based scheduling in wireless networks

It is well-known that maximum weight scheduling, with link weights which are either functions of queue lengths or the ages of the Head-of-Line (HoL) packets in each queue, maximizes the throughput region of wireless networks with persistent flows. In particular, with only persistent flows, it does not matter for throughput optimality whether one uses queue lengths or HoL ages as weights. In this paper, we show the following interesting result: when some flows in the network are dynamic (i.e., they arrive and depart from the network and are not persistent), then HoL-age-based scheduling algorithms are throughput-optimal while it has previously been shown that queue-length-based algorithms are not. This reveals that, age-based algorithms are universal in the sense that their throughput optimality does not depend on whether the arriving traffic is persistent or not. We also present a distributed implementation of the proposed age-based algorithm using CSMA techniques, where each flow only knows its own age and carrier sensing information. Finally, we support our analytical results through simulations. The proof of throughput optimality may be interesting in its own right: it uses a novel Lyapunov function which is the sum of the ages of all the packets in the network.