Simple Contention Resolution via Multiplicative Weight Updates

Abstract

We consider the classic contention resolution problem, in which devices conspire to share some common resource, for which they each need temporary and exclusive access. To ground the discussion, suppose (identical) devices wake up at various times, and must send a single packet over a shared multiple-access channel. In each time step they may attempt to send their packet; they receive ternary feedback {0, 1, 2+} from the channel, 0 indicating silence (no one attempted transmission), 1 indicating success (one device successfully transmitted), and 2+ indicating noise. We prove that a simple strategy suffices to achieve a channel utilization rate of 1/e − O( ), for any > 0. In each step, device i attempts to send its packet with probability pi, then applies a rudimentary multiplicative weight-type update to pi. pi ←  pi · e upon hearing silence (0) pi upon hearing success (1) pi · e− /(e−2) upon hearing noise (2+) This scheme works well even if the introduction of devices/packets is adversarial, and even if the adversary can jam time slots (make noise) at will. We prove that if the adversary jams J time slots, then this scheme will achieve channel utilization 1/e− , excluding O(J) wasted slots. Results similar to these (Bender, Fineman, Gilbert, Young, SODA 2016) were already achieved, but with a lower constant efficiency (less than 0.05) and a more complex algorithm. 2012 ACM Subject Classification Networks → Network protocols, Mathematics of computing → Probabilistic algorithms