Guard zone-based scheduling in ad hoc networks

Abstract

Scheduling algorithms in ad hoc networks allow nodes to share the wireless channel so that concurrent transmissions can be decoded successfully. On one hand, scheduling needs to be efficient to maximize spatial reuse and minimize retransmissions due to collisions. But on the other hand, the scheduling algorithm needs to be easily implementable in a distributed fashion with little, if any, coordination with other nodes in the network.In this paper we propose and evaluate a simple scheduling technique that suppresses transmissions by nodes around the desired receiver. Using stochastic geometry, we derive a near-optimal guard zone which can be easily realized in a distributed manner, and exhibits about a 2–40 fold increase in capacity compared to ALOHA; the capacity increase depending primarily on the required outage probability and node density. The capacity loss is about 15–25% compared to a well-known near-optimal centralized scheme. In contrast to centralized scheduling (which is highly impractical), our scheme lends itself to distributed implementation and also protects active links. Our derivations cleanly capture how the optimal guard zone size varies with different network parameters like path loss, outage, spreading gain, and node density, and we show how these results can be used to provide protocol design guidelines.