The effects of synchronization on topology-transparent scheduling

Topology-transparent scheduling is an attractive medium access control technique for mobile ad hoc networks (MANETs) and wireless sensor networks (WSNs). The transmission schedule for each node is fixed and guarantees a bounded delay independent of which nodes are its neighbours, as long as the active neighbourhood is not too dense. Most of the existing work on topology-transparent scheduling assumes that the nodes are synchronized on frame boundaries. Synchronization is a challenging problem in MANETs and in WSNs. Hence, we study the relationships among topology-transparent schedules, expected delay, and maximum delay, for successively weaker models of synchronization: frame-synchronized, slot-synchronized, and asynchronous transmission. For each synchronization model, we give constructive proofs of existence of topology-transparent schedules, and bound the least maximum delay. Perhaps surprisingly, the construction for the asynchronous model is a simple variant of the slot synchronized model. While it is foreseen that the maximum delay increases as the synchronization model is weakened, the bound is too pessimistic. The results on expected delay show that topology-transparent schedules are very robust to node density higher than the construction is designed to support, allowing the nodes to cope well with mobility, and irregularities of their deployment.