Distributed synchronization and medium access in wireless mesh networks

Implicit local coordination of nodes in a wireless network using mechanisms such as Carrier Sense Multiple Access (CSMA) is conceptually attractive and relatively easy to implement, but often leads to performance that is far inferior to what is possible using explicit global coordination strategies such as Time Division Multiplexing (TDM). In this paper, we give two examples showing that appropriately designed implicit coordination strategies that employ learning and memory can provide performance competitive with that obtained using explicit strategies, while requiring minimal overhead. The first example is an algorithm for distributed timing synchronization maintenance using the timing information already present in ongoing communication in the network. The second example is a distributed medium access control protocol that achieves performance close to time division multiplexing (TDM) without requiring explicit resource allocation: nodes lock into communication patterns that have been found to work, with enough randomization to prevent locking into poor schedules. While the general philosophy of exploiting learning and memory in the design of network protocols is of broad applicability, our numerical results emphasize 60 GHz networks with highly directional links: effective coordination is particularly important for such networks, in view of the “deafness” caused by directionality.