The configuration space of duty-cycled CSMA-based wireless MACs

Wireless sensor network (WSN) applications vary widely in their traffic and node density patterns. Conventional wisdom says that a medium access control (MAC) protocol that performs well for one application can perform poorly for another. Perhaps as a result of this view, a large number of MAC protocols have been proposed, often with specific performance metrics in mind; many of the widely used ones have focused on the low duty cycle case. In this paper, we study how the choice of the MAC protocol as well as the configuration of its parameters impacts performance for diverse traffic rates and node densities. Specifically, we classify CSMA-based MAC protocols in terms of critical MAC-design factors and introduce a framework for performance modeling of each MAC class as a function of key protocol parameters. We use this framework to analyze various performance metrics comprehensively across the configuration space of the protocols; extensive experimentation corroborates our analysis. Our results serve not only as a basis for comparing protocols, they also yield insight into how to adapt MACs to changing traffics in a distributed way. Although the framework focuses on single-hop traffic patterns, potential for extending the framework to analyze richer application scenarios is also investigated and discussed. A surprising finding of our comparative evaluation is that one class of MAC protocols consistently achieves the best or close to the best performance for various metrics across much of the configuration space.