WSN MAC protocols must utilize the hardware resources on a sensor node thoughtfully to save energy and prolong the network lifetime. Many researches have been carried out at this end. As mentioned earlier and illustrated in Figure 1, two general classes for sensor network MAC protocols exist: synchronous protocols and asynchronous or random protocols.
Taxonomy of WSN MAC protocols
Scheduled MAC protocols attempt to organize sensor nodes so their communications occur in a predefined order (Akyildiz et al., 2002), while unscheduled protocols attempt to conserve energy by allowing sensor nodes to operate independently with a minimum of complexity.