There is provided a communications system comprising an access network node and a plurality of resource limited nodes. The access network node comprises: a control unit operable to estimate a belief on a network condition for a resource limited node of the plurality of resource limited nodes based on network observations and a history profile of the network observations; dynamically update the belief for the resource limited node in the access network node; determine that the severity of the updated belief in the network condition is indicative that a change in sleep duty cycle of the resource limited node is required; determine that correlation between the resource limited nodes within the plurality of resource limited nodes is indicative that a change in sleep duty cycle of the resource limited node is required; and update the sleep duty cycle of the resource limited node to optimize the overall energy consumed in the resource limited nodes while achieving a specific detection threshold.