A mobile gateway device collects identities of a first set of radio nodes which are within one hop of the mobile gateway; and checks at least the collected identities against a first table and a second table. The first table lists node identities and corresponding data validity timers. The second table lists node identities and no corresponding data validity timers. From the checking the device selects a group of radio nodes to activate for collecting and reporting data. The device determines parent child relations among the radio nodes, which are sensor nodes of a wireless sensing network in an embodiment, and uses the list to activate only those nodes for which it does not have valid data to sense new data and transmit their sensing results.