Patent ID: 8340053

Claim:
A method for performing communication by a lower node in a wireless sensor network having at least one upper node and a plurality of lower nodes including the lower node, comprising: receiving a beacon message from the upper node, wherein the beacon message distinguishes an indirect transmission interval, in which the upper node transmits downlink data to at least one receiving lower node of the plurality of lower nodes, from a direct transmission interval adjacent to the indirect transmission interval, in which the upper node receives uplink data from at least one transmitting lower node of the plurality of lower nodes; determining the indirect transmission interval and the direct transmission interval from the beacon message received; determining whether a time slot is allocated to the lower node from the beacon message received; receiving, if the time slot is allocated to the lower node, the downlink data from the upper node in the indirect transmission interval; transmitting the uplink data to the upper node in the direct transmission interval; switching an OFF state to an ON state in the lower node during the allocated time slot to the lower node; and switching to the OFF state in the lower node when receiving the downlink data is completed; wherein the upper node allocates at least one time slot to the indirect transmission interval, allocates the time slot to at least one of the lower nodes, and generates the beacon message.