A wireless sensor network may be implemented as a distributed system of nodes, each equipped, for example, with a radio transceiver, a microcontroller and one or more sensors and/or actuators. Nodes in such networks may be required to be small in size and inexpensive, which may impose certain limitations with respect to energy storage and consumption. Therefore, reducing the amount of energy consumed by the node may be an important factor in its design.
One way to conserve energy is to have one or more receiver nodes of the network employ a low-power/sleep mode according to a certain duty cycle, which is shown in FIG. 1. Here, the receiver node sleeps most of the time and periodically wakes up for a short period of time to check the broadcast channel for a certain signal in a particular frequency (e.g., a predefined broadcast tone), which is sometimes referred to as the “RF wakeup signal”. If during the wakeup period, the receiver node notices that the signal strength is higher than a certain threshold, this may indicate that another node is attempting to send a message to the receiver node. In this instance, the receiver node will remain active and attempt to receive the message from the sender node. Thus, in this scenario, in order to transmit a message to the receiver node, the sender node must first awaken the receiver node by sending the proper RF wakeup signal with the proper frequency on the proper channel, each of which must be known by the receiver node.
A node may be awakened unnecessarily due to noise or interference in the channel even when there is no transmitter. If the frequency channel in which the RF wakeup is to be performed is too noisy or being used or interfered with by other systems, the nodes may switch to another frequency channel to avoid having to be unnecessarily woken up by the excessive noise or interference. However, once the switch to another frequency channel is made, all neighboring nodes of the receiver node, that is, all potential transmitters of a message to the receiver node, should be informed of the switch so that they aware of the proper frequency channel in which to send any subsequent RF wakeup signals in the future. This in turn creates additional overhead for the network, which may require additional energy resources.
Thus, it may be desirable to adaptively change the frequency channel at which the receiver node listens for the RF wakeup signal so that the channel with the least noise and interference is always used, but such an adaptive change may require that the RF wakeup be performed more often and may also create additional overhead for the network since for each switch in frequency channel all neighbors of the receiver node will need to be informed.