Wireless Sensor and Actuator Networks: Algorithms and Protocols for Scalable Coordination and Data Communication

1.8 SLEEP AND ACTIVE STATE MODELING

Energy consumption is one of the key problems in WSNs. Several energy consumption models have been studied in the literature. The following discussion and the graph (Fig. 1.6) are based on the study by Barrenetxea et al. (2008). The graph shows energy consumption of a TinyNode sensor mote in different states. The experiment shows that the calculation of the sensor node's receiving costs depends on the assumption of the node's status. If it assumes that the radios of the nodes are always on, the energy consumption of the receiving costs is negligible since the cost for receiving packets has been included in the cost for keeping the radios on. More precisely, the energy consumption is equal to 2 mA when the radio is off but is equal to 16 mA when the radio is on for reception. This means that it takes about eight times more energy for listening compared to sleeping state. The total energy consumption for receiving depends on how long the radios need to be on to receive an incoming packet. Using the example in Figure 1.6 below, we suppose that transmitting a packet at 15 dB consuming 60 mA takes 5 ms. Receiving the packet takes at least 5 ms. However, it is not possible for the node to turn on exactly at the time the packet is sent. That is, to receive the packet, the node should turn on its radio for more than 5 ms (according to the used protocol). In Figure 1.6, the energy consumption of the radio is 15 mA. Therefore, if the total time the radio ...