4.1. Scaling Properties

4.1. Scaling Properties

The power and energy available to a node may vastly change over time. Several key characteristics need to be described:

Event energy: The energy used in a single event, such as a packet transmission. Often, one of the larger contributions to the event energy is the radio energy used for the actual transmission; pre-transmission and post-transmission energy contributions, such as radio calibration and local computations/cache lookup necessary to prepare the parameters for transmission, may significantly add to that. Depending on the node architecture, turning on a device may cost some fixed amount of energy, independent of the energy expended while the device is on. (Sometimes, there is a fixed energy budget available for the event, regardless of whether it is actually expended, such as with duty cycling that uses the same time period for sleep and transmission.)

Time spent in different power states: Here, power states are characterized by the current draw in this state. For constrained nodes, there are typically various sleep states that trade off some power consumption for a more immediate availability of the node when needed. A much higher power consumption state is the power state where the node is fully turned on; there might be multiple different levels of this state. Such levels might correspond to working states like radio listening, radio transmitting, or processing; they might also correspond to different power states, such as when different CPU speeds are used.