# A Sigfox Energy Consumption Model
## 5 Evaluation
### Impact of Critical Parameters on the Model  
This subsection studies the impact of critical parameters, such as the sleep current, the Sigfox device transmit power, and the uplink frame size, on the model presented in this paper.  
A parameter with a crucial impact on energy consumption metrics is the sleep current, \(I_{sleep}\). As discussed in Section 4.1, the sleep current in the device used for this work is 16 \(\mu\)A, whereas transceiver datasheets may indicate a sleep current in the order of 1 \(\mu\)A. Figure 12 depicts the average current consumption for \(I_{sleep}\) settings such as 16 \(\mu\)A and 1 \(\mu\)A, for different transaction types, and FLR = 0. An uplink bit rate of 100 bit/s is assumed. As it can be seen, impact of \(I_{sleep}\) increases with the transaction period, since \(I_{sleep}\) is the asymptotic current consumption value (note that \(I_{self\_dis}\) needs to be considered as well when a battery is used, with a relative impact that increases as the transaction period decreases). For bidirectional transactions, and a 12-byte payload, the \(I_{sleep}\) settings considered lead to significant current consumption differences for a \(T_{Period}\) of around 100 min or greater. For unidirectional transactions, and a 1-byte payload, current consumption differences arise for lower \(T_{Period}\) values (e.g., 10 min), due to the lower overall current consumption in unidirectional transactions.  
Another parameter that is relevant in terms of energy consumption is the Sigfox device transmit power. The device used in our evaluation only supports one transmit power value (i.e., 14.5 dBm). Such a value matches the maximum allowed device transmit power according to EU regulations, and for this reason it is commonly used as the default or the only transmit power setting in other Sigfox hardware platforms [9; 10; 11; 13]. However, from the point of view of the model, the transmit power used has an influence on the performance parameters considered in this paper, since \(I_{tx}\) depends on the transmit power setting.  
Figure 13 illustrates the impact on the average current consumption of considering different \(I_{tx}\) values, such as the one obtained with our measurements, i.e., 27.6 mA, and 15 mA, different transaction types and uplink payload sizes. An uplink bit rate of 100 bit/s is assumed. As shown in Figure 13, the transmit power, and thus \(I_{tx}\), is relevant for low transaction periods. The impact of \(I_{tx}\) is greater for unidirectional transactions, since in bidirectional transactions the Sigfox device consumes a significant amount of current during the receive window.  
Figure 11: Energy cost of data delivery, for unidirectional and bidirectional transactions, as a function of \(T_{Period}\), for uplink payload sizes of 1 byte and 12 bytes, for an uplink bit rate of 100 bit/s, and for different FLR values.  
Finally, another relevant parameter is the uplink frame size. Note that this parameter grows linearly with the uplink frame payload size and, as already illustrated in Sections 5.1-5.3, it has a relevant impact on device current consumption, device lifetime and energy cost of data delivery. However, another important aspect to consider regarding the uplink frame size is its relationship with the FLR. A frame may be lost due to bit errors (e.g., due to poor received signal, challenging signal propagation conditions, interference, etc.), and it may also be lost due to collisions [7]. Increasing the uplink frame size increases the FLR for both reasons.  
As shown in Sections 5.1 and 5.3, the FLR affects current consumption for bidirectional transactions (mostly increasing current consumption for \(FLR>0.5\)), and a non-zero FLR increases the energy cost of data delivery.