# Energy Performance of LR-FHSS: Analysis and Evaluation
## 5 Evaluation
### Current Consumption  
We evaluate the current consumption of an LR-FHSS ED, both with and without confirmed transmissions, using Equations (1) and (14), respectively. We use the minimum FRM Payload size of 1 byte and the maximum allowed FRM Payload size for the LR-FHSS DRs and for DR0 and DR5 of LoRa.  
As introduced in Section 3, as the ED works over the EU863-870 MHz band, the 1% duty cycle limitation must be considered in the evaluation. Since \(T_{Tx}\) varies depending on the DR, we provide the minimum interval between consecutive transmissions for each DR (see Table 8) allowed by the 1% duty cycle restriction.  
Figure 10 shows the ED's average current consumption for different DRs, the maximum allowed FRM Payload size for each DR, and for both unconfirmed and confirmed transmission. As expected, regardless of the DR, the current consumption tends to converge towards the sleep state consumption of around 500 nA as the interval between transmissions (labeled \"Period\" in Figure 10 and subsequent figures) increases.  
As expected, the average current consumption for confirmed transmission is consistently higher than that of unconfirmed transmission. Specifically, the differences between the confirmed and unconfirmed operational modes for the LR-FHSS DRs (i.e., for the DR8/DR10 and DR9/DR11 pairs) are around 3%. However, these differences rise to 5.7% and 18.4% for DR0 and DR5, respectively. Note that confirmed transmission can reduce the energy consumption as the probability of receiving the confirmation in the first receive window, \(p_{1}\) (cf. Equation (14)), increases. The results show the tendency of faster DRs, which have a shorter time on air (ToA), to reduce current consumption by a factor of up to around 10. Nonetheless, this pattern does not apply to DR9 and DR11, as these DRs exhibit higher current consumption than DR0 although having a higher data rate. This oddity can be explained by the fact that the maximum FRM Payload size for DR9/DR11 (115 bytes) is substantially larger than that of DR0 (51 bytes) or DR8/DR10 (50 bytes), resulting in a noticeably longer ToA for uplink transmission with DR9/DR11.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**DR**} & \multicolumn{2}{c}{**Minimum Frame Transmission Period (s)**} \\ \cline{2-3}  & **1-Byte Payload** & **Max Payload** \\ \hline
0 & 105.7 & 279.3 \\
5 & 6.550 & 39.96 \\
8/10 & 157.3 & 408.7 \\
9/11 & 90.35 & 382.8 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Minimum interval between two consecutive transmissions in order to comply with the 1% duty cycle regulation, depending on the DR and FRM Payload size from Table 1. Values for DR0 and DR5 are obtained from prior work [20].  
However, when the payload size is the same for all DRs considered (e.g., as shown in Table 6 for a 1-byte FRM Payload), the \(T_{Tx}\) values correspond, in descending order, to DR8/DR10, DR0, DR9/DR11, and DR5. This behavior is clearly illustrated in Figure 11, where average current consumption follows the same pattern. On the other hand, there is a non-negligible difference between confirmed and unconfirmed transmission, with the former being more energy-consuming, especially for faster DRs.