# Energy Performance of LR-FHSS: Analysis and Evaluation
## 6 Conclusions  
In this article, we provided the first energy consumption model of a Class A LoRaWAN ED using the novel LR-FHSS physical layer. We also evaluated the impact of variables like the use of confirmed transmissions, DRs, and FRM Payload sizes. The key metrics considered were the average current consumption, battery lifetime, and energy cost of data transmission. The model was created based on data collected using a real LoRaWAN network in which all of the components support LR-FHSS. From the evaluation of the model, a first general conclusion is that LR-FHSS DRs exhibit energy performance comparable to that of the most robust LoRa DR (i.e., DR0) but worse than a fast LoRa DR such as DR5. Figure 16: Energy cost of confirmed data transmission as a function of \(T_{Period}\) when sending the maximum allowable FRM Payload and a 1-byte FRM Payload for DR8/DR10, DR9/DR11, DR0, and DR5. Figure 15: Energy cost of unconfirmed and confirmed data transmission as a function of \(T_{Period}\) for the maximum FRM Payload sizes for DR8/DR10, DR9/DR11, DR0, and DR5. The average current consumption for DR8/DR10 was consistently the highest in both the maximum and 1-byte FRM Payload cases, reaching a peak of around 0.27 mA. The average current consumption for DR9/DR11 behaved very similarly to the former when using the maximum FRM Payload size, although it decreased when using a 1-byte FRM Payload. For a constant FRM Payload size, the average current consumption decreased with the physical-layer bit rate due to the impact of the latter on ToA. DR5 achieved up to approximately six-times lower current consumption. Regarding the use of ACKs, the ED consumed less current when using the unconfirmed approach (e.g., around 3% lower for all LR-FHSS DRs). Overall, the current consumption tended to decrease with the period between uplink transmissions, since the influence of sleep current increased as well. The theoretical battery lifetime of an ED with a 230 mAh button-like battery is ~20 years for a transmission period of 500 min, unconfirmed transmission, DR9/DR11, and a 1-byte payload. Under the same conditions, DR8/DR10 reaches a maximum of around 14 years, DR0 yields an intermediate lifetime of ~18 years, and DR5 is the best-performing among the considered DRs. When maximizing the payload in an infrequent interval, such as a one-day period, the battery lifetime for DR9/DR11 is 16 years. As expected, battery lifetime decreases with payload size and sleep current consumption. Nonetheless, although DR9/DR11 uses a faster bit rate than DR8/DR10, their lifetimes are similar when using the maximum FRM Payload permitted by each DR. The outcome is that maximizing the bit rate, minimizing the payload size, and not using ACKs enhances the lifetime of EDs. Finally, the energy cost per transmitted bit is lower for DRs that feature a higher bit rate and a larger payload size. For example, the energy cost of DR9/DR11 is lower than that of DR8/DR10, with differences of up to around 2.5 times. Not using ACKs is more energy efficient regardless of the DR, but by a mild margin. It should also be noted that the energy per bit tends to increase as the period between uplink transmissions increases due to the higher total energy consumption for the same amount of transmitted data. Conceptualization, R.S.-V., C.G. and E.G.-V.; methodology, R.S.-V. and B.H.-S.; software, R.S.-V., L.C. and B.H.-S.; validation, R.S.-V., L.C. and R.V. ; formal analysis, R.S.-V.; investigation, R.S.-V., L.C., B.H.-S. and C.G. ; resources, L.C. and R.V. ; data curation, R.S.-V., B.H.-S. and R.V. ; writing--original draft preparation, R.S.-V. and B.H.-S.; writing--review and editing, R.S.-V., L.C., R.V., C.G. and E.G.-V.; visualization, R.S.-V. and B.H.-S.; supervision, L.C., C.G. and E.G.-V.; project administration, C.G. and E.G.-V.; funding acquisition, E.G.-V. All authors have read and agreed to the published version of the manuscript.