## 5 Conclusions and Recommendation  
This paper analyzed the energy-efficient operation of a LoRa-based wireless sensor network intended for precision agriculture. This type of sensor network may be used for crop condition monitoring by measuring essential environmental parameters. The paper proposed a concise presentation of information in the packet payload (a 6-byte payload format, which provides the same amount of useful information as the 11-byte payload used with commercially available devices). The given example of the selected smaller packet size is a more suitable solution in terms of energy saving.  
Furthermore, the difference in the analyses carried out in this paper compared to the analyses carried out in the literature so far lies in the definition of an adequate transmission rate. While the analyses carried out so far have assumed fixed values of the transmission rate, in this paper it was assumed that the transmission rate changes with each sending, considering the amount of data in the sent packets, i.e., the size of the packet. This affects the results, because in this paper it was proven that for better energy efficiency of communication, it is important to adjust the transmission speed to the actual size of the packet. So, the high transmission rate can be more energy-efficient method when sending smaller packets.  
By testing LoRa communication modules in real case study conditions, the results collected through field measurements, simulations, and laboratory tests were compared. An optimized energy model for LoRa sensor nodes was presented. It was shown that the consumed energy changes with different parameter settings. Optimizing LoRa parameters, such as SF and CR, regarding the required long-range communication is crucial in reducing the energy consumed by the sensor nodes in the case study areas. However, it is proven that, regardless of SF values, if the payload size decreases, the energy per useful bit decreases as well.  
Moreover, it is evident that ADR should be used in the analyzed scenarios since substantial energy savings can be achieved by enabling ADR. After receiving 20 up-link messages, the network will respond with adequate ADR parameters to accommodate non-optimal propagation. Therefore, LoRa devices should send smaller packets to adapt to the channel faster since this will reduce air time and energy consumption for packets sent with non-optimal parameters.  
Finally, it was concluded that receiving a transmission acknowledgment consumes energy, which considerably reduces the sensor node lifetime. Therefore, another contribution of the paper is the graph showing the limits of reliable data transmission. According to the obtained graph, it is possible to identify areas within which it is not necessary to send acknowledgments, which can significantly reduce energy consumption based on the last measured SNR and RSSI values. Moreover, the selection of the frequency of sending acknowledgments must also be compliant with the ETSI and LoRaWAN standards, which also apply to gateways.  
Conceptualization, V.K. and K.G.; methodology, V.K.; software, V.K.; validation, V.K., K.G. and D.Z.; formal analysis, V.K.; investigation, V.K. and J.S.; resources, V.K. and J.S.; data curation, J.S.; writing--original draft preparation, V.K.; writing--review and editing, K.G.; visualization, V.K.; supervision, D.Z.; project administration, D.Z.; funding acquisition, D.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the project \"IoT-field: An Ecosystem of Networked Devices and Services for IoT Solutions Applied in Agriculture\" co-financed by the EU from the European Regional Development Fund within the Operational Program Competitiveness and Cohesion 2014-2020 of the Republic of Croatia grant number KK.01.1.1.04.0108.  
The data presented in this study are openly available in repository FigShare at 10.6084/m9.figshare.23663982.  
The authors declare no conflict of interest.