# Modeling the Energy Performance of LoRaWAN
## 2 Related Work  
Most of the research done on LoRa/LoRaWAN has focused on features such as coverage, robustness, capacity, scalability, delay and throughput [3; 5; 6; 7; 8; 9; 10; 11; 12]. However, a characteristic such as energy consumption, which is crucial considering that many LoRa/LoRaWAN devices will not be grid-powered, has received limited attention. We next review the literature on LoRaWAN energy consumption. We first focus on current consumption details of LoRa/LoRaWAN devices reported in published works, and secondly we discuss the few existing models of LoRa/LoRaWAN energy consumption, node lifetime or energy cost of data delivery. Several works provide current consumption data of LoRa/LoRaWAN devices, obtained from a datasheet or by empirical means [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. Such details, which are summarized in Table 1, correspond to sleep, transmission and reception device states. As it can be seen, sleep current ranges from 7.66 uA to 34 mA (or between 30.9 uA and 3.4 mA excluding LoRa-only and custom devices). Sleep current for the considered hardware platforms is up to several orders of magnitude greater than that of their transceivers (see Table 2), which can be near or even lower than 1 uA. One important conclusion is that current LoRa/LoRaWAN nodes are far from the degree of optimization exhibited by platforms that use other low power technologies. For example, IEEE 802.15.4 and Bluetooth Low Energy (BLE) commercial devices feature a sleep current near 1 uA [23; 24]. Therefore, in order to achieve attractive node lifetime figures (e.g., in the order of years), current LoRaWAN nodes need batteries with greater capacity than typical button cell batteries, e.g., of AA type, which however have bigger size and are more expensive. We attribute the sleep current in LoRaWAN devices to suboptimal hardware integration of device components, e.g., the microcontroller and the transceiver. Based on the characterization of sleep, transmit and receive states of a LoRa/LoRaWAN device, a few analytical models of LoRa/LoRaWAN energy consumption, node lifetime or energy cost of data delivery have been published [13; 22; 25; 26]. However, these models are too simple, since there exist several other states for a LoRa/LoRaWAN device involved in a communication that need to be considered (see Section 4). Next, we briefly present the main results and other limitations of these works. An accurate calculation of message transmission time is only provided in [25], however the study only focuses on LoRa, and therefore it does not model the MAC layer mechanisms defined in LoRaWAN, such as use of acknowledgments, receive windows, and retransmissions (see Section 3). In [13], which focuses only on optimizing downlink communications, fixed LoRaWAN settings (i.e., a single DR and acknowledged transmission) are considered. Energy consumption of 0.05-0.44 mJ and a battery lifetime between 13 and 1 year, respectively, are obtained for a device running on two AA batteries, when transferring data from 1 to 10 times per hour. However, one of the most important values used in the model, the sleep current (of 2 uA), is without explanation significantly lower than the corresponding value in the datasheet published by the manufacturer (i.e., 30.9 uA). In [26], only the energy related to the activation of a LoRaWAN node by using the On-The-Air Activation (OTAA) mode is modeled. In [22], the battery capacity consumed during a day by a device is calculated assuming 100 events detected and 10 frame transmissions performed by the device. The result is 222.66  uAh, which corresponds to a lifetime of 21.5 months for a 150 mAh button cell battery. Neither the impact of using acknowledgments, nor the influence of the DR configured are considered. Finally, the impact of errors due to corruption on LoRaWAN energy performance has not been modeled in publicly available works.