# A Survey of LoRaWAN for IoT: From Technology to Application
## 6 MAC Layer Performance Evaluation
### Power Usage  
Device power consumption is crucial for proper operation, as LoRaWAN is used for application employing constrained devices. Thus, it is needed to model the power usage profile of LoRaWAN end node and to determine the battery lifetime. The presented power consumption values are based on empirical measurements done with certain end nodes [35; 79; 80]. They include all the phases that an end node will transit during its transmission phase: sleeping time, wake-up time, transmission time, listening in the first receive window and receiving phase.  
Figure 7: Interference scenarios that are taken into account in LoRaWAN models.  
In [79], a power profile modeling of LoRaWAN end node is shown. The model considered the impact on power consumption of residual bit error rate (BER) after the bit error correction is done using FECs. In addition, collision probability impact is considered too. It models both type of transmissions: acknowledged and unacknowledged ones. Evaluation is done based on the values for current consumption by mDot end node at each of the transmission phase. It is shown that, by sending a packet (51 bytes) every 10 min, battery life can be up to one year for SF7-SF10, for a battery capacity of 2400 mAh. On the other hand, for SF12 and SF11, the battery lifetime will be lower, 0.5 and 0.8 years, respectively [79]. For less frequent transmission, lifetime will extend. It is shown also that the power consumption in unacknowledged uplink traffic case is higher than the case when the acknowledgment is received in the first receive window. Such an observation is not intuitive. In the latter case the second receive window as well as the phase between the first receive window and the second receive window does not happen. This makes possible for the node to go to sleep right after the reception of ACK packet. In the former case, as there is no ACK, end node still needs to open both receive windows and to pass the phase between two receive windows. This will introduce higher power consumption than the reception of small ACK in RW1.  
In [80], authors compared the battery lifetime for different LoRaWAN end device classes. First, voltage and current drain measurements for each end device class are done. Based on the measurements, the results are benchmarked with the end node data-sheets. Then, the battery capacity for a period over 10 years for different packet lengths, transmission periods, SFs and different device classes are calculated. In all cases, an-acknowledged traffic is supposed.  
A LoRa energy efficiency study is presented in [81]. It is shown that energy consumption is increased faster by increasing the SF while keeping the transmit power the same. Thus, more desirable for ADR mechanism is, first, to increase the transmit power for increased range before the SF is increased. In [82], the benefit of using ADR scheme and long packet length in LoRa energy performance is shown. The ADR mechanism reduces the energy consumption five times per payload byte. Energy consumption for payload byte decreases also for longer data packets due to lower header overhead [82]. However, this cannot be true in congested network where longer packets are prone to higher error rates and need to be retransmitted. In [83], power consumption profile for Semtech SX1272 chip is modeled. The average battery lifetime is calculated to be 1-5 years for sensing interval of 1-5 min, respectively. If energy harvesting from renewable energy sources is used, battery lifetime can go from 4 to 12 years for the same sensing interval range.  
In Table 6, studies that deal with power consumption modeling are collected by showing what type of traffic is considered.