# Modeling the Energy Performance of LoRaWAN
## 5 Evaluation
### End-Device Current Consumption
#### 5.1.2 Acknowledged Transmission  
We next use the values shown in Tables 6-8 and Equations (18)-(28) to compute the average current consumption of the end-device in acknowledged transmission. In order to compare results of unacknowledged and acknowledged transmission, Figure 9 depicts the results, as a function of \(T_{Notif}\) for various DR settings, and for BER = 0. Since some of the curves of DR2 and DR3 overlap with those of DR4, results for DR2 and DR3 are excluded from Figure 9.  
Overall, when BER = 0, the average current consumption of acknowledged transmission follows a tendency with \(T_{Notif}\) that is similar to the unacknowledged transmission one: it decreases with \(T_{Notif}\), it tends asymptotically to the sleep current, and it decreases with the DR used. Figure 8: Average current consumption of the end-device in unacknowledged transmission, as a function of \(T_{Notif}\), and for different DR settings. A remarkable result, which is apparently counterintuitive when considering typical behavior of acknowledged link layer protocols other than LoRaWAN, is the fact that acknowledged transmission yields lower current consumption than that of unacknowledged transmission. Note that in acknowledged transmission, the acknowledgment may be received by the end-device in the first or in the second received window. The latter leads to greater average current consumption than in unacknowledged transmission (since the acknowledgment has to be completely received, as opposed to the duration of the second window where no message is received by the end-device). However, the former involves significantly lower current consumption compared to unacknowledged transmission, since then neither a second receive window nor its previous wait time exist. This leads to an overall average current consumption in acknowledged transmission that is lower than the one in unacknowledged transmission. The maximum current consumption difference between unacknowledged and acknowledged transmission is \(\sim\)16%, which is found for DR6 and a notification period of 0.5 min. For other DRs, such maximum difference tends to decrease, down to \(\sim\)3% for DR0, although such decrease is not monotonical (e.g., the maximum difference for DR4 is lower than that for DR1). Recall that we are considering a frame payload of the highest possible size for each DR, and the maximum frame payload size does not decrease proportionally to the bit rate as the DR decreases. It is also interesting to consider the case of acknowledgments being always transmitted in the first receive window (i.e., \(p_{1 win}=1\) and \(p_{2 win}=0\)). Such conditions lead to the lowest possible LoRaWAN end-device current consumption. In that case, the current consumption in acknowledged transmission decreases by up to 45.1% (for DR5 and a notification period of 1 min), compared to the unacknowledged one. However, such decrease is only significant for low notification periods. We also evaluate impact of the frame payload size on current consumption. Figure 10 illustrates the average current consumption of an end-device in acknowledged transmission, for a single-byte and also for a maximum-sized frame payload, which provide the lower and the upper bound on average current consumption for a given DR, respectively. The difference between the lower and upper bounds is significant for a low notification period (e.g., \(\sim\)49% for a notification period of 1 min, and \(\sim\)59% for a notification period of 5 min, for DR5 and DR0, respectively). Such difference decreases with \(T_{\mathit{Notif}}\) since sleep current then becomes dominant, and it also decreases with the DR, since higher bit rates reduce the relevance of active communication states on average current consumption. Figure 9: Comparison of the average current consumption of the end-device in acknowledged and unacknowledged transmission, as a function of \(T_{\mathit{Notif}}\), and for different DR settings, for BER = 0 and \(p_{\mathit{coll}}=0\).