## 4 915 MHz/2400 MHz Bands' Performance in SG-oriented IoTs
### Scenario 1: Presence of 2400 MHz Co-Existing Devices  
In this scenario, we consider an environment in which the 2400 MHz band is extensively employed by many other devices and hence, suffers moderate interference levels with an average noise floor of \(-\)87.4 dB. The 915 MHz band, on the other hand, as it is not usually shared with other technologiesnowadays, remains relatively free from interference, presenting an average noise floor of \(-93.85\) dB. These exact noise values have been obtained from the real SG under consideration using the Rhode & Schwarz(r) FSH3 spectrum analyzer and are incorporated in the TOSSIM simulator.  
The results obtained are shown in Figure 5a for the packet reception rate (PRR), Figure 5b for the mean network delay (MND), and Figure 5c for power consumption per packet transmission (PCPT).  
The first and most notable highlight of Figure 5a is the good behavior of the 915 MHz band (blue, upper lines) compared with the 2400 MHz band (red, lower lines) in terms of PRR. The reason for this is threefold: firstly, differences in LNSPL models (presented in Table 1) reveal the tendency of the 2400 MHz band to attenuate signals more than the 915 MHz band. Secondly, the 2400 MHz band experiences a higher noise floor level due to the presence of other co-existing devices. Finally, the OQPSK modulation (employed in the 2400 MHz band) tends to perform slightly worse in terms of PRR versus signal-to-noise ratio than the FSK modulation (used in the 915 MHz band) [44].  
Both bands face the typical effects of the distance on the PRR. When \(\alpha\) (and thus \(\overline{D}_{in}\)) increases, the received power decreases, leading to a larger number of packet losses and a decrease of the PRR. However, this KPI is not affected evenly in both bands, as the 2400 MHz band deteriorates slightly faster than the 915 MHz band due to higher path-losses. Regarding the packet size, larger packets produce smaller PRR values; given a certain bit error rate, an increment of the payload length always implies a smaller PRR. However, we can claim that packet size is not a crucial variable as it entails a PRR drop of less than 5%, on average, when increasing the payload length from 6 bytes to 24 bytes.  
When the number of packet losses increases (and hence, the PRR decreases) a higher number of retransmissions is issued. This leads to an increment of the MND as this KPI takes into account the extra time taken by retransmissions (Figure 5b). Therefore, it should be noted that even though the  
Figure 5: Results of the Scenario 1 for different packet sizes and resizing factors. (**a**) PRR, (**b**) MND, and (**c**) PCPT.  
transmission rate of the 2400 MHz band is higher, due to big differences in terms of PRR, the MND of the 2400 MHz band is, on average, four times larger than that obtained for the 915 MHz band. Under these circumstances, this phenomenon makes the 2400 MHz band less adequate for delay-sensitive applications. As with the PRR, an increment of the scaling factor (\(\alpha\)) negatively affects the MND in both bands. Again, due to differences in path-losses, the 2400 MHz band is much more sensitive to \(\alpha\) than the 915 MHz band. Considering the dependency of MND with \(\alpha\), the 2400 MHz band grows seven times faster than the 915 MHz band.  
Figure 5c illustrates the PCPT. The very low value for the 2400 MHz band is, again, produced by the large volume of retransmissions, which greatly increases the power consumption. The 2400 MHz-band consumption is up to 120 times larger than the 915 MHz one (1187 joules versus 9.7 joules per packet transmission for a packet length of 24 B and \(\alpha=1.5\)). Therefore, the latter band should become the preferred choice for energy-constrained IoT deployments.