# Accurate Energy Consumption Modeling of IEEE 802.15.4e TSCH Using Dual-Band OpenMote Hardware
## 5 Evaluation
### Frequency Band Consumption Comparison
#### 5.4.1 Simulation Setup
The same effect is observed in the results for 25 nodes: 60% of the nodes that use 2.4 GHz consume less than the nodes using 868 MHz. These nodes represent leaf nodes and nodes that do not have to forward many data packets originating from children in the routing graph. Apart from these nodes, there are also other intermediate nodes, as indicated by the 2.4 GHz hop count of 2.49 (\(\sigma=1.21\)) for the grid scenario with 25 nodes, which have to relay many more packets towards the root and consume more energy. When using 868 MHz, the average hop count was 1.01 (\(\sigma=0.1\)), which means that all nodes are directly connected to the root and thus do not relay other packets. For both the grid networks of nine and 25 nodes, the root nodes for 2.4 GHz consume less than those of 868 GHz, which again can be expected by looking at the consumption values in Table 19.  
Looking at the absolute energy consumption values for both 868 MHz and 2.4 GHz, an increased energy consumption for all sub-1-GHz communication is expected. However, these simulation results show that due to the longer-range capabilities of sub-1-GHz communication, there can be nodes that consume less energy compared to when using 2.4 GHz communication. In the third TSCH simulator experiment, we observe the lifetime of all TSCH nodes in a grid of 25 nodes for different packet periods. Each node is assumed to be running on two AA batteries, i.e., a battery capacity of 2000 mA h. Figure 12 shows the results. The total number of children are all children of a node, e.g., the root node will have 24 children. It is clear that in the case of 2.4 GHz communication, there is much more variability in the number of children a node has, compared to when using 868 MHz communication. This is due to the longer range communication of 868 MHz that allows nodes to directly connect to the root over longer distances. In this 25-node grid topology, however, it is still possible that a 868 MHz leaf node needs multiple hops to reach the root: as observed in Figure 12, there are some nodes that have one, two or three children, which indicates that the signal of those children to their parent was better compared to the signal of their link to the root. With 2.4 GHz communication that lacks such longer range capability, a packet typically has to traverse more hops to reach the root. For 2.4 GHz, there is also more variability in the lifetime of nodes with the same amount of children. For 868 MHz, we do not observe this effect. This is because the quality of the different links between the 2.4 GHz nodes differs in every experiment, resulting in a variable number of transmission cells and retransmissions that are necessary to deliver packets, which in turn also influences the energy consumption. Most 868 MHz nodes however are directly connected to the root with good link quality, resulting in almost no variability. The results show that for a higher packet frequency, the average number of days a node lasts decreases, e.g., the average lifetime for 1 packet/s is 204 days compared to 487 days when having a frequency of 1 packet/h, for 2.4 GHz. The graph also shows that on average, the lifetime in a 868 MHz  
Figure 11: Comparison of charge drawn per cycle per node for 868 MHz and 2.4 GHz frequency communication in a grid topology of nine nodes and 25 nodes. (**a**) Grid topology of nine nodes; (**b**) grid topology of 25 nodes. network is lower, because of the higher consumption values shown in Table 19. However, the results in Figure 11 showed that this does not necessarily hold for all nodes in a TSCH network.