# Accurate Energy Consumption Modeling of IEEE 802.15.4e TSCH Using Dual-Band OpenMote Hardware
## 5 Evaluation
### Slot Frame Charge Consumption  
When considering the charge consumption in the different time slots, the energy consumption of a slot frame can be calculated. To further verify the accuracy of our model, the calculated slot frame charge consumption of a small-scale, real-world 6 TiSCH network is compared with the measured values, for both 868 MHz and 2.4 GHz.  
The experiment network topology, depicted in Figure 8, used the OpenMote-CC2538 and the OpenMote-CC2538/OpenUSB board combination as hardware nodes for 2.4 GHz and the 868 MHz measurements, respectively. The root node is connected to a computer using OpenVisualizer to monitor the network. The leaf mote was configured to send a packet of 127 bytes (including CRC) every two seconds. The slot frame size was 51 time slots. Since there are 51 slots in a slot frame and every time slot lasts 15 ms, the duration of each slot frame is 765 ms. The first time slot in every slot frame was reserved for management messages, e.g., EBs, RPL DIOs, RPL Destination Advertisement Objects (DAOs) and 6 TiSCH Operation Sublayer (6 top) messages, but these were not considered. As such, the first time slot in each slot frame is thus considered to be of type RxIdle.  
The slot frame of the leaf mote always consists of one RxIdle slot and at least 49 Sleep slots. The last slot will either be of the type TxDataRxAck when there are data to send or another Sleep slot when there are no data. As such, two slot frame types were considered for the leaf node: a slot frame where no data were sent and a slot frame where the packet was sent in a TxDataRxAck slot. The charges consumed in each of these two slot frame types are represented by:  
\[Q_{leaf\_Sleep}=Q_{RxIdle}+50\times Q_{Sleep} \tag{3}\]  
and:  
\[Q_{leaf\_TxDataRxAck}=Q_{RxIdle}+Q_{TxDataRxAck}+49\times Q_{Sleep} \tag{4}\]  
For the relay node, a slot frame was considered where the packet coming from the leaf was received in the first slot of the slot frame; subsequently, the relay forwarded the packet to the root, but no acknowledgment was received, followed by a successful retransmission. As such, there are RxDataTxAck, TxDataRxNoAck and TxDataRxAck slots when a packet was received and forwarded, while the remaining 48 slots are Sleep slots. The charge drawn during the slot frame of the relay node is represented by the following formula:  
\[Q_{relay}=Q_{RxDataTxAck}+Q_{TxDataRxNoAck}+Q_{TxDataRxAck}+48\times Q_{Sleep} \tag{5}\]  
The charge consumption of the root node is not considered as the root device is typically connected to a computer using OpenVisualizer, serving as a gateway to the Internet. Therefore, the root typically does not run on batteries. Additionally, the serial communication between the root and OpenVisualizer cannot be disabled, making the comparison between the measured consumption and the proposed model invalid.  
We measured the charge consumed over the length of an entire slot frame for both the leaf and relay node and compared these values to the values calculated using the proposed model and Equations (3)-(5). Table 17 shows the results. On average, the error between the calculated and measured values is lower than 1%. The differences between the CC2538 measured and calculated consumptions, for the leaf and relay nodes, are limited to 1.3% and 1.03%, respectively. For the CC1200 radio, the differences are even slightly smaller: respectively 0.88% and 1.01%. The consumption  
Figure 8: Topology used while comparing the consumption of a slot frame.  
comparison results again show that our model is accurate, even when measuring across an entire slot frame.