## 3 WSAN System Models
### Performance Metrics
#### 4.1.3 Energy Consumption Problem  
Figure 7 illustrates the energy consumption at each interval of time (every 250 s) during the simulation. The sum of all sample values for each CBR rate in Figure 7 equals to the total energy consumption of all nodes in the network for each CBR rate as in Figure 6. Figure 7 emphasizes that nodes consume much more energy when they try hard to establish/re-establish a route. For example, at the CBR rate of 2.00 Mbps as in Figure 7(b), packet collisions due to the hidden node problem at node IDs 7, 8, 9 and 3 have occurred for a long period of simulation time. The route re-establishment procedure is more repeated at this CBR rate. Therefore, nodes largely consume their power for all  
Figure 5: IAE _vs._ CBR rate. (**a**) Vary the CBR rates from 0 to 2.00 Mbps. (**b**) Vary the CBR rates from 2.25 to 3.25 Mbps.  
intervals of simulation time. At the CBR rate of 3.25 Mbps as in Figure 7(c), the energy consumption is highest at times between 500 s and 750 s. However, route changes after a time of 750 s can lead to reduce the energy consumption of the network. This is because when the upper path is often selected, the probability of the packet collision and the retransmission procedure are getting reduced.  
In addition, the total energy consumption of nodes directly depends on the varying of the CBR rates at the communication pair between node IDs 7 and 8. When the CBR rate is increased, Node IDs 7 and 8 consume their energies higher than other nodes in the network. Node IDs 9 and 3 as the joint nodes between upper and lower paths also largely use their energies due to the idle listening affected by node IDs 7 and 8. Therefore, the energy consumption of node IDs 7, 8, 9, and 3 will largely impact the total energy consumption of the network. This confirms by some selected results as shown in Figure 8. At the CBR rate of 0 Mbps as in Figure 8(a), node IDs 9 and 3 consume their energies higher than other nodes due to the effects of their locations in the selected path. However, the energy consumption of each node is likely the same at this CBR rate. At the CBR rate of 2 Mbps as in Figure 8(b,c), the AODV routing still tries to select the lower path. Node IDs 7, 8, 9 and 3 consume too much energy, respectively. For this network scenario, if nodes IDs 9 and 3 die due to the lack of powers, the desirable control target cannot be achieved ever. Finally, at the CBR rate of 3.25 Mbps as in Figure 8(d,e), effects of the buffer overflow at node IDs 7 and 8 and the route change mechanism as previously discussed can lead to improve the energy consumption.  
From the simulation results in Subsection 4.1, we can summarize that the original AODV routing protocol designed without considering the relationship between control and communication cannot be appropriately applied in WSANs. The control objective cannot be achieved in time, and nodes consume more energy resources.  
Figure 6: Total energy consumption _vs_. CBR rate.  
Figure 7: Energy consumption at each window interval _vs_. CBR rate. (**a**) Vary the CBR rates from 0 to 0.75 Mbps. (**b**) Vary the CBR rates from 1.00 to 2.25 Mbps. (**c**) Vary the CBR rates from 2.50 to 3.25 Mbps.  
Figure 8: Energy consumption of each node at each window interval _vs_. CBR rate. (**a**) At the CBR rate of 0 Mbps. (**b,c**) At the CBR rate of 2 Mbps. (**d,c**) At the CBR rate of 3.25 Mbps.