## 5 Analysis of the Solution and Simulation
### Simulation Results and Comparison with ZigBee  
Figure 11 illustrates the average node power consumption (PC) of our proposed solution _vs._ a non-beacon ZigBee-based network for three different cases: good, moderately harsh and harsh scenarios respectively. The higher power consumption of the non-beacon ZigBee solution is mainly caused by the absence of duty-cycling mechanisms in full function devices, which, in turn, leads to faster FFDs' batteries depletion. When routing nodes (FFDs) exhaust their batteries, some WSN devices in the network may become partially isolated, being impossible for these nodes to dispatch their messages successfully to their destination. This is why the _network lifetime_ (as a concept) is defined as the time elapsed between the beginning of the network operation and when the first node depletes its battery. Under this consideration, the expected network lifetime is shown in Table 2.  
As written in Table 2, our solution lasts from 16 to 20 times longer than a non-beacon ZigBee-based network. Even in the harshest scenario, our proposed network is expected to be operating for more than 16 months. Thereby, SENSED-SG is more appropriate for deployments in remote locations or hard-to-reach areas. This long-lasting feature can be further enhanced by reducing the sensing or reporting period; for instance, if physical data is acquired every 15 min (instead of every 5 min), the network will operate for more than 24 months under good propagation conditions. On the contrary, the experiments reveal that a non-beacon ZigBee network is not suitable for deployments where inexhaustible power sources are not available, discarding it as a potential solution for almost every segment of the Smart Grid (such as the Generation and the T&D segments). Figure 10: Simulated topology. As regards to the packet delivery ratio, Figure 12 shows the average PRR and its standard deviation with a 95% confidence interval, obtained from 15 simulations carried out with different seeds. Results evidence that SENSED-SG performs adequately even under harsh environments. This is achieved by combining retransmission algorithms with appropriate modulation techniques and by carefully selecting the best MAC settings (e.g., the active/sleep period, retransmission times, _etc._). It is worth highlighting the obtained robustness of our solution to harsh propagation conditions, decreasing in just 3.08% the PRR if the probability of packet loss increases from 5% to 25%--as opposed to a decrease of 26.16% in the PRR in non-beacon ZigBee networks. Since routing nodes (FFDs) remain in awake mode all the time in non-beacon ZigBee-based networks (and, therefore, these nodes do not have to wait an AP for sending messages), the delay obtained is lower with this approach than with the SENSED-SG. However, in our proposal, the attained average network delay is kept below 1.2 s in every scenario, with a maximum peak of 2.3 s reached in the node No. 5 (the farthest WSN device from the sink-node). These results satisfy the delay requirement imposed to WSN operating in Smart Grids, which must be lower than 15 s. \begin{table}
\begin{tabular}{l c c} \hline
**Network Lifetime** & **SENSED-SG** & **Non-Beacon ZigBee Network** \\ \hline Good Propagation Conditions & 20.75 months & 30.28 days \\ Moderately Harsh Propagation Conditions & 18.71 months & 30.13 days \\ Harsh Propagation Conditions & 16.54 months & 29.91 days \\ \hline \end{tabular}
\end{table} 
Table 2: Network expected lifetime. Figure 11: Power Consumption of SENSED-SG _vs._ a non-beacon ZigBee-based network for three different scenarios. To summarize, we would like to highlight and further comment the simulation results:  
* The network lifetime obtained with SENSED-SG in each scenario (good, mild and harsh) is: 20.85, 18.9 and 16.8 times higher respectively than the one obtained with a ZigBee-based network. * The PRRs achieved with SENSED-SG in each scenario (good, mild and harsh) are 13.4%, 19.6% and 56.2% higher than the ones obtained in a ZigBee-based network.