# EEMIP: Energy-Efficient Communication Using Timing Channels and Prioritization in ZigBee
## 4 Results and Discussion
### Discussion  
Based on the experimental results, we can summarize that the proposed method can indeed increase energy efficiency of the ZigBee communication. However, it has also its disadvantages and is limited to specific kinds of communications. The advantages and disadvantages of the proposed method are summarized in Table 13. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**2\% Packet Loss**} & \multicolumn{2}{c}{**3\% Packet Loss**} & \multicolumn{2}{c}{**10\% Packet Loss**} & \multicolumn{2}{c}{**20\% Packet Loss**} \\ \hline
**Bytes** & **Nonbeacon ZigBee** & **EEMIP ZigBee** & **EEMIP ZigBee** & **Nonbeacon ZigBee** & **EEMIP ZigBee** & **EEMIP ZigBee** \\ \hline \(S_{all}\) & 317,130 & 330,680 & 326,610 & 339,560 & 334,260 & 330,110 & 320,520 & 331,670 \\ \(R_{all}\) & 315,480 & 330,080 & 321,060 & 338,810 & 320,910 & 328,910 & 297,720 & 328,070 \\ \(R_{data}\) & 115,680 & 135,300 & 115,560 & 140,730 & 116,910 & 135,930 & 108,720 & 137,490 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Simulation data for a more realistic scenario with various amount of congestion. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Bytes** & **2\% Packet Loss** & **3\% Packet Loss** & **10\% Packet Loss** & **20\% Packet Loss** \\ \hline \(S_{all}\) & +4.27\% & +3.96\% & \(-1.24\%\) & +3.48\% \\ \(R_{all}\) & +4.63\% & +5.53\% & +2.49\% & +10.19\% \\ \(R_{data}\) & +16.96\% & +21.78\% & +16.27\% & +26.46\% \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Comparison of the two simulation modes for a more realistic scenario with various amount of congestion. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Bytes** & **2\% Packet Loss** & **20\% Packet Loss** \\
**Bytes** & **Low Priority** & **High Priority** & **Low Priority** & **High Priority** \\ \hline \(S_{all}\) & \(-5.99\%\) & +6.57\% & \(-11.34\%\) & \(-2.74\%\) \\ \(R_{all}\) & \(-6.15\%\) & +6.57\% & \(-11.76\%\) & \(-2.98\%\) \\ \(R_{data}\) & +0.67\% & +18.08\% & +11.96\% & +17.39\% \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Comparison of the two simulation modes for corner cases. The proposed EEMIP method increases energy efficiency (by reducing collisions and retransmissions) for most of the star-based sensor networks using ZigBee, since these are usually periodic, collecting measured data in regular cycles. However, it is not suitable for mostly non-periodic communication (i.e., event based), since it can slightly delay important messages (due to waiting for the time slot). In periodic communication, the waiting time is eliminated using EEMIP. The method uses a control protocol, which increases the overhead. That is why it is unsuitable for occasional communication (e.g., once a day). However, such communication is a domain of other low-power IoT technologies, such as LoRa or Sigfox. The centralized architecture also represents a big downside, since the coordinator represents a single point of failure. However, most of the Internet-connected (via gateway) ZigBee networks have this kind of problem. It can be alleviated in further work by introducing a redundant (grid-powered) coordinator, which would take the role of coordinator in case of failure. The efficiency of the proposed method also depends on the accuracy of the crystal oscillator used in ZigBee devices. Cheap oscillators often suffer from a high inaccuracy, which can result in desynchronization of the end device and the coordinator, and thus disrupt the transmission schedule. In such a case, the coordinator is forced to resend the Offer message to the desynchronized end device, which decreases the energy efficiency if it happens too often. For example, if the end device would send data once a day and due to an inaccurate oscillator it would be received outside the scheduled time slot, the ineffective resynchronization would even increase the energy requirements of such communication. However, the precise boundary point when the proposed method becomes energy efficient depends on the oscillator.