## 4 Relay Based QoS-Aware Routing Protocol for I2O WBAN
### Performance Evaluation and Results  
The topology is introduced as follows, a coordinator is located in the center of the human body and six in-body sensor nodes are also positioned within the body. The coordinates of the coordinator and the in-body sensor nodes are summarized in Table 6. All in-body nodes have the same initial energy of 0.5 Joules. The number of relays is limited to two with coordinates (1.65, 0.75) and (0.9, 1.65). As presented in (24), a probabilistic approach (random uniform model) with a probability of packet loss of 0.3 is utilized in all simulation cases in agreement with [36]. The packet size is set as 2000 bits, which is defined as the maximum payload based on the IEEE 802.15.6 standard [22]. Simulation parameters are summarized in Table 7.  
Figure 12 illustrates the comparison of the stable period and total network lifetime for the proposed protocols. It can be seen that the incremental relay-based routing protocol achieves a longer stability period and total network lifetime than the two-relay based protocols with two different transceivers. This is because the second relay node only receives and forwards the data from the in-body sensor nodes when the first relay fails and therefore minimizes the network energy consumption. The stability periods of the incremental relay-based protocol are circa 4000 rounds using the using nRF2401A and circa 1500 rounds with the CC2420, whereas the two-relay based delivers 3400 rounds and 1200 rounds, respectively. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Node ID** & **X-Coordinate** & **Y-Coordinate** \\ \hline
1 & 0.2 & 1.6 \\
2 & 0.4 & 0.4 \\
3 & 0.3 & 0.1 \\
4 & 0.6 & 0.35 \\
5 & 0.7 & 1.5 \\
6 & 0.9 & 1.65 \\ coordinator & 0.45 & 0.85 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The Coordinates of In-Body Nodes and Coordinator. \begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Parameter (Unit)** & **Value** \\ \hline Number of in-body nodes & 6 \\ Network Initial energy (Joule) & 3 \\ Payload size (bits) & 2000 \\ Electromagnetic wave speed (m/s) & \(3\times 10^{8}\) \\ Packet loss probability & 0.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Simulation Parameters. Figure 12: The relationship between the number of dead nodes and network lifetime. Figure 13 presents the comparison of network residual energy of two protocols for the two transceivers considered. The nRF2410A-based incremental relay-based protocol has the highest network residual energy and thus leads to the longest network lifetime. Figure 14 demonstrates that the average energy consumption per round of the incremental protocol is 0.27 mJ and 0.57 mJ when deploying nRF2401A and CC2420, which achieves nearly 52% and 45% less energy consumption when compared to the two-relay based protocol. Reasons for the above results are as follows: (a) relay nodes forward data even if when it is not necessary, resulting in channel resouce waste; (b) an alternative data transmission link only starts to work when the first link fails. Data loss is usually caused by transmission attenuation and shadow fading as presented in Section 3[21]. Figure 15 shows the number of successfully transmitted information packets in the network and Figure 16, the network delay. It can be seen that the two-relay protocol can promise higher data transmission rates than the incremental relay-based protocol when deploying the same transceiver. The number of total transmission packets depends on the number of alive, in-body sensor nodes and the total network lifetime. The shorter lifetime of the two-relay routing technique is the major factor in its decreased throughput. The propagation delay depends on the overall I2O WBAN communication distance. Moreover, it can be seen from Figures 15 and 16 that more information packets generated by the system leads to higher propagation delays in the network. Figure 14: Average energy consumption per round. Figure 13: The residual energy versus the network lifetime.