## 5 Performance Evaluation
### Simulation Results
#### 5.3.2 Packet Delivery Ratio  
In the previous subsection, we argued that hot spot ratio will affect packet delivery ratio because the number of available routing paths decreases as the hot spot ratio increases. Especially, since the number of nodes constituting WBAN is very small, the influence of hot spot ratio on the packet delivery ratio will be great.  
Table 10 illustrates the packet loss ratio with increasing traffic bit rate. Obviously, case 2 of EMTARP shows the best performance in Figure 5a because the weight of link metric is higher than other metrics. More specifically, if the selected next hop moves out the transmission range of the source node, MAC layer could not receive any ACK for the retransmissions. This implies that the retry counts for packet will reach limitation of MAC. Since both MTARP and case 1 of EMTARP try to forward the data packet to the node with lower hop count or lower temperature, the performance is lower than in case 2 of EMTARP. However, it is notable that the ratio of no available node sharply increases as the traffic bit rate increases in case 2 of EMTARP. The reason is that the traffic load will be concentrated on the stable node as the traffic bit rate increases so the node becomes a hot spot quickly and the number of available routing paths becomes insufficient. As a result, the performances of case 1 and case 2 do not show great difference even though the weight of link metric in case 2 is the highest. Figure 5c supports this claim that as the hot spot ratio increases, the number of available nodes and the packet delivery ratio decrease together.  
In addition, the hello packet interval affects the packet delivery ratio. In Figure 5b, we can see the best performance when the hello packet interval is set to 5 s. Since we set the mobility interval to 3 s, even if the hello packet interval is set to 5 s, it is unlikely that the node set to the next hop will move out of the communication range of the source node. Therefore, frequent sending of unnecessary hello messages leads to an increase in the hot spot ratio, which degrades performance. On the other hand, as the hello packet interval increases, the node selected as a next hop can move out of the transmission boundary of the source node because the node moves more frequently than the neighbor table update rate.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Protocol** & **Traffic Bit Rate (bits/s)** & **No Available Node (\%)** & **Retry Threshold Exceeded (\%)** \\ \hline MTARP & 1000 & 0 & 100 \\ MTARP & 2000 & 13 & 87 \\ MTARP & 3000 & 17 & 83 \\ MTARP & 4000 & 25 & 75 \\ MTARP & 5000 & 32 & 68 \\ MTARP & 6000 & 40 & 60 \\ \hline EMTARP-case 1 & 1000 & 0 & 100 \\ EMTARP-case 1 & 2000 & 10 & 90 \\ EMTARP-case 1 & 3000 & 14 & 86 \\ EMTARP-case 1 & 4000 & 20 & 80 \\ EMTARP-case 1 & 5000 & 26 & 74 \\ EMTARP-case 1 & 6000 & 34 & 66 \\ \hline EMTARP-case 2 & 1000 & 0 & 100 \\ EMTARP-case 2 & 2000 & 14 & 86 \\ EMTARP-case 2 & 3000 & 20 & 80 \\ EMTARP-case 2 & 4000 & 26 & 74 \\ EMTARP-case 2 & 5000 & 34 & 66 \\ EMTARP-case 2 & 6000 & 46 & 54 \\ \hline \hline \end{tabular}
\end{table}
Table 10: The reasons for packet loss varying traffic bit rate.