## 5 Performance Evaluation
### Latency Analysis of Emergency Transmission
Hence, Figure 8 shows the higher differentiation results of both protocols in high traffic environment. Contrary to Figures 7 and 8, the latency of the emergency data transmissions show different results as illustrated in Figure 9. In this experiment, we constantly fixed the number of nodes as 4 and also fixed the normal data transmission amount on each node as shown in Table 2. Then, we set another node to transmit only emergency data with varied traffic amount. We finally measured outperforming results comparing with any other scheme as shown in Figure 9.  
The differentiation of each transmission rate in the results of IEEE 802.15.6 protocol can be explained with the same reason described in Figures 8 and 9. However, we have to focus on the emergency data transmission on aSymMAC. In this protocol, every emergency data can obtain high opportunity to be transmitted by prioritized IFS (i.e., SIFS), preliminarily to normal data that has relatively longer IFS. Consequently, Figure 9 shows narrow differentiation results of this case. Figures 10 and 11 show the saturated throughput with various payload length and the amount of external interference. The saturated throughput presents the relative value of bandwidth efficiency where the maximized value (i.e., 1.0) implies that the given channel is being constantly used for data transmission at every time. Hence, the value of 1.0 is ideal and unrealistic because some overheads are essentially required (e.g., packet header, Ack, IFS, Back-off, etc.) to be operated by MAC protocol. In the results of IEEE 802.15.6 and normal data transmission of aSymMAC in Figure 10, both protocols similarly present that less payload length makes lower bandwidth efficiency due to the heavy overhead; header and Ack mechanism are commonly applied even if data payload is too small. On the other side, we can see that the excessive payload length makes worse performance caused by that too larger payload length overflows assigned time slot and aggravates competition on contention period. Moreover, this can make more collisions. Meanwhile, the case of emergency transmission on aSymMAC shows better performance because every emergency transmission can preliminarily preempt the channel regardless of slot assignment. Figure 9: Average delivery time of emergency data transmissions according to the traffic amount with fixed normal data transmissions compared with IEEE 802.15.6 protocol. In addition, we evaluate the robustness of these protocols by giving external interference on the same frequency. We employed IEEE 802.15.4 as an interference method with the change of frequency and channel space. Note that the value of 100% implies that IEEE 802.15.4 fully occupies the given channel in time domain. All results at 100% of the interference are not equal to zero because IEEE 802.15.4 also performs CSMA/CA during contention period. As a result, we can see the better performance from the case of emergency transmission on aSymMAC. The emergency transmission can take more opportunities due to cutting off CSMA/CA while IEEE 802.15.4 does the opposite. \[L_{CP}^{\epsilon}=L_{d-TP}^{\epsilon} \tag{10}\]0 Average saturated throughput depending on bandwidth efficiency according to the external interference on the same frequency compared with IEEE 802.15.6 protocol. \[L_{CP}^{\epsilon}=L_{d-TP}^{\epsilon} \tag{10}\]1 Average saturated throughput depending on bandwidth efficiency according to the payload length per a packet compared with IEEE 802.15.6 protocol.