## 4 Performance Evaluation
### Results  
#### 4.3.1 Throughput  
Figure 5 shows saturation throughput of the proposed scheme for a different number of nodes in class 5. For BER = \(10^{-5}\) and BER = \(10^{-4}\), it is observed that the use of the RTS/CTS scheme significantly increases overall throughput when compared with the basic IEEE 802.15.6 CSMA/CA protocol. However, the throughput is decreased both for the RTS/CTS scheme and basic protocol when we increase the value of BER. For example, for 17 nodes, the saturation throughput of the proposed RTS/CTS scheme is 0.80 when the value of BER = \(10^{-5}\); however, the same protocol achieves 0.55 saturation throughput for BER = \(10^{-4}\). We also observe in the figure that the performance of the IEEE 802.15.6 CSMA/CA decreases when the number of nodes (including hidden nodes) contending for the medium increases. Unlike the RTS/CTS scheme, where only the RTS packet is transmitted after winning access to the channel, the IEEE 802.15.6 CSMA/CA transmits the data packet, which decreases channel utilization and throughput in case of collisions, or when hidden nodes are present in the network. The throughput of the IEEE 802.15.6 CSMA/CA depends on the network size, while the throughput achieved by the RTS/CTS scheme is less sensitive to network size. This shows that employing RTS/CTS scheme is efficient and scalable for larger networks.  
However, when we analyze the saturation throughput of the RTS/CTS scheme for different priority classes, we note that high priority classes result in higher throughput due to small contention window size. This is because the RTS packets are immediately transmitted by high priority nodes, and hence, they achieve quick access to the channel. This is shown in Figure 6, where the proposed scheme achieves 0.8 saturation throughput for 15 nodes in class 5 with BER = \(10^{-5}\), while the same scheme achieves 0.6 and 0.4 throughput values for class 3 and class 1, respectively. It is important to explain that the IEEE 802.15.6 CSMA/CA also achieves the same throughput trend for different priority classes, as explained in our previous work [32]. We found that it achieves higher throughput for high priority classes due to small backoff duration; however, the difference is that the throughput decreases as a function of network size, as discussed above. The effect of contention window size on the saturation throughput is presented in Figure 7. This figure considers nodes of the same priority with the same contention window sizes in a network. For BER = \(10^{-5}\), the figure shows that overall  
Figure 5: Saturation throughput of the RTS/CTS scheme for IEEE 802.15.6.  
throughput of the proposed scheme largely depends on the size of the contention window of the same priority nodes, i.e., larger contention window size is able to accommodate a large number of nodes, thus increasing the throughput. When the value \(CW\) is 16, the RTS/CTS scheme obtains 0.85 throughput compared with the basic scheme, which is 0.75. The afore-mentioned results show that the RTS/CTS scheme achieves significant throughput when compared with the conventional IEEE 802.15.6 CSMA/CA protocol for different BER values and number of nodes.  
Figure 6: Saturation throughput of the RTS/CTS scheme for different classes with BER = \(10^{-5}\).  
Figure 7: Saturation throughput of the RTS/CTS scheme for different contention window sizes.