## 6 IoT AP Performance Evaluation
The existing bandwidth occupation by Wi-Fi network is set as a percentage ranging from 40% to 90%. The proposed IoT AP outperforms the IoT gateway [12] in terms of response time. This occurs because that the time required for transmitting data from gateway to the Internet AP has been saved in the proposed IoT AP. Table 2 shows the measured response time of handheld devices connected to the IoT AP through Wi-Fi connection and using HTTP communication protocol to control the ZigBee devices. The Wi-Fi channel is configured to CH 1 and ZigBee channel is configured to CH 15. Thus, ZigBee and Wi-Fi do not affect each other. As shown in Table 2, the average time is maintained at about 97 ms and the shortest time period is up to 31 ms. This result occurs because that the CPU performance of RT3052 development board is quite high. Figure 13: The impact of Wi-Fi throughputs variation on the ZigBee response time. Figure 15 shows the response time of command execution which is sent from a handheld device to the IoT AP through the Wi-Fi network with a variation of Wi-Fi throughputs. The Wi-Fi channel is set to CH 1, whereas the ZigBee channel is set to CH 12. In Figure 15, the Wi-Fi throughput is varied from 0 to 5000 (KB/s). The horizontal axis represents the variation of Wi-Fi throughputs, whereas the vertical axis represents the sum of HTTP response time and ZigBee response time. As shown in Figure 15, when the Wi-Fi throughput ranges between 0 KBps and 3000 KBps, the total Wi-Fi response time has minimal impact. When the Wi-Fi throughput exceeds 3000 KBps, the HTTP response time and ZigBee response time are affected by background interference, which results in longer response time. To verify the reliability and performance of the proposed IoT AP, this section focuses on the ZigBee response time by varying two parameters, including the ZigBee/Wi-Fi band variation and the Wi-Fi throughput. Based on a number of simulations, it is observed that the lower probability of packet collisions can improve the ZigBee response time. To minimize the interference affected from Wi-Fi, the developed IoT AP can automatically detect the channels occupied by APs and other Wi-Fi devices and subsequently notify _ZigBee device management module_ for determining the optimal communication channel for establishing a ZigBee network with low interference. The proposed channel configuration allows Wi-Fi and ZigBee to function independently with no issue. Finally, when the proposed IoT AP controls the ZigBee devices, it has a relatively short HTTP response time. Figure 16 investigates the energy consumptions of the proposed IoT AP and the existing product which is composed by an IoT gateway and a Wi-Fi AP. Because the hardware and firmware components can be highly integrated in the proposed IoT, the energy consumptions can be saved accordingly. Most existing systems [12,24] require the IoT devices firstly transmitting data to IoT gateway and, subsequently, the gateway further forwards the data to the AP. This method raises additional energy consumption for data exchange between the IoT gateway and the AP. As shown in Figure 16, the proposed IoT AP can reduce about 12% off energy than the IoT gateway and AP.