## 4 Smart Home Control System Prototype and Performance Evaluation
### Performance Evaluation of VLC-Based Smart Home Control System  
The demonstration of a VLC-based smart home control system consisting of three VLC lightbulbs and the user smartphone app is presented in Figure 10. These three VLC lightbulbs are programmed with different ID codes, named Light ID 1, 2, and 3 separately, which are stored in the memory unit of the BLE module. Then, we record the corresponding location data and Bluetooth MAC addresses of the smart devices in the cloud server with the ID code of the lightbulb. The cloud-server-based architecture provides several advantages. Firstly, it guarantees the safety of data storage; secondly, it simplifies the management of the SHS with remote control function; lastly, the modification of the smart home network can be conveniently processed on the cloud server by changing the stored information in the LUT.  
Figure 8: Experiment setup for measuring the VLC link distance.  
Figure 9: Impact of diffuser diameter and illuminance of lightbulbs on the VLC link distance: (**a**) diffuser diameter versus VLC link distance; (**b**) illuminance versus VLC link distance.  
It can be seen in Figure 10 that the location of the lightbulb with ID code 1 is the kitchen and there are smart devices in the kitchen that can be controlled. ID code 2 identifies the dining room, where three controllable devices are located. Lastly, ID code 3 indicates the bedroom where three devices can be managed. When the user moves from the kitchen where lightbul 1 is installed to the dining room where lightbulb 2 exists, the location and device information provided on the smartphone screen changes from kitchen to dining room correspondingly. At the same time, the Bluetooth connection between the smartphone and smart devices is updated automatically when a different VLC ID code is received. Therefore, the whole control region is divided into separate small regions according to the position of the VLC lightbulb. This region division method can solve the low control accuracy problem by avoiding interference from devices in other rooms. Moreover, it guarantees the safety of the proposed system as the information of devices in one region will not be provided to users outside of this region. In other words, the user can only manage the smart devices in a specific room after entering the specific room.  
When considering the evaluation of the proposed system in real-world applications, possible concerns about the operation of this application and light interference are raised. This smartphone application is not left running in the background all the time for energy effectiveness. It is only utilized to choose the working states of smart devices instead of maintaining the operation of these devices, and the user can exit this smartphone app after the working states of smart devices are decided. As for the interference from other illuminating infrastructures, it will not severely affect the performance of our system. The background light is several orders of magnitude less than the LED light signal itself. When the camera sensitivity is set to be so low that only a direct LED light signal can be detected by the image sensor by changing the ISO of the camera, the background light is automatically filtered out to eliminate the interference. As for the light from other light sources nearby that might have the same strength as the VLC lightbulb, it is detected in the same way as the VLC lightbulb. However, during the signal decoding stage, such lightbulbs are filtered out by the software-supported receiver as regions outside of the ROI since they do not provide the rolling shutter patterns for carrying the signals.  
Figure 10: Demonstration of proposed VLC-based smart home control system [17].