Design and Implementation of Wireless Optical Access System for VLC-IoT Networks

With the development of information technology, the Era of the Internet of Everything led by the Internet of Things (IoT) has arrived. The development of traditional Internet of Things based on radio frequency (RF) communication is increasingly perfect, but it is difficult to apply in electromagnetic sensitive industries such as nuclear power plants, engine rooms, hospitals, and industrial control. Under the background of limited spectrum resources, crowded space is filled with a lot of RF communication waves, and the electromagnetic environment is extremely complex. Traditional IoT is also difficult to apply in the high secrecy industries. In these special scenarios, the development of the IoT based on visible light communication (VLC) is particularly important. To realize the VLC-IoT, in this paper, the crosstalk phenomenon in the full-duplex real-time VLC is studied, and the crosstalk phenomenon is suppressed by reducing beam angle and field angle, power isolation, and ground plane segmentation. And the transmitter and receiver in the full-duplex VLC system are integrated on a single printed circuit board (PCB). Combined with the existing mature network, a full-duplex real-time VLC system based on fast Ethernet is implemented, which can be also considered as the wireless optical access system for VLC-IoT networks. Among them, the combination of a red LED and APD430A/M (optical receiver designed by Thorlabs) can achieve 100 Mbps Ethernet transmission of 30 m, and the combination of a white LED with the same optical power and the receiver with a blue light filter designed in this paper can achieve 100 Mbps Ethernet transmission of 4 m. The change of communication distance is because the latter only uses the blue light component to transmit information, which leads to the decrease of signal optical power and the low responsivity of the optical receiver at short-wave strength. All the above wireless optical access systems for VLC-IoT networks have been tested for packet loss rate and communication rate. In the daily lighting environment, the above systems can realize the transmission of 10(8) packets with zero packet loss and 94.9 Mbps transmission rate, in line with the characteristics of Fast Ethernet transmission rate, fully meeting the platinum user standard in the Carrier Ethernet. Based on this experiment, the key performance of the receivers is quantified in this paper. The noise equivalent power (NEP) of the receiver designed in this paper at peak response wavelength is 3.7 nW, which is better than the 5.5 nW of APD430A/M. With the help of the wireless optical access systems designed in this paper, a VLC-IoT networks experiment is realized, and multiple terminal devices can access the VLC-IoT networks at the same time by the wireless optical.