Experimental demonstration of hidden node problem in visible light communication networks

In this paper, hardware investigations show the effects of the hidden and exposed node problems in visible light communication (VLC) networks. Furthermore, the request to send/clear to send (RTS/CTS) mechanism, as a physical layer-independent solution, is used for solving the hidden node problem in VLC networks. A VLC hardware system, called VLCIoT, which was designed and implemented in our laboratory based on PHY I of the IEEE 802.15.7 standard, is used for the physical layer. The medium access control layer of the IEEE 802.15.7 is considered for the network. We implement the multiple access protocol of the IEEE 802.15.7 and the RTS/CTS mechanism on the microcontroller of each device using the C programming language. Goodput, message loss ratio, fairness, average delay, energy efficiency, network load, frame size, number of hidden nodes, and number of contending nodes are the evaluated parameters. The results show that for the IEEE 802.15.7 increase of the hidden nodes decreases the goodput and energy efficiency and increases the message loss ratio and the average delay. But, using the RTS/CTS mechanism, the hidden nodes do not affect the goodput, the message loss ratio, the energy efficiency, and the average delay because this mechanism solves the hidden node problem. The results show that the RTS/CTS mechanism increases the saturation goodput by 300%, decreases the message loss ratio by 94%, decreases the average delay by 50%, and increases the energy efficiency by 300%. The results show that at higher network load, higher data frame size, and more contending nodes, the performance of the RTS/CTS mechanism is better. Also, in symmetric networks, in which all nodes are hidden, or no hidden node exists in the network, fairness is better than the asymmetric networks, in which some nodes are hidden while others are not