VDIU: VLC-Based Debugging Information Upload Method for Self-Powered Sensor Nodes

Currently, more and more self-powered sensor nodes have been deployed in remote and inaccessible areas, and thus online debugging of sensor nodes becomes more necessary and important. However, the existing sensor online debugging approaches mainly rely on original network infrastructure (such as Zigbee or NB-IoT). Once the communication infrastructure is invalid, it is almost impossible to retrieve debugging information and repair the lost self-powered sensor nodes. To this end, in our previous study, we employed the onboard optical modules of the self-powered sensor node to realize a visible light communication (VLC)-based hybrid communication debugging system (VHCDS). In this article, to improve the efficiency of uploading debugging information, we propose VDIU to optimize the digital pulse interval modulation (DPIM) applied in the uplink of VHCDS. This method reasonably groups and sorts the origin data to reduce the number of empty time slots (unused time slots) and complete data compression in source coding for saving energy. To improve the reliability of the uplink, we also design two frame synchronization mechanisms suitable for the receiver-side optical cameras of the uplink. One mechanism considers lightweight synchronization design via restricting the position of the frame header; the other one focuses on reducing the occupation of the downlink of VHCDS via predicting the position of the frame header using a temporal convolutional network (TCN). Experiment results illustrate that the upload efficiency using VDIU is higher at 78% and 28% than DPIM and DH-PIM. Both synchronization mechanisms can arrive the similar performance, but the predicting mechanism reduces the 93% occupation on the downlink.