Timing Synchronization for Smartphone-Based Optical Camera Communication

The advent of industry 4.0 sets high and divers requirements for wireless communications. Visible light communication (VLC) is a technology that is able to address a set of those requirements. Within the area of VLC, we focus on optical camera communication (OCC) with a light emitting diode (LED) as sender and a complementary metal-oxide-semiconductor (CMOS) image sensor as receiver. The rolling shutter mechanism of the CMOS image sensor allows the system to achieve higher symbol rate than the frame rate. However, the sampling frequency of the rolling shutter is an unknown parameter that varies between smartphone models and therefore needs to be estimated if the system is required to work with a wide range of CMOS cameras. In this work, a non-data aided (NDA) digital timing synchronization algorithm employing a rolling shutter image sensor was analyzed using a spectral approach for application in an OCC system. The algorithm viability and wide applicability was demonstrated using the cameras of six different smartphone models.