Single-LED Multichannel Optical Transmission With SCMA for Long Range Health Information Monitoring

This paper proposes a prototype single light-emitting diode (LED) multiple-channel transmission system with visible light communication (VLC) for electromagnetic wave-free indoor healthcare monitoring. Sparse code multiple access (SCMA) is employed for the transfer of multiple medical data with higher bandwidth efficiency in real time. Multiuser data spread to time domain chips with non-orthogonal codebook are simultaneously transmitted using a single LED, where each chip signal is transmitted as a difference voltage level, and LED illumination is detected by a single photodiode (PD). The received signal, which includes multiuser data, is separated by the message passing algorithm with high reliability, and is simultaneously rearranged for transmission to a user interface (PC or mobile). The collected multiple data are then monitored in real time and analyzed for the appropriate medical care service. With SCMA, VLC can achieve higher bandwidth efficiency (50%-200%). Furthermore, the proposed system is designed with a simple structure (single LED to single PD) for practical deployment, and multiple medical signals can be monitored via a designed user interface in real time.