Optical Power Domain NOMA for Visible Light Communications

We propose an optical power domain non-orthogonal multiple access (OPD-NOMA) scheme for visible light communications. OPD-NOMA superposes user messages in the optical power domain based on a light-emitting diode (LED) array. The maximum driven current for respective circuits is reduced compared to that of conventional NOMA, in which the LED-array-module is driven by a single circuit. OPD-NOMA reduces the gain and bandwidth requirements for the driver circuit of light source. The nonlinear power-current response of LED largely restricts its usable dynamic range and thus the transmit power. In OPD-NOMA, signals with lower powers suffer from reduced nonlinear distortion. The experimental results show that, OPD-NOMA offers improved transmission performance compared to conventional NOMA using the same driver circuit, since it can make a better use of the linear dynamic range of the LED’s power-current response

Optical Filter-Less WDM for Visible Light Communications Using Defocused MIMO

This paper experimentally investigates, for the first time, a new wavelength-division multiplexing-based visible light communications link based on a defocused non-imaging multiple-input multiple-output (MIMO), which removes the need for tuned optical bandpass filters paired with each receiver. The proposed system is based on using the natural diversity of the individual light emitting diodes (LEDs) within a single light source to generate an H-matrix, which is independent of spatial diversity. We show that, by transmitting K-independent sets of non-return to zero on-and-off keying signals on separate wavelengths, the received superposed symbols can be demultiplexed. The non-imaging MIMO diversity is achieved by considering the power-current characteristics of the light emitting diode, the responsivity of the photodetector array, and the defocused beam spot. The system is empirically verified for K = 3 using red, green, and blue LEDs with Q-factors of 7.66, 7.69, and 4.75 dB, respectively