Investigation into Using Compensation for the Nonlinear Effects of the Output of LEDs in Visible Light Communication Systems

Abstract

This paper investigate the effects of the nonlinear output power to the input current transfer function of a light emitting diode (LED) used as the transmitter in visible light communication systems, and proposes a compensation technique to mitigate the non-linearity. Using an off the shelf red, amber, blue, green (RAGB) LED the nonlinear transfer function is measured and then compensated for. The results show that, for the green LED, which has the highest degree of nonlinearity, an improvement in the received error vector magnitude (EVM) of almost 7 dB can be achieved. We also show that, the improvement in EVM over the uncompensated scheme decreases with increased LED linearity.

Bandwidth Dependency of (O)LEDs on Bias current

“…However, biasing the OLEDs to a high level in a communication system can introduce nonlinear effects on the signal due to the saturation limit on the optical output power. These effects are more severe on the multilevel and analogue modulation schemes (such as multiple carrierless and phase modulation (m-CAP) [27] or orthogonal frequency division multiplexing (OFDM) [28]), than on binary level modulation such as OOK or pulse position modulation (PPM). Furthermore, having to biasing at a high level can be detrimental to the overall lifetime of the device.…”