Can linear pre-emphasis mitigate the nonlinear distortion of light-emitting diodes?

Abstract

Transmitter pre-emphasis is one of the techniques proposed to improve the relatively poor frequency responses of light-emitting diodes (LEDs) used in visible light communications (VLC) as light sources. However, according to the communications theory in linear channels, pre-emphasis may only be as good as the not particularly efficient feed-forward equalizer (FFE). Given the increase in peak-to-average power ratio (PAPR) caused by pre-emphasis, its use in place of receiver equalization can be considered counterproductive. In this study, we show that the performance of the transmitter pre-emphasis is indeed equivalent to the FFE at low input powers, where the LED is a linear system. However, at higher modulation voltages, the transmitter pre-emphasis has a clear advantage over FFE, as it mitigates the nonlinear distortion of the LED. This mechanism is for the first time to our knowledge explained in both theory and experiment.