Novel Post-Distortion to Mitigate LED Nonlinearity in High-Speed Visible Light Communications

This paper addresses dynamic nonlinear effects in the response of typical illumination Light Emitting Diodes (LEDs) to increase the reliability and data rate in Visible Light Communication (VLC) systems. These power LEDs have a limited bandwidth of only several MHz. To conceive a practical receiver, we describe the LED transient response by a nonlinear dynamic differential equation from the physical mechanisms in the Quantum Well (QW) of Double Hetero-structured (DH) LEDs. It includes the transient nonlinear relation between the input current and injection electron concentration, as governed by the dynamic rate equation. Also, we consider the static nonlinear (typically quadratic) relation between the injection electron concentration and output optical power is described by a square operator. Further we consider the static nonlinear relation between the injection current and output optical power, caused by the efficiency droop. We propose a novel post-distorter to overcome LED nonlinearities for high-speed Pulse Amplitude Modulation (PAM)-4 systems. Its performance is validated with measurements of a commercial blue LED.