An LED Model for Intensity-Modulated Optical Communication Systems

作者：Elgala Hany^*; Mesleh Raed; Haas Harald

来源：IEEE Photonics Technology Letters, 2010, 22(11): 835-837.

DOI：10.1109/LPT.2010.2046157

• Direct detection
• intensity modulation
• light-emitting diodes (LEDs)
• nonlinearity
• optical wireless communication
• orthogonal frequency-division multiplexing (OFDM)
• visible light communication (VLC)

Modulating the intensity of light-emitting diodes (LEDs) with analog signals, especially in the case of the bipolar optical orthogonal frequency-division-multiplexing (O-OFDM) signal, leads to significant signal degradation due to LED nonlinearity. The LED transfer function distorts the signal amplitude and forces the lower peaks to be clipped at the LED turn-on voltage. Additionally, the upper peaks are purposely clipped before modulating the LED to avoid chip overheating. The induced distortion can be controlled by optimizing the bias point or backing-off the average O-OFDM signal power. In this letter, a model that incorporates amplitude distortion and that provides a parameterized upper clipping is proposed. Through Monte Carlo simulations, the model can be used to determine the optimum bias point and to optimize the O-OFDM signal power. In this context, a novel concept of soft-clipping of the upper peaks is presented. It is shown that soft-clipping is an effective approach to reduce nonlinearity distortion and to enhance symbol error performance.

• 出版日期2010-6-1