A study of LED nonlinearity effects on optical wireless transmission using OFDM

Orthogonal frequency division multiplexing (OFDM) is a promising technique to realize high-speed indoor optical wireless (OW) links through the exploitation of the high peak-to-average power ratio (PAPR) for intensity modulation (IM). However, non-linear distortions in the transmission chain can significantly compromise the performance of OFDM as they incur inter-channel interference. The light emitting diode (LED) is the main source for such distortions due to its nonlinear behavior. Distortion levels can be controlled when the LED operates in a quasi-linear segment of its characteristic around a bias point. The severity of non-linear distortions and the dependence of the bias point on the chosen digital modulation scheme are analyzed in this paper. In this context, the bit-error performance is determined as a function of the bias point and the applied power back-offs.