Non-linearity effects and predistortion in optical OFDM wireless transmission using LEDs

Orthogonal frequency division multiplexing (OFDM) is a promising technique to realise high-speed indoor optical wireless (OW) links through the exploitation of the high peak-to-average power ratio (PAPR) for intensity modulation (IM). However, the non-linear characteristic of a light emitting diode (LED) imposes limitations on the performance. In this paper, the impact of the non-linear characteristic on bit-error performance is analysed using a commercially available LED (OSRAM, SFH 4230). Also, the paper proposes a predistorter to overcome the non-linearities. The performance without compensation and after compensation is analysed via simulations in an additive white Gaussian noise (AWGN) environment. In this context, the bit-error performance is determined for different bias points and power back-off values applied to the OFDM signal modulating the LED intensity. It is shown that LED non-linearity can significantly degrade the performance. It is also demonstrated that this degradation can greatly be mitigated by using the proposed predistortion technique.