Lower bounds on the channel capacity of ASCO-OFDM and ADO-OFDM

In this paper, we compare the lower bounds on the channel capacity of asymmetrically and symmetrically clipped optical (ASCO)-OFDM and asymmetrically clipped DC biased optical (ADO)-OFDM for an additive white Gaussian noise (AWGN) channel with an average transmitted optical power constraint. The lower bound of channel capacity can be obtained by calculating the maximum mutual information between transmitter and receiver over all possible input distributions. By using the distribution of ADO-OFDM, the lower bounds are obtained for different constellation cases and they depend on different DC bias levels. In order to calculate the lower bounds of ASCO-OFDM, the general probability density function (PDF) of ASCO-OFDM is derived. Simulation results show that ASCO-OFDM has larger channel capacities than ADO-OFDM for a large range of signal to noise ratio (SNR).