Transmitter and receiver methods for improving asymmetrically-clipped optical OFDM

This paper introduces a new constellation mapping scheme for asymmetrically-clipped optical OFDM (ACO-OFDM) that puts more bits on the low-frequency subcarriers. The lowpass nature of the wireless optical channel motivates the use of this generic bit-loading scheme. This scheme has no knowledge of the channel at the receiver; it performs significantly better than the traditional constant constellation mapping on all subcarriers in a variety of channels. The average bit-error rate (BER) curves for the new modulation scheme have up to a 5 dB improvement for signal-to-noise ratios (SNRs) where the BER is in the order of 10^-3. In addition to the generic low-frequency bit-loading, this paper also proposes clipping the ACO-OFDM signal at the receiver to mitigate the additive electronic noise.