Digital Modulation Techniques for Optical Asymmetrically-Clipped OFDM

We present a new modulation scheme for asymmetrically-clipped optical OFDM (ACO-OFDM). We show that a generic bit-loading scheme that puts more bits on the low-frequency subcarriers is more efficient for wireless optical channels than the constant modulation scheme typically used in radio frequency (RF) OFDM schemes. We discuss the low- pass nature of the wireless optical channel that motivates the use of this generic bit-loading scheme. This scheme performs significantly better than the traditional constant modulation on all tones 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 where the BER is in the order of 10 ^-3.