Jean Paul M.G. Linnartz, Xiong Deng, “Continuous phase Flip-OFDM in optical wireless communications,” Signal Processing, vol. 182, 2021

Abstract: Intensity Modulated (IM) optical communication over an LED channel requires the use of a non-negative signal that can also cope with the low-pass nature of LEDs. For this purpose, dedicated schemes such as Flip-OFDM and Assymetrically Clipped Optical (ACO)-OFDM have been proposed. We derive a common mathematical description on which both schemes rely. Exploiting this insight, we propose Continuous Phase Flip-OFDM (CP-Flip-OFDM) as an enhancement to Flip-OFDM. It ensures phase continuity at the transition between the two successive copies of the OFDM blocks, thereby it obviates the Cyclic Midfix between the first OFDM block and its flipped copy. Simultaneously, we derive a less compute-intensive way to generate and detect ACO-OFDM. Instead of creating an Hermitian-symmetry at the transmit Inverse FFT input, which is common in optical IM OFDM, we use zero padding. After the transmit IFFT, a phase ramp-up, i.e., a multiplication with a complex-valued exponential, is applied before truncating to a real and non-negative signal.