FOFDM Based on Discrete Cosine Transform for Intensity-Modulated and Direct-Detected Systems

In this paper, three basic intensity-modulated and direct-detected (IM/DD) fast orthogonal frequency division multiplexing (FOFDM) schemes are compared, including Flip-FOFDM, asymmetrically clipped optical FOFDM (ACO-FOFDM) and DC-offset FOFDM (DCO-FOFDM). The modulation/demodulation processing of FOFDM employs the discrete cosine transform. Compared with conventional OFDM based on discrete Fourier transform, FOFDM exhibits lower computational complexity because of its simple one-dimensional modulation and real-valued operation. To the best of our knowledge, Flip-FOFDM is first reported. We analyze the key parameters of three basic IM/DD FOFDM schemes in detail, including spectral efficiency, computational complexity, bit-error-ratio performance, and power efficiency. We categorize ACO-FOFDM and Flip-FOFDM in U-FOFDM. The spectral efficiency of DCO-FOFDM is twice that of U-FOFDM. However, due to the large DC bias of DCO-FOFDM, DCO-FOFDM is less efficient than U-FOFDM in terms of optical power when the bit rate/normalized bandwidth is less than 5, but DCO-FOFDM becomes more efficient than U-FOFDM when the bit rate/normalized bandwidth is greater or equal to 5. FOFDM shows great potential for application in IM/DD systems.