Enhanced asymmetrically-clipped optical OFDM

Asymmetrically clipped optical orthogonal frequency-division multiplexing (ACO-OFDM) is a technique that sacrifices spectral efficiency in order to transmit an orthogonally frequency-division multiplexed signal over a unipolar channel, such as a directly modulated direct-detection fiber or free-space channel. Several methods have been proposed to regain this spectral efficiency, including: asymmetrically clipped DC-biased optical OFDM (ADO-OFDM), enhanced U-OFDM (EU-OFDM), and spectral and energy efficient OFDM (SEE-OFDM). This paper presents a new method that offers the highest receiver sensitivity for a given optical power at spectral efficiencies above 3 bit/s/Hz, having a 7-dB sensitivity advantage over DC-biased OFDM for 1024-QAM at 87.5% of its spectral efficiency, at the same bit rate and optical power. OCIS codes: (060.2330) Fiber optics communications; (060.4080) Modulation; (060.1660) Coherent communications. Author’s Note 7th Nov. 2015 A recent post of Arxiv on a modified SEE-OFDM (Emily Lam, Sarah Kate Wilson, Hany Elgala, Thomas D. C. Little, “Spectrally and Energy Efficient OFDM (SEE-OFDM) for Intensity Modulated Optical Wireless Systems,” 28 Oct. 2015, arXiv.org > cs > arXiv:1510.08172) has drawn my attention to Qi Wang, Chen Qian, Xuhan Guo, Zhaocheng Wang, David G. Cunningham, and Ian H. White “Layered ACO-OFDM for intensity-modulated directdetection optical wireless transmission” (Optics Express, 4 May 2015, Vol. 23, No. 9, p. 12382, https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-9-12382), which uses the same harmonic sequences as my proposal here, and also a method of reconstructing the clipping noise from the estimated constellation values. My work herein presents more comparisons on the relative performance of EACO-OFDM versus other techniques particularly DCO-OFDM, and also up to the high levels of spectral efficiency, where I have identified the greatest performance gains. I have also verified that the power penalty over a single ACO channel can be accurately calculated by considering the DC levels of individual chords/layers of the ACO sub-channels. My comments on SEE-OFDM in the Introduction refer to the original paper [17], and not the latest Arxiv version (28th Oct. 2015). Author’s Note 9th Mar. 2016 Arthur James Lowery, "Comparisons of spectrally-enhanced asymmetrically-clipped optical OFDM systems," Opt. Express 24, 3950-3966 (2016) https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-4-3950 Note also that there is a more recent paper by Harald Haas’s group that also proposed a layered ACO-OFDM scheme, coincidently called Enhanced ACO OFDM: Mohamed Sufyan Islim, Dobroslav Tsonev and Harald Haas, “On the Superposition Modulation for OFDMbased Optical Wireless Communication” GlobalSIP, Orlando, Florida, Dec. 2015. Session: WbOW-L: Modulation and Coding, Paper 1. Thus this is a very active field with important outcomes for improving the performance of intensity-modulated optical communications systems. Please search for more recent papers, regularly.