Spectrally efficient optical orthogonal frequency division multiplexing

Abstract

<jats:p>This paper charts the development of spectrally efficient forms of optical orthogonal frequency division multiplexing (OFDM) that are suited for intensity-modulated direct detection systems, such as wireless optical communications. The journey begins with systems using a DC-bias to ensure that no parts of the signal that modulates the optical source are negative in value, as negative optical intensity is unphysical. As the DC-part of the optical signal carries no information, it is wasteful in energy; thus asymmetrically clipped optical OFDM was developed, removing any negative-going peaks below the mean. Unfortunately, the clipping causes second-order distortion and intermodulation, so some subcarriers appear to be unusable, halving spectral efficiency; this is similar for unipolar and flipped optical OFDM. Thus, a considerable effort has been made to regain spectral efficiency, using layered techniques where the clipping distortion is mostly cancelled at the receiver, from a knowledge of one unpolluted layer, enabling one or more extra ‘layers/paths/depths’ to be received on the previously unusable subcarriers. Importantly, for a given optical power and high-order modulation, layered methods offer the best spectral efficiencies and need the lowest signal-to-noise ratios, especially if diversity combining is used. Thus, they could be important for high-bandwidth optical fibre systems. Efficient methods of generating all layers simultaneously, using fast Fourier transforms with their partial calculations extracted, are discussed, as are experimental demonstrations in both wireless and short-haul communications links. A musical analogy is also provided, which may point to how orchestral and rock music is deciphered in the brain.</jats:p> <jats:p>This article is part of the theme issue ‘Optical wireless communication’.</jats:p>

Optical wireless communication

“…Therefore, new digital modulation techniques have been developed based on multi-stream, or layered data transmission in conjunction with superposition modulation and iterative detection. This issue features a comprehensive review article on layered transmission techniques by Lowery [30], who has developed many novel digital modulation techniques for IM/DD systems.…”

The Evolution of Optical OFDM

“…Several survey papers have been published comparing the performance of LACO-OFDM to other O-OFDM schemes [44], [51], [73], [74]. Their contributions are summarized and boldly contrasted to our work in Tab.…”

“…IV. Explicitly, the mathematical BER and PAPR performance analyses of various O-OFDM schemes was carried out by Sun et al [44], while a survey authored by Lowery [74] focused on the associated transceiver signal processing and spectral analysis. However, the family of error correction techniques designed for O-OFDM schemes -which is a vitally important component of any practical implementation -has hardly been touched upon in the related survey papers.…”

A survey of applied machine learning techniques for optical orthogonal frequency division multiplexing based networks

“…In communication systems, ML is very useful in fault management [12], routing and traffic control [13], resource allocation [14] and channel equalization [15]. On the other hand, orthogonal frequency division multiplexing (OFDM) is a mature technology extensively implemented in both wireless and optical communication systems [16,[17][18][19][20]. OFDM can enhance the spectral efficiency of a generated signal and can maximize transmission performance by employing high order modulation formats per OFDM subcarrier [21].…”