Digital Predistortion Techniques in Radio-Over-Fiber Systems

The integration of digital predistortion (DPD) within radio-over-fibre (RoF) architectures addresses the fundamental nonlinearity and memory impairments arising in optical and radio-frequency transmission chains. In typical RoF links, optical modulators, semiconductor lasers and power amplifiers introduce harmonic distortion and intermodulation products that degrade signal fidelity, reduce spectral efficiency and increase error vector magnitude (EVM). DPD techniques pre-process digital baseband signals to apply an inverse nonlinearity, compensating for distortions and extending spurious-free dynamic range. Traditional approaches employ polynomial-based models—such as Volterra series, memory polynomials and generalized memory polynomials—to capture static and dynamic characteristics of the link. Recent work has expanded towards complexity-reduction strategies, multi-dimensional DPD for sparse multi-band signals and hybrid analogue-digital linearisation to handle tens of gigahertz operational bandwidths. More recently, machine-learning frameworks, including neural networks and convolutional structures, have been exploited to model and invert complex nonlinearities, offering adaptive real-time compensation with lower manual tuning. These developments underpin practical deployments in 5G and beyond, enabling high-throughput, low-latency fronthaul links for distributed MIMO, millimetre-wave and small-cell applications, while meeting stringent standards for adjacent-channel leakage and error performance.

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Digital Predistortion Techniques in Radio-Over-Fiber Systems publication trend

The graph below shows the total number of articles in digital predistortion techniques in radio-over-fiber systems across all publications each year (not limited to Nature Index journals).

Technical terms

Digital predistortion (DPD): A signal processing technique that applies the inverse of a system’s distortion characteristics to a digital signal before transmission, thereby linearising the end-to-end link.

Radio-over-fibre (RoF): A technology that transports radio-frequency signals over optical fibre, combining broad optical bandwidth with wireless access.

Memory polynomial model: A DPD model that captures both instantaneous nonlinearities and their memory effects through polynomial terms and tapped delay lines.

Volterra series: A generalised polynomial expansion used to model nonlinear systems with memory, representing higher-order intermodulation contributions.

Adjacent Channel Power Ratio (ACPR): A measure of spurious emissions in neighbouring frequency channels, indicating spectral regrowth due to nonlinearity.

Error Vector Magnitude (EVM): A metric quantifying the difference between ideal and received symbols, reflecting distortion and noise in digital modulation schemes.

References

1. Linearization Technologies for Broadband Radio-Over-Fiber Transmission Systems. Photonics (2014).
2. Complexity-reduced digital predistortion for subcarrier multiplexed radio over fiber systems transmitting sparse multi-band RF signals.. Optics Express (2013).
3. Experimental investigation on multi-dimensional digital predistortion for multi-band radio-over-fiber systems.. Optics Express (2014).
4. Machine Learning Techniques in Radio-over-Fiber Systems and Networks. Photonics (2020).
5. Neural Network DPD for Aggrandizing SM-VCSEL-SSMF-Based Radio over Fiber Link Performance. Photonics (2021).
6. Experimental Demonstration and Performance Enhancement of 5G NR Multiband Radio over Fiber System Using Optimized Digital Predistortion. Applied Sciences (2021).
7. Practical Demonstration of 5G NR Transport Over-Fiber System with Convolutional Neural Network. Telecom (2022).