Delta-sigma modulation-assisted lookup table digital predistortion for discrete MultiTone signals in IM/DD systems

Lookup-table-based digital predistortion (LUT-DPD) provides a low-complexity approach to mitigating pattern-dependent transmitter nonlinearities. However, conventional LUT-DPD relies on discrete symbol levels for table indexing and is therefore difficult to apply directly to continuous-valued multicarrier waveforms such as discrete multitone (DMT) signals. In this paper, a novel LUT-DPD scheme based on delta sigma modulation (DSM) is proposed. The DMT waveform is first quantized using a fourth-order DSM, which enables pattern indexing with fewer amplitude levels and subsequent LUT predistortion, followed by signal reconstruction through low-pass filtering and downsampling. The proposed scheme is experimentally evaluated in a 132-Gbit/s C-band DMT 64-ary quadrature amplitude modulation (QAM) optical back-to-back intensity modulation/direct detection (IM/DD) link with a 25-GHz signal bandwidth. At the 7% HD-FEC BER threshold of 3.8e-3, receiver sensitivity improvements of 0.5 dB and 0.7 dB are achieved for LUT memory depths of 3 and 5, respectively. The results indicate that DSM-assisted indexing can extend LUT-DPD to DMT signals while maintaining manageable table sizes.