ROF-based antenna-PDM system employing DSM and DD-weight-pruning Volterra nonlinear equalization

The radio over fiber (ROF) system based on Delta-sigma modulation (DSM) can meet the requirements of the fronthaul system with its high signal fidelity and mature digital fronthaul interface specification. However, nonlinear impairments in ROF systems can seriously affect the performance of DSM signals. To reduce the impact of nonlinear effects on DSM signals with low complexity, we have designed a nonlinear equalizer based on the Volterra series. The complexity of the Volterra nonlinear equalizer (VNLE) is reduced through a weight pruning strategy. And by using directed decision instead of training sequences, we eliminate the redundancy introduced by VNLE while simultaneously ensuring its stability within the DSM system. Ultimately, we transmit one-bit single-carrier loaded DSM signals over 20 km of SMF-28 fiber and 3 m of wireless distance in an antenna polarization division multiplexing (APDM) intensity modulation and direct detection (IM/DD) system. For the first time, we add decision-directed weight-pruning Volterra nonlinear equalization (DD-PVNLE) algorithm in the APDM-IM/DD system to overcome the signal damage by the nonlinearity of the system. The BER of the Delta-sigma modulated on-off keying (DSM-OOK) signal reduces from 1 × 10⁻³ to 1.1 × 10⁻⁴. The high-fidelity 1024QAM, 2048QAM, and 4096QAM are recovered successfully whose BERs below the soft decision threshold 2.4 × 10⁻² and hard decision threshold 3.8 × 10⁻³ respectively.