Efficient Pre-BPF based Sigma Delta Radio over Fiber System for 5G NR Fronthauls

Sigma delta radio over fiber (ΣΔ-RoF) link as an optical front haul find its application in 5G cloud/centralized radio access network (C-RAN). The presence of 1-bit sigma delta (ΣΔ) modulation results in high quantization error that can be reduced by addition of band pass filter (BPF) at the receiver side. However, this BPF leads to an additional unwanted magnitude and phase noise that severely affects the signal integrity. In order to reduce the effects of conventional BPF, a Pre-BPF is proposed which is inserted before ΣΔ modulator to counteract the magnitude and phase response of conventional BPF. The proposed system is practically validated for 5G new radio (NR) 100-MHz signal with 256 quadrature amplitude modulation centered at 3 GHz with 5 km of link length. The experimental realization compares analog radio over fiber (A-RoF), conventional ΣΔ-RoF and Pre-BPF-ΣΔ-RoF. The experimental results suggest a significant reduction of error vector magnitude and adjacent channel leakage ratio for Pre-BPF-ΣΔ-RoF as compared to conventional A-RoF and ΣΔ-RoF system.