Analog Mobile Fronthaul Supporting 128 RF Chain With Nonlinear Compensator for B5G and 6G Ma-MIMO Beamforming

These paper details a fronthaul optical link using delay-division-multiplexing (DDM) scheme with Volterra based nonlinear compensator for beyond fifth generation (B5G) and 6G massive multiple-input multiple-output (Ma-MIMO) beamforming. Based on pre-allocated relative time delays, pre-processed signals can be deaggregated to different RF chain signals following spectral aliasing caused by the digital signal processing (DSP) at remote radio units. The Volterra based nonlinear compensator is used to compensate nonlinear distortion and IQ imbalance of the fronthaul link. By combined the DDM scheme and Volterra technique, we can easily deaggregate signals and mitigate the interference caused by nonlinear distortion and IQ imbalance at the same time. In experiments, the DDM scheme support 128 RF chain signals is demonstrated. With the Volterra compensator, the signal input power of Mach-Zehnder modulator (MZM) has 18 dB margin. IQ imbalance caused by phase misalignment can also be compensated by the IQ Volterra. It can keep the acceptable error vector magnitude (EVM) performance within a ±10° range. After 25-km optical link, the EVM of each RF Chain is underneath 8%. And the total received 128 RF chain signals will require CPRI data rate as high as 840 Gb/s.