Beamforming and Functional Split Selection for Scalable Cell-free mMIMO Networks

The cell-free massive multiple-input multiple-output (CF mMIMO) spectral efficiency (SE) enhancement achieved through beamforming puts new requirements on the fronthaul interface load. At the same time, O-RAN is gaining traction thanks to standardized interfaces allowing for seamless integration of radio access network (RAN) components from different vendors. We propose fronthaul load estimation formulas for CF mMIMO with 7-1 and O-RAN-defined 7-2 functional splits that differ in the location of the beamforming function, which is essential in the CF mMIMO networks. Additionally, we propose a methodology of dynamic beamforming and functional split selection to minimize the fronthaul load while maintaining high sum SE utilization.