Soft-stacked PON for soft C-RAN

Abstract—Cloud radio access networks (C-RANs) feature central pooling baseband processing units (BBUs) and lowcost remote radio headends (RRHs) with fiber-connected fronthauls between them, and they are promising for 4G. Researchers are redesigning the C-RAN with different split approaches to relax the fronthaul capacity for 5G with massive antennas, which is termed soft C-RAN. In this paper, we propose a soft-stacked passive optical network (PON) to support the soft C-RAN as an integrated solution. Two approaches are investigated in this paper. The first one is realized by employing an arrayed waveguide grating router (AWGR) and directly modulated tunable lasers, and it is promising for digital fronthaul and midhaul transmission and switching. The second is realized by employing wavelength-selective switches (WSSs) to allocate one-toone and many-to-many connections, and it is promising for analog fronthaul transmission and switching. Their performances are analyzed and measured with directly modulated lasers (DMLs) that are either fixed or tunable. A delay interferometer is used for the DMLs’ chirp and fiber dispersion management. The result is significant for future soft C-RANs and stacked PON.