R-FFT: Function Split at IFFT/FFT in Unified LTE CRAN and Cable Access Network

摘要

The Remote-PHY (R-PHY) modular cable network for Data over Cable ServiceInterface Specification (DOCSIS) service conducts the physical layer processingfor the transmissions over the broadcast cable in a remote node. In contrast,the cloud radio access network (CRAN) for Long-Term Evolution (LTE) cellularwireless services conducts all baseband physical layer processing in a centralbaseband unit and the remaining physical layer processing steps towards radiofrequency (RF) transmission in remote nodes. Both DOCSIS and LTE are based onOrthogonal Frequency Division Multiplexing (OFDM) physical layer processing. Wepropose to unify cable and wireless cellular access networks by utilizing thehybrid fiber-coax (HFC) cable network infrastructure as fiber fronthaul networkfor cellular wireless services. For efficient operation of such a unifiedaccess network, we propose a novel Remote-FFT (R-FFT) node that conducts thephysical layer processing from the Fast-Fourier Transform (FFT) module towardsthe RF transmission, whereby DOCSIS and LTE share a common FFT module. Thefrequency domain in-phase and quadrature (I/Q) symbols for both DOCSIS and LTEare transmitted over the fiber between remote node and cable headend, where theremaining physical layer processing is conducted. We further propose to cacherepetitive quadrature amplitude modulation (QAM) symbols in the R-FFT node toreduce the fronthaul bitrate requirements and enable statistical multiplexing.We evaluate the fronthaul bitrate reductions achieved by R-FFT node caching,the fronthaul transmission bitrates arising from the unified DOCSIS and LTEservice, and illustrate the delay implications of moving part of the cableR-PHY remote node physical layer processing to the headend.