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

TL;DR

This paper introduces R-FFT, a unified physical layer processing approach for cable and LTE networks that reduces fronthaul bitrate and enables shared infrastructure using a novel Remote-FFT node with caching capabilities.

Contribution

It proposes a novel Remote-FFT node that unifies cable and LTE physical layer processing, reducing fronthaul bitrate and enabling shared infrastructure in a hybrid fiber-coax network.

Findings

R-FFT caching significantly reduces fronthaul bitrate.

Unified processing enables efficient sharing of physical layer functions.

Delay analysis shows trade-offs in moving processing to the headend.

Abstract

The Remote-PHY (R-PHY) modular cable network for Data over Cable Service Interface Specification (DOCSIS) service conducts the physical layer processing for the transmissions over the broadcast cable in a remote node. In contrast, the cloud radio access network (CRAN) for Long-Term Evolution (LTE) cellular wireless services conducts all baseband physical layer processing in a central baseband unit and the remaining physical layer processing steps towards radio frequency (RF) transmission in remote nodes. Both DOCSIS and LTE are based on Orthogonal Frequency Division Multiplexing (OFDM) physical layer processing. We propose to unify cable and wireless cellular access networks by utilizing the hybrid fiber-coax (HFC) cable network infrastructure as fiber fronthaul network for cellular wireless services. For efficient operation of such a unified access network, we propose a novel Remote-FFT (R-FFT) node that conducts the physical layer processing from the Fast-Fourier Transform (FFT) module towards the RF transmission, whereby DOCSIS and LTE share a common FFT module. The frequency domain in-phase and quadrature (I/Q) symbols for both DOCSIS and LTE are transmitted over the fiber between remote node and cable headend, where the remaining physical layer processing is conducted. We further propose to cache repetitive quadrature amplitude modulation (QAM) symbols in the R-FFT node to reduce 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 LTE service, and illustrate the delay implications of moving part of the cable R-PHY remote node physical layer processing to the headend.