Challenges and Opportunities in Wireless Fronthaul

To date the evolution from traditional distributed radio access networks (D-RAN) towards fronthaul oriented centralized (C-RAN) architectures has imposed significant challenges for the underlying transport network. The processing and coordination benefits anticipated in C-RAN are generally underpinned with the assumption of a full fiber transport network capable of meeting the demanding performance criteria of fronthaul transport. Recent advances in Ethernet based fronthaul interfaces together with exploration of new mmWave and sub-THz spectrum bands present an opportunity for wireless solutions to also realize these fronthaul transport requirements. In this work, the requirements for promising new Ethernet based fronthaul interfaces are explored. These requirements are assessed against the measured capabilities of a state-of-the-art E-band (71-86 GHz) wireless transport solution. The experimental results are then used to forecast the performance expectations of future higher bandwidth systems operating above 100 GHz. A dimensioning and link budget analysis is performed for the various candidate spectrum bands and fronthaul interfaces to highlight the viability of fronthaul delivered over wireless transport. Finding show that transport solutions operating at mmWave and sub-THz frequencies are able to support the performance requirements of newly standardized fronthaul interface splits and as such present an opportunity to utilize wireless fronthaul transport in C-RAN architectures where fiber cannot otherwise be supported. Furthermore, analysis demonstrates that the hop lengths possible for 5G small cell configurations are well aligned with the expected inter-site distances of future dense urban cell deployments making wireless fronthaul a promising concept for realizing future C-RAN based cell densification.