This chapter focused on the practical aspects of fronthauling the next generation radio access networks. One of the important characteristics of 5G RAN is likely to be an increased degree of coordination between RAN nodes in networks that are becoming more dense. In this context CRAN becomes an interesting concept with overlaps with other emerging concepts such as NFV and MEC, however realisation of CRAN and associated requirements on fronthaul are dependent on the distribution of the RAN functions between central unit and the remote unit. This chapter provided an overview of the interdependence between RAN functions through the scheduling functions within a base station. One of the main observations highlighted in this chapter is that many backhaul technologies can support 5G fronthaul requirements, however there is a significant opportunity for optimisation. In particular, while the use of CPRI can be viable for point-to-point links, associated transport overheads may be prohibitive for a dense network, especially where base stations utilise some of the proposed 5G air interface techniques such as higher order MIMO over large channel bandwidths. Provided examples of real-world split RAN operation illustrate the viability of alternative split RAN architectures that can be more efficient from deployment perspective, and invite further research in the area.

Chapter Contents:

• 7.1 RAN functional split options
• 7.1.1 Splitting RAN air interface protocols
• 7.1.2 PDCP-RLC split
• 7.1.3 RLC-MAC split
• 7.1.4 Split MAC
• 7.1.5 MAC-PHY split
• 7.1.6 PHY split: FEC performed at CU
• 7.1.7 PHY split: modulation performed at CU
• 7.2 Radio access network technologies, architecture and backhaul options
• 7.2.1 Modern network architecture
• 7.2.1.1 Backhaul, fronthaul and midhaul
• 7.2.1.2 Network function virtualisation
• 7.2.1.3 Network slicing
• 7.2.1.4 Mobile edge computing
• 7.2.1.5 Service virtualisation
• 7.2.2 5G technologies and use cases
• 7.2.2.1 Integration of multiple air interfaces
• 7.2.2.2 Support for massive MIMO
• 7.2.2.3 Massive cooperation: multi-connectivity networks
• 7.2.3 Practical backhaul technologies
• 7.3 Current fronthaul solutions
• 7.3.1 CPRI in C-RAN
• 7.3.2 CPRI compression
• 7.3.3 Fronthaul or midhaul over ethernet
• 7.3.4 C-RAN integration in 5G: feasibility discussion
• 7.4 Market direction and real-world RAN split examples
• 7.4.1 Mobile backhaul
• 7.4.2 Centralised or Cloud RAN
• 7.4.3 Forward view to 5G
• 7.4.4 Industry 5G fronthaul initiatives
• 7.4.5 Split MAC trials
• 7.5 Conclusion
• References

Inspec keywords: radio access networks; radio links; next generation networks; cloud computing; 5G mobile communication; telecommunication scheduling; telecommunication computing; optimisation

Other keywords: 5G RAN; next generation radio access network; CRAN; dense network; scheduling functions; point-to-point links; central unit; base station; backhaul technology; CPRI; remote unit; 5G fronthaul requirements; real-world split RAN operation; optimisation; 5G air interface technique

Subjects: Radio access systems; Optimisation techniques; Optimisation techniques; Communications computing; Internet software; Mobile radio systems