A number of challenges face service providers with regards to being able to meet the 5G requirements. These challenges include a network bandwidth that doubles every 18 months and connected device numbers that double every 24 months.
In order to meet these challenges as well as widely varying requirements for performance, capacity and latency, the transport network must evolve and scale efficiently. This evolution needs to take place from the access network through to the core network.
Capacity – higher traffic demands in 5G will be presented through overall throughput increases and throughput per site increases. Peak user connection speeds in 5G will rise up to 20Gbps. In addition to this, a global average five-fold increase in traffic volume is predicted by 2025, 76% of which will be video traffic.
Connectivity – 5G will see the densification of cell sites which will drive the number of transport network access points that will be needed. It is forecast that this densification will mean a 3 to 4-fold increase in cell sites in new locations. In addition to this, new approaches to RAN deployments and virtualization of the 5G core will require more connection points, scalability and flexibility in the transport network.
Capability – transport networks will need new capabilities that can increase flexibility and agility, with an ability to provide the foundation for a distributed mobile network. In addition, techniques and technology used in 5G will facilitate increased coordination and MIMO (Multiple In Multiple Out) beamforming. This will see a requirement for low latency and improved synchronization, especially across the fronthaul network.
Complexity – the transport network needs to handle not only a huge increase in traffic but also a wide variety of network characteristics for each specific case. Some use cases will demand ultra-low latency connections, while others will have more relaxed requirements. Deployment of virtualized RAN, network slicing and distributed cloud networks will lead to more dynamic traffic patterns and more complex connectivity demands.
Cost – the advances enabled by 5G cannot be managed cost effectively simply by adding more capacity to existing transport network infrastructure. The transport network needs to become more integrated end to end, from radio access, through the fronthaul and backhaul to the core network using solutions that will optimize TCO (Total Cost of Ownership).
One main change that is noticeable when considering the evolution of technology from 4G to 5G is the split within the access network to incorporate centralization. This provides for greater flexibility and facilitates the virtualization of the RAN, but it does add to network complexity.
The C-RAN (Centralized RAN) approach introduces several advantages for the service provider:
Cost reduction – centralizing processing capability means that the cost of a DU (Distributed Unit) reduces.
Energy efficiency and power cost reduction – by reducing the hardware requirements of the cell site, general power consumption and also air conditioning costs can be reduced. This cost saving could be significant, especially with networks containing hundreds of thousands of cell sites.
Flexible hardware implementation – this in turn will result in highly scalable and more cost-effective RAN solutions.
Improved coordination – including performance optimization as a result of improved inter-cell interference coordination, as well as improved load management.
Improved offload and content delivery – aggregation of processing capability at the CU (Centralized Unit) provides an optimal place in the network for data offload or hosting of content.
Deployment flexibility – particularly with respect to where the functional split of the protocol stack lies, which in turn has an effect on the transport network.
Taking into account the implementation of C-RAN, the transport network can be broken down into three specific areas – fronthaul, midhaul and backhaul. Fronthaul transport is provided between the RRUs (Remote Radio Units) and the DUs, midhaul transport is provided between the DUs and the CUs, and backhaul between the CUs and the CN (Core Network). The different transport network characteristics between these are summarized below.
When analyzing the capacity requirements in the 5G RAN fronthaul there are a number of considerations to take into account as they all contribute to the overall calculation. These include the number of antenna ports being used, the radio bandwidth and also the subcarrier spacing being used. The NG-RAN (Next Generation – Radio Access Network) shall be able to support up to 1GHz system bandwidth, and up to 256 antennas. Calculations in relation to a possible transport deployment show that a theoretical maximum bitrate over the transport network of approximately 614Mbps per 10MHz per antenna port is needed.
Backhaul will provide the connectivity between small cells, macro cells, core networks and possibly numerous gateway nodes in between. The end points will be interconnected by a network of physical links, each with differing characteristics in terms of capacity, latency, availability, coverage, security, delay, synchronization, QoS, and physical design. Backhaul bandwidth capacity can be expected to be greater than 25Gbps and potentially up to 800Gbps. This will be dependent upon the amount of aggregation taking place and the deployment scenario (urban, rural, dense urban or indoor hotspot).
The increased demand for 5G eMBB is predicted to require the number of microcell sites to grow from 11 million to 14 million. As well as the challenges that 5G small cell sizes will bring this number increase will result in extra traffic. As such, during the planning phase of a deployment it is key that this is provisioned correctly. Failing to have adequate backhaul capacity can have detrimental effects.
