Sizing up spectrum: using transport the best way with new 5G assets

The first post in this series explored some of the backhaul capacity evolution aspects in a mobile network. Besides capacity, there are several other important aspects of the radio access network evolution that we need to consider from a transport evolution and planning perspective.

Transport becomes the backplane of a disaggregated radio solution

A significant evolution step is that the architectural way of building radio access networks is changing. Historically, we have been using the so-called Distributed RAN method. In this case we deploy all radio access network building blocks, such as basebands, radios and antennas on a common site and expose a single interface towards the core of the network.

But already today, this is just one of multiple potential options in a versatile toolbox. There are different architectural solutions such as Centralized RAN, Virtual RAN or Elastic RAN that can introduce significant improvements on the radio access side, however at the same time introduce some new requirements in the transport network.

The main concept of such architectural advancements is the radio protocol stack decomposition across different locations, which exposes previously internal RAN interfaces on the transport. These interfaces vary in characteristics, some of them carry small amounts but bursty and latency sensitive traffic, whereas others are more sustained in traffic volume and less latency sensitive.

Benefits of radio coordination

Referring to the previous blog post about capacity evolution, let’s consider a large capacity site, where multiple radio access technologies and many frequency bands are deployed. These locations usually provide excellent possibility to further improve end-user experience through radio coordination. With advanced network functions such as carrier aggregation or coordinated multipoint transmission, user equipment are capable to simultaneously transmit or receive using multiple different frequencies. This can introduce various benefits such as increased end-user throughput, better cell edge performance or UE power reduction.

With the introduction of higher frequency bands in 5G, these techniques will continue to play a significant role.  Advanced coordination functions together with Ericsson Spectrum Sharing solution can enable up to 60% larger mid-band 5G coverage area compared to standard Dual Connectivity (EN-DC) solutions.

These advanced radio coordination functions utilize a specific coordination interface, which is carried between different baseband nodes.  Some coordination techniques are carried out in very short periods of time (order of 100ns), meaning that traffic on this interface has a low latency budget and is bursty in nature.

Coordination through transport

Considering typical current deployments, these coordination functions usually operate within the boundaries of a single site. From a transport perspective it means that the site transport device, such as cell site router needs to ensure that different baseband units can coordinate with each other without delay and traffic drops. The main transport requirements are the following:

• Low forwarding latency. Since advanced coordination is latency sensitive, the transport devices must operate with low forwarding latency.   
• Buffers. In addition to low latency tolerance, coordination traffic can also be bursty in nature. Other, non-latency-sensitive traffic may need to be temporarily buffered while coordination traffic is passing through
• Hierarchical QoS. Many different traffic types need to be served at the same time, which requires a proper QoS functionality

As we evolve toward mainstream 5G deployments with a multitude of new radio architectures and use-cases, networks will become more heterogeneous. A user equipment could simultaneously connect to several different frequency bands, served by different radio units that may be located on different sites. These radio units will need to coordinate with each other through the backhaul to provide the best quality of experience to the end user.

The introduction of inter-site radio coordination means that radio-near transport segments, such as pre-aggregation or aggregation domains will also need to carry the previously mentioned coordination traffic. The requirements of low latency forwarding, large buffers and hierarchical Quality of Service will also apply in these network segments so that overlapping or neighboring sites can freely coordinate between each other.

Strict time and phase synchronization in transport

It is also important to note that radio coordination and 5G deployments in mid- and high-band drive the introduction of strict time and phase synchronization. This new requirement needs to be fulfilled regardless of the backhaul medium. Even if there is a GNSS receiver on the site, Ericsson recommends deploying remote backup synchronization sources and using the backhaul as the synchronization delivery vehicle. Satellite-based synchronization systems are prone to disturbances and such events can lead to service degradation, or in worst case to a complete service outage. Read more about synchronization challenges and solutions in our 5G is all in the timing blog post.

5G has more interaction with and bigger dependency on transport than any previous mobile generation. A high-performance transport network is needed to realize the full potential of 5G networks. Ericsson offers purpose-built transport solutions to address current and upcoming needs in building the best performance networks.  

Click here to learn more about how Ericsson 5G Transport solutions are enabling superior RAN performance.