Given the amount of data traffic expected with the rollout of 5G, SK Telecom has been trialing a 5G-PON fronthaul solution. It claims that this solution will drastically cut installation costs, and reduce operations and maintenance costs.
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Cloud RAN Needs Fronthaul
5G is expected to generate “a lot” of traffic. ABI Research estimates that, by 2026, 5G mobile telcos will be generating 777 exabytes of traffic annually, an amount that eclipses all of the traffic being carried on 4G LTE networks (768 exabytes annually). All of that traffic needs to be backhauled and aggregated to and from the core network.
One of the novel architectures that will be a key requirement for 5G networks is the Cloud Radio Access Network (C-RAN) and fronthauling. C-RAN is a centralized, cloud computing-based architecture for radio access networks. C-RAN takes advantage of innovations in wireless, optical, and IT communications systems. For example, it uses the latest CPRI protocol standard, and fiber-optic connections to allow transmission of a baseband signal over long distances, thus achieving a large-scale centralized basestation deployment. This architecture allows for potentially hundreds of thousands of remote radio heads (RRHs) to be connected to a centralized baseband unit (BBU) pool. In this architecture, the fiber-optic links fronthaul the traffic between the centralized baseband controllers and the RRHs at the cell sites. In theory, microwave links can be used, but for now, fiber-optic is primarily used. The first C-RAN deployment was in China by China Mobile in 2010. Since then, C-RAN deployments have been seen in Korea, Japan, and Singapore, among other locations.
A pressing concern that SK Telecom has faced when compared with LTE networks is that 5G networks will require dense small cell deployments that can deliver higher throughput. These requirements emphasize the significant role of fronthaul in transmitting the radio signals received from cell sites to the central units.
SK Telecom’s 5G-PON
In November 2017, SK Telecom trialed and then deployed a 5G-passive optical network (PON) fronthaul solution that can handle both LTE and 5G traffic. 5G-PON enables broader coverage for the 5G rollout by simplifying the installation of basestations and antennas without the need for any additional networks. In addition to simplifying the backhaul links, SK Telecom reports that 5G-PON ensures service sustainability through the application of ring topology and precise delay equalizer operations. As a result, if one link drops, communications services can be delivered through the other link in the ring. The architecture also uses passive nodes that do not require electrical power.
SK Telecom states that it has implemented the technology in 227 central office terminals in South Korea, which accounts for 10% of its network. By 2018, SK Telecom intends to expand the rollout to 30% of its network, covering a total of 85 cities, including Seoul, Busan, Daegu, Daejeon, and Gwangju. Interestingly, SK Telecom claims that the solution can help improve service coverage in rural areas, as it minimizes the need for fiber-optic deployment.
SK Telecom’s 5G-PON fronthaul network relies on bidirectional 3-gigabit and 6-gigabit module transceivers on a 20-km fiber-optic cable that connects 96 optical links on CPRI/OBSAI interface channel cards. In 2018, module transceivers will be upgraded to 10 gigabit and, eventually, 25 gigabit for its 5G network.
Hong says that, in 2018, SK Telecom will have bidirectional 10-gigabit tunable SFPs and will start developing 25-gigabit bidirectional tunable SFPs and eCPRI interface channel cards for its 5G radio access network.
It Is Not Just about Backhaul, but Also TCO
5G will place substantial demands on the mobile telco network. It is not just the additional traffic load from 4K, even potentially 8K video, but also the increased demand for lower latency. Mobile telcos will need to upgrade their backhaul infrastructure to meet these demands. Enhancements in millimeter wave and microwave backhaul solutions will increase the options for the mobile telcos, but ultimately, fiber-optics will be a key requisite for 5G. Solutions, like 5G-PON, will be welcomed by mobile telcos if it helps to minimize the need for fiber-optic, especially outside of major towns and cities. SK Telecom indicates that the 5G-PON solution does involve contributions from domestic infrastructure vendors, such as Solid, HFR, SunwaveTec, and Coweaver. SK Telecom is also confident that 5G-PON has cut the cost of installation in half, while operations and maintenance costs have been reduced by 70%, due to the intelligent operation and management of the passive nodes and the use of tunable SFPs at the remote sites.