Just recently, Nokia Bell Labs announced a significant breakthrough in the field of fronthaul, demonstrating how passive optical networks (PON) can transport traditional common public radio interface (CPRI) fronthaul. Then last week at the 5G World Summit in London, we took another step forward with the industry-first demonstration of a PON solution for fronthauling cloud and centralized RAN traffic.
Using PON for fronthaul and backhaul of mobile traffic solves two major challenges for operators. Firstly, it delivers on the low latency and high throughput promises for the thousands of small cells that will need to be deployed to support the mobile advancements towards 5G. Secondly, it keeps costs under control, as converging more services on existing fiber-to-the-home (FTTH) networks is more cost-efficient than building separate mobile transport networks.
So how do our latest announcements help?
The Nokia Bell Labs proof of concept demonstrates a very important technical breakthrough: PON can support the hyper-strict latency and synchronization requirements of CPRI. We used a specially designed CPRI-Ethernet gateway to deliver ultra-low latency CPRI traffic over standard fiber using XGS-PON (where X=10, G=gigabit, S=symmetrical PON). This can support up to four CPRI streams at 2.5 Gb/s per optical channel while next-generation PON variants could take that to 20 CPRI streams.
But traditional fronthaul is evolving. CPRI uses a permanent stream of traffic, so it is extremely bandwidth-hungry, and is only effective over relatively short distances. Smarter mobile interfaces are being developed, which incorporate a CPRI-Ethernet gateway function like the one that Nokia Bell Labs uses. The new interface is part of the 5G new radio access architecture and is based on disaggregated architectures, where the baseband unit functionality is split between distributed and centralized units.
There are a couple of split options being looked at by the industry, notably by 3GPP defining a new interface, called F1, for a higher layer functional split, and the new CPRI specification for 5G expected in August for a lower layer (physical) functional split. One principle that I’ve spoken about before, network function optimization (NFO) in software-defined access networks, is also a key factor here: mobile networks must keep highly latency-sensitive functions close to the cell site, while allowing others to be centralized and/or virtualized. The virtualized functions, centralized intelligence and SDN programmable interfaces increase operator agility and lead to optimization of networks for a wider range of services.
Split architectures combine different advantages: they reduce the interface bandwidth, which can scale in line with user traffic, while advanced coordination transmission schemes can still be applied to improve spectral efficiency. The load on the network can be further reduced if only scheduling data needs to be transferred between the different cells that are coordinating with each other.
And this is where PON comes to the fore.
PONs are perfectly suited for establishing cost effective connections to many radio sites in mobile networks, while meeting the strict timing and synchronisation requirements of existing 4G and future 5G technologies. The live demonstration at 5G World is the first commercial PON solution transporting such a higher layer fronthaul split. It uses Nokia XGS-PON technology to serve a Nokia AirScale Cloud RAN solution with distributed radio access units and centralized radio access controller. Compared to CPRI, the transported bandwidth is reduced by a factor of 15. The evolution doesn’t end here, as software-defined network slicing of the PON will further increase the ability to manage and operate the mobile traffic more efficiently and effectively.
What does all this mean for mobile operators?
It means we have removed the biggest barriers towards widespread deployment of 5G. By their nature and design, PON networks are found in the areas where operators will have the most challenges to provide cost-effective backhaul and fronthaul. We’ve already proven how PON makes sense for backhaul. With these breakthroughs, PON also nails the challenges presented by fronthaul.
5G fronthaul is a new frontier for mobile networks, and Nokia is boldly going where no-one has gone before.
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