The transport infrastructure for 5G is just as important as the other elements of the 5G network, and transport technologies are having to be updated for this next generation of wireless. Shane McClelland, VP of transport products at Ericsson North America, says that the way mobile backhaul has been handled up until now, won’t suffice in the 5G era.
“The industry has created new architectures for RAN,” said McClelland, speaking on a FierceWireless virtual panel, entitled “5G Transport: Challenges and Opportunites.” He said, “We used to have just a couple of simple interfaces in a distributed RAN world. We had CPRI, which connected our radios to our baseband over dark fiber. Then we had the S1 and X2 interface that went across the IP network back to the packet core location.”
But 5G introduces more complexity in the transport network. It introduces new architectures such as Cloud RAN and virtual RAN. There are front-haul and mid-haul interfaces. And CPRI is evolving to enhanced CPRI.
“Once you define these new architectures and interfaces, you find that each one of these interfaces has different requirements for capacity and latency as defined by 3GPP,” said McClelland. “No longer is just homogenous mobile backhaul going to work.”
Mark Gilmour, VP of mobile connectivity with Colt Technology, agreed that 5G is creating a more complex access network. Not only are there new transport architectures, but they overlap each other in the same footprint. “We will see front-haul, mid-haul and backhaul all over that same geographic footprint,” said Gilmour. “That means the underlying infrastructure needs to be flexible, programmable and adaptable to be able to deal with these multiple architectures on top.”
Jim Guillet, senior director of product marketing with Nokia, noted that 5G is using the mmWave frequencies with massive MIMO antennas. He said these antennas “compound the bandwidth way beyond what CPRI really could accommodate; and so we’ve introduced Ethernet based eCPRI.”
Integrated access backhaul
There was some discussion on the panel about integrated access backhaul (IAB), which could use wireless links in some instances instead of fiber for backhaul.
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Gilmour said, “I think IAB is the opportunity to partition some of that spectrum that you’ve got for access and use some of it for backhaul to a node where you’ve probably then got fiber. I see IAB as an extension of fiber networks.”
For example, in a dense metro with a lot of new small cells, some may be connected with fiber and others could be connected with wireless if fiber is not feasible. “I do see a disadvantage in that it uses precious spectrum that has been acquired through auction," said Gilmour. "It probably has more practical usability in the high frequency band.”
From Nokia’s perspective, Guillet said, “We envision a cluster of mmWave radios that are all interconnected and meshed and likely there’s some kind of centralized controller, probably cloud based that monitors user traffic and routes the backhaul traffic accordingly.” But he agreed with Gilmour that using IAB takes precious spectrum. “Maybe it’s an interim solution to buy time for your fiber crew to build out connectivity as they see which of the small cells generates the greatest traffic, and then you can move your fiber closer,” he said.