As the mobile network gets more complicated, it’s going to need more intelligence, probably in the form of software-defined networking (SDN). At Mobile World Congress last week, we found some examples in the cloud-based radio access network (cloud RAN) and the still-in-progress 5G standard for cellular networks.
Some of this has to do with the ubiquity of the network. Everybody expects mobile connections everywhere, but that means placing radios and backhauling them to the wired network. The cloud RAN is about pooling resources to do this more efficiently, and some products for putting that together are shipping today.
There’s also a widening variety in mobile communications that means one connectivity standard won’t be enough. LTE, with its need for continual synchronization, isn’t ideal for an Internet of Things (IoT) where batteries are expected to last a decade. Separately, operators want to take advantage of the Wi-Fi connectivity that’s hovering over urban centers and office parks. It looks like this multiplicity of standards will be the “standard” behind 5G.
Taking Mobile to the Cloud
The cloud-based RAN is the more immediate idea of the two. The idea is to move the baseband processing, currently attached to the radio, into the cloud, where it becomes part of a pool of resources.
“It means I can say this radio, at this point in time, is associated with this piece of baseband,” said Marcus Weldon, president of Alcatel-Lucent‘s Bell Labs, during an informal session with reporters (photo at right). “When that radio isn’t being used any more, I want to remove that association. That’s a very low-level [example of] SDN.”
At MWC, Cavium was showing a chip called the 7400, which keeps the baseband’s physical-layer processing — Layer 1 — in the cellular modem. The baseband’s Layer 2 and 3 processing can then go into the cloud.
Startup Altiostar does something similar, but it’s a systems company rather than a chip company. The startup, which launched in November, offers its own radio system to go on the cell tower, again including some of the baseband processing. It also offers a baseband system to sit in the central office as part of that pool of baseband resources.
Alcatel-Lucent has likewise designed a split architecture for the baseband: Layer 1 at the radio, Layers 2-3 virtualized. That’s planned for commercial release in early 2016, Weldon says.
The reason for keeping the Layer 1 processing at the radio is bandwidth. The radio can’t output Ethernet packets; instead, it sends out analog signals that eat bandwidth ravenously. “For LTE-Advanced, you need 10-Gb/s point-to-point links,” says Kuntal Chowdhury, vice president of marketing for Altiostar.
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By doing the Layer 1 processing at the radio, an operator only has to send an Ethernet payload into the cloud-based baseband. That lowers the necessary data rate to 100 or 200 Mb/s, says Rupert Baines, a longtime mobile-industry executive who’s working as a consultant for Cavium.
Early cloud RAN deployments are just taking the hit and using fiber to handle all that bandwidth.
“Japan can do it, Korea can do it, China grimaces at it, and for the rest of the world, it’s not possible,” Baines says.
NFV and the Cloud RAN
The next obvious step, as you might have gleaned from the word “pool,” is to turn that Layer 2-3 baseband into virtualized form, rather than big systems.
This is where network functions virtualization (NFV) would come into play, where the NFV orchestration layer could create new instances of virtual baseband as needed. SDN would come in for connecting those instances to the radios that need them, or to network the instances together. “By the time it’s real, there will be an SDN control plane” for it, Weldon says.
Virtualizing the baseband isn’t necessarily easy. “The latency between Layer 2 and Layer 1 in LTE is in microseconds,” Chowdhury says. That’s kept the LTE base station in the realm of specialty chips — ASICs and digital signal processors (DSPs). But all three companies mentioned above have started moving the baseband onto general-purpose processors.
Cavium was pitching the use of its ThunderX processor, which carriers 48 CPU cores based on the architecture from Intel rival ARM, as the foundation for a virtualized baseband.
Altiostar has a virtualized baseband as well, developed in partnership with Intel subsidiary Wind River.
Prepping for 5G
Separately, there’s the question of preparing the network for 5G. Standards work hasn’t truly begun, but there seems to be an early consensus as to what “5G” will mean.
“5G will clearly be multiple air interfaces. It’ll be LTE-U and millimeter wave and Wi-Fi and everything, and that will all be managed as one. We’ve all sort of agreed that 5G should inherit the best of what’s there and add only enough new [as] needed,” Weldon said.
Add to that a couple more possible interfaces, such as the Bell Labs-crafted Universal Filtered OFDM and the prospect of beam forming, an alternative to the 120-degree spread that antennas use today.
Even beyond that, though, the 5G network will be build around a different philosophy, said Tod Sizer, wireless research program leader at Bell Labs.
The idea would be to make the user the “center of the universe,” Sizer said. The mobile device would have all of its radios turned on, and the user would be connected to the appropriate network depending on what’s nearby and what kind of application is being used. Control-plane traffic might even get shunted onto an air interface of its own.
“So the model’s turned upside-down. Instead of the network being this solid thing, and people can add or not add to that network, we turn around and say the user is the most important thing,” Sizer said.
Alcatel-Lucent is taking an early step by virtualizing its 4G control plane, then using SDN to stitch together the virtual and physical networks. The company is calling this its “4.5G” cellular network.
It’s only a stopgap on the way to 5G and not something that will ever be standardized, Weldon said. But Alcatel-Lucent considers it a necessary step. “Virtualization, SDN, small cells — if you’re doing these things, you’re ready for 5G,” he said.
Progress might come faster than you’d think. The official 5G standard is due to be crafted between now and 2020. But with the Olympic Games coming to Pyeongchang, South Korea, in 2018 and Tokyo in 2020, you’ve got two high-tech nations that are very motivated to see 5G happen soon.
Photo: The Alcatel-Lucent stand at MWC’15.
MWC Disclosure: Craig Matsumoto was rejected for a Mobile World Congress press pass. He attended MWC 2015 on a pass supplied by Brocade and used the Ericsson stand as an ersatz press room.