China drives servers to base station role
The so-called Cloud Radio Access Network (C-RAN) initiative aims to lower the power consumption of cellular base stations by a factor of five and cut their costs by an order of magnitude. Intel, IBM, Huawei and ZTE were among the initial partners in the program kicked off last March by NGNM, a trade group of telecom operators and vendors.
The plan faces several technical and business hurdles. But proponents have already created demonstration systems, conducted field trials and hope to start development of commercial products as early as mid-2013.
“Fundamentally, we could shake up the standard layered philosophy and make the telecom network look more like a Web mash up,” said Bill Huang, general manager of the China Mobile Research Institute, the R&D arm of China Mobile that serves 650 subscribers.
The C-RAN concept is to pack the functions of as many as a thousand base stations on data centers connected by fibre to multiple radio head ends. Such centralized systems could provide 15 percent reductions in capital costs, 50 percent decreases in operating costs and 70 percent reductions in power consumption compared to today’s distributed 3G nets.
“With the current architecture, outdoor base stations already consume 67 percent of the network’s energy,” a slice set to increase, said Huang. “It’s mind boggling to imagine what will happen if we continue on this road of low power efficiency,” he said.
IBM and Intel helped move 3GPP standard processes to software running on x86 servers rather than the ASICs and DSPs in traditional base stations. Along with Huawei and ZTE they created two demo systems that also tapped general-purpose graphics processors and software-defined radio components.
“It’s clearly not product-ready technology, but we’ve demoed the potential that with modern processors and comms links it becomes viable,” said Huang.
Several China cities conducted experimental deployments of the systems. Some are already moving toward more centralized cellular nets, but not yet including the C-RAN concept.
“We hope over the next three to four years to bring this technology to volume shipments,” said Huang.
Separately, Intel recently introduced a companion chip for its Xeon processors that helps handle a range of packet-processing and network security processes. As part of the roll out it said it is working on a next0-generation chip to handle DSP jobs for base station tasks.
Plenty of hurdles are ahead, chief among them the lack of broadband backhaul links to serve such cellular data centers.
China Mobile advocates linking the radio heads and C-RAN via optical fibre because it has plenty of installed fibre. But most global operators use microwave or copper links because they lack installed fibre.
Indeed, some vendors say Cloud RAN could be limited to Asian operators who have the installed fibre the concept needs. Huang suggested a whole new backhaul interface may be needed as part of the C-RAN strategy.
As for the servers, they need a new generation of software-define network implementations that require less support hardware. They also must close the gap between current response times of a few seconds to required real-time responses in a few milliseconds.
“You can build a two-tier radio cloud that could consist of a real-time portion and a non- real time portion,” said Huang.
Even if those hurdles are overcome, it’s not clear how the power savings achieved in today’s big Web data centers could be leveraged in installations running radio networking jobs.
Beyond the tech hurdles, the C-RAN concept requires server makers acquire telecom expertise and telecom giants such as Alcatel-Lucent, Ericsson and Nokia Siemens Networks embrace server architectures. The question is how to foster “the kind of working co-opetition we need,” Huang said.
“In the last four or five years [traditional base station vendors] went from disbelief to devoting resources and now to being strategically focused” on Cloud RAN, said Huang.
The C-RAN concept also must come to grips with rising interest in small cell base stations seen as a way to cost effectively extend cellular coverage, particularly with new LTE networks in urban areas.
“My opinion is the big will get bigger and the small will get smaller,” said Huang. “It will become a world where one base station handles 10,000 transceivers and another is a single chip base station SoC,” he said.
Indeed, blended cellular and Wi-Fi small cells are widely expected to emerge. Huang said he has been working with silicon vendors to encourage design of cellular/Wi-Fi chip sets that could serve both handsets and small cell base stations.
“Today’s stringent requirements for cell sites could be relaxed so we can use handset chips to build them,” he said
Such a move could also pave the path for C-RAN hubs to use either x86 or emerging ARM-based servers.