小型基地臺叫好不叫賣，標準統一是最大障礙

Small cells still not ready for mobile prime time

Rick Merritt

SAN FRANCISCO – Engineers still have significant work ahead to deliver small cell base stations, a key piece of the puzzle for easing congestion on heavily loaded mobile data networks.

Powerwave Technologies (Santa Ana, Calif.) showed what it claimed was one of the first shipping small cell base stations at the NGMN Alliance conference here recently (below, left). Although it is being used in a small-cell network for a U.S. government department, the small cells do not yet interoperate with traditional macro base stations.

So far the traditional base station suppliers have not disclosed details of their X2 interconnects that companies such as Powerwave need to link to the macro cells. Release 10 of Long Term Evolution specifies an inter-cell interference mitigation standard over X2, but operators are not expected to start deploying Release 10 until sometime in 2013.

Qualcomm showed a demo at the event of the inter-cell interference technology working on prototype chip sets installed in base stations at its San Diego headquarters. It did not say when those chip sets will ship.

The amount of cellular coverage area subject to inter-cell interference grows from 25 percent with macro cells to 40 percent with macro and small cells, said Andrew Jun, vice president of network strategy at cellular operator KT in Korea that has created centralized pools of 144 to 1,000 cell sites.

“This is why we introduced [base station] virtualization” said Jun. “With one location managing multiple cells we could have coordinated transmissions to control interference, especially at the cell edge,” he said.

“It’s only a matter of when” until small and macro cell interoperability is ready, said Khurram Sheikh, chief technologist of Powerwave in a panel session at the event. He claimed his company’s small cells support both LTE and Wi-Fi and can increase an operator’s network capacity fifteen-fold while increasing battery life five-fold.

A carrier can increase its capacity as much as twenty-fold adopting heterogeneous networks of small and macro cells, but only if it pools all its spectrum into one combined 3G and LTE net, said Erik Ekudden, head of technology strategy at Ericsson. Most OEMs are still in the design phase for small cells with field trials starting next year, he added.

For its part, Huawei described at the event a merged LTE and 802.11n Wi-Fi hotspot based on Release 8. It can support downloads at about 1.2 Gbits/second using 256 QAM and is now in a lab prototype based on FPGAs and DSPs, said a Huawei engineer.

“Everybody has nice stuff on their slides, but go try to find a good commercial small cell--I can’t find a single vendor to supply one, said Konstantin Yurganov, chief technology officer at Yota, a 4G supplier in Russia, in a talk at the event.

The carrier has as many as 15 percent of its base stations heavily loaded in some cities with as many as 70 to 160 subscribers on a single base station, he said.

Ultimately, small cells will be deployed both in public areas such as lamp posts and in businesses such as cafes and offices. That’s opening up an opportunity for enterprise networking companies to participate.

In a keynote talk, Paul Mankiewich (right), chief technologist for mobility at Cisco Systems, called for a network API enabling broad virtualization across carrier and business nets. The API could build upon technology already in the works at the Wi-Fi Alliance to help identify traffic on public versus private Wi-Fi hotspots, he said.

“We don’t have coherence between enterprise and service provider networks today,” said Mankiewich. “All that depends on two sets of standards that don’t speak to each other today,” he said.