Amid growing interest in small cells, widely seen as an inevitable tool for carriers to deal with booming mobile data demand, there are now signs that it may be hard to derive the expected benefits from them in some cases.
Small cells made a big splash at Mobile World Congress earlier this year. This week's CTIA Wireless show featured less in the way of small-cell product news, but carriers, vendors and the chairman of the U.S. Federal Communications Commission all spoke out about the emerging need for these technologies. At the same time, some participants cautioned that there are hurdles on the way to the heterogeneous networks of the future.
Small cells encompass a broad array of radios, including Wi-Fi access points, that are smaller and less expensive than the traditional macro cells that cover whole neighborhoods. They can make more efficient use of existing frequencies and cover areas, such as indoor spaces, that are hard to reach with macro cells. This mission will become increasingly important as demand for network capacity grows along with consumer and business use of mobile data, a trend that some say will constrain consumers' and workers' mobile experience within a few years.
While carriers at CTIA said small cells would be part of their solutions to a spectrum crunch, FCC Chairman Julius Genachowski also advocated a multipronged approach to the problem that would include small cells. He even said the FCC would work on setting aside spectrum in the 3.5GHz band, well suited to short-range wireless, specifically for small cells.
However, setting up these radios and gleaning the promised impact from them will be harder than just buying equipment and finding spots that need more capacity, according to carrier and vendor executives and others at the show. Standardization is still a work in progress, there may be hidden costs behind the relatively low prices of small cells and carriers may end up fighting over spots to set them up.
The Small Cell Forum, the biggest cheerleader of the technologies, released test results on Tuesday that showed setting up just one small cell near a macro cell, both on the same channels, can offload 20 percent of the local data traffic to the smaller radio. With four, the offload grows to 56 percent, the group said.
That represents the spectral efficiency gains that small cells can offer, said Simon Saunders, chairman of the 137-member industry group. But to prevent interference, the macro and small cells need to be coordinated. The Forum advocates common standards that would let any vendor's cells communicate with any other's, which could foster innovation by newer manufacturers.
However, the biggest of the established infrastructure vendors raised doubts whether that approach will rule the day. In both 3G and 4G networks, there are proprietary protocols for coordination among cells small or large, said Hans Beijner, portfolio marketing manager for Product Area Radio at Ericsson. Tests at Ericsson using the company's own gear throughout a network indicate much greater efficiency gains are possible than what the Forum described, Beijner said.
Asked about vendors' inclination toward proprietary networks, Bob Azzi, Sprint Nextel's senior vice president - Network, said service providers just have to force them to work with others. Carriers need to start by demanding standards compliance in their requests for proposals, he said.
"And then, what happens is, the vendors deliver it, and they're all different, and then we ... test them, and then we get them all to fix it so it works together," Azzi said. "The standards get you 80 or 90 percent of the way there."
Other issues with small cells are more down to earth. For one thing, even though the cells cost much less than macro equipment, each still needs to be installed and have a fast backhaul connection, which is usually wired. Small cells mean more cells in a given area, so more wires and bandwidth charges for the mobile carrier.
"If you keep on adding on these small cells to the market, you're going to exponentially grow your backhaul requirements," Ovum analyst Daryl Schoolar said during a session at the show. "If not handled right, it could actually probably destroy any economic value and operator is going to get out of deploying small cells." And along with the cost of the backhaul comes the time and expense of getting zoning approval for a small cell.
"Finding street furniture you can actually zone in this lifetime is extremely [hard]. It will be stuck in a zoning box, so you never get anything built," said John Saw, senior vice president and chief technology officer at Clearwire. Saw said his company has deployed WiMax small cells in a few locations in major cities where it is even more difficult to find sites for macro cells.
Sprint's Azzi predicted small-cell mounting locations will become a scarce commodity in busy urban areas.
"We're going to all be after that street corner," Azzi said. If the lease on a well-situated lamp post or in a popular coffee shop goes to the first bidder and other carriers are locked out, that could stifle competition and innovation and hurt subscribers, he said. The solution might be a model in which all service providers share sites. However, it's not yet clear how such a system might be set up, Azzi said.
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