Small cells could raise big problems

Stephen Lawson | May 11, 2012

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.

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